# Why so few planes that fired thorugh the propeller hub?



## Rufus123 (Sep 17, 2013)

I am going to guess that many plane designs do not work will with this set up?

Was it the inverted V that got it to work on the 109?

Would this have worked on a Spitfire or would it require too many design changes? Would it work on a Mustang?


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## GregP (Sep 17, 2013)

Most V-12 engines were very simply not designed with the ability to shoot through the V even considered by a designer.

Wouldn't work for a Merlin or Griffon and would only work for the Allison if it were an "E" series engine with a driveshaft.

Definitely not a possibility for radials ...

In fact, it was abnormal for a WWII fighter.


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## Shortround6 (Sep 17, 2013)

You have to design the engine from the start to have clearance for the gun or gun tube ( the receiver is ALWAYS behind the engine). Otherwise there is just too much stuff in the way. The prop shaft has to be the right distance from the crankshaft which affects the size of the reduction gears and the reduction gear case ( part of which is usually part of the crankcase casting). Intake manifold may or may not allow room, this may be the easy part. Accessories and supercharger have to be placed to allow room for the gun. Picture of Hispano V-12:







Germans mounted superchargers on the side of the engine to free up space at rear of engine. 

trying to add it at a later date requires changing some fundamental parts of the engine.

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## Aozora (Sep 17, 2013)

Just off the top of my head the only engines able to accommodate centre-line weapons were:
DB 600 series
Jumo 211 213 series
Hispano-Suiza 12Y series
Klimov M-105 series (derivatives of 12Ys)
Some Allison V-1710s

Can't think of any other important, production engines.


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## Shortround6 (Sep 17, 2013)

the Allison didn't really accommodate the gun _in_ the engine but used an extension shaft to allow the gun to be placed between the propeller/reduction gear and the engine. 

At least one Italian engine and one model of the Ranger Inverted V-12 were arranged to have the gun on the outside of the V with the reduction gear made large enough to allow the Prop shaft to line up with outside of the crankcase. Can't find the proper picture right now but: 






Imagine gun mounted to top of engine with prop-shaft raised to take the barrel. Of course the increase in frontal area tends to put a damper on the idea.


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## wuzak (Sep 18, 2013)

This shows why the Merlin couldn't have a hub cannon.

http://www.digitalcombatsimulator.com/images/mustang/mustang-7.jpg


With regards the Ranger, for the hub cannon (in the XP-77, for example) to be mounted the reduction gear and prop shaft were above the crankcase (teh Ranger being inverted), so about as far away from the centre of are of the engine as possible.

This shows layout for an "improved" XP-77 with a 37mm cannon in place of the 20mm...

http://d1kqib0uq4v1gs.cloudfront.ne...mproved-bell-xp-77/improved-bell-xp-77-04.jpg


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## davebender (Sep 18, 2013)

Fighter aircraft built in France, Germany and Soviet Union which were powered by V12 engines had hub cannon. That's three major aircraft producers.

USA didn't believe in cannon, hub or otherwise. Not much point in having a hub mounted M2 .50cal MG.

Except for Ki-61 all Japanese fighter aircraft were powered by radial engines. 

Italy was in similar position until they began license production of DB601.

Britain is the real puzzle. They could have required RR Merlin and RR Griffon engines to be designed for a hub cannon. Then Spitfires could have centerline mounted weapons similar to Me-109. An arrangement many RAF fighter pilots considered superior to wing mounted weapons. After RR Merlin engine development began it's too late to change specifications. You fight with what you developed during peacetime.


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## Aozora (Sep 18, 2013)

davebender said:


> Britain is the real puzzle. They could have required RR Merlin and RR Griffon engines to be designed for a hub cannon. Then Spitfires could have centerline mounted weapons similar to Me-109. An arrangement many RAF fighter pilots considered superior to wing mounted weapons. After RR Merlin engine development began it's too late to change specifications. You fight with what you developed during peacetime.



Why should Britain be a puzzle simply because it didn't necessarily follow a small contingent of countries that made provision for centreline cannon? The USA didn't demand that Allison design the V-1710 for hub cannon. The only pre-war German fighters to use hub mounted weapons were a few 109 prototypes with the 109s only regularly adopting centreline cannon with the advent of the F series in late 1940. When Japan did get the DB 601 none of the fighters designed around the licence-built variations used hub cannon. In fact the only country adopting such weapons as a matter of policy during the 1930s was France - Russia followed once it adopted and adapted the French 12Y into the Klimov series.

To require Rolls-Royce to design the Merlin and Griffon for hub cannon would have meant throwing away everything that had been learned about the rear mounted supercharger in order to design a completely new side mounted system (possibly with the help of the French). This would then have led to protracted and probably even more problematic development of the Merlin, higher costs, and a possibly inferior supercharger - all to facilitate a centreline cannon which wasn't a part of RAF policy of the time, apart from some experimentation with spec F.10/27.


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## wuzak (Sep 18, 2013)

Aozora said:


> To require Rolls-Royce to design the Merlin and Griffon for hub cannon would have meant throwing away everything that had been learned about the rear mounted supercharger in order to design a completely new side mounted system (possibly with the help of the French).



Why the French?

As far as I can tell, the Hispano didn't have a side mounted supercharger - just a small one.


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## davebender (Sep 18, 2013)

> To require Rolls-Royce to design the Merlin and Griffon for hub cannon would have meant throwing away everything that had been learned about the rear mounted supercharger in order to design a completely new side mounted system


A rational decision. However IMO it wasn't a good decision as a centerline mounted 20mm cannon has such an advantage over wing mounted weapons.


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## wuzak (Sep 18, 2013)

davebender said:


> Britain is the real puzzle. They could have required RR Merlin and RR Griffon engines to be designed for a hub cannon. Then Spitfires could have centerline mounted weapons similar to Me-109. An arrangement many RAF fighter pilots considered superior to wing mounted weapons. After RR Merlin engine development began it's too late to change specifications. You fight with what you developed during peacetime.



When Rolls-Royce designed the Merlin did the RAF have a cannon worthy of the name?


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## davebender (Sep 18, 2013)

> When Rolls-Royce designed the Merlin did the RAF have a cannon worthy of the name?


Germany had no 20mm aircraft cannon worthy of the name when Daimler-Benz began designing DB601 engine. That didn't prevent them from planning for a future when aircraft cannon might become important.


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## Jabberwocky (Sep 18, 2013)

davebender said:


> USA didn't believe in cannon, hub or otherwise.



False.

The US military establishment officially recognised the necessity of using cannon on aircraft as early as 1936. It sent research groups to Europe to see what was being done there and began work on its own cannon. The USAAF actually ordered 40,000 20 mm cannon *before Pearl Harbour*.

The US used 37 mm and 20 mm cannon in its fighter aircraft during the war, they just bollocked up the designs, meaning they were forced to rely on the M2 as their primary armament. The US also tested aircraft with the 23 mm Madsen and various 20 mm Oerlinkon designs. Then there were the four different .60 (15.25 mm) and four different .90 (23mm) cannon tested and eventually discarded during the war.


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## Marcel (Sep 19, 2013)

GregP said:


> Definitely not a possibility for radials.


In Finland they had machineguns mounted inside a Brisol Mercury engine, firing through the propellor. And these were radials. This was on Fokker D.XXI's


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## Aozora (Sep 19, 2013)

davebender said:


> A rational decision. However IMO it wasn't a good decision as a centerline mounted 20mm cannon has such an advantage over wing mounted weapons.



I doubt whether the advantages of having a centreline cannon would have outweighed the problems inherent in having to design a new supercharger system, when there was already such a deep fund of knowledge that had been built up over years of experience in designing and running high powered aero engines. Why create new risks and further impede the development of the Merlin based on the hope that some time in the future a cannon suitable for the installation would emerge? Experience with the 12Y and derivative engines shows that the small, side mounted supercharger wasn't nearly as efficient or capable of future development as Rolls-Royce's, and it was the supercharger that was central to the Merlin's success. 

Both Daimler-Benz and Junkers were designing their engines and superchargers from scratch at huge expense, and it still took years of headaches and development before the installation of a centrally mounted cannon was perfected. It is significant that Japan and Italy used variants of the DB 601/605 series yet did not adopt central cannon, indicating that making such an installation work, even with an engine designed to have central cannon and with a fund of experience from the Germans, was not as easy as you would like to believe. 



Marcel said:


> In Finland they had machineguns mounted inside a Brisol Mercury engine, firing through the propellor. And these were radials. This was on Fokker D.XXI's


Rifle calibre machine guns yes, but there was no possibility of mounting anything bigger to fire between the cylinder banks without creating some serious engineering problems.


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## stona (Sep 19, 2013)

davebender said:


> IMO it wasn't a good decision as a centerline mounted 20mm cannon has such an advantage over wing mounted weapons.



Not proven, not provable so that's just what it is........your opinion.
The RAF's cannon armed fighters did just fine without a centreline weapon. That's weapon, singular, by definition.
Cheers
Steve


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## Shortround6 (Sep 19, 2013)

Marcel said:


> In Finland they had machineguns mounted inside a Brisol Mercury engine, firing through the propellor. And these were radials. This was on Fokker D.XXI's



If you use a 9 cylinder radial it is quite possible to run barrels or blast tubes or bullet channels between the cylinders. this was done of the Gloster Gladiator for one:






and Fokker 21

http://www.dutch-aviation.nl/pictures/Fokker/Military/Fokker D21 with Bristol Mercury engine.jpg

BUT the guns still need to be synchronized. And it is quite a bit different than firing though the propeller _hub._

With a 14 or 18 cylinder radial this possibility goes away. 

DaveBender


> Germany had no 20mm aircraft cannon worthy of the name when Daimler-Benz began designing DB601 engine. That didn't prevent them from planning for a future when aircraft cannon might become important.



The French started the through the propeller cannon idea in WW I with a 37mm cannon (single shot) through the prop hub of a Few Hispano V-8 powered fighters. The French were the major proponents of this during the 20s and early 30s. However NOBODY had a _good_ aircraft cannon during this time. The _first_ German aircraft cannon during the 30s was a large, heavy, powerful weapon with a low rate of fire. Perhaps it was not _worthy of the name when_ Daimler-Benz began designing DB600 engine or Junkers began designing the Jumo 210 but the idea was certainly there and NO, they were not allowing or planning for the future 6-7 years down the road. They were trying to run simultaneous programs but the relative failure of the first gun sent them to fall back positions. 
The First French fighters in the 1930s to use 20mm guns in the prop hub (the Dewoitine D.501 with fixed landing gear) used Hispano licensed Oerlikon FF S guns called Hispano H.S. 7. These had a lower rate of fire than later 20mm guns and the first HS 404 guns had a rate of fire of just 400 rounds per minute. Designing an engine around one of these guns as the _primary_ armament of the fighter took a lot of faith. 1000hp engines of the time provided ONLY enough power for ONE cannon and 2-4 Machine guns. The cannon didn't really mature until 1938-39 and even then??? 
The Germans don't get the through the hub gun to really work until 1941. Even MG 17s having trouble with over heating forcing the installation of wing mounted guns to get acceptable fire power.


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## davebender (Sep 19, 2013)

That's to be expected when an airforce starts from scratch during 1935. 

If Germany had army and navy air services operating throughout 1920s (i.e. similar to most other nations) I suspect hub cannon technical problems would have been solved long before 1941.


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## Aozora (Sep 19, 2013)

davebender said:


> That's to be expected when an airforce starts from scratch during 1935.
> 
> If Germany had army and navy air services operating throughout 1920s (i.e. similar to most other nations) I suspect hub cannon technical problems would have been solved long before 1941.



Theoretical and unprovable - it's also possible that had the Germans had air services operating through the '20s the development of their aero engines and other technologies would have gone in a completely different direction. In fact, more than likely, they would have been as war weary and bankrupt as the other major powers, so that their air services would have been just as poorly funded and forced to use left-over WW1 technology for years afterwards.


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## Shortround6 (Sep 19, 2013)

davebender said:


> That's to be expected when an airforce starts from scratch during 1935.
> 
> If Germany had army and navy air services operating throughout 1920s (i.e. similar to most other nations) I suspect hub cannon technical problems would have been solved long before 1941.



You expect wrong and you don't listen or read. The German air force did NOT start from scratch in 1935. 

That is a misconception you have being either believing or trying to foist off for quite a period of time.

The Luftwaffe had hundreds of aircraft IN SERVICE in 1934. They started design and construction of aircraft in 1932-33 if not before. The Dornier *F* first flew May 7th 1932, it was renamed the Dornier 11 in 1933 and the first production examples were completed in late 1933. In Oct 1933 they established an auxiliary bomber group. By March 1st 1934 the auxiliary bomber group had only 3 Do 11s due to late delivery of engines to Dornier but had 24 Ju 52/3e bombers. 
The Arado 65a prototype fighter first flew in 1931, the Arado 65d first flew in 1932 and production models (65e) were being delivered in 1933. 
Heinkel had a number of designs in production before 1934. I have listed them before but you chose to keep repeating the claim that the Germans didn't even _start_ to re-arm until 1935. A very easily refuted form of revisionism.

The Luftwaffe issued a requirement for a fighter armed with either one cannon or two machine guns in 1932. Once again work did _NOT_ start in 1935.


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## DonL (Sep 19, 2013)

Aozora said:


> Theoretical and unprovable - it's also possible that had the Germans had air services operating through the '20s the development of their aero engines and other technologies would have gone in a completely different direction. In fact, more than likely, they would have been as war weary and bankrupt as the other major powers, so that their air services would have been just as poorly funded and forced to use left-over WW1 technology for years afterwards.



Do you have any single clue about German history between 1919-1933?
Germany was the most bankrupted major country through the Versaille Treaty, reparations, Ruhr occupation, inflation and later the world economy crises, nevertheless they could develop something like the Panzerschiffe and start to develop advanced aero engines since 1929 as they were totaly bankrupted.

Your argumentation is absurd and as always in your posts anti german bias! It is obvious that many members in this forum react totaly with anti german bias, when it comes to obvious german technology advantages, they will be always denied or negated, because of national biases.




> You expect wrong and you don't listen or read. The German air force did NOT start from scratch in 1935.
> 
> That is a misconception you have being either believing or trying to foist off for quite a period of time.
> 
> ...



And what do you want to tell us with your post? Other countrys had nevertheless at least a 10 years advantage from 1919-1929! So the next absurd post!


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## Shortround6 (Sep 19, 2013)

The Germans did start from behind some other nations but they DID NOT START IN *1935.*

That is false and any look at German types of aircraft easily shows it. 

If you call stating the truth about when Germany started to rearm "absurd" what are you trying to push? 

The Allied nations (except for Russia) did have the decade from 1919-1929 to gain design experience with engines, airframes and armament. Most of them didn't advance very far during those 10 years and most of what was learned was pretty much on the open market. The Siemens Big radial being a licence built Bristol Jupiter and the BMW 132 was a licensed P W Hornet. But the Germans started from scratch designing aircraft engines in 1935???? 

The actual engine designs from 1919-1929 were out of date by 1939 and _only_ the Wright Cyclone and Bristol Mercury and Pegasus powered first line aircraft by 1939-40. AND all three of those engines had seen considerable modification. 

The Germans did design and build some advanced engines, airframes and weapons in the WW II period ( and surface equipment too) but lets please knock of off the bull***t that they were such geniuses that they did it all starting in 1935.


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## DonL (Sep 19, 2013)

I haven't said with one word they start at 1935!
They start at 1929-1930 but with very very little budget. The real increased budget to develop was not comming until 1933 with the takeover.

This are facts you can read in any good researched book. The USA, GB and France had at least 10 years advance from develop tools, engines and in general could experiment in different directions. The german aero industry (through the nazi aggressiveness) had no time to experiment, they must develop first rate engines (and no inline engine was on the free market), production tools and good a/c's from the start with very very little zones to do mistakes, to be competetive.


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## Shortround6 (Sep 19, 2013)

You did not say 1935 but another forum member has said it and said a number of times even after being repeatedly shown that a number of German aircraft types were starting production in 1933. 

You have shown me a number of things I did not know before and I thank you for that. 

A lot is made of the engine type inline vs radial, that is actually not where some of the important developments took place. It is in the details like better valve springs, sodium cooled valves, better alloys, better bearings, constant speed propellers (which the Germans licensed while the British ignored them for several years), the Germans did a marvelous job with fuel injection.
All nations benefited from better lubricating oil instead of using WW I or early 20s medical grade castor oil. Pressure oil lubrication of valve gear instead of grease fittings. If nothing else German engineers could look at some other coutries 1920s engines and see how NOT to do things. 

the octane scale was not introduced until the late 20s, without that advances in compression or boost went nowhere. 

German engineers did do great work on their engines but they were NOT picking up where they left off in 1918, any more than the airframe makers were starting where they left off in 1918. There was a lot of movement of individual between countries and companies and a lot of information going back and forth ( some German ideas/techniques being used in other counties) at least until several years into the Nazi regime.


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## DonL (Sep 19, 2013)

I agree with your post.

Many things were no secrets and the german engineers learned a lot from foreign countries at the inter war period.

What irritate me, you can "appreciate" a good work or performance other members can't.

The advertisement of the german inlines (1929) was from the beginning upside down and able to connect a cannon between the cylinders.
Now we can discuss if the complexity was worth it, but what it is realy obvious "you" have much more flexibility.
Without the engine cannon the Bf 109 F or G would be far away from it's aerodynamics and also at the whole Tank 152 project the engine cannon plays a major role.

To me the engine cannon was an advantage and I think, if technical engineers from Junkers and DB had argumented against the cannon, because of too much complexity, the RLM had droped it. We can look and see this at the FW 190 A and FW 190D-9, but I think without a engine cannon, I have my doubts about a production Bf 109 later then 1942.


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## Njaco (Sep 19, 2013)

oh cool! A thread where EVERYONE gets banned!! Makes it easier for us Mods.

and thanks for convincing me that changing my siggy was needed.


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## DonL (Sep 19, 2013)

What is your intention Njaco?
As you have seen, some clear words could adjust the atmosphere, SHR6 and I needed not more then 3-4 post and all is good.
Why it is such a problem at this forum to argument sometimes a little bit harder to get good results or to to hustle someone to rethink his posts?

We are all not made of porcelain and nobody has made serious insults. Sometimes I beg you, to handle the reins a little more easy.


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## DerAdlerIstGelandet (Sep 19, 2013)

DonL, we are just tired of the same people fighting over and over.

Do you know how many complaints we recieve about the same people over and over? Did you know that several good members have left, and told us before that it is because if the same people over and over.

Frankly I am tired of the tit for tat anti/pro German/Allied BS bickering from you, Aozora and a few others. You guys act like a bunch of Kindergartners. Actually I know kids that behave better.

Both of you, and some others need to grow up. If someone farts you call them "Anti German". If some disagrees with Aozora, they are a revisionist.

People don't want to read pages of "My dad could beat up your dad" BS. Discuss the facts and quit bitching. It detracts from the thread.


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## DonL (Sep 19, 2013)

Sorry, if have done harm to this forum with my posts, I apologize.
Seriously, I haven't realised it and it wasn't at any time my goal or intention.

To me a discussion isn't only monotone, sometimes an issue could race my blood and at any discussion I have seen this (from me and other discussion members) as an enrichment. Perhaps I underlay the impression, that I'm sometimes the last corrective if it comes to german WWII technology, after so much other members were banned. But this could be a very personal impression and not objective.

I have had my fights with Parsifal with a bunch of issues, but several times we have come (Parsifal and me) to an "agreement" also with Stona. Also I think my goal was most of the time to bring forward informations to all members.

I can accept your argumentation, but to me, for a healthy discussion sometines it could be a little more "agressive", if you have something to post/provide.
If this is a bad reputation for this forum, or you are qualifying this as Kindergarden, I don't will post much in the future, because as I have written above it wasn't neither my goal nor my intention.

I realy like this forum and I have appreciated many discussions.


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## DerAdlerIstGelandet (Sep 19, 2013)

All we ask is that you all remain civil. 

Is that too much to ask?

And again the others were not banned because they were "pro German", they were banned because of being told over and over agsin to act civil.

A discussion can be "aggressive" as you call it, without insulting or belittling others. You are not the only one. There are several others. Some are "pro allies". 

Some purposly try and bait you "pro German" guys to draw you into a fight in order to get you banned. That also is not tolerated.


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## DonL (Sep 19, 2013)

DerAdlerIstGelandet said:


> All we ask is that you all remain civil.
> 
> *Is that too much to ask?*
> 
> ...



No!

I can see your argument, but you should also "respect" (sorry I have no other word), which memebers are "insulting" each others, and what they have done in the past to control their differences. I bet a month salary, that nobobdy of your moderators have ever believed that Parsifal and me come at anytime to a heathy discussion culture, and I don't want to be at anytime arrogant, but we have provided many different sources and argumentations (to several issues) and many members could have built their own opinion. To me something like this is an enrichment to "any" forum.

Anyway I have understood your message and I will do my best to take it seriously at the future, but I can't guarantee it, if my spirit will go through with me, but I hope I have explained from which "side" I come.

Thanks for this very enlightening discussion (Seriously)!


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## Njaco (Sep 19, 2013)

I have no problem with discussion.

I have a problem with the name-calling, the hurtful sarcasm and the constant "pro-Allied" stance that this forum is constantly being accused of.

Its one thing to forcefully discuss the topic but altogether another issue when some just don't like the tone of some members (which in my opinion is the majority of the attacks on Parsifal. Unlike everyone else who attacks him, he will change his opinion if you bring facts to the table which RARELY happens!) I'm just tired of reading a good thread only to have it blown up because this "one is an idiot" or that "one has no clue".

And just so we are clear: I like the Luftwaffe (I'm sure Adler does also). I have numerous books about the Luftwaffe and models of the planes. Ask Marcel, he has been to my home. I am not anti-German. There is no bias here. People are banned because of the way they act and not because of some conspiracy to weed the membership of pro-Germans. Its ridiculous and anybody who believes that obviously has a poor research technique or they would have found the reasons for those who were banned.

and I'm getting tired of having to explain this over and over.


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## DerAdlerIstGelandet (Sep 19, 2013)

DonL said:


> Anyway I have understood your message and I will do my best to take it seriously at the future,* but I can't guarantee it, *if my spirit will go through with me, but I hope I have explained from which "side" I come.



If it can't be said without insulting someone, then don't say it. If you can't do that, then maybe you should post someplace else. Simple as that. 

As we have said, no more warnings will be given to anyone of the repeat offenders. That I can guarantee...



Njaco said:


> I have no problem with discussion.
> 
> I have a problem with the name-calling, the hurtful sarcasm and the constant "pro-Allied" stance that this forum is constantly being accused of.
> 
> ...



Ditto...

Now back to watching Vick loose the game for the Eagles.


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## DonL (Sep 19, 2013)

I agree with your post Njaco.

The examples between me and Parsifal were examples! It wasn't at anytime my intention to denigrate him , more the opposite!
If you have read many threads from us the last 1 year you will see this.
We will be not "lovers" in the future, but I think we respect each other and this was the goal to several hard discussions.

Also I have with NOT one word said that other members were banned of their pro german view.
I have only assess that I'm to my opinion one of the last remaining "pro german" (to german technology) corrective, nothing else!
This was no accusation, it was only my personal feeling, which could be wrong!

Sometimes I have the feeling you (all moderators) have a very long rein, and sometimes especially in this thread the reins are very very short, because the dicussion hasn't realy developed. That's somtimes very irritating.


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## silence (Sep 19, 2013)

I think the point our (probably overworked) moderators are trying to make is simply that arguments can (and even perhaps should) be aggressive, but the _presentation_ of these arguments need to remain civil. Its simple to say but sometimes very difficult to achieve.

And, Don, this forum is very fair compared to far too many others. I can think of one in particular that I peruse but do not participate simply because the bias of the members, moderators, and site owners is, in my eyes, far too extreme. 

Personally, I troll forums for a long time before I decide if it is worth my time to participate actively; this site, for example, I followed for at least a year before joining. (Otherwise, I'd have a lot more posts!!)


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## DerAdlerIstGelandet (Sep 19, 2013)

DonL said:


> Sometimes I have the feeling you (all moderators) have a very long rein, and sometimes especially in this thread the reins are very very short, because the dicussion hasn't realy developed. That's somtimes very irritating.



Because if we don't have "short reins", then this thread will become like all the other threads...

You: You are clueless!

Them: You are a revisionist!

You: You don't know what you are talking about!

Them: More Ueber German BS!

You: You are just an Anti German!

And in the end no one has learned anything, just a thread of bickering BS...

That is the course of so many threads.

I am finished discussing this. *Get this thread back on topic, do it civil, or the thread is closed!*


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## Shortround6 (Sep 19, 2013)

I apologize for a getting a bit sarcastic at times. I try to keep an open mind and argue facts (or at least time lines). My feelings are that ALL countries had people that had _some_good ideas and _some_ bad ideas. I am talking about technical stuff here and leaving politics out of it. 
Sometimes there was more than one way to reach a certain goal and different countries/companies took different routes. It doesn't mean either one was _wrong._ Later developments sometimes affect how we perceive things now, but were anything but clear at the time when some decisions were made. 
AS an example, I have been fairly critical of some French engines in another thread. They happen to be among the oldest basic engines in use in WW II. They way they were designed may have made good sense in the late 20s when 70-77 octane was as good as the fuel got. Why build a heavy engine capable of standing up to high cylinder pressures if the available fuel will not allow high cylinder pressures? They knew better fuels were coming, but they didn't know when. The choices they made were valid choices when the engines were designed. Problems came when they had factories tooled up for these engines and they were "stuck" with a basic design that didn't have a lot of growth. The designers were not stupid or dumb, the country they were from is not a stupid or dumb country. 
The same with many German or Allied engines or designs, it takes years to go from drawing board to service use and often things beyond the designers control changed. 

No engine, airplane, gun, tank, or ship is "better" simply because it was made by one country or another. And no engine, airplane, gun, tank, or ship is "worse" because of it's country of origin. Each one has to stand on it's own merits _and in the time it was conceived/used_ few aircraft managed to have careers that spanned 10 years in front line service from 1935-45. 

Hopefully this forum is a place where we can work towards some sort of "truth" instead of some of the partisan press release stuff that was published in past years (Forked Tail Devils and 400mph P-40s,etc) we may not agree exactly but there should be more room in the middle than on the fringes. 

The US made some very good airplanes, It also made some real clangers ( junk), which makes me suspicious of "paper" airplanes that never flew. Claims that one country's engineers were "better" or didn't make mistakes probably won't stand up. 

BTW I have had A BMW motorcycle, A German Ford Capri, several older German cameras and a number of German rifles and pistols. While I would take the BMW over a Triumph Bonneville as a day to day machine the BMW cracked it's frame 3 times in exactly the same spot due to vibration in under 24,000 miles and couple of the rifles have a flaw or two that casts doubt on "German engineering". Over all they were very good but they were not infallible.


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## DerAdlerIstGelandet (Sep 19, 2013)

Shortround6 said:


> BTW I have had A BMW motorcycle, A German Ford Capri, several older German cameras and a number of German rifles and pistols. While I would take the BMW over a Triumph Bonneville as a day to day machine the BMW cracked it's frame 3 times in exactly the same spot due to vibration in under 24,000 miles and couple of the rifles have a flaw or two that casts doubt on "German engineering". Over all they were very good but they were not infallible.



You are clueless! You are anti German!

See how it goes...


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## DonL (Sep 19, 2013)

DerAdlerIstGelandet said:


> Because if we don't have "short reins", then this thread will become like all the other threads...
> 
> You: You are clueless!
> 
> ...



Ok, I have got it, that I have received a yellow red card (from soccer)!

The next time I don't will write: Do you have any single clue about German history between 1919-1933?
I will write: Are you aware about german history between 1919-1933?!

It is difficult and hard, but I will do it, promised!


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## Shortround6 (Sep 19, 2013)

I am also a really slow typist, 

Several posts while I was getting through that and I don't have the excuse of having to look up something


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## Matt308 (Sep 19, 2013)

...and DonL we too appreciate that English is your second language. Sometimes posts by folks with English as a second language come across condescending or appear insulting when that is not your intention. We are sensitive to that too. If in doubt, PM a Mod and let's resolve it behind the scenes so we don't hijack a thread like I'm doing now. 

As DerAdler said, let's get back to it...


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## Aozora (Sep 19, 2013)

I too apologise for letting some of my comments get out of hand. Like everyone else here I am first and foremost an_ AVIATION_ enthusiast and I do have a real affinity for German engineering, including owning several Anschütz rifles which to my mind are unsurpassed for accuracy and reliability J.G. ANSCHÜTZ GmbH Co. KG - Hunting Line Unfortunately I've had some really unpleasant and protracted run-ins with fanatically biased internet trolls and I've let those experiences colour some of what I say here. I'll sit down and have a talk to myself and think harder before I put finger to keyboard. 

To Don-l and DerAdler and others; ich bitte inständig um Verzeihung.

And yes, I do understand what happened to Germany post WW1 and the injustice of the Versailles Treaty and the reparations demanded by the Allies.

What I was trying to say was:

_ Had _the Germans had air services during the 1920s the evolution of their aero engines might have taken a different direction to the way they did develop - so we cannot really know whether inverted vee-twelve engines would have been adopted, nor can we know whether provision would have been made for centre-line cannon. Chances are had the Germans had air services during the 1920s, like other nations, they would have been hamstrung through being bankrupt, and would have had to rely on surplus WW1 equipment.


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## Shortround6 (Sep 19, 2013)

To get back on track the Hispano 404 didn't exist when work on the Merlin started. The Hispano company was licencing Oerlikon guns and at some point Marc Birkigt decided he could design a better gun. The actual number of available gun designs in the early 30s was pretty small and some had some rather large drawbacks, like the size of the ammo supply in drums and rate of fire. While some of these were improved it was by no means certain and a number of proposed or advertised guns of the late 30s came up way short of the promises.
Hispano themselves once advertised 4 different calibers (HS 404=20mm, HS 406= 23mm, HS 408=25mm, HS 410=30mm) but only the 20mm was a working product in the 30s. 

Picking the right gun out of several competing prototypes may have been hard. Since the "hub" gun not only interferes with the supercharger and accessories on the back of the engine but also intrudes into/through the fire wall and into space used for the "normal" fuselage tank or into the cockpit:







On the 109 the gun was even further to rear, it was not mounted on the engine but on the aircraft itself, engine could removed leaving the gun behind, and only a short (somewhat) section of barrel went into the 70mm tube that was provided through the engine. . 

While you can juggle the cockpit and fuel tank around somewhat the hub cannon does dictate some of the fuselage layout in addition to the rear of the engine layout.


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## DonL (Sep 19, 2013)

> To Don-l and DerAdler and others; ich bitte inständig um Verzeihung.



This is much too much!

It is realy ok, if you say, it isn't that hard as I wrote it, because as I said, I'm not out of porcelain! But I see your intention and I realy appreciate your post.


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## OldSkeptic (Sep 20, 2013)

There is a side issue in all the, V engines vs inverted V engines. The inverted V engines made it a lot simpler to put a hub gun (not getting in the road of so much plumbing basically), but paid several prices. The most obvious was oil build up in the cylinder head if left (radials suffered this too on the lower cylinders), but it could cause (if not carefully engineered out) issues with oil starvation to the crankshaft/bearings under positive G. In a similar way to oil starvation to the cams in a Merlin under negative G.

Then of course if you start packing the engine bay with extra stuff (and you want to keep the external profile as small as possible) you end up with all sorts of compromises in superchargers, inlets and so, costing power and/or compromising aerodynamics.

As usual in aircraft design, compromises, compromises...


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## wuzak (Sep 20, 2013)

OldSkeptic said:


> The inverted V engines made it a lot simpler to put a hub gun (not getting in the road of so much plumbing basically)



I disagree.

If Rolls-Royce had continued on their original aim for the PV12 as being an inverted V-12 it would still have had that supercharger and associated plumbing in teh way. It would not have been any easier to mount a gun - it would have been as impossible as it was historically.


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## nuuumannn (Sep 20, 2013)

> In Finland they had machineguns mounted inside a Brisol Mercury engine, firing through the propellor. And these were radials.



These fired between banks of cylinders of the engine through the propeller arc, not through the prop hub. There's a difference.


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## DonL (Sep 20, 2013)

Some Off Topic to engine development:

What is to me very impressive, are the Russians and the Hispano-Suiza 12Y.
To license an aero petrol engine and develop out of this engine a very good and reliable diesel tank engine.
For this timeline it is impressive, but also they had enough raw materials like aluminium.


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## tomo pauk (Sep 20, 2013)

Wasn't the V-2 the offspring of one of the airship engines?


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## Shortround6 (Sep 20, 2013)

How much it was based on the Hispano is subject to question. Some Russian accounts say the V-2 predecessor (the BD-2)was being worked on in 1933-34 which is before the Russians really got going on building the Hispano. The cylinder heads are totally different, 4 valves instead of 2, dohc instead of sohc, intakes inside the V , the engine uses a longer stroke. 

A version of the BD-2 was developed for aircraft use and test flown in 1936.


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## fastmongrel (Sep 21, 2013)

I have read many times that a through prop cannon was rated as worth 2 in the wings. Has anyone ever done any research into this or is it a "Some guy my father once knew said its so" fact.


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## stona (Sep 21, 2013)

fastmongrel said:


> I have read many times that a through prop cannon was rated as worth 2 in the wings. Has anyone ever done any research into this or is it a "Some guy my father once knew said its so" fact.



Not that I've ever seen.
Between 29th June and 26th July 1944 150 Wing's Tempests shot down 500 V-1s with wing mounted cannon. They almost invariably attacked from directly astern, the V-1 is a small target from that position. That would suggest to me that accuracy was not a significant problem for wing mounted armament. Obviously a V-1 wasn't trying to evade the attack, but if you don't point your weapons in the right direction you won't hit anything with them, wherever they are positioned.

A far more important factor in the accuracy of air to air gunnery is the gun sight. Better sights have a statistically provable effect on accuracy. Essentially the more the sight computes and the less is left to the pilot the more accurate the shooting.

Cheers
Steve


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## Rufus123 (Sep 21, 2013)

fastmongrel said:


> I have read many times that a through prop cannon was rated as worth 2 in the wings. Has anyone ever done any research into this or is it a "Some guy my father once knew said its so" fact.



I understand it was a German Ace that said that.... The name is on the tip of my tongue but I can't think of which German aviator supposedly said that.


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## Greyman (Sep 21, 2013)

*repost from a different message board:*



> This sounds familiar. It might be from a document that details an official survey/interviews of a half dozen or so of the top Squadron Leaders in the RAF around about 1942. The report indicated that that their answers were all independent and remarkably similar. In this case they indeed expressed a preference for centreline armament, saying that a fuselage gun was worth two wing guns.
> 
> Alright, got home and a hold of the document.
> 
> ...


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## stona (Sep 21, 2013)

The crucial word in the final sentence is "feel".
It is completely unscientific clap trap. For example how many of those eminent officers questioned had ever actually used an aircraft equipped with a centre line weapon in combat? At least that that might give them a basis for an informed comparison, still hardly a proper study, but at least with first hand empirical evidence. As it is, it is nothing more than _opinion_ and certainly does not constitute evidence that one centre line weapon was worth two in the wings.
I still have never seen the evidence from a proper study or trials to support this _opinion_.
You can add Bader to that list as he too expressed the same view......doesn't make it right though.
Cheers
Steve

Reactions: Winner Winner:
1 | Like List reactions


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## DonL (Sep 21, 2013)

At which range (normal circumstances) were wing mounted guns adjust, that the shells meet in the centerline?

Could Hartmann has fought his style, to close to 100m and below at the enemy, with wing mounted guns?


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## Juha (Sep 21, 2013)

DonL said:


> At which range (normal circumstances) were wing mounted guns adjust, that the shells meet in the centerline?
> 
> Could Hartmann has fought his style, to close to 100m and below at the enemy, with wing mounted guns?



Finns adjusted to 150m. RAF began with 300/400y but later moved to 250y?

On Hartmann, IMHO yes, simply adjusting aim point to certain amount left or right, still shells from one cannon would hit the fuselage. This was old Mölders vs Galland argument on armament. Galland was not alone among LW aces, Hans Philipp told to Finns, who usually preferred the fuselage guns, in 42 how impressed he was by the Huricane's 8/12 mgs armament. IMHO central placement of guns was better for good shooters who did the most damage, but good aerial shooters were not so common and wing armament gave an average shooted better chances of hitting but with less concentrated firepower.

Juha


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## Aozora (Sep 21, 2013)

stona said:


> The crucial word in the final sentence is "feel".
> It is completely unscientific clap trap. For example how many of those eminent officers questioned had ever actually used an aircraft equipped with a centre line weapon in combat? At least that that might give them a basis for an informed comparison, still hardly a proper study, but at least with first hand empirical evidence. As it is, it is nothing more than _opinion_ and certainly does not constitute evidence that one centre line weapon was worth two in the wings.
> I still have never seen the evidence from a proper study or trials to support this _opinion_.
> You can add Bader to that list as he too expressed the same view......doesn't make it right though.
> ...



Could be a case of RAF officers who felt that using a centreline weapon was similar to using a rifle or shotgun? Just looking at the names mentioned and noting that all were expert shots with rifles, shotguns and pistols - Sqn Ldr Edward Preston Wells, for example, was nicknamed "Hawkeye" - Group Captain 'Hawkeye' Wells - Telegraph 



> Wells's amazing eyesight and superb shooting skills made him one of the RAF's outstanding pilots. Johnnie Johnson, the RAF's most successful fighter pilot during the Second World War, considered him the "complete Wing Leader and the finest shot and most accurate marksman in Fighter Command".


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## stona (Sep 21, 2013)

Aozora said:


> Could be a case of RAF officers who felt that using a centreline weapon was similar to using a rifle or shotgun? Just looking at the names mentioned and noting that all were expert shots with rifles, shotguns and pistols - Sqn Ldr Edward Preston Wells, for example, was nicknamed "Hawkeye"



Maybe, if they were indeed all good shots. I know that many were of the opinion that being a competent sporting shooter helped them to shoot more accurately, at least it may have given them a better understanding of deflection/angle off which most pilots simply could not estimate accurately.
A good shot will be a good shot wherever his weapons are situated. The convergence of wing mounted weapons was adjusted to some extent to compensate for the inability of most to shoot accurately and again a centre line weapon won't help that. 
It is interesting that in the example I gave above for the 150 Wing Tempests against the V-1s that their cannons were point harmonised, something that Squadron Leader Beamont had to argue forcefully for with 11Group. He got his way and it obviously worked.

To answer DonL, I believe that a good airman and good shot like Hartmann would have made whatever armament layout he was equipped with work, just as the good shots on the other side made theirs work.

The layout of the armament cannot make a bad shot better, nor will it prevent a good shot being successful. A good computing gun sight will make the average pilot a better shot, whatever weapons he is using.
It was the opinion of some pilots that a centre line weapon might have been better than their wing mounted armament but they had no way of knowing if this was actually so. The grass is always greener etc.....

Cheers

Steve


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## Greyman (Sep 21, 2013)

DonL said:


> At which range (normal circumstances) were wing mounted guns adjust, that the shells meet in the centerline?



Difficult to really answer this, because things changed throughout the war (both due to doctrine and technical aspects of specific aircraft). Plus, wing-mounted weapons usually formed specific patterns and crossed at different ranges and heights.

But generally ...

British - 250 yards / 228 metres
French - 246 yards / 225 metres
German - 220 yards / 200 metres
USA - 350 yards / 320 metres


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## fastmongrel (Sep 21, 2013)

Hartman could have been armed with a single Lewis Gun and he could still have shot a lot of planes down. Unfortunately he was one in tens of thousands the average pilot from all airforces struggled to hit a barn door at 100 yards. Did the RAF ever investigate wing root mounted synchronised cannons such as some models of 190 carried, that would seem a compromise for a Merlin powered plane.


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## Shortround6 (Sep 21, 2013)

I am not sure how far the investigation would have gone, you can't synchronize a Hispano gun. This means you need a whole new gun. 

You also cannot synchronize the entire pre-war and war time Oerlikon line of guns. Germans had to go to electric primers to synchronize the Mg 151. 

So far I have not seen any real study of the one in the fuselage=two in the wings question, that was done in an armament research establishment. We have a lot of opinions by pilots, some of whom were very experienced. But few of these opinions have any real depth to them. Depth as to _which_ guns they were talking about,_which_ targets they were considering, _what_ ranges they firing at, etc. 

Some of the British firing patterns were less than ideal. They were trying to compensate for lack of ability of their pilots (in part due to poor gunnery training) with a 'shotgun' pattern (aiming guns in different directions and _never_ getting a concentration of guns at any range). Blaming that effect on wing mounting of the guns isn't following a true cause and effect path. 

A P-47 had it's outer guns about 20ft apart. some smaller fighters had their guns (or at least their cannon) only 12-13 feet apart. Shooting at a skinny fighter plane this may make a difference, shooting at a bomber with fuselage over 6ft wide and an 70-100 ft wide wing? 

I can certainly believe that one hub mounted MG 151 was worth two wing mounted MG/FFM cannon but we are not comparing the same thing anymore. Is one hub mounted MG 151 worth two _under_ wing mounted MG 151s? 

was there a problem with the gondola mounted guns? like did they have a bigger dispersion pattern due to flex in the wing or mounting? Maybe they didn't, just pointing out a possibility.

the Hub gun is mounted close the the center of of the aircraft vertically, firing the gun will have little (if any) effect on the attitude of the plane (pitch up or down). Wing mounted guns _may_ cause a pitch down when fired. Not so much on things like an F4F with it's mid mounted wing or the P-47 and F6F but on planes with wings at the very bottom of the plane? Guns mounted _under_ the wing have even more leverage to cause pitch down. But this is going to vary from plane to plane. 

Some modern fighters with off center guns have the computer controlled rudder automatically feed in deflection when the gun is fired. 

Those pilots believed what they said, but detailed explanations seem to be lacking.


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## Shortround6 (Sep 21, 2013)

DonL said:


> At which range (normal circumstances) were wing mounted guns adjust, that the shells meet in the centerline?
> 
> Could Hartmann has fought his style, to close to 100m and below at the enemy, with wing mounted guns?



In part, it depends on the target. Shooting at Yaks, Laggs and even IL-2s the wing mounted guns _might_ have missed more. Shooting at even DB-3/IL-4s???

diagram for a P-47:







This is about as bad as it gets for for a single engine fighter. Please note that with a 250 yd convergence the mean impact points are about 12ft apart at 100 yds. from 200 to 300 yds the mean impact points are _never_ more than 4 ft apart.


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## stona (Sep 21, 2013)

Good stuff. That 4' of divergence isn't going to miss much. The fallacy in the centreline argument is that that same 4' divergence makes the wing mounted armament more likely to score hits for the vast majority of pilots.
I do think some of the RAF's patterns were erring too far in favour of the bad shot, and in so doing penalising the few who could actually hit something. It's the result of the data they had collected showing just how bad _most_ of their pilots were at air to air gunnery.
Cheers
Steve


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## swampyankee (Sep 21, 2013)

davebender said:


> USA didn't believe in cannon, hub or otherwise. Not much point in having a hub mounted M2 .50cal MG.


The P-38, P-39 and FM-1 were spec'd with cannon armament well before ww2: the P-38 and P-39 in 1937 and the FM-1 somewhat earlier.


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## Ivan1GFP (Sep 21, 2013)

stona said:


> A good shot will be a good shot wherever his weapons are situated. The convergence of wing mounted weapons was adjusted to some extent to compensate for the inability of most to shoot accurately and again a centre line weapon won't help that.
> It is interesting that in the example I gave above for the 150 Wing Tempests against the V-1s that their cannons were point harmonised, something that Squadron Leader Beamont had to argue forcefully for with 11Group. He got his way and it obviously worked.
> 
> The layout of the armament cannot make a bad shot better, nor will it prevent a good shot being successful. A good computing gun sight will make the average pilot a better shot, whatever weapons he is using.
> It was the opinion of some pilots that a centre line weapon might have been better than their wing mounted armament but they had no way of knowing if this was actually so. The grass is always greener etc.....



I will have to disagree with you on this because I don't believe your assumption makes sense.

Yes, a good Marksman is a good Marksman regardless of the weaponry. The weaponry, however, DOES determine how critical and useful marksmanship can be. For small arms, a man with a shotgun cannot be effective beyond 50-100 yards no matter how good he is. A good accurate rifle will reward tbe better marksman.

For aircraft armament, if we have a few wing machine guns mounted as on a Spitfire all harmonised to 250 yards or so, regardless of the skill of the pilot, the armament cannot produce a useful concentration of fire out at say 750 yards. If the guns have similar ballistics such as the centerline armament of a Me109F/G, then a good marksman can still make hits out at a distance if he can calculate the proper elevation.

Regardless of actual experience with centerline armament, a good marksman will figure out that the configuration on something like a Spitfire is not effective at a distance.

The case of Tempest versus V-1 is a very special case. There is no need to make deflection shots and the target is non-evading so there is the opportunity to set up for a known distance shot to optimise the effectiveness of your armament.

Regardless of skill, there are certain armament configurations which are entirely unsuited for certain things. A while back I remember seeing an argument about why the mixed armament of the A6M was unsuited to deflection shooting because of the different trajectories of cannon versus MG.

Regards.
- Ivan.


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## stona (Sep 21, 2013)

Ivan1GFP said:


> I will have to disagree with you on this because I don't believe your assumption makes sense.
> 
> Yes, a good Marksman is a good Marksman regardless of the weaponry. The weaponry, however, DOES determine how critical and useful marksmanship can be. For small arms, a man with a shotgun cannot be effective beyond 50-100 yards no matter how good he is. A good accurate rifle will reward tbe better marksman.
> 
> ...



The chances of anyone hitting anything at 750 yards, even with late war gun sights is almost zero, a very lucky shot. SR6 already posted evidence for the P-47, on which the guns are about as far apart as any aircraft and considerably further than most RAF types, that from 200-300 yards, the range at which a good shot would reasonably expect to score some hits, the divergence was never more than 4' .
If a pilot aims 2 or 3 feet off with these weapons he will still score hits from 250-300 yards. A centreline weapon under the same circumstances will miss.
The average pilot is more likely to score hits with some kind of pre-determined convergence pattern. Which pattern works best was and still is an on going argument. It's why it was done. I don't see how a single centre line weapon can bestow any advantage except for the VERY rare good air to air gunners or an occasional and statistically insignificant lucky long range shot.
Someone has already pointed out that all the statistics support that the vast majority of pilots couldn't hit a cow's ar*e with a banjo.
The Newchurch Wing Tempests were a special case, it's why they alone adopted a single point synchronisation. They hit 500 V-1s in a month and I absolutely guarantee they were not all hit from the exact range at which that point was set. I don't have figures for the Tempest but given that the guns are closer together than on the P-47 it is reasonable to estimate that they would have at least a 100 yard window in which they might hit a target as small as a V-1. It didn't take many 20mm cannon shells to put one down.

Given your comment about the Zero what makes the armament of the Bf 109 suitable for deflection shooting?

Cheers
Steve


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## Shortround6 (Sep 21, 2013)

Trying to fire at 750 yds air to air depends on sheer luck. 400-500meters is pushing it even against bombers. Luftwaffe figured the _effective_ range of most of their guns as 400 meters _against_ bombers. And BTW the guns on a 109F/G did NOT have similar ballistics. The muzzle velocities may have been close but shape of the projectiles and sectional density means their times of flight and trajectory at long range (400 meters and more) started to diverge rather sharply. 

Lets just look at gravity. At the end of 1 second our bullet/projectile will have dropped 16 ft and is falling at 32feet per second. The drop is gotten around by aiming the gun up somewhat. BUT at the end of the 2nd second of flight the total drop is 48 ft and the bullet is falling at 64 feet per second and increasing. 1/10 of second is worth over 6 feet of drop. 

Time of flight to 600 meters for some German guns was 1.1 to 1.6 seconds ( with a few guns like the 15mm MG 151 being a big exception) but velocities had dropped 41-60% at that distance. This is measured at sea level and time to distance at higher altitudes is a bit shorter. But then our hero pilot has to try to figure the difference depending on the altitude he is flying at??? 

At 300 meters only the worst guns (MG/FF and MK 108) had times of flight over 0.5 seconds. 

You can deflection shoot with mismatched weapons, you just have to do it at short range.


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## Juha (Sep 21, 2013)

Ivan1GFP said:


> I will have to disagree with you on this because I don't believe your assumption makes sense.
> 
> Yes, a good Marksman is a good Marksman regardless of the weaponry. The weaponry, however, DOES determine how critical and useful marksmanship can be. For small arms, a man with a shotgun cannot be effective beyond 50-100 yards no matter how good he is. A good accurate rifle will reward tbe better marksman.
> 
> ...



Hello Ivan
life is too complicated to that kind certainties.

The last but one Neville Duke's kill (Bf 109G-8/R5, Duke flying Spit VIII) DUke opened fire, according to him from 600-800y, according to his wingman from 800y and got immediately cannon hits in.
Another one, 2Lt Olli Puhakka, flying not his regular plane but the only FiAF Fokker D. XXI armed with 2 20mm Oerlikon wing cannon, FR-76, tried to catch a fleeing Soviet DB-3 bomber from 53 DBAP, he got 500-700m behind it but when he noticed that distance rather increased than decreased opened fire firing 3 short bursts, first went under the target but other two hit. That in spite of the fact that one of the cannon didn't fire. The DB craslanded and the crew was captured.

Juha


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## Ivan1GFP (Sep 21, 2013)

This is a cool little bee's nest, but we are all friends, right? So here goes:

I personally have no experience in air to air gunnery except in flight simulators, but I do have a reasonable amount of experience with small arms at short to medium ranges, so I will be using a few analogies from that area. I have never fired any metallic cartridge guns that were any more powerful than a .50 Browning. I have no experience with cannons of any kind but do recognise that the ballistic coefficients are much higher as the caliber goes up.

First of all, this discussion was about the superior / expert marksman. I don't disagree that the average fellow could not hit anything past about 300 yards or so. The same is true with small arms. The distances are also remarkably similar against man sized targets, but that is not the target here. The target here is somewhere between the size of a dump truck and a semi-trailer with bombers being even larger. Aeroplanes are not small.

Machine guns are also terribly inaccurate. A good rifle should be able to put 5-10 rounds into 1 inch at 100 yards (1 Minute of Angle). A typical bipod mounted Light Machine Gun (Browning Automatic Rifle) might hold a 1 foot group at 100 yards if fired single shot. A typical tripod mounted Light / Medium MG might do well to put its rounds into a 3 foot circle. I expect an aircraft MG to be even worse than that because of the abuse that they take. The point here is that a 3 inch or 6 inch or even 1 foot difference in trajectory is pretty much meaningless. A one foot difference at 100 yards is still only 10 feet at 1000 yards and your targets are bigger than that.

Gravity does have the 32.16 feet / 9.8 Meters per second effect, but the drop numbers quoted in a prior message are working on the assumption that the projectiles are launched at zero elevation. Guns are typically mounted with some elevation to zero them at a particular range..... Well MOST guns. Consider that the motor cannon on a Me 109 is sitting behind several feet of blast tube, so I don't imagine you could crank in much elevation. (I don't know what the inclination of the thrust line is in the 109 and believe that the aircraft flew a touch nose down.) The cowl guns, however, would have no issues with elevation.

Point blank range is a term that is used a lot but seldom correctly. It is the distance at which a shot can be properly aimed at a target without any elevation adjustments. A flat trajectory (better ballistic coefficient round) increases the distance. A larger target ALSO increases the distance. (A tank gun PBR is typically around 2 kilometers.)

When the US Army used the M1903 Springfield RIFLE, its Maximum PBR was calculated at 550 yards. This meant that a shot aimed at a man's belt line would go no higher than the top of his head or lower than his feet out to 550 yards. This is on a 6 foot man. Aeroplanes are a LOT bigger which would increase the PBR.
Ballistically, the .30 Cal M1 (172 grain FMJBT 2600 fps) is pretty comparable to the 7.92 mm Heavy Ball round (196 grain FMJBT 2500-2600 fps). 

The MG 151/20 has a muzzle velocity of between 2300 and 2625 fps depending on ammunition. Bigger rounds are ballistically more efficient but these projectiles are also a lot less aerodynamic. The other cowl gun was the MG 131 which had a fairly low MV of only 2450 fps.

The MK 108 MV is only 1650 fps so it should fly a LOT worse than the rest even though the projectile is even larger.

I haven't run these numbers through a ballistics program to do a more exact comparison though. I believe that the differences in flight path would be entirely hidden in the typical dispersion of an automatic weapon.

With the A6M series, the Type 99-1 cannon had a MV of only around 1722 fps so that would also make it a lot worse than the other guns being discussed except for the MK 108.

Thoughts?
- Ivan.


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## DonL (Sep 21, 2013)

> The last but one Neville Duke's kill (Bf 109G-8/R5, Duke flying Spit VIII) DUke opened fire, according to him from 600-800y, according to his wingman from 800y and got immediately cannon hits in.


That's one of the most suspicious post I ever read! You will tell me he hit immediately at 800 Yards? Is this some story for your Grand Grandmother?
And you are a person who questions in a strong way the kills of Hartmann and will tell somebody opens fire at 800 yards and hit immediately?

Are you realy believing this ****?

I'm out!


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## wuzak (Sep 21, 2013)

Ivan1GFP said:


> Machine guns are also terribly inaccurate. A good rifle should be able to put 5-10 rounds into 1 inch at 100 yards (1 Minute of Angle). A typical bipod mounted Light Machine Gun (Browning Automatic Rifle) might hold a 1 foot group at 100 yards if fired single shot. A typical tripod mounted Light / Medium MG might do well to put its rounds into a 3 foot circle. I expect an aircraft MG to be even worse than that because of the abuse that they take. The point here is that a 3 inch or 6 inch or even 1 foot difference in trajectory is pretty much meaningless. A one foot difference at 100 yards is still only 10 feet at 1000 yards and your targets are bigger than that.



And yet the M2 Browning, which was used as an aircraft gun in WW2, would later be used as a sniper rifle.

M2 Browning - Wikipedia, the free encyclopedia

I understand that a machine gun firing in automatic or semi automatic mode when mounted on a tripod or bipod would not be able to maintain accuracy. But why would they be inaccurate in single shot mode? Is it simply because machine guns are made less precisely?


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## Shortround6 (Sep 21, 2013)

I believe your estimates for the accuracy of the bipod mounted mg and tripod mounted mg are way off. While not lazer beams and not as good as a rifle (and BTW WW II service rifles were only good for about 3-4 minutes of angle, 6-8 in groups with _service_ ammunition at 200 yds) a "tuned" water cooled Browning could make a 10 shot group, all bullets touching on the 1000 inch (27.7 yds) range. In fact it had better be able to shoot that good if the Unit machine gunners were to earn their "expert" Badges. Tripod mounted MGs were intended for long range fire, granted it was area fire and not point fire but a gun that fired a 3 ft group at 100 yds would be rather unpredictable at 2000yds. These guns were used for "overhead fire" or shooing over the heads of troops hundreds of yards in front of the guns, guns/ammo that "dropped" ocasional rounds 10-15ft below the intended flight path at 1000 yds would NOT have been looked on with favor. Group sizes tend to grow as sort of a bell or curve, not straight lines. Aircraft _should be no worse_ unless the mounts were designed for dispersion as a deliberate policy, or there is a weakness in the mount/supporting structure. 

I mentioned the drop as a comparison between guns/ammo. I did say that you could point the guns up a bit ( and it only takes 1/3 of a degree or _less_ to zero for 600yds. It is after these ranges that things can very weird, very quick. a weapon that has 0.2-0.3 seconds longer time of flight to 600 yds than another gun mounted on the same plane can be zeroed for the same impact at 600 yds/meters _*BUT*_ it will not match at other ranges, and on a moving target it requires a different lead. 

My long range .308 using a pretty streamline bullet and a MV of 2950fps ( do not use this load in a semi auto) drops 5 feet between 900 and 1000 yds. and one mph of cross wind is worth "about" 1 minute of angle on the sights (14 mph cross wind needs 14 minutes or 140 inch correction) If I remember right. And 'windage' is another example of long range gunner problems, doubling the range usually increases the wind drift about 3 1/2 times for the same value wind, due to the longer flight times. 

A few inches here or there is not of much concern. and at close ranges are nothing to worry about. At long ranges (500-600yds/meters and more) ALL the errors keep piling up making successful long range aircraft fire increasingly iffy. Other pilots may do better but some British pilots in "tests" misjudged the range by up to a factor of 3. That is opening fire at 3 times the range they had been instructed to do so.


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## Shortround6 (Sep 21, 2013)

wuzak said:


> And yet the M2 Browning, which was used as an aircraft gun in WW2, would later be used as a sniper rifle.
> 
> M2 Browning - Wikipedia, the free encyclopedia
> 
> I understand that a machine gun firing in automatic or semi automatic mode when mounted on a tripod or bipod would not be able to maintain accuracy. But why would they be inaccurate in single shot mode? Is it simply because machine guns are made less precisely?



The gun normal fires open bolt. When the trigger is pressed the bolt is released and flies forward, feeding a round into the chamber and then releasing the firing pin after the bolt locks up. This is a fair amount of time and a lot of moving weight and banging around before the gun goes off. The gun (M2 Browning)can be adjusted or "tricked" into the bolt closing on a live round without releasing the firing pin. The Firing pin is released separately for single shot fire. some other guns cannot do this. 
Also note that Sgt. Hathcock used a tripod with elevation and windage controls like this one.






They were sure not trying to use pintel mounts. 

A hand wheel on a threaded rod to control elevation and a lock on the traverse bar under the elevation rod to fix the gun in position. A generous allowance of sandbags would also be used to help hold the gun/tripod in position. One of the pre war tricks on the .30 cal water cooled was to use a tent stake behind the rear tripod leg to prevent vertical stringing. Or 






Note tripod leg ends fitting into cleats on the T shaped firing platform. 

what the "gun" could do and what the gun/mount combination could do are not the same thing.

Please remember that a 300mph airplane is covering 440 feet per second or 44 ft in 1/10 of second. Even if you are behind an aircraft at exactly 6 o'clock and at a distance that takes 1 second time of flight ( and yes your shells do get a boost in velocity) the target aircraft will move forward 440 ft. before the shells get there. Will that cause you to shoot low? Tracers will tell you where you should have been aiming one second ago. 

This is the big difference between air to air shooting and ground shooting. Say you are at 6 O'clock but not perfect. target aircraft is actually flying at 3 degrees to your course, can you see it? as it moves 440ft (147 yds) it will wind up 14-15 ft to side of where you aimed. 

I can believe somebody opened fire at 800yds and hit right away, the question ( actually the 2nd question) is could he do it again the next day 

1st question is how did they KNOW it was 800yds, what were they using for a range finder? 

People have gone to Las Vegas or Monte Carlo and rolled sevens 7 times in a row playing craps. It is the stuff of legends, but all the rest of the gamblers who try are what keep the casinos making big money


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## Aozora (Sep 21, 2013)

I came across some RAAF instructions on harmonising the P-40E's guns

View attachment RAAF P-40 Harmonisation.pdf


The RAAF stipulated that the .50s be harmonised at 300 yards.


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## Aozora (Sep 21, 2013)

DonL said:


> That's one of the most suspicious post I ever read! You will tell me he hit immediately at 800 Yards? Is this some story for your Grand Grandmother?
> And you are a person who questions in a strong way the kills of Hartmann and will tell somebody opens fire at 800 yards and hit immediately?
> 
> Are you realy believing this ****?
> ...


 
There's no reason not to believe that Duke got in a lucky shot, because such things do happen. The actual report reads:



> I engaged the port E/A from astern at 10,000 ft, fired a short burst at very long range (6-800 yards) in an attempt to slow it down, and observed a bright flash in the fuselage from cannon strikes. I rapidly closed and fired another burst, observing the hood fly off and what appeared to be the pilot leaving the a/c. E/A was seen going down and catch fire by F/O Hamer, my No.2, in area M.5820.
> I then continued after the other two E/A still going NW at approximately 10,000 ft. E/A started diving and then went into a steep climb up to about 14-15,000 ft. I quickly caught E/A in the climb as my supercharger came in and closed with the leader as he levelled off. After firing a burst at fairly long range (3-400 yards) and observing no strikes I closed to about 200 yards and scored strikes behind the cockpit, presumably in the rear petrol tank, as E/A started to burn in the fuselage.



Lt Raynor Field: S/Ldr Neville Duke

Duke was probably as surprised as anyone that he hit the 109 because all he was trying to do was force the pilot to slow down - the next 109 he went after he missed at 3-400 yards.


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## Ivan1GFP (Sep 21, 2013)

Shortround6 said:


> I believe your estimates for the accuracy of the bipod mounted mg and tripod mounted mg are way off. While not lazer beams and not as good as a rifle (and BTW WW II service rifles were only good for about 3-4 minutes of angle, 6-8 in groups with _service_ ammunition at 200 yds) a "tuned" water cooled Browning could make a 10 shot group, all bullets touching on the 1000 inch (27.7 yds) range. In fact it had better be able to shoot that good if the Unit machine gunners were to earn their "expert" Badges.


First of all, the numbers I quoted for machine guns were not estimates. They are from what I recall from gun tests in various publications over the years. Perhaps my memory is faulty but I don't believe so.
From having fired many 20th century military rifles, 2.5-4 MOA sounds like typical accuracy from a rack grade M1 Garand firing service ammunition (we were shooting LC 67 and LC 68 ). A typical bolt-action does a bit better at around 2 MOA to 3 MOA with oddballs like the Swedish Mausers doing a LOT better. Some examples do better, some do worse, but this is typical of what I have encountered.

Ammunition for MGs for overhead fire during training comes from select lots which are much better quality than typical service ammunition (at least for the US military). I don't know if this is the same stuff used for qualifications.

Think about what you just claimed for your water cooled Browning: perhaps a 1 inch 10 shot group at 27 yards? Would that be around 4 MOA? I am curious as to how these guns were tuned. Perhaps all shots touching is a bigger group than that?
Also keep in mind that recoil operated guns are notoriously inaccurate which is why other than the Johnson rifle, pretty much no one uses this type of action in a semi-auto rifle. For MGs and pistols, it doesn't matter.



Shortround6 said:


> I mentioned the drop as a comparison between guns/ammo. I did say that you could point the guns up a bit ( and it only takes 1/3 of a degree or _less_ to zero for 600yds. It is after these ranges that things can very weird, very quick. a weapon that has 0.2-0.3 seconds longer time of flight to 600 yds than another gun mounted on the same plane can be zeroed for the same impact at 600 yds/meters _*BUT*_ it will not match at other ranges, and on a moving target it requires a different lead.



Agree with you on elevation: 42-44 MOA (0.75 degrees) from a 100 yard Zero to get to a 1000 yard Zero with a typical 168-175 grain boat tail spitzer at 2600-2650 fps. I have never fired AP rounds at targets, but a .30 cal AP bullet has about the same weight and MV though it isn't a Boat Tail.
Disagree with you on what the result is. Keep in mind we are discussing what an expert air to air marksman can do. Making a high deflection snap shot in a twisting dogfight changes everything.



Shortround6 said:


> My long range .308 using a pretty streamline bullet and a MV of 2950fps ( do not use this load in a semi auto) drops 5 feet between 900 and 1000 yds. and one mph of cross wind is worth "about" 1 minute of angle on the sights (14 mph cross wind needs 14 minutes or 140 inch correction) If I remember right. And 'windage' is another example of long range gunner problems, doubling the range usually increases the wind drift about 3 1/2 times for the same value wind, due to the longer flight times.
> .



Sounds like you have a Palma rifle. They aren't really representative of service guns. Keep in mind that because the .308 cartridge is mandated for competition, folks are playing all kinds of tricks to juice up the MV to keep a HPBT Match bullet above the trans sonic range out to 1000 yards. Your objective is target accuracy. We are discussing aeroplane hitting accuracy and the reason I picked 750 yards is because I believe rifle caliber bullets aren't that different from a medium velocity cannon out that far. My typical .308 load of 168 grain HPBT at 2640 fps is closer to what a rifle caliber AP round would be doing in my opinion. I push these same bullets out to a bit past 3000 fps in other guns, but that also isn't terribly relevant to a rifle caliber MG.

Your 14 MOA correction is interesting but a bit simplistic. The correction isn't a constant MOA. The MOA increases as range increases. In any case, the REAL question is how different a rifle caliber round flies as compared to a 20 mm cannon round, and I do not believe there is a great difference.



Shortround6 said:


> A few inches here or there is not of much concern. and at close ranges are nothing to worry about. At long ranges (500-600yds/meters and more) ALL the errors keep piling up making successful long range aircraft fire increasingly iffy. Other pilots may do better but some British pilots in "tests" misjudged the range by up to a factor of 3. That is opening fire at 3 times the range they had been instructed to do so.



I contend that a few inches is not all that important when your target is the size of an aircraft and your dispersion is typical of a machine gun. I figure even 10 feet isn't all that important. Regarding your "some British pilots", these guys were obviously NOT the expert marksmen we were discussing.

I believe the discussion was about whether there was an advantage for centerline armament for an expert marksman which presumes he knows how to judge distance and proper lead.

Regards.
- Ivan.


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## Rufus123 (Sep 22, 2013)

I know this strays off topic a bit.

I don't know what the typical MOA is of most military rifles is but a 1903 Springfield I once had was much better than the numbers talked about. I got a large number of sub moa groups out of it but was using a Leupold 1.75 x 6. I also got quite a few 1.5 moa groups most of them were closer to 1 moa.

Maybe this was a better than ordinary example and I don't know how much it being a sporter had to do with it.


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## Juha (Sep 22, 2013)

DonL said:


> That's one of the most suspicious post I ever read! You will tell me he hit immediately at 800 Yards? Is this some story for your Grand Grandmother?
> And you are a person who questions in a strong way the kills of Hartmann and will tell somebody opens fire at 800 yards and hit immediately?
> 
> Are you realy believing this ****?
> ...



Combat reports of Duke and his wingman in verbatism on Dike's War Diaries, but why I believe it, it is confirmed on Beale's D'Amico's and Valentini's Air War Italy 1944 - 45 (1996), p. 103. Duke didn't claim it as 109G-8/R5 :=) but the exact designation comes from the fact that we know the victim either Ofw Holstein W.Nr. 200685, Black 3 or Uffz Möller W.Nr. 200023, Black 1 both from 1./NAGr.11. The other was shot down immediately afterwards by Duke. His last 2 kills. So we have combat report, confirming witness statement and confirmation from opponent's (in this case LW's) docus. What else you want? Gun camera film would be nice, I admit, but IMHO fairly well documented case.

Juha

PS On Puhakka's case, Puhakka's combat report, 2 witnesses and the damage on the DB, 20mm hits on the upper skins of wings, with that distance and with fairly low muzzle velocity Oerlikon he had had to aim considerably above the DB to compensate the shell drop at that distance. Puhakka was returning from an interception sortie and was about to land when he saw the bomber and got behind it by a climbing turn, he opened fire while behind the bomber not above it.


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## stona (Sep 22, 2013)

I have read hundreds of combat/encounter reports over the years and there are many instances of aircraft being hit from long range, so I would have no reason to doubt that Duke got in a lucky shot. He was not the only one to do it. I would _always be very cautious of the estimates of range given in these reports _because gun camera footage almost invariably confirms that most pilots were very bad at estimating this. They were even worse at estimating angle off.
There are far more instances of pilots opening fire at long or extreme range (600-800 yards) followed by comments like "no strikes observed" or "no visible effect". A lucky shot is a lucky shot, by definition rare but not impossible. Nobody in their right mind is going to set their weapons up to cater for a remote possibility.

The range and accuracy of weapons fired on the ground has almost nothing to do with their accuracy when fired from an aircraft travelling in one direction at 300mph at an aircraft travelling in another direction at a similar speed. Frankly it is amazing that anyone hit anything before more sophisticated gun sights were introduced. It's the reason why most didn't.

I would love to see a study on the different arrangements of weapons on WW2 fighter aircraft. I never have done. It is possible that no such study was undertaken because, given the other far more significant variables of air to air combat, it was considered irrelevant and unlikely to yield a statistically significant result. I certainly can't see anyway it would have supported the 2 for 1 opinion of those pilots who ventured their view early in the war.

The RAF didn't adopt armament in the wings, outside the propeller arc without careful consideration. The eight gun fighter was born as a result of careful analysis of bullet densities produced by various installations by the Air Ministry's Armament Directorate. It was discovered that a six gun installation would achieve sufficient density at 240 yards and eight guns at 280 yards.
It was Sorley, in a paper to the Air Ministry's Air Fighting Committee who rejected the idea of a centreline cannon. He did not dispute the effect of a 20mm cannon round on another aeroplane but as he said. 

"The basis of discussion, however, is not of the result which is obtained, but rather one of the chances of obtaining the result in the minimum time."

The single engine mounted cannon concept was rejected because in a short burst, all that it was expected their would be time for, the gun would fire so few rounds that it was unlikely that any would hit a vital part of the target.
Sorley continued.

"If the problem of rigid wing mountings for 20mm guns can be solved we should be able to fit four 20mm each with sixty rounds for approximately the same weight as eight machine guns."

He proposed that the Air Ministry should convert the suspended F.10/35 requirement to carry four cannon. The wing mounting problem was not solved as quickly as he would have liked, but this did lead directly to the development of the cannon armed Whirlwind.
It's also why Hawker Typhoons and Tempests were armed with four 20mm cannon in the wings, making them amongst the heaviest armed production fighters of the war.

Cheers

Steve


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## Juha (Sep 22, 2013)

Hello Stona
my points are
a) usually pilots underestimate the range
b) to hit from those distances one had to have guess the range fairly accurately, otherwise they could not correctly compensate the shell drop by aiming the certain amount above the target necessary for a hit. In Puhakka's case, because the fairly low muzzle velocity of the Oerlikon the amount was IIRC some 3m over. The sight helped on this as in range estimation, in both cases pilots knew the span of their targets. In hub mounted cannon that was what was neede but with wing mounted cannon one needed also take into consideration the amount of lateral off needed which was IMHO more difficult to estimate. So there was a considerable amount of luck needed. When I now think it, maybe Puhakka was helped by the fact that only one of his cannon worked, the jaw this produced might have helped him by reducing the lateral off.

Juha


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## stona (Sep 22, 2013)

Hi Juha. 
Point one, absolutely correct. RAF pilots in the BoB were revealed to be opening fire at 1500 yards when they had estimated the range at 300 yards. Things did get better but the tendency to underestimate remained.
Point two. I don't believe any pilot correctly estimated the various criteria needed to make a successful air to air shot at extreme ranges. They took a best guess and hoped. Those with more experience were more likely to guess correctly, but it was still a slim chance. The occasions when this actually worked were few and far between. The arrangement of the weapons had little to do with it, luck had a lot.

My point is equally simple. The average pilot, firing from ranges for which his weapons have been harmonised, is more likely to score hits with his numerous wing mounted guns than an average pilot with a centreline weapon. In other words Sorley, way back in the mid 1930s, was correct.

Cheers

Steve


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## Juha (Sep 22, 2013)

Hello Stona
I more or less agree with the first part of your message and completely agree with the end. In theory during the fairly long chase Duke would have had opportunity to utilise the range estimation feature of his sight because he knew the span of 109. I don't know if he did that. Anyway his purpose was to try to slow down the enemy by hitting him or missing him so closely that he would began to wave. Both Duke and Puhakka very good fighter pilots, the DB was Puhakka's 5th confirmed kill (and his 4th in reality) and he ended the war with, using the British system, 41 confirmed, 5 probablies and 10 damaged.

Yes, it was generally thought that an average pilot could only hit from fairly close range with no deflection. The sight really helped an average pilot only if his wings were level otherwise he needed to compensate the error produced by the bank.

Juha


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## Shortround6 (Sep 22, 2013)

> First of all, the numbers I quoted for machine guns were not estimates. They are from what I recall from gun tests in various publications over the years. Perhaps my memory is faulty but I don't believe so.



It would be interesting to see these "tests". There can be a world of difference between the mechanical accuracy of a gun bolted down to a large immovable bench and a gun fired from a service bipod/tripod sitting on the ground. In the first case you are testing the accuracy of the gun and ammunition, in the second case you are testing the ability of the bipod/tripod to support the gun. It may give you the "practical" accuracy of the gun/gun mount in service conditions but tells you very little about the gun in question.



> From having fired many 20th century military rifles, 2.5-4 MOA sounds like typical accuracy from a rack grade M1 Garand firing service ammunition (we were shooting LC 67 and LC 68). A typical bolt-action does a bit better at around 2 MOA to 3 MOA with oddballs like the Swedish Mausers doing a LOT better. Some examples do better, some do worse, but this is typical of what I have encountered.



Some rifles do better than average but there was a _minimum_ acceptable standard that a gun had to pass for acceptance and it was 3-4 minutes of angle in some countries. Again this is with "test" ammo, whatever that was (selected service lots?) . Ammo was often tested in special test guns, Universal receivers with large, heavy barrels. 




> Think about what you just claimed for your water cooled Browning: perhaps a 1 inch 10 shot group at 27 yards? Would that be around 4 MOA? I am curious as to how these guns were tuned. Perhaps all shots touching is a bigger group than that?


 Not one inch but but more like 1 1/4- 1 1/2. 

Information is from an article published in the "Infantry Mailing List" of 1937-38 and reprinted in Johnson and Haven's book Automatic arms. Section is 12 pages long and includes diagrams of shot patterns for examples of loose packing gland, proper headspace, headspace 3 notches loose, head space 6 notches loose, Play in elevating mechanism, Play in traverse mechanism, looseness in the cradle, Cycle rate ( each gun needs to fire smoothly, faster or slower is not always better), supporting the trail and riding the gun (unnecessary pressure on the grip). Please note that of the 8 things listed only 3 have to do with the gun itself. The rest have to do with the mount and firer. 



> Sounds like you have a Palma rifle. They aren't really representative of service guns. Keep in mind that because the .308 cartridge is mandated for competition, folks are playing all kinds of tricks to juice up the MV to keep a HPBT Match bullet above the trans sonic range out to 1000 yards. Your objective is target accuracy. We are discussing aeroplane hitting accuracy and the reason I picked 750 yards is because I believe rifle caliber bullets aren't that different from a medium velocity cannon out that far.


 Yes. Yes. Service rifle bullets were somewhat different. a bit more later.



> Your 14 MOA correction is interesting but a bit simplistic. The correction isn't a constant MOA. The MOA increases as range increases.



I beleive I covered that with " doubling the range usually increases the wind drift about 3 1/2 times for the same value wind"



> In any case, the REAL question is how different a rifle caliber round flies as compared to a 20 mm cannon round, and I do not believe there is a great difference.



Problem here is that there is a lot more variation between the 12.7-13mm bullets and the various 20mm shells than there were between the various rifle rounds. The champs among the high production guns are the US .50 and the Russian 12.7mm, high velocity and well shaped bullets, good enough that they beat any WWII 20mm gun for truly long range fire( over 1000yds). German 13mm and Italian/Japanese/British 12.7mm guns are not only lower velocity they use lighter bullets of poorer sectional density and poorer shape. The 20mm cannon are even worse as far as difference goes. The 20mm Hispano will match the US .50 out to around 600yds pretty well (within a few inches) It's higher sectional density offset by it's much worse shape. The 20mm Hispano is as good as it gets. The rest of the 20mm shells are either as good (roughly) as the Hispano and fired at a _much_ lower velocity or they are lighter with poorer sectional density and no better shape and still fired at lower velocity (except the Russian 20mm) 

Time of flight for German rounds to 300 and 600 meters.

7.92mm AP 10 g............0.453..........1.159
13mm HEI 34 g.............0.49............1.22
15mm HEI 57.5g...........0.357...........0.816
20mm HEI 92g..............0.551..........1.428 (from a MG/FFM)
20mm HET 117g...........0.477...........1.101 (from a MG 151)
30mm HEI 330g............0.696...........1.66 (MK 108 ) 

From a different source: time of flight to 600 yds for US .50 cal. 0.72 sec and for the 20mm Hispano 0.84 sec. Granted it is a 10% shorter distance. 



> I believe the discussion was about whether there was an advantage for centerline armament for an expert marksman which presumes he knows how to judge distance and proper lead.



At 300 yds/meters most guns will hit the same ( with a few exceptions) at 600yds/meters the differences are starting to show up a lot more and at longer ranges it gets worse quick. From a German test the 20mm Hispano was still doing 500m/s at 600 meters, the 20mm mine shell from the MG/ffM is doing 281m/s, the 20mm HET from the 20mm MG 151 is doing 422m/s and the 30mm mine shell is doing 254m/s. The Hispano shell is traveling at 600meters as fast as teh 3MK 108 shell was at the muzzle. 

The Germans used mixed belts of ammo. They mixed the 92g and 117g shell in the same belt. Now in either the MG/FFM or the MG 151 the muzzle velocities changed for the two shells which means the difference in timing/trajectory isn't quite what the above figures suggest but our intrepid pilot in _either_ a German or Soviet plane trying to fire at 600 meters _plus_ had better pick _which_ gun he is going to try to hit with because different guns in his plane will NOT hit to the same time and place. It the case of the German pilot he may have to decide which _type_ of ammo he is trying to hit with from his 20mm MG 151 as the mine shell and the heavier rounds will not arrive at the same point in space/time. 

Before I get jumped on, this is referring to long range fire, like in excess or well in excess of 400 meters. At closer ranges the differences fade to insignificant the mis-matched guns co-ordinate very well. This is not which country was better ( I have left out rates of fire, weights of guns, weights of ammo, weight of HE, etc) this is only referring to problems in getting hits at long range. 

In theory the fuselage mounted weapon had a lot going for it, in practice it had a lot of problems with implementation in WW II. Designing a weapon system (gun/engine/airplane) that only a very small percentage of pilots can make use of is not the smart way to go.


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## stona (Sep 22, 2013)

Shortround6 said:


> Designing a weapon system (gun/engine/airplane) that only a very small percentage of pilots can make use of is not the smart way to go.



Yes, and having that small percentage use the same system that is designed to optimise the performance of the majority will not suddenly render them less effective.
Cheers
Steve


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## Njaco (Sep 22, 2013)

A good marksman - an expert - will be able to take his weapon of choice and use it to his advantage every time regardless of what can or can't be done. If Hartmann had a spitball gun that was only effective at 1200 yards then that would be the parameters that he would work within to succeed. If I remember that was one reason Hartmann was so successful- he was able to get in very close without being noticed. In that instance I'm sure many of us would be successful. He was a master of it - and I would say regardless mostly of what the weapon was.


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## Ivan1GFP (Sep 22, 2013)

Rufus123 said:


> I know this strays off topic a bit.
> 
> I don't know what the typical MOA is of most military rifles is but a 1903 Springfield I once had was much better than the numbers talked about. I got a large number of sub moa groups out of it but was using a Leupold 1.75 x 6. I also got quite a few 1.5 moa groups most of them were closer to 1 moa.
> 
> Maybe this was a better than ordinary example and I don't know how much it being a sporter had to do with it.



That is an awfully small telescope for high precision work. 
How many shots in your groups? 
I am typically shooting 5 shot groups because I believe it is enough to be fairly representative without being overly wasteful of ammunition. Statistically you can work out what a 10 shot group size would be from this also.

A lot of the lack of accuracy in military rifles is due to the ammunition that was issued. As an example with a particular M1 Garand (glass bedded): With fairly good handloads 1.00 inch to 1.25 inch. With M72 Military Match ammunition: 1.75 inch. With Lake City M2 Ball ammunition 2.5 inch. With French .30-06 FMJ ammunition, 3-5 inch groups were more common. The accuracy varied a bit but this was typical with this gun shooting off sandbags and using a 3-9X telescope.

In theory, a sporter stock should improve accuracy but personally I have not found that to be the case. My experience is that unless there is a problem with a pressure point somewhere, a fully military stock will often shoot as well as what you are describing at least with Mauser 98s, M1903s, Swedish Mausers, Mosin Nagants and Lee Enfields in both No.1 and No.4 and with Pattern 14 and M1917s. I don't have enough experience with Japanese or French bolt actions to come to any conclusion. This is not to say they all shoot this well, but at least on a couple examples that did not, taking the rifle apart revealed something that was wrong.

Hope this helps.
Pardon the digression.
- Ivan.


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## Ivan1GFP (Sep 22, 2013)

Shortround6 said:


> Not one inch but but more like 1 1/4- 1 1/2.


That works out to 4.5 to 5.4 MOA which is still amazingly accurate.



Shortround6 said:


> Information is from an article published in the "Infantry Mailing List" of 1937-38 and reprinted in Johnson and Haven's book Automatic arms. Section is 12 pages long and includes diagrams of shot patterns for examples of loose packing gland, proper headspace, headspace 3 notches loose, head space 6 notches loose, Play in elevating mechanism, Play in traverse mechanism, looseness in the cradle, Cycle rate ( each gun needs to fire smoothly, faster or slower is not always better), supporting the trail and riding the gun (unnecessary pressure on the grip). Please note that of the 8 things listed only 3 have to do with the gun itself. The rest have to do with the mount and firer.



I actually have the book "Automatic Weapons" by Melvin Johnson. Is this the book? Do you happen to know where in the book. Now I just need to find where the book is hiding.



Shortround6 said:


> Problem here is that there is a lot more variation between the 12.7-13mm bullets and the various 20mm shells than there were between the various rifle rounds. The champs among the high production guns are the US .50 and the Russian 12.7mm, high velocity and well shaped bullets, good enough that they beat any WWII 20mm gun for truly long range fire( over 1000yds). German 13mm and Italian/Japanese/British 12.7mm guns are not only lower velocity they use lighter bullets of poorer sectional density and poorer shape. The 20mm cannon are even worse as far as difference goes. The 20mm Hispano will match the US .50 out to around 600yds pretty well (within a few inches) It's higher sectional density offset by it's much worse shape. The 20mm Hispano is as good as it gets. The rest of the 20mm shells are either as good (roughly) as the Hispano and fired at a _much_ lower velocity or they are lighter with poorer sectional density and no better shape and still fired at lower velocity (except the Russian 20mm)



Sounds like the centerline gun arrangement on the P-38 is quite good!
If the US and Soviet .50 cals were quite good and 20 mm and 12.7 mm guns from other countries were worse, then how different would a German MG 151/20 and the MG 131 be?



Shortround6 said:


> At 300 yds/meters most guns will hit the same ( with a few exceptions) at 600yds/meters the differences are starting to show up a lot more and at longer ranges it gets worse quick. From a German test the 20mm Hispano was still doing 500m/s at 600 meters, the 20mm mine shell from the MG/ffM is doing 281m/s, the 20mm HET from the 20mm MG 151 is doing 422m/s and the 30mm mine shell is doing 254m/s. The Hispano shell is traveling at 600meters as fast as teh 3MK 108 shell was at the muzzle.



Many years back, I was interested in getting good accuracy from the Sierra 168 grain MatchKing HPBT bullet out to 1000 yards when launched from a .308 Winchester. This bullet has a reputation for excellent accuracy as long as it stays above the speed of sound. The ballistics programs I was using were predicting that when launched at 2600 fps, the velocity at 1000 yards was still around 1300 fps (400 M/s).

Turns out that the bullet starts to misbehave when it enters the trans sonic range and not just when it drops below the speed of sound. The point here is that 1300 fps is still fairly decent velocity though actual field conditions would likely bring the velocity down a touch.



Shortround6 said:


> In theory the fuselage mounted weapon had a lot going for it, in practice it had a lot of problems with implementation in WW II. Designing a weapon system (gun/engine/airplane) that only a very small percentage of pilots can make use of is not the smart way to go.



Not disagreeing with you here. The general issue weapon has to suit the majority of the operators. Thus the AK-47 is a fairly good weapon for general issue. The point I believe we were discussing is whether or not an expert would be able to better utilise a different weapon. I believe an expert marksman would be more effective with something like a M14 rifle even if the average soldier would not. Similarly I believe an expert aerial marksman would see an advantage in centerline armament on a fighter even if the average pilot would not.

- Ivan.


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## yulzari (Sep 22, 2013)

Ivan1GFP said:


> folks are playing all kinds of tricks to juice up the MV to keep a HPBT Match bullet above the trans sonic range out to 1000 yards.
> .



Keeping off topic (apologies). This is exactly what musket target shooting requires. Except at 100 metres instead of 1,000 yards. As soon as a round musket ball drops into the transonic range it destabilises and accuracy flies out of the window.

The usual choice is a large load of powder to chuck the thing down range hard enough for a reasonably flat trajectory as far as the target so that it is still supersonic at 100 metres (or 50 metres in my case).

In principle the alternative is to load light to ensure it leaves the muzzle below transonic speeds and thus remains stable until it simply runs out of puff. However you have trajectory of a badminton shuttlecock and the time of flight leaves the ball vulnerable to wind even at 100 metres. With care you can actually see the thing in flight.

There were good reasons why musket fire beyond 100-150 yards was not a battlefield norm and this is one of them. Once the ball drops to transonic speed it is beyond the control of even the best marksman and the holdover is measured in yards not inches.

Smooth bore muzzle loader hunters adjusted fixed sights with variable loads so that the point of aim and point of impact matched the sights at different ranges. But now we are veering too far off the topic.


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## fastmongrel (Sep 22, 2013)

yulzari said:


> But now we are veering too far off the topic.



I dont think so the topic has become more about range than the original post. Good topics mature and spread out and so far this is a good one long may it continue in any direction the discussion takes it. Neville Dukes Golden shot sounds unbelievable but is backed up by some evidence. Stranger things have happened in life, I once saw someone take aim with an 100 year old plus Enfield Martini .303 lever action single shot at a Pigeon at approx Football pitch distance and blow it out of the sky, no one was more surprised than the shooter.


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## yulzari (Sep 22, 2013)

Possibly the pigeon?


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## fastmongrel (Sep 22, 2013)

Doubt the Pigeon had much time to be surprised before it turned into a dead Pigeon


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## Shortround6 (Sep 23, 2013)

> I actually have the book "Automatic Weapons" by Melvin Johnson. Is this the book? Do you happen to know where in the book. Now I just need to find where the book is hiding.



"Automatic Arms" is copyright 1941. "Automatic Weapons" is copyright 1945, it may have a number of changes. 





> Sounds like the centerline gun arrangement on the P-38 is quite good!
> If the US and Soviet .50 cals were quite good and 20 mm and 12.7 mm guns from other countries were worse, then how different would a German MG 151/20 and the MG 131 be?









Again, thanks to Zeno's. 

Time of flight is within 1/10 sec at 600yds, I don't believe the German guns matched quite that well. 
In one of Tony Williams books there is a trajectory chart for the Me 410B-2/U1 armed with two MG 131s, Two MG 151/15s and a 5cm BK 5. the last two are rather out of the ordinary but the MG 131 has a trajectory that starts about 90cm below the line of sight, crosses the line of sight at about 120 meters, peaks at about 80cm above the line of sight at just over 300 meters and drops to the line of sight at 500 meters. The curve on the chart stops at that point but if you were to extend the curve it may be 80cm low before it gets to 600 meters and over 160 cm low before it gets to 700 meters. In a single engine fighter using it as cowl gun with the guns closer to the line of sight you either have a shorter distance to the the 2nd crossing of the line of sight or an even higher 300-350 meter trajectory point. 80cm=32in= 2 2/3 feet. On a bomber ypou will still be on target but it seems a lot is made of wing guns being off 3-4 feet laterally at combat distances. 



> Many years back, I was interested in getting good accuracy from the Sierra 168 grain MatchKing HPBT bullet out to 1000 yards when launched from a .308 Winchester. This bullet has a reputation for excellent accuracy as long as it stays above the speed of sound. The ballistics programs I was using were predicting that when launched at 2600 fps, the velocity at 1000 yards was still around 1300 fps (400 M/s).
> 
> Turns out that the bullet starts to misbehave when it enters the trans sonic range and not just when it drops below the speed of sound. The point here is that 1300 fps is still fairly decent velocity though actual field conditions would likely bring the velocity down a touch.



Off topic but many years back I pulled pit for a man using 168 grain bullets from a semi auto at 800, 900, and 1000yds. He did pretty good at 800 and 900, probably better than I could with a service rifle. At 1000yds 16-17 out of 22 rounds fired showed some evidence of tipping as they went through the target. Everything from slightly oval holes to full profiles of the bullet, size of the "group" went from several feet at 900yds (extreme spread) to just about the entire 6' x 6' target at 1000 yds. I can't remember if there were one or more misses. I don't think any one who was in the pits that day would be tempted to use 168s at 1000yds.


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## pinsog (Sep 23, 2013)

Shortround6 said:


> "Automatic Arms" is copyright 1941. "Automatic Weapons" is copyright 1945, it may have a number of changes.
> 
> 
> 
> ...


 
.308 Winchester/7.62 NATO goes subsonic at around 880 yards, from all the data I have ever seen (give or take a few yards depending on bullet choice, and I am talking about high ballistic coefficient bullets) so beyond that point accuracy is going to suffer very badly. I believe US snipers consider 800 meters to be the max effective range for a .308 Winchester using a sniper rifle.


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## Shortround6 (Sep 23, 2013)

Bullets behave differently. The old 172-173 grain boat tail military bullet may not have had the sub one minute of angle accuracy of the Sierra 168 grain but it tended to stay point on when when it went subsonic. Or at least with the same MV as the 168 grain Sierra it stand supersonic longer. 
The other things affecting "max effective range" is range and wind drift. 

The difference between 900 yds and 1000 yds with a .308 and 2600fps MF using 168-172 grain bullets ( generic ballistic calculator) is about 100 inches of drop ( 8ft) and in a 10mph cross wind _another_ 20 inchs of drift. Without a _good_ laser rangefinder or GPS on known co-ordinates even a 50yd error in range estimation can mean a vertical miss of several feet and horizontal miss of about 1 foot even the wind is guess 100% right.


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## GregP (Sep 23, 2013)

Just getting nack to this. Replying to Marcel's post #14.

There were NO radials with cannons firing through the hub. The center of the master rod was NEVER in line with the prop hub at any point during rotation and you can't fire through the center of it since there are rods in the way.

The FEW radials with guns firing through the engine all had single-row radials with the guns firing between the cylinders, as on the Boeing P-26. It was one solution but not a good solution since fighters were very quickly going to require multi-row radials, effectively meaning no space between the cylinders at all. They had to find other places for the guns.


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## Ivan1GFP (Sep 24, 2013)

pinsog said:


> .308 Winchester/7.62 NATO goes subsonic at around 880 yards, from all the data I have ever seen (give or take a few yards depending on bullet choice, and I am talking about high ballistic coefficient bullets) so beyond that point accuracy is going to suffer very badly. I believe US snipers consider 800 meters to be the max effective range for a .308 Winchester using a sniper rifle.



Properly stated: A 168 grain Sierra (or Hornady or Speer or similar) HPBT bullet at a muzzle velocity around 2600 fps goes TRANS-sonic at around 880 yards.

The launching cartridge doesn't matter. The muzzle velocity does.
The same cartridge in different guns has different effects: There is going to be a velocity difference when launched from a 18 inch barrel (H&K G-3) versus a Remington 700 Varmint Gun with a 26 inch barrel versus a Palma rifle with a 30 inch barrel.

One other thing worthy of note is that the velocities specified on US Match / Sniper ammunition is actually instrumental velocity at about 78 feet from the muzzle. Actual MV is typically about 50 fps faster. The velocities I have recorded are at 7 feet from the muzzle which I do not correct back to actual MV. The difference is so little (guessing 3-5 fps) as to be below the shot to shot variation and about 1/5 of the standard deviation in velocities (about 15 fps) on a good load.

There may be others, but these are the issued US 7.62 mm NATO Sniper cartridges I know about: M118 (173 grain FMJ-BT), M852 (168 grain Sierra HPBT or similar), M118LR (175 grain Sierra HPBT). The Federal .308 Gold Medal Match I do not believe is issued, but very similar to the M852. There is a difference: The M852 is not SAAMI spec because it is typically loaded to OAL of 2.810-2.815 inch which is over max of 2.800 inch.
Of these, I believe only the 168 HPBT is known to have serious yawing / stability issues when dropping through the trans sonic range.

Target shooters have all kinds of ways of working around this issue and the fact that the .308 / 7.62 cartridge has so little case capacity. Most of these methods exceed SAAMI specifications one way or another and thus can no longer be considered a .308 Winchester cartridge in my opinion.

I can go on quite a bit more about this topic, but I am pretty sure this already is pretty seriously off the original topic. I picked examples of .308 Win ballistics to illustrate what could be expected of Rifle Caliber machinegun projectiles such as those used in the US .30 cals and the Germal 7.92 x 57 mm.
If this topic (and I am sure a bunch of us like to talk about guns), we should move this to another thread and post a link in this thread.

Thanks.
- Ivan.


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## Aozora (Sep 24, 2013)

Getting way back to topic: apparently the RAF did consider the use of a central cannon but rejected the idea because it was calculated that a short burst from one cannon wouldn't put enough shells on target to do decisive damage; a paper was written in 1935 by Sqn. Ldr. Sorley stating:



> The decisive effect of one 20mm or larger calibre projectile on a modern aircraft is, I think, indisputable....The basis for discussion, however, is not of the result which is obtained but rather one of the chances of obtaining the result in the minimum of time....*The single cannon mounted on the engine can only be regarded as a first step*...if the problem of rigid wing mountings for 20 mm guns can be solved we should be able to fit four 20 mm each with sixty rounds for approximately the same weight as eight machine guns.


 (bold underline added)

National Archives: AIR5/1137 Air Fighting Committee, 15th meeting _Further Review by O. R. of the Use For Air Fighting of a Gun of Larger Calibre than Machine Guns_ 26/07/35

From: Niall Corduroy _Whirlwind: Westland's Enigmatic Fighter_ [Fonthill 2013] page 13


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## GregP (Sep 25, 2013)

Tell us how you really feel DonL!

Ivan, I believe point blank means the bul;let will hit where it is aimed exactly. So a point blank range of 5800 yards doesn't say anything about rise and fall, it says the bullet will hit the belt at 500 yards if aimed exactly there. 

To find the bullet rise between the gun muzzle and the impact point at 500 yards, you have to go to the ballistics characteristics of the round with the length of the barrel or, more correctly, the distance between the chamber and the gas port known. However, if you are interested in hits, the rise doesn't matter if you can hit the target ... unless you are shooting under something. That's rare in combat.

As for the differening ballistic characteristic of armament in fighters, if you shoot anywhere NEAR the point blank range, it doesn't matter. If you shoot closer or farther away by a significant amount, it does. That;s why the Zero allowed the pilot to select the MG, the cannon, or both ... to account for shooting at bombers from a distance. He could turn off the MG and just use the cannon.


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## DerAdlerIstGelandet (Sep 25, 2013)

Don't bait other members...


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## Ivan1GFP (Sep 25, 2013)

Hello GregP,

Perhaps I didn't explain the concept of Point Blank Range very well, but I believe you are not using the term correctly. The problem is that there is common usage and the technically correct meaning.



GregP said:


> Ivan, I believe point blank means the bul;let will hit where it is aimed exactly. So a point blank range of 5800 yards doesn't say anything about rise and fall, it says the bullet will hit the belt at 500 yards if aimed exactly there.



PBR does take into account the maximum height of the bullet's trajectory:

PBR is the maximum range at which a shooter can aim directly at his target without adjusting the elevation.
PBR is a function of the gun / ammunition and the target size.
Take for an example a common .30-06 rifle.

If my target is a basketball, my bullet cannot rise or fall more than about 5 inches or so if I aim at the center. To get the maximum PBR, I adjust the zero on the rifle so that the maximum height of the bullet is never more than 5 inches. At some point, the drop of the bullet will be 5 inches from my line of sight. THAT will be at the maximum PBR. As a guess, I would figure that to be around 250 yards or so.

If my target is a person, the US army figured out with the M1903 rifle that the maximum PBR was 550 yards (probably with around a 300-something yard zero). The bullet would not go higher than the target's head or drop below the target's feet within 550 yards.

Aeroplanes are much bigger than people, so I am assuming the distance to be considerably more than 550 yards. I didn't try to figure out how far, but my GUESS was around 750 yards or so. Perhaps I guessed wrong?



GregP said:


> To find the bullet rise between the gun muzzle and the impact point at 500 yards, you have to go to the ballistics characteristics of the round with the length of the barrel or, more correctly, the distance between the chamber and the gas port known. However, if you are interested in hits, the rise doesn't matter if you can hit the target ... unless you are shooting under something. That's rare in combat.



Actually barrel length, chamber length, gas port locations and internal ballistics considerations are pretty much irrelevant. All that is important is the Muzzle Velocity and the flight characteristics typically represented by a Ballistic Coefficient and ballistic model. Most people use the G1 model which is based on a 1 inch diameter projectile that looks pretty much like we expect a "bullet" to look. This was the Krupp standard bullet. That is why you get things like ballistics coefficients that change with velocity range: because the modern rifle bullet really doesn't follow that kind of flight path. Interestingly enough, a typical aircraft cannon shell DOES bear a pretty good resemblance to a Krupp standard bullet. The modern boat tailed spitzer bullet is better represented by the G7 model.



GregP said:


> As for the differening ballistic characteristic of armament in fighters, if you shoot anywhere NEAR the point blank range, it doesn't matter. If you shoot closer or farther away by a significant amount, it does. That;s why the Zero allowed the pilot to select the MG, the cannon, or both ... to account for shooting at bombers from a distance. He could turn off the MG and just use the cannon.



You are assigning a tactical reason to the armament configuration of the A6M. I have no knowledge of why this was done. I do know that the FW 190 series had guns selectable as well and there were less ballistics differences between the cannon and MG. (This ballistics similarity is the point I have been arguing all along.) I have always thought that the gun selection and trigger on the A6M was much less than optimal. The throttle is just not the right place to put the trigger IMO.

Regards.
- Ivan.


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## Greyman (Sep 25, 2013)

Ivan1GFP said:


> Aeroplanes are much bigger than people, so I am assuming the distance to be considerably more than 550 yards. I didn't try to figure out how far, but my GUESS was around 750 yards or so. Perhaps I guessed wrong?



The Brits gave 600 yards in their instruction during the war (.303 gunnery).


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## Ivan1GFP (Sep 25, 2013)

Greyman said:


> The Brits gave 600 yards in their instruction during the war (.303 gunnery).



Velocity of the .303 is also a bit lower: 2450 fps versus 2600 for the 7.92 and 2800 for the US .30 Cal.
Not sure it makes much of a difference but it is a difference. Besides, Instructions tell you what to do, they don't necessarily tell you what the weapon is capable of.

- Ivan.


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## Greyman (Sep 25, 2013)

In terms of bullet drop the .30 generally seems to travel about 50 extra yards to equal the same drop distance of the .303


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## swampyankee (Sep 25, 2013)

I remember reading somewhere (this means I've no clue as to a citation) that the US 0.50 in MG bullet was modified to _increase_ dispersion, as they felt that increased dispersion would make it a more effective anti-personnel weapon. Was the ammunition used in aircraft installations the same as that used in ground installations?


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## fastmongrel (Sep 26, 2013)

swampyankee said:


> I remember reading somewhere (this means I've no clue as to a citation) that the US 0.50 in MG bullet was modified to _increase_ dispersion, as they felt that increased dispersion would make it a more effective anti-personnel weapon. Was the ammunition used in aircraft installations the same as that used in ground installations?



I know some MG tripods were built so that the gun could move automatically side to side during firing to increase the width of the stream of fire but never heard of bullets being modified.


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## Shortround6 (Sep 26, 2013)

Quality control of Military ammunition ( and especially war time ammunition) is NOT the same as commercial ammo and commercial ammo has gotten a lot better from the 1930s to the last 2-3 decades. There were minimum standards however. Ammo might have to group 3-4 minutes of angle, fired from heavy test barrels in heavy receivers mounted on concrete or heavy timber benches. They were testing ammo, not guns. Some batches were better than others, sometimes much better. My father and his friends had one lot number of early 1950s 30-06 AP that would group better than 2 min of angle out of any of 5 different accurized M-1s. This does NOT mean that the lots produced before and after it were "designed" to be less accurate. BTW this group of shooters had a number of members who worked for Winchester at the time, a few of which shot for the Winchester team and had access or knew men who worked in the under ground test tunnel. 

As far as shooting at airplanes goes, it rather depends on the airplane, Most single engine fighters are not more than 6 feet tall once the landing gear is retracted, tail fins and P-47s excepted  Bombers on the other hand??? 

Point blank range against stationary "tanks" is _roughly_ the muzzle velocity + 10%. smaller or larger tanks change the distance and type of projectile will affect distance. WW II Heat rounds with poorer than normal ballistic co-efficient are a bit shorter while APDS. and APDSFS are quite a bit longer. 

Once again, the American .50, the Russian 12.7mm and the German 15mm mg 151/*15* were in a class of their own and the mg 151/15 was used to a large (thousands) extent. The 20mm Hispano comes close and just about every _common_ WW II aircraft gun is worse, some much worse. 

I rather doubt the Japanese were using the 20mm guns in the Zero for long range fire, at least the early ones. It had about the _worst_ MV of ANY WW II 20mm gun. It would need the best estimate of range and speed, the most elevation of the gun and the greatest lead on a moving target. It also had the 60 round drums which means they didn't get too many "chances to guess" before they were out of ammo. Not to say a few pilots didn't try but it doesn't seem like a sound tactical practice.


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## Ivan1GFP (Sep 27, 2013)

Shortround6 said:


> Quality control of Military ammunition ( and especially war time ammunition) is NOT the same as commercial ammo and commercial ammo has gotten a lot better from the 1930s to the last 2-3 decades. There were minimum standards however. Ammo might have to group 3-4 minutes of angle, fired from heavy test barrels in heavy receivers mounted on concrete or heavy timber benches. They were testing ammo, not guns. Some batches were better than others, sometimes much better. My father and his friends had one lot number of early 1950s 30-06 AP that would group better than 2 min of angle out of any of 5 different accurized M-1s. This does NOT mean that the lots produced before and after it were "designed" to be less accurate. BTW this group of shooters had a number of members who worked for Winchester at the time, a few of which shot for the Winchester team and had access or knew men who worked in the under ground test tunnel.



I have heard that AP ammunition steel cores would wreck the barrel of a rifle. This was a before and after test on a M1 Garand that was about to be re barreled anyway. How did these rifles fare?
3-4 MOA was NOT being met with 7.62 NATO ammunition for quite some time even with the test rifles. Typical accuracy out of the Army's new M14 rifle was around 6 MOA for a while with service ammunition and special lots of ammunition had to be made up for rifle acceptance testing.



Shortround6 said:


> As far as shooting at airplanes goes, it rather depends on the airplane, Most single engine fighters are not more than 6 feet tall once the landing gear is retracted, tail fins and P-47s excepted  Bombers on the other hand???



Height wise I agree, but at the many different angles you can approach a typical fighter, on the average, it is a whole lot bigger than a 6 foot diameter circle.



Shortround6 said:


> Point blank range against stationary "tanks" is _roughly_ the muzzle velocity + 10%. smaller or larger tanks change the distance and type of projectile will affect distance. WW II Heat rounds with poorer than normal ballistic co-efficient are a bit shorter while APDS. and APDSFS are quite a bit longer.



How many and which WWII tank guns actually used HEAT, APDS or APDSFS ammunition????

- Ivan.


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## Aozora (Sep 27, 2013)

Ivan1GFP said:


> How many and which WWII tank guns actually used HEAT, APDS or APDSFS ammunition????
> 
> - Ivan.



AFAIK no WW 2 tank gun used HEAT or APDSFS but a few, such as the 6 and 17 pdrs, used APDS and APCBC Great Britain's Gun Penetration Tables - World War II Vehicles, Tanks, and Airplanes


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## Juha (Sep 27, 2013)

Aozora said:


> AFAIK no WW 2 tank gun used HEAT or APDSFS but a few, such as the 6 and 17 pdrs, used APDS and APCBC Great Britain's Gun Penetration Tables - World War II Vehicles, Tanks, and Airplanes



At least GB, Germany, Soviet Union and Finland had HEAT tank ammo.


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## Aozora (Sep 27, 2013)

Juha said:


> At least GB, Germany, Soviet Union and Finland had HEAT tank ammo.


 
Doh! For some reason I was thinking of HESH. Yes there were primitive HEAT rounds used during WW2, but HEAT was more effective when used in unrotated projectiles such as Panzerfausts, Panzerschrecks and PIATs and the like.







Waaay OT - Come to think about it didn't the Petard Spigot mortar used on some of the Churchill AVRE's use HESH?


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## fastmongrel (Sep 28, 2013)

Aozora said:


> Waaay OT - Come to think about it didn't the Petard Spigot mortar used on some of the Churchill AVRE's use HESH?



Not during the war it was simply a blast weapon and known as the "Flying Dustbin". HESH didnt get into service till after the war, the later 165mm AVRE gun used HESH rounds.


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## Ivan1GFP (Sep 28, 2013)

Juha said:


> At least GB, Germany, Soviet Union and Finland had HEAT tank ammo.



Can you comment on which guns had them and when? I had only heard of APDS used in a 6 pounder and 17 pounder.

- Ivan.


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## Juha (Sep 28, 2013)

Hello Ivan
GB: 95mm
Germany: at least 75mm round, others for field artillery and A/T units at least
Soviet Union: at least 76,2mm
Finland: at least 114mm, in fact GB 4.5" field howitzer round modied to take German 105mm HEAT round, used in BT-42. see e.g. BT-42 - Wikipedia, the free encyclopedia

Juha

Forgot the time, Germans were the first ones, introduced the 75mm HEAT round mid-1940 just after the Battle of France.


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## silence (Sep 28, 2013)

Juha said:


> Forgot the time, Germans were the first ones, introduced the 75mm HEAT round mid-1940 just after the Battle of France.



Didn't they bring it in to make the short-barrel Pz MkIV more effective in tank-vs-tank combat?


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## fastmongrel (Sep 29, 2013)

The Italians used Effeto Pronto shells which I think were HEAT but I cant read Italian 

High Explosive Anti-Tank - Wikipedia


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## Rufus123 (Sep 29, 2013)

I am obviously a super novice on the topic of aircraft but I find the subject interesting and have wonder why things are the way they are hence my strange questions.

One of the reasons I was curious over firing through the hub and it sounding like a good idea was filling a void at all ranges.

I have thought that 3 cannon with one in the hub might be better than 4 in the wings for this reason. At very close range there could be a gap in the shell strikes if the pilot did a perfect job of aiming. If the aim was slightly off to the right or left the wing gun would strike where to pilot was trying to aim. I do realize that the individual hits will be spread out because both aircraft are moving. I have wondered if when using three cannon if the wing guns should be parallel rather than converge creating a wider damage zone at all ranges of fire.


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## Juha (Sep 29, 2013)

silence said:


> Didn't they bring it in to make the short-barrel Pz MkIV more effective in tank-vs-tank combat?


 
Originally yes, and of course also the early StuG IIIs, but later also KwK 40, the long barrel 75mm gun of later PzKpfw IVs and the 88mm L/56 of Tiger got HEAT rounds to be used on longer ranges where they had better penetration power than traditional APCBC shells, at least in theory, but how common was their use, I cannot recall.

Juha


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## douvie (Oct 17, 2013)

In the discussion between whether "centre fire (hub)" was better than "wing platform" configuration, I have read in several books and mags, that most German Ace pilots believed that the "wing platform" configurations were more effective for the following reasons:

1). There was more "lead" thrown at the target with a wing platform arrangement.
2). It was more difficult to bring the weapons to bare with the hub arrangement, especially in dog fight situations.

Another thing not mentioned in the discussions so far, is that a relative number of Hurricanes and Spitfires did have 2 40mm wing-mounted cannons in addition to 6 machine guns on the Hurricane and the 4 machine guns on the Spitfires. 

Also, I'll get the quote if necessary, many German pilots complained that if they fired too long the 30mm cannon would cause them to lose airspeed. RAF pilots had a similar experience if they fired the 40mm cannons too long. 

I've got the info I just need to get it scanned in.


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## tyrodtom (Oct 17, 2013)

What would the German aces know about wing platform armament, except from being on the receiving end of it ?

They had no fighters with wing armament alone, all were centerline armed, some with added wing guns.

Some FW190 had fuselage guns, wing root cannons, and cannons further out on the wings, but the majority of it's firepower would be considered centerline.


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## tomo pauk (Oct 17, 2013)

douvie said:


> In the discussion between whether "centre fire (hub)" was better than "wing platform" configuration, I have read in several books and mags, that most German Ace pilots believed that the "wing platform" configurations were more effective for the following reasons:
> 
> 1). There was more "lead" thrown at the target with a wing platform arrangement.
> 2). It was more difficult to bring the weapons to bare with the hub arrangement, especially in dog fight situations.
> ...



I look forward to the scanned stuff. In the meantime:
-most of the German aces racked up kills with 'central battery'
-2 x 40 mm was never installed in/on a Spitfire (bar for trials?), the Hurri with 2 x 40 mm was the tank buster, with 2 x .303 installed, too


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## Jabberwocky (Oct 17, 2013)

4 x 20 mm was used on the Spitfire, but only in limited use.

Mk Vc's with the SAAF used the configuration in the MTO and some Mk VIIIs with the RAAF used it in the PTO.

The major problem wasn't the weight, or the slightly adverse effect on roll response, but the fact that the second 20 mm was much more prone to jamming, due to issues with gun heating related to the ducting. The Hispano was tempremental if not treated properly.

When the wing was redone for the Mk 21, the ducting was redesigned and the problem solved, so 4 x 20 mm was adopted as standard. They also went with the Hispano Mk V, which had a better (and smaller) feed design, that also reduced jamming. Around 50% of all Hispano Mk II jams in 1944-1945 were traced to feed problems, at least with the 2 TAF.


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## Rufus123 (Oct 17, 2013)

douvie said:


> In the discussion between whether "centre fire (hub)" was better than "wing platform" configuration, I have read in several books and mags, that most German Ace pilots believed that the "wing platform" configurations were more effective for the following reasons:
> 
> 1). There was more "lead" thrown at the target with a wing platform arrangement.
> 2). It was more difficult to bring the weapons to bare with the hub arrangement, especially in dog fight situations.
> ...



I thought the Germans really liked center line weapons if they will work on the plane. I wonder how three 20mm (one in the hub and 2 in the wings) would compare with 4 20mm in the wings against fighters. Run in parallel the center gun fills the void in the center. Go with a 30 in the hub for bombers.


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## Rufus123 (Oct 17, 2013)

If they had put a single 20mm in each wing of the 109 along with the hub gun as well as the pair of 13mm in the cowl sounds like a strong combination.


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## silence (Oct 17, 2013)

Rufus123 said:


> I thought the Germans really liked center line weapons if they will work on the plane. I wonder how three 20mm (one in the hub and 2 in the wings) would compare with 4 20mm in the wings against fighters. Run in parallel the center gun fills the void in the center. Go with a 30 in the hub for bombers.



That's your FW 190 D-13 setup (D-12 had a 30mm in the hub). The Ta-152H was the same as the D-12. The Ta-152C had 20mm in each wing root, 2x20mm on the cowl, and a 30mm through the hub.

Personally, I love this setup.


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## silence (Oct 17, 2013)

Rufus123 said:


> If they had put a single 20mm in each wing of the 109 along with the hub gun as well as the pair of 13mm in the cowl sounds like a strong combination.



That was the projected K-14, although the wing armament could also be 30mm.

Here's a some nice pictures of a 109 model customized as a K-14:

http://109lair.hobbyvista.com/models/bn1/bn1_k14/bn1_k14.htm

(love the four-blade propeller!)


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## modelwiz (Apr 19, 2019)

Shortround6 said:


> How much it was based on the Hispano is subject to question. Some Russian accounts say the V-2 predecessor (the BD-2)was being worked on in 1933-34 which is before the Russians really got going on building the Hispano. The cylinder heads are totally different, 4 valves instead of 2, dohc instead of sohc, intakes inside the V , the engine uses a longer stroke.
> 
> A version of the BD-2 was developed for aircraft use and test flown in 1936.



As far as I have found out, he V-2/VD-2 was a direct descendant of the AM-38 diesel aero engine, itself derived from the AM-35. An aero diesel V12 seems quite the advanced concept to go for in 1933-34, what with aluminium tech barely started in the USSR and all. The AM-35/38 seems to have been quite different from the 12Y in many ways. No doubt the Russians learnt a whole lot from HS (and everybody else) but their engineering seems to have been first rate (their production methods may have been a different story). The V-2 is a sturdy and fairly efficient design, even if the fuel injection is rather simple. The same goes for the aero engines. And there is no way they could have adapted the design for a gun mounting through the prop hub. I am not aware of what other engine they used to do that with.

I am in the process of finishing a functional 3D model of the V-2 and have been toying with making an AM-38 (and -42!) but then the V-2 itself has had 80 years worth of descendants-the V-92 that powers the T-90 tank develops TWICE the power of the original for the same displacement and nearly the same envelope. And I want to produce models of several of them. I already have too many projects!!

It is nearly impossible to separate an engineering achievement from the political scene that gave it rise, but I do try. I am very happy to read fairly learned discussions like the ones in this forum. I do need to research the 12Y further.

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## tomo pauk (Apr 19, 2019)

modelwiz said:


> As far as I have found out, he V-2/VD-2 was a direct descendant of the AM-38 diesel aero engine, itself derived from the AM-35. An aero diesel V12 seems quite the advanced concept to go for in 1933-34, what with aluminium tech barely started in the USSR and all. The AM-35/38 seems to have been quite different from the 12Y in many ways. No doubt the Russians learnt a whole lot from HS (and everybody else) but their engineering seems to have been first rate (their production methods may have been a different story). The V-2 is a sturdy and fairly efficient design, even if the fuel injection is rather simple. The same goes for the aero engines. And there is no way they could have adapted the design for a gun mounting through the prop hub. I am not aware of what other engine they used to do that with.



Could you please elaborate about the V2 being a direct descendant from the AM-38? AM-38 being diesel aero engine?


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## Shortround6 (Apr 19, 2019)

Early (late 20s early 30s) Soviet engine development is a mess. 
The V-2 diesel dates to the early 30s and it's first use was in the BT-8M tank?

However a comparison of the bore and stroke shows it to be bigger than the Hispano engines and smaller than the AM series of engines. Building a diesel by boring (or using larger cylinder liners) and stroking an light weight aircraft engine seems dubious. Using thicker cylinder walls and a shorter stroke than the AM series of engines seems more likely but the branch of point would have been the M-34 engine and not the later ones. 
The V-2 was in production and being fitted to tanks in 1939 (?)/1940.


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## fliger747 (Apr 19, 2019)

Distribution and type of armament varied in favor depending on the marksmanship and experience of the pilot. Not that their opinion was usually asked. The P-38 and F7F Bearcat had unusually powerful concentration of firepower on or near the CL. Better marksman and fliers appreciated a concentration of firepower. Wing guns were generally harmonized for a convergence at a certain distance, say 400 yards. A close grouping of the rounds would favor a pilot able to achieve a short accurate burst. More of a shotgun effect was more likely to obtain some hits for others. Against a lightly built aircraft, this might be enough. A tougher aircraft needing a more concentrated effect.


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## Milosh (Apr 20, 2019)

I think an edit is required.



fliger747 said:


> The P-38 and *F7F Bearcat*


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## modelwiz (Apr 22, 2019)

tomo pauk said:


> Could you please elaborate about the V2 being a direct descendant from the AM-38? AM-38 being diesel aero engine?


AFAIK the AM-34 (M-34), which was developed in the early 30's, had a distinctly different layout not used in any contemporary engine-everything was shaft driven through bevel gears (it must have been torture to build a prototype!). Not a belt or chain anywhere. And it was a V-12 aero diesel. The AM-35 and AM-38 were further developments. All had superchargers. The VD-2, that was mounted in the BT-7 and BT-8 tanks in about 1937-38 was a reduced size imitation of the AM-38 with no parts really in common but even the bore and stroke had the same proportions. I should have stated that the V-2 design was a direct descendant of that of the AM-38. The V-2, which was used in the T-34, KV and even IS tanks of WWII was a further refinement of the VD-2. And it has been redeveloped, produced in mass quantities and installed in most tanks and many armoured vehicles and even tractors ever since WWII. It is a remarkably sound design. And creating a functional 3D model of it has been a tour de force of engineering study for me. I am not aware of any other significant aero diesel engine than the AM's in the 30's and 40's. The AM-38 and later AM-42 powered the Illyushin Il-2 ground attack aircraft. For more info you could google двигатель М-34 and tanslate the results - wikipedia in Russian has an excellent article on it in _АМ-34 — Википедия_


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## tomo pauk (Apr 22, 2019)

modelwiz said:


> AFAIK the AM-34 (M-34), which was developed in the early 30's, had a distinctly different layout not used in any contemporary engine-everything was shaft driven through bevel gears (it must have been torture to build a prototype!). Not a belt or chain anywhere. And it was a V-12 aero diesel.



The M-34 was not aero diesel, it used gasoline - just like most of other aero engines in service in the 1930s. Belts and chains were rarely used on aero engines of the time.
M-34 was a descendant of the M-17 engine, that can trace it's lineage to the unsupercharged BMW VI engine, that was a V12 version of engine that 1st run back in ww1. All of whom used gasoline.
Version of the M-17 was also used to power tanks.



> The AM-35 and AM-38 were further developments. All had superchargers.



Of course all of them had superchargers. 
The supercharged versions of the M-34 were also produced, can be denoted by suffix 'N'.



> The VD-2, that was mounted in the BT-7 and BT-8 tanks in about 1937-38 was a reduced size imitation of the AM-38 with no parts really in common but even the bore and stroke had the same proportions. I should have stated that the V-2 design was a direct descendant of that of the AM-38. The V-2, which was used in the T-34, KV and even IS tanks of WWII was a further refinement of the VD-2. And it has been redeveloped, produced in mass quantities and installed in most tanks and many armoured vehicles and even tractors ever since WWII. It is a remarkably sound design. And creating a functional 3D model of it has been a tour de force of engineering study for me. I am not aware of any other significant aero diesel engine than the AM's in the 30's and 40's. The AM-38 and later AM-42 powered the Illyushin Il-2 ground attack aircraft. For more info you could google двигатель М-34 and tanslate the results - wikipedia in Russian has an excellent article on it in _АМ-34 — Википедия _



I'm having a hard time understanding how the VD-2 engine of 1937-38 was any kind of imitation of AM-38 engine of 1941. Both bore and stroke of V-2 and Mikulin's engines were different. 
As above - there were no AM aero diesels around, for example the M-40 diesel was designed by Charomskiy. AM-42 powered no Il-2, apart perhaps prototype/test beds. Version of the M-34 for tanks was called GAM-34VT.
Don't think that anyone here is questioning the validity of V2 engine.
BTW - care to elaborate a bit on VD-2 engine? Googling about it returns nothing.


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## wuzak (Apr 22, 2019)

There are zero belts or chains in a Merlin, Griffon, V-1710 or DB 601/3/5 either.

They all used some sort of gear drive for cam shafts, supercharger drive, oil pumps and other accessories.


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## GrauGeist (Apr 22, 2019)

tomo pauk said:


> M-34 was a descendant of the M-17 engine, that can trace it's lineage to the unsupercharged BMW VI engine, that was a V12 version of engine that 1st run back in ww1. All of whom used gasoline.


Tomo, going by memory, I thought the AM-34 was born from a Fiat design and shared nothing in common with the M-17 except both being roughly the same size?


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## Reluctant Poster (Apr 22, 2019)

GrauGeist said:


> Tomo, going by memory, I thought the AM-34 was born from a Fiat design and shared nothing in common with the M-17 except both being roughly the same size?


The analysis of the V2 by the British School of Tank Technology (May 1944) points out the similarities to the M34 and even includes a photo, although it does point out that there maybe internal differences. It further notes that the M34 was thought to have been originally designed by Fiat.


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## tomo pauk (Apr 23, 2019)

GrauGeist said:


> Tomo, going by memory, I thought the AM-34 was born from a Fiat design and shared nothing in common with the M-17 except both being roughly the same size?



It shared plenty with M-17 - bore, stroke, and, unlike Fiat V12s, articulated connecting rods. Contrary to the M-17, it was an en-bloc engine, with DOHC valvetrain featuring 4 valves per cylinder (indeed, like Fiat's V12s). Why would the Italians design a big engine to the ideological enemy in early 1930s, while not making one for themselves is a mystery to me.



Reluctant Poster said:


> The analysis of the V2 by the British School of Tank Technology (May 1944) points out the similarities to the M34 and even includes a photo, although it does point out that there maybe internal differences. It further notes that the M34 was thought to have been originally designed by Fiat.



The V2 might as well be a derivative of M-34 engine - it shared features found on the later, including DOHC, 4 valves per cylinder, articulated connecting rods.
FWIW, no Soviet source states the M-34 as foreign-designed engine.


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## Reluctant Poster (Apr 23, 2019)

tomo pauk said:


> It shared plenty with M-17 - bore, stroke, and, unlike Fiat V12s, articulated connecting rods. Contrary to the M-17, it was an en-bloc engine, with DOHC valvetrain featuring 4 valves per cylinder (indeed, like Fiat's V12s). Why would the Italians design a big engine to the ideological enemy in early 1930s, while not making one for themselves is a mystery to me.
> 
> 
> 
> ...


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## tomo pauk (Apr 23, 2019)

Reluctant Poster said:


> Agreed. The Fiat connection seems to have been western speculation. Gunston claimed the M34 was a monoblock M17, but others are not so sure. If it was true that would mean the V2 was originally a BMW design, which is what the Germans claimed.



While BMW genes can be traced from BMW VI -> M-17 -> M-34 -> V2, I'm not sure why would we accept that V2 was originally a BMW design. The 1st monobloc BMW V12 engine was the 117 of 1934 (36L, fork-and-blade rods) - the M-34 pre-dates it.


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## GrauGeist (Apr 23, 2019)

tomo pauk said:


> It shared plenty with M-17 - bore, stroke, and, unlike Fiat V12s, articulated connecting rods. Contrary to the M-17, it was an en-bloc engine, with DOHC valvetrain featuring 4 valves per cylinder (indeed, like Fiat's V12s). Why would the Italians design a big engine to the ideological enemy in early 1930s, while not making one for themselves is a mystery to me.


The Germans were selling technology to the Soviets even by the late 30's, so an Italian designed engine made available to the Soviets comes at no surprise.

In regards to the M-17's similarities to the M-34: many engines in the aviation industry had parallels.
The V-1710 was a 60° V with four valves per cylinder driven by an overhead cam, just like the Merlin. They both had a 6" (152mm) stroke and a nearly identical bore: 5.4" (137mm) for the Merlin and 5.5" (140mm) for the Allison.
That however doesn't mean they shared any lineage as they were both developed independantly.

Also, from a visual standpoint, the M-17 doesn't bear much of a resemblance to the M-34.
However, the M-34 looks a great deal like Fiat's engines from the same time period, such as the AS.3 or the larger A.25 for example.


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## tomo pauk (Apr 23, 2019)

GrauGeist said:


> The Germans were selling technology to the Soviets even by the late 30's, so an Italian designed engine made available to the Soviets comes at no surprise.



Granted, even the Italians were selling blueprints to the Soveiet Navy yards, however the statements of M-34 being an Italian design are a surprise, since the only thing the M-34 and Italian V12s have had in common was the layout of valvetrain.
Curiously enough, we don't have any Italian or Soviet sources claiming that Fiat designed the M-34.



> In regards to the M-17's similarities to the M-34: many engines in the aviation industry had parallels.
> The V-1710 was a 60° V with four valves per cylinder driven by an overhead cam, just like the Merlin. They both had a 6" (152mm) stroke and a nearly identical bore: 5.4" (137mm) for the Merlin and 5.5" (140mm) for the Allison.
> That however doesn't mean they shared any lineage as they were both developed independantly.



Nobody ever accused Merlin and V-1710 for sharing a lineage.



> Also, from a visual standpoint, the M-17 doesn't bear much of a resemblance to the M-34.
> However, the M-34 looks a great deal like Fiat's engines from the same time period, such as the AS.3 or the larger A.25 for example.



Visual inspection of a complete engine will not reveal bore, stroke, or what type of rods the engine uses. That M-34 shared with M-17, and didn't share with any Fiat V12 engine.
Also, unlike the M-34, looks like the A.25 and AS.3 have had separate cylinders..


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## modelwiz (Apr 24, 2019)

tomo pauk said:


> It shared plenty with M-17 - bore, stroke, and, unlike Fiat V12s, articulated connecting rods. Contrary to the M-17, it was an en-bloc engine, with DOHC valvetrain featuring 4 valves per cylinder (indeed, like Fiat's V12s). Why would the Italians design a big engine to the ideological enemy in early 1930s, while not making one for themselves is a mystery to me.
> 
> The V2 might as well be a derivative of M-34 engine - it shared features found on the later, including DOHC, 4 valves per cylinder, articulated connecting rods.
> FWIW, no Soviet source states the M-34 as foreign-designed engine.



Russian/ex-Soviet sources state that the M-17 was derived from the BMW VI. The M-34 was designed to replace the M-17, but was not based on it. It was an aero diesel; all 4 valves were exhaust valves. A significant feature of the Mikulin engines was perforated sleeves in the cylinders that supplied intake air from the manifold directly connected to the block. I doubt it was based on any other design other than in a very general way. In engineering, as in many other fields, one uses anything one knows, including information of foreign developments. The M-17 itself was installed in an unknown number of early T-34's, and they tended to burn or even explode when penetrated-crews were extremely critical.
The VD-2 (not BD-2) was the initial design of a scaled down AM-34, and like the V-2 also had perforated free sleeves as well as the features you list. Versions of the AM-34 were used in numerous aircraft, but also in a number of tanks and even small torpedo boats.
The Il-2M and Il-10 were designed around the M-71 and AM-42, respectively, but the Il-2M ended up being produced with th AM-42 anyway.


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## GrauGeist (Apr 24, 2019)

Yes, the M-17 was based on the BMW IV, no the M-34 was NOT a diesel engine.

The Soviets had a diesel aircraft engine, which was the ACh-30, primarily used in the Pe-8 and Yer-2.

The Kharkiv V-2-34 was a diesel engine developed by the Kharkov Locomotive Factory and had nothing to do with any Mikulin engines.
The V-2-34 was used in the KV series, the BT-7, the T-34and IS series. The closest the V-2 series ever came to an aircraft, is the fitting of a supercharger from an AM-38, designated V-2SN and used on the larger KV tanks.

No M-34/AM-34 engine was ever used in a Soviet tank.


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## modelwiz (Apr 24, 2019)

With apologies for my mistake, VD-2 was a very early designation of the V-2. The earliest version (450 HP) was used in the BT-7 tank.


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## tomo pauk (Apr 24, 2019)

modelwiz said:


> Russian/ex-Soviet sources state that the M-17 was derived from the BMW VI. The M-34 was designed to replace the M-17, but was not based on it.



Agree on #1. As for the #2 - you're probably right, the M-34 have had enough of new & modern features that we can consider it a new engine. We also cannot avoid the fact that M-17 and M-34 also shared several important design details, as mentioned before.



> It was an aero diesel; all 4 valves were exhaust valves. A significant feature of the Mikulin engines was perforated sleeves in the cylinders that supplied intake air from the manifold directly connected to the block. I doubt it was based on any other design other than in a very general way. In engineering, as in many other fields, one uses anything one knows, including information of foreign developments. The M-17 itself was installed in an unknown number of early T-34's, and they tended to burn or even explode when penetrated-crews were extremely critical.



Please post the sources for the numerous claims here (M-34 being a diesel, all 4 valves used for exhaust only, M-17 installed on early T-34s).



> The VD-2 (not BD-2) was the initial design of a scaled down AM-34, and like the V-2 also had perforated free sleeves as well as the features you list. Versions of the AM-34 were used in numerous aircraft, but also in a number of tanks and even small torpedo boats.



Yes, there was a version of the AM-34 that was used on 'surface' vehicles. As above, please post sources for V-2 having valves for exhausts only.



> The Il-2M and Il-10 were designed around the M-71 and AM-42, respectively, but the Il-2M ended up being produced with th AM-42 anyway.



Soviet terminology does not know the designation 'Il-2M' (or the often quoted 'Il-2M3'). Please quote a source that proves any Il-2 being powered by AM-42, on anything that is more than prototype or test bed aircraft.


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## Shortround6 (Apr 24, 2019)

Uh, if all four valves are exhaust valves and the intakes are through ports in the cylinder walls that 
A, makes the engine a two stroke?
B means the engine needs a supercharger to run to blow the air in through the cylinder ports?

Unless there is a seperate sleeve valve the ports would be uncovered when the pistons are near the bottom of their stroke and making little suction to suck fresh air in.


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## fliger747 (Apr 24, 2019)

To reduce the question originally asked to the basics? Almost foremost in a fighter's performance is the engine. Most improvements model to model showing real performance involved engine development. Firing through the hub is going to cause compromises in engine design, a luxury perhaps not eventually compensated for by any purported advantage by such an armament configuration. Smaller fighters with smaller wings did have issues with finding room for guns and ammo. For larger planes (ie. USA) the wings were larger and not having such issues as where to store wheels, guns and whatnot.


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## GrauGeist (Apr 25, 2019)

When the hub weapon idea really took hold, was in the days when most aircraft had cowl and/or wingroot weapons, which had to fire through the propeller arc, thus slowing their rate of fire through synchronization.
This problem had plagued fighter aircraft since WWI and several remedies were tried, like the Foster mount used in WWI, which saw the MG mounted to the upper wing above the propeller arc and the Hispano mounted a Lewis in the "valley" of a SPAD's HS-36 engine, firing through the hub - making it the first hub weapon.

As monoplanes matured, so did their engines and with the V-engine came the idea that a weapon can be mounted in the "valley" of the Vee and fired through the hub.
Several advantages to this: first, no synchronization and secondly, there is no convergence as the weapon is firing from the aircraft's centerline.


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## Shortround6 (Apr 25, 2019)

In part the gun through the hub was to allow the mounting of guns of such size and power than mounting them in multiples would affect aircraft performance severely. Or allowed the pilot access to the gun while flying.





French setup close to that used in the SPAD XII. manually loaded 37mm cannon. 
On WW I and early 20s aircraft mounting heavy recoiling guns was a bit of challenge. 

I would also note that once a country started down a certain path it was hard to get off of it.

Some of the 1930s V-12 Hispano engines used the same bore spacing (or very close) which allowed some of the same machinery used to make the old V-8s to be used on the V-12s. The V-12s seeing a much larger increase in stroke.


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## modelwiz (Apr 25, 2019)

Shortround6 said:


> Uh, if all four valves are exhaust valves and the intakes are through ports in the cylinder walls that
> A, makes the engine a two stroke?
> B means the engine needs a supercharger to run to blow the air in through the cylinder ports?
> 
> Unless there is a seperate sleeve valve the ports would be uncovered when the pistons are near the bottom of their stroke and making little suction to suck fresh air in.


Suction is generated by the down stroke of the piston. Air is drawn from the perforations towards the top of the cylinder. The original V-2 was normally aspirated. Postwar versions added a turbocharger, different pumps, an electric starter even. There may not have been any original part of the engine that has not been replaced, redesigned or improved in these last 80 years of development and production. The original had an air distributor through which compressed air was supplied for starting.


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## modelwiz (Apr 25, 2019)

tomo pauk said:


> Agree on #1. As for the #2 - you're probably right, the M-34 have had enough of new & modern features that we can consider it a new engine. We also cannot avoid the fact that M-17 and M-34 also shared several important design details, as mentioned before.
> 
> 
> 
> ...


АМ-34 — Википедия
В-2 — Википедия
М-17 (двигатель) — Википедия
For starters
I also based myself on a set of 1942 manufacturing drawings and several wartime and postwar user, maintenance and repair manuals, particularly for the V-2; I would not have attempted a virtual engineering model without.


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## tomo pauk (Apr 25, 2019)

modelwiz said:


> АМ-34 — Википедия
> В-2 — Википедия
> М-17 (двигатель) — Википедия
> For starters
> I also based myself on a set of 1942 manufacturing drawings and several wartime and postwar user, maintenance and repair manuals, particularly for the V-2; I would not have attempted a virtual engineering model without.



You might want to be a bit more specific. For example, this is what the Russian-language Wikipedia entry says about the fuel distribution system and fuel used on the AM-34:

_Топливная система
карбюраторная

Тип топлива
этилированный бензин 2Б-70, 3Б-78(93), 4Б-74, Б-95_

Meaning:

_Fuel system
Carburetor

Fuel Type
Leaded Gasoline 2B-70, 3B-78 (93), 4B-74, B-95_

So, as before - please post specifics that prove your points.


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## Shortround6 (Apr 25, 2019)

modelwiz said:


> Suction is generated by the down stroke of the piston. Air is drawn from the perforations towards the top of the cylinder. The original V-2 was normally aspirated.



Ok, what closes off the perforations as the piston goes back up?
Something has to or the air in the cylinder will be blown right back out as the piston rises, let alone what happens the charge burns with piston going down.

Not say you can't build an engine with both sleeve valves and popper valves but it does seem to be a huge _compilation_. (sorry complication is what I meant)


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## tyrodtom (Apr 25, 2019)

When I look at the pictures of the m-34 I see a exhaust manifold on the outside of the V, and a intake manifold on the inside of the V at the same height as the exhaust. 
The cutaway pictures show no holes in the upper cylinder, nor any way of feeding air to them if they were there, or any way of shutting off that air so the engine could build compression.

Looks like just any other 4 valve engine, two valves for exhaust, and two for intake.

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## elbmc1969 (Apr 25, 2019)

Shortround6 said:


> Some of the 1930s V-12 Hispano engines used the same bore spacing (or very close) which allowed some of the same machinery used to make the old V-8s to be used on the V-12s. The V-12s seeing a much larger increase in stroke.



All of the 12X and 12Y engines used the exact same bore spacing as the older V-12s and the V-8s, per Manuel Lage, *Hispano Suiza in Aeronautics.* This was one of the reasons that the engines hit a power plateau: the bore couldn't be increased to increase displacement. Changing the bore spacing was a problem because Marc Birkigt customed-designed all of the critical machine tools for manufacturing his engines (Birkigt was Hispano Suiza's chief engineer, the designer of the original Hispano Suiza V-8, the credited chief designer of the HS-404 20mm cannon which because the chief US and UK aircraft cannon of WWII, and much more). Changing the bore spacing would have required retooling at a basic level. It's hard to believe, I know.


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## GrauGeist (Apr 26, 2019)

modelwiz said:


> Suction is generated by the down stroke of the piston. Air is drawn from the perforations towards the top of the cylinder. The original V-2 was normally aspirated. Postwar versions added a turbocharger, different pumps, an electric starter even. There may not have been any original part of the engine that has not been replaced, redesigned or improved in these last 80 years of development and production. The original had an air distributor through which compressed air was supplied for starting.


I'm going out on a limb here, based on observation, and think that you're not all that familiar with how an internal combustion engine works.
A engine's valve set is designed to allow the intake of fuel and the removal of exhaust.
Two, four or twenty valves mean nothing unless they have a specific purpose.

On a four stroke engine, you have a "cycle", and that is Intake, Compression, Ignition and Exhaust. During that cycle, the Intake valves open and allow the air-fuel mixture into the cylinder as the piston starts it's downward stroke (the vacuum created by the plunging piston creates the draw for the air-fuel mixture), then the intake valve closes and the piston starts it's upward climb, compressing the air-fuel mixture in the cylinder to a considerable degree.
Then the spark plug ignites the compressed volatile mixture, violently forcing the piston downward (turning the crankshaft as it goes) and once the piston reaches the end of it's travel, the exhaust valve opens and the upward travel of the piston drives out the exhaust gases in the cylinder.

Many engines have a single intake and exhaust valve per cylinder, high-performance engines will have two per set (two intake, two exhaust) to increase performance.

And all of the Soviet engines were either crank-started (by hand) or used an electric starter (late war).
Pneumatic starters are typically used on diesel engines in commercial trucks (again, the Soviets only had ONE diesel aircraft engine in service during the war - the ACh-30)


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## modelwiz (Apr 26, 2019)

GrauGeist said:


> I'm going out on a limb here, based on observation, and think that you're not all that familiar with how an internal combustion engine works.
> A engine's valve set is designed to allow the intake of fuel and the removal of exhaust.
> Two, four or twenty valves mean nothing unless they have a specific purpose.
> 
> ...


But this is not how a DIESEL operates. And I was referring to the V-2, which was a diesel with four exhaust valves per cylinder operated by two separate camshafts. But of course you knew that. You know everything. You know me so very well. Thank you for the lecture and condescension.


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## Milosh (Apr 26, 2019)

The 2 stroke diesel engine, How Diesel Two-Stroke Engines Work


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## modelwiz (Apr 26, 2019)

And BTW, when the exhaust valves open the pressure differential between the burnt fuel air mixture and outside air also create what you would call a vacuum as the piston moves upward in the exhaust stroke. In all kinds of internal combustion engines.


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## GrauGeist (Apr 26, 2019)

modelwiz said:


> But this is not how a DIESEL operates. And I was referring to the V-2, which was a diesel with four exhaust valves per cylinder operated by two separate camshafts. But of course you knew that. You know everything. You know me so very well. Thank you for the lecture and condescension.


My apologies if you seemed to think my post was condescending, however, you seem to fail to grasp the basics of either gasoline or diesel engine function. I have no idea where this "four exhaust valves" thing is coming from, but it's not even close to accurate.

The V-2-34, which was the actual production engine, the V-2 was the early prototype of the series, had a regular configuration. This means it had two Intake valves and two Exhaust valves per cylinder driven by overhead camshafts.

In this diagram of the V-2-34, please note the Intake valve(s) facing inboard and the Exhaust valve(s) facing outboard.

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## tomo pauk (Apr 26, 2019)

modelwiz said:


> But this is not how a DIESEL operates. And I was referring to the V-2, which was a diesel with four exhaust valves per cylinder operated by two separate camshafts. But of course you knew that. You know everything. You know me so very well. Thank you for the lecture and condescension.



I don't think that anyone went ad hominem against you. Trouble might be that you've provided next to no evidence to prove numerous points you've made, despite repeatedly being challenged to do so.

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## Shortround6 (Apr 26, 2019)

Detroit diesel 











It has four exhaust valves in the head. Now you need to get the fresh air in. The Detroit diesel used ports in the bottom of the cylinder that are uncovered and covered by the movement of the piston. The Fresh air is forced in by a supercharger.

If you want the piston to push the exhaust out and to the suck the fresh air in you need some sort of port/passage for the fresh air to come in *and *some sort of valve or seal to keep the combustion pressure from blowing back out through the intake. A sleeve, rotating valve, reed valve, something that opens when the piston is going down on the intake stroke and ONLY opens when the piston is going down on the intake stroke. Then it has to _close_ and be strong enough to _contain the combustion pressure_, which on a diesel can be over 1500 psi for a brief period of time. With out some sort of device (sleeve, rotating valve, reed valve) to seal of the ports/perforations/slots the intake air came in through the combustion pressure is going take the easy way out and go out through the intake rather than push the piston down.


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## modelwiz (Apr 27, 2019)

tomo pauk said:


> I don't think that anyone went ad hominem against you. Trouble might be that you've provided next to no evidence to prove numerous points you've made, despite repeatedly being challenged to do so.


And where is YOUR evidence? You are obviously not interested in whatever I might have to say, so any further involvement on my part is fruitless. I am sorry I wrote to such eminent authorities in my attempt to contribute to a dialogue. I will not try it again

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## Shortround6 (Apr 27, 2019)

modelwiz said:


> And where is YOUR evidence? You are obviously not interested in whatever I might have to say, so any further involvement on my part is fruitless. I am sorry I wrote to such eminent authorities in my attempt to contribute to a dialogue. I will not try it again



Well, when you present a timeline that has an engine (engine A) developed _from _an engine (Engine B) that didn't exist and would not exist for several years after Engine A was introduced there are going to be some sceptics.

Perhaps we are have language barrier or perhaps you a working from a less than ideal translation of a foreign book/article. Some of your descriptions of how engines work are contrary to common knowledge. For example.

"And BTW, when the exhaust valves open the pressure differential between the burnt fuel air mixture and outside air also create what you would call a vacuum as the piston moves upward in the exhaust stroke. In all kinds of internal combustion engines." 





We have high pressure in the cylinder when the piston reaches the bottom of the power stroke, at least higher pressure than the outside air. It is much lower pressure than when the fuel is injected and the combustion is taking place but it is still higher than the outside air. The rising piston does NOT create a vacuum. it creates even more pressure to help force the burned gases out of the cylinder. Vacuum doesn't start to occur until the piston is moving down on the intake stroke. This is true for both Diesels and gasoline engines. 
This is the conventional accepted knowledge which can be found with practically any google search on a variety of web sites. 
If someone wants to claim they are all wrong then I believe it is up to the challenger to provide some proof or sources, not up to the people who are on the side of the common.old and easily referenced knowledge.

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## tomo pauk (Apr 27, 2019)

modelwiz said:


> And where is YOUR evidence?



In post #152 here.



> You are obviously not interested in whatever I might have to say, so any further involvement on my part is fruitless. I am sorry I wrote to such eminent authorities in my attempt to contribute to a dialogue. I will not try it again



Indeed, I'm not interested in _whatever_ one might have to say. What I'm interested is that people can support their opinions with sources and facts. So far we you have not provided any source or a fact that will support your statements that:
- V-2 was a version of AM-38
- that either AM-34 or AM-38 were diesel engines
- that all 4 valves of the Mikulin engines and of the V-2 were exhaust-only.

Have a good day.


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## swampyankee (Apr 27, 2019)

This has gotten rather far afield. To go back to the OP's question, I think we need to see some data (not anecdotes or little quips from fighter pilots) about the actual value of through-hub vs synchronized vs wing mounted weapons. I suspect that it doesn't exist, and almost certainly doesn't exist in any meaningful form.

The questions these data should answer are:

How much did through-hub weapons compromise engine, propeller, gearbox, and cowling design? An extreme case is the P-39. How much loss of engine and aircraft performance resulted from, for example, the location of the supercharger and inlet and exhaust plumbing for the engine? How did they effect c/g travel as ammunition was expended? Did they impair forward visibility by pushing cockpit location back or increasing cowling bulk?
Were through-hub weapons significantly more accurate at normal combat ranges? If so, how do you quantify that? Would it take 20 rounds fired for a through-hub cannon to destroy an aircraft vs 40 with wing mounted guns? Could that difference be reduced or eliminated by training and sight design?
If these data don't exist -- as I said, I suspect that they do not -- we can argue until pigs naturally evolve flight and won't have an answer.

Why do I think the data don't exist? Simple: the air forces that used through-hub weapons had already determined they were superior and were not going to revisit that assumption., and those that did not had already determined that the through-hub weapons were not superior or at least not enough superior to wing-mounted guns to be worth the design compromises in engine, propeller, gearbox, and cowling to be worth the bother.

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## tomo pauk (Apr 27, 2019)

swampyankee said:


> This has gotten rather far afield. To go back to the OP's question, I think we need to see some data (not anecdotes or little quips from fighter pilots) about the actual value of through-hub vs synchronized vs wing mounted weapons. I suspect that it doesn't exist, and almost certainly doesn't exist in any meaningful form.
> 
> The questions these data should answer are:
> 
> ...




I'm not sure that there were any 'bad' compromises with regard to the engine, prop, or gearbox. Cowling and exhaust plumbing were same as with 'classic' V12 engines, bar the P-39 as specific case.
Appeal of the hub weapon was ability of, otherwise weak aircraft with weak engine, to have a shell-firing gun installed and usable. You can have one such gun, and go out and kill other aircraft. Trying to install such two guns (they being much heavier and bulkier than LMGs most people used from ww1 on) in the wings might involve unacceptable loss of performance and maneuverability. So our Spad XIII will be able to have one 37mm cannon installed in the Vee, but not two such cannons in/on the wings. This is before we can attest that Spad's wings can actually carry such two cannons in the 1st place. Engine warmth keeps the weapon warm by default, mount is as rigid as it will ever be, ammo feed is usually reliable.
Once we move in 1930s, the equation still holds - one 700-800 HP engine can propel the fighter with single big cannon (talk Hispano or the big Oerlikon) and it's amo well enough, but less well when it has two big cannons, no need to provide heating either. Granted, we can install two smaller and lighter cannons (tipically a version of the Oerlikon FFF), and accept trade-off between shell MV and total RoF. Main purpose of many air forces' fighters being killing the bombers that are about to bring doom via bombing and gas.
Once at 1100-1300 HP, the big 30-40mm cannon is a possibility for the fighter that has a suitable engine in the 1st place. Some cannons being better than the others, some engines being better then the others.
Once engine power is high, talk 1500-2000 HP and fighters can carry up to 4 big cannons, the appeal of hub weapon seems moot - the excess power should be able to cater for increase of weapon weight. Hub weapon still has appeal if your fighters are expected to kill enemy bombers and/or tanks on daily basis, so we have Ta-152 series and latest Bf 109 with the modified MK 103 firing through the prop as option. MK 103 being less than ideal as wing weapon, and probably impossible for the 109 to carry at all.
Granted, Germans and Soviets were thinkering about even bigger cannons, 45 to 55 mm, as hub weapons.

Sorry if this lengthy piece does not answer your questions


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## Shortround6 (Apr 27, 2019)

swampyankee said:


> Simple: the air forces that used through-hub weapons had already determined they were superior and were not going to revisit that assumption., and those that did not had already determined that the through-hub weapons were not superior or at least not enough superior to wing-mounted guns to be worth the design compromises in engine, propeller, gearbox, and cowling to be worth the bother.



I agree somewhat with that but the way that some air forces "determined" that through the hub was better seems to be pretty sketchy. The French seem to have started in WW I but I am not sure any tests were done, aside from seeing if it work at all.
The attraction of through the hub was than a heavy gun could be carried with the engines of the time (late teens/20s/early 30s) that were not powerful enough to provide good performance with more than one heavy gun. Wing guns were a rarity until the 1930s for much the same reason. More than 2 machine guns (or up to four) was too much of a performance penalty for the engines and propellers of the time.
An exception that proves the rule was the Sopwith Snark with two Vickers guns in the fuselage and four Lewis guns under the lower wing.
It was a triplane powered by the infamous ABC Dragonfly engine of 360hp (rather good for 1918-19 but the engine could have lost the air war for the allies in 1919 it was so bad).
It was about the only fighter to use wing mounted guns (aside from over the pilot ) until the 1930s. However the guns (with their 97 round drums) could not be reloaded nor could the pilot even beat on the gun with a gloved hand to try and clear a jam. Wing mounted guns would require another generation of guns of higher reliability.

Hispano got on the through the Hub band wagon and designed their 1920s engines with pretty much a clear area between the cylinder banks even though Hispane had no gun to put there at the time. This carried on through the 1930s and the licence built Russian M-100 through M-105 series. 
The 1-0 was designed for _either _two cowl mounted machine guns OR one hub mounted cannon. The hub mount does, as you know, do away with the need to synchronize the gun. 
The First German cannon was a real beast firing the same cartridge as the Flak 30 AA gun and weighed 64kg (as much as five 7.9mm MG 17s) so carrying multiples of this gun was pretty much out of the question with a 600-700hp engine. The 20mm MG FFs in the wings of a 109 were under 30kg each. 
So the Hub mounted advocates had picked their path and started designing guns and engines to suit without any real combat experience (2-5 aircraft shot down in WW I by hub mounted cannon and most/all? by one pilot?) or even testing. The wing mounted machine gun/cannon crowd also fell into position almost by accident. You can't use a hub mounted gin on a radial, the Merlin wasn't designed for hub mounting (neither is the Allison but it is late to the game). and most of the 20mm and larger in 30s could not be synchronized so fitting such a gun inside the prop disc area to simulate a through the hub gun (at a lower rate of fire was out. 

The US and Japanese didn't fit wing guns to much of anything until 1939 or after. Italians didn't fit wing guns to fighters very often until after the war started. They did use wing guns on a few attack planes. 
The French, Germans and Russians were pretty much the proponents of the hub mounted gun.


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## swampyankee (Apr 28, 2019)

I think the way they determined hub guns were better was more "gee, if we do this, we don't need to synchronize" than the result of actual testing of wing vs through-hub guns.


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## Shortround6 (Apr 28, 2019)

A lot of the automatic cannon of the 20s and 30s could NOT be synchronized which rather ruled out any sort of single fuselage mount that fired through the propeller disc. 

You either figured out a way to shoot through the prop hub or resorted to something like this.





Great if the Germans kept building Zeppelins, otherwise............................ 

The Germans had this in WW I but were trying to figure out how to use it in a single seat, single engine fighter.





I know it says tank but it was used as a flexible gun on some Zeppelins and two/multi seat aircraft. It was tested in an Albatross firing down at an angle to clear the propeller. 
However it weighed 30Kg and the magazines were only 10 and 15 rounds. Loaded 15 round one went 5kg (?) rate of fire was about 300rpm
MV was only 490M/S so as a whole it doesn't show up that well against a multiple machine gun battery.

Some people could see the potential but is would take a lot development to turn it into the Oerlikon gun/s we are familiar with.

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## sotaro (May 3, 2019)

Shortround6 said:


> A lot of the automatic cannon of the 20s and 30s could NOT be synchronized which rather ruled out any sort of single fuselage mount that fired through the propeller disc.
> 
> You either figured out a way to shoot through the prop hub or resorted to something like this.
> 
> ...


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## Snowygrouch (May 3, 2019)

tomo pauk said:


> I'm not sure that there were any 'bad' compromises with regard to the engine, prop, or gearbox. Cowling and exhaust plumbing were same as with 'classic' V12 engines, bar the P-39 as specific case.



The main disadvantage of putting the blower on the side to allow for the prop-cannon, was not envisaged by Germany when the RLM drew up the guidelines in
something like 1930 (sadly I have never found the original document, only refereces to it). This was that if one wishes later to have a two-stage
supercharger, the packaging suddenly gets a lot more unpleasant than something like a Merlin-60. This is because you either double-stack
the blowers which is VERY difficult to then fit into something like a 109 without it poking right out into the airstream, OR you fit one
blower on each side of the engine, which then leaves you with a real birdsnest of ducts to put in. The idea of a 2-stage supercharger being
a likely service requirement in 1930 was probably not on the minds of most people - although it was not far fetched either.

Later, Germany certainly placed a great deal of store in considering gun "weave" in firing, and at least during the war produced a very lengthy report on
improving aerodynamic stability of fighters purely for the purpose of keeping the guns on target. I have this report in English as it was translated by
the R.A.E. in 1946. Its mostly full of maths, but has some practical conclusions scattered about. Directional stability of the 109 seems to have been
a bit less than pilots found comfortable so it says.

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## sotaro (May 3, 2019)

Snowygrouch said:


> The main disadvantage of putting the blower on the side to allow for the prop-cannon, was not envisaged by Germany when the RLM drew up the guidelines in
> something like 1930 (sadly I have never found the original document, only refereces to it). This was that if one wishes later to have a two-stage
> supercharger, the packaging suddenly gets a lot more unpleasant than something like a Merlin-60. This is because you either double-stack
> the blowers which is VERY difficult to then fit into something like a 109 without it poking right out into the airstream, OR you fit one
> ...



Very impressive work you are doing on your book.


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## ThomasP (May 4, 2019)

Hey guys,

For anyone who is interested, modelwiz is correct in his statement:

"And BTW, when the exhaust valves open the pressure differential between the burnt fuel air mixture and outside air also create what you would call a vacuum as the piston moves upward in the exhaust stroke. In all kinds of internal combustion engines."

modelwiz used the words "as the piston moves upward in the exhaust stroke" instead of 'during the exhaust stroke' which may have contributed to a misunderstanding, but what he meant is correct.

In the Merlin engine at +18 lbs of boost the piston rising only pushes about 5% of the combustion gases out of the cylinder, the exhausting high pressure/high speed gases draw the other ~95% out of the cylinder. In a naturally aspirated diesel with a 22:1 compression ratio the piston would only push about 3% of the combustion gases out, with the other 97% being drawn out by the exhaust gases.

The reason one can conceptually know this applies to an internal combustion engine is due to the piston velocity vs the exhaust gas velocity. The piston velocity in the Merlin is only 50 ft/sec at 3000 rpm. If the exhaust gases were being pushed out by the piston the maximum velocity of the gases would be about 570 ft/sec and there would be a loud harsh hiss (for lack of a better descriptive) instead of the bangs that we hear. The reason we hear the bangs (of course) is that the gases are expanding/traveling at more than the speed of sound (typically around 1700-2000 ft/sec). The pulses of high velocity expanding/traveling gas in effect act as short-lived virtual pistons being thrown away from the exhaust ports, creating a low pressure area in their wake while traveling down the exhaust manifold (and to a lesser degree after they leave the manifold), drawing the gases out of the cylinder. In the Merlin, by the time the piston has traveled ~1/2 of the way up on the exhaust stroke over 90% of the exhaust gases have already left the cylinder.

This is all due to the same principle under which a wing generates lift, i.e. the Bernoulli effect.

The above principle is the majority of the reason for putting 2 exhaust ports in a cylinder, the minority of the reason being a more uniform effect within the cylinder. If it were practical to increase the single exhaust port to the same area as the cylinder area (say by using the entire top of the cylinder as an exhaust port) it would be more efficient to do so.


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## Milosh (May 5, 2019)

Shouldn't the word be pressure differential rather than vacuum?


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## Timppa (May 5, 2019)

Snowygrouch said:


> This was that if one wishes later to have a two-stage
> supercharger, the packaging suddenly gets a lot more unpleasant than something like a Merlin-60. This is because you either double-stack
> the blowers which is VERY difficult to then fit into something like a 109 without it poking right out into the airstream, OR you fit one
> blower on each side of the engine, which then leaves you with a real birdsnest of ducts to put in.



Jumo 213E had three-speed, two-stage supercharger, poking nastily to the right hand side airstream.



Snowygrouch said:


> Later, Germany certainly placed a great deal of store in considering gun "weave" in firing, and at least during the war produced a very lengthy report on
> improving aerodynamic stability of fighters purely for the purpose of keeping the guns on target. I have this report in English as it was translated by
> the R.A.E. in 1946. Its mostly full of maths, but has some practical conclusions scattered about. Directional stability of the 109 seems to have been
> a bit less than pilots found comfortable so it says.



I think I have read pretty much all the German and Finnish 109 pilots bios there are. There was much to complain about the Bf109. But directional stability was not among them.
Possibly they did not read the RAE math.


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## Snowygrouch (May 5, 2019)

Timppa said:


> Jumo 213E had three-speed, two-stage supercharger, poking nastily to the right hand side airstream.
> 
> I think I have read pretty much all the German and Finnish 109 pilots bios there are. There was much to complain about the Bf109. But directional stability was not among them.
> Possibly they did not read the RAE math.



213E was never fitted to a 109 - but you know this so I dont really understand what your comment is trying to imply.

The RAE report was TRANSLATED from German, the original report and its conclusions about directional stability of the 109 were all written by Eisenmann, 
after many test flights at Rechlin by their test pilots.

"Flight tests were made on Me108, Me109F, Me109G, Me210, Me410, Me262. The aim of these tests was to find a means of improving the objectionable
yawing oscillation behaviour of the aircraft as quickly and as simply as possible without very large alterations to the type in production. 
Systematic scientific measurements were largely abandoned and the observations were confined to the influence of the particular remedies proposed...."


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## Shortround6 (May 5, 2019)

ThomasP said:


> Hey guys,
> 
> For anyone who is interested, modelwiz is correct in his statement:
> 
> ...



He is incorrect when he states " also create what you would call a _vacuum_ as the piston moves upward"

We already know there is a pressure differential between the gases in the cylinder and the outside air. Now if the out rushing gases did create a vacuum as they left the cylinder they would actually be sucking the piston up (slightly) due the higher pressure in the crankcase. 





You don't get a 'vacuum' until the piston starts down on the intake stroke. 

A better diagram




Bottom is the _ideal_ Otto cycle which never happens in a real engine. 

Or laid out in a line





Now we obviously have some very large pressure variations occurring in a very short space of time but getting lower than atmospheric pressure in a cylinder without the piston going down is going to be a real trick. 

We can twist and pull these diagrams to cover different engines but there are reasons for valve overlap (both intake and exhaust valves open at the same time) in the real world.
One is that valves do not open and close instantly (on most engines, lets leave modern formula I engines and their kin out of this) so the valves have open early in order to be fully open at the right time. Another reason is better scavenging. The incoming "fresh" air helps displace the remaining exhaust gases allowing for more fuel/air mixture (or more fresh air in the case of the diesel/direct injection engine).


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## tomo pauk (May 5, 2019)

Snowygrouch said:


> The main disadvantage of putting the blower on the side to allow for the prop-cannon, was not envisaged by Germany when the RLM drew up the guidelines in
> something like 1930 (sadly I have never found the original document, only refereces to it). This was that if one wishes later to have a two-stage
> supercharger, the packaging suddenly gets a lot more unpleasant than something like a Merlin-60. This is because you either double-stack
> the blowers which is VERY difficult to then fit into something like a 109 without it poking right out into the airstream, OR you fit one
> ...



BTW - will the DB 601C/D get any coverage in your book?


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## ThomasP (May 5, 2019)

Hey Milosh and Shortround6,

We would have to ask modelwiz to be sure why he used the term vacuum, but most likely he was trying to express the 'vacuuming' (verb in the english language) effect of having a lower pressure area next to a higher pressure area, similar in effect to using a vacuum cleaner. The term 'drawing vacuum' is commonly used in some (many?) countries to describe this effect, usually specifically at the air intake to a naturally aspirated engine describing a lowering of the MAP, but sometimes elsewhere in the system also. If you look in an English language automotive maintenance book you will see the terms like "vacuum system" and "vacuum leak" used to describe the various effects in the engine, but usually not relative to the exhaust. There is no total lack of air pressure in the engine that the physics term vacuum implies.


from Shorround6's post#178,

"Now we obviously have some very large pressure variations occurring in a very short space of time but getting lower than atmospheric pressure in a cylinder without the piston going down is going to be a real trick."

Keep in mind that the effect modelwiz is referring to occurs due to the pressure differences relative to the area 'behind' the exhaust gases and the remaining combustion gas pressure in the cylinder, not relative to the incoming air pressure or ambient air pressure.

Using the idea of air foil lift created by the Bernoulli effect, if you increase the ambient air pressure to the same internal cylinder pressure as in the Merlin, the local pressure on top of the wing would still be lower than the pressure on the bottom of the wing, causing lift. In the same way, the local pressure behind the exiting exhaust gases is lower than pressure remaining in the cylinder, causing 'suction'.

If we use the bottom graph you posted above (very nice by the way) you can see that from the time the exhaust valve opens to the time the piston has traveled ~1/2 the distance on the upstroke (i.e. at about 270º) the pressure due to the remaining combustion gases in the cylinder has dropped from a value of ~100 to a value of ~20 for a drop of about 80% - not the 90% value I quoted but that is likely due to the different parameters used in the engine model of the graph. If the boost pressure/peak pressure is lower in the graph's engine model, the difference between the pressure at the point of exhaust valve opening and the pressure at the ~1/2 upstroke position would be lower (i.e. 80% rather than 90%), plus different valve timing could have some effect also.

Another example of the effect we are talking about here is a bore evacuator (aka fume extractor) - the somewhat odd looking cylinder usually located at about the midpoint on the barrel of modern tank guns. The same process modelwiz referred to occurs in the bore of the gun, but without any incoming fresh air. (File:Rauchabsauger.gif - Wikimedia Commons)


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## Shortround6 (May 5, 2019)

Gun bore evacuator as you posted link to. 







You don't have a 'reservoir' of high pressure gas in an engine cylinder with ports orientated in the proper direction to govern the gas flow. Most aircraft engines didn't use a manifold that had high speed moving gas flowing past the exhaust ports of other cylinders. 

I don't have a problem with contributors for whom english is not their first language getting something wrong in translation. Me trying to post anything on a French language board (or any other language) would be a disaster. 
I do have a problem with a new poster claiming stuff most of us have known(or think we know) for years is all wrong, then give no sources, botched technical descriptions (translation problems?) and when we ask for sources or clarification get told we are a bunch of stuck up know-it-alls. 
If you are going to join a forum and challenge conventional wisdom you better have all your facts lined up and sources ready. Just saying you read it _someplace_ is't going to go very far.
I have read a bunch of stuff in books and on the internet on a variety of subjects that was just wrong. I had one book on aircraft armament that had over 20 typos or mistakes in captions before I gave up counting (stuff like calling a B-25 an A-20 in a picture caption). 

Every real engine would have a slightly different graph and trying to grab them off the internet in hurry means compromises. Obviously a supercharged engine might not ever have a vacuum in the cylinder as the positive pressure in the intake manifold would pressurize the cylinder even as the piston moves down on the intake stroke.

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## Snowygrouch (May 5, 2019)

Shortround6 said:


> will the DB 601C/D get any coverage in your book?



I have about six DB test and development reports on the 601C/D, so yes you will find out some things about it from the book, although 
I do not have more than about two photos, which is dissapointing.

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## ThomasP (May 5, 2019)

Hey Shortround6,

Although the moving exhaust gases from one cylinder passing by the second cylinder as they move down an exhaust manifold would increase the effect, it is not necessary for the scavenging/suction/vacuum that modelwiz was talking about.

I know you are familiar with the Bernoulli effect and the lift/drag equations but I am going reiterate them below for (hopefully) increased clarity of what I am saying.

Any time you have gases moving at a higher speed than other proximal gases, you have a difference in pressure in the area between, resulting in 'suction'/'vacuum'/lift/etc.

It does not matter if the different velocity gases are on opposite sides of an airfoil or in front/behind of each other in open air, a relative pressure differential is established and the gases will try to move from the higher pressure area to the lower pressure area (this plus 'weight' of air due to gravity equals atmospheric phenomena such as wind, tornadoes, hurricanes, etc.). If there is an object (airfoil, leaf, newspaper, building, mass of air, etc.) in between the high and low pressure area, the movement of the gases will try to 'draw'/'suck'/'push' the object with it. The higher the velocity differential, the higher the pressure differential (hence the v^2 in the lift and drag equations), the greater the lift/'suction'/'vacuum'/etc. Because of the extremely high velocity differential between the leading edge/bow wave of the 'pulse' of the exhaust gases and the 'stationary' gases inside the cylinder, you get an extremely high 'suction' effect immediately behind the 'pulse'.

If you are familiar with the movement of a child's toy called the Slinky (TM) after some one gives it a push, you can use the movement to visualize the behavior of the exhaust gases as they exit the cylinder. The end of the Slinky pushed in the direction of movement can be considered the high velocity leading edge/bow wave of the exhaust 'pulse', the center section can be considered the low pressure area, and the remaining gases in the cylinder and be considered to be the object to be 'dragged'/'drawn'/'sucked'/lifted. The kinetic energy of the pushed end of the Slinky effectively 'drags' the rest of the slinky along in its wake.


The UK did actually move from 6 individual ejector exhausts per bank to 3 two-cylinder type, because of the increase in efficiency. The effect of the front cylinder's exhaust gases traveling down the manifold past the rear cylinder's exhaust ports increased the scavenging effect, but the rear cylinder also effected the suction at the front cylinder's exhaust port, which also increased efficiency. The enclosed manifold sort of averaged the effect.


And yes, the bore evacuator example uses a reservoir, but all that does is allow a prolonging (or second 'pulse'?) of the effect we are talking about, resulting in a more efficient scavenging of the gases in the barrel.

I think the graph you posted is quite appropriate to our discussion.


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## modelwiz (May 10, 2019)

ThomasP said:


> Hey guys,
> 
> For anyone who is interested, modelwiz is correct in his statement:
> 
> ...


Thank you for giving me the benefit of the doubt. Strictly speaking, the intended correct term would have been pressure differential. And yet, you would never call out "pressure differential-assisted brakes". In technology vacuum tends to describe a negative pressure differential actuated system or mechanism. Technically, vacuum is a space devoid or nearly devoid of matter (e.g. outer space) which does not occur anywhere in the mechanical systems of atmospheric aircraft (or vehicles, or ships, or....). I was being colloquial rather than rigidly technical. Sorry for the many misunderstandings.


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## Shortround6 (May 10, 2019)

I can certainly understand the difference between absolute vacuum and a pressure differential and I have driven vehicles with both "pressure differential-assisted brakes" and " pressure differential-assisted windshield wipers". 

However I have bit of trouble swallowing the pressure differential explanation in a cylinder with a rising piston. On a Kharkiv model V-2 diesel at 1800rpm the piston is rising at an average speed of 17.75ft per second or 1065fpm. This is average speed with the piston starting at a dead stop and ending at a dead stop every 7.1 inches of travel and this speed is only for the piston moving in one direction. The piston completes this one way trip in 1/60th of a second (0.0166 seconds) and we are to believe that the out rushing gases leave with such velocity that they create a lower than atmospheric pressure in the cylinder even as the piston rises and reduces the volume in the cylinder 14-15 times in that 17/1000 of second. Or in other words, even if the the pressure in the cylinder had been magicly reduced to just a bit over 1lbsq/in at the bottom of the stroke the rising piston would have raised the pressure to just about normal atmospheric pressure (14.7psi) by the time it reached the top if the exhaust valves were closed. 
There is no doubt that the pressure in the cylinder is much higher than the pressure outside (normal atmospheric pressure) when the exhaust valves open but in order for there to be _less than 14.7psi_ (our colloquial vacuum) the out rush of gas has to suck the remaining gasses out of the cylinder faster than the piston is rising.


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## tomo pauk (May 10, 2019)

Shortround6 said:


> ...
> I do have a problem with a new poster claiming stuff most of us have known(or think we know) for years is all wrong, then give no sources, botched technical descriptions (translation problems?) and when we ask for sources or clarification get told we are a bunch of stuck up know-it-alls.
> If you are going to join a forum and challenge conventional wisdom you better have all your facts lined up and sources ready. Just saying you read it _someplace_ is't going to go very far.
> ...



This is what it's all about here, and in another 2-3 recent threads. Where we can read a comment, for example: 'all of the participants were misinformed' in the ww2 ammo thread - really??


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## ThomasP (May 16, 2019)

Hey ShortRound6,

Once more into the breach? Sorry it took so long to get back to you on this.

First, because I am an AR type and because I figure you would like to know when you are mistaken, I should point out that you made a math error concerning the average piston speed of the V-2. Using a simplified formula to calculate the piston speed we get:

1800 rpm x ((7.1" up + 7.1" down) / 12") = 2130 ft/min

2130 ft/min / 60 sec = 35.5 ft/sec

Not a big deal. You figured the time available for the combustion gases to exit the cylinder correctly, so it does not effect your argument.

(7.1" / 12") = .5817 ft traveled one way from BDC to TDC.

.5817 ft / 35.5 ft/sec = .0164 sec travel time from BDC to TDC.

The link below is a website you can use to calculate the actual velocity of the piston at any point in its movement from TDC to BDC, with 0º being TDC:

(L&M Engines, Inc. - Piston Velocity Calculator)

If you do not have the particulars for the V-2, the necessary numbers are:

Bore: 5.9055"
Stroke: 7.087" (master rod bank)
Rod Length: 12.598" (master rod bank)
RPM: 1800 per your example


Second, please read my and modelwiz's posts again. Nowhere in them did we say that the pressure in the cylinder would be, or had to be, reduced to less than ambient pressure.

What I said (and what modelwiz tried to say if I understand him correctly) is that a relative pressure differential occurs between the front of the high speed exhaust wave and the remaining exhaust gases in the cylinder.

This creates a suction (per the Bernoulli effect and other named principals) which helps draw out the exhaust gases faster than the piston can push them out. (If you disagree with this I would suggest that you have someone help you figure out just how fast the 0-71 ft/sec piston would push the gases out by itself. Then try to explain why the gases at the end of the exhaust manifolds/stubs are traveling at supersonic speeds.)

This suction will continue to take place until the velocity of the exhausting gases equals the velocity of the gases being pushed out of the cylinder by the piston/incoming charge.

Again, nowhere did we say that the pressure in the cylinder would be, or had to be, reduced to less than ambient pressure.


Third, although modelwiz and I did not say that the pressure inside the cylinder would go below ambient due to this effect, it can and often does. It will occur in one regime or another, sometimes all regimes, in any naturally aspirated 4-stroke engine if it is reasonably efficient depending on the rpm, size/# of exhaust/intake ports, valve overlap, timing, etc.

See the link below:

(https://www.enginelabs.com/engine-tech/exhaust/performance-exhaust-system-design-and-theory/)

I think you will find the entire article interesting as it is very informative about the entire exhaust system, but the most important section relative to what we are discussing is about mid-way down the page under "A Little Theory First: Backpressure And Scavenging" and includes the graph, the next 2 paragraphs, the photo of the inside of the cylinder during valve overlap, and the 3 paragraphs below the photo.

In supercharged 4-stroke aeroengines this suction effect occurs also, but the pressure inside the cylinder will usually only go below ambient in certain regimes. It is difficult to say exactly what regimes as ambient pressure, boost, and what type of exhaust manifolds/ejector stubs are used all have an effect, in addition to the factors mentioned above for the naturally aspirated engine. In general, the lower the boost the more likely you are to have cylinder pressures below ambient. But if you are using ejector exhausts you may never have cylinder pressures below ambient.

In 2-stroke diesels the suction effect also occurs, but I am unaware of any conventional 2-stroke diesel where the pressure inside the cylinder would drop below ambient during normal running.


Hope this helps.

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## DerAdlerIstGelandet (May 16, 2019)

modelwiz said:


> But this is not how a DIESEL operates. And I was referring to the V-2, which was a diesel with four exhaust valves per cylinder operated by two separate camshafts. But of course you knew that. You know everything. You know me so very well. Thank you for the lecture and condescension.



Kettle, pot, black?

I didn’t feel there was any condescending tone in his response. This is a forum, used to exchange ideas and facts. Most of the time there are various views, interpretations and opinions. You have to provide facts and sources to back up posts. That goes for everyone.

So how about you relax a lil?

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## tyrodtom (May 16, 2019)

And then there's the problem with the V2 diesel, it does not have 4 exhaust valves.
It has 2 exhaust valves, and 2 intake valves, like any other 4 valve, 4 cycle engine.
Just a quick look at the cutaway pictures of a V2 diesel will tell you that, if you know what to look for.


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## Shortround6 (May 16, 2019)

First, thanks for the correction on the piston speed. 
Next. 


modelwiz said:


> And BTW, when the exhaust valves open the _pressure differential between the burnt fuel air mixture and_* outside air *_also_ _create what you would call a vacuum_ as the piston moves upward in the exhaust stroke. In all kinds of internal combustion engines.





ThomasP said:


> Second, please read my and modelwiz's posts again. Nowhere in them did we say that the pressure in the cylinder would be, or had to be, reduced to less than ambient pressure.





ThomasP said:


> Again, nowhere did we say that the pressure in the cylinder would be, or had to be, reduced to less than ambient pressure.



Sorry for the confusion but to me when the pressure inside a container, engine cylinder, device, what have you is below the pressure of the* outside air *you have your pressure differential/"vacuum". 

Outside air=ambient air. It doesn't have to equal seal level standard pressure. 



ThomasP said:


> Third, although modelwiz and I did not say that the pressure inside the cylinder would go below ambient due to this effect, it can and often does. It will occur in one regime or another, sometimes all regimes, in any naturally aspirated 4-stroke engine if it is reasonably efficient depending on the rpm, size/# of exhaust/intake ports, valve overlap, timing, etc.



It can but for how long?





graph from Grumpyvette. And this is for a gas engine in a racing state of tune? 

Applying race engine theory/tricks to production engines is an area with several difficulties. 

see;





for a one cylinder engine, but most aircraft/tank engines are not single cylinder





graph for a four cylinder engine. This article is concerned with the best exhaust flow pattern for a turbo-charger on a modern car. The cylinders interfere with each other and reduce the pressure of the exhaust pulse to the turbo, not something we are concerned with here but shows things are not simple.

Also note that these are pressures in the exhaust manifold and not necessarily pressures in the cylinder. 





The engine (or close relative) that we are talking about. notice the cast iron "log" exhaust manifold. You are going to get a lot of interference between the cylinders and you can also kiss goodbye to any idea of exhaust pulse pressure waves bouncing back and forth from the exhaust outlet (on the rear of the tank deck) to the exhaust ports. 

On most V-12 aircraft engines you can also kiss that idea goodbye because it depends on the speed of sound and the length of the exhaust pipe/duct/track vs the RPM and the aircraft engines don't run at anywhere near the rpm needed to get to get this effect to work well with the length of exhaust used. General rule of thumb for aircraft engines was _no more than 3_ cylinders per exhaust pipe. Two cylinders per exhaust outlet was the usual compromise. 




ThomasP said:


> In 2-stroke diesels the suction effect also occurs, but I am unaware of any conventional 2-stroke diesel where the pressure inside the cylinder would drop below ambient during normal running.


Considering that the intake ports are uncovered well before the Piston hits BDC and you have positive pressure from the supercharger in the intake manifold the chances of less than ambient pressure in the cylinder are indeed, pretty slim.

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## modelwiz (May 16, 2019)

DerAdlerIstGelandet said:


> Kettle, pot, black?
> 
> I didn’t feel there was any condescending tone in his response. This is a forum, used to exchange ideas and facts. Most of the time there are various views, interpretations and opinions. You have to provide facts and sources to back up posts. That goes for everyone.
> 
> So how about you relax a lil?



 * GrauGeist said: *
* 
 I'm going out on a limb here, based on observation, and think that you're not all that familiar with how an internal combustion engine works.
*
What part of this statement does not seem condescending to you? Let me know so that I can clearly explain it to you.


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## DerAdlerIstGelandet (May 16, 2019)

modelwiz said:


> * GrauGeist said: *
> *
> I'm going out on a limb here, based on observation, and think that you're not all that familiar with how an internal combustion engine works.
> *
> What part of this statement does not seem condescending to you? Let me know so that I can clearly explain it to you.



I guess I just have thicker skin.

He was making an observation based off of what he read. It is a hell of a lot less condescending than this comment:

_”I am sorry I wrote to such eminent authorities in my attempt to contribute to a dialogue. I will not try it again”_

So I would suggest everyone takes a step back, relax a lil, and have some discussions like an adult.

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## pbehn (May 16, 2019)

There is a huge difference between how a two stroke and four stroke engine we learn about at school work and how a high performance engine works. I think the problems start at the concept of "vacuum".

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