Why so few planes that fired thorugh the propeller hub?

[Matt308]

...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...

 

[Aozora]

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.

 

[Shortround6]

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.

 

[DonL]

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.

 

[OldSkeptic]

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...

 

[wuzak]

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.

 

[nuuumannn]

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.

 

[DonL]

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.

 

[tomo pauk]

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

 

[Shortround6]

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.

 

[fastmongrel]

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.

 

[stona]

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

 

[Rufus123]

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.

 

[Greyman]

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.

Three Fighter Stations visited and six commanders questioned:
Group Captain Broadhurst, DSO, DFC, AFC (Station Commander Hornchurch)
Wing Commander Rankin, DSO, DFC (Wing Commander Training, 11 Group)
Wing Commander Tuck, DSO, DFC (Wing Commander Biggin Hill)
Wing Commander Boyd, DFC (Wing Commander Kenley)
Squadron Leader Wells, DFC (OC 485 Squadron)

In spite of our superiority of fire power over that of the enemy, many pilots would prefer the armament of an Me.109 with its one cannon firing through the airscrew hub and two machine guns mounted in the fuselage. They feel that despite its inferiority to our armament the concentration of parallel fire more than counter-balances our criss-cross pattern.

The document is authored by Wing Commander (Tactics) W.M. Churchill and dated 31 Dec 1941.

Interestingly enough, I have a similar survey from an RAF mission to French Squadrons before the Battle of France and the French pilots said the exact same thing in 1940; preference for centreline armament, and that one fuselage gun was equivalent to two wing guns.

 

[stona]

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

 

[DonL]

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?

 

[Juha]

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

 

[Aozora]

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

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".

 

[stona]

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

 

[Greyman]

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