# Allied tests of captured Bf-109's



## Soren (Mar 22, 2008)

Well since another thread was closed whilst this issue was being discussed I thought it be an idea to have a thread for this issue specifically.

Now, and this goes to all sides, no snide remarks as the mods don't like it nomatter if it's just or unjust. We can discuss this matter without having to resort to name calling.

Onwards;

_______________________________________

Glider,

Eventhough Bill claims you have put things into context you really havent;

As explained the jolt/snatch and disturbance to the flight path was eliminated with the introduction of the F series, and thus the comment about the 109 being "_Embarrased by its slots opening near the stall_" can't have been refering to this. (Would've been a very odd way of refering to such regardless!) The comment only serves as the clear sign that the a/c wasn't flown to its limits, something which isn't unnormal as it was a foreign a/c with some unfamiliar advanced features not seen on any British a/c at the time. 

Dave Southwood, 109 pilot:
_"One interesting feature is the leading edge slats. When these deploy at low speeds or in a turn, a 'clunk' can be heard and felt, but there is no disturbance to the aircraft about any axis. I understand that the Bf109E rolled violently as the slats deployed, and I am curious to know the difference to the Gustav that caused this."
"_

As further evidence the German, Soviet Finnish tests with the 109 all confirm the fact that the British didn't push their captured 109's to their limits. And then there's all the modern day pilots who fly the Bf-109 today confirming this as-well, all saying without a doubt that the Bf-109 Spitfire are VERY close when it comes to turn performance, AND that the P-51 is hoplessly behind by comparison.

And finally there's the aerodynamics, which fully prove that the British did NOT fly their captured 109's to the limit, even the most basic aerodynamics support this. (And when I'm talking basic I'm talking Wing-loading power-loading alone)

So you haven't put anything into context Glider, eventhough Bill oddly claims you have. Surely you must see this as-well now.


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## claidemore (Mar 22, 2008)

Hi Soren,
Thanks for starting this discussion again, I was thinking about doing the same thing myself. 

Like you, I also hope that everyone can leave out the little insults and shots. Even if we never agree on something, we can still respect the other persons right to have a different opinion, no matter how boneheaded we think it is! 

One bone of contention seems to be the "embarrassed by the opening of its slats" quote. This sentance is written in typically confusing British parlance of the 1940s, something that is often hard to understand except by Brits from that generation. It's a poor turn of a phrase IMO. 

Soren your interpretaion of the statement is assuming the word means "to humiliate" which isn't used in proper english to refer to an inanimate object like a plane. You can humiliate or embarrass a person, but not an object. 

The word embarrassed has several different meanings. The definition that I believe applies in this case, according to Websters dicitonary, would be * 3: to make intricate, complicated*. 

A better choice of words would have been; "The 109 is _complicated _by the opening of its slats."

This agrees with the other quotes from the tests posted by others, where the pilots talk about flying the plane past deployment of the slats. 


I believe Hunter asked which pilots flew the plane in the AFDU trials. 
Flt. Lt. Lew Lewendon was the primary pilot, and the one who had the least trouble with the plane. (this was the 109G2 captured in North Africa and known as *Black 6*)
It was also flown by Flg Offc. Doug Gough, FO Jack Staples and FO Lewis-Watts and Flt Lt. Dick Forbes. 

Black 6 was flown in a tactical trial against a Spitfire VC while still in the Middle East, and against a Tempest, Mustang III, Spitfire XIV, Corsair, Hellcat, and a Seafire III with AFDU in England. 

The results in the 1944 AFDU trials, showing the FW190 turning better than Black 6 are suspicious I agree. However, I don't think we can attribute those results to the test pilots. I think it is much more likely the fault of the plane itself, which had the ignition harness replaced after the test, had a few different propellers and had some parts that were cannibilized from a 109F and a second 109G2. The original engine had low hours though. 

If we are to say that the 1944 tests are not indicative of the actual performance of the airplane, I think the condition of the plane would carry more weight than the test pilots.

Going back to the 109E tests done at RAE, they came up with a turn radius of 885 feet at 12,000 ft alt. The Baubeschreibung document gives us 557 ft at Sea Level and 1050 feet at 6000meters alt. If you plot those three radius figures on a graph, you get a nice neat line, indicating that all three numbers are relavant and reasonably accurate for the altitudes they represent.


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## Glider (Mar 23, 2008)

Hi Soren. 
The test pilot reports explain what happens when the slats are deployed and most importantly what happens when you continue to fly the aircraft past the deployment. Indeed one even reports what happens when the stall occurs when the turn has continued past the deployment.
This alone proves that the British Pilots didn't stop when the slats deployed. 

Re the planes being embarrased by the deployement of the slats this seems to have been accepted in the 109E as common. 
The same comment about the later versions we simply don't know why it happened. All we do know is that the pilot experienced this when flying the aircraft, sufficient for him to report the sensation in his report. He had no reason to make it up, or exagerate anything so the only conclusion is that it happened.
There are two obvious potential explanations:-
a) There was a problem with the aircraft at the time, 
b) Something in the way that the pilot approached the turn could have made one wing stall before the other, not uncommon in a tight turn. The deployment of one slat before the other would almost inevitably had some reaction.
There may well be another reason, we simply don't know.

As mentioned by a number of people the height of the test is an important factor, what doesn't get the same publicity is the speed at which the aircraft are travelling. 
At low speed I don't think that anyone would deny that the 109 had a good rate of turn but it does seem to be more suseptable to problems at high speed, even against the P51. The tests don't generally tell you what speed the aircraft were going and this may be a factor in the results.


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## Kurfürst (Mar 23, 2008)

Soren said:


> Dave Southwood, 109 pilot:
> _"One interesting feature is the leading edge slats. When these deploy at low speeds or in a turn, a 'clunk' can be heard and felt, but there is no disturbance to the aircraft about any axis. I understand that the Bf109E rolled violently as the slats deployed, and I am curious to know the difference to the Gustav that caused this."
> "_



109E and early F had the slats operated by wing arms, the late F and all G series had it deployed by bearings, probably hence the much smoother operation noted by Southwood on the G-2. Changes in the K also had the slats made out of steel.

Condition of the aircraft is an interesting thing, as all the 109 tested by the Brits were in damaged state; the 109E WNr 1304 was captured by the French after it belly landed behind the lines, and had some engine troubles with the oil; the F-2 they had a similiar story, but was probably in the worst shape of all; I believe they got a belly landed F-4, but I have no details of it; the G-2/trop Black Six was found in the desert in North Africa, with battle damage, splinters on the propeller and malfuncitioning radiator flaps. 

Only the G-6/U2 that landed in error in Britainwas in normal condition, however that one had gunpods, being a Wilde Sau nightfighter (and probably some service history and repairs/rebuilds behind it, given it supposed to be GM-1 carrier, yet had no GM-1 system and was issued to a Wilde Sau unit.. probably rebuilt as a normal Gustav after sustaining battle damage).

@claidemore,

Do you have more information on Black Six? I have two tests of it on my site, and I`d always love to give some background information about these captured planes..


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## claidemore (Mar 23, 2008)

Kurfurst:

I have a pdf I found online that lists the history of Black 6, it gives dates, pilots who flew it etc. I'll send it to you if I can figure a way to do it via pm, or try to find the link again. 

Claidemore


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## Hunter368 (Mar 23, 2008)

Perhaps the 109 is much like the P-38. Both good planes in the hands of a average pilot. But truely lethal in the hands of a expert who knew the limits of the plane and how to push those limits.

Just a thought


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## DerAdlerIstGelandet (Mar 23, 2008)

*To all posters in this thread.

Due to how all these other threads on this topic have gone, the first person to take this thread in the wrong direction will recieve a 3 day ban and the thread will be closed.

I am tired of it and so are the other mods!*


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## Hunter368 (Mar 23, 2008)

Good idea Chris, we are tired of it also.


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## claidemore (Mar 23, 2008)

Totally agree. 
Seems only fair and just to take action against the individuals who cross the line. 
It would be nice if the thread could remain open for those who can remain civil and wish to continue the discussion and hopefully learn something.


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## Soren (Mar 23, 2008)

Glider,

The RAE test pilots mentioned no such thing when flying the Emil, so something must have stopped them going any further in the later captured 109G. That the report itself says that the a/c was embarrased by the opening of its slots can only mean that the pilot didn't go past slat deployment, it's that simple, and there's no reason for complicating it. Also to support that this was the case two VERY experienced LW pilots explain that it was normal for new pilots in the type to be vary of the slats.

Also don't confuse stalling a plane a low G's compared to stalling one at high G's. Stalling the 109 at low G's isn't what was scary to the new pilots in the type, it was the loud heavy jolt given in a high G maneuver which scared them. 

The fact that the British first tested the Emil is probably what caused them to be more cautious about the slats on the later types, as the Emil both suffered from a violent slat deployment as-well as the highly dangerous but frequent jamming of one of the slats, causing violent spins, something which would've undoubtedly scared any pilot and seriously did scare Rall. 

And to support this we have all the veteran modern 109 pilots as-well as aerodynamics.

That having been said, both a/c were excellent fighters and the most closely matched of all fighters in terms of turn rate, roll rate, climb rate speed.


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## kool kitty89 (Mar 24, 2008)

Kurfürst,
Didn't you also mention that some of the British figures were calculated, not from tests?


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## drgondog (Mar 24, 2008)

Does anybody seriously think Gunther Rall was 'afraid' of the Me 109?

Does anybody have a reference that would leave them to believe this?

If not, is anyone offended by the thought that a top German ace and one of the greatest wariors Germany had to offer is described 'as seriously afraid' of the leading edge slats on a 109?

Jez curious why a statement like that would be accepted on this forum without some serious proof.

Regards,

Bill


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## claidemore (Mar 24, 2008)

Soren: Did you read my explanation of the word 'embarrassed' in my above post? I really think that statement is being taken completely out of context and AFAIK it was only mentioned in the trial vs the Tempest. 
The report is saying, "the turn of the 109 is _complicated _by the opening of its slats" , ie you have to be aware that your firing solution will be momentarily disturbed when they snap open, but that you can continue to turn tighter until you feel the 'juddering' indication of a stall. It is clearly stated in other parts of the test that the pilots flew the plane in turns past the opening of the slats. The word ''embarrassed is seldom used in that context in modern english, but in 1944, for educated british types, it was. I used to write for a newspaper, words were my stock in trade, trust me on this one. PLEASE! 

From the 1944 AFDU report on the 109G2:



> This is particularly noticeable when manoeuvring. For example, if the stick is pulled back in a tight turn, putting additional g on the aircraft, the slots open at quite a high airspeed; as they open, the stick suddenly snatches laterally through several inches either way, sufficiently to upset a pilot's aim in a dog fight. The snatch appears to be associated with the opening of the slots, for once they are fully open a steady turn can be done, with no aileron vibration, until the stall is approached.



This statement though it does show the pilots flying the plane past opening of the slats, also shows a bit of nit-picking. They point out the possibility of losing aim during a turn as a deficit, but in fact it would be a minor problem easily and quickly corrected. 

From the RAE test of 109E in 1940:



> Even in a very tight turn the stall was quite gentle, with no tendency for the aircraft to suddenly flick over on to its back and spin. The Spitfires and Hurricanes could follow the Me. 109 round during the stalled turns without themselves showing any signs of stalling.



As we can see, they flew the plane *in a very tight turn*, and experienced a *stall* while doing it, (the slats had to be open if the plane stalled) and gave the 109 credit for a quite gentle stall. 

We have to remember here that we are talking about test pilots with hundreds or thousands of hours in many types of planes, not low time trainee pilots which would have been the case with most Luftwaffe pilots flying their first circuits in 109s. Don't forget, automatic slats are often called 'Handley Page slats', and Handley Page is British. Slats were not unknown technology. 

While I agree that the 109 should have shown better turn characteristics in the AFDU trials, I don't believe it was because of the pilots not flying the plane properly. 

BTW Black 6 had it's cannon removed while in the Middle East, and I've seen no indication that it was replaced, so the plane may have been even lighter than normal in the trials in 1944. It had one wing from another plane, had the oil cooler radiator wired open at one point, had the canopy fly off twice, as well as numerous other mechanical problems. The trial against the Tempest V had to be cut short, because carbon monozide was affecting the pilot (Lewendon). The problem was not mentioned in the subsequent trials.


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## Soren (Mar 24, 2008)

Claidemore,

I'm more than familiar with the British language as I was raised with it, and embarrased means embarrased.



> Quote:
> This is particularly noticeable when manoeuvring. For example, if the stick is pulled back in a tight turn, putting additional g on the aircraft, the slots open at quite a high airspeed; as they open, the stick suddenly snatches laterally through several inches either way, sufficiently to upset a pilot's aim in a dog fight. The snatch appears to be associated with the opening of the slots, for once they are fully open a steady turn can be done, with no aileron vibration, until the stall is approached.
> "



That isn't from a test with a 109G2, it's from the RAE's tests with the Emil.

And I repeat; The problem with the slats causing a jolt/snatch disturbance in the flight path as-well as jamming in high G turns was a problem only the Emil suffered, the problem was completely eliminated with the introduction of the F series. 

As for the Emil tested by the RAE well like I said, it suffered from not only being run with the wrong fuel but also from an already underperforming engine.


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## kool kitty89 (Mar 24, 2008)

Soren, 
According to Kurfürst's last post the slat problems were still present on the initial Bf 109F as well and it was solved on later F models:


> 109E and early F had the slats operated by wing arms, the late F and all G series had it deployed by bearings, probably hence the much smoother operation noted by Southwood on the G-2. Changes in the K also had the slats made out of steel.


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## Kurfürst (Mar 24, 2008)

claidemore said:


> From the 1944 AFDU report on the 109G2:
> 
> 
> 
> > This is particularly noticeable when manoeuvring. For example, if the stick is pulled back in a tight turn, putting additional g on the aircraft, the slots open at quite a high airspeed; as they open, the stick suddenly snatches laterally through several inches either way, sufficiently to upset a pilot's aim in a dog fight. The snatch appears to be associated with the opening of the slots, for once they are fully open a steady turn can be done, with no aileron vibration, until the stall is approached.



This one is _still_ from the 1940 RAE trials with the 109E, *not with the G-2.*

_Messerschmitt Me. 109 Handling and Manoeuvrability Tests BY M. B. MORGAN, M.A. and D. E. MORRIS, B.SC., September 1940. Section 4.6. Flying Controls, _

Which you will be soon able to read on my site in full anyway.

Again the experience with and pecularities of the 109E in 1940 are getting mixed up with the 1944 trials with the 109G-2/trop.

Its simple, really. In the September 1940 test, they had plenty of experience with the 109E, and found that, if its flown to the limits, they can turn with Spitfires, which were more harder to be flown to the limits because of its nastier stall and control characteristics.

In the 1944 tests with the G-2 by AFDU, the pilot appears to be rather inexperienced with the type, he did not push the Gustav to its limits, reported that in turns he was _emberassed _ by the opening of the slats, and probably eased back too early, leading to odd turn results.


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## Kurfürst (Mar 24, 2008)

kool kitty89 said:


> Soren,
> According to Kurfürst's last post the slat problems were still present on the initial Bf 109F as well and it was solved on later F models:



I am not sure if they still present with the early F model - the mechanism was similiar, but the slat design was already different, as was the wing, ailerons were now of the Friese type etc.

Unfortunately, there are no 109F trials to shed light on the issue.


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## lesofprimus (Mar 24, 2008)

> Does anybody seriously think Gunther Rall was 'afraid' of the Me 109?


I dont think Mr. Rall was afraid of anything, let alone an aircraft he knew better than his own penis... Any pilot with Ralls experience would use any advantage his aircraft had over an opponent to maximum effectiveness...

No hesitation...

Efficiently....

With deadly consequences....

Ive met Gunther Rall in the past and it only solidified my feelings above... I bet that BS about him being afraid of the slats was started up by some Soviet Propagandaist....

As far as all this trials stuff goes, let me ask a couple questions....

Who here believes that an English Test Pilot Officer can fly a Bf 109EFG as effectively and expertly as Gunther Rall, or Theo Osterkamp, or Heinz Baer, or Erich Hartmann, or Von Bonin or Reschke or Kupinski or Graf????

Is it possible to believe that the 109s in question, if they were operating perfectly under perfect conditions, with the best Test Pilot the Brits could provide, such as Flt. Lt. Lew Lewendon, would be flown better if a German Ace with 150+ kills to his credit, such as Walter Kupinski, were doing the maneuvers instead of someone who never really pushed the limits of the aircraft before???

All these flight tests are subjective at best and really dont shed that much light on determining which performed "better"... I think its retarded to use a poorly performing, unserviced enemy aircraft to compare ur countries aircraft to in combat maneuvers...

No matter how good Flt. Lt. Lew Lewendon was, or how much stick time he had accumulated, there is no way he flew any enemy aircraft to its limits....

None...

Thats comes from my Grandfathers own lips...


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## drgondog (Mar 24, 2008)

Here is the 109 that was used to familiarize US fighter pilots - at Steeple Morden, Jan 1944.

Below that are the 109/190 two seaters that my father got to fly at Gablingen in July-Sept 1945


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## FLYBOYJ (Mar 24, 2008)

Slam dunk Dan!!!!


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## Glider (Mar 24, 2008)

Lesof
There is a lot of sense in this posting. If we stand back and look at the situation there were three main questions
a) Did the test pilot take the aircraft past the deployment of the slats. *Yes*
b) Was Gunther Rall afraid of his aircraft *No*
c) Could a British test pilot get the absolute best our of a foriegn aircraft *No*

Taking C a little further. Did it matter?
The idea behind these tests it to equip your pilots with the best information on how to handle a foriegn pilot who is in combat with you. If the Test pilot can get a similar level of performance out of an aircraft that an average opposing squadron pilot can obtain, then I suggest the job has been done.
Aces can always get the extra 5% out of an aircraft.

Re the 109, the average German Pilot couldn't turn inside the Spitfire, indeed a number of experienced pilots even expert pilots couldn't turn inside the Spitfire.
The fact that (possibly) in certain circumstances the 109 might have a theoretical advantage is almost irrelevant, as the average Allied pilot could and did turn inside the 109.

There are numerous quotes from pilots of all levels of experience that the Spitfire did this and precious few examples on the 109 doing this.


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## claidemore (Mar 24, 2008)

I don't know if Lew Lewendon is still with us, but I'll bet if you asked him if he was as good a pilot as Rall or Graf or Krupinski, he would just shrug his shoulders and smile. Ask Corky Meyer the same question, probably get a similar reaction, as well as an explanation on the differences between a fighter pilot and a test pilot, apples and oranges. 

BTW; the allied planes were not flown by expereinced ace pilots either, they were flown by the test pilots at AFDU. Two planes being flown by two test pilots, arguably with equal skill and experience. The planes themselves were specifically selected to match the performance of those in service. In fact the first Spit XIV was found to have better performance than operational planes, so another MkXIV was used. 

For comparison purposes, the trials provide useful information. (despite dummies like me misquoting from the wrong tests!)

AFDU, Air Fighting Developement Unit, was developed specifically to test captured enemy equipment. It grew out of RAE Farnborough which had been testing and developing planes since Word War One. They tested and flew 109E/F/Gs, Bf110/410, Ju88, 4 different FW190s, He111, He177, and others. They were also the guys responsible for sticking a Merlin in the P51. Not exactly a bunch of noobs. 

https://www.airforcehistory.hq.af.mil/PopTopics/airtechintel.htmamateurs. 

AFDU was responsible for developing tactics to counter these various e/a, they were very successful in that role, with the allied airforces attaining complete air superiority over Europe.


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## Kurfürst (Mar 24, 2008)

Glider said:


> Re the 109, the average German Pilot couldn't turn inside the Spitfire, indeed a number of experienced pilots even expert pilots couldn't turn inside the Spitfire.
> The fact that (possibly) in certain circumstances the 109 might have a theoretical advantage is almost irrelevant, as the average Allied pilot could and did turn inside the 109.
> 
> There are numerous quotes from pilots of all levels of experience that the Spitfire did this and precious few examples on the 109 doing this.



That`s your opinion of course. I am not sure on what it is based on.

And this is RAE`s opinion, on the 109E :

_
When the Me.109 was following the Hurricane or Spitfire, it was found that our aircraft turned inside the Me.109 without difficulty when flown by determined pilots who were not afraid to pull their aircraft round hard in a tight turn. In a surprisingly large number of cases, however, the Me. 109 succeeded in keeping on the tail of the Spitfire or Hurricane during these turning tests, merely because our Pilots would not tighten up the turn suficiently from fear of stalling and spinning.

...

The gentle stall and good control under g [of the 109E] are of some importance, as they enable the pilot to get the most out of the aircraft in a circling dog-fight by flying very near the stall. As mentioned in section 5.1, the Me.109 pilot succeeded in keeping on the tail of the Spitfire in many cases, despite the latter aircraft's superior turning performance, because a number of the Spitfire pilots failed to tighten up the turn sufficiently. If the stick is pulled back too far on the Spitfire in a tight turn, the aircraft may stall rather violently, flick over on to its back, and spin. Knowledge of this undoubtedly deters the pilot from tightening his turn when being chased, particularly if he is not very experienced._

Note that RAE didn`t even use flaps to aid the turn in the 109E.

That`s a very nice picture of that 109F, Bill, that you for sharing ! Do you have any more details on that aircraft, experience with it, perhaps?


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## Soren (Mar 24, 2008)

kool kitty89 said:


> Soren,
> According to Kurfürst's last post the slat problems were still present on the initial Bf 109F as well and it was solved on later F models:



The design wasn't the same, only parts of the hingearm mechanism, some linkages were removed and the design of the slat itself was new.


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## Soren (Mar 24, 2008)

Glider,

There's more than enough evidence to prove that the British test pilots did NOT go beyond slat deployment in the 109G, alone the comment made in their own report more than settling that fact.


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## drgondog (Mar 24, 2008)

That`s a very nice picture of that 109F, Bill, that you for sharing ! Do you have any more details on that aircraft, experience with it, perhaps?[/QUOTE]

*Kurfurst - I had than one mislabeled as the G2 some time ago and noticed only recently that it was an F. 

Short answer - no. I think it was the F that you mentioned earlier that had crash landed and was repaired. It was part of a show in which a Ju 88, an Me 110 and the 109F were flown by the RAF to each US base to familiarize American pilots with flight controls (as a potential escape vehicle) as well as lectures on the characteristics.

I'll dig around and see if I can find the others. Of course you are welcome to use it - thyere are no copyright issues that I can imagine.

Regards,

Bill*


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## Glider (Mar 24, 2008)

This is my posting from the previous thread. The sections in bold report what happened after the slats deployed and pressure continued until the stall.
That they should do this one one aircraft and not another makes no sense. 

_Apart from their excessive heaviness at high speeds, the most serious defect of the Me. 109 ailerons is a tendency to snatch as the wing tip slots open. This is particularly noticeable when manoeuvring. For example, if the stick is pulled back in a tight turn, putting additional g on the aircraft, the slots open at quite a high airspeed; as they open, the stick suddenly snatches laterally through several inches either way, sufficiently to upset a pilot's aim in a dog fight. The snatch appears to be associated with the opening of the slots, *for once they are fully open a steady turn can be done, with no aileron vibration, until the stall is approached.* 

When doing tight turns with the Me. 109 leading at speeds between 90 m.p.h. and 220 m.p.h. the Spitfires and Hurricanes had little difficult in keeping on the tail of the Me. 109. During these turns the amount of normal g recorded on the Me. 109 was between 2J and 4 g. The aircraft stalled if the turn was tightened to give more than 4 g at speeds below about 200 m.p.h. The slots opened at about 1\2 g before the stall, and whilst opening caused the ailerons to snatch; this upset the pilot's sighting immediately and caused him to lose ground. *When the slots were fully open the aircraft could be turned quite steadily until very near the stall. If the stick was then pulled back a little more the aircraft suddenly shuddered, and either tended to come out of the turn or dropped its wing further, oscillating meanwhile in pitch and roll and rapidly losing height; the aircraft immediately unstalled if the stick was eased forward.* Even in a very tight turn the stall was quite gentle, with no tendency for the aircraft to suddenly flick over on to its back and spin. The Spitfires and Hurricanes could follow the Me. 109 round during the stalled turns without themselves showing any signs of stalling.

The comments about the 109 being embarrased clearly refers to the 109 losing its sighting position which is quite understandable_
--------------------------------------------------------------------------------

In Kurfurst earlier posting the interesting thing is that both of the quotes he mentions state that the Spitfire had a tighter turning circle but that if an experienced pilot was up against a less experienced pilot then the 109 had a chance.
There should be no suprise there.

AS for the comment that _Note that RAE didn`t even use flaps to aid the turn in the 109E._
As far as I can see it doesn't say that it did or didn't.


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## Glider (Mar 24, 2008)

As an aside I would hate to fly the 2 seat 109 from the back. The engine, nose and front seat gets in the way of half the visibility. The wing looks like it gets in the way of the rest.


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## Hunter368 (Mar 24, 2008)

Glider said:


> This is my posting from the previous thread. The sections in bold report what happened after the slats deployed and pressure continued until the stall.
> That they should do this one one aircraft and not another makes no sense.
> 
> 
> That was covered already why that would not be true Glider. See post #4 on this thread, it covers it nicely and clearly.


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## drgondog (Mar 24, 2008)

Glider said:


> As an aside I would hate to fly the 2 seat 109 from the back. The engine, nose and front seat gets in the way of half the visibility. The wing looks like it gets in the way of the rest.



Flying a 51 from the back seat can't be much better.. I had to wind my way down the transient to the active but it wasn't that bad taking off. 

By his accounts it was a pleasant aircraft to fly, but felt the Fw 190 was lighter on the controls and more fun to fly at medium to high speeds.


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## Glider (Mar 24, 2008)

So the theory is that the pilots made it up?

Has anyone got a link to the full comparison report. I thought that I did but it seems to be missing some parts that you are all quoting from. That may well be the cause of some of my confusion


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## Hunter368 (Mar 24, 2008)

Glider said:


> So the theory is that the pilots made it up?
> 
> Has anyone got a link to the full comparison report. I thought that I did but it seems to be missing some parts that you are all quoting from. That may well be the cause of some of my confusion



Glider I was referring to the following comments:


"109E and early F had the slats operated by wing arms, the late F and all G series had it deployed by bearings, probably hence the much smoother operation noted by Southwood on the G-2. Changes in the K also had the slats made out of steel.

Condition of the aircraft is an interesting thing, as all the 109 tested by the Brits were in damaged state; the 109E WNr 1304 was captured by the French after it belly landed behind the lines, and had some engine troubles with the oil; the F-2 they had a similiar story, but was probably in the worst shape of all; I believe they got a belly landed F-4, but I have no details of it; the G-2/trop Black Six was found in the desert in North Africa, with battle damage, splinters on the propeller and malfuncitioning radiator flaps. 

Only the G-6/U2 that landed in error in Britainwas in normal condition, however that one had gunpods, being a Wilde Sau nightfighter (and probably some service history and repairs/rebuilds behind it, given it supposed to be GM-1 carrier, yet had no GM-1 system and was issued to a Wilde Sau unit.. probably rebuilt as a normal Gustav after sustaining battle damage)."


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## drgondog (Mar 24, 2008)

What is and has been missing from these discussions and candidly from just about every comparative report I have ever seen is the Test Plan.

Every Test Program should have well articulated objectives and the strategies to achieve them.

If one of your objectives is to try to get enough data to draw conclusions, you not only should fly within repeatable boundary conditions but also with different pilots flying the same profiles to sort out some of the subjectivity that will be introduced by skill variances.

I haven't yet seen anything in Any report, or any book on the subject of Axis vs Allied Fighter comparisons which even contains the following:

Turn Comparison Tests;
Three airspeed values, three altitudes - left and right turns.
Start in Trail, pursue aircraft in front until gain or lose ground in the turn.
Repeat series after exchanging pilots
Repeat series for different flap settings within airspeed limitations 
etc, etc

This is a key difference between cobbling together a flight comparison between two skilled pilots who encounter each other and decide to 'rat-race' and professional test pilots trying to filter out as many variables as much as possible.

In the example Dan gave, he is of course right about skill levels of a Krupinski or Rall or a Preddy or Gabreskis against even a skilled test pilot.. but I would add something here also.

Give Rall or Yeager or Krupinski 50 hours (probably much less) in your airplane and he will whip you one on one in his 'new bird' - this is the difference between talent and situational awareness versus a skilled excution of describable manuevers and flight conditions in a test program.

So, one can say they don't believe the test results for a variety of reasons - 

but I haven't seen anyone put a finger on exactly what the Test Plan was, whether it was detailed in execution, what conditions they set for comparisons, etc., or even the differences described quantitatively?

What we have seen are persistent comments regarding why the Test Plan was flawed - and I believe they could well be flawed - just nobody has pulled out the smoking gun... 

Fear of leading edge slats is not high on the list of 'probable cause' explaining the report. 

Having said that, if the 109G2 airframe was bent, if the engine was below standard, if one pilot or low time pilots flew the 109 against superior talent, if something was mechanically wrong with the slats, if flight control surfaces were damaged or improperly rigged, etc - any of those parameters would affect a well designed objective comparison for specific profiles.

I'm in agreement with Dan that a Comparison Flight Test is not The 'answer' but it is, if properly planned and executed, a potential high value approach to yielding conclusions regarding relative strengths and weaknesses.


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## Hunter368 (Mar 24, 2008)

Agreed


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## Soren (Mar 24, 2008)

Fact still is that the captured 109G wasn't flown to its limits, as both German, British, Finnish Soviet testimony as-well as aerodynamics confirm. 

Furthermore the a/c tested were all either damaged, featuring gun-pods, underperforming engines, flown with the wrong fuel and last but not least flown by pilots extremely inexperienced in the type, not even having recieved any pre-flight instructions on any of the a/c's characteristics.

And thus the British trials with the 109 are, like I've always said, worth completely nothing.

If we want to compare a/c accurately we must only rely on aerodynamics and the figures achieved by the a/c's country of origin, as this is the only way to ensure that the a/c is in prestine condition and performing its best.


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## drgondog (Mar 24, 2008)

Hunter368 said:


> Condition of the aircraft is an interesting thing, as all the 109 tested by the Brits were in damaged state; the 109E WNr 1304 was captured by the French after it belly landed behind the lines, and had some engine troubles with the oil; the F-2 they had a similiar story, but was probably in the worst shape of all; I believe they got a belly landed F-4, but I have no details of it; the G-2/trop Black Six was found in the desert in North Africa, with battle damage, splinters on the propeller and malfuncitioning radiator flaps.
> 
> Only the G-6/U2 that landed in error in Britainwas in normal condition, however that one had gunpods, being a Wilde Sau nightfighter (and probably some service history and repairs/rebuilds behind it, given it supposed to be GM-1 carrier, yet had no GM-1 system and was issued to a Wilde Sau unit.. probably rebuilt as a normal Gustav after sustaining battle damage)."



Hunter - I think the 109F pic I posted above is the F-4


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## drgondog (Mar 24, 2008)

drgondog said:


> Hunter - I think the 109F pic I posted above is the F-4



The second thing I wonder is why we would assume the aircraft remained in damaged condition? 

God knows there were lots of damaged aircraft captured in Sicily and Italy to scavenge parts - and failing that the Brits knew how to work with sheet metal, etc to rebuild what they didn't have parts for?


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## Hunter368 (Mar 24, 2008)

Soren said:


> Fact still is that the captured 109G wasn't flown to its limits, as both German, British, Finnish Soviet testimony as-well as aerodynamics confirm.
> 
> Furthermore the a/c tested were all either damaged, featuring gun-pods, underperforming engines, flown with the wrong fuel and last but not least flown by pilots extremely inexperienced in the type, not even having recieved any pre-flight instructions on any of the a/c's characteristics.
> 
> ...



I would have to agree, both of Allied planes and Axis planes.


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## kool kitty89 (Mar 25, 2008)

Glider, 
Let me try to sum up what's wrong with the reasoning on the "embarrassed" issue:

You say that the "embarassed by opening of the slots" statment refers to the aileron snatch, but this quote is from the 1944 Me-109G vs Tempest turn tests. And the test reffering to the "snatch" is a 1940 Bf 109E test. And as explained the 109G would not have suffered from aileron snatch.


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## Juha (Mar 25, 2008)

Now Eric Brown wrote on his flights in the G-6/U2 that the opening of the slots ruined sighting and noticed that the flaw of 109E was still there. Brown flew the plane, after all. But on the other hand I have always thought that he was overcritical on 109G-6.

Finns wrote that when the slots opened one felt jerks/twitchs on the stick and elevators lightened but the control remained up to extreme limits.

Juha


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## Glider (Mar 25, 2008)

Juha said:


> Now Eric Brown wrote on his flights in the G-6/U2 that the opening of the slots ruined sighting and noticed that the flaw of 109E was still there. Brown flew the plane, after all. But on the other hand I have always thought that he was overcritical on 109G-6.
> 
> Finns wrote that when the slots opened one felt jerks/twitchs on the stick and elevators lightened but the control remained up to extreme limits.
> 
> Juha



Exactly the point I have been trying to make.


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## Glider (Mar 25, 2008)

Double post, apologies


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## Kurfürst (Mar 25, 2008)

Brown said that flying into the slipstream of a heavy bomber throw the plane around and upset the aim. Which is what has been described for other fighters in similiar situation anyway, slats or no slats, it isn`t too special.

BTW Brown flew the G-6/U2 for an hour in total, and it was his first flight try in a 109.


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## Juha (Mar 25, 2008)

Kurfürst
Brown first made turns, noticed that that the opening of the slats ruined sighting and noticed that the flaw of 109E was still there. And according to his writing he continued after slats opened up to stall, which was mild.
Because he was interested in the working of slats, he tested them further and made mock attacks against a Lanc and fought a mock combat against Mustang flown by a fellow RAE pilot. In both cases, with the Lanc AND with the MUSTANG the slipstream got slats open unevenly and spoiled the sighting.

Brown had tested also 109E, I cannot now remember exactly when, but anyway after 40-41 timeframe.

Source: Wings of LW pp 151 and 155.


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## Glider (Mar 25, 2008)

Anyone who flies into the slipstream of any aircraft is going to get thrown around. I suspect that slats might make it worse if it caused the slats to deploy.
Its only of academic interest, as no one could draw a bead on anything in that situation


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## claidemore (Mar 25, 2008)

The slats on the 109 opened instantly, for there to be no felt effect on flight, they would have to be power assisted and open gradually. 

Opening of the slots changed the lift coefficient from somewhere around 1.4 to 1.7.(arguably) That has to affect flight path and require some correction for sighting. Wolfram also mentions this characteristic. 

Just off the top of my head, the RAE/AFDU trials included turns in either direction and included tests with both planes starting in trail position on the other in turns. They did not switch pilots in the 1944 AFDU trials. 

Not sure about different altitudes, speeds etc, as all I've read are conclusions and summarizations in the report. I believe Kurfurst is going to put the entire reports on his site, hopefully there will be original graphs and charts there as well.


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## drgondog (Mar 25, 2008)

Glider (and Kurfurst) - true and worse for heavily loaded a/c with respect to trailing turbulence.

The tip Vortex is much worse for a heavy aircraft than propwash or jet turbulence and reaches maximum 'down velocity' at centerline (and below) the aircraft... decreasing over distance because air is not a perfect inviscous fluid. If it was the lifting line vortex would, in theory, extend from point of lift before take off all the way to point of 'no-lift' after landing (or crashing)

The tip vortex for a 70,000 pound B-17 or 60,000 pound F-105 would be far more severe than behind a Spitfire, for example. The rotational flow behind the engines is dominated by the prop tip vortices but much less than tip vortex effect and disperses rapidly in comparison.

The turbulence which 'caused' a 109 slats to engage would most likely be a very high local angle of attack due to the turbulence - not a result of the normal free stream vector. Theoretically it could happen in a thunderstorm or any CAT condition with high indicial gusts...


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## kool kitty89 (Mar 25, 2008)

claidemore said:


> The slats on the 109 opened instantly, for there to be no felt effect on flight, they would have to be power assisted and open gradually.
> 
> Opening of the slots changed the lift coefficient from somewhere around 1.4 to 1.7.(arguably) That has to affect flight path and require some correction for sighting. Wolfram also mentions this characteristic.
> 
> ...



The combat/maneuvering flaps would also have a major effect on CLmax. (a feature which the Spitfire and Hurricane lacked; hence why the P-51 had a higher CLmax than the Spit even with a lower lift airfoil)


I'm also not sure about the gradual slat deployment since the Me 262 used a similar design as the later Me 109's (I think) and had gradual deployment of slats. Soren, info and corrections on this point would be appreciated.


And for refrence here's this again:


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## drgondog (Mar 25, 2008)

kool kitty89 said:


> The combat flapswould also have a major effect on CLmax. (a feature which the Spitfire and Hurricane lacked; hence why the P-51 had a higher CLmax than the Spit even with a lower lift airfoil)
> 
> *There are too many anecdotal references to a P-51D unable to close (but not lose ground), with a 109G/K in a prolonged turning manuever at low altitude and airspeed, by reducing flaps. The reference to the Mustang not improving its performance in turn through use of flaps against the Spit XIV in the RAF tests bear this observation out also.*
> 
> ...



I have seen a lot of discussions about positive combat results obtained by dropping flaps, lowering gear, etc - but in my opinion what they do for a 51(or any other fighter) is give it a huge increase in drag, enabling a tighter turn because of the lower speed.. meaning if he didn't get his deflection shot he was potentially in trouble now that his adversary possibly had more energy (and options)..

And BTW, there were structural limitations on flap settings as function of airspeed and lowereing gear. These are all about low speed desparation tactics..

Manuevering flaps on a P-38L were much smaller and could be deployed at a higher speed to get same effect, then pulled back in quickly, to reduce the energy loss.


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## claidemore (Mar 25, 2008)

Agree drgondog.

109G2 manual says you cannot operate flaps above 250kph, and it takes 4 turns of the wheel to get them to 20 degrees (takeoff position).


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## kool kitty89 (Mar 26, 2008)

I think you misunderstood me, I said the P-51 had a higher CLmax with maneauvering flaps out than the Spitfire did. I didn't say it could turn better, I was just pointing out what a difference flaps can make. However, the higher CL is still far from enough to cancel the Spitfire's wingloading advantage and resultant lift loading advantage over the P-51. (lift loading= wing loading x CL)

As you pointed out, flaps are not always the best option. However, maneauvering flaps usualy have a higher max operating speed than take-off or landing settings. And, of course, slats have no such problem.

I think that most Spitfires and 109's would be able to out turn most P-51's in most conditions.

The Hurricane would out-turn all three in a fair comparison, but lets not go there... (at least in the fighter versions of the Hurri ie Mk.I/II/IIA/IIB/IIC)


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## kool kitty89 (Mar 26, 2008)

Soren,

(in case you missed it) I'd still like to know if this is correct:

I'm also not sure about the gradual slat deployment since the Me 262 used a similar design as the later Me 109's (I think) and had gradual deployment of slats. Soren, info and corrections on this point would be appreciated.


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## Kurfürst (Mar 26, 2008)

claidemore said:


> Agree drgondog.
> 
> 109G2 manual says you cannot operate flaps above 250kph, and it takes 4 turns of the wheel to get them to 20 degrees (takeoff position).



That would refer to TO or landing configuration, ie. 20/40 degrees down. I have a 109E 'safe flap speeds' curve somewhere, the *combat flaps* could be used up to quite high airspeeds. 

Bill is absolutely right about flaps though. They allow you to pull a much tighter turn (radius), but neccesessary a _faster_ sustained turn, because they also add some amount of drag. The exact characteristics should differ from aircraft to aircraft though.. if you have the speed and radius with flaps though, you can calculate the turn time.


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## Hunter368 (Mar 26, 2008)

Interesting


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## claidemore (Mar 26, 2008)

kool kitty89 said:


> Soren,
> 
> (in case you missed it) I'd still like to know if this is correct:
> 
> I'm also not sure about the gradual slat deployment since the Me 262 used a similar design as the later Me 109's (I think) and had gradual deployment of slats. Soren, info and corrections on this point would be appreciated.



AFAIK the 109 slats had no damping system and were spring loaded (very light spring, finger tip moves them), so they should 'pop' open.


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## Soren (Mar 26, 2008)

There are no springs of any kind at all Claidemore, the slats operate by means of air-pressure, so they are in effect AoA dependant devices, that's what makes them such ingenious devices.

Koolkitty,

The slats on the late Bf-109's and the Me-262 are of exactly the same design.


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## Hunter368 (Mar 26, 2008)

Hmmmm


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## kool kitty89 (Mar 26, 2008)

A little off topic, but did the F-86's LE slats use the same mechanism? (It would make sence since the Me 262, and HG variants, had alot of influence on the Sabre iirc)


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## claidemore (Mar 26, 2008)

Soren said:


> There are no springs of any kind at all Claidemore, the slats operate by means of air-pressure, so they are in effect AoA dependant devices, that's what makes them such ingenious devices.
> 
> Koolkitty,
> 
> The slats on the late Bf-109's and the Me-262 are of exactly the same design.



Thanks Soren, we needed an expert opinion on this. 
I stand corrected. 
There's quite a few sources that mention springs, but heres a hobby site with some good diagrams. 

basepage


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## drgondog (Mar 26, 2008)

The 'suction' described above in this model is usually denoted as "lift" and the other regions in the model are areas of flow separation. Check the Lednicer report attached, carefully.

The P-51D for example has better laminar flow over the wings AND the canopy and hence less drag due to Profile Drag than the modelled Spitfire IX and Fw 190D9.

You will note that the predicted Lift distribution over the model P-51 is slightly better than the fw 190 but inferior to the Spit.. This is a function of both the washout as well as airfoil differences and planform geometry (spit close to eeliptical and 51/190 trapezoidal).

As to HP of 51B (with -3) versus H (-9), there is a maximum difference of about 300-330 BHP difference between the H and the B when the H is boosted to 80" with water... as noted below


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## drgondog (Mar 26, 2008)

Intersting report - not specifically tagged to the 109 but in comparing 51 to fw 190D and Spitfire on Drag.

The total drag coefficients predicted by Lednicer's model is in very close agreement (and the same between the P51B and D) with wind tunnel tests.

This seems true despite the fact that the P-51D has a greater 'wetted area' than the P-51B. The 190D is closest to 51 in total wetted Drag but I haven't found an equivalent study on the 109.

The primary reason for better Bubble vs Birdcage or malcolm/blown hood' seems to be 1.) the better flow characteristics over the bubble top than the Bird cage canopy 

This discussion and model would yield a nice comparison to the contrast between the 109 and the 51, particularly in predicting rate of energy loss in a manuevering fight.

Make your own judgements. 

I like the model and the assumptions they made to set it up and the explanations for the variances. The 'singularities' used to simulate the finite element distribution of flow are source/sink pairs to create the 'circulation' and then they have to do iterations to introduce boundary layer growth to point of 'positive' pressure creating separation (and 'no lift') and resultant profile drag.


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## drgondog (Mar 26, 2008)

this belongs in the 'other thread'


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## pbfoot (Mar 26, 2008)

claidemore said:


> Thanks Soren, we needed an expert opinion on this.
> I stand corrected.
> There's quite a few sources that mention springs, but heres a hobby site with some good diagrams.
> 
> basepage


I looked at them today and there are no springs it appears to me they work on airpressure from the airflow they can be pushed in and out with one finger , but it was once stated that they got jammed up by dirt ,sounds like poor maintainence to me as there as there is very little airborne dirt


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## drgondog (Mar 26, 2008)

pbfoot said:


> I looked at them today and there are no springs it appears to me they work on airpressure from the airflow they can be pushed in and out with one finger , but it was once stated that they got jammed up by dirt ,sounds like poor maintainence to me as there as there is very little airborne dirt



Pb - I believe you are right. The one at the Smithsonian has no springs. The more I think about it there is no reason for it... the reduction in dynamic pressure as the wing in the slat region start to get separated flow in that area , the condition of lower freestream pressure on the nose of the slat than behind it - ought to 'actuate' the slats I would think.

From a design point I would be concerned about a spring jamming or otherwise artificially holding one slot open but not the other? 

I suspect the jamming would be caused by getting 'crud' on the rail/slot interface (but I do not know this to be true)


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## Soren (Mar 27, 2008)

Call it suction or seperation, it's the same and it creates drag and this is the prime reason for the P-51B being faster than the P-51D, as-well as the dive speed issues.

The reason the P-51H is so much faster than the P-51 is not only because of the much more power available (It ran at 90" Hg) but also the different wing.



kool kitty89 said:


> A little off topic, but did the F-86's LE slats use the same mechanism? (It would make sence since the Me 262, and HG variants, had alot of influence on the Sabre iirc)



Yes exactly the same, but the F-86 pilot was also given the option of locking them in place incase of a jam or other mechanical issues, otherwise they operated just the same.


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## Soren (Mar 27, 2008)

Guys as already explained the LE edge slats operate by means of airpressure alone (There are no springs what'so'ever), extending as the pressure on the top of the wing decreases while the AoA increases. Thus the speed of the deployment is completely dependant on how quick the increase in AoA is, so if it's slow and gradual than so is the deployment, and if it's fast and gradual then so is the deployment.

It is therefore that automatic LE slats are AoA dependant devices.


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## drgondog (Mar 27, 2008)

Soren said:


> Call it suction or seperation, it's the same and it creates drag and this is the prime reason for the P-51B being faster than the P-51D, as-well as the dive speed issues.
> 
> *No, Soren - and no.
> 
> ...



The 51H is also 'so much faster' than the P-51B. Hp makes a difference, weight reduction made more of a difference in my opinion... prove otherwise?


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## drgondog (Mar 27, 2008)

Soren said:


> Guys as already explained the LE edge slats operate by means of airpressure alone (There are no springs what'so'ever), extending as the pressure on the top of the wing decreases while the AoA increases. Thus the speed of the deployment is completely dependant on how quick the increase in AoA is, so if it's slow and gradual than so is the deployment, and if it's fast and gradual then so is the deployment.
> 
> It is therefore that automatic LE slats are AoA dependant devices.



Soren, you may not have the notion of pressure distribution, causes of boundary layer separation and stall, quite clear. 

Briefly - before getting to Slat 'physics' and pressure conditions causing them to deploy as brief summary of Principle of Flight.

What causes 'lift' is essentially bernoulli's principle. Faster flow DECREASES local pressure relative to the freestream passing over a tube. It is the same principle as flow travels up and over the top and bottom surface of the airfoil from the relative Zero angle of attack. Nature wants desparately for the flow stream elements to arrive at the trailing edge at the same time. 

Conceptually, the point at which the freestream separates into 'top' and 'bottom' flow is called a stagnation point on the leading edge. 

As the AoA increases from Zero Lift Angle of Attack, the velocity over the top surface must travel faster to reach the trailing edge than the flow over the bottom surface.

This results in the LOWER relative pressure (to Freestream) on the bottom of the wing and EVEN LOWER relative pressure on the top surface of the airfoil. ece between the Lower pressure on the bottom and the Even Lower Pressure on the top is usually called a Pressure Differential.

If one is flying inverted, one wants the airflow AoA to be Below the reference Zero AoA, so that the airflow on what used to be the bottom surface of the airfoil is now faster than the flow on what used to be top surface... otherwise there is contact with a solid surface.

People call this Pressure Differential 'suction', with a positive vector UP normal to plane of the wing in the case of Lednicer's model, and Lift to aerodynamicists.

When the AoA reaches the region called CLmax, the energy of the flow for that wing has a critical point where the boundary layer is not 'attached' and has grown to point where the local pressure behind the boundary layer is HIGHER than the flow in front. As the AoA moves a little more there is an onset of turbulent flow which has more energy than the laminar flow in front. When that region of turbulent flow reduces the area of Suction/Lift to point where the resultant positive force is adequate to sustain level flight and velocity, or local flow over control surfaces like ailerons, we now have a condition some people call 'STALL'.

Now for the So, what?

Now, those wonderful inventions called Slats are locally affected as the laminar flow behind it are disrupted to point where the local Lift/Suction still exists on the top surface of the Slat, but not behind it, and it deploys- having the effect of letting the freestream air which now has more energy than the stalled region, flow under the slat and thence to the leading edge of the wing and beyond, restoring boundary layer flow, sorting out chaos in the turbulent area, and restoring lift in that area.

At the point where the slat deploys, the pressure distribution behind and then to the slat have become relatively 'positive' with respect to pressure distribution over the Slat

Regards,


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## Soren (Mar 27, 2008)

Oh when it comes to the issue of pressure distribution and boundary layer seperation I see things quite clearly Bill, and nothing of what I explained is wrong, nothing.

The slats start to deploy at very low AoA's as the pressure on the top of the wing becomes lower than the pressure under the wing, making the slats extend. Quite simple.

Moving on..

I trust Lednicer very much, no doubt about it, and here's his words exactly:







Stronger suction = more drag. Very simple Bill, no need to complicate it.

And furthermore from the very same article:






Again like I said, the P-51B features less drag than the P-51D, and primarily because of the bubble canopy. A bubble canopy creates more drag than the razor back configuration, that's a common known fact Bill, deal with it.

And as for the P-51H's wing, it's slightly smaller = less drag (Decreased Root chord) and there's plenty more power available to the a/c, hence the higher speed.


As for the dive issues, well because of the bubble canopy and cut down aft fuselage the D series suffered from directional instability, something which was shared by the P-47's featuring bubble canopy's as-well. This is the cause for adding the dorsal fins.


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## drgondog (Mar 27, 2008)

Soren said:


> Oh when it comes to the issue of pressure distribution and boundary layer seperation I see things quite clearly Bill.
> 
> And I trust Lednicer very much on this as-well, no doubt about it, and here's his words exactly:
> 
> ...



I think I mentioned the reason for the strake and the other mods that made first the P-51D safer than the B, and then the H much safer than the B in dive. Your point is what? 

As to 'directional instability' that would be an incorrect overstatement also.

Correct would be 'slightly less yaw stability' between the two at top dive The pitch stability was the same for the same speeds. Yaw stability slightly favored the P-51B until the changes were applied to the D (and H). 

ALL Mustangs exibited tendency to pull right as Mach number increased The P-51D apparently had a higher safe dive speed over the B when the modifications were applied (including metal elevators, increased rudder spar strength at fuselage attach points, improved ammo door stiffness, wheel door uplocks

Here is the RAF Dive tests performed without metal elevator modification, in which the a/c was dived up to .85 Mach

Note on Dive Tests on ‘Mustang IV’

You still think 'suction' is drag in Lednicer's model? Would you care to educate all of us on the Graphical representation of the pressure distribution by 'color' and interpretation'? I would be interested in learning why I don't understand what he is saying. 

And perhaps explain why he doesn't know what he is talking about when he describes the Drag term as 'Stream wise components' versus what I think you are describing ('suction' which is a normal component) as drag?


As to difference in predicted CDwetted between the models, I draw your attention to page 8, Section VII, Table II and the explanation below by Lednicer (for context). 

According to VSAERO model, CDw for P-51B = .0033, P-51D = .0031 for the model condition I just described from his report. Which of these two numbers would you rather have?


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## Soren (Mar 27, 2008)

This is ridiculous Bill, 

Are you claiming that bubble canopies don't increase drag over the razor back configuration or not ? I need you to answer that question specifically.

Lednicer's graphs does indeed show a similar CDwet for both a/c, but that doesn't mean that the bubble canopy doesn't provide any additional drag over the razorback configuration, esp. seeing there were other design changes between both a/c. In short a stronger suction means more drag Bill, it's that simple really.

And as for the British tests, well why use them and not the US ones ?? If I wanted to compare the P-51B D I'd use data from its country of origin, i.e. the same place, leaves out many possible discrepancies. 

But since you don't want to realize any of the above I guess it'll take a vet P-51 pilot to convince you;

*Robert C. Curtis, American P-51 pilot:*
_"The P 51 was redlined at 505 mph, meaning that this speed should not be exceeded. But when chasing 109s or 190s in a dive from 25-26,000 it often was exceeded, if you wanted to keep up with those enemy planes. The P 51b, and c, could stay with those planes in a dive. The P 51d had a thicker wing and a bubble canopy which changed the airflow and brought on compressibility at lower speeds."_


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## drgondog (Mar 27, 2008)

Soren said:


> This is ridiculous Bill,
> 
> Are you claiming that bubble canopies don't increase drag over the razor back configuration or not ? I need you to answer that question specifically.
> 
> ...



He must have been flying a different Mustang from what he thought he was flying. Actually both were redlined at 505mph TAS and both often exceeded 505, in some documented cases past 550mph.. but he is wrong about the wing. Are we at the point you want to change the subject to anecdotal discussion or - do we stick to your understanding of Lednicer model and results?

The P-51D wing is only different by having a longer Root chord at the Cl which results in the greater 'sweep' of the leading edge of the section inboard of the guns. Same primary airfoils, same tip airfoils, same specs on area and wingspan, etc. Even though the specs indicate same wing area as for the B, I would suspect the D has slightly greater wing area... very slightly

the set tail incidence is slightly different, the only material change was the elimination of the birdcage canopy and the turtledeck behind it and replace with streamlined teardrop canopy, adding two extra .50 cal guns plus ammo and some additional structure in tail spar fitting, wheel uplock kits and a slightly larger fuselage fuel tank. 

In other words, the differences in surface area (for friction drag calcs) was the very small increase of the inboard leading edge in front of wheel well and a very small decrease in the surface area behind the canopy. In other words some of the wing surface increase was offset by lowering the deck aft of the canopy... somewhere the 51D gained about 4 sq ft. Every other material change was the incremental weight and the difference in aero dynamics of the canopy.

Now to the analytical part. 

Surface area on P-51D slightly greater. Would you assume the friction drag was slightly greater? I would

The Induced Drag of the P-51D due to extra weight for the same speed would be *greater* with the same wing? Yes?

That leaves us with Form Drag/Wake Drag. Correct? Two increase over the P-51B, leaving us with one last component.

If the P-51D was the same shape, same wing span, same airfoil, same length, tail, elevator, engine cowling, lines, lower radiator fairing, etc - except the Birdcage canopy/turtledeck vs the tear drop canopy. Right?

So, two of the three components of Drag (not 'suction') of the 51D are greater than the 51B - yes? And neither relate to the canopy shape.

But the TOTAL CDwet of the two airframes are Exactly the same.

What does the math then say about the Profile Drag of the B? It says to me that the Profile drag of the 51D is LESS than the 51B. Says so in Lednicer's Table II and his write up. 

It says to me that flow around the P-51D canopy remains laminar almost to back of canopy as Lednicer shows. It says that the flow separates on a P-51B and the Spitfire IX right on the top area of the forward windscreen. What does it 'say' to you? 

Lednicer's model demonstrates this as well as presents the differences in tables.

So, If you agree with everything he says, as you said earlier, how do you rationalize 'suction' with drag - or describe the 'suction' in the model as a streamwise force vs Vertical?


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## drgondog (Mar 27, 2008)

Soren said:


> Oh when it comes to the issue of pressure distribution and boundary layer seperation I see things quite clearly Bill, and nothing of what I explained is wrong, nothing.
> 
> The slats start to deploy at very low AoA's as the pressure on the top of the wing becomes lower than the pressure under the wing, making the slats extend. Quite simple.



Forgot to touch on this.

Your thesis is that somewhere close to level flight, in all regions of the flight profile, at the above described 'low AoA', that the Me 109 slats deploy? 

That Must have been very annoying. particularly on a routine climb to altitude or final approach at any speed.

Further such sensitivity to low AoA must have created very annoying asymetrical forces like a gentle turn when the upwing slat opened as it's local relative AoA gained slightly over the AoA for the lower wing. You know the induced drag, and hence the local AoA, is greater for the upwing?

Why would Messerschmidt design team do that? Most other design teams want, and only want the slats to deploy at stall in that local area - just to prevent them from suprising pilots in ordinary flight envelope.


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## lesofprimus (Mar 27, 2008)

It would be interesting to see Soren actually respond to all the questions u've put in ur posts Bill.... 

I too feel that he is not interpreting some of the issues brought up in the report correctly, and would really like to see him, in his words, answer some of the insights u have about the Lednicer Report...

I cant really understand how one extremely intelligent person can interpet a set of facts completely different from another extremely intelligent person...

This is a very interesting discussion, way beyond my grasp on several levels, but learning new stuff is always a treat... But honestly, Im confused at the discrepancies between u two guys...


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## drgondog (Mar 27, 2008)

lesofprimus said:


> It would be interesting to see Soren actually respond to all the questions u've put in ur posts Bill....
> 
> I too feel that he is not interpreting some of the issues brought up in the report correctly, and would really like to see him, in his words, answer some of the insights u have about the Lednicer Report...
> 
> ...



Dan - I can't really explain the difference in opinions regarding Lednicer's analysis and his conclusions. Those are hard to overlook per se... but

If Soren believes the 'suction' term that Ledicer uses is either a drag component or somehow related to induced drag due to lift, it would explain his perception and follow on arguments. Lednicer makes it clear that all drag in the dicussion are the forces in the streamwise direction - I think he used 170 stream tubes which would be roughly one every 2/10 foot on a 35 ft wingspan.

The stream tube does not permit spanwise flow, only chord wise parallel to a/c axis.

The reason I was delighted that Gene (Crumpp) sent me these reports is that this is the kind of 'stuff' I was doing when I first entered the airframe industry and went from aero models using finite element/rigid structures, then to finite element/elastic structures, then on to pure Structural models when I went to Bell.

Lednicer's VSAERO application seems more sophisticated in the context of building in boundary layer and thence to separation conditions.. I know the theory but it was beyond my then current ability to 'model' the iterative process to get reasonable correlation.. and everybody else's in 1968-1969.

But the distribution of singularities in each of the panels it was exactly the same approach.

Having said all this, the experience in the airframe industry in which manuever performance had to consider this type model plus consider aeroelasticity, stability and control parameters, thrust in asymetric flight etc.. make me smile when I see the discussion come to 'simple physics'.. and I repeat - I am an amateur.. the degrees and the industry experience I have scratched the surface - but I know what I don't know. 

I suspect there will not be direct answers to the questions but I would like that kind of discussion on both the Lednicer model and cause/effect on slat deployment.

Good to chat - I've about drained the swamp on this discussion. I'm gonna get up and scrtach some ears. 

Say, how do I engage (and with whom) the loading of the 5-7 mb portraits of 30 + 355th side elevations for my book. Steve Daisley is a pretty good little artist and perfect for my book

Regards,

Bill


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## lesofprimus (Mar 27, 2008)

I would just start a new thread and start adding the pics Bill... Make a disclaimer in the Thread Title **56k NO WAY** or something like that... Its gonna take awhile to upload em that way, but damn they'll be pretty for anyone willing to wait for them to load....

Or......

U could try and email me a few at a time due to mailbox size, I'll shrink em down to a more manageable size, and email u for more.... In a few days, we could get em all done...


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## drgondog (Mar 27, 2008)

lesofprimus said:


> I would just start a new thread and start adding the pics Bill... Make a disclaimer in the Thread Title **56k NO WAY** or something like that... Its gonna take awhile to upload em that way, but damn they'll be pretty for anyone willing to wait for them to load....
> 
> Or......
> 
> U could try and email me a few at a time due to mailbox size, I'll shrink em down to a more manageable size, and email u for more.... In a few days, we could get em all done...



just sent you a PM


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## kool kitty89 (Mar 28, 2008)

The suction issue was braught over from *"Best Piston Engined Fighter Ever
"*...

I'm not sure that was intentional, but oh well.


I think some of the confusion is coming from interpretaion of terminology. (though most of this, particularly the specifics, is over my head)



Maybe this will help to bridge the canopy issue: How does the Malcolm hood P-51B/C compare to the "birdcage" or teardrop/bubble canopy?


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## drgondog (Mar 28, 2008)

kool kitty89 said:


> The suction issue was braught over from *"Best Piston Engined Fighter Ever
> "*...
> 
> I'm not sure that was intentional, but oh well.
> ...



Good question. It didn't seem to help per se in the lednicer model but he made a specific comment that the Spit IX wind screen had a larger angle from the P-51 D and suspected that was more of a problem than the geometry aft of that.. in other words separation high on thr windscreen in his model. Go back and look at the reports I posted and see if he amplifies


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## Soren (Mar 28, 2008)

Ok fair enough Bill, I apologize for the sarcasm then. And let's be objective about this. 

About the slats first;

My thesis is not and has never been that the slats deploy fully in conditions close to straight flight, and I honestly can't really understand how you interpret it that way either. Also I don't bring forth any thesis on this subject only the facts.

You need to understand that the slat deployment process is gradual, the slats starting to deploy at a very low AoA's, not fully extending ofcourse, but extending out slightly. And so in climbs, landing approaches and slow turns a pilot wont even notice the slats popping out unless he looks at them as the deployment process is so slow and the slats themselves not fully extended. However if the pilot banks hard where the Critical AoA of the original airfoil is reached nearly instantly, then he will feel a very slight notch on the stick as the slats pop out to their fully deployed position almost instantly.

Furtermore the slats aren't linked together, they're completely independant of each other, and thus so is the deployment process. So if one wing is starting to stall before the other then the slat on that wing is also further extended.

As Mark Hanna puts it: 
_"As the stall is reached, the leading-edge slats deploy-together, if the ball is in the middle and slightly asymmetrically, if you have any slip on."_


Anyway got get back to work now, will address the rest later.

PS: Glad we can discuss this in a calm objective manner Bill.


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## drgondog (Mar 28, 2008)

Soren said:


> Ok fair enough Bill, I apologize for the sarcasm then. And let's be objective about this.
> 
> About the slats first;
> 
> ...



Soren - this is the statement which triggered my comments

_Oh when it comes to the issue of pressure distribution and boundary layer seperation I see things quite clearly Bill, and nothing of what I explained is wrong, nothing.

The slats start to deploy at very low AoA's as the pressure on the top of the wing becomes lower than the pressure under the wing, making the slats extend. Quite simple._

Typically leading edge slats deploy at near stall conditions. Low angle of attack typically is not near stall for any aircraft until low speeds. Typically at medium to high speeds in normal flight regimes the stagnation pressure on the zero lift/flow diversion point.. 

from a theoretical point the flow is brought to a specific point on the nose of the airfoil and changes its momentum at that point - then travels over the top and bottom surface of the airfoil.

So, the slat at that point of the wing for free stream impingement, is experiencing 'positive pressure (relative to freestream) then as the flow travels normally back and over the top surface, the pressure distribution in comparison to the free stream (and the stagnation point on the slat) becomes rapidly 'negative' over the surface of the airfoil for the maximum lift region, then drops rapidly to freestream pressure as separation begins and finally to freestream pressure in the region of the boundary layer wake.

So, from my perspective the only way a slat should deploy is when the pressure behind the slat is at same or slightly higher dynamic pressure behind the slat as the dynamic pressure on the nose of the slat - which is a typical stall condition.... otherwise the slat is conceptially 'pressed' against the wing surface behind it.

If the slat deployment occurs in level flight at low AoA versus either level flight at high AoA at low speed or medium AoA in a normal turn, then I would not happily fly that a/c because it implies that indicial gusts in normal flight or even in a relatively slow turn could cause the slat to deploy. 

The F-86 slat deploys at high AoA. I had read from Mustang Designer that it was a close design approach to the Me 262 slat... so I am confused by your statement that the Me 109 slat deploys at low AoA for all the reasons I just relayed above.

If you were to draw a free body diafram mappring out the forces on the leading edge slat at low AoA, how would you describe it..


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## Soren (Mar 28, 2008)

You misunderstand me abit Bill.

The slats don't start to extend at 0.1 degrees AoA, but they don't start first at 15 or 16 degrees either (Assuming the critical AoA is 17 degrees). Infact there's a MTT document mentioning the AoA at which the slats start to extend, and it's low (Compared to the critical AoA when they're deployed), around 10 to 11 degree's IIRC.

Holtzauge has the data as he posted it months ago somewhere on this forum.

As for the F-86's slats, they're exactly the same as the Me-262's, no difference, except they drop down abit on deployment, but they operate just the same.

Moving on to the drag debate and the bubble canopy,

Looking at Lednicer's figures I do find ONE thing strange, and that is the smaller wetted area of the P-51B, AFAIK the P-51B has a larger wetted area than the P-51D which hasn't got that big aft fuselage anymore. Ofcourse the D series has a slightly larger wing as I have already mentioned (enlarged root chord), but that doesn't make up for the loss of a huge chunk of the aft fuselage area. Don't you find that strange ?

Furthermore just from experience bubble canopies are known to cause higher drag than the razor back configuration, the sudden drop of the rear canopy causing boundray layer seperation and thus a turbulent flow to the rear, the reason behind the directional instability - a problem which also plagued the P-47 when it first got the bubble canopy, and even with the added dorsal fins the problem was never fully solved.


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## Hunter368 (Mar 28, 2008)

Good debate guys


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## drgondog (Mar 28, 2008)

Soren said:


> You misunderstand me abit Bill.
> 
> The slats don't start to extend at 0.1 degrees AoA, but they don't start first at 15 or 16 degrees either (Assuming the critical AoA is 17 degrees). Infact there's a MTT document mentioning the AoA at which the slats start to extend, and it's low (Compared to the critical AoA when they're deployed), around 10 to 11 degree's IIRC.
> 
> ...



Actually that is what modelling is all about. 

'Known and Well Known' are terms not particularly useful in this discussion. You are the first person that has described the problem -as 'a sudden drop of the canopy causing boundary layer separation and thus turbulent flow to the rear' to me. That doesn't make your statement untrue. On the other hand I was in the modelling business for awhile and have yet to see that occurance in either a wind tunnel or design calcs or model results. 

As an example, only a few operational fighters in the USAF or any other modern program from the 1970's forward, in which computer modelling to the sophistication of VSAERO has been available, have ever had anything BUT a bubble canopy. If turbulent flow was aroused then all fighters would have canopies like an F-102 or F-106 

Nothing is certain to that extent. I imagine if the Brits had seen Lednicer's model they would have looked at sloping the windscreen more to look at the next stage past it to see whether the Malcolm Hood design was optimal.

The stated design problem for NAA in trying to reduce or eliminate the increased yaw at .7-.8 mach for the D from the B wasn't separation, it was the elimination of the 'long' rudder strake surface as represented by the turtledeck.. had nothing to do with increase to turbulent flow according to their perspective. 

Those comments are anecdotally referenced in Both "Mustang" by Gruenhagen and "Mustang Designer" about Edgar Schmeud and the Mustang through F-100 era at NAA.

I suspect, but do not know that the removal of the P-47 turtledeck had a similar consequence.

Thinking it through, if the issue was increase in turbulent flow, the entire rudder and horizontal stabilizer would be affected and why would a small ventral fin help much there. Turbulent flow would not be 'fixed' by a ventral fin.. but the ventral fin area, added well behind the cg at the tail, would be more effective that larger vertical surfaces at or closer to the cg.

As late as 1973 I was involved as a consultant from GE, in various studies using Ansys and Nastran as well as working with GD engineers to look at various F-16 canopy models. The problem to be solved was called in the trade, "The MIL SPEC _Chicken Test". 

The theoretical analysis - pre computer finite model analysis - was having a hard time defining the 'certain' design specs for the canopy which would satisfy the wind tunnel drag targets but also satisfy resistance to failure of a 3 pound have frozen chicken 'projectile' head on - to similaute bird strikes at low altitude while in a landing pattern. The problem was both failure and also an associated travelling 'wave' deflection interferring with the space the pilot's head was in.

We solved it by changing the thickness of the canopy at the forward region, then tapered back to constant thickness of the Acrylic Shell - it was an expensive solution... but I saw all the aerodynamics from both a model and wind tunnel test because we also had to consider changing the lines and see what the associated 'aero' effect was to increasing heighth of canopy top.

If you have a reference discussing turbulent flow issues as a result of the bubble canopy I would like to see it and would like to understand the background of both the tests and the resultant design approach to solve.


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## kool kitty89 (Mar 29, 2008)

Maybe he should have said 'realitively low AoA'


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## claidemore (Mar 29, 2008)

This is a little off the 'off the topic' topic, lol, but...

I believe it's been mentioned that during the RAE trials of 109E that the British pilots didn't use 'combat flaps' in the 109. I was reading one of the reports (Wing Commander G.H. Stainforth) and noticed this:



> The rate of turn obtained was the maximum possible in every case. The effect of putting the flaps down about 10 degrees was tried but this had little, if any, effect.



Claidemore


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## drgondog (Mar 29, 2008)

claidemore said:


> This is a little off the 'off the topic' topic, lol, but...
> 
> I believe it's been mentioned that during the RAE trials of 109E that the British pilots didn't use 'combat flaps' in the 109. I was reading one of the reports (Wing Commander G.H. Stainforth) and noticed this:
> 
> ...



The use of flaps in a Mustang did not help in the turn comparisons of the 51 vesus the Spit IX or XIV either for those tests in 1944. There was no mention in what I saw that flaps were used in the 109G vs 51B turn comparisons.

I have seen anecdotal reports expressing some positive results in a turning fight with a 109 but an equal number saying the 51 did not gain an advantage by dropping 10-20 degrees.


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## drgondog (Mar 29, 2008)

kool kitty89 said:


> The suction issue was braught over from *"Best Piston Engined Fighter Ever
> "*...
> 
> I'm not sure that was intentional, but oh well.
> ...



I re-read the report. There is an obscure reference to an experiment in which a 'more rounded and sloped windscreen' tried in 1943, resulting in 12 mph increase in speed at .79 mach for the Spit IX. The comments are on page 88.

A more interesting point is that the 190D (fig 11) with blown hood has a better region of suction/lift on the canopy behind the windscreen than the 190A-8 (fig 10) model. The Table 1 Cdwet also shows a distinct advantage of the 190D over the 190A-8.

The Spit w/malcolm hood shows better suction than 51B but much larger region of positive pressure forward and on the the windscreen.

Speculatively, the Malcolm Hood should be a beneficial addition to the 51B.

It would be interesting to see a 109G with the basic square angle canopy in comparison. I suspect it would be the worst of all the models compared.

Having said all of this, the primary advantage in drag for the Mustang vs the Spitfire and Me 109 was a.) the wing, and b.) the radiator design.


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## Soren (Mar 29, 2008)

I'm abit busy at work so I only have 5 min, so this will be a very short reply..



> Having said all of this, the primary advantage in drag for the Mustang vs the Spitfire and Me 109 was a.) the wing, and b.) the radiator design.



Versus the 109 it was only the wing really, since the 109 benefitted from a similar radiator design generating very little drag and a little thrust (Meredith effect).

However I do believe that the Mustangs radiator produced more thrust than that on any other a/c of WW2 except for the Do-335. IIRC it was the same has having an extra 300 HP, not bad..


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## drgondog (Mar 29, 2008)

Soren said:


> I'm abit busy at work so I only have 5 min, so this will be a very short reply..
> 
> 
> 
> ...



Whether Lednicer was correct or not in his interpretation of the difference between the Me 109F and all previous models, he states the different design for better boundary layer control as reported by Brown and Smelt "Aerodynamic Features of German Aircraft", Journal of Royal Aeronautical Society, August 1944. He states from this source that Messerschmidt redesigned the intake specifically to address this drag component, and the new design was incorporated in F and subsequent models.

Your source to the contrary would be? 

The actual thrust of the radiator design of the Mustang was far below the calculated value. 

I have seen various reference from 18 to 75 pounds, but never higher than 75.. Lednicer discusses some of the reasons why, as discovered in the modelling of Strega in attempts to improve flow characteristics in that area and below/aft the inboard wing/body interface.

What is your source for the Do335 'Thrust" values?


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## Soren (Apr 10, 2008)

Long time no see! Been very busy at work, but now I've got a two week holiday, so nice 

Bill,

The DO-335 utilized the exact same radiator design as the P-51, so the gain in thrust would've been similar for both.


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## Soren (Apr 15, 2008)

> Whether Lednicer was correct or not in his interpretation of the difference between the Me 109F and all previous models, he states the different design for better boundary layer control as reported by Brown and Smelt "Aerodynamic Features of German Aircraft", Journal of Royal Aeronautical Society, August 1944. He states from this source that Messerschmidt redesigned the intake specifically to address this drag component, and the new design was incorporated in F and subsequent models.
> 
> Your source to the contrary would be?



Contrary ?? Bill you've only confirmed what I said.

The Emil's radiator design is completely different from the F series and beyond, the F series and beyonds radiators benefitting from the meredith effect and actually providing a little thrust.


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## drgondog (Apr 16, 2008)

_Soren sez -Huh ?

And what's with the sudden paranoia Bill? You seriously think I've been away from the forum because of a discussion we had ? Bill I could care less, besides the discussion was over in my eyes. 

And as to suction, well I thought we had settled this already, and yes suction equals drag. A razorback design has less drag than a bubble canopy one, the simple reason being that there's not the turbulent area right behind the canopy creating extra drag. I thought you understood this.

*In the Lednicer Model there are three basic values of Pressure assigned to colors.

Red is 'suction', is lower than Freestream pressure, to laymen it is called Lift as it is a force PERPENDICULAR to freestream. In a freebody diagram it is opposite direction to Gravity 

Blue - at the base of all the canopies and the intersection of horizontal stabilizer and horizontal stabilizer, is Stagnation Pressure, resulting in a force PARALLEL to Freestream and opposing Thrust. 

Lednicer spends some time talking about this (Blue) as a flaw in Spitfire Canopy/windscreen design as well as the benefits of 'suction' (Red) to the 51D canopy*

The sudden drop over the top of the canopy is what causes the boundary layer to seperate, causing turbulence to the rear(Hence the stability issue), and therefore extra drag. It's the same with bullets Bill, if you say cut way the boattail you'll get sooner seperation and more turbulence which means more drag, hence why spitzer bullets aren't as drag efficient as boattailed ones._

You are 100% *incorrect* in both statements. First, there is essentially zero difference in the calculated Pressure distribution between the two (P-51B and D models) aft of the canopy/cockpit area. This is a FLOW model Soren not a STABILITY AND CONTROL MODEL. There is a difference, and one you frequently do not seem to grasp in this discussion

If you read and comprehend the entire reports - you will note that the entire region of Red includes the top surface of the Wings and Canopy top for the P-51D. 

The Red includes the Wings of the P-51B (exactly same distribution as P-51D with same wind) and a small portion on the top of the forward Canopy.

The Red includes the Wings (smaller region due to non-laminar airfoil) and no Red on the Top of the Spitfire Canopy and a LOT more BLUE on the windscreen due to 'steeper' angles which Lednicer discusses in detail.

Correspondingly, the P-51B does NOT have a 'low pressure distribution' over the top of the canopy. Why? you should ask? Because the flow over the P-51B (non Malcolm Hood) windscreen separates (as does the Spitfire but further back) and the pressure distribution from that point aft approaches freestream pressures.

Lednicer goes on to illustrate the separation caused by the Stagnation Pressure Buildup on the Spitfire and the subsequent 're-attaching' the Boundary layer on the top of the Canopy to give it better suction than the P-51B.

*NET of Lednicers models. P-51D most aerodynamic canopy, P-51B had less lift over top surface but also less Pressure Drag than the Spitfire windscreen.*

Fundamentals for you Soren.

Pressure Drag is in fact a function of separated flow and the resultant force is a.) *opposite of thrust, and b.) absent Thrust, in the same direction of Free Air stream. *

Induced Drag is a function of lift, wing geometry and is a resultant force in opposite direction to Thrust and 'nearly' same direction as freestream flow.

Friction Drag is a function of surface roughness and is a force in parallel to freestream.

All of these DRAG forces will be aligned in a free body diagram to oppose Thrust axis of the body analyzed.

Lift forces in Lednicer's model are ORTHOGONAL to both induced drag and Pressure Drag (and friction drag).. Suction is the Red 'thingy' area represented on Lednicers Wings and Canopy of the 51D.

Repeat - He didn't have a model that had a force (pressure) distribution in orthogonal directions for same values. He didn't illustrate the Red region over the top of the model wings as "PRESSURE DRAG".. any more than the Red region over the canopies

Repeat - RED is LOWER (attached) PRESSURE DISTRIBUTION region than FREESTREAM PRESSURE. Those that are knowledgeable about Aerodynamics will usually call those forces "LIFT"

BLUE is HIGHER PRESSURE DISTRIBUTION region than FREESTREAM PRESSURE. Those that are knowledgeable about Aerodynamics will usually describe those forces as PRESSURE DRAG..

The Model is a Potential Flow singularity distribution model with subroutines and Iterative calculation solution methods to intruduce boundary layer separation. By definition Potential Flow is a perfect inviscous flow so the other modelling capabilities have to be introduced to approach realistic/wind tunnel results.

The areas where there are little diiferences in freestream pressure and the boundary layer pressures are represented by the collage of color different from RED and BLUE.



Hope this clears up your confusion a little.


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## Soren (Apr 16, 2008)

> You are 100% incorrect in both statements.



No I'm not Bill. The sudden drop WILL and DOES create turbulence to the rear which means extra drag, and it's EXACTLY the same with bullets, hence the transition from flat based spitzers to boattailed ones. So I'm 100% *correct*.

The problem is you're relying on data from computer generated models of the -51 in this discussion, and obviously something isn't entirely right about these seeing the -51D is shown to have a higher wetted area than the -51B which wetted area should be larger because that huge hunk of extra fuselage.

It is interesting to note the slightly lower pressure on the -51D's aft fuselage though, again confirming the reason to the stability issues.

What I did notice just now though, from looking closely at the two a/c's profiles, and this DOES alter the argument, is the -51D's higher windscreen slope compared to the -51B's which is much more straight, something Lednicer oddly doesn't mentioned. This increased slope will help maintain the boundary layer while the -51B's windscreen will cause seperation right away, which kinda offsets the advantage of the razorback design. This difference in windscreen design will have a very direct effect on how the pressure distribution is over the rest of the canopy, and this explains Lednicers illustration. In short had the front windscreen been the same (Which I thought it was) Lednicer's results would've been very different.

So like I said, a razorback design is less draggy than a bubble canopy one IF (and this is normally the case) the front windscreen remains atleast similar.


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## drgondog (Apr 16, 2008)

Soren said:


> No I'm not Bill. The sudden drop WILL and DOES create turbulence to the rear which means extra drag, and it's EXACTLY the same with bullets, hence the transition from flat based spitzers to boattailed ones. So I'm 100% *correct*.
> 
> *His model shows  exactly the opposite conclusion from yours, namely the flow remains attached and is less pressure for the P-51D all the way to the aft fuselage deck - than the freestream around it. The 51B separates almost immediately off the top of the canopy*
> 
> ...




Like you said - you are flat wrong. The angle of the flat windscreen between the A-K model Mustangs is same. The top surfaces differ for the Malcolm Hood and D/K in that there is a continued angle at the top of the windscreen transitioning gradually to the top of the canopy about 18 inches behind windscreen rail, then on aft and downward very much like a fat airfoil.

The Malcolm hood on the Spitfire loses the nice lower pressure distribution it regained as it nears the aft part of the malcolm Hood to the (parallel) transition of the fuselage.. On the P-51D it loses the lower pressure transition when it reaches aft fuselage deck behind the canopy... same reason but the low pressure laminar flow region is greater on the P-51D than the Spitfire (and the Fw 190D) and far greater than the P-51B.

The P-51B never really has reattachment except for the very small portion as it leaves flat windscreen top.

Your conclusions are exactly opposite Lednicer's and exactly opposite the grahically presented data from the VS Aero Model, and exactly wrong relative to Razorback vesrus Bubbltop drag.

And your definition of what Lednicer meant by Suction is?? You still think it is Drag or the equivalent to wake drag on a bullet?


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## Soren (Apr 16, 2008)

So you don't see the difference in windscreen slope ? 











More ??



















Is it not VERY apparent to you ???



> Er, this ISN'T my PROBLEM. This DISCUSSION is ABOUT the results of the computer generated Model and the data extracted from it and the conclusions drawn about the results.



NO, it isn't! It's about the difference between a razorback and bubble canopy design!

And as to the lower pressure area I observed, what's a matter with it ? Did I not read it correctly ? Perhaps I got it the opposite way around ?


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## kool kitty89 (Apr 17, 2008)

Soren, I think the slope difference might be an optical illusion, look at these:


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## Soren (Apr 17, 2008)

Hehe, those aren't accurate KK, you can clearly see that by comparing to the real thing, the cockpits on the B C look completly wrong, but it is what it would've looked like if they had used similar front windscreen.

In reality the P-51D's front windscreen is clearly more sloped than the P-51B C's, there's no doubt about it at all.


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## Soren (Apr 17, 2008)

There's clearly a difference in slope, somehitng which will have a big difference on the pressure distribution over and behind the canopy.


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## Graeme (Apr 17, 2008)

Soren said:


> those aren't accurate



These aren't either, but I am leaning towards your assertion that the P-51D had a more acute angle for its front windscreen. Problem is resolution on such a small aspect of an aircrafts frame. Soren, the photos don't illustrate the angle, to my eyes anyway. Clave would be the man to illustrate the differences better.


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## drgondog (Apr 17, 2008)

Soren said:


> So you don't see the difference in windscreen slope ?
> 
> 
> 
> ...



Soren - Lednicer discusses the angle of the windscreen in his report. It is the same in the 51D and B. The angle is "35 degrees for the Spitfire, 22 degrees for the fw190's and 31 degrees for ther 51's" pg 87 just above Figure 4 showing the pressure distribution of the P-51D.

I have the Drawing package for the 51A-51K. The angle between the cowling and the windscreen is 31 degrees for ALL of them. Go get a good reference rather that try to use an artist representation. Lednicer used the NAA drawings as well as Ed Horkey's refernces (Chief Aero at NAA and the principle Aero under Eddgar Schmeued).

Are you seriously using an artist representation against those documented references? ROFLMAO.

And NO - once again it is about the your definition of Suction versus Lednicer's (in your confusion) versus Lift, and Suction= Drag (in your confusion) based on the pressure distribution over the P-51D bubble canopy versus the Pressure Distribution over the Malcolm Hood of the Spitfire versus the Pressure Distribution over the P-51B birdcage canopy.

You simply don't know what you are talking about when you use such terms - you just don't have a clue Soren. 

At one time I wasn't quite as sure about your academic credentials in Aerodynamics because you talk a fair game about fundamentals of 'rule of thumb' practical calculations.. but you really don't understand either theoretical Fluid Mechanics or Aerodynamics - and you don't connect the challenges in Stability and Control when using those calcs to arrive at pre Flight Test conclusions. 

We wouldn't be having this argument if you did.


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## drgondog (Apr 17, 2008)

Soren said:


> Hehe, those aren't accurate KK, you can clearly see that by comparing to the real thing, the cockpits on the B C look completly wrong, but it is what it would've looked like if they had used similar front windscreen.
> 
> In reality the P-51D's front windscreen is clearly more sloped than the P-51B C's, there's no doubt about it at all.



Soren - you are dancing and 'spinning' around the issue. Independent of whether Lednicer modelled the windscreen angle correctly or incorrectly, the fundamental question is your knowledge and interpretation of the model results.

You interpreted (incorrectly) the pressure distribution over the P-51D canopy as 'Drag'.. you componded your misunderstanding of the model and Fluid Mechanics by comparing that pressure distribution to wake drag behind a bullet.

I suspect that you now realize what everyone else realizes - that you were wrong. At least the ones that read the report and contemplated the plots and re-read to reflect on what he said... but rather than say "You know, I missed that one - you're right about what Lednicer's model says - even if I disagree with accuracy of model contours" - you spin and dance and talk about lots more stuff you don't know anything about to divert attention.

It is Simple. 

You didn't know what you were talking about regarding the theory of the model or interpretation of the results, you called me out on it and I have been relentless about rubbing your nose in it because of your previous snide remarks questioning my knowledge of aerodynamics...

I am willing to let this slide and will be civil in the future - but I ask you to do the same.


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## DerAdlerIstGelandet (Apr 17, 2008)

*Originally from drgondog (sorry I thought it was a duplicate post before I read it):*

PS - I just looked at the drawings of the P-51B and D. Soren is correct about the angle of the windscreens. It is steeper for the P-51D than for the P-51B.

The Fuselage station for the canopy/windscreen interface is the same. The bottom forward location for the windscreen is the same... but

the P-51B windscreen is 31 degrees and at the top rounds off and transitions back to the canopy/windscreen interface. The top of the canopy of the P51B at that point is slightly higher than the P-51D.

The P-51D windscreen slopes more, and runs straight to the top of the forward part of the canopy.. in other words there is no transition or round off to go from 'slope to horizontal' as there is in the P-51B. It references the Lines drawings so there is no WL referece to the P-51D canopy. By inspection it (top of windscreen/canopy interface) the P-51D is slightly lowere there.

I'll have to dig more to get the specific angle of the P-51D windscreen but it is more like the Fw 190D than the P-51B. As I re-read Lednicer's report it is possible that when he went from the P-51B model to the D model he assumed the windscreens were the same - as he states in the windscreen slope comparisons.

I suspect the results would be even better for the P-51D than the existing model if a.) he made the error and b.) he pulled the windscreen back more like the Fw 190.

I would love to have access to VSAERO and the compute power to model a Malcom Hodd on the P-51B to see if the possible improvement in flow would yield similar results to P-51D bubble canopy.


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## Soren (Apr 17, 2008)

Bill,

You're being unduly unfair and harsh at the moment, which I don't appreciate. So I misread the color chart, so what ?? Is that a crime ? I'm not familiar with VSAREO, never used it, so can I be blamed of being clueless ?? Hardly.

Fact still is that a razorback configuration is more drag efficient than a bubble canopy (Assuming the same front windscreen ofcourse), you can dance around this fact all you want Bill, it's really common knowledge within the aero industry. It was certainly clear to the guys who designed the P-51 as they obviously altered front windscreen angle to offset this disadvantage.

Had the front windscreen angle been the same in Lednicer's model we would've seen quite different results than we did, cause the boundary layer would've then like on the B C series started to seperate right near the base of the windscreen, and the flow over the entire canopy and rear fuselage would've then been a lot different and turbulent. If the B C series had the same front windscreen as the D series then the flow distribution would've been completely different and more drag efficient than on the D series.

Anyway I'm looking forward to your start at being civil.


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## Kurfürst (Apr 17, 2008)

Hmm... thread title says:

Allied tests of captured Bf-109's


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## drgondog (Apr 17, 2008)

Soren said:


> Bill,
> 
> You're being unduly unfair and harsh at the moment, which I don't appreciate. So I misread the color chart, so what ?? Is that a crime ? I'm not familiar with VSAREO, never used it, so can I be blamed of being clueless ?? Hardly.
> 
> ...



I think after this post that deal is off. Check back with me some other time on this.

So, let's summarize.

a. Model has same angle 31 degrees for both the P-51B and P-51D. 
b. The Model assumptions for the panel size, the contours and the singularity distributions over both models were the same - Except for cutting the turtledeck and building the bubble canopy for the P-51D
c. The Plots were given Red for Pressure < Freestream, Blue for Pressure > Freestream. 
d. The results were presented and compared to wind tunnel results.
e. Conclusions were made regarding the model data and differences between Wind Tunnel and Model data were discussed and explained.
f. Significant time was spent discussing the results of the windscreen and canopy results including the 'interesting' distribution over the entire P-51D canopy versus the P-51B

So, The P51B RAZORBACK was less Drag efficient than the P51D Bubble Top

The Spitfire with Malcolm Hood was more Drag efficent in canopy region than the P-51B.

Lednicer concluded that had the Spitfire design team seen these results they would have changed the slope of the windscreen to improve it more.

You continue to argue points with no fact basis ("common knowledge in areo industry that razorbacks are more drag efficient", etc - then you say that I am 'dancing'??


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## DerAdlerIstGelandet (Apr 17, 2008)

Everyone lets tone it down a bit allright!


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## pbfoot (Apr 17, 2008)

I think the testers missed a really important item in their rating of the 109 which gives me pause for thought on their insights , there isn't anywhere for the pilot to take an over night bag


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## DerAdlerIstGelandet (Apr 17, 2008)

pbfoot said:


> I think the testers missed a really important item in their rating of the 109 which gives me pause for thought on their insights , there isn't anywhere for the pilot to take an over night bag



You had to go there didn't you? 

Get ready pb!


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## drgondog (Apr 17, 2008)

pbfoot said:


> I think the testers missed a really important item in their rating of the 109 which gives me pause for thought on their insights , there isn't anywhere for the pilot to take an over night bag



German engineers very pragmatic - why waste space for overnight kit when you can't fly far enough to need one... hell there was no space in that airframe for a condom kit, much less an over night bag.


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## pbfoot (Apr 17, 2008)

drgondog said:


> German engineers very pragmatic - why waste space for overnight kit when you can't fly far enough to need one... hell there was no space in that airframe for a condom kit, much less an over night bag.


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## Soren (Apr 17, 2008)

> But even here you are missing the point... and falling back to snide remarks about 'dancing'



Ha! You perhaps didn't say this in the post just before mine?:
*"Soren - you are dancing and 'spinning' around the issue"*

Or what ???

Sure I'm the one making the snide remarks around here 



> He SAYS the angles of the "51's are 31 degrees. That means the angle of the P-51B and the angle used for the P-51D are the same - 31 degrees



What ?! No it doesn't Bill, that's just something you're wishing to be the case!

What Lednicer says is: 
_"The Spitfire's windscreen is at a 35 degree angle to the forward deck, while the FW-190's is at a 22 degree angle and the P-51's is at a 31 degree angle"_

The question that then arises is: *Which P-51 ??* 

If you look at the 3D models you can clearly see that they arent the same, furthermore they couldn't have been the same cause as Lednicer himself says: 





So the models in the flow simulation obviously didn't have the same slope windscreen cause they're based on North American's own drawings, also if they did have the same windscreen they would've looked like the profiles KK presented and Lednicer would've definitely known that wasn't right! 

Or don't you trust that Lednicer was thurough enough to ensure that the a/c were accurately recreated in the flow simulation ?? If he wasn't the whole article is worth nothing and a waste of time.


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## drgondog (Apr 17, 2008)

Soren said:


> Ha! You perhaps didn't say this in the post just before mine?:
> *"Soren - you are dancing and 'spinning' around the issue"*
> 
> Or what ???
> ...



It was an excellent presentation independent of whether he was right or wrong about the P-51D windscreen slope. 

It led you to expose the fact that you a.) know very little about Potential Flow/Singularity Distribution models, b.) do not know the difference between Suction, Lift and Drag, and c.) do not know how to interpret either his model, his results or his conclusions.

In short I found it excellent!!

Have a good day.


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## Soren (Apr 18, 2008)




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## Soren (Apr 18, 2008)

Yeah Lednicer definitely used the same windscreen for both


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## drgondog (Apr 18, 2008)

Soren - carefully. There are three discussions going on about the Lednicer Report. 

Terminology (i.e. Suction, Drag, Stagnation, etc)
Accuracy (i.e. The angles for the windscreen, canopy model, describing the angles)
Interpretation (Razorback drag efficiency versus Bubble top drag efficiency in this model) 

Accuracy
If Lednicer said in his report that he used 31 degrees for the 51's - as you pointed out earlier, he should have used something closer to 26 degrees for the P-51D. 

But, carefully, as you have noted by reproducing what he said, he didn't say they were different angles, and then specify the difference. He said he 'used 31 Degrees for the 51's" Correct?

Then he said he built the model from the North American Drawings from Arthur Bently in the UK. They are the same drawings I have from the Microfilm Collection I got from NASM. The entire package is contained in T.O. 01-60J-13 and contains 24 rolls of microfilm for P-51A, B, C, D, K, and H, including Tooling, parts, assy, standards, and methods.

The windscreen Assy and Inst'l drawings are 83-31826 for A-C, 106-318226 for D/K and 117-318131 for the P-51H. A little later I will dig into them and give you the answer for the Windshield angle referenced to the forward Cowl line at the bottom of the windshield.

Having said that it looks like the P-51D windshield slopes more acutely to the cowl line than the 51B.

In your blow up of the plots it seems to me that Lednicer did in fact model the two windshields correctly with the 51D showing the angle closer to 26 degrees. Correct? 

So, he either misspoke when he said he used "31 degrees for the 51's" because he din't realize that there was a difference, but in fact modelled it correctly with the WL/FS reference points for both ships. Correct?

Or, conversely the model did in fact use 31 degrees incorrectly and we are seeing an optical illusion on the plot. Correct? Any other possibility?

So, either his model used an incorrect and greater angle for the P-51D than he should have but the model, even under such adverse assumption, still shows attached flow and lower pressure distribution (i.e Suction) over the bubble top..

or he used the correct lesser angle for the 51D and the model shows attached flow and lower pressure distribution over the bubble top than over the Razorback canupy/windscreen combo.

Which way do you want to go? Less efficient Razorback in case 1 or less efficient Razorback in Case2?

I think we have dissected this enough. I think we have rounded up all the tangential excursions away from the prime questions.

Is the Razorback in this model a.) more efficent with respect to Drag than the P-51D based on your interpretation now that we have gone through this exercise?

Is Suction as Lednicer used the phrase to describe the pressure distribution over the Bubble canopy of the P-51, the same meaning as Drag as you claimed, and further illustrated with wake drag behind boat tail/spitzer bullets?

You have claimed and repeated YES to both of these questions. Is that still your claim?

_*Oh when it comes to the issue of pressure distribution and boundary layer seperation I see things quite clearly Bill, and nothing of what I explained is wrong, nothing.



And what's with the sudden paranoia Bill? You seriously think I've been away from the forum because of a discussion we had ? Bill I could care less, besides the discussion was over in my eyes. 

And as to suction, well I thought we had settled this already, and yes suction equals drag. A razorback design has less drag than a bubble canopy one, the simple reason being that there's not the turbulent area right behind the canopy creating extra drag. I thought you understood this.

*The sudden drop over the top of the canopy is what causes the boundary layer to seperate, causing turbulence to the rear(Hence the stability issue), and therefore extra drag. It's the same with bullets Bill, if you say cut way the boattail you'll get sooner seperation and more turbulence which means more drag, hence why spitzer bullets aren't as drag efficient as boattailed ones.
_


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## kool kitty89 (Apr 18, 2008)

If you do remember my original question that sparked this debate (on the best pison engine fighter ever thread iirc) was in context to the P-47's bubbletop/razorback canopy...

And also a question (not by me) why the 109 wasn't adapted to a bubble canopy, on an earlier thread.


And another thing is that the ballistics example of boat-tailed vs spitzer isn't completely comparable as a spitzer has a sheer drop off compared to a slight taper of a boat-tailed bulled. But in our comparison we're comparing a tear drop shaped canopy design to one with it fared int the fuselage. (like comparing an extremely tapered bulled on the trailing edge to a very long bulled with a gentler trailing edge taper)


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## claidemore (Apr 18, 2008)

Nothing to do with planes, but a friend of mine made himself a little fishing boat out of aluminum. It was flat bottomed, 6 feet long, and 3 feet wide, and was designed to fit on a custom made frame to be pulled behind a 4 wheel drive ATV. He wanted it to ride low, as the trail to the lake was 40 miles long, and extremely rugged, so he cut 'wheel wells' into the sides so the boat could sit down over the tires on the trailer. Basically it looked like a pickup truck box with the front end bent up, a design and engineering marvel to say the least! 
Unfortunately, he didn't test it before we headed out into the bush. Spent 2 days on the trail, 3rd day he sticks the boat into the water, puts a 3.5 hp motor behind it, fires it up, and roars away..... at about 1 1/2 mph. 
The boat held 2 guys, with plenty of freeboard, but those two cutouts for the wheels created an enormous amount of turbulance. The water literally foamed along the sides, even at that painfully slow speed. It was pretty funny, motor screaming, water foaming, and I could walk along the shore faster than they were going. 

Not quite the same as in the models being discussed, but a graphic illustration of how an interruption in air/water flow creates problems.

O yeah, they did catch some nice lakers, but they were always late gettin back for supper.


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## Soren (Apr 22, 2008)

Bill,

It is quite obvious that Lednicer used the right dimensions for both a/c in his flow simulation, hence the flow models. And this directly affects my argument as it from the start was assuming a similar windscreen, ofcourse. The P-51D, C B however don't share a similar windscreen, something which I hadn't noticed to begin with, so I was in disbelief when I examined Lednicers results really, until I noticed the further slope of the D series windscreen which explains it. This further sloping of the windscreen decreases drag and helps the flow over the canopy stay non turbulent a longer way. 

So if I had to choose between your questions it would be nr.2.

But I still stand by what I said from the beginning, razorbacks are more drag efficient than bubble canopies. (Assuming similar windscreen)

Oh and suction does create drag, I stand by that as-well. But I admit Lednicer wasn't refering to this.


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## drgondog (Apr 22, 2008)

Soren said:


> Bill,
> 
> It is quite obvious that Lednicer used the right dimensions for both a/c in his flow simulation, hence the flow models. And this directly affects my argument as it from the start was assuming a similar windscreen, ofcourse. The P-51D, C B however don't share a similar windscreen, something which I hadn't noticed to begin with, so I was in disbelief when I examined Lednicers results really, until I noticed the further slope of the D series windscreen which explains it. This further sloping of the windscreen decreases drag and helps the flow over the canopy stay non turbulent a longer way.
> 
> ...



Suction in a blow job will create minor drag in the direction you are looking at - but not the 'suction on the wing/body (canopy)' that Lednicer presented, which was orthogonal to the freestream flow

Lednicer wasn't referring to Suction as Drag, but *you* equated 'lower pressure distribution' over the bubble canopy as Drag. You were simply wrong but you can't simply say that. You can't admit you didn't know what you were talking about.


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## slaterat (May 21, 2008)

Back to the original topic of the post. Many ea were captured during the war. One area often overlooked in post war studies is the North African theatre. Rapid changes of the forward lines and quick deployment of aircraft lead to many captured aircraft on both sides. The Desert Airforce had its own unit for evaluating ea.

On November 19 1942 ground units of 260 sqd RAF captured 12 109s, 4 completely servicable , at Martuba. Canadian ace Stocky Edwards was able to test fly/ evaluate one on four occassions during late Feb 43. I'll try to post a picture of it.

Slaterat


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## slaterat (May 21, 2008)




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