BF 109 Dive Rate

[Mike Williams]

An additional note:

In many Pilot's manual only one IAS speed is given (e.g. for Typhoon).
Tempest limiting speed is given as 540mph below 10,000ft.
P47N:
564 mph at sea level
522 mph at 5,000ft
482mph at 10,000ft
So there are many caveats in this graph.
Btw. very big thanks to Micdrow for most of the pilot's manuals.

Nice table timppa. Re: your additional note: I just was composing a post to that effect - I might qualify/clarify that by noting that the rankings will change somewhat as altitude increases. For example the Spitfire IX and Me 109G will flip places over ~ 16,000 ft. The documents below further support that view.

Below please find documentation regarding Me 109 dive limitations:

Bf 109 E Flugzeughandbuch

Bf 109 G-2, G-4, G-6 Bedienungsvorschrift-FL

 

[drgondog]

Hi Bill:

Girbig puts German casualties at 87 for November 26, 1944 and notes a loss of at least 90 machines. US claims were what, about 98 – 100 destroyed? Do you have a LW loss list in detail for 26 November 1944? Fwiw here's the 361st Fighter Group's Mission Summary Report of 26 November 1944. Interestingly their claims were adjusted up from 19 to 23 destroyed after review.

Mike - I do not, but Erich has compiled a detailed list of the JG 301 losses which include 355/361 and 339 clashes from ene Celle to Dummer Lake.

I'm having a hard time getting to JG 1 and JG 6 losses for the same area.

 

[drgondog]

Mike - note 4. regarding painted ailerons is interesting - wondering if they believe the increased drag (implied) has an effect to yaw or tip loads?

 

[Mike Williams]

Mike - I do not, but Erich has compiled a detailed list of the JG 301 losses which include 355/361 and 339 clashes from ene Celle to Dummer Lake.

I'm having a hard time getting to JG 1 and JG 6 losses for the same area.

Thanks Bill:

Here's what I have on JG 1 losses from 26 November 1944; from Prien:

 

[Mike Williams]

I had forgotten about this British document relating to Me 109 dive which translates material found in German documents .

 

[Mike Williams]

Hi Bill Dave:

Mike - That definitely is one I would like translated!

...could I ask for a copy of this as well, better still load it onto your site and put a link on.

Here's a translation of that report that Dietmar Hermann sent me yesterday:

Translation of Me 109 high speed trials

 

[Kurfürst]

I made a graph of allowed dive speeds [mph, IAS]. Iin case of German and Russian fighters the limits are probably minimum requirements rather than their actual limits, because the speeds are the same (750 and 650km/h respectively).

The sources are mainly "America's Hundred Thousand" and Pilots manuals.

In case of F4F and Fokker the speeds are actually their terminal speeds.

You might find the dive limits for the 109K also useful for this kind of chart (left coloumn for clean aircraft and also valid with for gondola cannons, right colomn with external stores ie. bombs etc.)

 

[Glider]

Many Thanks

 

[Kurfürst]

Hop - From the Dive tests at Wright Pat - I'll try to find the Boscomb Down report but it is similar. The Spit had a slightly higher M for recommended maximum but your P-51 figures are understated and out of context from the actual USAAF and RAF dive test results and reports.

Additionally the 51 did not have much of a 'tuck effect' in dive, or high stick forces, with test noting that the biggest danger was over controlling the stick in a dive or entering a tuve from a roll or steep turn at high altitude and airspeed.

Summary
Manual - limit Dive = .75M recommended
Test - limit Dive = .8 M recommended as maximum

Test Summary
Compressibility effects noted at .76

Ultimate Dive = .81 to .83 (attain at high risk)

.84 to .85 actual achieved and with significant damage and very high risk - maximum dive attained in the Tests

Porpoising effects believed to be initated by 'ballooning' of fabric elevators (true - and fixed with metal elevator modifications in production P-51D-10 and retro fit kits for all prior models.

Actual Report
TSCHEP 5R/RLB/MEM/2-6258
Wright Field, Dayton, Ohio
Date:- 9th October, 1944

url
Note on Dive Tests on 'Mustang IV'


Details/summary
1. Reference is made to Inter-Office Memorandum, P.W. Nosker:ffc: 51 dated 27 June, 1944 and Lt. D. B. ParkerC:51 dated 10 July, 1944 from Chief, Aircraft Laboratory to Chief, Flight Section requesting that compressibility dive tests be conducted on the P-51D airplane.
2. A series of thirty-one dives was conducted by the Flight Research Branch between 3 August, 1944 and 16 September, 1944. These dives included high and low altitude tests and limited stability tests at high Mach numbers. A complete report of these tests is in the process of preparation at the present: however, the necessary information is forwarded so that it may be made available immediately for operating instructions.

3. The results indicate that the airplane should be restricted to a Mach number of 0.80 due to compressibility difficulties which become increasingly dangerous beyond that point. It is recommended that the airplane be placarded with the following limit diving speeds:-


Pressure Altitude (Ft.) Pilot's IAS (m.p.h.)
40,000 275
35,000 310
30,000 345
25,000 385
20,000 425
15,000 470
10,000 505
5,000 505

4. Porpoising.- The P-51D airplane, at high speeds, is subject to the longitudinal instability commonly referred to as porpoising. The results to date indicate that the condition may be induced at a Mach number of 0.70 and above, but may be encountered at somewhat lower Mach numbers at low altitude. It is known that the fabric bulge in the elevator surfaces is more critical at low altitudes and may be related to the airplane's increased tendency to porpoise at lower Mach numbers in that range.

The porpoising is not a severe condition and can be controlled. In the first place, the condition is usually induced by the pilot, since any ununiform elevator stick force will result in the porpoising at high Mach numbers. Any effort on the part of the pilot to counteract this effect will result in increasing amplitude. It may actually be stopped by holding the stick firmly in one position or, in fact, eliminated by trimming forward gradually to near zero stick forces as the dive is entered, thus reducing the amount of forward stick forces necessary to maintain the dive angle.

5. Rolling.- As a Mach number of 0.75 is approached , a slight amount of rolling may become apparent with a simultaneous reduction in aileron sensitivity. This rolling does not become severe, and may be easily controlled.

6. Vibration.- At a Mach number of 0.76 a true effect of compressibility becomes evident in the form of a complete vibration of the airplane. This vibration is caused by a combination of compressibility effects on the wing and the horizontal stabilizer. The condition becomes increasingly severe as the Mach number increases and could eventually cause a primary structural failure.

7. Maximum Limit of Combat.- The airplane has been dived to a maximum Mach number of 0.85 and on several occasions to 0.84. In each case the pilots reported that the vibration became extremely heavy beyond 0.80. In each dive to 0.84 or above the vibration became so severe that the airplane was damaged. The leading edge skin of the wing flap was buckled between rivets, a coolant radiator cracked and hydraulic line broken due to vibration on various dives to 0.84 and above. In extreme war emergency the airplane can be dived to a Mach number of 0.83 (400 m.p.h. Indicated Airspeed at 25,000 ft.), if a very gradual pull-out is made.


From the P-51D Manual ( same as P-51-B)
P-51 Mustang Pilot's Flight Manual - Google Books

I think you would find interesting the findings of A&AEE at Boscombe down a fully armed Spitfire Mk IX, ie. the fighter variant tested in dive trials.

As you probably know the often referenced Mach 0,89 dives with were performed with an unarmed photo-recce Mk XI variant. As I recall however this report does not describe the behaviour of the aircraft during the dive, only records the speeds measured with a pitot (which as you noted was not a particularly accurate device at those speeds).

This variant had no cannon stubs or gun ports in the wings, neither it did have the armored windscreen of the fighter variants, ie. it was considerably different aerdynamically than the normal fighter variants. Personally it strikes me as illogical to compare a fully armed fighter such as the P-51 with the additional burden of armament with an unarmed photo recce.

Below you will find the details of the dive with the said Spitfire Mk IX fighter variant. It strikes me that the general behaviour was not at all different from the results with the Mustang in the test you quoted - normal in operation up to Mach 0.70, clear danger signs at around Mach .75, and begun to loose control at anywhere above Mach 0.80+.

If the Spitfire manual said Mach .85 as a limit, it was certainly a very bold suggestion for the pilots.

 

[drgondog]

I think you would find interesting the findings of A&AEE at Boscombe down a fully armed Spitfire Mk IX, ie. the fighter variant tested in dive trials.

As you probably know the often referenced Mach 0,89 dives with were performed with an unarmed photo-recce Mk XI variant. As I recall however this report does not describe the behaviour of the aircraft during the dive, only records the speeds measured with a pitot (which as you noted was not a particularly accurate device at those speeds).

This variant had no cannon stubs or gun ports in the wings, neither it did have the armored windscreen of the fighter variants, ie. it was considerably different aerdynamically than the normal fighter variants. Personally it strikes me as illogical to compare a fully armed fighter such as the P-51 with the additional burden of armament with an unarmed photo recce.

Below you will find the details of the dive with the said Spitfire Mk IX fighter variant. It strikes me that the general behaviour was not at all different from the results with the Mustang in the test you quoted - normal in operation up to Mach 0.70, clear danger signs at around Mach .75, and begun to loose control at anywhere above Mach 0.80+.

If the Spitfire manual said Mach .85 as a limit, it was certainly a very bold suggestion for the pilots.

Kurfurst - you may recall the spirited debates about Drag last year and in particular Lednicer's VSAERO modelling results. It demonstrated the stagnation pressure region in front of and on the windscreen of the Spit IX - at only ~ 300kts model speed.

Your report points to the possibility that as the 'Q" pressures built up over another 120 kts there should be quite a bit of turbulence at the forward portion of the Malcolm Hood before it re-attaches

 

[Kurfürst]

Of further interest, diving restrictions for Supermarine Spitfire Mk II, from Pilots manual issued July 1940. Some may appear familiar.

One particular difference was that the Spitfire had to be trimmed into dive to avoid excessive G pullouts and structural failure. The correct operation of the Bf 109 was the opposite, leaving the aircraft trimmed for level flight, ie. as before the dive commenced.

 

[Kurfürst]

From "Suggested method of keeping in range of Me 109 diving to Evade" - a tactical issue of No. 11 Group describing the roll-and-dive manoeuvre to circumvent negative-G cutouts, July 1941. The similiarity with the warnings placed in the Bf 109 G-2, G-4, G-6 Bedienungsvorschrift-FL is again, striking.

 

[Kurfürst]

Apparently the precautions laid down in the Spitfire II manual about the dangers of excessive accelerations during pullout were to be taken seriously.

Due to size restrictions, I will only post the summary here, but I don't think many are familiar with report in its full, so it would be probably a good idea to create a PDF from it, and upload to the flight tests.

 

[Kurfürst]

Kurfurst - you may recall the spirited debates about Drag last year and in particular Lednicer's VSAERO modelling results. It demonstrated the stagnation pressure region in front of and on the windscreen of the Spit IX - at only ~ 300kts model speed.

Your report points to the possibility that as the 'Q" pressures built up over another 120 kts there should be quite a bit of turbulence at the forward portion of the Malcolm Hood before it re-attaches

Personally, I am simply amazed that today, with a reasonable accurate 3d model of the aircraft, it is possible to get a fairly accurate picture of the flow behaviour that was, 70 years ago, unpredictable for the very best of the aircraft industry ! Indeed the actual flight test results from the 40s demonstrate that the VSAERO analysis was fairly accurate.

 

[Juha]

Hello Kurfürst
thanks for the Spit IX dive behaviour info.

Juha

 

[drgondog]

Personally, I am simply amazed that today, with a reasonable accurate 3d model of the aircraft, it is possible to get a fairly accurate picture of the flow behaviour that was, 70 years ago, unpredictable for the very best of the aircraft industry ! Indeed the actual flight test results from the 40s demonstrate that the VSAERO analysis was fairly accurate.

Equally interesting was the fact that the P-51D had the best of the comparisons with its greater slope than the P-51B, and after the P-51 was the Fw 190, then the Spit. This was significant in Cd0

Had the Spit designers been aware of these results they would have sloped the windscreen earlier to reduce turbulence over the Malcolm Hood.

I was heavily involved in potential flow aero models in late 60's and those were better than classic aero formula but childs play for today's models

 

[Juha]

Hello Drgondog
I'm not sure that the problem of Spit IX was the slope of the windscreen because IIRC it was the same in Spit PR XI, and its critical Mach number was very high for a prop plane. IMHO the "bullet proof" windscreen, long cannon barrels, gun blisters and the mirror were the main culprits that the max dive speed flown by Spit IX was 0,6M lower than that of Spit XI. Spit IX and P-51B/D seemed to have had more or less same critical Mach number and only info I recall for Fw190 is that Vanir gave, namely that it had trim changes at 0.78 Mach.

Juha

 

[Shortround6]

From what I understand the exterior bullet proof wind screen on the Spitfires was worth about a 6mph loss.

I am not saying changing the slope wouldn't have helped but that much drag from such a small item seems to indicate it was doing something to the airflow in the region.

 

[drgondog]

Hello Drgondog
I'm not sure that the problem of Spit IX was the slope of the windscreen because IIRC it was the same in Spit PR XI, and its critical Mach number was very high for a prop plane. IMHO the "bullet proof" windscreen, long cannon barrels, gun blisters and the mirror were the main culprits that the max dive speed flown by Spit IX was 0,6M lower than that of Spit XI. Spit IX and P-51B/D seemed to have had more or less same critical Mach number and only info I recall for Fw190 is that Vanir gave, namely that it had trim changes at 0.78 Mach.

Juha

Juha - What I intended to say, if misinterpreted, is that based on Lednicer's VSAERO analysis, there was a stagnation pressure region all along the windscreen of the Mk IX windscreen which would lead to initial separation at the forward portion of the Malcolm Hood -------> explaining Kurfurst's article regarding observations of the turbulence over the canopy.

Having said that, further observation is that the slope of the P-51D windscreen was ~ 31 degrees, the P-51B was around 34 and the Mk IX was around 38 degrees which appears to be reflected in the graphical plots of pressure distribution.

Of course the wing was the much larger determinant in drag but that isn't what I was commenting about.

 

[drgondog]

From what I understand the exterior bullet proof wind screen on the Spitfires was worth about a 6mph loss.

I am not saying changing the slope wouldn't have helped but that much drag from such a small item seems to indicate it was doing something to the airflow in the region.

Shortround - try this for some insight

http://www.ww2aircraft.net/forum/flight-test-data/p-51-performance-thread-12670.html - see post #4 for the Lednicer VSAERO study that I brought into the P-51 Performance section.

Lednicer and his consulting group has been used by the Dago Red and Strella teams to study and solve various P-51 related drag issues.