REDUCE Rate of Change for Trim - Bf109

[Venturi]

One of the Bf109's greatest limitations was a compressible elevator at high speeds. This was a common problem for many warbirds of the era but the Bf109 was particularly impacted. It was a notable historical limitation of the plane and was a point of notice between its flying characteristics and other Luftwaffe designs.

 

However, this is currently not a problem for many players.

 

What is being done by Luftwaffe flyers is a work-around:

 

They map the stabilizer trim to a joystick axis, and because of the immediate responsiveness to the trim, can, within a second, go from full negative trim to full positive trim. Which enables the Bf109 to almost immediately, mid-dive, pull miraculously hard and out of the elevator compressibility and avoid any negative effects.

 

In reality, the trim wheel on the 109 was a laborious affair - it could only be moved with one hand, slowly, using a large wheel - about 1/4 revolution at a time. It took several complete revolutions of the trim wheel to achieve "lock-to-lock" trim. Also, as the compressibility of the elevator went up, so did the difficulty of moving the trim wheel.

 

What I propose is to slow the trim changes on the Bf109 to more accurately model the real limitations of the real aircraft, and thus improve how the plane behaves in sim in relation to the real Bf109.

 

 

 

 

 

[Original_Uwe]

I'd agree actually.

After we get a proper P-40, Russian aircraft that leak poisonous gas into their cockpits, shoddy Russian quality control, reflector sights so poor that reticles are drawn on the front glass with grease markers, and speeds taken from frontline fighters rather than prototypes, etc etc as infinitum.

[Venturi]

I think that changing the rate of change of trim so that it can't be changed from full up to full down in a second and a half is very easy to do, and has important implications for how the major Luftwaffe fighter is flown.

 

Not quite the same thing as modeling engine fumes.

[Original_Uwe]

Sure it would. Forcing vvs pilots to fly with canopies open should dramatically effect their performance and limit max altitude.

Shoddy construction quality makes their airplanes fall apart unpredictably and causes them to fly far more conservatively.

Grease marker gunsights makes gunnery far less accurate.

A P-40 that can stand nearly toe to toe with the Emil would just be accurate.

[Venturi]

Flying with canopies open does limit performance.

Shoddy aircraft construction? Says who?

Grease marker gunsights? Haven't heard of that either. 

P-40s are good aircraft.

 

Next.

[LukeFF]

Uwe, try to be more informed next time before making such nonsense replies. BTW, Soviet aircraft specs are taken from frontline aircraft. That's very old news by now.

[Dave]

I would love to see this improved.

The way things are currently, being able to use stabiliser trim to overcome elevator ineffectiveness renders one of the 109s biggest weaknesses non-existent. Possibly due to the way stabiliser trim changes affect (or rather don't seem to affect) AOA rate limits it has the added strange behaviour of allowing the 109 to overcome its high wing loading and radically alter its AOA without any apparent penalty.

 

Every aircraft was a design compromise and when weaknesses like stabiliser trim responsiveness at high airspeeds are so poorly modelled it prevents opponents from exploiting the only advantages they have within a limited corner of their envelope.

 

In a similar vein, the 109 aileron authority being well in excess of documented constraints at high speed undermines the FW190's strengths such that, relatively speaking, a 190 pilot pays for the shortcomings of its design but doesn't seem to realise any appreciable benefit for its strengths. This may be part of the reason 190 fans felt cheated concerning roll rate in the 190 - that it rolls little better than the 109 at speeds where the 109 roll rate was documented to be about 12 degrees per second.

 

edit: 109 roll rate at 600km/h was actually 45 degrees in 4 seconds not 90 degrees in 4 seconds

Edited April 22, 2016 by Dave

[Dave]

I request more specifically that the rate of change of stabiliser trim be an inverse function of airspeed. At 400km/h the trim "wheel" should be quite stiff. at 600km/h it should be immovable.

Standard behaviour at the moment in-game is to trim into the dive (which was expressly forbidden) to allow steeper dives to be maintained beyond full forward stick force and to then trim up rapidly (which should be impossible) to follow aircraft more manoeuvrable at high speed.

[Dave]

Sure it would. Forcing vvs pilots to fly with canopies open should dramatically effect their performance and limit max altitude.

It does reduce performance. It also improves visibility most of the time so I fly canopy open a lot. It should not limit maximum altitude (other than by the small amount of additional drag lowering the ceiling when open - which it does). These aircraft aren't pressurised and oxygen is delivered via the mask.

 

 

Shoddy construction quality makes their airplanes fall apart unpredictably and causes them to fly far more conservatively.

 

This did occur in a very limited number of cases apparently early in Lagg3 production as the Russians were still developing wood laminates. I'm OK with this being added for such aircraft in 1941 if at the same time we model ersatz fuels and low grade oils for the Luftwaffe on the Eastern Front for most of the campaign.

 

A P-40 that can stand nearly toe to toe with the Emil would just be accurate.

Wing Commander, how did you find the difference between flying the Kittyhawk and the Messerschmitt 109 which you eventually did fly?

 

 

The first 109 I flew was a 109F and I carried out comparative tests with it with a Spitfire Mark V and the Kittyhawk. We all started in line abreast. The Messerschmitt ran away. The Spit V came fairly well after in climb and speed and they both left the Kittyhawk quite badly. And later when we captured the 109G at Gambut, it had been slightly damaged and it was repaired by my squadron engineering officer, Ken McRae. I then flew it forward to the base at Mersa Matruh - no, from Gambut up to the Martuba aerodromes, escorted by two Kittyhawks. While I had it there I carried out some simulated attacks on my squadron. By then the German Air Force had retreated out of range so I was able to do this with safety. My people knew I was up there. But I found after two or three attacks I could have shot down one of my pilots each time, so I desisted it, I gave that away; I didn't want to spoil their morale. The purpose had been basically to let them see - some of the new boys see - what a 109 looked like. But its performance was quite terrific. Kittyhawk could out turn it quite comfortably and if the Messerschmitt boys came in and tried to dog fight, they were gone. We could dive away from them. If we started with same speed and they dived away, we could catch them in the dive. But with climb, they could out climb us to blazes. Our best fighting ceiling was twelve to fifteen thousand feet, above that the Kittyhawk went off badly. The 109 was good up to thirty-odd thousand feet and so always we had them sitting up above us. Almost never would we find them on our level.

 

You gave a demonstration to your squadron pilots which nearly ended up in you crashing the aeroplane.

 

 

 

Well, that was the first 109F that I flew on the first take-off, as I've just said, I had trouble with the thermostatically controlled gills. On the next flight I came in at high speed - I don't know what I would have been doing, probably 400-odd - and carried out a normal round-out as I would have done with a Kittyhawk. I hadn't allowed for the higher wing loading on the Messerschmitt and I splurged almost onto the aerodrome. I think it was purely ground effect that held me off. The boys on the side said the propeller looked as if it was hitting the desert and the tail was almost on the desert also, and I went past with a great cloud of dust coming up. So it was a very close call and frightened the hell out of me.

[II/JG17_HerrMurf]

_{The flap and stabilizer speed is fine. It is an average time once the key is pressed or the axis is moved to full down and full up. How complicated this might be to use two hands in combat situations can't really be modeled. This has already been addressed by the DEV's in other, EA, discussions. I don't remember if it is based on anecdotal information or pilot interviews but I don't see it changing.}

[Sokol1]

They map the stabilizer trim to a joystick axis, and because of the immediate responsiveness to the trim, can, within a second, go from full negative trim to full positive trim. 

 

 

Assign the Bf 109 "Stabilizer Adjust" to a axis on joystick (Y), throttle, pedal... dont make thismove "whitin a second" - the time to full travel remain the same need to move pressing key/button.

 

But yes, people can cheater with this, as setting in axis they dont need bother in press and hold keys/buttons or turn wheels.

 

In flight games the trial in deal with this kind of "cheater" result in failure, the IL-2 CloD "Anthropomorphic Control" -

as the pilot are not like this - more due fault user hardware, joysticks with spike axis, than the concept per si... But as CloD became synonymous of "how don't do the things" dont expect see this anymore in flight games.

 

Anyway is fool try limit this, Warthog, CH stick... users can create trim for all Bf 109 axis with his software, external to game.

Edited April 19, 2016 by Sokol1

[Venturi]

That is why a reduction of hard coded RATE of change is needed, specifically for this a/c.

 

There is no problem with putting it on a joystick axis. The problem is that it only takes a second to go from full down to full up.

 

Read the original post. Reduce RATE of change.

[II/JG17_HerrMurf]

What you are saying is simply not true. It does not move within one second stop to stop. Move along, nothing to see here.

[Sokol1]

The problem is that it only takes a second to go from full down to full up.

 

 

This "a second" is Internet "legend".

 

The time is ~ 9 seconds with keys/joy button and ~6 seconds with axis - with axis the adjust is not delayed with some friction around the center position present in key/button adjust. 

[Turban]

When it comes to the stabilizers (not trim) :

 

 

I have never seen it reach 100% . It kicks in to "max manageable effect" way before that (80% maybe?). Pulling 100% would be madness. I should try though, for science.

 

Anyway, the use of stabilizers on the joystick makes it almost instantaneous. Definitely less than 1 sec for "full effect" (and probably also for 100% if you get there).

The effect is so violent it requires a more gentle touch, but the gain in blitz maneuvering is quite clear, 

 

Just did a quick test before bed to refresh my memories. The AoA you achieve is probably about the same but it comes much quicker. Also a nice benefit is that you get extra pitch maneuverability at high speed. You can tear your wing appart no problem if you go all the way. Basically you enhance the pitch capabilities of the 109 which are probably the best in the game already.

 

Pretty sure it's something I have seen online. But hey no proof, (I haven't really looked) so...

 

All and all, definitely think it shouldn't be allowed on the same axis as pitch. 

Edited April 20, 2016 by Turban

[=362nd_FS=RoflSeal]

The report on the captured Bf-109G-2 Black 6 mentions that the trim wheel becomes almost solid at high speed.

 

http://www.wwiiaircraftperformance.org/me109/me-109g2-trop.html

 

Also mentioned on the G-6 trials that elevator trim "is practically impossible to operate" above 350mph IAS

 

http://www.wwiiaircraftperformance.org/me109/me109g6-tactical.html

 

Would be interesting to see what German documents say.

Edited April 20, 2016 by RoflSeal

[Venturi]

The report on the captured Bf-109G-2 Black 6 mentions that the trim wheel becomes almost solid at high speed.

 

http://www.wwiiaircraftperformance.org/me109/me-109g2-trop.html

 

"13.      The Elevators harden up at high speeds and retrimming is necessary, which is difficult as the twin wheel hardens up and becomes almost solid in a dive. Some force is needed on the stick, but accelerations as high as the pilot can stand can be put on."

 

Also mentioned on the G-6 trials that elevator trim "is practically impossible to operate" above 350mph IAS

 

http://www.wwiiaircraftperformance.org/me109/me109g6-tactical.html

 

"11.           The rudder is fairly heavy but not uncomfortably so. As there is no rudder trimming device, it is necessary to apply right rudder for take-off and left rudder at high speeds. The ailerons become increasingly stiff with the increase in speed especially at speeds in excess of 350 I.A.S. At speed below 180 I.A.S. the ailerons are not positive and as the stall is approached they are almost non-effective. The elevators also become increasingly difficult to operate as the speed increases. Above 350 I.A.S. this unpleasantness is accentuated as the elevator trim is practically impossible to operate."

 

 

 

 

This "a second" is Internet "legend".

 

The time is ~ 9 seconds with keys/joy button and ~6 seconds with axis - with axis the adjust is not delayed with some friction around the center position present in key/button adjust. 

 

I stand corrected, it is 6 sec in a dive at 700kph, to change the trim from lock to lock.

 

I still say it needs to be reduced, a lot. 

[II/JG17_HerrMurf]

When it comes to the stabilizers (not trim) :

 

 

I have never seen it reach 100% . It kicks in to "max manageable effect" way before that (80% maybe?). Pulling 100% would be madness. I should try though, for science.

 

Anyway, the use of stabilizers on the joystick makes it almost instantaneous. Definitely less than 1 sec for "full effect" (and probably also for 100% if you get there).

 

The effect is so violent it requires a more gentle touch, but the gain in blitz maneuvering is quite clear, 

 

Just did a quick test before bed to refresh my memories. The AoA you achieve is probably about the same but it comes much quicker. Also a nice benefit is that you get extra pitch maneuverability at high speed. You can tear your wing appart no problem if you go all the way. Basically you enhance the pitch capabilities of the 109 which are probably the best in the game already.

 

Pretty sure it's something I have seen online. But hey no proof, (I haven't really looked) so...

 

All and all, definitely think it shouldn't be allowed on the same axis as pitch. 

The Dev's have acknowledged this flaw. The more we talk about it the more people will use it. Self fulfilling prophecy................congratulations.

[Venturi]

The Dev's have acknowledged this flaw. The more we talk about it the more people will use it. Self fulfilling prophecy................congratulations.

 

 

Wait, so people use it on the JOYSTICK axis so that they are getting stabilizer pitch change AS WELL when they pull back on the stick?!?!

[Dave]

The report on the captured Bf-109G-2 Black 6 mentions that the trim wheel becomes almost solid at high speed.

 

http://www.wwiiaircraftperformance.org/me109/me-109g2-trop.html

 

Also mentioned on the G-6 trials that elevator trim "is practically impossible to operate" above 350mph IAS

 

http://www.wwiiaircraftperformance.org/me109/me109g6-tactical.html

 

Would be interesting to see what German documents say.

 

This.

I was digging through my stuff to find it but you've beat me there.

Bobby Gibbes (the first allied pilot to fly Black 6) also commented that the stabiliser was very hard to move at high speed. Which is hard to misconstrue given his otherwise flowing praise for the 109.

 

4.62. Elevator. – The elevator is an exceptionally good control at low speeds ; it is fairly heavy, and is not over sensitive during the approach glide, while response is excellent. Throughout the speed range the elevator is heavier than that of the Hurricane or Spitfire, but up to 250 m.p.h. this is not objected to, since it is very responsive. Above 250 m.p.h. the elevator becomes definitely too heavy for comfort, and between 300 m.p.h. and 400 m.p.h. is so heavy that maneuvrability in the looping plane is seriously restricted; when diving at 400 m.p.h. a pilot, pulling with all his strength, cannot put on enough g to black himself out if trimmed in the dive.

 

4.7. Aerobatics. – Aerobatics are not easy on this aircraft. Loops must be started from about 280 m.p.h., when the elevator is unduly heavy; there is a marked tendency for the slots to open near the top of the loop, resulting in aileron snatching and loss of direction, and in consequence accurate looping is almost impossible.

 

At speeds below 250 m.p.h. when the ailerons are light and very effective, the aircraft can be rolled very quickly, but there is a strong tendency for the nose to fall in the final stages of the roll, and the stick must be moved well back in order to keep the nose up.

 

Upward rolls are difficult; the elevator is so heavy at high speed that only a gentle pull-out from the preliminary dive is possible, and a considerable loss of speed is thus inevitable before the upward rolls'can be started.

It seems that this decline in elevator effectiveness at speed is actually modelled in game. But what is missing is:

[StG2_Manfred]

One of the Bf109's greatest limitations was a compressible elevator at high speeds. This was a common problem for many warbirds of the era but the Bf109 was particularly impacted. It was a notable historical limitation of the plane and was a point of notice between its flying characteristics and other Luftwaffe designs.

 

However, this is currently not a problem for many players.

 

What is being done by Luftwaffe flyers is a work-around:

 

They map the stabilizer trim to a joystick axis, and because of the immediate responsiveness to the trim, can, within a second, go from full negative trim to full positive trim. Which enables the Bf109 to almost immediately, mid-dive, pull miraculously hard and out of the elevator compressibility and avoid any negative effects.

 

In reality, the trim wheel on the 109 was a laborious affair - it could only be moved with one hand, slowly, using a large wheel - about 1/4 revolution at a time. It took several complete revolutions of the trim wheel to achieve "lock-to-lock" trim. Also, as the compressibility of the elevator went up, so did the difficulty of moving the trim wheel.

 

What I propose is to slow the trim changes on the Bf109 to more accurately model the real limitations of the real aircraft, and thus improve how the plane behaves in sim in relation to the real 

 

What do you mean with 'high speed' ? According to the attached document (an internet found, which I found after a quick research) the problems begin/begun to occur at 850 kph and higher, which I think we already have in-game. This document has to be verified of course.

Edited April 20, 2016 by StG2_Manfred

[Turban]

What do you mean with 'high speed' ? According to the attached document (an internet found, which I found after a quick research) the problems begin/begun to occur at 850 kph and higher, which I think we already have in-game. This document has to be verified of course.

 

 

The document states it's about the FW 190 and Me109.

 

I wouldn't be surprised if those speed were about the FW 190 , not the 109. What does the rest of the document looks like?

Edited April 20, 2016 by Turban

[StG2_Manfred]

The document states it's about the FW 190 and Me109.

 

I wouldn't be surprised if those speed were about the FW 190 , not the 109. What does the rest of the document looks like?

 

I'm not interested about what you are suprised or what not. It is clearly stated for both planes. Do your own research and post your results here!

[Turban]

I'm not interested about what you are suprised or what not. It is clearly stated for both planes. Do your own research and post your results here!

 

 

lol. No need to be agressive. And no I won't.  The document you show go against everything else I've read and that others have quoted and showed. And I'm with them so I'll just chill.

 

I'm not the one trying to make a point that the 109 had elevator control till 900 kph. lol

[Dave]

I stand corrected, it is 6 sec in a dive at 700kph, to change the trim from lock to lock.

Above 600km/h the trim wheel should be immovable - period. That is the function for the trim effectiveness multiplier should tend rapidly toward 0 above 500km/h.

This is why the LW issued updates to flight manuals for the 109 stating that pilots MUST NOT trim into a dive. Because once in the dive the aircraft accelerated quickly to a speed above which the stabiliser trim became immovable thus preventing exit from the dive. This update came after many 109s were lost diving into the ground.

Edited April 20, 2016 by Dave

[Dave]

850 kph and higher

Lol. Vne for all 109 variants is 750km/h. The plane disintegrates before 800. I find it interesting that that very official looking typed document with SECRET stamps and classification revision stamps is all in ENGLISH.

Edited April 20, 2016 by Dave

[StG2_Manfred]

Well Dave, if you would quote my whole post and not only the part you want to discredit, you would sound more serious. I also said this document has to be verified, correct? Furthermore I said, I found it after a quick Internet search. And I didn't say it's right or wrong, correct?

 

You are referring to updated LW flight manuals regarding trim use. Can you post sources of those manuals please. Get me right, I'm just interested, because I have the original flight manuals for most of the German planes. Thanks

[MiloMorai]

Edited April 21, 2016 by MiloMorai

[Venturi]

Is that good enough for you?

[6./ZG26_5tuka]

Above 600km/h the trim wheel should be immovable - period. That is the function for the trim effectiveness multiplier should tend rapidly toward 0 above 500km/h.

This is why the LW issued updates to flight manuals for the 109 stating that pilots MUST NOT trim into a dive. Because once in the dive the aircraft accelerated quickly to a speed above which the stabiliser trim became immovable thus preventing exit from the dive. This update came after many 109s were lost diving into the ground.

http://www.deutscheluftwaffe.de/archiv/Dokumente/ABC/m/Messerschmitt/Me%20109/Hochgeschwindigkeits_Versuche_Me109.pdf

 

The trim wheel was moveable in a dive. There's no reason for it to "lock up" in any way. There's also a finish test on it where the test pilot explicticly mentioned to have used flaps to recover from a high speed dive instead of the recommendation of using trim because the later was very sensetive at high speeds, but unfortunately I lack the link to that doc.

 

Also, 750 km/h is Vne + safety margin. 50km/h as safety margin is totally unrealistic considering how inaccurate airpseed indicators at the time were not to menntion in a a high-mach number dive.

Edited April 21, 2016 by 5tuka

[StG2_Manfred]

@5tuka: Am I reading correctly, they reached up to 906 km/h in dive tests?

 

@Dave: Have you read the doc 5tuka posted, it's all written in GERMAN there, so much more trustworthy lol

Edited April 21, 2016 by StG2_Manfred

[III/JG52_Otto_-I-]

One of the Bf109's greatest limitations was a compressible elevator at high speeds. This was a common problem for many warbirds of the era but the Bf109 was particularly impacted. It was a notable historical limitation of the plane and was a point of notice between its flying characteristics and other Luftwaffe designs.

 

However, this is currently not a problem for many players.

 

What is being done by Luftwaffe flyers is a work-around:

 

They map the stabilizer trim to a joystick axis, and because of the immediate responsiveness to the trim, can, within a second, go from full negative trim to full positive trim. Which enables the Bf109 to almost immediately, mid-dive, pull miraculously hard and out of the elevator compressibility and avoid any negative effects.

 

In reality, the trim wheel on the 109 was a laborious affair - it could only be moved with one hand, slowly, using a large wheel - about 1/4 revolution at a time. It took several complete revolutions of the trim wheel to achieve "lock-to-lock" trim. Also, as the compressibility of the elevator went up, so did the difficulty of moving the trim wheel.

 

What I propose is to slow the trim changes on the Bf109 to more accurately model the real limitations of the real aircraft, and thus improve how the plane behaves in sim in relation to the real Bf109.

I think that changing the rate of change of trim so that it can't be changed from full up to full down in a second and a half is very easy to do, and has important implications for how the major Luftwaffe fighter is flown.

 

Not quite the same thing as modeling engine fumes.

1/ There is a bug in the Bf-109 elevator trim Handwheel.

Now in the BoS, we have ONLY ONE turn in the handwheel from full nose-up to full nose-down

In the real aircraft you have about FOUR turns of handwheel, from full nose-up to full nose-down,

 

2/ Unlike to allied aircrafts, Bf-109 was equipped with THS (Trimmable Horizontal Stabilizer) this kind of trim system is designed specifically for trimming the aircraft at high speed, with more autority than servo-tabs and lower drag. This system is able to recover a dive at hight speed, or helping to maneuvering at hight speed moving the trim handwheel finely, when stick forces are uncomfortably large .

 

3/ I.A.W. Mtt AG. Dive test Bf-109 is able to recover dives about 906 km/h TAS puling with stick

"" Reached speed was IAS Va = 737 km/h at 4.5km after peeling off at 10,7km over sea level with continuous 100% throttle in a 70-80° dive. It followed from the analysis that this was TAS Vw = 906km/h and a mach number of 0.8"

Diving_Test_Bf-109F_W.Nr.9228_ger_eng.pdf

Edited April 21, 2016 by III/JG52_Otto-I-

[Venturi]

So, rate of change is off, and the rotations need to be more. In other words, it needs to be slower, and it needs to have more revolutions.

 

I believe that is more or less, what I said to begin with. Thank you for the graphs, I think that I wouldn't want to go >750kph in that plane if any yaw would rip off the outer parts of the wings. Not sure the wing tips ripping off with yaw at high speed (>750kph) is modeled. But it should be.

[Dave]

Well Dave, if you would quote my whole post and not only the part you want to discredit, you would sound more serious.

How then would you know which part I was laughing at? I don't need to provide context - you already have one or two posts above it.

 

I also said this document has to be verified, correct? Furthermore I said, I found it after a quick Internet search. And I didn't say it's right or wrong, correct?

If you haven't even done basic validation on the authenticity and can't name the source of a document please don't post it as evidence. In that scenario it is just FUD and clutters the thread.

 

You are referring to updated LW flight manuals regarding trim use. Can you post sources of those manuals please. Get me right, I'm just interested, because I have the original flight manuals for most of the German planes. Thanks

I don't have the resulting edited flight manuals. What I have is the English translation of captured orders (amongst masses of documents seized) instructing units of the immediate imposition of new additional constraints on all Bf109 models up to and including the G series which was in production at the time of the orders being issued. They have been authenticated post-war and have been posted many times already. They can be found at wwiiaircraftperformance.org.

I will search for them and post a link.

Edited April 22, 2016 by Dave

[Dave]

Also, 750 km/h is Vne + safety margin. 50km/h as safety margin is totally unrealistic considering how inaccurate airpseed indicators at the time were not to menntion in a a high-mach number dive.

Vne is "never exceed". There is no safety margin. That doesn't mean the plane self-desctructs at 751km/h. It means structural failures or stress fractures have been recorded or are expected at airspeeds beyond the given IAS in smooth air and unloaded. I seem to recall early Bf109Fs (pre-acceptance I think) experienced self-reinforcing oscillations or flutter of the horizontal stabiliser at speeds below the Vne at the time which resulted in several tails tearing off. You may be lucky - you may be unlucky and have the plane shed a wing at 745km/h because yesterday you went to 755 and applied G. 

Vne is the maximum for the "unloaded" state in smooth air. You still have to effect recovery before it if you are diving, requiring G which puts you outside the limits for Vne. Additionally that speed doesn't take into account any asymmetric loading of the airframe, as will occur when rolling or yawing even slightly. This is exacerbated even further by rolling-G (applying G beyond about 1-2 whilst rolling - which incidentally we were always cautioned never to do in mock ACM or aerobatics). It is a misconception that there is much latitude designed into Vne. Aircraft manufacturers at the time were spending vast sums to gain an extra 10km/h out of aircraft and ground crews were frantically polishing airframes for an extra 5km/h. They weren't about to give that away with a >50km/h buffer on Vne.

 

What's more, airspeed indicators read IAS or CIAS. Most of the time IAS will be a good indication of the forces the airframe is experiencing. Airframe stresses are considered in relation to dynamic pressure Q. Q = 0.5 * rho * v². The ASI is a dynamic pressure registering device. So at flow velocities below which compressibility becomes significant, structural airspeed limits are expressed in IAS. At very high speed airframe stresses have to consider compressibility and therefore Mach number (becomes a consideration above about 200mph). Because of this, the indicated airspeed at which airframes experience intolerable stresses actually decreases slowly with altitude. Search for "dynamic pressure" - whilst not specifically about Vne you will find informative discussions about compressibility effects, airspeed and density. BTW airspeed indicators weren't that inaccurate at low airspeeds (~300mph) and altitudes (<10,000'). TAS is really only important at higher altitudes, higher speeds and for navigation purposes.

 

edit: added some more detailed discussion, corrected a poorly worded absolute, removed a reference to Reynolds number as it really isn't relevant here, added anecdotal reference to early 109 tail losses

Edited April 22, 2016 by Dave

[Dave]

@5tuka: Am I reading correctly, they reached up to 906 km/h in dive tests?

 

@Dave: Have you read the doc 5tuka posted, it's all written in GERMAN there, so much more trustworthy lol

You seem to be confusing Angezeigte (indicated) and Wirkliche (true) airspeeds.

The max IAS documented in the summary of that document under the given conditions (dive entry at ~10.7km altitude @ 240km/h and with a 70-80 degree dive angle) was 737km/h. (13km/h below the Vne I have quoted - and about 20km/h above estimated Vne for 4500m).

Note the shape of the corresponding plot. It suggests that the pilot exceeded the estimated Vne at 7000m by about 80km/h and had increasing difficulty holding in sufficient forward stick to maintain his initial acceleration as speed increased. This is because the stabiliser was set at 1.25 degrees (trimmed level flight at max power).

 

The maximum IAS attained in those tests was 737km/h @ 4500m altitude in the dive.

Maximum TAS was 906km/h @ 5800m.

Maximum mach number was 0.8 @ 7000m.

 

Note that what was recorded was IAS. Everything else is an estimate based upon temperature and pressure gradients which were also recorded but with reduced accuracy due to the position of the static port on the airframe and the Bernoulli effect. The only "buffer" in Vne is in the use of standard temperature and pressure curves for extrapolations of Vne at altitudes above 10,000'. That is to say, depending upon the pressure and temperature at altitude on a given day airframe failure may occur above or even below the projected maximum safe diving speed at that altitude. The Vne marked on the ASI was the higher figure for altitudes below 10,000'.

 

On the plots there is one that appears to max out at 770km/h IAS @ 3500m. It may be an outlier. There also appear to be two plots overlaid (i.e. there are 3 axes on that graph). Important elements on the plot are illegible.

 

edit: added bold emphasis and some additional explanation

Edited April 22, 2016 by Dave

[6./ZG26_5tuka]

Everything is given with a safety tolerance if not explicticly mentioned otherwise. Thats the whole point of engineering. I know ssome pilots that briefly went over the red line and their aircraft didnt desintegrate midair, either.

 

Furthermore Vne is not always tied to structural limits. The F series for example revealed vibrations and aileroun fluttering when diving beyond 650km/h which is why it had a lower Vne than the G2 as this behaviour could lead to fatal crashes if pilots didnt react accordingly.

 

Another example is the P-38 E, which had a lower than average Vne not because it had a weak structure but because of the by that time unresolved compressebility issues.

 

If you still believe in your theories of "no error margin" I recommend reading that finnish report on G series testing.

Edited April 22, 2016 by 5tuka

[Dave]

Everything is given with a safety tolerance if not explicticly mentioned otherwise. Thats the whole point of engineering. I know ssome pilots that briefly went over the red line and their aircraft didnt desintegrate midair, either.

Yeah - I get that. "Briefly [going] over the red line" is very different to pulling G to recover a dive at the "850 kph and higher" that Manfred introduced to this conversation, and which is the subject of my response.

Also the "safety tolerance" isn't some value in km/h. It exists in taking into account that the Vne is expressed in terms of unloaded flight in smooth air at standard sea level air temperature and barometric pressure. That is not manoeuvring, not pulling out of a dive, not rolling, not yawing and sure as hell not effortlessly flicking on maximum stabiliser trim up at 750km/h to pull up with the quarry you just dove on from 5k.

 

Furthermore Vne is not always tied to structural limits. The F series for example revealed vibrations and aileroun fluttering when diving beyond 650km/h which is why it had a lower Vne than the G2 as this behaviour could lead to fatal crashes if pilots didnt react accordingly.

Vne is absolutely tied to structural limits. They are the sole reason for its existence either directly due to structural failure due to flutter, or indirectly due to it being impossible to recover without exceeding the limits of the airframe, or control authority being overcome by dynamic pressure or inversion.

I already mentioned the tail flutter of the F. Its vibrations were due to insufficient internal bracing of the empennage following removal of the struts. The G2 and prior models all had the same Vne - 750km/h.

 

If you still believe in your theories of "no error margin" I recommend reading that finnish report on G series testing.

They aren't "theories of mine" - they were burned in during pilot training. Vne is so named (never exceed) for a reason.

Edited April 22, 2016 by Dave

[6./ZG26_5tuka]

Yea and according to you trim should magically lock up because it would fit your believe of aircraft balance well...

 

Luckily I have my own mind and sources on that matter to not have to take your opinion as a fact for sth that is not proved empiricly by documental data.

[Dave]

Yea and according to you trim should magically lock up because it would fit your believe of aircraft balance well...

 

Luckily I have my own mind and sources on that matter to not have to take your opinion as a fact for sth that is not proved empiricly by documental data.

 

No. According to me test pilots for the Luftwaffe, RAF and USAAF all reported extreme difficulty in actuating the stabiliser trim as airspeeds above 350mph, with one of them (and IIRC also Bobby Gibbes who wasn't a test pilot) reporting that the trim wheel became "immovable" and "solid" at "about 600km/h".

Its not my "opinion" it is in written test reports of the time. The docs as I have said are available on wwiiaircraftperformance.org. Links to them have already been posted near the top of this thread so I haven't double-posted them.