The sound barrier

[claidemore]

Krazykraut: Your conclusions are pretty much the same as those reached by me with my 'speculative arguments'.
"Eliminate the unlikely and unprobable and what remains is the truth." As you pointed out, there isn't much evidence, so we have to use a little logic and deductive reasoning.

 

[drgondog]

Bill if a panel like the gun cover were to be ripped off a Me-262 at Mach .85 then it can only be serious. Hae you seen how big that panel is and where it is located ??

Soren - that whole 'what if' had zero to do with Mutke's account, had zero to do with lending credibility to German QA issues relative to the Me 262.

Ripping anything large in front at high speed is not going to improve the aero - yes we can agree. So what?

Again only a few exhibited this behavior.

Sez you.

It was a key entry in the February, 1947 "Evaluation Tests of the me 262" at Wright Patterson. The two ships tested were T-20711 and T-2-4012. The summary indicated as 'handling characteristics were poor at all speeds above 350 mph. The airplane would not make a satisfactory gun platform because of a tendency to hunt directionally which resulted in snaking at speeds above 400 mph IAS".

It further recommended solution to couple aileron and elevator servo tabs.

Every account I have read from the survivors, including USAAF, Soviet (Kochetkov), RAF (Gosling) and German (Lindner and Baur)test pilots also all describe the same pitch phenomena - namely onset severe vibration and buffeting, then increasing stick forces required to maintain attitude up to increased stick forces at 50kg range to such a level as to almost make it impossible to free one hand to retard throttles - all occurring between .82 and .84 M (estimated). Vibration and pitch reduced to controllable levels once the throttles were retarded successfully.

So which ones DIDN'T exhibit this behavior? Do you have any documented rebuttals? If not -Why would you say 'only a few exhibit this behavior?

Lindner further stated to USAAF interrogators that the Max speed ever attained by the Me 262 was 1004kph (600mph) at 13,000 feet in a 25degree dive. (Appendix B pg 194 Stormbird Rising) for a corrected mach number of .86

Can you provide one documented example in the speed range over 1004Kph True Airspeed for this discussion?

The flight wasn't recorded Bill, so it's a matter of opinion wether one believes the Me-262 went supersonic or not, different arguments popping up in support of both scenarios.

I think you have stated before that it is UNQUESTIONABLE that the Me 262 could achieve Mach 1. You cited the report by PROFESSIONAL AERODYNAMICISTS and Mutke to support that thesis. Are you backing away from the assertion?

I have asked for specific references in that Report by someone who has read it and understands the issues encountered at .82-.86 M, with regard to possible yaw issues, pitching moment issues in transonic cp change, structural analysis with the aero loads imposed on the airframe. You aren't that person.


Further, to be credible the Report must TAKE INTO CONSIDERATION the Yaw and Pitch issues, the details to support structural integrity with those assumed loads - and a sound thesis for discussiong post .86M speeds (and loads) all the way through Mach 1 to show that those (and other heretofore unknown) issues did not resurface.

But I get You... and Mutke. I really am interested in facts, but still I get You and your opinions - not supported by facts but supposition, speculation, reference to a report by Professionals - but no 'meat'... All the issues and more I haven't even thought of would have to be addressed, modelled and presented to be a Professional Study.

I KNOW the flight (Mutke) wasn't recorded. Lindner's were. I KNOW what the state of the art was in Instrumentation as well as predictive flight mechanics for transonic conditions in 1945. ZILCH.

I KNOW what the art (Flight Mechanics, Aerodynamics, Aeroelasticity and airframe structures analytics) was capable of in the 1950's and 60's because that was the foundation for Aero education when I got my degrees. It STILL SUCKED relative to predictive flight mechanics. It is much better today depending on the tools available and the references.

On the 'references' and the Report - I would be very curious to know exactly which additional (other than aerodynamic and stability/control models) advanced analytical tools were used to perform the aeroelastic and structures analysis. To get a MODEL, you would have to have access to a.) the old drawings - complete package with all detail parts, assemblies and installations, specs on bolts, rivets, etc, skin thickness, rivet spacing, castings/forgings and heat treat specs, and b.) most desirable but not mandatory if the complete drawing dwg pkg is available, would be the structural analysis as a place to start.

For example, If I had the structures analysis I would look at the entire tail section and fuse attach points to see what was near 'ultimate' stress at 1.5 Design Limit at which airspeed. I would be curious to the linking aero analysis which drove the pressure distribution predictions leading to those loads.

If any of that exists in the Professional report - would you know it and more importantly be able to follow the analysis? If so, please present it, or provide a reference to read or order it - or simply acknowledge that you are dealing from speculation and a belief system that I don't subscribe to and we can agree to disagree?

 

[DerAdlerIstGelandet]

Bill if a panel like the gun cover were to be ripped off a Me-262 at Mach .85 then it can only be serious. Hae you seen how big that panel is and where it is located ??

Again Soren:

No not necessarily. Only if it were a structural panel, and then it still might not happen.

Any normal panel (no matter what size it is) is not necessarily and probably not going to do anything.

Do you know the difference between a structural panel and a normal old access panel or cover panel?

 

[drgondog]

I have no doubt that his account is true.

I have doubts about his interpretations. Instruments weren't reliable regarding True airspeed in the transonic to supersonic regime. The whole transonic shockwave and relocation of center of pressure aftward was little known and less understood. Schlierran photography was in its infancy.

The question is if the evidence is enough to conclusively say that the man broke the sound barrier. Which it is imo not. The symptoms he described also occur when an aircraft nears the sound barrier or can be attributed to the actions he took. So I agree with you that while it is possible he broke the sound barrier, there is no conclusive evidence that he wasn't just close to it.

Actually the symptoms he described were completely consistent with the onset of compressibility over the Me 262 wing, as well as huge stick forces as the true airspeed progressed along the .82+ range, as well as the final desparate step of taking one hand off the stick to retard the throttle.

The first question that always to come to mind is about the TAS. If Lindner said the highest he ever took it was to 1004 Kph (calibrated) what was the IAS? I can't find a reference.

The second question that comes to mind is his recollection of sequences. The sequence of nose down, accelerate, experience increasing buffeting and increased stick forces during pitch down, retarding throttle, reducing speed and gaining manageable stick forces are all part of the Me 262 dive recounts.

His apparent recollection of 'reducing throttle' then vibration abatement for a time as he is pulling out, then increasing vibration certainly dovetails to a normal recovery from .85+ M but in no way substantiates Mach 1.

Examining the possibilities

So, at 1100 TAS @ 40K = 593 kts = 1.03M Not possible as this was max ceiling of the Me 262.

@ 30 K = 1100 TAS = 593 kts = 1.006 M
@ 20 K = 1100 TAS = 593 kts = .96 M
@ 13 K = 1100 TAS = 593 kts = .93 M

Lindner never exceeds 1004 m/hr@ 13000 feet = 541 kts = .858 M which was calibrated apparently by 70 separate pressure sensors and then further measured against known distances on the deck..

Willy M. sets placard at .84 for not to exceed but even that is an unclear reference to IAS.

Back to your point (and Claidmore's, and Mine).

There are no facts to support actual speed > .86 Mach. There is a wide body of evidence to support dire consequences above .86 Mach as well as several crashes during dive tests.

Even the much discussed Me 262 Study/Professional Report" is not in evidence with respect to boundary conditions established for an analytical approach to speculate on the feasibility, nor the supporting caveats relative to structures or flight mechanics..

We can say the same thing for Welsh, even though there are witnesses to a 'boom' that the witnesses believed to be a supersonic shock wave.

Yeager's event was monitored and recorded and validated and repeated.

Is there any more in the way of evidence or facts that hasn't been exhausted?

 

[kool kitty89]

Quote:

It would be more serious if the nose tuck kept putting extraordinary forces on the tail

Again only a few exhibited this behavior.
.

I think he misspoke here Bill, since Soren seems to be responding to the snaking issue again, while you were commenting on the pitch-down behavior at Mcrit. (something Soren hasn't disputed)

The flight wasn't recorded Bill, so it's a matter of opinion whether one believes the Me-262 went supersonic or not, different arguments popping up in support of both scenarios

And I don't think Soren is contradicting himself here. He's saying we can't know for sure if Mutke's Me 262 reached Mach 1 and it really depends on what you want to believe.

However, I don't think he's questioning the Me 262's ability to reach Mach 1 under the right circumstances.


I personally think Mutke may have possibly done it, but it's unlikely. (there's no way to be sure) But I do think the Me 262 was capable of reaching Mach 1 in the right circumstances. (though probably not without serious warping to the airframe)

It should be noted that Mutke's aircraft was scrapped due to the damage resulting from this event.



Also, I think the Me 262's CAS reading would still be exaggerated. (with TAS probably being ~910-920 km/h when the CAS indicator maxed out)

The IAS reading would be interesting as it would still be giving a reading when the CAS needle was maxed out.

 

[Erich]

Mütkes interview after the accidental dive is on the net on several spots, noteworthy is Bert Hartmanns luftwaffearchiv. I wrote Guido years ago and out of this event feel he truly did so in the dive, not on the level. you can say what you want but the flight was all recorded for the groundtechs and evaluators galore his 262 was nearly torn apart under his own admission to me

 

[kool kitty89]

I agree Erich, I believe his story, but I'm not sure (one way or the other) if he actually broke the sound barrier, probably alt least made it to Mach ~.99 (where his engines would have stalled) which obviously overstressed the a/c from the excessive buffeting and aerodynamic loads.

The page on luftarchive.de unfortunately no longer seems to exist as I mentioned on the last page. Any other links to his story?

 

[kool kitty89]

Another interesting note on IAS speeds in similar conditions is that according to: The Amazing George Welch: Part two

The IAS during Welch's dive was in the high 400 mph to low 500 mph range, peaking at ~520 mph when he pulled out at 25,000 ft. (giving an "uncorrected TAS" of 720 mph -1,160 km/h- which would be ~1.04 Mach) How would the accuracy of the XP-86's instrumentation of 1947 compare to the Me 262's?

 

[drgondog]

I think he misspoke here Bill, since Soren seems to be responding to the snaking issue again, while you were commenting on the pitch-down behavior at Mcrit. (something Soren hasn't disputed)

I was commenting on both. Disputing the 'snaking/hunt' comments by the USAAF test flights on two airplanes is difficult either way. On one hand you need a specific comment from the LW test pilots saying the 262 was completely steady or assume it occurred but wasn't particularly noticeable. I noted in the the USAAF reports that directional stability was a frequent line item to check off. An example is all versions of the Mustang

And I don't think Soren is contradicting himself here. He's saying we can't know for sure if Mutke's Me 262 reached Mach 1 and it really depends on what you want to believe.

IIRC - he earlier said it was unquestionable' - I will have to go back for exact quote [/I]

However, I don't think he's questioning the Me 262's ability to reach Mach 1 under the right circumstances.

I actually do question it because of the Jumo engine 'delicate nature' and zero indication that the pitch down problem was ever solved


I personally think Mutke may have possibly done it, but it's unlikely. (there's no way to be sure) But I do think the Me 262 was capable of reaching Mach 1 in the right circumstances. (though probably not without serious warping to the airframe)

I don't for all the reasons I have posed, and for zero facts entered into evidence to support that it can

It should be noted that Mutke's aircraft was scrapped due to the damage resulting from this event.

That is normal for severe damage. What is unknown are all the facts such as true airspeed, potential damage due to shock wave and buffeting, stresses at peak pitch down cycle, etc



Also, I think the Me 262's CAS reading would still be exaggerated. (with TAS probably being ~910-920 km/h when the CAS indicator maxed out)

The simple fact is - we don't know

The IAS reading would be interesting as it would still be giving a reading when the CAS needle was maxed out.

I honestly don't know what the 'peg' is for the 262 airspeed indicator. Lindner said the Mach meter didn't work and that true airspeed had to be calibrated after the tests from the pressure recordings filmed during test flights.

 

[drgondog]

Mütkes interview after the accidental dive is on the net on several spots, noteworthy is Bert Hartmanns luftwaffearchiv. I wrote Guido years ago and out of this event feel he truly did so in the dive, not on the level. you can say what you want but the flight was all recorded for the groundtechs and evaluators galore his 262 was nearly torn apart under his own admission to me

Erich - I don't presume he was lying about his impressions.

If the flight was recorded where are either the data or the tech reports after analyzing the data? If Willy M, or Lindner were aware of near to actual Mach 1 why didn't they report it it? Why would Messerschmidt keep this confidential - his greatest achievement?

You couldn't convince Deacon Priest that he wasn't doing 620mph indicated airspeed chasing a 109 in his Mustang until after he got his aero degree several years after the war. My old man would cackle like a hen when Deac had a few scotches and recalled the Nov 2 mission.

The archives are full of 600+ mph recounts with trimming required to pull out in time.

No way any of those Mustangs were doing .85 mach with a combat config - the instruments said it and the damage implied it - but it didn't happen. I buy that the late model Spit exceeded .85 because of the wing - but I don't know if I believe .9 either...

and then for the 262, with those stupid nacelles buried under the wing with all the implied inlet potential issues, a relatively fat wing, potential wing-body-nacelle interference in the transonic range and a pitch down phenomena that should have no relief until actual supersonic flight is achieved - leaves a lot of unknowns between .86 M and 1.0.

Unless and until the actual data surfaces with cross correlation to corroborate the claim - I just don't buy it.

 

[FLYBOYJ]

I agree Erich, I believe his story, but I'm not sure (one way or the other) if he actually broke the sound barrier, probably alt least made it to Mach ~.99 (where his engines would have stalled) which obviously overstressed the a/c from the excessive buffeting and aerodynamic loads.

My belief as well.....

 

[Soren]

Again Soren:

No not necessarily. Only if it were a structural panel, and then it still might not happen.

Only ? Adler the gun cover panel on the Me-262 was large and if torn away would create a very large gap in the nose and as-well as a large blunt area directly facing the airstream.

Any normal panel (no matter what size it is) is not necessarily and probably not going to do anything.

Perhaps not, but it depends alot on its position compared to the incoming airstream.

Do you know the difference between a structural panel and a normal old access panel or cover panel?

Absolutely, but like I said much depends on its position in regards to how dangerous it is to loose it midflight.

 

[Soren]

Erich - I don't presume he was lying about his impressions.

If the flight was recorded where are either the data or the tech reports after analyzing the data? If Willy M, or Lindner were aware of near to actual Mach 1 why didn't they report it it? Why would Messerschmidt keep this confidential - his greatest achievement?

You couldn't convince Deacon Priest that he wasn't doing 620mph indicated airspeed chasing a 109 in his Mustang until after he got his aero degree several years after the war. My old man would cackle like a hen when Deac had a few scotches and recalled the Nov 2 mission.

The archives are full of 600+ mph recounts with trimming required to pull out in time.

One big difference: The P-51 only has trim tabs, and if indeed the a/c reached the transonic region then they wouldn't work and the a/c would just continue to dive without the pilot being able to do anything about it, unlike the all moving tail plane on the Me-262 which would work! Mutke was able to recover from his dive only because of the all moving tail plane.

No way any of those Mustangs were doing .85 mach with a combat config - the instruments said it and the damage implied it - but it didn't happen. I buy that the late model Spit exceeded .85 because of the wing - but I don't know if I believe .9 either...

and then for the 262, with those stupid nacelles buried under the wing with all the implied inlet potential issues, a relatively fat wing, potential wing-body-nacelle interference in the transonic range and a pitch down phenomena that should have no relief until actual supersonic flight is achieved - leaves a lot of unknowns between .86 M and 1.0.

That is simply nonsense Bill, the Me-262's wing was thinner than the Spitfires (and swept), so how can you call that a fat wing when you attribute the Spitfire's dive speed to exactly its "thin" wings ?! You're contradicting yourself Bill.

As for the pitch down, again the all moving tail plane could effectively counter that (Which is a proven fact), hence it's use on both the M.52 and X-1.

Furthermore in a steep dive the pitch down wouldn't have time to develop enough negative G's before the a/c went supersonic, hence why the 1999 study makes it clear that the Me-262 would only be able to break the sound barrier in a steep dive. In a shallow dive, like that simulated by MTT, the a/c will remain too long inside the transonic region and there will be enough time for the Mach tuck to develop enough negatie G's to break the a/c apart.

Unless and until the actual data surfaces with cross correlation to corroborate the claim -

Like the 1999 study..

 

[Soren]

I think he misspoke here Bill, since Soren seems to be responding to the snaking issue again, while you were commenting on the pitch-down behavior at Mcrit. (something Soren hasn't disputed)

Yes I read through his post abit too quickly, I was referring to the snaking issue caused by the rudder on a few a/c, not the Mach tuck.

 

[kool kitty89]

Soren do (or did) you have access to the 1999 University of Munich study on the Me 262 and if so, how much have you read. Do you know how others here could get access to it?


Bill, I agree that actuall access to the report would be necessary to be sure of what their conclusions were specifically. From what Delcyros has posted on it I tend to believe that it shows the distinct possibility of the Me 262 exceeding Mach 1 under the right conditions, but the only actual peice of the report i've seen is the speed vs altitude graph for the dives on pg.1.


For refrence, here's all the statements Delcyros posted on it:

There is scientific evidence, proposed by the technical university of Munich in an study which covers structural integrity of the Me-262 at different dive conditions. It shows that it is theoretically possible to exceed Mach 1.0 under certain conditions in a certain altitude with a certain load (You guess it- everything has to fit to make it through, which in turn makes it unprobable). Something which surprised me.

This study so far was never disprooved. The results of the study were challenged but not on scientific grounds.

Unfortunately not my friend. The study isn´t avaibable online. You might use the KOBV-Fernleihe to see the 1999 paper in question. The below page is from appendix II and shows how narrow to frame for reaching Mach 1.0 is at a pure vertical dive.

The idea behind the study is of more theoretical nature. Following Guido Mutke´s claims in the late 90´s, the TU Munich investigated the possibility.
The initial dive condition -as far as I understood- was estimated to be very steep, >60 deg. At this condition, the nose down pitch at Mach >.86 would stabilize the -262 at a near or full vertical dive (90 deg) while the negative g-forces generated by the nose down pitch at a lower dive angles would be to excessive and lead to desintegration of the airframe. The steeper the initial dive angle, the higher the probability to stabilize in the vertical after loss of elevator authority due to nose down pitch. Or in other words: If the nose down pitch is small (requiring high dive angles), the airframe may survive. If thenose down pitch is to strong, the negative g-forces would become excessive (finally overmatching 90 deg). Elevator controll is blanked in this speed region but may or may not be restored once the speed of sound is exceeded, according.

Drag is still a considerable problem. Only once full power is applied (at this altitude the generated thrust is more like 500-600 Kp for each turbine @ 100% but weight of the airframe adds another 5-6tons thrust) and vertical dive established the study showed that Mach 1.0 may be approached temporarely at a specific altitude. Once SoS is approached at this altitude, probability is high that a compressor stall cannot be avoided, zeroing out the engines. The technology was not there to prevent this.
As the plane dives down to lower altitudes (still vertical dive), the drag increases as does the speed of sound due to higher density, resulting in a rapid reduction of the relative mach fraction. It is possible that elevator controll may be restored at in between 3000m and 6000m.

Quote:

Thanks a lot! I had seen this single page before, but didn't know it was for a purely vertical dive. So I take it you have read the complete report? I would be interested to know if it only addressed the performance question or if it considered stability and control as well.

I have read the paper a few years ago. But I admit that I didn´t understood everything due to the very theoretical aspects and methodology. As I underlined above, the study only shows the possibility but concludes that it is well beyond probability that it really happened. Structural Issues (the Verwindungsbruch is mentioned here several times) are taken into consideration. The specific circumstances in the dive entry (low load and max. ceiling at specific speed are good, high load will render recovery in time problmatic), the high initial dive angle and structural issues make it very questionable that a normal -262 will survive the event.

The Me-262 is not a transsonic plane.

In the case of the engines flaming out, the weight alone may have been enough to push it through. At 5-6,000 kg and the engines producing ~1,200 kp (kgf) total the engines would only be providing ~16-18% of the thrust, prior to the flamout.

 

[kool kitty89]

One big difference: The P-51 only has trim tabs, and if indeed the a/c reached the transonic region then they wouldn't work and the a/c would just continue to dive without the pilot being able to do anything about it, unlike the all moving tail plane on the Me-262 which would work! Mutke was able to recover from his dive only because of the all moving tail plane.

It would depend on how elevator control was lost at/near Mcrit. If it was excessive stick forces the trim tab would help. If the tail was emersed in turbulence from the wing, even an all-moving tailplane wouldn't help. -and the stick would not be frozen- If the wing-body design was such that the stabilizer was not blanked, the stabilzer's mach limit would be the limiting factor, but even then I think trim may still work depending on the characteristics of the shock/turbulence developed at the stabilizer.

That is simply nonsense Bill, the Me-262's wing was thinner than the Spitfires (and swept), so how can you call that a fat wing when you attribute the Spitfire's dive speed to exactly its "thin" wings ?! You're contradicting yourself Bill.
As I mentioned, the root/center cection of the Me 262's wing is not truely swept, it just had an extended LE with greater taper to match the swept portion outboard of the nacelles. The outboard section does get a reduction in thickness of ~5% while the root stays the same. Additionally the root has a max thickness at 35% chord opposed to 40% for the outboard sections, further reducing its critical mach number compared to the outboard section. -note the section just outboard of the nacelles is still 11% thick, but with the sweep it's ~10.5% thick, and again has the max thickness 5% farther back.



As for the pitch down, again the all moving tail plane could effectively counter that (Which is a proven fact), hence it's use on both the M.52 and X-1.

Actually the all flying tail will only help if the wing-body design ensures that the entire tailplane isn't blanked by wing turbulence. And I believe the M.52 was to use a true all-flying tail, rather than a trimmable tailplane with elevator.

And the pre-E model Sabres featured a conventional -boosted- elevator plus tailplane trim. However I have not seen refrence to use of trim in recovery of supersonic dives in the accounts I've read and heard. So it would seem the elevator was still effective at transsonic speeds and thanks to the boosted controls there was no "concrete stick" problems. 9in fact, if the Me 262's loss of elevator control was due to frozen stick, the elevator may still have been effective, but would need boosted controls to be usable)

I think the case with the F-94C and CF-100 is similar, not sure about the Skystreak though. Also, I think the F-89 may have been capable of exceeding Mach 1, but I havent seen a refrence for it. (given the comparison to the Starfire and Canuck, it should be capable, as long as the controls were satisfactory.


Furthermore in a steep dive the pitch down wouldn't have time to develop enough negative G's before the a/c went supersonic, hence why the 1999 study makes it clear that the Me-262 would only be able to break the sound barrier in a steep dive. In a shallow dive, like that simulated by MTT, the a/c will remain too long inside the transonic region and there will be enough time for the Mach tuck to develop enough negatie G's to break the a/c apart.

In addition to the longer time spent in the damaging transsonic and -G inducing region in a shallow dive, accorfing to delcyros, the report stated that the pitch-down stabilized at a vertical dive atitude. So there would be no -G issues with a true vertical dive.

An interesting note to allied tests is that all seem to state that "no vertical dives were attempted." and that no attempt at exceeding the mach limit was made. (though given some of the statements in the Wright field Me 262 handbook, it would seem that vertical dives had been experienced in flights, though not specifically tested, particularly comments on recovering from dives exceeding Mcrit, though such conditions were not to be attempted)

 

[kool kitty89]

Bill (or anyone else knoledeable on this), for a swept wing aircraft (ie the F-86) the airfoil sections listed would not be taking sweep into account correct?

Would there be any excepions to this? (and I know delta wings wouldn't apply, as there is no sweep affecting the airfoil, its simply a planform with a highly swept LE, likewise with most of the wings on modern fighters)

 

[Soren]

KK,

The Me-262's horizontal stabilizer isn't emersed in turbulent flow, that's the reason it is placed so high, to keep that from happening. The thing that is causing the elevator trim tabs not to work is the shockwave forming near the rear of the horizontal stabilizer, causing turbulent flow over the control surfaces, the elevator trim tabs, rendering them ineffective. That is why the all moving tail plane works and the elevator trim tabs don't.

The Me-262's stick never froze or became stiff, the control forces remained light throughout the speed range.

Actually the all flying tail will only help if the wing-body design ensures that the entire tailplane isn't blanked by wing turbulence. And I believe the M.52 was to use a true all-flying tail, rather than a trimmable tailplane with elevator.

True, again the reason for mounting the tail plane high. The reason for the all moving tail plane being used as the main control surface for pitch was to improve maneuverability in transonic supersonic flight.

 

[drgondog]

Bill (or anyone else knoledeable on this), for a swept wing aircraft (ie the F-86) the airfoil sections listed would not be taking sweep into account correct?

Would there be any excepions to this? (and I know delta wings wouldn't apply, as there is no sweep affecting the airfoil, its simply a planform with a highly swept LE, likewise with most of the wings on modern fighters)

KK - the effect of sweep angle at the .25 Chord point is simply and effectively redeuce the freestream flow vector to a.) a chordwise component of the airflow over the chord, and b.) a spanwise component.

This has the effect of reducing the actual velocity chordwise - thereby enabling higher velocities before experiencing transonic flow over the airfoil. The 'bad' effect is the spanwise flow component. Same effect for Delta wing.

You aren't "wrong" by describing the effect of sweepback as reducing the t/c ratio, except that mathmatically speaking you need to reduce the freestream velocity to Vcos(sweepback angle at 1/4 chord) to get the right flow distribution over the 'real airfoil'

The latter is why vortex generators and wing fences are useful on highly swept wings, to help 'realign the spanwise flow' component.

The two primary advantages of a Delta wing over straight wing and swept wing for supersonic aircraft are 1.) a smaller shift in aerodynamic center from pre-transonic to supersonic. (i.e ~.35 to .50 versus .25 -.50) which is very significant for stability and control purposes.

For all intents with respect to S&C, the Me 262 behaved like a straight wing in that respect. IMO this is the primary issue for the Nose down pitch problem
described for all the dive tests.

 

[drgondog]

One big difference: The P-51 only has trim tabs, and if indeed the a/c reached the transonic region then they wouldn't work and the a/c would just continue to dive without the pilot being able to do anything about it, unlike the all moving tail plane on the Me-262 which would work! Mutke was able to recover from his dive only because of the all moving tail plane.

The 51 reached transonic in a dive, the elevator (and tabs) were not eliminated from acting and the 51 was able to pull out without the nose tuck issue. The max recorded and verified dive for a Mustang was .84/.85M for both the Mustang IV at RAE and the P-51D at Wright Pat.. with a fatter wing than both the Spit and the 262.

It is entirely probable that Mutke was able to pull out because of the movable horizontal stabilizer.


That is simply nonsense Bill, the Me-262's wing was thinner than the Spitfires (and swept), so how can you call that a fat wing when you attribute the Spitfire's dive speed to exactly its "thin" wings ?! You're contradicting yourself Bill.

I believe the me 262 had an 11% root and constant through the nacelle, then tapered to 9%. NACA 00011-0.825-35 and 00009-1.1-40 respectively.

You had compared the 262 as having same wing as the F-86 to illustrate your case for a supersonic dive. The F-86 has the NACA 0009.5-64 at root and 0008.5-64 at the tip with a straight taper. The 86 has a thinner wing with no interference effects than the 262.

The Spit had the NACA 2213 at root and 2209 at the tip.

I called it a relatively fat wing because of the nacelle effect - in actuality I have not seen the actual wind tunnel effects so you are correct in questioning my belief in that regard - on the other hand neither have you. Nevertheless the 262 had basically the same thickness as the Spit, but slightly less, with slight sweep and based on the wing alone should have less drag.

As for the pitch down, again the all moving tail plane could effectively counter that (Which is a proven fact), hence it's use on both the M.52 and X-1.

Soren - nobody has disputed the advantage of an all moving tailplane. What is under question for the 262 is in fact the huge leverage that an all moving tailplane can apply to the 262 tail structure - when aerodynamic movement of the aero center from .25 to .5 causes a huge nose down pitching moment.

The P-38 had a similar problem, the P-47 had a similar problem but apparently the Spit and the Mustang did not.

In ALL of the above a/c the factory issued glaring warnings to NOT use trim to pull out of the dive - which is a much smaller application of leverage on the tail than an entirely movable slab tail. This warning was a gentle reminder that the pilot would not survive with the tail ripped off.

Get the point?

Furthermore in a steep dive the pitch down wouldn't have time to develop enough negative G's before the a/c went supersonic,

BS alert. Negative G's wasn't the problem if the slab tail had complete effectiveness and permitted the a/c to fly with proper attitude and angle of attack.

The problem Soren is that the actual elevator forces on the airframe were so great - as to cause such tremendous stick forces to keep it from the continued tuck - as to probably cause failure in the tail section. This condition was (probably) not anticipated in the aero analysis or a.) the elevator controls would have been boosted and the aft section of the 262 would have been beefed up to take the additional load.

I don't KNOW this, but this is the area of the technical section I would look at to believe the 262 could survive Mach 1.

hence why the 1999 study makes it clear that the Me-262 would only be able to break the sound barrier in a steep dive. In a shallow dive, like that simulated by MTT,

the a/c will remain too long inside the transonic region and there will be enough time for the Mach tuck to develop enough negatie G's to break the a/c apart.

IIRC - Mutke's recount is that he was forced from the shallow dive to the vertical - he didn't just 'decide' to point his nose straight down. If I am correct in that assumption then he must, presumably have migrated from say 20 degrees, through 30 and so on until he could actually maintain a stable attitude - presumably 90 degrees.

You have a different version?


I believe the report has been cited that it is IMPOSSIBLE to maintain the dive in a shallow angle as the pitch down forces were too great to maintain a steady dive angle - forcing it into a vertical dive.

But I haven't seen anything to explain why the pitch down forces 'disappear' at the vertical, and at what mach number, before the a/c goes supersonic.

Everybody talks about the Report but nobody is providing quotes from the combined aero and structures analysis to cite the supporting details - explaining how the 262 survived the experience from .86 through 1.0.

Nobody seems to provide the trim requirements necessary to retard a serious negative G condition from the continued nose down tuck from 20 degrees to vertical in that speed range. Nobody speaks to the elevator loads above design limit load and points to an airframe that can survive the forces on either the tail or the wings.

Why not?