The sound barrier

[delcyros]

Does the study suggest how the nose down pitching moment is overcome during transonic shock wave movement?

I'm on shaky ground here but believe I recalled multiple references to the 262 tucking under in Mcrit dive? IIRC the elevator was blanked in that region of airspeed

Regards,

Bill

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.

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.

 

[mad_max]

One piece of an article I have basically says once past Mach .83 you may live to
tell the tale. In the same article Leutnant Karl "Quax" Schnorrer, Erprobungskommando
262, Kommando Nowotny JG7 says,

"Beforehand other pilots told me that the 262 is not difficult to fly. But do everything in the climb, not the descent. If you let the aircraft get into a dive and the speed rose over 1,000km/h (620 mph), you might not get it out of the dive."

FWIW

 

[Velius]

I keep reading in certain articles (I am however skeptical due to lack of decent sources; I'm just bringing this out on the floor) that the BA 349 might have inadvertantley broke the sound barrier during it's first manned flight. Some suggest that it MIGHT have been able to exceed Mcrit due to it's near 1:1 thrust to weight ratio. I know this doesn't necessarily mean speed of sound; but what does everyone think?

 

[drgondog]

I keep reading in certain articles (I am however skeptical due to lack of decent sources; I'm just bringing this out on the floor) that the BA 349 might have inadvertantley broke the sound barrier during it's first manned flight. Some suggest that it MIGHT have been able to exceed Mcrit due to it's near 1:1 thrust to weight ratio. I know this doesn't necessarily mean speed of sound; but what does everyone think?

Critical mach number is that flight profile which results in transonic flow over the airfoil in which a shock wave first forms.. frequent side effects are flow separation and movement of center of lift aft - both bad things if elevators are rendered ineffective.

 

[delcyros]

I too have serious concerns about Bachem claims. While much is possible in conditions of accidents, I cannot imagine how the Bachem airframe, structurally made entirely from wood will survive the stress imposed by flying high Mach fractions. I know that the Bachem dataset was composed from wind tunnel tests made at Braunschweig and Berlin, dating to january, 30th, 1945. None of those tests allows any conclusion from a pure drag point of view, which could support the claim. The manned start of BP-20 M23, dating to 1st of march 1945 lasted only 50 seconds. It is not reasonable how the plane could lift off, accelerate, turn and dive with reaching the speed of sound in such a short timeframe.

 

[renrich]

There was an interesting film called "Breaking the Sound Barrier" that showed a Spitfire diving into compressibility in the first scene and later a British jet by the name of Prometheus ( I can't remember what actual AC it was) broke the sound barrier in a dive. I remember the dialogue of the pilot screaming, "nose heavy, trimming back." It was a British film and quite good.

 

[Graeme]

a British jet by the name of Prometheus ( I can't remember what actual AC it was)

The Supermarine 535. Forerunner of the Swift.

 

[delcyros]

It´s a BEAUTY!

 

[renrich]

Thank you Graeme, that is it. It was agood looking AC. Was it kin to the Supermarine Attacker?

 

[Graeme]

Was it kin to the Supermarine Attacker?

Yes. The lineage starts off with a swept wing version of the Attacker, the Supermarine 510, then the 528, the 535 and then the 541 or Swift as it became known.

The Supermarine 510 had a couple of 'firsts' in its career. It was the first British jet-powered aircraft to fly with sweepback on the wings and tailplane. It was also the first swept wing aircraft in the world to land and take-off from an aircraft carrier. . however it required assistance from rockets to take off.

It now resides at the Duxford museum.

 

[Elvis]

No.

None of the WWII designs coupled all the 'lessons learned' into one airframe

• swept wings to delay transonic flow
• thin wings for same reason
• slab elevators to operate in high compressibility
• wing/body design to ensure that elevators were not blanked by wake turbulence

The engines weren't anywhere near powerful enough to brute force the airframe through compressibility and the aircraft were not designed well enough, given that kind of power, to prevent ugly stability and control issues from causing the aircraft to 'depart' and fail structurally in the process.

The F-100A, first supersonic fighter was the last of the US century series fighters designed before Whitcomb collected a lot of prior work into his theory of area rule to address better wing body performance in transonic regions. I'm trying to remember whether the F101 or F102 was designed to embody the area rule

The crafty Crumpp will soon swoop by to give you the 10 reasons I forgot

Area rule was what pinched the middle of the F-102 and got it renamed the F-106.
You've got the 102, 104 and 105 in production before that happens.
How can the F-100 be the last of the century fighters built before Area Rule became known?

As for WWII aircraft reaching the speed of sound, its said that many a pilot either died or almost died because they lost control of their airplanes in a steep, fast dive.
I don't think any plane in WWII actually broke the sound barrier, but I believe many came very close. At least up to .9 mach, as there are many stories of pilots reaching 700MPH in a dive (seems mostly from P-38 pilots).

...but you also mentioned how compressability "fooled" the a/s indicators.
Could you please explain that in more detail?
I am curious how that situation could exist and what did NASA (NACA) do to modify the a/s indicator on "Glamourous Glennis" so that it would read corrrectly?






Elvis

 

[renrich]

One of the best diving fighters for the US was the P47 and it's dive limit was .82 mach and at that number it was well into compressibility. As you know, the speed of sound varies only with air temperature so the further you dive which equates to more speed, the faster you have to go to reach a higher mach number. I strongly doubt any ww2 piston fighter ever reached .90 mach.

 

[kool kitty89]

Do you have to have a slab, all-moving, all-flying, variable incedence, or fully-trimmable tail to maintain elevator control at transsonic speed?

From what I read on the F-86, the E model was the first to use the all-flying tail, so earlier models must have had a normal elevator combined with a fully-trimmable tail. So Welch would have had to use trim to maintain controll in the XP-86.

The F-94C was also able to dive through mach 1.0 as was the CF-100, so they must have trimmable tails too. (One interesting note is that the 1946 Su-9,11 had a variable incedence tailplane among its inovations)

So this would also mean the Me-262 HG-III would need a variable-incedence tail to function as planned.

Personaly I think Welch's acheivement is more impressive than Yeager's as the Saber was able to takeoff and land under its own power and used an air-breathing powerplant. (not to mention it was a combat craft) The XP-86's sonic boom (the second one done less than 1 hour prior to Yeager's) shattered windows miles away, while Yeager's was mugh more subdued, more like thunder. (which, of course, is a sonic boom)
The Miles M.52 would hav been more impresive to see than the X-1, had it been completed. (plus it used Whittles reverse-flow W.2/700 albeit with reheat)

see: The Amazing George Welch: Part two


While possible that the Me 262 broke the sound barrier and survived it, the pilot's story could just as easily be explained as approaching mach .9+ and then regaining control in denser air.

The weirder part is what the US test pilot's handbook supposedly said in these cases. The US pilots clearly didn't exceed the speed of sound, what they seem to have experienced is exceeding .86 mach and regaining control at lower altitude.

from: The Story of my First Supcrsonic Flight on 9 April 1945 over Innsbruck

This report describes the experiences of a pilot in breaking through the sound barrier with an aircraft Me 262 which was designed for subsonic flight. The main characteristics of crossing the sound barrier in such an aircraft can be summarised as:

Firstly extreme buffeting and vibration
Followed by a short period in which the control surfaces are totally ineffective
The flame-out of the engines
After passing the barrier, normal control is restored.

Astonishingly it is reported on page 13 of the "Me 262 A-1 Pilot's Handbook" issued by Headquarters Air Materiel Command, Wright Field, Dayton, Ohio as Report No. F-SU-1111-ND on 10 January 1946:

"Speeds of 950 km/h (590 mph) are reported to have been attained in a shallow dive 20° to 30° from the horizontal. No vertical dives were made. At speeds of 950 to 1000 km/h (590 to 620 mph) the air flow around the aircraft reaches the speed of sound, and it is reported that the control surfaces no longer effect the direction of flight. The results vary with different airplanes: some wing over and dive while others dive gradually. It is also reported that once the speed of sound is exceeded, this condition disappears and normal control is restored." * See attached link above "Me 262 Handbook"

This report indicates that the effects experienced both during and after the transonic period were already known and this information could only have been obtained from the results of flights by English or American test pilots in 1945.

Also, prop driven (at least mixed-powered) a/c have broken the sound barrier.

From wikipedia.org

McDonnell proposed a naval version of the XF-88, a two-seat operational trainer, and a reconnaissance variant, but none were built. The first prototype was modified to XF-88B standard, with a nose-mounted turboprop engine added to the two existing turbojets. This was used for flight testing through 1956, and achieved speeds slightly exceeding Mach 1.0,[2], the first propeller-driven aircraft to do so. Both prototypes were scrapped by 1958.

 

[drgondog]

Area rule was what pinched the middle of the F-102 and got it renamed the F-106.
You've got the 102, 104 and 105 in production before that happens.
How can the F-100 be the last of the century fighters built before Area Rule became known?

Good catch. You are right about the 102. I was disconnected there because it was first applied to 102 design (after flight test) because of dramatic difference in actual performance with 102 body versus predicted performance. The F106 was the first production ship using whitcomb area rule.

Whitcomb first tested the 'area rule' in a NACA wind tunnel in 1952. By the time of his eureka the 100 was in production and the 102 had not flown yet but was in advanced design. The first flight of the 102 was in late 1953 and by that time the F-104 design was nearly finished - ditto F-105 so they were too late to fix.

As for WWII aircraft reaching the speed of sound, its said that many a pilot either died or almost died because they lost control of their airplanes in a steep, fast dive.
I don't think any plane in WWII actually broke the sound barrier, but I believe many came very close. At least up to .9 mach, as there are many stories of pilots reaching 700MPH in a dive (seems mostly from P-38 pilots).

That is all about major airspeed indicator errors due to full lack of knowledge about pitot tube corrections in transonic to supersonic speeds. I suspect nobody got much more than .01 -.02 above Machcr at the very most before losing control completely when the shock wave started moving aft.

...but you also mentioned how compressability "fooled" the a/s indicators.
Could you please explain that in more detail?
I am curious how that situation could exist and what did NASA (NACA) do to modify the a/s indicator on "Glamourous Glennis" so that it would read corrrectly?

Elvis

In Incompressible flow there is no assumed change in density as a function of velocity nor are temperature effects below transonic flows important. So velocity readings from stagnation pressure would yield a pretty accurate velocity... whic assumes constant density and no temp change.

But in compressibility regions, reading simple stagnation pressure goes out the window as both density and temperature changes as a function of velocity.

None of the instruments in WWII made any corrections for compressibility.

I do not know what Glamorous Glennis used instrumentation wise.

 

[kool kitty89]

Also, even in the later 1940's publication movie, the narrator says "the first time in level flight" and "for the first time, except in dives" obviously implying the actions of the XP-86. Though the Sabre's feats were never officially accepted, they've never been denied officially either. There also were 2 sonic booms to to substanciate Welch's 2 dives.

While Delcyros showed that it is technically possible for the Me-262 to survive Mach-1, its hard to proove that it was done. Plus no sonic booms were noted, though these may have been confused with explosions from the crashing 262 that the Mustang had shot down. And it was war so such sounds would not be as closely scrutinized I guess.


Is it true that conventional Elevators will regain control once the sound barrier is broken? Or is this incorect.

And I still dont know about: Do you have to have a slab, all-moving, all-flying, variable incedence, or fully-trimmable tail to maintain elevator control at transsonic speed?

From what I read on the F-86, the E model was the first to use the all-flying tail, so earlier models must have had a normal elevator combined with a fully-trimmable tail. So Welch would have had to use trim to maintain controll in the XP-86.

The F-94C was also able to dive through mach 1.0 as was the CF-100, so they must have trimmable tails too. (One interesting note is that the 1946 Su-9,11 had a variable incedence tailplane among its inovations)



I wonder if it would have been possible for the P-80 to do so too... (if any it would have been the more-powerful C model with 5,400 lbf with W/M injection)

 

[HoHun]

Hi Kitty,

>So this would also mean the Me-262 HG-III would need a variable-incedence tail to function as planned.

The Me 262 actually had a variable incidence tail that was moved for trim.

Regarding the resulting control forces, here is an interesting comment by Eric Brown (from Flight Journal Special Winter 2000):

"In the dives from 30,000 ft, the nose started to drop at Mach 0.83 and a 30-pounds pull was required to maintain the 25-degree dive angle. As the Mach number increased a violent buffeting set in, and the aircraft became progressively nose-heavy, so a pull force of about 100 pounds was necessary at Mach 0.86 to keep the dive angle constant."

His dives were carefully prepared in order to measure the maximum possible Mach for the Me 262, including carefully pre-setting the optimum dive trim on the ground.

Regards,

Henning (HoHun)

 

[kool kitty89]

I was just wondering if conventional control surfaces (elevators) work once the barrier is broken. (as has been suggested several times)

Otherwise all a/c that use conventional elevators and have broken the sound barrier in dives must have had trimmable tails to maintain controll. (ie pre-E model Sabres, F-94C starfire, CF-100, possibly Me 262) But welch makes no mention of trimming durring his flights, so did the XP-86 have an all-flying tail?

Technically the X-1 could have broken the sound barrier much sooner, utilizing dives, but it still wasn't able to take-off on its own, and wasn't air-brething. Plus it seems the AAF took-over the project from Bell, so a millitary officer would be the first to acheive it. The Miles M.52 would have probably beaten both of them though IMHO. (at least in dives)

 

[davparlr]

Area rule was what pinched the middle of the F-102 and got it renamed the F-106.
You've got the 102, 104 and 105 in production before that happens.
How can the F-100 be the last of the century fighters built before Area Rule became known?

Elvis

This is incorrect. Even before the YF-102 first flight, it was known that it was likely that it was incapable of going through the sound barrier. Four YF-102A were constructed implementing the "area rule" with longer nose, pinched in waste and added fairings to the tail section. The YF-102A succeeded in breaking the sound barrier. The F-106 was an entirely different bird. All the other aircraft you mentioned came after the "area rule" was implemented on the F-102A and all have "area rule" incorporate in their design.

 

[davparlr]

It is hightly unlikely that any pilot, in this era, could accurately report passing Mach 1 without an aircraft properly instrumented to detect Mach 1 flight.

 

[magnocain]

Perhaps if someone rode in a Grand Slam with a little motor hooked up to it...that would break the sound barrier.