The sound barrier

[Soren]

Going supersonic was definitely possible for the Me-262, however that it did happen and the guy who experienced lived to tell the tale I doubt abit. The Me-262 would be uncontrollable in pitch after 1,100 km/h, so diving to Mach 1 and surviving it would've been a great feat!

[drgondog]

Originally Posted by delcyros

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.

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

[Soren]

Above 1,100 km/h the Me-262 would start to pitch down with no means of stopping this, only rudder and aileron control remained.

So kudos to any pilot who survived a Mach 1 ride in the Me-262 !

[HoHun]

Hi Delcyros,

>The below page is from appendix II and shows how narrow to frame for reaching Mach 1.0 is at a pure vertical dive.

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.

Regards,

Henning (HoHun)

[Hop]

Not quite correct Aussie.

The Spitfire was a PR XI.

The pilot Martindale landed the Spitfire (EN409) but the reduction gearbox was missing as was the prop. The main engine bearer had buckled.

There's a lot of confusion about the speed the RAE got, and what happened to the Spitfire involved.

The RAE report from January 1944 gave a figure of mach 0.89 obtained in the dive. They thank the pilot, Squadron Leader Tobin, and say the aircraft involved was EN409. They give a chart showing the speeds, g forces etc, which indicates a normal pullout. There is no mention of damage sustained.

Several months later the same Spitfire, EN409, was involved in the incidents you relate whilst flown by Martindale. I haven't seen any reliable record of the speed obtained on those flights.

So EN409 got up to mach 0.89 with no reported damage when flown by Tobin, and suffered problems some months later when flown by Martindale, at an unknown speed.

[delcyros]

Originally Posted by drgondog

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]

Originally Posted by 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?

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]

Originally Posted by renrich

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]

Originally Posted by renrich

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.