The sound barrier

[Crumpp]

As Bill points out, the measurement of velocity in the transonic realm was problematic in the late 1940's.

All power producer subsonic designs will have a very similar mach limit. The fact they have a propeller puts them in the same range for mach limits.

I calculated out Mutke's claims and under the conditions he states there is no doubt that he would have exceeded mach 1 IMHO.

However I highly doubt the conditions where as he stated. First his airspeed indicator is going to be very inaccurate in the transonic realm.

Secondly but most importantly, he would be exceeding the q-limits of the airframe. The q-limits for the Me-262 were in the vicinity of mach .8, well below mach 1.

The airframe simply cannot go that fast without turning itself into confetti. Could Mutke's airframe have been a fluke? Highly unlikely and just about requires a pointy tin foil hat to be worn.

Now this does not mean that everything in the cockpit and the behavior of the aircraft did not lead Mutke, who was not an engineer, to very reasonably conclude he exceeded the speed of sound.

All the best,

Crumpp

[kool kitty89]

Also, the non-area-ruled Convair XF-92, the first delta wing fighter, (and the first powered delta a/c to fly iirc, first in early 1948 for the experimental proof-of-concept craft) and the forerunner to the F-102 and F-106 was able to easily dive through Mach 1, even (albeit not as well) with it's original lower-powered J33 (5,200 lbf), and could almost sustain Mach 1.0+ after leveling out with the 7,500 lbf and later 8,400 afterburning J33. (providing a .5-.6 thrust/weight)

Also, the Skyray, which flew in 1951, well before the YF-100, was capable of exceeding Mach 1.0 in level flight, albeit not at SL, and didn't do so until after the F-100 had iirc, but the Skyray also held the world speed record over the Super Sabre for a time.

And actualy, Delcyros showed that, in verticle dives there is far les stress on the airframe, particularly the wings (as there is far lower wing loading on the lift surface), and that if a ~60 degree or steeper dive were attempted, it is possible to dive the 262 through Mach 1.0 from high altitude, albeit the window for conditions to allow this is fairly small. The airframe could survive, with some warping and only if trim was used to maintain control.

The F-84 could have probably dived through mach 1 had it used thin, low drag wings, as the fusalage mach limit was very high, though still trim would be needed to maintain control. The thick wings were a heavily limiting factor on the plane as exceeding Mach .80 at SL would result in violent pitch-up and if this was maintained, the airframe tended to desitegrate. (though on at least one occasion an F-84G did this intentionally to escape 2 Migs on his tail, one actualy crashed, while the F-84 survived with heavy warping to the wings) At higher altitude, exceeding mach .8 resulted in heavy buffetting.
The very clean airframe, despite the thick wings, can be seen in that The XP-84 was capable of 592 mph at sea level with only 3750 lbf (less thrust than the early P-80A) at a heavy weight of ~16,000 lbs. (thrust/weight of ~.23 and even lower on some later models, at MTO, except for the D and G, and even then <.25 @ MTO, due to weight increasing more than thrust)

The (wet) wings though, allowed for a 1,300 mi range on internal fuel only and a max range of 2000 mi with the F-84G with a top-speed of 622 mph at SL. So a thin wing would have been useful for a shorter ranged craft, but not for escort and should have made an excelent intereceptor. Even such a re-winged version should have ~1300 mi range with droptanks, better than the Sabre, and would still have some escort capabillities. Speed would probably increased to ~620 mph at altitude and 650+ at SL.

[davparlr]

Originally Posted by drgondog

Dave - I don't doubt the quote but it's awfully hard to see any pinch on 104 - especially from below.

I whole heartedly agree but the cross sectional area of those little razor blade wings would be VERY small so the fuselage corrections would also be very small and probably difficult to detect. Any info on the F-101?

In pilot training, we had a student from Afghanistan who was terrible but since this dad was the chief of the Afghanistan AF, he was basically ordained to complete the course. It took him two years to finish a one year course. After graduation he went on to fly F-104s. He is probably dead.

[drgondog]

Originally Posted by davparlr

I whole heartedly agree but the cross sectional area of those little razor blade wings would be VERY small so the fuselage corrections would also be very small and probably difficult to detect. Any info on the F-101?

In pilot training, we had a student from Afghanistan who was terrible but since this dad was the chief of the Afghanistan AF, he was basically ordained to complete the course. It took him two years to finish a one year course. After graduation he went on to fly F-104s. He is probably dead.

Dave - I agree that if the 104 had area rule design it would be tough to spot and no,even on the usual on-line references on the 101, I can't find any discussion on area rule. It's first flight was in same year as F-104

[kool kitty89]

It was mentioned earlier that slab elevators, all-flying tail, all-moving tailplane, stabilators were require to maintain controll in the trans-sonic region and to maintain control past Mach 1.0. Or short of this, requiring a fully trimmable/variable incidance tailplane to recover from a supersonic dive. (which the Me 262 had, and the early F-86)

Originally Posted by drgondog

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.

I know some of this had already been dealt with and Delcyros listed the study showing it was possible for the 262 in the right conditions. And, though stick forces would have been to heavy to recover with, trimming the tailplane would work.

I finally found an answer to my earlier question about normal elevators' effectiveness in the trans-sonic region and at Mach 1.0+ and their functionallity. The first thing that made me question this is that the XP-86 and early production F-86's used a normal elevator with a fully trimmable tailplane, but from pilot accounts (and Welch's notes) trimming the tailplane to recover from supersonic dives is not mentioned.
When nearing Mach 1 a shockwave will develop on the tailplane which will become increasingly strong as speed increases, making the the stick forces for the elevator very high and eventually useless. Hence why this cannot be used for the 262.
Then I read a little more into the XP-86/F-86 anf found out tha while they still used conventional elivator system but with hydrolicly boosted controls which allowed much more force to be applied than a pilot is capable of with manual controls. Thus, while the elevator controls still become less responsive at trans-sonic speeds they will still function.


And also there have been a number of straight winged fighters capable of controlled supersonic dives. They include the F-94C Starfire, CF-100 Canuck and a couple others. (all being all-weather interceptors iirc)

[SoD Stitch]

Originally Posted by drgondog

Dave - I agree that if the 104 had area rule design it would be tough to spot and no,even on the usual on-line references on the 101, I can't find any discussion on area rule. It's first flight was in same year as F-104

AFAIK, the first aircraft to have the "area rule" applied to it was the F-102, and only after it failed to achieve supersonic speeds in level flight; after the fuselage was given the "area rule" treatment, it achieved Mach 1+ with no problem, even on the under-powered J-57.

[samd]

My G-pa claimed that they had a P-47 in the South Pacific that he swore broke the sound barrier in a dive. It appears there are a number of technical issues that makes this seem impossible. He was awfully sure of this claim and he was very a intelligent engineer and understood what it meant to accomplish this. He clearly spoke of the mechanical limitations of the aircraft and he still smiled and said "we did it long before everyone else!" What could the explanation be? Did the pilot get an inaccurate airspeed reading? Was he just trying to impress the grandkids?

[Soren]

Well, if any a/c could have done it in WW2 it would've been the Me-262, and recent aerodynamic studies made in Germany have confirmed that it is perfectly possible that it did as the airframe was capable of it. I personally believe that it could. Another a/c which is also claimed to have broken the sound barrier before Yeager is the F-86 Sabre, and there is no doubt about this one IMO cause I don't see a single reason for why it shouldn't be capable of it. Still there are people who insist Yeager was the first, which I believe is bullcrap really.

As for the P-47, no chance, the propeller wouldn't allow it along with the larger frontal area.

[FLYBOYJ]

The F-86 was capable of breaking the sound barrier with ease and did so on many occasions including during its initial flight testing. We had the thread about George Welch who allegedly did it just prior to Yeager’s flight just to piss him off, and that event was witnesses by many people who heard the sonic boom.

Yeager's flight will alwasy be recognized as the first because of the actual telemetry tracking and witnesses on hand - it was an "official" event.

[Waynos]

The highest recorded speed achieved by a piston engined aircraft was mach 0.94 in an 84 Sqn Spitfire F.22 over Hong Kong in 1954 just prior to the Spit's final retirement from the RAF.

It was concluded in a series of RAE tests during, and immediately after the war that the Spitfire was the fastest diving aircraft of WW2, including jets, due to its extremely thin wings which were the thinnest on any production fighter and delayed the onset of drag sufficiently for the Spit to pull ahead in a dive against *anything* else.

There are various references to this research in several books, one of the them is the Putnam volume on Supermarine aircraft and another is Jonathan Glancy's biography of the Spitfire. A quote from one of the test pilots which I love was "we flew everything from Spits and P-51's to the newest jets, our own and the Germans, our job was to dive as hard and as fast as we could and then fire the guns to see if the wings came off".

Nice job!

I also have a book (Buttler - German Secret Projects) that attests to RAE findings that the Me 262 and 163 were aerodynamically and structurally incapable of exceeding m 0.86 being confirmed by Willy Messerschmitt himself who said that this was never a consideration in their design and if it had been both aircraft would have looked very different.

[pbfoot]

Originally Posted by FLYBOYJ

The F-86 was capable of breaking the sound barrier with ease and did so on many occasions including during its initial flight testing. We had the thread about George Welch who allegedly did it just prior to Yeager’s flight just to piss him off, and that event was witnesses by many people who heard the sonic boom.

Yeager's flight will alwasy be recognized as the first because of the actual telemetry tracking and witnesses on hand - it was an "official" event.

It was standard training for all the Sabre drivers to bust mach and with a little search on google came up with this
F-86 Sabre Mach Busters Club card, issued by North American Aviation

[Waynos]

I also found this photo of Sqn Ldr Martindales aircraft following the mach 0.89 dive;

[HoHun]

Hi Samd,

>What could the explanation be? Did the pilot get an inaccurate airspeed reading? Was he just trying to impress the grandkids?

There are several factors that tend to exaggerate the speed reading, one of them being the speed indicator's inability to account for compressibility effects. Another aspect is that to get your true airspeed, you'll have to correlate indicated air speed and altitude, and the altimeter had errors of its own, especially at high speeds and during rapid altitude changes. You also need to keep track of the exact temperature - everthing combined, it's quite difficult to reliably track the data if no recording device of some kind is used.

I'm sure your grandfather honestly considered his speed figures accurate, as many other people associated with high speed dives during WW2 believed too that they had achieved speeds that - as we know from hindsight - were unrealistic for the aircraft type in question.

High-speed dive tests were at the leading edge of scientific progress in these days, and I think it's quite credible that people with good education but no access to the latest research results would tend to over-estimate speed readings despite striving for the best possible accuracy. This was not an uncommon experience - you'll find similar stories for several aircraft types, both by Allied and Luftwaffe personnel.

Regards,

Henning (HoHun)

[kool kitty89]

Originally Posted by Waynos

The highest recorded speed achieved by a piston engined aircraft was mach 0.94 in an 84 Sqn Spitfire F.22 over Hong Kong in 1954 just prior to the Spit's final retirement from the RAF.

It was concluded in a series of RAE tests during, and immediately after the war that the Spitfire was the fastest diving aircraft of WW2, including jets, due to its extremely thin wings which were the thinnest on any production fighter and delayed the onset of drag sufficiently for the Spit to pull ahead in a dive against *anything* else.

Maybe for absolute speed, but certainly not for dive acceleration. Even the former would seem rather unlikely. The Spitfire had a NACA 2213 (13% thickness) airfoil at the root (tapering to 2209.4 at the tip, the root being the limiting factor as far as critical Mach is concerned). Both the Meteor (12.5% tapering to 10%) and the Me 262 (11% to 9%) had wings significantly thinner than the Spitfire's. The P-80 used a 13% laminar flow arfoil along the entire wing and the P-84 used a continuous 12% airfoil.

I also have a book (Buttler - German Secret Projects) that attests to RAE findings that the Me 262 and 163 were aerodynamically and structurally incapable of exceeding m 0.86 being confirmed by Willy Messerschmitt himself who said that this was never a consideration in their design and if it had been both aircraft would have looked very different.
I'm not sure of the Me 163's wing root TR, the LE wing slots may also have been a problem, as may have been the wooden wing, I'm not sure. In the case of the Me 262, as I already mentioned the Me 262's wing was considerably thinner than the Spitfire's. Additionally the airfoil (a modified NACA 00011-00009 airfoil) was symmetrical, had a sharper leading edge, and had the max thickness farther back (35% root, 40% tip, compared to the normal 30%) which would have increased critical Mach of the airfoil.

The main cause of disintegration of the Me 262 in Mach .86+ dives would be excessive -G loading resulting in the pitch-down behavior resulting from changes in trim from Critcal Mach. As its elevator is ineffective in these circumstances, trimming the (all moving) tailplane should be able to correct the pitch down and allow some pitch control (and the ability to recover) at these speeds.

I'm also not quite sure what "looked quite different" would imply. (Swept Wings and tail surfaces?

I've read this about the Spitfire before, and it bothered me as (using high-speed a/c with similar wing thickness as comparisons) those Mach values should be well over the Spitfire's critical Mach number. (~.80-.82 going by the P-80, Meteor, and P/F-84) So either the data is wrong, or the Spitfire's elevator remains effective above critical Mach.

[kool kitty89]

http://www.ww2aircraft.net/forum/avi...speed-802.html (WW2-fighter and critical Mach speed)

Actually It seems the Spitfire didn't have any pitch control ability (except maybe trim) at these high Mach numbers, though maybe it didn't suffer the same pitch-down problems as many others at Critical Mach. (like the Me 262, aileron control remained due to the thinner outer wing)


also see: The Incomplete Guide to Airfoil Usage
for airfoil info