The sound barrier

[Juha]

Soren
I asked independent proof, like flight test recorder. Not what someone claimed 20 years after the test.

Juha

[Waynos]

Yes, it was 13% at the root tapering to only 9% further out. I think this is what made the difference, from what I have read other fighters wings did not do this, though I stand to be corrected if this is not the case.

As I mentioned earlier, during the 1946 tests Supermarine were quite perturbed to learn that their brand new, laminar flow winged, Spiteful was actually slower in the dive than the Spitfire was, especially as this same wing was being grafted onto their new jet fighter, the type 392, which had started its development as a jet-Spitfire! The production Attacker emerged with a max level speed of 590 mph in 1947, about 50 more than the 262, but it still could not outdive the Spitfire.

[kool kitty89]

Tapering the wing thickness/chord was a rather common feature, the P-36/P40, for example, had a root section of NACA 2215 (15%) and 2209 (9%) at the tip. It seems tohave been rather uncommon for a wing to feature constant thickness. (though iirc the Whirlwind featured a constant NACA 23015 from root to tip, and the P-63 featured a constant 16% laminar flow airfoil)

The Me 262's airfoil was 11% at the root and 9% at the tip. (~8.6% taking sweep into acount)

However it would be the root (as it's the tickest) that would reach critical Mach first.
If the Spitfire's tailplane was thin enough and the tail didn't become immersed in turbulent flow from the wing above critical Mach, the elevator would still function up to until the tailplane its self reached critical mach.


As to the a/c being able to recover from a terminal dive, as can be seen in Ponsford's chart, the spitfire was only above ~.82 Mach from ~33,000 ft to ~22,000 ft. (for a total of ~22 seconds, and above .84 Mach for ~18 seconds) And the recovery was made well below these altitudes.

[kool kitty89]

Originally Posted by Soren

The British however don't seem to have known about the full use of the fully movable horizontal stabilizer trim and used only the trim tabs, which explains their findings.

Soren did the Me 262 feature functioning elevator trim tabs?

According to US reports, the a/c tested a Wright field apeared to be intended to used adjustable trim tabs for both the elevator and ailerons, but the ailerons were only fitted with ground-adjustable tabs, and the elevator tabs had been riveted in place. (trim being effected by the adjustable tailplane) The rudder being the only surface fitted with an in-flight adustable trim tab.

The US manual on the Me 262 also warned against using stabilizer trim changes when entering or recovering from dives as it could lead to overcontrol and possible overstressing of the airframe. (the manual did make many refrences to the stabilizer trim, so, at least for tests at Wright field, they were well aware of its use)

[ponsford]

Originally Posted by Juha

Hello Ponsford
you beat me by 20 minutes, I just dug out my copy of that report from the hard drive of my second pc (ret.). But the main thing is that the report is posted here.
The key word is TYPICAL, it wasn't just one odd dive but series of dives flown by the pilots of High Speed Flight Section, one of which was certain Lt Cdr Eric Brown.

Juha

Addition, Ponsford, P-51B might well have done better, if not for other reason at least it could have climbed higher, Allison Mustang dives were started at 28000ft because of its ceiling limitations.

Sorry about that Juha. It wasn’t intentional, honest Good point about the altitude of the Mustang. That hadn’t occurred to me. I just remembered this report on the P-51 D dive:

Compressibility Dive Tests Part I on North American P-51D Airplane (Mustang IV), AAF No. 44-14134

“The airplane was flown to a maximum true Mach Number of 0.85 during the twenty-sixth dive on 9 September 1944 and to a maximum calibrated airspeed of 486 MPH during the twenty-eighth dive on 9 September 1944.”

“In extreme war emergency the airplane can be dived to a Mach Number of 0.83 (400 MPH Indicated Airspeed at 25,000 feet) if a very gradual pull-out is made.”

[drgondog]

I have seen several references from NAA, USAAF and RAF that detailed terminal dives - all peaking at .85, and very descriptive of the 51D/Mustang IV at 'the edge' - particularly the strengthened ammo cover door bulge..and severe buffeting

It is also clear that the Spitfire dive tests under similar test conditions and calibrations achieved a higher Mach than the 51.

Instrumentation being what is was in 1944-1946 leads one to obtain a full report to determine the methods of calculation - most of which were instrumentation corrections using analytical methods for compressibility.

I have yet to find a definitive dive report on the 262 (i.e. not anecdotal) which describes the dive, the tuck and the methods used to a.) warn of the phoenomena and b.) the approved Me method of recovery. Perhaps Soren has one.

[Soren]

Originally Posted by kool kitty89

Soren did the Me 262 feature functioning elevator trim tabs?

Yes ofcourse, I have no idea why the one at Wright field didn't.


For reports on the Me-262 read here:
Flying the Messerschmitt Me-262

[drgondog]

Originally Posted by Soren

Yes ofcourse, I have no idea why the one at Wright field didn't.


For reports on the Me-262 read here:
Flying the Messerschmitt Me-262

So, now that you acknowledge that a trim tab existed on the 262 slab tail - what is the answer to the high mach tuck issue? and why the trim tabs weren't the solution?

[Soren]

Acknowledge ? Bill I've never claimed there weren't any, I just pointed out that the entire horizontal stabilizer was used for trim, esp. in cases where the trim tabs weren't enough. (The Bf-109 had the same feature, which is what allowed it to recover from high speed dives quicker than other fighters)

The only way to get out of the negative G dive the Me-262 would start after 1,100 km/h was to utilize the movable horizontal stabilizer, the elevators and therefore also trim tabs being rendered useless because of turbulent flow.

[kool kitty89]

http://www.zenoswarbirdvideos.com/Im...otHandbook.pdf

Soren, that site had the very manual I was referring to. (with the comment of no functioning trim tabs) Accordingly, all trim changes for pitch are made by adjusting the horizontal stabilizer.

Elevator trim tabs would seem redundant given the stabilizer trim, did the Bf 109 feature elevator tabs as well?

I didn't see any mention of elevator tab controls in the cocpit instument pannel diagrams, but I haven't read the other articles there yet.

[Soren]

Soren, that site had the very manual I was referring to. (with the comment of no functioning trim tabs) Accordingly, all trim changes for pitch are made by adjusting the horizontal stabilizer.

But that is the Me-262 at Wright field, not the one in Britain. That the Me-262 at wright field featured rivetted trim tabs is very unusual.

As for the 109, it has elevator tabs as-well yes.

[kool kitty89]

http://www.zenoswarbirdvideos.com/Im...E262WendeL.pdf

I finished reading through the British article and found no menthin to elevator trim tabs, the rudder tab was mentioned several thimes though. Also, the tailplane trim was mentioned in this article as well.

[Soren]

Here's a picture of the RAE Me-262, you can slearly see the tabs:

[kool kitty89]

Soren, I know the tabs exist, but that doesn't mean they were used.
Accoring to this extensive article on the Me 262's construction: http://www.enginehistory.org/German/...Airframe_2.pdf

It mentions that:

As is the case with several other German planes, the 262's all metal stabilizer is adjustable, the incidence being changed by a small electric motor operating a screw jack mounted inside the fin fairing on the front face of the frame to which the vertical fin is bolted. This unit is

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mass-balanced trim tabs set near the inboard end. These tabs were apparently designed as interchangeable servo units, for a small arm at the outboard end extends up from the right one and down from the left, and captured enemy documents show an anchoring arm designed into the stabilizer trailing edge. However,the operational experience or Allied bombing made completion of this plan impossible, for the tab arms were not connected to the stabilizer and, in fact, the tabs had been riveted into immobility by small gusset plates at each end. Nevertheless, each tab had four hinges, with ball bearing units at each end and pins through yokes forthe two in the middle. As is the case with the rudder trim tab, the trailing edges of the tabs are nicely flush riveted..

(the article also mentions the aileron tabs being intended to be of the in flight adjustable servo type, but were simple ground adjusted tabs in practice)


In any case, that British pilot's notes on the 1945 tests makes it clear that they were at least aware of the use of the tailplane trim. Indeed, there is no other mention to pitch trim than that pertaining to the variable incedence tailplane. (wether that trim function was used in dives is another issue)

[kool kitty89]

I believe one of the riveted gusset plates is visible in this immage:



Look closely at the inboard trailing edge of the tab on the right.



And on a somewhat different note:

Originally Posted by Waynos

Don't forget also the Miles 'Gillette Falcon', the first aircraft in the world to use an all-flying tail specifically intended for control at high speeds. It flew in 1944 and was built specifically in response to the need to be able to control the Miles M.52 at supersonic speeds. It is recognised that without this device Yaegers attack on the sound barrier in the X-1 could not have been successful so yes, the British were quite well up on this asp0ect of controllability at the time.

It should also be noted that, whaile not developed for high Mach number control, both the Bf 109 and Fw 190 featured variable incidence tailplanes. (for trim purposes; I believe the 109's mechanism was very similar to that of the Me 262)