Call for Me262 structural strength info

[Krusty]

This thread is to collect data on the structure and limits of a 262 in regards to maximum allowable G-forces.


In another thread, HoHun mentioned something:

"I just looked up the construction description for the Me 262, re-produced in Radinger/Schick's "Me 262", and it points out a maximum G load of G=7 for a maximum weight of 5700 kg. With the technical standards of the day, that would probably include a 50% safety margin before ultimate failure (which accordingly would have to be expected to occurr at G=10.5)."

He also mentioned that 262s had higher amounts of steel in their construction than other LW aircraft, and that possibly the wing spars were steel.


Main questions for this thread: Were the wing spars made from steel? If not were they particularly strong? What official records or other credible info is there in regards to how many Gs a plane could survive (not counting the pilot, we all know humans can black out, I'm interested in structural failure).

The intended goal for this thread is to supply new info and (hopefully) shed light on the 262 to get the current AH2-modeled wing snapping changed to a more tolerable limit. That is the goal. Whether the info supports it, I don't know.

If you have any info that might help this thread please chime in.

[EagleDNY]

I've got a couple of good books on the 262.  The following comes from "Me-262 arrow to the future" by Walter Boyne.  We picked it up at the Air & Space museum because it has a big section on the museums restoration of their 262, along with quite a few pictures of the 262 in semi-disassembled condition.  Good book folks - pick one up if you get to Air & Space.

Quote: (Pg 108)
  Even though early technical documents describe the Me 262 wing as being single spar, it is actually a two spar wing, with a very small channel section rear spar.  The main spar is an I beam which tapers from about 14 inches at the aircraft center line to three inches at the point where the wing tip attached.  The spar is made up primarily of chrome molybdenum steel, with aluminum webs, and is located at the point of maximum thickness in the wings, about 40% of the chord.  The entire structure creates a torsion box, except for the space aft of the main spar which houses the retracted landing gear strut, and with its heavy aluminum skin it was able to withstand great loads and was relatively easy to manufacture.  The aluminum skin was not anodized.  Early models were painted for corrosion control but even this was eliminated later in the war.
  The wing is made in two halves which were joined together before fuselage assembly.  The rear spar caps are connected by two steel plates, one above and one below.  The main landing gear wheels retract into the central space between the two spars.  The wing rib here is of steel and has doubler plates and reinforcements either riveted or spot welded as necessary.  It acts as a beam to transfer the vertical shears on the spars into the fuselage, and all the torsion in the wing into the two spars as vertical shears. (note: don't ask me what that means - I'm not an aeronautical engineer, but I gather its damn strong - EagleDNY).
  The wing is attached to the fuselage by means of the heavy ribs mentioned previously; a 20mm diameter bolt in single shear at the forward end is very accurately fitted and is the key for positioning the wing.  A similiar bolt near the rear spar has a looser fit, reflecting the German design philosophy of trading accuracy for ease of assembly.
  The slats are made of steel of .040 inch thickness, for strength and rigidity, and they run on tracks.  The slats are in three sections in each wing, with the two outboard sections being pinned together.  There is no syncronization with the inner wing slat.  The slats would begin to open at about 186 mph in a glide and 279 mph in a climb.  
  Each aileron is made in two pieces for installation purposes, with each half slipped over a hinge at its far end and then the other hinge bolted in via an access door in the top surface.  Self aligning ball bearing hinges acted as connecting points for the two sections also.  There is a ground adjustable tab for trim.
  The all metal flaps extend in two sections, one on each side of the nacelle; they run on completely internal tracks, and operate by one hydraulic cylinder in the right wing which drove them via a system of bell cranks and push rods.
  Altogether, the impression of the wing construction is one of elegant simplicity;  there seems to be an absolute minimum of structure, yet all components are of adequate size; some indeed seem to be oversize, because simplicity of manufacture came before weight control.
---------

They have wing loading figures for the 262, but I don't see anything on maximum G's before failure.  The pictures of the inside of this wing show the main I-beam spar, and it is a heavy looking beast.  

Now I must confess that I actually haven't ripped a 262 wing off as many describe.  I've managed to lose control in a dive and be unable to pull out, which is nothing other than straight up pilot error.  I figure on hitting the training arena and seeing what it takes to rip it.

EagleDNY
$.02

[Wolfala]

Wonder if Widewing has any NACA reports on them putting a wing up on jacks and testing it to failure like United Steel did with the Mooney wings.

[Krusty]

I don't think they'd do that at NACA -- they often preserved their craft for later testing, and the scarcity of 262s and the fact that no more were being made (thus no need to test their breaking point) probably means they didn't do this.

New designs I bet they would, but old designs? I think they'd stop after figuring out how well it flew.

[Debonair]

maybe the guys at stormbirds.com have a POH or something similar online.
they got a ton of info on their website...

[EagleDNY]

You'd think the luftwaffe would've had data if there were ANY wing failures.  Frankly, in all the reading I've done on the development and testing of the 262, I've yet to read anything about wing failure.  

Are there any good sites with translated luftwaffe docs on the 262?

EagleDNY

[EagleDNY]

Well, I did my testing, and yes, at high speed you can rip the wings off a 262 like it was an old french biplane.  

At 300 IAS - no problem - pulled up hard (pegged at 9 G's) and wings held up fine.
At 400 IAS - same thing, no problem
At 500 IAS - hard pull up left wings behind.

Also had her in control at the end of a dive at 640 IAS, and was able to pull her up and out fine as long as I didn't pull up hard.

I'm not sure this indicates a problem with the flight modeling as much as with the controls.  I'm not even sure that there is a problem with the controls other than the pilot on the other side of the screen not feeling the G's he's putting the plane through.  For sure, at high speed a sudden jerk of the stick pegs you out at 9+ G's and you rip it - but there is no way to tell exactly how many G's of stress I put on the wings in that case.  

Should the controls be stiffening up and preventing me from pulling these kinds of ultra high-g maneuvers at high speeds?  I don't know - I don't have any data (or even pilot notes) that tells me what the controls should feel like at 500 kts.  Should they stiffen up appreciably?  Should that prevent me from pulling up hard enough to rip the wings off?

I think I'd rather take my chances on ripping it instead of having the controls get neutralized at high speed.  Now that I know what rips it, I figure its pilot error from now on.

EagleDNY

[Mace2004]

OK, I did some quick tests off-line at 100%, 50%, and 25% fuel loads.  I used 300, 350 and 400 mph at 4kft.  Once stabilized at the test speed and alt I snatched the stick back as quickly as I could for a non-rolling pullout then went back and looked at the recordings.

Regardless of the weight I could pull 5.5g max at 300mph and at least 9g at 350mph without damage.  I say at least 9g since the G meter tops out at 9g.

At 400 mph, regardless of the weight, I could easily pull the wings off.
At 100%, 400mph I pulled off both wingtips.
At 50%, 400mph I pulled off one entire wing.
At 25%, 400mph, I pulled off one wingtip.

So, based on just this course quicklook, it appears that you should be safe in a wings level pull up to 350mph regardless of your fuel weight.  The airplane as modeled in AH can achieve it's structual load limit, regardless of fuel weight between 350mph and 400mph.

This does not seem correct to me but then I don't have any maneuvering diagrams to provide g available at the higher speeds and different weights.  What concerns be most is there doesn't appear to be any difference between light and heavy loads.  I would expect structual failure to happen at considerably lower airspeeds at high weights compared to low, this does not appear to be the case and may be incorrectly modeled.  A much more detailed test would better define the limits between 350 and 400mph and it woud be real nice if someone has the maneuvering diagrams so we can see what g is available.

Mace

[gripen]

AFAIK most late war German fighters were stressed for the H5K loading class at assumed combat loading, which means 7g with safety factor 1,8 ie breaking load factor would have been 12,6g. There were several exceptions, say various Bf 109 models with additional load, like cannons, which were stressed for H4 loading class.

The material of the structure is pretty much irrelevant assuming that the designers were able to do their work ie the specified loading classes were the same regardless the used material. There might be differences in the claimed lifespan of the structure depending on the material but that's an another story.

gripen

[HoHun]

Hi Krusty,

>He also mentioned that 262s had higher amounts of steel in their construction than other LW aircraft, and that possibly the wing spars were steel.

I have just found the relevant quote in Radinger/Schick's "Me 262" (p. 11):

"Weitgehende Verwendung von Stahl als Werkstoff, z. B. Flügelholm-Gurte aus keilförmig gewalzten Stahllaschen. (Zum Vergleich Me 109: 0,95 t Leichtmetall auf 1 t Flugzeug, Me 262: 0,55 t Leichtmetall auf 1 t Flugzeug.)"

Translation:

"Extensive use of steel as material, for example wing spar belts (walings?) from steel rolled into wedge shaped plates (lugs?). (For comparison Me 109: 0.95 t light alloys per 1 t aircraft, Me 262: 0,55 t light alloys per 1 t aircraft.)"

(Would be interesting to know the percentage for a MiG-15 or an F-86! :-)

Steel has different properties from aluminium, for example a more extensive region of plastic deformation so that there might be a fair region of the envelope where the spar bends without breaking, allowing a landing even if the aircraft has to be written afterwards. (This was the usual result of exceeding permissible dive speeds - it seems that you either pulled out or augered in, but always in one piece :-/

Regards,

Henning (HoHun)

[Krusty]

Originally posted by HoHun
Steel has different properties from aluminium, for example a more extensive region of plastic deformation so that there might be a fair region of the envelope where the spar bends without breaking, allowing a landing even if the aircraft has to be written afterwards. (This was the usual result of exceeding permissible dive speeds - it seems that you either pulled out or augered in, but always in one piece :-/

That is what I would have expected.

Funny that a 262 in AH can rip wings off (oh, and I've done it at 300mph and less, not the 400 in the tests), and a 190F-8 can rip both wingtips off in a vertical dive from 10k and pulling up at 3k (dropped a centerline bomb then pulled up).

Back when the new spits came out they ripped wings off at the drop of a hat. There was a bug with the G's being pulled. I suspect (wild guess) that this is also found elsewhere, just less noticable and thus un-corrected.

[HoHun]

Hi Krusty,

>There was a bug with the G's being pulled. I suspect (wild guess) that this is also found elsewhere, just less noticable and thus un-corrected.

Subtle bugs are the worst :-( If it strikes only very rarely, it can be very difficult to understand the exact circumstances and fix it!

I once read a book on steam engines, including a giant American engine with a front cab and the ability to control a second identical engine from the first one.

It was a marvel of engineering, but the railroaders despaired because it was so complex and unreliable. They said: "On a normal steam engine, it takes three minutes to find the problem, and three days to repair the engine. On this engine, it takes three days to find the problem, but only three minutes to fix it!"

They couldn't know it at the time, but such is the nature of bugs :-/

Regards,

Henning (HoHun)

[Charge]

"Funny that a 262 in AH can rip wings off"

It's almost as funny as 190F8 breaking wing tips in dive with bomb racks installed... It probably has so weak wing because the wing is so small and much of its weight is in wing structure...

-C+

[Krusty]

Note that the bomb was released when I pulled up, ripping both wingtips off. No more weight than usual.

[Debonair]

I wonder if Cory Lidle's last words were "this FM sux"