The sound barrier

[kool kitty89]

Ok Bill, I was using .86 Mach. (I'd though the .84 was from the British test only)

Going back to the 560 kt comment on the Me 262 Project video, that value would fit very well with .84 Mach at seal level. (almost exactly for 20*C, 527.7 Rankine)

[drgondog]

Originally Posted by kool kitty89

Ok Bill, I was using .86 Mach. (I'd though the .84 was from the British test only)

Yes and yes from the reports I have read. Msmt test pilot Lindner recount

Going back to the 560 kt comment on the Me 262 Project video, that value would fit very well with .84 Mach at seal level. (almost exactly for 20*C, 527.7 Rankine)

Yes it would, but to get to that speed I believe he would be in a shallow dive? The guys on the Stormbird Project are very serious about a max 540mph on the deck placard according to the website

I just finished reading the Lindner debriefing report detailing the handling characteristics of the dive issues starting at .83 and increasing up to .86 at around 6,000 meters. The issue was a.) severe onset buffeting in the nose tuck and b.) major increase in stick forces from 15g to 50kg in that Mach range. The issue in getting out of this situation was on one arm a "110 pound curl to move the stick slightly aft" while freeing up the other hand for the trim wheel.

This suggests to me that the experience was the rearward movement of the aircraft wing center of pressure as the ship experienced Mcrit and the shock was was moving to the 50% chord region. It sounded like the slab tail was still 'effective' in the sense that it wasn't totally immersed in the turbulent flow.

Correspondingly the major stick forces in the cockpit suggest huge bending loads in the aft section at the vertical stabilizer/tail section attach points to
the fuselage... that should be the area of major potential failure

BTW - .86Mach at 6,000 meters is ~ 1001km/hr for STP as you probably know. About 529kts and 609mph.

I'm still digging to try to find any example of a complete push over to anything remotely looking like a vertical dive. By all accounts so far the factory Do Not Exceed was 950 with recommendations for nose up trim.

The Stormmbird Rising book by Morgan seems pretty comprehensive

[delcyros]

From what I have read, Messerschm. werkspilots carried out several test programs to establish high speed trials with the Me-262. The procedure was a gradual increase in dive angle which lead to a number of fatal accidents and was concluded with the established Mach numbers reported not to exceed.
This procedure was very dangerous for the airframes due to stress loads and no vertical dives were attempted.

[Soren]

According to the POH the dive speed limit is 1,050 km/h.

[pbfoot]

Originally Posted by Soren

According to the POH the dive speed limit is 1,050 km/h.

Whats a POH , Pilots operating handbook?

[Soren]

Roger that Pbfoot.

[Soren]

Correction, the dive speed limit listed in the POH was 1,000 km/h.

[kool kitty89]

That would be the indicated speed, correct?

[Soren]

Doesn't say, but the Me-262 had two air speed indicator needles, one listing IAS the other TAS so I suppose it is TAS.

[kool kitty89]

It wouldn't really give TAS though, it would be an altitude corrected value, but still with some limitations. (was temperature taken into account?) You mentioned earlier that the Me 262's airspeed indicator featured compressibility correction as well, correct?

[Soren]

I agree it wouldn't be the true TAS but rather an approximation of it. And yes AFAIK compressibility effects were taken into account as-well.

As for temperature, no idea mate, if so I would assume it needed to be punched in manually via observation.

[drgondog]

Originally Posted by Soren

Bill,

The reason the reproduction Me-262's aren't pushed past 500 mph should be quite clear to you. It isn't because of doubts regarding wether the a/c will disintigrate or not, it is for other obvious safety reasons only. They don't push Mustangs to 430 mph today either, or F-86's to 600 mph, again for safety reasons.

That's why Strega and others are doing 500mph on the deck - a much higher stress loading than 430 at 25,000 feet?

From the site:

The fact remains that the airframe was never designed to handle the stress loads encountered at speeds in the 600 mile per hour range. To push the aircraft into this environment simply because additional power "happens to be available" is a highly dangerous and ill-advised move.

Soren - what does "the fact that the airframe was never designed to handle the stress loads at speeds in the 600 mile per hour range" - mean to you?

In the interest of safety, the Me 262 Project will be placing a placarded airspeed limitation upon the jets in the vicinity of 500 MPH. The official position of the project is that there is simply no need -- or benefit -- in flying these aircraft any faster.

Re read it again - they are very explicit about concerns for the structural integrity of their 'new' Me 262s above 560TAS

Or would you advice them to put millions of dollars on stake just to try and break the sound barrier ?

Not if they believe it will disintegrate

Anyway I believe modern research done by professional aerodynamicists more than any hunch someone might have.

And the 'aerodynamic report has a Structural analysis and Stability and Control analysis section? I know I would go immediately to look for three sections. 1.) drag rise profile and engine inlet characteristics in the Transition Mach range, 2.) the control forces required to maintain pitch controls, 3.) the structural loads in the tail section.

Also - The 262 was also supposed to 'hunt' in yaw at speeds above 400kts, increasing as speeds went higher. If that characteristic worsened (why would it cease?) then rudder loads in that same transition area would force more torsion on the fuse/tail connect area of the 262.

Now Soren, how fast do you think a cloud of debris can fly? and what substantiation from 'professional design team' comprised of aeros, structures and Stab/Control guys lead You to think it is 'doable'? You are an expert capable of making those judgments absent the data?

I have been out of the design biz for a long time - so perhaps you can enlighten me in the latest technology for aero analysis that predicts asymmetric loads in transonic flow conditions?? So that we can look at yaw and dutch roll initiation, get the combined rudder/elevator trim requirements and look at the incremental loads from those two?

Does your 'professional study' detail these conditions? Can you interpret the 'study'? Have you read the study?

A pure Aero Analysis might show that with enough power you could shove that beast past mach 1 - but a pure aero analysis would not include a structural analysis unless it was further modelled with the aero loads into something more sophisticated than NASTRAN or Stardyne. You have THAT report handy?

Produce it please?

Show us the report Soren.

[drgondog]

Originally Posted by Soren

I agree it wouldn't be the true TAS but rather an approximation of it. And yes AFAIK compressibility effects were taken into account as-well.

And if it is an 'approximation' - how reliable is it?

As for temperature, no idea mate, if so I would assume it needed to be punched in manually via observation.

A thermocouple inserted in the fuselage aft of the cockpit would serve. It would be easy to determine what the speed of sound would be at the altitude the 262 was flying - it would not be affected by compressibility effects.

Getting TAS is quite another issue altogether anywhere near .8-.9 M in those days... and therefore any reference to actual Mach based on 262 instruments would be 'suspect'

[davparlr]

Originally Posted by Soren

Doesn't say, but the Me-262 had two air speed indicator needles, one listing IAS the other TAS so I suppose it is TAS.

Aircraft performance limitations are typically given in IAS/CAS, which closely reflect the aerodynamic forces on the aircraft. For pilots, TAS is mostly used for navigation purposes. TAS is also used in comparing absolute performance comparison between aircraft, as with this site.

[drgondog]

Originally Posted by davparlr

Aircraft performance limitations are typically given in IAS/CAS, which closely reflect the aerodynamic forces on the aircraft. For pilots, TAS is mostly used for navigation purposes. TAS is also used in comparing absolute performance comparison between aircraft, as with this site.

Absolutely - the IAS also has to be coupled with knowledge of altitude in the case of these birds - and was similarly screwed up by compressibility effects anywhere near .8 M.