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]

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]

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]

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]

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]

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]

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.

 

[Soren]

Bill,

The study no doubt took in to account the structural integrity of the a/c, infact that is mentioned, otherwise it wouldn't be a serious study. However it was a serious in depth study Bill, not some amateur's go at trying to resolve some issue by assuming this and that.

And just because I don't have the report doesn't mean it isn't valid Bill, don't try to muddy the waters by suggesting such nonesense. I don't have to prove why the Me-262 could go supersonic in a dive, professional aerodynamicists have proven that it could by taking all aspects into account, otherwise it wouldn't be a serious study. So I am truly sorry Bill but I believe the professionals who took the time to study the issue in its entirety more than some hunch by a retired aero engineer.

So stop the twisting and turning and accept what the professionals have said on the subject, or are you suggesting you know better than them ? I aint.

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.

Only a few exhibited this behavior Bill, not all, which can be attributed to the varying degree of quality the a/c were being built to depending on which factory they came from.

 

[Juha]

Soren
Delcyros, who has read the study wrote: "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."

Compare it to your own comments for ex. Your #61
"It has been solidly confirmed by studies done in Germany that the Me-262 was perfectly capable of breaking the soundbarrier."

And Mutke, who was a very "green" Me 262 pilot at the time, still in his training phase, made his claim public only in 90s

Juha

 

[Soren]

A normal Me-262 in 1945 wasn't of very good quality Juha, so obviously there would be structural issues. But a Me-262 built to the standards of those made in mid 44 would be perfectly capable of breaking the soundbarrier without breaking apart. However, and yes I read the report as-well, distortion of the wings and popped rivets are to be expected.

But as the report states even a "normal" Me-262 could break the sound barrier, but damage to the airframe was to be expected. Still it holds true that the a/c was perfectly capable of breaking the sound barrier, but it was no walk in the park and it was dangerous.

Btw, Mutke isn't the only Me-262 pilot to have claimed breaking the soundbarrier.

 

[Soren]

Anyway the British claimed they reached 0.9 Mach with the Spitfire which is a propeller driven a/c with zero thrust at such speeds, while the Germans claim to have gone Mach 1 in a dive with a Jet fighter which not only was much cleaner but also had available a lot of thrust at such speeds.

 

[drgondog]

Bill,

The study no doubt took in to account the structural integrity of the a/c, infact that is mentioned, otherwise it wouldn't be a serious study. However it was a serious in depth study Bill, not some amateur's go at trying to resolve some issue by assuming this and that.

If there is 'no doubt' they took structural integrity into account could you please show the discussion? I haven't seen or read the report so I make no claim one way or the other. Is what Delycros and Juha correct regarding what they read? Yes or No.

And just because I don't have the report doesn't mean it isn't valid Bill, don't try to muddy the waters by suggesting such nonesense.

Soren you have already demonstrated your inability to read a technical report and comprehend what it says - vis a vis the Lednicer report. I am not suggesting the 'professional aero's' didn't know what they were doing - I am suggesting that You don't know what you are talking about.

Muddying waters in this case is posing questions that concerned Messerschmidt at .83-.86 Mach, but you, in your infinite technical capability assume that the 262 could achieve Mach 1 - intact - without any analytical evaluation, or producing any technical analysis by competent people.

You seem offended when you make BS statements about subjects you really aren't competent to discuss - and people ask you for substantiation in the form of reports or sources.

I don't have to prove why the Me-262 could go supersonic in a dive, professional aerodynamicists have proven that it could by taking all aspects into account, otherwise it wouldn't be a serious study.

Soren, no you don't have to prove it. You are not capable of proving it.

However if you cite a respected reference as proof - then a.) cite the source and b.) produce their analysis. The report could be an excellent report and in all probability WAS a serious study. Your ability to a.) read it, b.) understand it, and c.) report your understanding true to the report - is what I am questioning.

Otherwise the phrase you ought to cling to is "I believe this to be true but I can't produce the evidence - you (the audience) will just have to accept my opinion on this"

So I am truly sorry Bill but I believe the professionals who took the time to study the issue in its entirety more than some hunch by a retired aero engineer.

Soren - you demonstrate a charming characteristic of believing what you want to believe - independent of the facts or different opinions supported by facts.

So stop the twisting and turning and accept what the professionals have said on the subject, or are you suggesting you know better than them ? I aint.

I don't believe I have been 'twisting and turning' with you - I am willing to accept what the 'professionals said' based on the report I read, understand the assumptions that were made, and understand the analysis that was performed based on the assumptions. At that point I will depend on my own judgement to accept, or reserve judgement.

What is your method in evaluation of aerodynamic or stability and control or structures modelling? Share it with us so we can be enlightened? I would REALLY LOVE to hear your thoughts on modelling an airframe structure.

Only a few exhibited this behavior Bill, not all, which can be attributed to the varying degree of quality the a/c were being built to depending on which factory they came from.

Soren, are you the same guy that shouted everyone down on the superior quality of German manufacturing a year or so ago?

For the sake of arguement, what are your facts on the quality of the 262 being built in 1945? Do you have manufacturing quality reports from Erding, etc? Where is your evidence of superior quality between factories? What were the standards for airframe acceptance? What components do you believe constituted sub quality with respect to Messerschmidt published standards?

Where was the 'point of failure' for the 262 when it did fail in a dive? Can you link that to quality or Structural failure based on stresses beyond limit load design?

You are exceptionally slippery when you get cornered.

1.) you point to 'professionals' and the report as acceptable to you, but you fail to submit the report and/or specific quotes from that report which a.) state the 262 unequivocally can attain Mach 1 with no question regarding stability or structural issues, and b.) support the conclusions with the analytics.

2.) you launched into a BS claim regarding 'commonly used aero term of 'Lift Loading' in context of performance criteria - and claimed that Lift Loading is WL/Clmax and is a comparison of turn performance.

3.) You cite Mutke's report of exceeding Mach 1 based on his interpretation - but not substantiated nor evidence in fact from a third party - but you reject other claims by Brit tests regarding a Spit diving speed held under test conditions, or Encounter reports claiming '660 mph' dive in a Mustang. In other words you are selective in parsing statements until you find one you like - that then becomes your 'fact' foundation.

You can call me an amateur aero or structures guy if you wish. I have been out of the business for 30 years. But the ad hominem attack does nothing to bolster your own credentials or even provide a basis to attack mine.

You are a funny guy Soren..