Ki-84's Most Absurd Feature

[2bighorn]

Post-war tests... The enemy was no longer relevant.

For the record, early 1945 (January-March), enemy was still very relevant, especially in the Pacific

[Brooke]

Howdy, Nrshida.

If you look into the structure of this aircraft you can see how it is a little unusual and should have a good deal more integrity than a Spitfire, say.

No one can tell at all from looking at the structure.  You can't tell by eye if a control surface will experience catastrophic flutter at a particular speed.  As one example, there was a fatal crash at Reno Air Races a while back where an unlimited racer (based on P-51 but with a Learjet horizontal stab) flew through the wake of another racer, which triggered flutter on the tail, which then failed.  A Learjet tail is plenty strong and able of course to fly at very high speeds usually, but the aerodynamics were such that on the P-51, it could get into a regime where flutter could be triggered and result in catastrophic failure.  Not only would you not see that coming by looking at the structure of the Learjet tail or knowing that it routinely flew at near Mach 1, but the designers and crew (much more experienced in building and modifying high-speed unlimited-class racing aircraft than you or I) obviously didn't.  There are examples of very capable aircraft designers not knowing this based on structure or design, either, and only knowing it once seeing it happen in test flights.

The loss of sets of surfaces can't be modelling flutter as they detach exactly at the same time.

They can.  Flutter can happen for both at about the same time.  In fact, since they are nearly identical in design, one's first thought should be that both ailerons should could very well experience flutter at about the same time.  Here are a couple videos of planes suffering failure to both left and right wings and/or both left and right wingtips at the about the same time:
http://www.youtube.com/watch?v=n06WNSS4tFs
http://www.youtube.com/watch?v=LPbhQS6IljU

Besides the evaluation aircraft went faster than ours does this, without incident.

There are two aspects here.  One is that you say this, but what is the situation and what is the reference?  Did one person dive a Ki-84 to 550 mph and recover without damage to the aircraft while several other references state that it comes apart at 550?  Also, failures in real life are stochastic things.  There are some P-38's that tore apart in terminal-velocity dives and many P-38's that didn't.  To model a P-38, you then need to choose whichever mode is more typical, or if you have enough data statistically, you could model it as a random process of failure of 1 in N terminal-velocity dives, but you'd need a lot more statistics than are likely available to judge that and to set N correctly.

[Karnak]

On March 19th of 1945 the crew of the USS Franklin certainly found the enemy relevant.

[2bighorn]

When we were forced to run 100 LL fuel in our R-1820s, we had to re-index the props and had MAP limitations. This reduced available power, and correspondingly reduced climb and speed (not that we ran at full power very often). Essentially, we were down just over 200 hp.

Lets say you'd be forced to use higher grade than what you normally had, without MAP change, would you gain the power? Nope...

Japanese aircraft were generally limited to fuel with an octane rating of 88 or less.

Myth. They had sufficient quantities of 88 and 92 avgas. Their aircraft engines were designed to run on these grades of fuel.

When tested using 115/145 avgas, the full power of the engine was available and there was a significant increase in speed.

Well, KI-84 wasn't tested with 115/145 avgas. Ki-84 tests at Clark field were done with 92 avgas (plus methanol for WEP). Same fuel Japanese used to fuel their KI-84s. Even if it would be fueled with our higher grade avgas, it wouldn't matter, since no performance enhancing modifications were made on the aircraft.

This was exacerbated by the finish of the aircraft being far better than the typical service aircraft.

Irrelevant. AH does not model maintenance issues.

 

[nrshida]

Howdy, Nrshida.

No one can tell at all from looking at the structure...

Hi Brooke,

That comment was directed at those who feel the aircraft should be more fragile to damage from gunfire, not about the surfaces.

They can.  Flutter can happen for both at about the same time.  In fact, since they are nearly identical in design, one's first thought should be that both ailerons should could very well experience flutter at about the same time.  Here are a couple videos of planes suffering failure to both left and right wings and/or both left and right wingtips at the about the same time:
http://www.youtube.com/watch?v=n06WNSS4tFs
http://www.youtube.com/watch?v=LPbhQS6IljU

I'll watch those videos when possible, I have seen footage of flutter before but my first thought was that a structural failure would unlikely happen to two separate areas exactly at the same time. Are you conjecturing this is the explanation in AH or do you know this is the reason?

There are two aspects here.  One is that you say this, but what is the situation and what is the reference?  Did one person dive a Ki-84 to 550 mph and recover without damage to the aircraft while several other references state that it comes apart at 550?  Also, failures in real life are stochastic things.  There are some P-38's that tore apart in terminal-velocity dives and many P-38's that didn't.  To model a P-38, you then need to choose whichever mode is more typical, or if you have enough data statistically, you could model it as a random process of failure of 1 in N terminal-velocity dives, but you'd need a lot more statistics than are likely available to judge that and to set N correctly.

No it was the pre-production evaluation aircraft upon which our version is based. I'll fetch the reference for you tomorrow. I can find no mention whatsoever to flutter or detaching surfaces in the literature.

I was wondering if Karnak found evidence for the Mosquito doing the same in the literature? If not then that might be suggestive.

[Karnak]

I've never read of the Mosquito losing control surfaces.  The closest I have read of is the skin peeling off due to manufacturing defects, but those instances were always far below maximum allowed speed.  I am aware of at least one Mk XVI that dove to speeds well above the maximum allowed as it tried to escape an Me262.

[Brooke]

I'll watch those videos when possible, I have seen footage of flutter before but my first thought was that a structural failure would unlikely happen to two separate areas exactly at the same time. Are you conjecturing this is the explanation in AH or do you know this is the reason?

I don't have any inside knowledge of how or why HTC models things, so anything I post like this is my conjecture.  My thought is that, if one aileron is experiencing flutter, the other probably is within a very small speed range of doing the same.  Given that failure in AH is often when the plane's speed is increasing, it would seem to me that both ailerons would experience flutter about the same time and thus fail about the same time.

[Schen]

As most of us don't have the manuals and information on the internet can be flawed, we can really just speculate. My 2 cents having a pilot licence is this;

All aircraft have a Vne:

 a maximum allowed speed, now im guessing most if not all ww2 pilots had ground school and were schooled in max speeds,maximum g load, and dive speeds not as many real pilots would do half the things we do in ah lol. That being said and the fact i like the ki i agree over 450 and ur fighting outside ur element.

[GScholz]

I think you have misinterpreted what I wrote.


If you look into the structure of this aircraft you can see how it is a little unusual and should have a good deal more integrity than a Spitfire, say. Anyone who has any actual data which implies the AH Hayate is overmodelled I'm sure HTC would love to see it as much as I.

The loss of sets of surfaces can't be modelling flutter as they detach exactly at the same time. Besides the evaluation aircraft went faster than ours does this, without incident.

I was referring to your comment on German engineering.

[GScholz]

For the record, early 1945 (January-March), enemy was still very relevant, especially in the Pacific

Which would make it not post-war.

[nrshida]

I was referring to your comment on German engineering.

Respectfully I think you misunderstood my comment about German engineering.


Yes thanks Brooke. Good points. 

I think it is interesting that the Mosquito shares this feature and that it is similarly unsupported in literature. My feeling is: a little bit of artistic licence, which is alright I suppose. Let's just home this and the other minor discrepancies are reconsidered if they redo the type.

[GScholz]

I hate to be the small boy explaining about the Emperor's new clothes, but that opinion is in face more due to modern marketing and manufacturing techniques (which are basically international). German engineering was / is also imperfect, especially in that period.

I don't mind if poor manufacture is modelled, but let's have it modelled equally across the board...

What's to misunderstand? You think that German engineering was "imperfect", especially in "that period". I assume that period is the 1930s and '40s. Would you care to clarify your meaning?

[nrshida]

What's to misunderstand? You think that German engineering was "imperfect", especially in "that period". I assume that period is the 1930s and '40s. Would you care to clarify your meaning?

Really GScholz, are you still getting customers with this approach? You remind me of Monty Python.

[GScholz]

Customers? With what approach?

I'll just consider you a "little Englishman" then; with noting left than an overstated ego and pride in a Britain long since turned to sheit. Certainly the German car industry has fared far better than the British, and the same goes for most fields of engineering. You remind me of Jeremy Clarkson, just without the charisma.

[nrshida]

Customers? With what approach?

  GScholz you're a bit transparent.

I'll just consider you a "little Englishman" then; with noting left than an overstated ego and pride in a Britain long since turned to sheit. Certainly the German car industry has fared far better than the British, and the same goes for most fields of engineering. You remind me of Jeremy Clarkson, just without the charisma.

Well there you go, the true you comes out 

That's an awful lot of vitriolic and stereotypical assumption from such an insignificant and actually incidental comment. Shame you didn't actually understand my point, so sensitively wrapped in your bias as you are.

Do so. Enjoy yourself.