A6M5b "Zero" Diving Speed - 100mph error

[2bighorn]

A6M5b "Zero" diving speed limit was 400kn (~460mph).

In AH, altitudes between 30.000 and 10.000 ft, A6M5b can dive with max speed of 600mph. I have a film where A6M5b reached 616mph.

If we assume that the diving speed limit had a safety margin of about 50mph, AH Zero is still 100mph too fast in dive at high altitudes.

Seems to me that high altitude FM in AH for most of the low performance planes is kinda buggy (C47, TBM, A6M5b, etc).


A6M model 21: 340kn dive speed restrictions
A6M model 32: 360kn dive speed restrictions
A6M model 52: 400kn dive speed restrictions

[Batz]

try the a6m2, it seems many of the planes in ah are able to dive at very high speeds.

[2bighorn]

Yes, not only diving but climbing as well.

Try this:
Take Me163B and autoclimb to about 5000 ft. Level out until you reach the speed of about 450 mph.
Go vertical and you can climb at 85-90 degree angle to about 65,000+ ft (until the fuel is out).

With the thrust of about 3,750 lbs and empty weight of about 4,200 lbs this would be impossible in real life...

[dtango]

2bighorn:

Is the diving speed limit on the A6M5b given in TAS or IAS?  Also what altitude is that dive speed given for?

Tango, XO
412th FS Braunco Mustangs

[Angus]

I would think it's in IAS, since that indicates better the mass of airflow.

[2bighorn]

As far as I know all measurments for speed and climb were in TAS, and at/to altitude of 19,685 feet (6000m) - altitude of maximum speed (348mph). From which altitude the dive speed was measured, I don't know.

It was fitted with same heavy gauge wing skin as A6M5a wich made possible dive speed of 460mph (A6M5 - 410mph).

Now, in AH, try to dive in P51 (from 30,000ft). At 510mph TAS you'll start shaking, at 550+ you're compressed, at 600 you're toast.

In A6M5b at 550mph TAS is still controlable, and if dive isn't too steep, you can pull out at 600 TAS (above 10,000ft alt). True, in 1 out of 5, you may loose elevators or ailerons, but most of the times you'll survive.

Kinda silly watching 190s compress whilst chasing Zero, no?

[2bighorn]

Originally posted by Angus
I would think it's in IAS, since that indicates better the mass of airflow.

Might as well be, but I can hardly imagine that in real life Zero could outdive p51 at medium and high altitudes.

[dtango]

My limited exposure to max diving speeds are typically placards for pilots which means they are in IAS.  Just helping us double check to make sure we're comparing apples to apples regarding speeds .  460 mph seems a little low to me if it's in TAS but that's just based on intuition and not any calculations.  If we assumed 460 mph is EAS and about 10K alt then max dive speed in TAS is 536 mph.  That's mach .71 which is perhaps a little high but more in the realm of what I would expect.

I'd agree with you that a P-51 would compress at higher speeds vs. a Zero assuming equivalent altitudes and speeds for the dive.  Again this is just based on simple assumption that the P-51 wings are thinner than the Zero's.

Tango, XO
412th FS Braunco Mustangs

[joeblogs]

It never occurred to me, but does AH model compressibility? I've never noticed that it does, but I typically don't fly the really clean planes where the effects appear.

As for the A6m2, you ought to rip the wings or tail off trying to pullout at 650mph.

-Blogs

[dtango]

joeblogs- yes in general the FM's do model compressibility.

Tango, XO
412th FS Braunco Mustangs

[Widewing]

2bighorn's dive data is already converted to TAS. Early Zeros would wrinkle the wing skins if the pushed much beyond 400 mph in a dive. Later models used thicker gauge aluminum, but the problem was only partially solved because the underlying structure wasn't strong enough to tolerate the aero loading in the first place. Beyond 430 mph, the A6M2 would suffer from aileron flutter which would rapidly shred if allowed to continue for more than a few seconds. I seem to recall that the critical Mach for the Zero was around 0.72. However, it simply lacked the strength to get to, much less sustain that speed without serious damage. If you can dive a Zero to 500 mph and still have wings, the flight model is wrong. Grumman test pilot Corwin (Corky) Meyer has written extensively about the Zero (which he tested extensively) and confirms 2bighorn's dive restriction numbers.

My regards,

Widewing

[Ecliptik]

I tested this yesterday, you can take an A6M2 to about 600 mph in AH.

[Batz]

I posted an image when the a6m2 was first introduced in ah that showed my speed @ 610mph I was able to pull out using aileron trim.

If you have 10bears germany map you can switch to rook and up from 51 (IIRC) and airstart at 17k.

Or use the okinawa terrain and spawn from 41.

I tested many of the planes in ah and everyone was able to dive and pull out in a similiar manor. None suffering structural damage. Some planes would lose their "moving parts" (rudder aileron elevator) if operated at higher speeds but when using trim only you could pull out with out damage.

All planes would break up at higher gs during pull out.

[Soda]

What always surprised me is how different the A6M2 and A6M5b feel in AH in a dive.  The A6M2 can dive to very high speeds and while it becomes heavy on the controls, it never really gets into deep trouble.  The A6M5b on the other hand has real problems diving, it locks up very early, in the 350mph range it starts to have problems.  Why the difference?  I always thought the M5b modeling was probably more accurate while the M2 modeling was suspect.  Was there any significant structural difference between the two that would account for this?  If anything I would have guessed that the later model would have been better in a dive.

[Angus]

TAS or IAS, the a6m in AH can dive too fast, and can recover from an incredibly fast dive. It also rolls too well at high speed (should be almost stuck at 250 mph, and impossible to roll at 350).
Guess they'll have to look into it.