FM Question/New F4U's climb slower??

[F4UDOA]

Squire,

It is an actual flight test, I have the entire report of 7 pages non of which makes reference to using ADI any longer than 5 minutes.

The actual duration of ADI in the aircraft was 8.5 minutes (10 in the Hellcat) not the 5 minutes that is rrequently referred to. Which is more than enough to get to 20K.

The climb at 20K in the text of the report states the climb to be over 2500FPM. The climb chart indicates 2300FPM which would seem to show a reduction in power at that altitude.

[Squire]

Perhaps testing them to 16k (within 5 minutes) would be a better test, at least that would indicate with no doubt how the two compare.

Of course, as with all the climb tests, I have to ask as to method in real life. From brakes release? or after airborne? or? it can be the difference of a minute sometimes.

It can get pretty messy, as we have seen in many other debates on climb rates in the past.

The F4U-1A seems to climb according to the AH chart (for the F4U-1D), it holds @2500 fpm untill 17500 ft, then starts to drop off.

...I will let Pyro sort it all out I guess.

[F4UDOA]

Pyro,

I have run this many times in prior version at different weights and loading. It is unquestionably slower than prior versions and even when removing weight via fuel the problem does not correct.

Under 10K I would say that it is more noticable.

[F4UDOA]

I tested the F4U-1C thinking it may have been unchanged.

8 Minutes 7 seconds to 20K at WEP until it expired and then mil power.

Definitely a pronounced change from the previous version.

[Angus]

So it climbs slower than a Spit I?

[F4UDOA]

Slower than the Hindenburg towing a B-52.

Slowwwww.

[Angus]

Originally posted by F4UDOA
Slower than the Hindenburg towing a B-52.

Slowwwww.

[Widewing]

When the drag model was revised the first time, I tested many of the aircraft for changes in climb rate and compared the data to the previous modeling. There was no difference other than normal testing variations.

Today, I tested several aircraft using the same method.

This method begins by flying at 50 feet ASL at 300 mph TAS. I then engage auto-climb and engage WEP. I measure the time required to reach 10,000 feet. This method introduces the zoom-climb factor, and thus, does not measure pure climbing ability alone. A similar method was used by the USAAF to help define what they called "combat climb". Only between 4,000 and 10,000 feet does the aircraft climb at its steady-state rate.

Whether or not this is a fair measurement of climb is not important, because the data is repeatable, and therefore perfectly acceptable to determine if the flight model changed with a new update.

Previous data/current data

F4U-1D: 2:24.47/2:27.96
F4U-4: 1:55.67/1:57.04
F4U-1C: 2:32.74/2:33.35
F6F-5: 2:15.67/2:15.63
Spit14: 1:47.13/1:46.53
Spit16: 1:39.90/1:40.25
190D-9: 2:03.35/2:01.63
109K-4: 1:45.69/1:44.25
Tempest: 2:05.38/2:03.86

As you can see, the differences are within what could be considered Normal Test Variation (less than 2% on average).

My regards,

Widewing

[Krusty]

You see, the old one had the cowl flaps CLOSED... but you can clearly see they're OPEN now...

That's what's slowing you down!!

[Angus]

Widewing, - I cannot but admire your dedication on the subject.
I've done some testing, but not to that amount on a single subject.
I did some testings with friends in the training arena. Not so easy to clock like this (how do you clock anyway, - stopwatch?), I was doing turn-tests like 109F vs Spit IX with various loads etc. What I got out was enough for a little frame of truth, such as that a lightly loaded 109F would turn on a pair with a Spit IX with full tanks etc.
I did some climb tests, and found the Spit XIV too slow to 20K, the 109G too fast, and in comparison, the Spit XVI is probably climbing too well, - well, it's a rather tight ballpark anyway.

[Widewing]

Originally posted by Angus
Widewing, - I cannot but admire your dedication on the subject.
I've done some testing, but not to that amount on a single subject.
I did some testings with friends in the training arena. Not so easy to clock like this (how do you clock anyway, - stopwatch?), I was doing turn-tests like 109F vs Spit IX with various loads etc. What I got out was enough for a little frame of truth, such as that a lightly loaded 109F would turn on a pair with a Spit IX with full tanks etc.
I did some climb tests, and found the Spit XIV too slow to 20K, the 109G too fast, and in comparison, the Spit XVI is probably climbing too well, - well, it's a rather tight ballpark anyway.

I prefer to test offline, with fuel burn set at zero. This eliminates one variable.

Here's a general outline of the tests I perform.

Acceleration at SL, 5,000 ft, 10,000 ft, 20,000 ft and where applicable, 30k as well. I measure 150 mph to 250 mph and 250 mph to 350 mph or max attainable speed.

Max speed at SL, 10k, 16k, 20k, 25k and at best altitude. Sometimes done in increments of 1k to establish speed curve. Consumes huge chunks of time.

Turn radius and rate at SL, with full flaps, 25% fuel.
Turn radius and rate at 10k, with full flaps, 25% fuel
Turn radius and rate at 20k, with full flaps, 25% fuel

Turn radius and rate at SL, clean, 25% and 100% fuel
Turn radius and rate at 10k, clean, 25% and 100% fuel
Turn radius and rate at 20k, clean, 25% and 100% fuel

Rate of climb; combat climb, 300 mph TAS from SL to 10k, 25% fuel.
Rate of climb; from stop on runway to 10k, 25% fuel.
Rate of climb; from stop on runway to 20k, 25% fuel.

Dive speed from 25k to 10k, max speed recorded.
Dive acceleration, from 25k; Bunt over at 300 mph TAS, record time to accelerate to 500 mph TAS.

Roll rate at 150 mph, 250 mph, 300 mph and 350 mph. Testing done at 1,000 ft ASL.

Max range, recorded from E6B at best RPM/MAP for max range.

As you can imagine, this testing takes 8 to 10 hours per aircraft....

My regards,

Widewing

[straffo]

What is deck speed for a F4U-1A ?

I had lot of trouble shacking one from the tail of my yak9U the F4U-1A  looked to be faster than the yak.

[Overlag]

Originally posted by straffo
What is deck speed for a F4U-1A ?

I had lot of trouble shacking one from the tail of my yak9U the F4U-1A  looked to be faster than the yak.

once up to speed its a very fast plane... it just has sucky acceleration.

[Widewing]

Originally posted by straffo
What is deck speed for a F4U-1A ?

I had lot of trouble shacking one from the tail of my yak9U the F4U-1A  looked to be faster than the yak.

If you fly it clean, it will reach 366 mph at sea level. If you have taken a bomb or drop tank, the pylon/shackles cannot be dropped and it will reduce your max speed at sea level to 360 mph.

My regards,

Widewing

[straffo]

So it's faster than a yak.