Low alt performance of Big Planes in AH

[fire_ant]

I wanted to ask, if not actually gripe, about the low altitude performance, especially in speed and acceleration, of the really big BnZ fighters such as the P-47 and the Corsair.  I notice these things are very very fast at low altitude in AH and out run practically anything.  My question is, is this historically accurate?  Do big high drag fighters go fast at sea level?  Or is the entire AH arena situated on a 10,000' high plateau?  Because this doesn't jibe with what I'd understood from historical accounts.
Has anyone on this board read Ira Kepfords famous anecdote of barely escaping from 3 zero's in his corsair by using the new water injection WEP system and a lot of luck?  If I understand what he had written there, a zero could easily out-run a corsair on military power at sea level if the F4U wasn't in some high E state from diving.  I dont think a zero would be able to get anywhere near a fleeing corsaair in this game, WEP or not.
I have read similar accounts by many other pilots, inlcuding Saburo Sakai's account of a zeros performance, and various accounts regarding the P-47 in the ETO and MTO, in which low altitude performance was considered a problem.  

But if the AH developers are going by the numbers, and I don't have those in front of me, I guess this is just how reality looked.  It seems things are stacked heavily in favor of the BnZ fighters over the TNB.

DB

[wells]

The problem with being low is that anyone can dive on you.  It's easy to gain 100 mph in a dive that could give a speed advantage to even a zero.

[Citabria]

if you have enough alt to dive to get 350mph when you have a real fast zero comin at ya all you have to do is a 90 degree break turn to get away. they cant follow cuz their ailerons are locked up past that speed

[funked]

Maybe you misunderstood Kepford.  Every flight test I have seen shows the F4U to be faster than the Zeke at all altitudes.  Maybe Kepford was in a situation where he was accelerating from low speed.  In that case the Zeke had the capability to stay near the Corsair until 200-250 mph or so.

Also size has nothing to do with top speed.  An F-105 is a lot bigger than an F-84, but it's a lot faster too.  All that matters is thrust and drag.

[This message has been edited by funked (edited 08-08-2000).]

[Vermillion]

Fire_ant the speeds are correct. And yes in AH the maximum level speed of your aircraft changes with altitude.

If you look in the Help section, you will find charts for almost all the planes with speed vs. altitude, and climbrate vs. altitude.

What you are describing is the the age old engineering problem of design tradeoffs. In other words, to get an increase in one performance characteristic you must usually give up performance in another area.

Like Funked said, maximum speed is a function of thrust (engine power) and drag. To get the most engine power, you usually had to go to bigger and heavier engines (US type planes). And when you make the aircraft heavier (and keep the wings the same size), it makes the aircraft perform worse in turnrate.

Now there are alot of other factors, including increasing engine performance without increasing size or weight, so this isn't always true. But its a good generalization.

------------------
Vermillion
**MOL**, Men of Leisure
"Real Men fly Radials, Nancy Boys fly Spitfires"

[F4UDOA]

Fire-ant,

Real quick and dirty. The F4U was one of the fastest birds at sea level. It put out 2250HP at sea level and had a very low power to weight ratio at low alt. Weight devided by power that is(The Me109G10 is king in that regard). At 10K the HP dropped off to 2000HP, and 20k it was at just over 1900HP. These three Alts are the three engine stages or "Blower shift points".

So don't be deceived by size. Even a P-51D only has the slimest of margins at low alt vrs the F4U or Vrs the P-47D30 at any alt.

Bye the way. The A/C chasing Kepford in his daring escape were not Zero's. They were
Ki-44 Shoki's. A much faster bird than the Zero. Especially at sea level but still not as fast as the F4U.

Later
F4UDOA

[niklas]

the F4u is indeed way too fast. Iīll never believe that 2250HP can push a 12000lb fighter with a wingarea of ~315ft^2 to 359Mph at sealevel. Unpossible!

All AH planes with the exception of the pony have a Cd0 of ~0,23-0,25, the F4U  has a Cd0 of ~0,17, though it had a bad wing design, poor surface quality and due to the huge engine a big frontal area and a lot of surface area for the fuselage...

 


 

[PC]

niklas, thats a good one! Do you have any idea what you talking about?  

PC

[Fishu]

Often I've read about P-47 being good at altitudes above 22-25k, but in AH that plane is good at any altitude almost. (perhaps mostly because of supercharger and poor performance of LW planes at those altitudes?)

P-47 was amazing, but in AH it has even more amazing performance at low altitude if talking about maneuvering.

From my understanding low flying P-47 were in fight sort of brick vs. mosquito, which I don't think it is in AH  

Though, it has seem to lost part of that unbelievable E retaining during latest patch or second latest?

[funked]

Fishu - WATER INJECTION!!!

Niklas - There is some variation in flight test data for the F4U-1D but the lowest numbers I have seen are still in the 350 mph range at sea level.

[This message has been edited by funked (edited 08-08-2000).]

[F4UDOA]

Niklas,

I'am surprised that you feel a larger WW2 fighter would be slower for some reason.
Not only is the F4U listed sea level max speed at 360MPH with combat power but in flight test vrs the FW190, P-51B and A6M-5 it exceeded that number in side by side speed runs at sea level.

I will give you 4 reasons the F4U-1 was so fast at sea level compared two it's contemporaries.

1. The front cowl area is much smaller than either the F6F or P-47 due to the oil coolers being moved to the wing roots. Reducing the area most responsable for drag in a radial engine.

2. The wings attach to the fuselauge at a 90 degree angle. This is the most efficient means of attaching a wing to the body and further reduces drag.

3. Air intake into the engine at nuetral and low blower stages is taken in more directly into the engine and creates a RAM air effect.
Even though the manifold pressure is rated the same in an F6F and F4U the Grumman engineers swore that this was the reason for the Corsairs superior performance at low alt.

4. The reason I think is most responsable.
The Prop blade on the F4U is a more efficient prop. Even on the F4U-1 somewhere in 1943, the Vought people switched the blade type on the F4U-1's from a three blade 6443A-21 also used on the F6F to the three blade 6501A-0. The F4U-4 used the same blade only a 4 blade prop. Grumman did not change to this blade type through out production.
I am reading this directly from the F4U-1 Flight manual.
Quote "Production airplanes are normally equiped with Hamilton Standard Hydromatic three blade 6443A-21 or 6525A-21 propellers with a diameter of 13'4". Hamilton standard blades designated 6501A-0 and 6541A-0 having a diameter of 13'1" may also be used on these airplanes. These latter propellers should be used whenever available since they improve performance".

Combine those 4 reasons in combination with one another and the fact that it's speed was measured independantly in 4 different flight test and it becomes even more believable.

Then consider the F4U-4 had only 200hp more and had a top speed of 380MPH at sea level and a 4.9 minute climb time to 20,000ft.and was a heavier airplane. I believe Boone Guyton the cheif test pilot of the F4U descibed it best "The F6F was an airplane of evolution and the F4U was an airplane of revolution"

Later
F4UDOA

For F4U-4 flight data
 http://www.history.navy.mil/branches/hist-ac/f4u-4.pdf  

[niklas]

funked, test data or calculated data??

You find for example 316MPH for the 2000HP type, that would mean maximum ~330mph for 2250HP
(from 214th.com)

[F4UDOA]

Niklas,

214th.com is a gaming website. Do you have any more reliable historic data??

F4UDOA

[niklas]

f4udoa

214th.com/ww2/usa/f4u  is a gaming website?
I donīt think so. BTW they have your PDF document there.

or check  www.odyssey.dircon.co.uk/f4u.htm
they list f4u-1a with maxspeed 395MPH (compared to 417MPH from 214th)

   

1. The front cowl area is much smaller than either the F6F or P-47 due to the oil coolers being moved to the wing roots. Reducing
             the area most responsable for drag in a radial engine.

ahh the oil coolers are in the wing roots? That means air that passes through the wing canīt flow over the wing and produce lift right? And the 30° angel of the wingroots to have a low gear means that you lose another 15% lift in the wingroot section...
 

2. The wings attach to the fuselauge at a 90 degree angle. This is the most efficient means of attaching a wing to the body and
             further reduces drag.

Youīre right, planes like the cessna which are optimized for high speed and low drag have the wings 90° attached to the fuselage, while planes like modern jet airliner where low drag isnīt very important are build with wings swept back.
And of course 90° for the F4U makes a big difference to 80-85° designs of the other WW2 fighters.
The only reason why the F4U has wings with 90° angel attached to the fuselage is because they needed so much wingarea (the heavy engine...)! Thatīs why it has an almost rectangular wingdesign, to realize an acceptable wingloading without loosing to much rollrate. Because big wingspan means low rollrate. The result is the lowest aspect ratio of all ww2-fighters that i know, and withit a lot of induced drag in a slow flight!
   

3. Air intake into the engine at nuetral and low blower stages is taken in more directly into the engine and creates a RAM air
             effect.
             Even though the manifold pressure is rated the same in an F6F and F4U the Grumman engineers swore that this was the reason for
             the Corsairs superior performance at low alt.

Ahh something like the mystically engine heat factor/radiator energy recovery of the P51 eh? Maybe AH should be named Secrets weapons of the USAAF...

The propeller...Do you really think it can give you 30-40MPH more topspeed??
BTW i donīt compare the F4u to the P47, and not to the F6F. I compare it to all other planes included in AH. And you canīt tell me that the F4U has a 30% better Cd0 than all other AC of AH except the P51!


Now to your F4u chart. According to the chart the F4u-4 can go with ~2500HP up to 10k feet- it even has in 10k more power than at sealevel with WEP, while  nominal  engine power gets less (compare climbrate, climbrate @10k with wep is higher than @0k)
Can you pls explain me how the F4u-4 can go with 2500HP up to 10k and a F4U-1D with 2250HP only up to 3K AND why power increases with altiute and wep while power decreases with altitud and nominal power?
And compare the critical altitudes of climb and speed: the difference is even 4k... thatīs a lot!

I have the P51-F4u chart btw. The P51B is listed with 360MPH @ sealevel with only 1440HP....
This chart is not based on flight tests, itīs a calculation. And i think for a simple comparison they neglected for both AC something, interference between wing and fuselage for example.
Like i said i donīt believe it!
niklas

[This message has been edited by niklas (edited 08-09-2000).]

[This message has been edited by niklas (edited 08-09-2000).]

[funked]

Niklas, I'm talking about tests.  

You sure that 316 wasn't knots?

If you're gonna start a "Secret Weapons of the US" campaign, why don't you look into the climb rate of the Fw 190A-5, or the top speed of the Me 109G-10.  Neither one of those makes much sense if you look at power, weight, and drag.

Or what about the Typhoon?  Similar size and power to the F4U, but 20 mph faster.