Author Topic: F4u climb rate ? (Read 1916 times)

J_A_B · « **Reply #45 on:** April 30, 2002, 11:11:40 AM »

"AW F4U climbs very close a p51 since 12k a lot better since 17k. But AH is AH (or maybe La7landia,nikilandia and spitlandia) "

The AW F4U-1D could also climb at 2900 FPM at 30,000 feet. It was more than a "little" over-modeled.

J_A_B

Lephturn · « **Reply #46 on:** April 30, 2002, 12:43:55 PM »

Quote

Originally posted by F4UDOA
If only I had 20 more points on my IQ instead of having enormous genitals;)

LOL! Hehehe, thanks for the laugh.

F4UDOA · « **Reply #47 on:** April 30, 2002, 01:26:15 PM »

BigCrate,

No I abosolutely do not think the F4U-1 series should outclimb the P-38 at any alt. However if a P-38F is modeled then yes the F4U-1D would outclimb it. The F4U-3, F4U-4 and F2G would also outclimb the production P-38's at most alts.

Hitech,

You are correct about your FM matching the charts. I do not question that at all(although I do not know how to confirm initial climb rate). I am only questioning the addition drag of the external stores pylons when other A/C such as the P-51, P-47 and F6F used the same typr of pylon. The F4U-1D is the only one modeled with a drag penalty regardless of loadout.

Here is the second column.

hitech · « **Reply #48 on:** April 30, 2002, 02:31:20 PM »

Once again f4udoa, your confusing me, why do you think AH has drag from the external pylons?

If they are showing on the plane , it does not meen that the drag for them is there.

F4UDOA · « **Reply #49 on:** April 30, 2002, 03:01:44 PM »

Erhh,

Because the top speed of the F4U-1D in AH is 358MPH at sea level and 409MPH at approx 20K with combat power. This matches the charts exactly in combat condition. IE. with external pylons attatched. Without external pylons the top speed is measured in the "Clean Condition". 366MPH at Sea Level and 417MPH at Combat power. Military power would also increase to some degree as would climb rate marginally. This would put the F4U-1 and -1D top speeds almost identical with the -1D being slightly faster on the deck.

F4U-1D In AH currently modeled FM
Combat Power/ Combat condition(with Pylons)
Top speed
sea level= 358MPH
19,000FT= 409MPH

F4U-1D Not modeled in AH FM
Combat power/ Clean Condition(no pylons)
Top Speed
Sea Level= 366MPH
19,000FT = 417MPH

Here is the data for the "clean" condition.

BigCrate · « **Reply #50 on:** May 01, 2002, 01:16:22 AM »

Wait Wait!!
If there was a P-38J-5 modeled it would have a climb rate of about 3400fpm(no WEP)at SL now thats coming in about 16500lbs.. So if a 38J-5 was modeled the F4u-4 would out climb it??? I'm not saying the F4u-4 couldn't do it just saying I always read the 38 was the best US climber during the war. Am I wrong in this??

Cw
=Twin Engined Devils=

F4UDOA · « **Reply #51 on:** May 01, 2002, 08:46:23 AM »

BigCrate,

The F4U-4 could out climb it. But not the -1 series. However the P-38 had a turbo supercharger giving it a very linear climb rate all the way up. So at some alts the P-38 may have the upperhand. Especially over 20K were the air gets thin.

The F4U-3 also had a turbo supercharger and had an outstanding climb rate and was the fastest of all the F4U's with a top speed of about 490MPH!! at 27,000FT. However only about 30 were built and they never saw combat. They did however stay in the Naval inventory until the late 40's doing high alt research.

HITECH,

You still out there??

Hooligan · « **Reply #52 on:** May 02, 2002, 06:12:12 PM »

Kind of curious about the pylon issue and wondering what the answer is....

Hooligan

F4UDOA · « **Reply #53 on:** May 02, 2002, 08:09:14 PM »

Heya Hooligan,

Me too. I hope he understood my point. Did you or did I not make my point?

dtango · « **Reply #54 on:** May 02, 2002, 11:04:52 PM »

F4UDOA:

Engine BHP/Weight ratio is a wholly inaccurate predictor of rate of climb. This method assumes incorrect variables for evaluation and entirely leaves other important aerodynamic variables out.

As Wells pointed out:
ROC = (T - D) * V / W

[list=1]

Engine BHP does not equal Thrust. BHP is only the ideal maximum power available from the engine that can be used for the production of thrust.
You correctly pointed out prop efficiency in adjusting BHP ("ideal power available") to thrust horsepower (THP - "real power available"). Prop efficiency is a correction factor/ratio to help us determine THP available from BHP. However THP does not equal thrust either. THP is just a the power available for the production of thrust, not thrust itself. One equation for Thrust using prop efficiency is:

Thrust = BHP * prop eff. / Velocity

So thrust is a function of THP and velocity. The point is neither Engine BHP or THP = Thrust.

In actuality determining thrust is even more complex than the above equation. E.g. using momentum theory, prop diameter, actual prop revolutions, air density and velocity are all variables that determine thrust.

BHP, prop efficiency, thrust all vary based on various conditions and are not constant. BHP varies with changing air density and the engines ability to perform combustion. This is where differences between differing engines turbo-supercharging shows up. Prop Efficiency varies with the aerodynamics of the prop blades, pitch, speed, and revolutions of the prop.
In your analysis through this thread you also left out certain key variables. Considering the ROC equation above T-D is broken down to:

T-Di-Dp

You talked about the induced drag differences between the P-38 and F-4U. You left out entirely the parasite drag part of the equation. This is a substantial part of the drag calculations that directly impacts the excess thrust available for climbing.
[/list]

Tango, XO
412th FS Braunco Mustangs

DmdNexus · « **Reply #55 on:** May 03, 2002, 11:21:01 AM »

But but... can this dog hunt...

With ordance loaded AH F4u performs as charted.
With out ordance loaded AH F4u should be faster.

Agree/Disagree?

dtango · « **Reply #56 on:** May 03, 2002, 04:01:27 PM »

The peformance data regarding the pylon vs. non-pylon F-4U performance is interesting.

However a single report regarding aircraft performance is hard to gauge as THE definitive source detaling its performance.

[list=1]

Pilot "error" / accuracy plays a part in the performance numbers. Wells shared with me an interesting bit from a book that showed the deviation between performance characteristics of the same aircraft for the same flight conditions. It was interesting to see.
Atmospheric conditions also vary in real life. I believe Pyro told me that AH uses a uniform atmospheric density where air density is uniform for a given altitude around the whole AH arena. In real life this is not true. Wind conditions also are different in real life. All this to say that environmental variables affect the outcome of flight tests.

The point is it is hard to gauge an aircraft's performance on a single flight test report because there are numerous variables in real life that affect its outcome. Which flight test report is right? The answer is probably they all are given the specific flight conditions they were performed in! The question is how does HTC make judgements about this? I'm glad I'm not Pyro or HiTech who have to sort through all this complexity and translate this to a flight model that is as accurate as possible

.

Let me close by saying that I think analyzing flight models is a good exercise. Just keep in mind the complexity and nuances involved (physics, flight test data, etc. etc.).

Tango, XO
412th FS Braunco Mustangs

HoHun · « **Reply #57 on:** May 03, 2002, 07:03:46 PM »

Hi Dtango,

>All this to say that environmental variables affect the outcome of flight tests.

Environmental variables in flight tests affect the measured figures. However, by taking the environmental variables into account, it's possible to arrive at standardized performance values even from a test under non-standard conditions.

The aircraft standard characteristics were prepared with slide rules as much as with stick and throttle, and they were meant to give the most accurate picture of the aircraft they are describing.

If the actual aircraft (or the actual atmospheric conditions) deviated from the standard aircraft (or the standard day) in any way, that would make it deviate from the standard aircraft performance values as well.

Still, the standard aircraft characteristics make it possible to compare the performance of different aircraft types and predict their performance under different conditions or in different configuations - such pylons for air-to-ground ordnance installed or removed.

Regards,

Henning (HoHun)

hitech · « **Reply #58 on:** May 13, 2002, 04:05:10 PM »

Punt for so pyro can find this.

Pyro · « **Reply #59 on:** May 16, 2002, 09:42:22 AM »

You can look at it as being too slow or you can look at it as being too fast if you look at the footnote about rocket rails. In the game, I try to go with what is typically inherent to the plane when that much information is available. For example, a -1D with it's pylons removed would be pretty atypical and even in the docs you cite, it's only mentioned as a footnote. There's other things that affect top end speed such as whether the gun ports are taped over or not that we don't go into either. Tops speeds are not absolutes and small differences add up quickly when you consider that parasitic drag is a squared term(a plane at 400 mph has 16 times the parasitic drag that it did at 100 mph).