Author Topic: F4u climb rate ? (Read 1940 times)

F4UDOA · « **Reply #30 on:** April 28, 2002, 05:57:17 PM »

Wells,

I would not even question what you are saying except for this.

The climb differance between the F4U-1D and P-38L is very large even at the F4U's best rated alt at sea level. The power loading as you say is 1%. If not better for the F4U then equal. Ok then the variables.

1.Prop efficiency at climb speed. => If the differance between the prop efficiency of a paddle blade and a standard prop is only 7% then how much of a gap in efficiency could there be? Surely less than 7%? 7% of 4000FPM is 280. So the climb differance couldn't be more than that could it?

2. Two prop nacelles providing independant thrust.=> I can't even imagine what this means in terms of climb rate or if any engineer would even calculate this into his climb rate prediction. I have never seen anything to lead me to believe that twin engines would be more efficient in climb than a single. Surely the added drag penalty would be greater than the benifit of two engines.

3. Higher climb speed providing higher climb rate. => I was always under the impression that wing loading was the deciding factor in climb speed? Even late model F4U's have higher climb speeds because of higher weights than the early models. The climb speeds of Zero's, Spits and 109's are lower than the F4U's and yet their climb rates are higher than the P-38's. Certainly there is no rule dictating this.

4. High aspect ratio and induced drag=> I know the benifit of high aspect ratio is low induced drag however. Lift is also tied to induced drag. So if the F4U has higher induced drag then it also has high lift correct? So doesn't that mean it takes less power to fly?? Also since the Cl of the F4U-1D was reduced to 1.49(no flap) shouldn't that reduce the induced drag as well? I thought those two things are directly proportionate. The Spitfire had an extremely low Clmax as well giving it low induced drag and better E retention I believe.

I know all of these points are my limited understanding of aeodynamics but none of these things seem to account for the dramatic differance in rated climb.

HoHun,

What do you mean by the F4U not having rated power at climb speed? I don't understand what that means?

Thanks
F4UDOA

HoHun · « **Reply #31 on:** April 28, 2002, 06:53:55 PM »

Hi F4UDOA,

>What do you mean by the F4U not having rated power at climb speed? I don't understand what that means?

The exhaust thrust of its engine contributes to propelling the F4U. By how much is speed-dependend - the faster it goes, the more power from the thrust.

If the power rating is for high speed, it might be that it includes a number of horse powers for thrust ("shaft-equivalent power") though it doesn't benefit from them at a lower speed.

The P-38's turbo-supercharged Allison engines don't provide any exhaust thrust, so their rating hardly varies with speed.

Regards,

Henning (HoHun)

hitech · « **Reply #32 on:** April 28, 2002, 09:34:25 PM »

F4UDOA In answer to your questions

1. If you increase EFF by 7% say from 63 to 70 plus look at the fact that lets say 20% of the 63 % is used up by drag you are increasing available climb HP from 43 to 50 or aprox 14% change in climb rate.

2. Props can be more effecint for the same resones a padle blade raises eff,basicly you don't need to make each prop as big. So weather 2 props or 1 prop is better is not a simple question.

3. Best climb speed is a function of 2 items for a prop plane.

A. is prop eff (varies with speed),and B is total drag on the plane.

The CL you are quoting is a MAX Cl, the Induced drag is the Id CO * Current CL ^2
i.e. Induced drag =(Id * CL^2 * ro/2 *V^2 * (wing area))
max CL only comes into play at MAX AOA.

This question
So if the F4U has higher induced drag then it also has high lift correct? the answere is no. Gliders are a great example, very high lift but low induced drag.

F4UDOA · « **Reply #33 on:** April 28, 2002, 11:09:06 PM »

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

Anyway back to reality.

1. If you increase EFF by 7% say from 63 to 70 plus look at the fact that lets say 20% of the 63 % is used up by drag you are increasing available climb HP from 43 to 50 or aprox 14% change in climb rate.

OK, then shouldn't the same apply from F4U-1 to F4U-1D? If the F4U-1D benifited 20% by the addition of a paddle prop should have raised the climb from 2900FPM to 3500FPM not including the increase in HP from 2135hp to 2250HP?

The question about multi engine or single engine is really a product of the P-38 which I am using for comparison. Not because I have a problem with the 38 but because it is a comparison between one of the best climbing and one of the worst.

These two A/C are opposites in every way. And in my eyes the F4U holds many of the cards. Thrust to weight and profile drag. While the 38 has aspect ratio and total thrust.

This question
So if the F4U has higher induced drag then it also has high lift correct? the answere is no. Gliders are a great example, very high lift but low induced drag.

I know that high aspect ratio (a glider) reduces induced drag. However this is my question. If the F4U has high induced drag should it not also have high lift.

My understanding is that induced drag is a by product of lift (minus either a high aspect ratio or elliptical wing) . So if there is high induced drag then where is the lift? And the benift of the lift?

Conversely the F4U-1D had a spoiler strip lowering MaxCl. Did this not also reduce induced drag. Note: Your equation may have explained that but I can't figure that out (see the genital reference above).

HoHun,

Thanks, I understand what that means fianlly. That information is posted in the F4U pilots manual as well as the P-38 manual. It does not list HP with or without RAM but it does increase critical Alt. However it does the same in both the F4U and P-38??

Hitech,

I have a theory on why the F4U's climb is not higher based on your information that would correspond to the Flight test comparisons I have with the A6M5, FW190, and P-51

The F4U-1D in AH is the only bird modeled with twin external stores pylons regardless of loadout and the drag penalty that comes with it. The P-47, P-51 and F6F all have similar pylons but do not have them modeled with the a/c at all times.

This chart shows the increase in speed without the pylons of 10MPH through out the speed range. Obviously the drag penalty would also reduce climb. Using the 20% prop efficiency gain would put the climb at approx. 3500FPM over the 2900FPM of the -1. The extra HP from 2135 to 2250 would increase it even further. This would be more in line with the comparisons of other fighter types.

F4U perf chart

wells · « **Reply #34 on:** April 28, 2002, 11:42:50 PM »

Quote

Wells,

I would not even question what you are saying except for this.

The climb differance between the F4U-1D and P-38L is very large even at the F4U's best rated alt at sea level.

I was not aware that the difference was that large. What are the climb rates you refer to? From the sim, flight tests, pilot manuals, what?

Quote

2. Two prop nacelles providing independant thrust.=> I can't even imagine what this means in terms of climb rate or if any engineer would even calculate this into his climb rate prediction. I have never seen anything to lead me to believe that twin engines would be more efficient in climb than a single. Surely the added drag penalty would be greater than the benifit of two engines.

If the P-38 could have a single 3200 hp engine turning same RPM, it would require a prop diameter of 13.2 ft, since prop diameter varies with power^(1/5). It would produce 13% *less* thrust than having two 1600 hp engines, each turning a 11.5 ft prop.

Quote

3. Higher climb speed providing higher climb rate. => I was always under the impression that wing loading was the deciding factor in climb speed? Even late model F4U's have higher climb speeds because of higher weights than the early models. The climb speeds of Zero's, Spits and 109's are lower than the F4U's and yet their climb rates are higher than the P-38's. Certainly there is no rule dictating this.

Here's the climb rate equation again.

climb rate = (T - D) * V / W

There are two things that go into climb rate, angle and speed. (T - D)/W is the sine of the angle. The best speed depends on slope of the drag curve. It's possible that one plane could have a faster climb speed at a shallower angle and still outclimb another plane with a slower climb speed and a steeper angle.

Quote

4. High aspect ratio and induced drag=> I know the benifit of high aspect ratio is low induced drag however. Lift is also tied to induced drag. So if the F4U has higher induced drag then it also has high lift correct?

Relative to itself, yes.

Quote

So doesn't that mean it takes less power to fly??

No, it means it takes less speed to fly. Power required depends on drag.

Quote

Also since the Cl of the F4U-1D was reduced to 1.49(no flap) shouldn't that reduce the induced drag as well? I thought those two things are directly proportionate. The Spitfire had an extremely low Clmax as well giving it low induced drag and better E retention I believe.

This is true, but the Cl is not 1.49 in a climb. If it were, you'd be looping.

hitech · « **Reply #35 on:** April 28, 2002, 11:49:02 PM »

Just curious about your pylon theory f4udoa, what makes you think it has extra drag in ah from the pylons?

f4udoa in my glider example i was showing you that a higher induced drag does not imply more lift, hence my glider example which has less induced drag and more lift. Max CLs are mostly do to the airfoil shape.

On induced drag it's easyer to think of it varing with the AOA ^ 2 for a given air speed. The spoiler strip on the f4u just lowered it's MAX aoa and hence lowered it's Max cl, the induced drag stayed the same for any given AOA, and lift changes propotently to AOA.

Ill have to double check with pyro, but I do not belive our 1d has a padle blade.

And on the % we were using, I was just picking numbers to show you how to do the math, what it realy changed between padle and not and the % of HP used for drag I would have to go work out.

But what it realy comes down to is the climb rates we use are listed for the 1d in a number of places.

J_A_B · « **Reply #36 on:** April 29, 2002, 01:29:50 AM »

"Ill have to double check with pyro, but I do not belive our 1d has a padle blade. "

That would explain everything

J_A_B

wells · « **Reply #37 on:** April 29, 2002, 02:52:03 AM »

There's also the possibility of cowl flaps being partially opened during the climb with the F4u. I believe the manual says 2/3 open for takeoff or something like that. With them being right in the propwash, the drag they create is amplified.

HoHun · « **Reply #38 on:** April 29, 2002, 03:00:29 AM »

Hi FAUDOA,

>If the F4U-1D benifited 20% by the addition of a paddle prop should have raised the climb from 2900FPM to 3500FPM not including the increase in HP from 2135hp to 2250HP?

I just noticed I made a slight mistake - the increase in absolute propeller effectiveness seems to be about 5%, not 7%.

Either way, this increase only suffices to explain the increase in climb rate from the real F4U-1 to the real F4U-1D. Just as I posted above, the F4U-1 with the F4U-1D's propeller would have achieved 3170 fpm instead of 2880 - that's a 10% increase.

If I consider the effect of the pylons 10 mph at sea level top speed and "remove" them from my simple model, the difference in propeller effectiveness is 6%, and the pylon-less paddle-blade power-boosted F4U-1 climbs with 3480 fpm now, a 21% increase over the basic pylon-less F4U-1 but only a 3% increase over the heavier, pylon-equipped F4U-1D.

(If it seems strange that the pylons have a much larger effect on the F4U-1 than on the -1D, that's just the normal bullwhip effect of reverse engineering ;-)

Regards,

Henning (HoHun)

F4UDOA · « **Reply #39 on:** April 29, 2002, 09:29:15 AM »

Hitech,

On the other issues on Physics I have to depend on others to tell me if I am right or wrong, however when it comes to F4U details I know the answer more often than not.

Your F4U FM's(F4U-1, F4U-1D, F4U-1C) match exactly two specific NAVAIR docs which I have full copies of. In those Docs it specifies the blade type used on the F4U-1 as 6443(non-paddle). On the F4U-1D/C doc it specifies blade type 6501A-0(paddle blade). The 6501A-0 is mentioned specifically in several sources as incresing the performance of the F4U. These are

1. The F4U-1D vrs FW190 test

2. The F4U-1A vrs P-51B

3. The F4U pilots manual which it says to use the latter blade type as it increases performance.

Second on the issue of weather the F4U-1D is modeled with external stores pylons is simple. Just look at your performance charts for the -1D and look at this note on the F4U-1D NAVAIR doc. It states an increase in performance from 358MPH at sea level to 366MPH at sea level. Also at 20k from 409MPH to 417MPH.

The Full report can be found here.
Notice it matches your FM speed, weight, climb etc. Also prop blade type is listed second to the last page.

F4U-1D charts

F4UDOA · « **Reply #40 on:** April 29, 2002, 09:37:32 AM »

Here is the second part of that document. I had to clip out the section because the doc is way to big.

F4UDOA · « **Reply #41 on:** April 29, 2002, 08:41:37 PM »

HT,

Did I loose your attention??

What do you think of this data?

BigCrate · « **Reply #42 on:** April 30, 2002, 01:25:01 AM »

hehehehehehehee Whose right on what

Ok one more ? for me to ask.

The P-47s and The f4s had paddle props installed and flew combat missions.. Right??
If the props improved performance why not have them in AH???
I have read some threads on the 47 drivers wanting paddle props on there 47s.. If these props were modeled it would even up the Jugs and Hogs more to fight the endless spits and niks.

DOA you have posted some big climb rate numbers for the F4s
Which are bigger the the P-38L climb rate numbers. So did the Hogs out climb the Fork Tails??

Cw
=Twin Engined Devils=

RatPenat · « **Reply #43 on:** April 30, 2002, 05:26:11 AM »

F4U-1 and D & C is blue with strange wings and then can't climb well. But everybody knows climb better all japanese planes except niki, climbs better F6F, climbs near P51 or better him.

No comments about F4U4 climb rate and speed (it's blue with strange wings too) who runs & climbs more p51 at real life. Of course climbs near or better a p38L.

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

Data from Navy or USAF only good when employed vs LW

Well Hog is a hog and Jug is a Jug

=S= ALL

hitech · « **Reply #44 on:** April 30, 2002, 09:09:15 AM »

Want to see the next column f4udoa, btw a 10mph speed differenct at top end do to added drag will only effect climb rate very slightly. as in 50 fpm range. But it apears to me we hit the 3370 climb rate. See our f4u1d climb rate chart.