Oh my god the pony is awful!

[Captain Virgil Hilts]

Badboy, is that strictly a difference between the crappy Curtiss Electric 3 blade prop on the P-38L as compared to the 4 blade Hamilton Standard prop on the P-51D? Which P-51 prop? Is it a high activity paddle prop?

[Stoney]

Originally posted by Badboy
I can generate prop curves for many other propeller/engine configurations, so if you need something specific just let me know.

Can you post the method?  In keeping with the previously mentioned aircraft, it could be helpful to have an LA-7, P-38L, P-51D, and Tempest comparison.

[Stoney]

Originally posted by Captain Proton
You made a good point about it not changing the relationship between aircraft, but that prop chart can't be right because all real prop charts drop away from maximum efficiency shortly after they reach it. It is probably only an idealised chart that ignores efficiency losses at high speed.

Also, using the same efficiency value for each aircraft isn't right. It isn't right, because different propellers with different diameters and different activity factors running at different rpms will have different efficiency even at the same speed. You can't use one single curve for all of them. And that will change the relationship between the aircraft.

Proton

During a detailed analysis, sure.  But, for merely doing some rough comparisons, a prop efficiency number around 70-80% is consistent with current methods.  After looking at Badboy's graph, Dtango's isn't too far off.
Comparisons such as WW's are helpful because they can become the catalyst for the next theoretical question.

[dtango]

Actually Stoney, my generalized prop efficiency curve I'm not too proud of .  I've never sat down to dissect methods for producing prop efficiency curves for different configurations.  Producing good prop curves can be quite challenging because of all the variability.  I'm impressed that Badboy has a method for doing so!  

I have Edmund Allen's 1940's paper and also the Hamilton Standard Redbook which let's you extrapolate prop curves for specific configurations given the right data.  I've toyed with the idea of sucking them from graphical form into a database to be used for lookups.

Secondarily from blade element theory there is a way to generate thrust coefficient and power coefficients to arrive at prop efficiency but the math is quite challenging as well requiring calculation by iteration as well as in stages from obscure propeller data points.

Tango, XO
412th FS Braunco Mustangs

[Stoney]

Well, just noticing that  the values are close enough for the girls we date.

Raymer suggests values of Eta-P as 75-80% for early comparisons.  He lists the full monty of equations for advance ratio, activity factor, power coefficients, etc.  He uses the Hamilton Standard book and another as references for these equations.  The Hamilton Standard book should be a gold mine for at least the U.S. prop efficiency numbers.

He lists Eta-P=Thrust X Velocity / 550*bhp

Thrust= 550*bhp*Eta-p / Velocity

If we have drag coefficients or flat plate areas, we should be able to solve for propellor efficiency since drag = thrust in unaccelerated flight.

[Anaxogoras]

Even if the fm was changed, I still find the 51 to be a very capable aircraft.  I can even land 4-5 kills with it now and then, and not even by vultching!  And if I can do that, it says something.

On the other hand, I still see plenty of other 51 pilots who love to dive down from 20k on me down when I'm extending away from Spixteens.

[PhantomBarron]

The P51

[Serenity]

Originally posted by Sketch
Wait, where is Serinity when we need him...

Never f34r! Serenity is here!!!

[Sketch]

Originally posted by Serenity
Never f34r! Serenity is here!!!

Great... all that time away and he still can't spell....