Oh my god the pony is awful!

[Charge]

"Perhaps someone with more familiarity can calculate the drag based upon the
flat plate area of 4.4574 sq/ft."

What do you mean with flat plate area in this case?

Is it this?

f = CDp x S

http://selair.selkirk.bc.ca/aerodynamics1/Drag/Page4.html

-C+

[Tilt]

Originally posted by Tilt
It is an La-7 and the data is from wind tunnel tests.

However it was to show Cx and Cy against attitude.(not altitude) and two levels of "trim" caused by a change to the fuselage. The lower level is the standard fully feathered setting.

All tests were at approx 40.5m/sec (89mph?) at 756 mm mercury (sea level'ish) at 26 deg C. The only graphs showing variance in air speed are showing Cx at fixed attitudes and then the line is flat regardless of speed.

Cy at 0 degrees attitude was approx 0.05 but it changes from -.1 at -2 degrees to +. 2 at + 2 degrees with hardly any change in Cx at all.

in the formulae attached showing various calculations Cx=f(V)

a figure for Fa is referred to frequently

Another brick wall  I guess. thanks anyway.

[Lumpy]

Originally posted by Stoney
No, but 1725X2 does...

And no P-38 has 1725x2 hp in-game. Which was my point.

[Lumpy]

Originally posted by Widewing
You missed this...

P-38J: 4.22 ft/sec/sec
P-38L: 4.70 ft/sec/sec (4.13 ft/sec/sec for 1600 hp rating)
P-51D: 3.85 ft/sec/sec

My regards,

Widewing

Yes you're right, I did.

[Captain Proton]

Originally posted by Widewing
P-38J: 375 x .8 x 3,200 / 150 mph = 6400 lb thrust
So, 6,400 lb thrust - 1676 lb drag / (16,480/32.2) = 9.23 ft/sec/sec

P-38L: 375 x .8 x 3,450 / 150 mph = 6,900 lb thrust
So, 6900 lb thrust - 1676 lb drag / (16880/32.2) = 9.97 ft/sec/sec

P-51D: 375 x .8 x 1,720 / 150 mph = 3,440 lb thrust
so, 3440 lb thrust - 845 lb drag / (10,208/32.2) = 8.18 ft/sec/sec

Propeller efficiency at 150 mph would be lower than 80% and probably around half that amount. So those acceleration values may be out by a large percentage. The relative difference between the aircraft would also be out by the same amount.

Proton

[Widewing]

Originally posted by Captain Proton
Propeller efficiency at 150 mph would be lower than 80% and probably around half that amount. So those acceleration values may be out by a large percentage. The relative difference between the aircraft would also be out by the same amount.

Proton

Actually, about 70% at 150 mph. I didn't want to muddy the water with that as it does not change the relationship between aircraft. We simply don't have details of the various propeller's efficiency, so we have to use a constant.

Here's a generalized chart provided by DTango.



I did make an error tho... I applied the drag associated with 250 mph to the 150 mph calculation. Drag for each aircraft would be about 50% of the value I used. It doesn't change the relationship between the aircraft, but it does change the acceleration values.

My regards,

Widewing

[Lumpy]

Widewing, if that chart is right how does planes even get rolling on the runway?

[gripen]

A common way to present propeller thrust is:

(p * e)/ v = t

where

p = engine output
e = propeller efficiency
v = speed
t = thrust

Formula is simple and works ok when the plane has some speed. However, at low speed it's obviously flawed because thrust increases endlesly when the speed decreases. So to get sensible values using this simple formula at low speed, the generalized efficiency function is a bit hacked at low end.

[Widewing]

Originally posted by Tilt


Another brick wall  I guess. thanks anyway.

Maybe not a brick wall.. Perhaps only a stockade fence. We can fudge some things.

The La-7 has a CDo a bit greater than the P-39Q, but has a smaller wing which produces a slightly smaller flat plate area. I'm going to guess and say that the La-7 would have a total drag in pounds of around 950 lb at 250 mph.

So, let drop in the balance of the data and see what pops out..

375 x .8 x 1,850 hp / 250 mph = 2,220 lb thrust

2,220 lb trust - 950 lb drag / (7115/32.2) = 5.75 ft/sec/sec at 250 mph

Lets do the P-39Q-1...

375 x .8 x 1,420 hp / 250 mph = 1,704 lb thrust

1704 lb thrust - 864 lb drag / (7570/32.2) = 3.57 ft/sec/sec at 250 mph

So, the P-39Q-1 should be very close to the P-51D in acceleration at sea level, but the La-7 will leave both behind with relative ease.

My regards,

Widewing

[Tilt]

thanks Widewing thats very interesting..........

is it fair to say that the 3.1m 3 bladed prop pulling over a radial engine housing would be as efficient as 80% ?

The la5Fn had greater drag to some unknown extent but (IMO) had less access to WEP.

Given this and your math above would it be reasonable to suggest that a WEP'ed out La7 only able to give 1600HP of thrust would be limited to less than  4.34 ft/s^2  and given it is also forced to open engine cooling vanes more likely 4.2 ft/s^2.

IMO WEP on the La5 FN was not available as long as it was on the La7 (engine heated much more readily) plus given its extra drag would it be totally unreasonable to assume a comparative figure for a WEP'ed out La5FN closr to 4.0 to 4.1 ft/s^2.   ?

[Charge]

Interesting, I guess that on the deck 190A8 would be a good accelerator too with its small wing...

-C+

[Captain Proton]

Originally posted by Widewing
Here's a generalized chart provided by DTango.

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

[Captain Proton]

Originally posted by gripen
However, at low speed it's obviously flawed because thrust increases endlesly when the speed decreases.

It is only a problem if you use constant efficiency in which case the thrust would increase to infinity, but don't forget that as the speed decreases increasing the thrust, so does the efficiency decrease, reducing the thrust and the two effects tend to balance each other out resulting in zero thrust at zero airspeed, which is obviously wrong, and why static thrust calculations are done differently.

Proton

[bongaroo]

Originally posted by BaldEagl
Running until you are out of icon range isn't re-setting a fight.  Extending 1-2K is re-setting.  What I'm saying is he ran away, then got all brave and came back for the kill once I was engaged with multiple cons.

Most on these bbs would be ridiculed for such cowerdice.  It is however, a good way to get a high K/D ratio.

I have a lot of respect for the AK's and count several as friends and most as worthy adversaries.  Unfortunately, AKDG falls into neither of those categories and I was (am) dissapointed in him given my high regard for the rest of the squad.

I hope that makes it a little clearer.

I despise people who do this!  Run until I turn away to let you go home and you immediately turn to try and pick me not looking.  Thats just a pansy way to fight and your wasting my time.  If your going to run away go ahead and go all the way back with your tail between your legs.

Funny thing about this type of fighting is that they make a mistake.  They turn back to fight.  Thats usually enough.

[Badboy]

Hi Widewing

Here are prop curves for the P-38L and P-51D. It shows the P-51D at 68.5% and the P-38L at 64% at 150mph. I can generate prop curves for many other propeller/engine configurations, so if you need something specific just let me know.



Hope that helps.

Badboy