Effects of Altitude on Required Coefficient of Lift

[Stoney]

Just some observations I made:

1.Computed standard day dynamic pressure for the following altitudes:  Sea Level; 5,000 ft; 10,000ft; 15,000ft; 20,000ft; 25,000ft at 200, 250, 300, and 350 mph per.

2.Compiled wingloading numbers for the P-51D, P-47D25, P-47N, and FW-190D9 using ingame weights and published wing area numbers.  All aircraft were loaded with 75% fuel.  P-51D weighed with 6X.50, and Jugs weighed using 8X.50 w/267 rpg.  Weights and wingloading:

P-51D:  9700lbs; 41.3 lbs/ft^2
P-47D:  14,000lbs; 46.7 lbs/ft^2
P-47N:  15,500lbs; 46.4 lbs/ft^2
FW190-D9:  9200lbs; 46.7 lbs/ft^2

Using that wingloading, I computed required coefficients of lift for 1G, 2G, and 3G maneuvers at each altitude/speed listed above.

I didn't have enough time to graph everything, and if the discussion encourages me, I'll post the tables/graphs in their entirety.

For example, based solely on wingloading:

In a P-51D, a 3G, 200 mph maneuver at 10,000 feet requires a Cl of 1.64, which should be in the stall range of the P-51D.
In a FW190-D9, a 3G, 200 mph maneuver at 10,000 feet requires a Cl of 1.85, which should be in the stall range.

The same maneuver at 200 mph and 25,000 feet requires 2.7 and 3.05 respectively.  The same maneuver at 350 mph and 10,000 feet requires .54 and .61 respectively.

Speeds are in TAS.

Is this relevant?  I understand the relationship between dynamic pressure, wing loading, and required Cl, but does this illustrate anything worthy of discussion?

[viking73]

If i'm reading this correctly then it seems to me that these stall maneuvers that the 51, f4, 109's are doing are impossible. At least to continue in the fight like they are.

[Chalenge]

Enlighten me please about the 'stall maneuvers' you mentioned that you think are impossible and please tell me why exactly it is impossible.

[Stoney]

Necro...

[USCH]

any new info on in game flight is  with me but being a non flight guy who just plays AH i would need a better explination on how the info matters... like are you saying that the aircraft are doing things they should not?

[jdbecks]

what about the TA152 at 25k?

[Pudgie]

Hi All,
What this says to me is that the necessary speed required to perform said manoevers (in terms of G's pulled at a given alt)is the difference maker & that makes this discussion very relevant IMHO Stoney.

As per your example if the plane is flying too slow to maintain the necessary Cl of the wing during the manoever at a given alt then the wing should stall & depart from flight until this relationship is restored.

Air density decreases as altitude increases thus the Cl should reflect this IMHO.

My 2 cents.

 

[Charge]

Interesting post Stoney. 

I'm sorry that I missed it when you posted it the first time.

-C+

[BnZs]

Stoney: But all the pilot has to do really is look at his gauge, right?

What I'm say, even at very high altitudes, won't how many Gs you can actually pull without stalling still be determined by your indicated air speed, regardless of what TAS may be? (Setting aside compression effects for the moment)

For instance, if the Pony can pull 7 at 270 or so IAS OTD, will that not hold true at 30K, even though the TAS will be much, much higher than 270?

Though handling at 30K in FSOs does sometimes remind of me of flying on Mar in the X-Plane series. 

[thorsim]

can't disregard TAS as that has to do with your mach number, TAS is a real concern in overpowered aircraft
such as the ones here.  it (mach number) may not be a factor all the time but it is always a concern ...

i think

Stoney: But all the pilot has to do really is look at his gauge, right?

What I'm say, even at very high altitudes, won't how many Gs you can actually pull without stalling still be determined by your indicated air speed, regardless of what TAS may be? (Setting aside compression effects for the moment)

For instance, if the Pony can pull 7 at 270 or so IAS OTD, will that not hold true at 30K, even though the TAS will be much, much higher than 270?

Though handling at 30K in FSOs does sometimes remind of me of flying on Mar in the X-Plane series. 

[BnZs]

can't disregard TAS as that has to do with your mach number, TAS is a real concern in overpowered aircraft
such as the ones here.  it (mach number) may not be a factor all the time but it is always a concern ...

i think

That is why I said "compressability aside"

Seems like MOST WWII airplanes can be above corner speed relatively high (30K) and still be below critical Mach though.

[thorsim]

That is why I said "compressability aside"

Seems like MOST WWII airplanes can be above corner speed relatively high (30K) and still be below critical Mach though.

ahh cc misunderstood ...

[Stoney]

Stoney: But all the pilot has to do really is look at his gauge, right?

What I'm say, even at very high altitudes, won't how many Gs you can actually pull without stalling still be determined by your indicated air speed, regardless of what TAS may be? (Setting aside compression effects for the moment)

For instance, if the Pony can pull 7 at 270 or so IAS OTD, will that not hold true at 30K, even though the TAS will be much, much higher than 270?

Though handling at 30K in FSOs does sometimes remind of me of flying on Mar in the X-Plane series. 

Well remember, your TAS is always correct, i.e. "true".  Due to lower air pressure at altitude, your IAS is lower than TAS.  You are correct though, that regardless of altitude the IAS dictates performance (stall speed, etc.)  But, what you'll notice here is why most of the planes start to turn like bullets at these high altitudes, and why they seem to stall with the onset of almost any G-load.

[TequilaChaser]

Heya Stoney,
doesn't Shaw's Book "Fighter Combat - Tactics & Maneuvering" cover something similar in the Fighter Performance Appendix Pgs 387 thru 417 ( mainly right around 388 thru 397 ).......
just curious.......



Heya BnZs,
When using IAS for speed, then Vc (Corner Speed) would actually remain constant....although piston powered aircraft lose more thrust the higher in alt they go....... and one would experience the onset of possibly stalling more abruptly......as Stoney has already posted ( doh, I just saw he posted the same thing.... my bad )

Stoney, are you calculating these using something like the V-n Diagram (Chart)?

interesting thread........

[Stoney]

Heya Stoney,
doesn't Shaw's Book "Fighter Combat - Tactics & Maneuvering" cover something similar in the Fighter Performance Appendix Pgs 387 thru 417 ( mainly right around 388 thru 397 ).......
just curious.......



Heya BnZs,
When using IAS for speed, then Vc (Corner Speed) would actually remain constant....although piston powered aircraft lose more thrust the higher in alt they go....... and one would experience the onset of possibly stalling more abruptly......as Stoney has already posted ( doh, I just saw he posted the same thing.... my bad )

Stoney, are you calculating these using something like the V-n Diagram (Chart)?

interesting thread........

Actually, this is merely manipulating the basic lift equation.  If you know the weight (equal to required lift) and wing area of the plane, and dynamic pressure (equal to the sum of the 1/2pV^2 expression of the lift equation), you can get the required Cl for that condition.  For higher G maneuvers, merely multiply the weight times the load (g) factor.  When I first wrote this thread 2 years ago, I was in the process of determining required Cl for the landing speed of a Formula 1 plane I was designing.  At the time, I was curious as to whether it would have any use in comparing aircraft in Aces High.  I've got dynamic pressure tables I made for myself at standard temperature and increments of speed and altitude, so referencing that number is quick for me.  Otherwise, you need to do the math to convert velocity to feet/sec and look up air density (in slugs) for whatever altitude you're looking for.

Ironically, this would be a great method to use to determine flap efficiency for aircraft in the game as well, using stall speed for the velocity with an without flaps at specific testing weights.  There may be more efficient methods--I don't know.