Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Stoney on April 07, 2008, 02:08:08 AM
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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?
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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.
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Enlighten me please about the 'stall maneuvers' you mentioned that you think are impossible and please tell me why exactly it is impossible.
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Necro...
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any new info on in game flight is :aok 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?
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what about the TA152 at 25k?
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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.
:salute
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Interesting post Stoney. :aok
I'm sorry that I missed it when you posted it the first time.
-C+
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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. :devil
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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. :devil
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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.
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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 ...
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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. :devil
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.
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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........
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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.
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rgr Stoney, thanks for the details.......I did not even notice you started this thread back nearly 2 yrs ago in 2008, until you just mentioned it.....
will keep an eye on this thread to see if I can learn something new, thx again :aok
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"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."
Ok, so you mean that weight is similar to the lift (L) for a wing at a specified angle of attack, i.e. it can be used to determine Cl. I understand that the wing-area would be meaningless if the profile lift i.e. Cl was unknown and what you want from the equation is lift (L) i.e. weight. :headscratch:
http://en.wikipedia.org/wiki/Lift_(force)
http://en.wikipedia.org/wiki/Lift_coefficient
-C+
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Well, all your doing is taking the basic lift equation and solving for Cl (as in the Coefficient of Lift equation on the Wiki page). If lift = weight, then you can substitute the weight of the aircraft into the equation for L (lift), determine the dynamic pressure, and use the known wing area to come up with the required coefficient of lift for that condition.
The result is the Cl for the entire aircraft, and not the wing only, or airfoil.
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The result is the Cl for the entire aircraft, and not the wing only, or airfoil.
I think that would require a whole plane area data, not just a wing.
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I think that would require a whole plane area data, not just a wing.
Well, as I understand it, the CLmax represents that data in itself. In other words, you can have two aircraft that have the same wingarea but because the other aircraft (whole aircraft, not just the wing) has higher lift coeffient it will stall at a slower speed at certain altitude. Lift coefficient is just a dimensioless figure that helps in understanding the lift characteristics of an aircraft.
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So, if you calculate Cl (say, with alpha 15deg for certain wing-profile) in desired condition and from that you can calculate L (lift) =weight that would result in, say 10.000kg you would know that with that alpha a plane with that Cl and weighing 3000kg (at certain air pressure) could pull a bit over 3Gs in conditions that were used to calculate the Cl in the first place? Also in effect of that the equation can give you the alpha at which that 3000kg aircraft would be flying level i.e. the L= "weight" would be 3000kg? :x
Calculating the Cl is tricky though as was evident in NACA document Gripen posted in other thread...
http://naca.central.cranfield.ac.uk/reports/1946/naca-tn-1044.pdf
PS. Bear with me, please, I really suck at math... :o
-C+
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So, if you calculate Cl (say, with alpha 15deg for certain wing-profile) in desired condition and from that you can calculate L (lift) =weight that would result in, say 10.000kg you would know that with that alpha a plane with that Cl and weighing 3000kg (at certain air pressure) could pull a bit over 3Gs in conditions that were used to calculate the Cl in the first place? Also in effect of that the equation can give you the alpha at which that 3000kg aircraft would be flying level i.e. the L= "weight" would be 3000kg? :x
Calculating the Cl is tricky though as was evident in NACA document Gripen posted in other thread...
http://naca.central.cranfield.ac.uk/reports/1946/naca-tn-1044.pdf
PS. Bear with me, please, I really suck at math... :o
-C+
You don't need AoA at all for this calculation. What this tells you is the required Cl for that condition. If the plane is capable of performing that maneuver, you know it's capable of that computed Cl. Therefore, if you know the stall speed, for example, of a plane at a certain configuration, then you can compute the Clmax the airplane is capable of at that configuration, regardless of AoA.
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Dear WMaker and Stoney,
If I understood this correctly, this calculation will give a whole plane Cl value, not a wing Cl value.
How this is relating directly to the wing area, I don't understand.
Thanks
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Dear WMaker and Stoney,
If I understood this correctly, this calculation will give a whole plane Cl value, not a wing Cl value.
How this is relating directly to the wing area, I don't understand.
Thanks
Because basically, the weight of the aircraft, divided by the wing area times dynamic pressure, gives you the Cl at that condition. It alludes to the fact that the wing provides almost all of the lift for the plane, and that the fuselage et al doesn't contribute that much more.
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... but... but (tossing a book pages around)
In below of the best cruising speed case, the wing is producing more lift, than a plane weight due tail -lift.
In above of the best cruising speed case, the wing is producing less lift, than a plane weight due tail +lift.
:confused:
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The wing area is just a commonly accepted reference area for dimensionless lift coefficient despite the other parts of the airframe might be involved in the creation of the lift.
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The wing area is just a commonly accepted reference area for dimensionless lift coefficient despite the other parts of the airframe might be involved in the creation of the lift.
Ah, I see. Thank you for the point out.
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Stoney, I think I figured out how this works way back in our discussion about IAS vs TAS in P47 glide numbers.
Physics wise, the IAS speed will dictate how much lift the wing can generate. TAS is irrelevant for lift considerations if you have IAS available.
What TAS DOES affect though is your turn radius. You will pull a MUCH wider turn radius at high altitude for the same amount of Gs (i.e., lift).
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In these stall tests, are there all figures calculated without power at the alt? Sorry if it is a silly question.
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This would be the power on 1G stall. As you climb higher your IAS decreases and when it reaches stall speed you're at your altitude limit.
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i thought ...
IAS was a measure of force of the air and relates to stress loads, lift, and in this case turn performance at relative altitudes.
i.e. speed limits related to forces ...
and ...
TAS is a measure of speed of the air and relates to airflow over the surfaces and how the surfaces and the air relates at different speeds.
i.e. speed limits relating to the ability for the air to flow "cleanly" over the surface of the aircraft.
that being the case i am unclear how TAS would be a determining factor of turn rate at altitude unless you guys are saying compression is coming into play ...
Stoney, I think I figured out how this works way back in our discussion about IAS vs TAS in P47 glide numbers.
Physics wise, the IAS speed will dictate how much lift the wing can generate. TAS is irrelevant for lift considerations if you have IAS available.
What TAS DOES affect though is your turn radius. You will pull a MUCH wider turn radius at high altitude for the same amount of Gs (i.e., lift).
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For a guy with a lot of opinions about flight modeling you seem to lack some very basic information. No offense. :devil
IAS is an air pressure measurement. IAS is how fast the wing thinks you're flying. TAS is how fast the ground thinks you're flying. When they're apart they disagree but when they come together they agree.
Note that Boomerlu said turn radius not turn rate. Since your True Air Speed is high your turn radius is big but since your Indicated Air Speed is low you are limited in how much G you can pull.
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ahh i see where you are going now ...
but FYI wings don't think
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Just to clarify my oversimple explanation, TAS isn't really ground speed because it's affected by wind direction. TAS is literally your true speed through the air.
I think you just got confused by mixing up turn rate with turn radius.
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yea i was in brain fart mode ...
i did not phrase my question well either ...
happens from time to time ...
+S+
t
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FLS nailed it. When TAS > IAS, same Gs, same turn rate, bigger turn radius as compared to when TAS = IAS.