Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: F4UDOA on July 13, 2000, 12:03:00 PM
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Gents,
I was reading the previous post on P-47 performance when I read that in an offline test the P-47 had the best ability to glide at 150Mph without loosing altitude so I decided to do some testing myself. Behold this is an accurate statement. The P-47 with 75% Fuel (I used 75% for all test) will hold a glide better than the P-51, A6M-5, P-38L and F4U-1C. I used these A/C to test because they offer a variety of flight Characteristics. The P-51D because it has the lowest drag of any WW2 fighter and it sank like a brick loosing 4K a minute compared to 2800FPM to 3000Fpm for the P-47. The P-51 also has better wing loading than the P-47. So I tried the Zero low drag but no lower and the best wingloading in the game. Nope, she sank like a brick too at 4k a minute worse than the Mustang. So then I thought of gliders and how they fly, and I chose the A/C with the most glider like features the P-38. It also has the highest aspect ratio in the game(wing span devided by chord, a feature made to increase range but detracts from maneuvering) Nope, brick city even with flowler flaps deployed. All test with flaps made the glide steepen and loose altitude and an increased rate, even the P-47. So I tried the F4U, the A/C with the lowest aspect ratio but with better wing loading but slightly higher drag. And that is as close as I got. The F4U varies between 3K and 3500fpm lose of alt in a 150mph glide. So it would seem that low aspect ratio combined with low drag would be the answer to best glide characteristics.
Briefly
P-51D
Aspect ratio= 5.87
Profile Drag= .0176<==Lowest
Wing loading= 40.74
P-47D-30
Aspect Ratio= 5.56
Profile Drag= .0251
Wing loading= 47.66 <===High for fighter
P-38L
Aspect Ratio= 8.26<==Highest
Profile drag= .0270<==Highest
Wingloading= 53.40<==Highest
F4U-1D
Aspect Ratio= 5.35<==Lowest
Profile drag=.0267
WingLoading= 38.21<==Lowest
I really don't know which factors have the greatest influence on glide but I would assume that they also affect zoom. Maybe Wells or Nikalas can explain what factors affect these characteristics as well as what other flight factors may be affected by it.
Later
F4UDOA
I do not have enough data on the Zero to be accurate. I will test the FW190 later.
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"I really don't know which factors have the greatest influence on glide but I would assume that they also affect zoom."
The factor that effects glide the most it decreasing the prop RPM (minus key) which I assume "feathers" the prop. (although my prop never stops or feathers in the P-47)
It alters your glide figures 1000-1500 FPM.
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You cant alter prop RPM when engine is off..
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I'm an aerospace engineering student, but i think the way pilots learn glide ratio is best (im a student glider pilot .. (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif) )
your glide slope is determined by your L/D ratio... Lift over drag. For exacple, the Scweitzer (sp?) glider that i am learning in has a L/D ratio of 22:1 at 60 knots, which means that its wings are producing 22 pounds of lift for every pound of drag on the airplane. This can be translated into a glide slope, in that the airplane will glide 22 feet forward in the air for every foot of altitude it loses. So, if you are at an altitude of 1000 feet, you better be within 22,000 feet of landing or you ain't makin it home (unless you catch a thermal (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif) )
The mustang actually doesn't have such a great drag coefficient at low speed F4UDOA. At slow speeds, induced drag is contributing more to drag then form drag, and since at low speed the wing must fly at higher AOA to maintain lift, the p51s laminar wing actualy produces MORE drag... the time when the p51 has its advantage is at high speed/low AOA when it is producing less drag because of its airfoil shape.
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Sure ya can Fishu. Feather the prop, it stops, unfeather the prop, the wind picks up the pitch of the blades, and away she turns.
Not sure about WWII props, but ya activate a oil pump that unfeathers the prop to restart a engine in flight.
My point was that I thought decreasing the RPM in this "game" simulated feathering of the prop, ala very little prop drag. Ya can't see it though with the graphics right now.
Just a guess, anyone know? It sure makes your glide better.
[This message has been edited by Creamo (edited 07-13-2000).]
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Zigrat,
So which A/C should have the best GlideRatio?
It seems somewhat unreasonable that a 14000lbs airplane with such high wingloading would have a better glide ratio than any of the A/C that I used for comparison. But I am not sure how to calculate the factors involved. Anyone want to take a guess?
F4UDOA
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You need to figure out the lift force acting on the plane, and the drag force, that will give you the L/D or glide slope.. please note that prop drag has a large role to play in this and I have NO clue how to calculate prop drag.
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from your tests it would indicate the L/D was about 4/1 for the hog, about 3.5/1 for the stang, and about 5/1 for the jug (there are all in head calculations so dont take them as too accurate ;0 ) This seems low since i know the f16 las a L/D in a glide config of 7/1 and my glider has a 22/1 L/D but then again i have no real data on the airplanes so .. (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif)
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Zigrat,
I seem to remember reading that the F4U had a glide ratio of 12:1. I am not saying that it is better or worse than any other fighter, it is just a number that I remember.
An F-16 is an Arodynamic brick at 4:1. And a sail plane quite a different story at 22:1 so 12:1 sounds reasonable for a WW2 fighter. The question I am pondering is how does this piece of the physics model affect the rest of the FM if it is wrong? Does it mean that all A/C are not aerodynamically "clean" enough and this is causing not only glide but but turning fights to degrade to quickly into slow speed maneuvering. Pyro said he was looking at some things in the FM's regarding sustained turn rates. I wonder if any changes were made in 1.04? It seems the more you look the more things point to the FM being a little to slow.
Later
F4UDOA
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The C47 has a glide ratio of either 15 or 17:1. In fact, its glide ratio was so good, it was better at gliding than the gliders used at D-Day. The army performed test on the C47 after the war to be used a towed glider. The test worked very well but gliders were just too slow by then.
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Originally posted by Creamo:
Sure ya can Fishu. Feather the prop, it stops, unfeather the prop, the wind picks up the pitch of the blades, and away she turns.
Wee, it actually does it now... couple times when I've ran out of gas, RPM havent move anywhere!
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The lift force is the weight of the aircraft. The lowest drag point would be where the induced and form drag curves cross each other. The induced drag coefficient (Cdi) is equal to the form drag coefficient (Cd0 in AHT). If you use the coefficients in AHT, solve for CL, you can figure the glide speed and drag force (2 * Cd0) to get an estimate on glide performance.
P-51D (9500 lbs, Aspect ratio = 5.8): CL = 0.57, V = 168 mph, Drag ~ 593 lbs. L/D = 16.0
P-38J/L (17500 lbs, aspect ratio = 8.25): CL = 0.84, V = 158 mph, Drag ~ 1129 lbs, L/D = 15.5
P-47D (14500 lbs, aspect ratio = 5.6): CL = 0.61, V = 176 mph, Drag ~ 1012 lbs, L/D = 14.3
F4u-1 (12000 lbs, aspect ratio = 5.35): CL = 0.67, V = 149 mph, Drag ~ 952 lbs, L/D = 12.6
F6f-3 (12500 lbs, aspect ratio = 5.5): CL = 0.69, V = 146 mph, Drag ~ 990 lbs, L/D = 12.6
Based on those numbers, the P-51 should glide very well. The above figures don't factor in the prop drag.
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Thank you, Wells.
But I doubt some of them will get it. (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif)
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Thanks Wells,
I thought that 12:1 figure sounded familier.
My question is now how would that affect the physics of the rest of Simm if the
E-retention is approx a 1/3 of what it should be? Does it slow turns as well? Does it affect accelleration? I think one side note that would come from changing any of these characteristics would be having to raise the G-force limits on the pilots to an increased time at high G. Otherwise high speed maneuvering will become impossible.
Later
F4UDOA
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Wells can you do the same calculation for the 109G10 please? I canīt believe that it has such a bad aerodynamics. thx
niklas
[This message has been edited by niklas (edited 07-14-2000).]
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Niklas,
I think the AH F4U is more like 4:1.
12:1 is just a number I remember reading but I have no proof of where it came from. So it looks like it is off by 2/3 of what it should be. The A/C that are really porked is the P-51 and P-38. They are much worse off in AH as far as my testing goes.
But looking at Wells numbers it seems like there is a window for glide speed to be effective. The P-51 seems to glide well but only at high speed were as the F4U and F6F are better at low speed. I belive this is because of the wing design of the Navy planes being more effective at High AOA.
If I can figure out how Wells did it I will try to see what happens to the P-51 When it slows down. My guess is that it falls like a rock. I need to retest and see how these numbers compare at the A/C best glide speeds.
Numbers like this give you a better Idea of what the A/C range of performance was designed to be. It is no accident that the Navy planes glide best at speeds aproaching their landing speed on a carrier.
Later
F4UDOA
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DOA, I got between 7-9 glide ratios. Are you feathering the prop? Use the keypad_minus key.
Niklas,
I will use 370 mph, 2000 hp, 80% efficiency and 7400 lbs to figure the drag coefficient. Wing area is 173 sq ft.
1620 lbs thrust
Cd0 = 0.0259
Cdi = 0.0008
For glide, Cdi = Cd0 = 0.0259
If Cdi = Cl^2 / (pi * aspect ratio), then
Cl = sqrt(Cdi * pi * aspect ratio)
Cl = 0.70 (aspect ratio = 6.1)
Then V = 155 mph to produce 7400 lbs of lift
Drag force ~ 551 lbs
Lift/Drag = 7400 / 551 = 13.4
It could be that thrust values in the sim are on the high side, necessitating higher drag to keep top speed and climb in check, but adversely affecting glide.
[This message has been edited by wells (edited 07-14-2000).]
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Wells had a technical answer but he was right. It's not as simple as picking a speed and seeing which plane has the best L/D. Each plane reaches there best L/D at a specific speed. You can't reasonably compare a Zero to a P51 at 150 mph, just like you can compare them at 400 mph. Each plane is different.
What is important in sailplanes, is a fairly flat polar curve. With L/D on the vertical and speed on the horizontal, the better the glider, the flatter the slope at any given speed. I believe the best L/D is where the minimum sink polar intersects the best glide speed.
Redcoat
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some glider ratios:
DG-600 1:49 at 119 Km/h (GREAT COOL PLANE)
LS-3a 1:40 at 100 Km/h (i fly usually)
NIMBUS-4 1:60 at 110 Km/h
ASW-22BLW1:62 at 110 Km/h
so pls model me a ASW-22 BLW.
DUCKWING can tow me up in a C47.
would be nice to do some hanggliding at the
AH mountains. ot may be thermals under the
clouds??
HABICHT
XO JG54
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Just to note the difference between glide for range and glide for endurance. While something like a P-47 may glide farther than an F4u, the Corsair might be able to stay in the air longer due to it's lower glide speed.
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Wells,
I have been testing my glides this way. I haven't however been able to feather the prop on my F4U. I think only certain A/C have that capabilty. First I set my auto speed for /.speed 150 then when speed is stable I kill the throttle. Wait for the decent to stabilize and measure it on the climb/dive meter. The P-47 is the best I've seen so far. I am surprised by it's ability to glide considering it's drag coefficient does not seem significantly lower that the F4U and it is over 2000lbs heavier. The Mustang and P-38 I would expect to glide well due to aspect ratio and the low drag of the P-51. Does the AOA of the wing vary in the equation? I thought that different airfoils also played a role in glide as well.
What do you think of the climb and accelleration of the P-47??
Later
F4UDOA