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Author
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Topic: Drag airfoils?
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Pang
Pilot
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posted 07-08- 02:09 AM
   
Instead of applying a CYL to the landing gear for the modelling of drag, would it be possible to create an airfoil.sm that contained a constant drag coefficient along with zero values for the lift and moment?IP: Logged |
bjorn
Pilot
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posted 07-08- 06:20 AM
Good idea indeed, Pang. This would be useful for adding drag on damage too.
_
/Bjorn.
IP: Logged |
Pang
Pilot
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posted 07-08- 06:25 PM
Oh boy, this was fun. I created an "airfoil" if you can call it that named DRAG.ppf. When in the Ju88a4, (in which I replaced the 'Cyl with the 'DRAG on the gear) I dropped the gear and as they slowly lowered, the elevator pressure needed slowly to be increased to hold a level attitude, and my speed began to drop. It was a wonderful feeling, but perhaps just a tad too strong. Not sure yet. Well, I tried a second flight where I lowered the gear at a safe speed like 160 or something, then went full throttle and put the nose down. At around 290 ias the gear began to bend back, and at just above 300, they broke off, but one at a time, and maybe a second in between!!If anyone wants to try this file, email me and I'll forward it, or you can make your own. I set the drag coefficient to around 2.5 (constant) and took the lift and moment down to .000001, in case of a division error. I zeroed all the randomizing coefficients, since they are generally zeroes in unstalled flight anyway. ------------------
Pang 33rd~GS
33rd Strike Group IP: Logged |
Pang
Pilot
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posted 07-08- 06:38 PM
in fact, here it is if you want to play with it.
http://home.flash.net/~kwheaton/DRAG.ppf IP: Logged |
Pang
Pilot
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posted 07-08- 06:40 PM
Hey Bjorn, what about making foils that were variations of the original that had reduced lift, and increased drag to simulate damaged wings? Theoretically you could impliment them at various damage levels, right?IP: Logged |
Nat
Pilot
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posted 07-08- 08:32 PM
Pang, gotta say, excellent work... this is something I'd love to see refined and added to all aircraft in the future Packs, ok, it's alot of work.. but damn it's gotta be so much better!IP: Logged |
Raider
Pilot
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posted 07-08- 09:25 PM
 Thank you, I have been messing with the P-51 gear without much luck. This should be just the thing.------------------
Raider 33rd~GS
Raiders Site
IP: Logged |
Tailslide
Pilot
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posted 07-08- 09:27 PM
This sounds like how it was acting when I used the CYL airfoil.. did you try making a version of the CYL airfoil without the lift and moment data to see how it affects the landings? Is there any difference in handling between decreasing the airK, increasing the airArea of the CYL airfoil and using the drag airfoil? TS [This message has been edited by Tailslide (edited 07-08-2000).] IP: Logged |
Pang
Pilot
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posted 07-09- 12:36 AM
Absolutely. There are no (or immeasurably little) components of lift or moment. I haven't messed around with the airK on the 'Cyl, so I couldn't really tell you what difference there is.I tried putting the DRAG.ppf on one side and the Cyl.sm on the other. The plane would pitch down and yaw toward the side with the DRAG.ppf. Also on the Ju88, when I'd take off, I saw a tremendous increase in climbout performance when I brought up the gear, when I had incorporated the DRAG.ppf. This is just a first attempt. I think this should have no lift or moment, but perhaps the drag should be a bit less in the lower alpha's and peak at 90 degrees, then slope back down, if that makes sense. This would model the side forces on a wheel better than the current DRAG.ppf. TS, plug this in on a model somewhere. I'm impressed with the way it works. It's very straightforward. I set it up on the Camel and it did just what I had hoped it would. The drag from the upper wings was pitching the plane up with tremendous force, and there was not enough drag in the wheels and struts to counterbalance it at all. With the DRAG.ppf there, it helps a bunch. To get this amount of drag with the 'Cyl, I had to take all that moment and lift where there should have been none. [This message has been edited by Pang (edited 07-09-2000).] IP: Logged |
Tailslide
Pilot
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posted 07-09- 01:46 AM
Ok, thanks! Will give it a try. TS
IP: Logged |
Tailslide
Pilot
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posted 07-09- 02:09 AM
Works great, excellent find Pang! The pancake effect doesnt happen with a simple drag airfoil. Heres what I used: Parsoft Property File
(
obData 'drag (
dataRowSize 7 dataRows -179.0,0,2,0,0.00000,0.00000,0.00000 180.0,0,2,0,0.00000,0.00000,0.00000 ))
IP: Logged |
Sv
Pilot
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posted 07-09- 07:24 AM
Great! I think this is the way to go... I added the same thing to my SE5a a while ago to simulate the drag from all the wires, but since I needed to bleed more energy ONLY AT HIGHER AOA I had to remove the drag airfoil from the fuselage in order to make the energy bleed variation relative to AOA more apparent.------------------
-Sv =FC=
WWI in SDOE!
IP: Logged |
Maury Markowitz
Pilot
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posted 07-10- 12:22 PM
quote:
Originally posted by Pang:
Instead of applying a CYL to the landing gear for the modelling of drag, would it be possible to create an airfoil.sm that contained a constant drag coefficient along with zero values for the lift and moment?
Stupid newbie questions: 1) wouldn't the drag depend on the angle? I would assume that a "bent back" gear (consider F4U) would have less drag than when the gear is all the way down. No? 2) No moment, is that because moment is "twisting" around the "long axis" of the airfoil? I assume the engine itself makes the nose-down force just by having the drag below the wing? 3) Can parts cover other parts from the wind? If so, how about a high-drag part place at the tips of guns, covered by a breakable part. On the Spit they covered the gun ports with fabric, would this work to simulate this effect? Maury IP: Logged |
Falck
Pilot
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posted 07-10- 12:47 PM
quote:
1) wouldn't the drag depend on the angle? I would assume that a "bent back" gear (consider F4U) would have less drag than when the gear is all the way down. No?
Having constant drag would be like holding a big rectangular piece of metal in the wind such that you always kept the same cross section relative to the wind. Is this accurate? No. Forturnately, openplane allows airfoils to be turned off and on, so when the gear is raised the effect of its airfoil goes away. quote:
2) No moment, is that because moment is "twisting" around the "long axis" of the airfoil? I assume the engine itself makes the nose-down force just by having the drag below the wing?
Correct. The airfoil will not try to torque around it's center of mass, though having a drag force below the aircraft's center of mass will pitch the aircraft's nose down. quote:
3) Can parts cover other parts from the wind? If so, how about a high-drag part place at the tips of guns, covered by a breakable part. On the Spit they covered the gun ports with fabric, would this work to simulate this effect?
Not sure on that. Though propwash is modelled i dont think shielded airfoils are modelled, though this is pure speculation. [This message has been edited by Falck (edited 07-10-2000).] IP: Logged |
Michael Harrison
General
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posted 07-10- 02:31 PM
just jumping in quickly....no. objects blocking the wind for other objects is not available currently.
gone again...
IP: Logged |
Maury Markowitz
Pilot
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posted 07-10- 04:53 PM
quote:
Originally posted by Falck:
Having constant drag would be like holding a big rectangular piece of metal in the wind such that you always kept the same cross section relative to the wind. Is this accurate? No. Forturnately, openplane allows airfoils to be turned off and on, so when the gear is raised the effect of its airfoil goes away.
That's cool, but I was thinking specifically of planes where the gear retract sequence can result in varying drag. The F4U is a good example of this, simply because the wheel laid flat and was likely very draggy when it first comes out of the well - and some lift too I'd suspect. I guess this just means that you need different DRAG airfoils for each plane. While on the topic, does anyone know what the F4U "dive breaks" did? I know they lowered the gear "cover", did they lower the gear too? quote:
Not sure on that. Though propwash is modelled i dont think shielded airfoils are modelled, though this is pure speculation.
But as you note above, "turning it off" has the same effect, so I'm no longer concerned about that. All very cool. Maury IP: Logged |
Tailslide
Pilot
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posted 07-10- 05:40 PM
This should do what maury is talking about although I don't need it for the yak gear. You could add more points to make the curves bell shaped. Actually just take the CYL airfoil and zero out the lift and moment, it has a drag profile like this but bell shaped.Parsoft Property File
(
obData 'drag (
dataRowSize 7 dataRows
-179.0,0,0.2,0,0.00000,0.00000,0.00000
-90.0,0,2,0,0.00000,0.00000,0.00000
0.0,0,0.2,0,0.00000,0.00000,0.00000
90.0,0,2,0,0.00000,0.00000,0.00000
180.0,0,0.2,0,0.00000,0.00000,0.00000
)) IP: Logged | |
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