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Author
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Topic: Airfoils Confusion
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Whirlwind
Pilot
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posted 02-10- 12:15 PM
   
Ok, I redid the Viper (the sucker is still black as night, regardless of color, but I have to fix it) import into a .sm file, and it appears to be suffering from wing stalls at around 360 mph. I listened to the noise for once that it was making and it was the thump thump of a stall. It wasn't wing shake because there are no longer any DOF's left on them (aside from the required airlerons).I'm clueless. I still need to finish the LOD rename parts, and add a cockpit, gear plus change the winding on three faces (periodically disappear but no problem, got a weekend). If I can't get it above 360mph, I might as well put the Me262 parts back on (zoomed out it looks really cool, like an experimental German jet plan). IP: Logged |
Zurawski
Pilot
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posted 02-10- 12:31 PM
Sounds like (Tail jump in where ya can...)... those tiny wings cannot generate enough lift. OR ... because of the small amount of lifting bodies (airfoils) you don't have enough thrust to overcome it. I'd either "fudge" larger airfoil surface ..or.. add an cylinder airfoil to the body of the craft ..or.. increase HP & RPM to generate more thrust. BUT then again ... I don't know squat ... Tail? IP: Logged |
Whirlwind
Pilot
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posted 02-10- 01:59 PM
It is a wobbley type deal, simular to wing flux from overspeed, which requires DOF's in the wings (any wing). I can keep accelerating in a generally level flight (with a great deal of plane jockeying - yeehaaa, cowboy!), but by 600mps you can expect a flay spin.IP: Logged |
Michael Harrison
General
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posted 02-10- 02:01 PM
Don't even think about making the airfoils the same size as the real wings on that sucker.  I would give them airfoils that would be the equivalent of an aircraft of the same size. Remember, the Viper didn't actually exist  and would never fly in an atmosphere with only those puny wings for lift. IP: Logged |
Whirlwind
Pilot
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posted 02-10- 02:03 PM
The general goal is to get rid of the false wings and go for the controlled rocket experience. I'm slowly getting enough data for doing just that .IP: Logged |
Zurawski
Pilot
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posted 02-10- 02:06 PM
I'd even go so far as add a couple "invisible" wings in the nose ...BTW ... the CofG has to be horrible on that thing!
[This message has been edited by Zurawski (edited 02-10-2000).] IP: Logged |
Tailslide
Pilot
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posted 02-10- 03:28 PM
BG trivia: I was watching a documentary about Battlestar Galactica.. one of the show's creators was Mormon and a lot of the legends in BG are loosely based on Mormon beliefs. (IE the 13th tribe of Isreal, the lost 13th tribe ..) Whirlwind, if you can get that sucker going fast enough you could get by with really tiny wings. The stall speed would be pretty high but they must have had some kind of landing boosters I could almost swear I could remember some VTOL like behaviour on those Vipers. Maybe your wings are too big for how fast you are going? Try making them smaller, also get rid of any incidence on the wing or tail and balance the CG so it flies straight with no trim at high speed this will cut down on some drag. TS
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Whirlwind
Pilot
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posted 02-10- 04:33 PM
I was thinking of attaching flap DOF's to the virtual propellers, but logic set in and I realized that that would simply push the nose down in a very horrible manner. All I would need to do is add a parachute to the aft and stiffen the main gear.I'll probably do an experiment or two by the end of the weekend with the 'realistic' size airlerons and such. IP: Logged |
Sv
Pilot
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posted 02-11- 06:20 AM
cylinder airfoil:Am I correct in assuming that a cylinder airfoil NEVER produces lift an any AOA, just drag? That is what I would expect. -Sv IP: Logged |
Zurawski
Pilot
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posted 02-11- 08:58 AM
... SV,an airfoil's and ailrfoil ... yes it'll produce drag. However, despite it's much reduced lift-properties ...it is STILL is a lifting body ... IP: Logged |
Tailslide
Pilot
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posted 02-11- 10:55 AM
Thats my understanding too Zur. I have a pretty cool picture of an Isreali F-15 that had it's wing completely blown off to the fuselage (no wing at all). The guy landed it. The manufacterer told them it was impossible when they asked, so they sent the photograph = ) Apparently the fuselage was generating enough lift to keep the plane horizontal. Not that their fuselages are anything like ours but pretty amazing. TS
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Michael Harrison
General
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posted 02-11- 11:08 AM
Even a flat plate will generate lift.IP: Logged |
Sv
Pilot
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posted 02-11- 11:14 AM
Ok,So how do you measure a cylinders AOA??? I thought cylinders were used because with a perfect cicle profile, there is no AOA, there for, if there is lift, the lift vector is.... ? I agree a flat plate will create tons of lift at a high AOA, but a cylinder? So how much lift does a cannon ball have acting on it as it flies through the air? I know I must be missing something, so please fill me in. I am using cylinder airfoils wrong if they do indeed create lift... Thanks,
-Sv IP: Logged |
Tailslide
Pilot
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posted 02-11- 11:26 AM
You're thinking of the flat front part of the cylinder and the plate SV. It's the air going over the top and bottom of the cylinder that gives the lift, ignore the flat part at the front. TS IP: Logged |
Sv
Pilot
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posted 02-11- 11:40 AM
Ohhhh! So it's not a "traditional" cylinder airfoil that is used for basic frontal drag then...I assummed a cylinder airfoil looked like a perfect circle on profile. This is used allot to simulate frontal drag that you don't want to create lift. - well at least my dad told my that when I was a kid... So not all "cylinder" airfoils are alike then, right? Depending on how long the plate is compared to the round part you will get different airfoil properties... right? Thanks for clearing this up... this makes a big difference on some of the FM stuff I am doing... -Sv IP: Logged |
Sv
Pilot
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posted 02-11- 11:49 AM
Wait... now I'm really confused.. are we talking about a cylinder like a tube of a rocket with a flat front? Then I see your point TS, but airfoils are always considered by profile, not planform, right? I need to understand this...thanks for the help.-Sv IP: Logged |
Tailslide
Pilot
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posted 02-11- 01:27 PM
It's just another airfoil.. it has as much drag or lift as you specify.. you can make your own cylinder airfoil with whatever properties you want. The way I understand it the 'CYL airfoil that comes with the game models the lift and drag properties of the sides of a cylinder to approximate effects of air over the fuselage. It wouldn't model the flat front of a cylinder since ww2 planes didn't have flat fronts. TS
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Whirlwind
Pilot
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posted 02-12- 06:38 PM
I moved the wingtips onto the false wings and managed to get the plane up to 475 before the thing started to show minor wigglings as mentioned before. At 600, I was in a bucking bronco. I deleted the parent wings (they looked so lonely) and adjusted the COG and outerwings so now the thing is a tad bit nose heavy, but flyable enough to to speed testing.I am thinking of resetting the winglet's transformations and having a go at it again. I might also try adjusting the winglet's AOA. Landing is out of the question right now because OOPPS, I deleted the landing gear... I would have needed to redo them anyways. This just bugs me to no small extent. I know I am probably missing something straight forward, but just can't see it. Of note, the Viper has 3 body sections and therefore 3 cylendrical airfoils. IP: Logged |
Sv
Pilot
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posted 02-13- 09:02 AM
I see exactly what you are saying now Tailslide, but I would like this verrified unless you are 100% sure. It seems from the behavoir of the rudder on the WW2 planes that this is not the case. Look at the force vectors when you apply rudder - I see no sideways force vector related to the AOA induced on this cyl airfoil. Either that or maybe it is too tiny to see easily. Well this is just what I think I see. you usually prove me wrong Tailslide LOL -Sv IP: Logged |
Sv
Pilot
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posted 02-13- 09:13 AM
OK TS, you are 100% correct I was looking at the wrong line heheh - there is a lift vector that is effected by AOA in all directions. This is cool. I will make my updates... So it seems we also need a cylinder airfoil like the one I spoke of. We can make this easy, right? Just an airfoil that has 0 lift for all AO, and a fixed flat drag line - the same drag for all AOA. This will simulate the cylinder I need.. does this make sense? I would use this in cunjuction with the current cylinder to simulate the drag of the fuselege. Also I could use it by itself to simulate the combined drag of the wing struts and wing wires... -Sv IP: Logged |
Tailslide
Pilot
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posted 02-13- 02:03 PM
If you have the same drag at all AoA the front of your plane would have the same drag when the plane is falling straight down or falling backwards as it would flying straight ahead. I'd make a drag graph that has a big bump in the center and tapers off to nothing at +/- 90 degrees (the airfoil files range +/-180 degrees). TS
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Sv
Pilot
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posted 02-13- 06:36 PM
I can dig it, thanks TS IP: Logged |
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