Fuselage Airfoils (was Knife Edge flight on General)

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Author	Topic: Fuselage Airfoils (was Knife Edge flight on General)
Pang Pilot	posted 06-25- 02:04 PM Ok, moved this from the General area for further discussion. Have any of you guys been using airfoils in place of the CYL for the fuselage? I found that Sv had made use of a fuselage airfoil, and when I tweaked the area and chord and airPt, I was able to sustain knife edge flight in a Sopwith Camel! I'm thinking this is a real step forward in the FM since it adds significant realism in side-slipping. ------------------ Pang 33rd~GS 33rd Strike Group IP: Logged
Tailslide Pilot	posted 06-25- 02:54 PM Razor, I see what you describe at airshows too. The pilots will go by fairly slowly and the tail will "hang" down so they are almost hanging on their prop as they go by, the airflow pulling their tail back so they are in a 45 degree angle. With the plane at such an angle I can't believe prop wash is having any effect (although in the SDOE world even in this position the prop wash will still be trying to force the plane into a "tail up" attitude). Do you have to use a special prop pitch to do this? It seems to me that SDOE props as they are currently implemented would stall out at such an extreme climb angle.. TS [This message has been edited by Tailslide (edited 06-25-2000).] IP: Logged
Tailslide Pilot	posted 06-25- 04:45 PM Pang, heres a brainteaser: I eliminated the fuselage airfoil on my plane and made my rudder airfoil so it only had an area of 1 square foot. When I try to transition to knife edge flight the tail refuses to fall and point the nose up.. whats holding the plane level to the horizon? The wings and horizontal stabs, fuselage are generating no lift. The only thing I can think of is the propeller blades may be generating more lift when they reach the top, pulling the plane into level flight??? TS IP: Logged
Mighty Pilot	posted 06-25- 06:02 PM Prop wash has a huge effect in that instance. That's a slow speed manuever under high power. Remember, it doesn't matter which direction the plane is pointing. The prop wash is still going to go generally down the length of the aircraft. The huge "sideslip" will cause turbulence, but there will still be a lot of air getting forced past the tail. IP: Logged
Tailslide Pilot	posted 06-25- 06:24 PM Ok... so I tried leaving the fuselage airfoil off and setting the vertical stab to normal or even really high values. The strange this is the larger area I gave the rudder the less able i was get the tail to point down. At the smallest setting (1 foot) the tail went down the most. I also tried setting huge values for propwash and the tail would still not go down. TS IP: Logged
Tailslide Pilot	posted 06-25- 06:27 PM I wonder if this could be related to the strange way planes yaw in level flight in SDOE.. IP: Logged
Tailslide Pilot	posted 06-25- 07:58 PM It seeems to me from watching real planes do it that the tail down aspect is more a function of the plane going so slow the weight of the plane rotates it tail down and the rudder is used to balance it in this position more than force it into this position. Maybe Razor can enlighten us.. TS IP: Logged
Pang Pilot	posted 06-25- 08:05 PM TS, wait a minute, you're saying that you are flying in knife edge here? IP: Logged
Tailslide Pilot	posted 06-25- 08:11 PM Thought this was interesting.. its instructions on trimming an RC plane. Sorry for all the posts but I think Pang hit on an interesting test case where the SDOE planes may not be behaving properly. -- 10. Dihedral: Fly on normal pass and roll knife edge. (left and right) A: Model holds knife edge; No adjustment needed. B: Model rolls in direction of rudder; Reduce dihedral. C: Model rolls opposite direction of rudder; Add dihedral. ************************************************************************ 12.Pitching in knife edge: Fly per test 10. A: No pitch up or down; No adjustment needed. B: Nose pitches up; * C: Nose pitches down; Reverse below. *Alternate cures: 1) Move C.G.aft 2) Increase wing incedence; 3) Add down trim to ailerons. IP: Logged
Tailslide Pilot	posted 06-25- 08:39 PM Yes Pang, knife edge. It seems like no matter how much propwash or how big a rudder the plane always wants to nose down in knife edge flight. It seems to me if you start out in a nose up attitude the weight of the plane would try to keep it in that attitude I'm not sure whats happening in SDOE to make the plane want to go nose down even with full rudder. Here's a pic i found of an R/C in knife edge: and heres some quotes: "> What's "knife-edge" flight? When the aircraft is travelling with it's wings straight up and down, one pointing to the sky, the other at the ground. The rudder then acts as the elevator and the elevator acts as a rudder. Some aircraft a barely or not capable of knife edge flight, such as many trainers. When done by a capable aircraft with a good pilot, knife edge flight can be really cool to watch, especially a knife edge loop" "In simple terms, knife edge flight occurs when the plane is flying with the wings perpendicular to the ground. The fuselage becomes the wing and the rudder becomes the elevator. The flying attitude is generally with a marked 'nose up' attitude. IMO one of the best models to fly or watch perform knife edge is the CG Bucker Jungman. The big fuse side on has a great airfoil and that huge rudder has to be seen in action...FWIW I always use a pull - pull system on the rudder to avoid rods/onnectors flexing when 'pushing'. see also Trimming etc (and tips on Ed Hartley's RC Pattern pages)= Aerobatics Pattern & F3D http://www.wtp.net/DBEST/allseq.html http://www.gsal.org/ http://www.wtp.net/DBEST/patternpage.html http://www.wtp.net/DBEST/trimchrt.html http://www.rcpattern.nxs.net/default.htm http://tigers.hypermart.net/imactips.html http://www.mini-iac.com/ http://web.one.net.au/~bdec/models.htm " IP: Logged
Tailslide Pilot	posted 06-25- 08:51 PM Here's the Yak in the same position.. the nose is falling even though I have full rudder on. IP: Logged
Tailslide Pilot	posted 06-25- 08:55 PM HA ! Interesting.. look at the incredibly hard to read yellow numbers! The vstab is generating almost no lift at AoA 4 if I am reading right ?!?! IP: Logged
Tailslide Pilot	posted 06-25- 09:17 PM Could this be because the deflected rudder is parallel to the direction of the plane's travel and OP does not account for the air streaming down the sides of the plane and around the stabalizer??? [This message has been edited by Tailslide (edited 06-25-2000).] IP: Logged
Tailslide Pilot	posted 06-28- 08:51 PM bump.. Pang you there? IP: Logged
Sv Pilot	posted 06-28- 10:02 PM Without a fuselage airfoil there is no "wing" in the knife edge. The cyl airfoil is soooo weak as far as lift that it is almost nada. If you add a fuselage aifoil near the CG to simulate the lifing effect of the fuselage itself you will get the expected knife-edge flight behavior. Now if the airfoil you use for the fuselage airfoil is given lots of drag I think it works good (not like mine), but one problem: In anything less than pure knife-edge (say 45 degrees roll with a high AOA) you get a diminished lifting effect with the rest of the force vectored into an enhanced yawing effect - this is wrong for a cylinder shaped fuselage. What is needed is a true cylinder aifoil to simulate frontal drag (all AOA has same drag coef and no lift coef), then a special new airfoil that produces lift and drag coef's based on AOA but vectors this lift against gravity ignoring any roll angle of the object. This would simulate the side of a cylinder fuselage through the air. This is the way the current cyl airfoil works, right? It is just that the lift of this airfoil seems to low, especially at higher AOA (like knife edge) Also isn't the airPoint of these cyl airfoils always near the nose? Shouldn't they be at or close to the CG? (really the center of area to be exact) Anyway I can not manage to edit the cyl airfoil, it is sm and the wing extractor crashes trying to load it... it must have a differnt format or something. As far as I know the lift force should always be vectored perp. to the airflow (not perp. the air object), but I am not sure how OpenPlane does this. Looking at your pic TS it looks like the prop lift is indeed perp to the airflow and not the prop itself, but maybe this has to do with prop twist? I am still curious abou this issue... -Sv IP: Logged
Hawk JAG	posted 06-28- 10:43 PM One thing you are not considering is power. I fly RC and it takes a very powerful engine and a big prop to perform knife edge. If you do not have enough power the nose will drop and the plane will fall out of knife edge or never achieve it in the first place. A large, heavy warplane could not do a good knife edge. It takes a light, powerful plane to do this manuever. IP: Logged
Tailslide Pilot	posted 06-29- 02:03 AM The Yak was the lightest plane of the war with the best climb rate and one of the largest rudders. I have no idea if it should fly knife edge or not though. I don't think what we are seeing in the pic is a power issue at it's still going 260 mph. It does this at 300mph. I even tried boosting the engine and the prop blade but same result. The plane keeps speed but noses over. The long lines from the fuse indicate it's generating a good amount of drag and lift. SV, don't you find it interesting in the screenshot is there is no yaw force at all being generated by the deflection of the rudder? At 4 degrees AoA the vstab is not stalled, why shouldn't it be exerting a force? Without any force on the tail the nose has to fall down. Hawk, is most of this force supposed to be generated by propwash? I tried bumping up propwash to 200% of what the prop was actually putting out but had the same result. TS [This message has been edited by Tailslide (edited 06-29-2000).] IP: Logged
Tailslide Pilot	posted 06-29- 02:52 AM OK I tried another experiment. I tripled the fuselage area (tons of drag,lift) I tripled the horsepower and I tripled the number of propeller blades. The yak can now climb straight vertical without losing speed However, it still noses over in knife edge. TS IP: Logged
Sv Pilot	posted 06-29- 08:38 AM TS, I can not see to clearly in the pic, do you have full left rudder? If so then the force could very well look like that, right? The high AOA on the fin would cause you to see allot of force yawing the plane nose-down. But since you have the rudder kicked left, that pushes the yaw nose-up - they cancel! Or you could think of it like this: The "real" AOA of the rudder in that pic is 0. When you defelct a control surface you are really changing the virtual AOA... a wing at 0 AOA with the aileron pointing downward is really acting like a wing in a higher AOA... the chord line of the wing has been altered. So my guess is that the plane will not knife edge because of a combination of these 2 things: 1. You need a more prodctive fuselage airfoil, either a cyl airfoil with more lift, or a vertical fin near the CG to simulate the fuselage lift. 2. The rudder is not able to puch enough AOA on the fuse to keep the plane in a knife-edge. BOTH these issues MUST be addressed I think. It is like a plane that has a wing (fuse in this case) that stalls in level flight... if you give the wing more lift it will help, but you also need an elevator that can push the wing into the needed AOA. But I don't understand airWash, so maybe I am way off base... maybe knife-edge is 90% prop based. But you can get the plane to knife-edge if you make the rudder more effective (NOT the fin!) and give the fuselage airfoil more lift... but I am not sure exatly how teh cyl airfoil works... it may not be vectoring it as expected... try a real airfoil - copy and past the fin to the CG... -Sv IP: Logged
Hawk JAG	posted 06-29- 09:33 AM I used to think knife edge was from pure power only, then I saw Benjiman fly the GEE BEE knife edge and realized that the big, fat airfoiled fuse was also helping. In RC, power is knife edge. Not speed, but power. I am not sure how the prop helps with the airflow over the body but it must be because the body becomes a wing at knife edge. I have seen very little knife edge from RC warbirds, even overpowered ones, but lots of them from Sukhois, Caps, ect. [This message has been edited by Hawk (edited 06-29-2000).] IP: Logged
Tailslide Pilot	posted 06-29- 10:24 AM I tried a fuselage with three times the area.. tons of lift and tons of drag as you would expect but with no force on the tail it still falls down. Putting a flat airfoil on the body makes the plane fly strangely. I'm stumped. The CYL airfoil looks ok looking at the pic.. lots of lift lots of drag. I wonder if the moment values for it are not contributing to the yaw. I saw no change in this aspect at all after tripling the size of the fuse airfoil. However, Razor said he's flown knife edge with only a pipe shaped fuselage so this may not be necessary for maintaining attitude. Altitude maybe, with a less powerful plane. SV, I'm more intersted in figuring out why the CYL airfoil is not working than adding in fins to make it behave a certain way. If we can figure this out it may solve other handling issues in the sim.. Yes, I have full left rudder applied. There should be some yawing force at all even if its not enough to keep the nose up though IMHO. SV, the rudder is not generating any yaw force at all so there is nothing to cancel out. TS [This message has been edited by Tailslide (edited 06-29-2000).] IP: Logged
Sv Pilot	posted 06-29- 12:42 PM I am confused, the red drag lines should be directed opposit the aircrafts actual heading through the air, right? If that is so, then the fuselage has 0 AOA; the drag lines are parallel with the fuselage. Shouldn't the drag vector lines look to be at 9:00 in this screenshot and not 7:00 as they apear to be? If you are at a high AOA knife-edge here then why is the lift vecotor of the cyl aifoil acting as drag? What is the drag vector of the cyl airfoil not opposite the aircraft heading? (It is almost exatcly parallel to the fuselage) Also note that in this pic that the wings are producing as much lift as the fuselage, not much. The cyl airfoil needs to produce more lift to hold the aircraft up, no? That AOA readout is cool! Is that in the latest beta build? I will try this out tonight, cool! -Sv IP: Logged
Mighty Pilot	posted 06-29- 12:47 PM One thing to keep in mind, here. As I remember the discussions between Eric, John and Michael when we introduced the cylinder airfoil, the problem we were addressing at the time was drag. As far as I know, nobody looked hard at the lift they were producing. So there's a good chance that the cylinder airfoil isn't producing appropriate lift or moments. I know Michael is planning on looking at why we can't do knife-edges in RC Sim. He or I will keep you informed on whether that research results in code changes, or just model changes. IP: Logged
Tailslide Pilot	posted 06-29- 01:00 PM SV, not sure how the drag calculations work in SDOE so I can't say if it is correct or not to have the drag vector parallel to the plane. I emailed off the pic to MH I hope he can provide his input when his schedule eases up. The reason the wings are providing lift is I am not perfectly 90 degrees. The nose falls fairly quickly and I'm not able to fly perfectly edge on in external view and take a screen shot at the same time. The more edge on I am, the faster the nose falls. I don't think the lift on the fuselage is necessary to keep the plane angled up if Razor was able to do this with an aircraft with a pipe body. I did try giving it three times the area (and three times the lift) and noticed no difference in attitude of the plane. SV, it's very cool! You can also output it all to a text file and graph it in a spreadsheet ! Has anyone been able to do a graph of the CYL airfoil? I can't get it to load into Etienne's editor. Thanks Mighty, please keep us posted if you hear anything ! TS [This message has been edited by Tailslide (edited 06-29-2000).] IP: Logged
Laika 801 Pilot	posted 06-29- 01:31 PM Booooaaaaaaa ! Thats really interesting (to read). I really hope that you FM-guys find more things out and get it working ! LK IP: Logged
Tailslide Pilot	posted 06-29- 02:16 PM For the curious.. IP: Logged
Tailslide Pilot	posted 06-29- 07:04 PM Looks like a normal airfoil but symmetrical.. I wonder if it would help to amplify the moment values to get it to pitch up more. TS IP: Logged
Pang Pilot	posted 06-29- 07:52 PM Here's the code I have in the Sopwith Camel right now, dunno if this helps... (obProto 'CAirfoil) (airWing) (airSection "ALBTAIL") (airK .5) (airAR 1) (airArea 40) (obAirfoil (airChord 18.75 airPT 0.283333, 2.277656, -0.100000 )) ALBTAIL is a modified NACA0010, aspect ratio much less than 1 really bleeds speed quickly, in fact probably too quickly right now. The model will go from about 100 kts to like 60 in a couple seconds in a side slip. The area is a guestimate, the Chord is the length of the fuselage. airPt is about 1/4 chord, which is forward of the CG. TS did you get your rudder area back up to the correct values for the plane? Could be that there's not enough lift to get and keep the fuse airfoil sideways. IP: Logged
Tailslide Pilot	posted 07-02- 05:13 PM Yes, I set the rudder back to the regular area. I've tried it with super large and super small rudders as well, it seems the larger the rudder the less the nose will stay up, which doesn't make sense to me. If the rudder is being modelled in openplane properly why would a larger rudder give you less yaw? I have my fuselage airfoil setup similarly, with the chord the length of the plane and the airPt 1/4 of the way back. TS IP: Logged
Pang Pilot	posted 07-02- 10:03 PM Well a larger vStab is in some ways harder to move thru the air from side to side than a small one. Windsock or windvane kinda effect, I think. There's alot of moment from the CG forward to the spinner on the Yak, I wonder if it's not part of the problem as well. If the "lever" of the aft fuselage section was longer, perhaps that would solve something. Maybe try moving the airPt forward a bit? In the Camel the section of fuselage forward of the CG is small compared to the Yak. IP: Logged
Tailslide Pilot	posted 07-04- 01:18 AM Yes, tried moving the airPt forward bit by bit until it was five feet in front of the nose. I also tried moving it back until it was at the CG. Thats a good point Pang.. what determines the ratio of stabilizer to rudder, is it hardcoded or is it input into CFL3D when the airfoil is generated? TS IP: Logged
Hawk JAG	posted 07-05- 01:45 PM Just read some interesting post on an RC forum and they claim real warbirds did not do knife edge. They would point nose down when attempting this manuever. They were designed to go fast and turn sharp but had no need to fly with one wing down for any length of time. IP: Logged
Tailslide Pilot	posted 07-05- 04:10 PM That's interesting Hawk! BTW, Pang, when you generate the airfoils with XFoil can you specify how much of the foil is the control surface when you do the up and down versions? TS IP: Logged
Pang Pilot	posted 07-05- 10:56 PM Hawk, thanks! I suspected as much, but I needed to know for sure. I'm not sure how much of this I'll implement in the final FM, but it's going to get played with, for sure! TS, yes, Xfoil can be set up at a percent of chord from the LE for the amount of control surface to model. This is another reason that not all the numbers are set in stone! There has to be some "fudging" allowed, but boy have we hashed that topic out enough or what!? LOL Pang IP: Logged
Tailslide Pilot	posted 07-06- 02:11 AM Would it take long to generate some NACA0012 airfoils for different control surface ratios? Like 25%, 50%, 75%? I'm still interested in figuring out how to make a plane knife edge in SDOE. TS IP: Logged
Hawk JAG	posted 07-06- 09:46 AM The Cap style plane was designed to knife edge. It's fuse has generous, square boxy side area and a very large rudder. It's engine and prop combo designed for slow, powerful flight to sustain knife edge and point rolls. Anyone that has seen one fly at an airshow knows how slow and powerfull these planes are. The average fighter of WWII had a small rudder used for correction mainly and it's fuse was slender, more rounded. A plane designed more for speed. http://home.earthlink.net/%7Epgrubich/ [This message has been edited by Hawk (edited 07-06-2000).] IP: Logged
Tailslide Pilot	posted 07-06- 11:31 AM Razor's able to knife edge an RC with a pipe fuselage.. and I tried boosting the power. The rudder airfoil is not yawing the plane enough. If I can change the control to vstab ratio it will yaw more. With the current airfoil simply making the vstab bigger actually makes the plane yaw less, presumably from the air hitting the stabilizer when the tail swings out? TS [This message has been edited by Tailslide (edited 07-06-2000).] IP: Logged
Pang Pilot	posted 07-06- 09:35 PM TS, Why don't you just bump up the lift coefficient in the unstalled regime, and rename the foil? It's really tough to get the foils to run with the control surfaces deflected, and we're not sure if they are actually modelled at 60degrees or 30degrees. The last foil I ran at 30 degrees returned values much higher than I expected, so I'm not sure if they are correct. IP: Logged
Tailslide Pilot	posted 07-06- 10:00 PM I was told by MH that it was based on 30 degrees up and 30 degrees down. That's interesting it's so different I guess there are still alot of variables there like thickness and reynolds numbers? TS IP: Logged
closterman Pilot	posted 07-07- 09:44 AM Bonjour! Just for your info. I have some R/C plane, and this is her knife-edge capability: Extra 300: very easy, unlimited knife-edge Cap 21: same as Extra Citabria: very hard to make, big aileron correction to stay in knif-edge Fw-190 D-9: the nose go down rapidly Spitfire MkIX: same as Fw-190 My aerobatic plane was setup with approx 30� of travel on each side. If i don't have enough travel, the knif-edge is hard to keep strait. Closterman =602 ieme= http://www.ckm9.com/moustic IP: Logged

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