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Design => Stunt design => Topic started by: Dennis Toth on September 10, 2010, 09:00:57 AM
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Guys,
Has anyone used a true sweep back wing for a stunt design, by this I mean that the tips of the tip cord are both the leading and trailing edge are behind those of the root cord (with flaps)? If so what ship.
Best, DennisT
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I am working on a King Sweep in which the wing is swept back. Have it up to where it is ready for the fuselage. Working on the stab/elevators now.
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I am working on a King Sweep in which the wing is swept back. Have it up to where it is ready for the fuselage. Working on the stab/elevators now.
Not quite what he meant:
... by this I mean that the tips of the tip cord are both the leading and trailing edge are behind those of the root cord (with flaps) ...
But then, from what aeronautical engineering texts I've read, any sweep is called "sweep", there's no magic about the amount sweep from root to tip exceeding the chord of the wing -- when sweep makes a difference it's the angle of the sweep.
Sweep, by the way, makes a plane fly better in the transonic and supersonic realms. At subsonic speeds it reduces the effectiveness of an airfoil by causing spanwise flow -- this is why the old jet fighter aircraft had fences and doglegs and whatnot on their swept wings.
But it looks cool...
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Jack Sheeks designed many swept wing planes that would fit your criteria.
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My buddy Mike Haverly has been flying a Jack Sheeks Freedom 45. Swept back wing. It's been, ah, interesting. The yaw/roll couplings is rather intense.
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Dennis,
There were many swept wing stunters. The King Sweep was mentioned above.
Jack Sheeks had a bunch. The Sheeks Swept wing Classics are:
10/65 FM Stuntliner I-Beam, Swept Wing
4/66 FM* Sea Vixen CF033 I-Beam,Swept wing, booms
8/66 FM* Demon CF049 I-Beam, Swept wing
1/67 FM* Swinger CF067 I-Beam, Swept wing
5/68 FM* Freedom 45 CF121 "C"tube Swept Wing
1/69 FM* Torino S CF149 I-Beam,Swept wing, booms
2/69 FM* Scottsman CF153 "D"tube,Swept Wing
The ME 262 was a collaboration of Sheeks and Vornholt.
More recently Don Hutchinson had a beautiful and great flying F-86 in Model Aviation, and also a profile F-86 (See picture)
And.... As a reminder to everyone, the Sheeks awards will again be presented at VSC in 2011. Awards are for the Best Sheeks Classic airplane, and the highest placing Sheeks Classic airplane.
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In addition to the several designs already listed, there are some others:
Cat's Whiskers, Air Trails Aug 53
VETO Model Airplane News, Jun 55
Curtis Special, Air Trails Dec 56
King Sweep, Flying Models Sep 59 (as shown by Doc Holliday above)
Super Sonic Flying Models, Jul 66
Novette, Flying Models, Jul 68
Arrowhead, Air Trails, Oct 47 (this is a swept back flying wing with a trike gear - pretty good for 1947)
There are probably others.
Keith
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Guys,
Has anyone used a true sweep back wing for a stunt design, by this I mean that the tips of the tip cord are both the leading and trailing edge are behind those of the root cord (with flaps)? If so what ship.
Best, DennisT
This is the second of 3 models that I "designed' and built in the 1969 '72 era. Sorry about the picture as I found it a few years ago in some piled away stuff, and placed it on the computer. Now, I have lost it again!
Edited to add: The first model, smaller, was a great flier using a Veco .35. This one was a super flier using a George Aldrich rebuilt ST .40.
The 3rd, I tried a stabilator and that was like trying to ride a bucking bronco bareback. mw~ It did not last long. The pictured model was sold after 3 years of flying as I was all RC at that time. DUMB!!! ''
There will be a duplicate in the spring.
My sweep does not exactly follow your prescription, but the main wing is fully swept. The flaps follow a formula that I picked out of the sky, which assures the taper does not go all the way to the tips and that the far end of the flap has a lesser percentage of chord than the flap at the fuselage. I always wonder why designers use full span flaps and/or same percentage of chord flaps on so many designs. It can only create tip wobble in tight turns.
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Hi Dennis - I saw Mike Haverty's sweep airplane in its initial trim flights at VSC 2 years ago. He really had his hands full, but it seemed to get better as he put in more flights/trim changes. I've also watched a few Fierce Arrows, one particular one in heavy turbulence at Lincoln Park. A survival flight, at best. Lots of pondering has lead me to believe that although there might be some small advantage in turbulence penetration, the yaw roll problems will pretty much outweigh any advantage. Experiment all you like, but my guess is that you'll wind up with the MAC at each airfoil station along a straight line at the quarter chord. The combat guys have all gone to the same sort of planform, strongly reminiscent of the Rhinehart Stuntwing and Larry Scarinzi's Greased Lightining. My guess is that for turbulent fields, steep taper might be more like it. Here's a photo of the latest in a series of flying tail sport ships with this layout. Three flights so far, still working to get the control throws sorted out. It does seem more comfortable in rough air than more conventional layouts. If it doesn't warm up, it won't make any difference because death by freezing is not far off. Merry Xmas to you and yours.
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Someone mentioned Jack Sheeks' swept wings, Jack certainly published a lot of designs, and as he has said, for every one he published there were probably 3 or 4 more that were not published. Certainly like any experienced designer he took what he had learned and applied it to the NEW design. Thus I think it is interesting to compare and trace the evolution of Jack's Swept wing designs. NO ONE else that I am aware of was even going there. I compiled this list awhile back:
Sheeks Swept Wing Progression:
Sweep @ Root Tip Frt Leadout
Name Publ. LE Sweep Hingeline Chord Chord Span Rel to LE
---------- ----- ------------- ------------ ----- ----- ---- ------------
Stuntliner 10/65 16° (7.75") 9.0° (4.5") 13.0" 8.00" 56" 1.56" fwd
Sea Vixen 4/66 16° (7.5") 7.7° (3.5") 12.0" 7.75" 52" 2.00" fwd
Demon 8/66 11.5° (5.5") 6.3° (3.0") 12.0" 8.50" 53.5" .50" fwd
Swinger 1/67 14.5° (6.75") 10.3° (4.75") 12.0" 9.00" 52" .50" aft
Freedom 45 5/68 14° (8.0") 5.8° (6.5") 13.0" 9.25" 64" 1.50" aft
Torino 1/69 9.3° (4.25") 2.8° (1.25") 11.5" 8.25" 52" 2.5" aft
Scotsman 2/69 Could not dimension, looks same as Torino
Measured from plans except Sea Vixen and Freedom 45 which were scaled off magazine plan page.
I have a Swinger, flies pretty well below 45 degrees, but have had issues on top of Hourglass mainly. Swept wings need TLC on balance (prone to be nose heavy) I need to try it with a pusher prop too. If I was going to build another I would opt for the Demon, Torino, or Scotsman.
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Dennis, I have a Torino, and the Scotsman is basically a Torino with a single fuselage. It uses a standard style, not I-beam wing. Jack told me he did that because it was looking like I-beamers were all he built. (paraphrased) Actually that's about right, but he drew the Scotsman up with a "C" tube wing.
My Torino is a decent flying plane once I made a few changes, like more chord on the elevator. I also used the same aileron stock that was used on the original. With the larger flap area, and the small elevator area, the turns were really soft.
I showed the plane, with these changes, and the reason for them, to Jack. He smiled and said that it now looked like the plane as he designed it. He told me that they had cut the elevator chord on the original so the corners were more to what the pilot liked.
Here's a pic of mine for the interested. They were taken before the extra elevator chord was added.
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.....Here's a photo of the latest in a series of flying tail sport ships with this layout. Three flights so far, still working to get the control throws sorted out. It does seem more comfortable in rough air than more conventional layouts.....
Hi Tom - The Agila is a nice looking plane. Since it's the latest in a series, and you have some experience with flying tails, I'd like to ask three questions if I may: How much control surface deflection do you think you are likely to end up with? You call them sport ships. How well do they corner? And are there any changes you think could turn this planform (which is reminiscent of the Humbug) into a bona fide stunt ship? Thanks.
Phil Cartier has said that planes with flying tails have a relatively narrow "sweet spot" in terms of CG and control surface deflection. I'm not sure how that spot is achieved, but I found the comment interesting.
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Hi Kim - The flying tail can be made to corner about as sharply as a conventional flapped airplane, albeit with big bobbles after every corner. If you make adjustments to both the CG and throws you can get smooth exits from corners, but at the expense of a somewhat wider turn. Both adjustments are very sensitive, and it will take a fair bit of tinkering to optimize things. Throws beyond 15 degrees are unusable. My guess is that this layout could built longer, and do somewhat better, but will never approach the turn and lock feel of a good flapped stuntship. This is probably due to the cross control (corner vs. stability) from the negative pitching moment with flaps.
Your comment about the Humbug is on point. The taper is different, of course, but so is the flying tail. The axle is at 25% MAC, so the tail becomes balanced, or somewhat self actuating. Only the smallest bit of line tension still allows you to steer even through fairly hard corners. So you might say that the flying tail layout postpones the Netzeband wall. The original Humbug had a conventional stab-elevator tail. Rich Porter's Ridiculous had a stabilator, but hinged at the leading edge. Both the Stuntwing and Greased Lightning had balanced elevators, with tabs forward of the hinge line. Many combat airplanes have stabilators hinged at about 15% MAC. I have tried a hinge line at 30% and found it to be inherently unstable. 25% is about as far as you can go.
It is also notable theat Bill Netzeband went from the LE sweep of the Fierce Arrow to the straight quarter chord line of the Humbug and Doodlebug.
Dennis, my apologies for a thread hijack.
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Thanks for the info, Tom, very helpful. Dennis, my bad on the hijack also (we need an emoticon showing knuckles being rapped with a ruler).
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Hi Dennis - Here's the link to Bill Netzeband's exhaustive derivation of all aspects of the question of sweep. He came to the same conclusion, that the yaw roll couple arising from a sweep planform is a real disadvantage. Better to have the quarter chord line square to the trangent of the circle. See
http://www.control-line.org/Portals/57ad7180-c5e7-49f5-b282-c6475cdb7ee7/Netzeband_Stunt_Design_Summary.pdf
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... Bill Netzeband's exhaustive derivation of all aspects of the question of sweep
That's exhaustive? I prefer http://naca.central.cranfield.ac.uk/reports/1952/naca-report-1098.pdf . If you look at Figure 8, you will see that you are on the right track with Agila 2. A rolling moment due to sideslip of zero (which you get with forward sweep and taper) will eliminate the effect of wind on roll.
Hinging the tail on the quarter chord is a bit sporty, but you sure won't have any of the deleterious effects of hinge moment.
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Hi Kim - The flying tail can be made to corner about as sharply as a conventional flapped airplane, albeit with big bobbles after every corner. If you make adjustments to both the CG and throws you can get smooth exits from corners, but at the expense of a somewhat wider turn. Both adjustments are very sensitive, and it will take a fair bit of tinkering to optimize things.
I don't believe there is anything intrinsic to the flying stab that makes it more or less prone to bobbling out of corners. Presuming you adjust it properly, of course. I have seen several that worked as intended with no detectable difference in the performance from a fixed stab/elevator.
The first big problem most people have it making it move 1:1 with the flap, which definitely will tend to make it bobble or over-rotate in the corners, because its like having a 2:1 or 3:1 ratio on a normal tail. Reduce it to 1:2 or 2:5 or so (depending on the size) and it's no different. The second big problem is that people tend to put the pivot much too far aft (like, the 50% mark) and that causes bobbles, and generally a whole lot of other problems since it's not stable by itself. Even the combination of the flap and flying stab seems to be unstable even if you put the pivot close to but still behind the 25% point. A whole lot of people (myself included) had the brilliant idea to do that for an aerodynamic counterbalance of the combined system, but I have never seen it work. I am pretty well convinced the pivot has to be 25% or slightly forward to ensure it is stable by itself, and you can't count on the flap stabilizing it.
Once you get it working properly, there's no apparent performance advantage to having a flying stab. And once you take into account the structural issues I think it's clearly a net negative.
Brett
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While (RC) sailplane flying, I learned to dislke the "feel" of flying stabs. They were prone to deadband around neutral and would give up (stall) when overworked. I changed most of my birds over to regular stab-elevator systems and every time I thought it was an improvement.
Only "advantage" I see with flying stab for CLPA is that it is easier to build as a plug-in (removable) unit on your suitcase sized travelin PRO stunter....
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Guys,
Has anyone used a true sweep back wing for a stunt design, by this I mean that the tips of the tip cord are both the leading and trailing edge are behind those of the root cord. <snip>
Best, DennisT
Do you mean that the tips come to a point?
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You want a swept wing? I give you a swept wing! >:D
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While (RC) sailplane flying, I learned to dislke the "feel" of flying stabs. They were prone to deadband around neutral and would give up (stall) when overworked. I changed most of my birds over to regular stab-elevator systems and every time I thought it was an improvement.
Agreed, I have always held that if you want more lift out of a wing its far more efficient to change its camber than its angle of attack and the range of effective attack angles with a flying stab becomes very limited.
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I did the original design work for the Estes Astro-Blaster a canard, 2 channel R/C Rocket Glider. In development, I could never get adequate control from a full-flying canard surface. I thought it would be just the ideal! However, it just would not do the job...not enough control power. A 50/50 surface of the same area was the solution. (The prototype is hanging over my desk as I type!)
Somewhere, I have a graph of elevator power efficiency as a % of horizontal tail chord. It peaks out around 25%, as I recall! I have not been able to find that particular chart recently, but when I do, you guys will have it available!!!
The full flying stab was used on transonic fighter jets to avoid loss of control due to mach wave interference and aeroelastic flexing. Basically, the elevator lift behind the mach wave became small compared to the lift ahead of the mach wave, but providee enough torque to flex the forward stabilizer in the wrong direction. OOPS, control reversal! At least that is the story I was told.