Tail Airfoils
05-20-2004, 11:39 AM
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Tail Airfoils
Anyone got any ideas in terms of Q500 tail airfoils?
I'm basically taking a flat slab of 3/16" and trying to sand a somewhat symmetrical airfoil into it coming to a sharp point at the front and back. I gotta figure that with testing, someone has determined a better way of doing this.
Is it sheeting foam tail cores, maybe going with a thicker stab (1/4"), or something else?
Just curious on making these go faster...
I'm basically taking a flat slab of 3/16" and trying to sand a somewhat symmetrical airfoil into it coming to a sharp point at the front and back. I gotta figure that with testing, someone has determined a better way of doing this.
Is it sheeting foam tail cores, maybe going with a thicker stab (1/4"), or something else?
Just curious on making these go faster...
05-20-2004, 12:16 PM
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RE: Tail Airfoils
Dave,
I used to use a sharp leading edge on the tailfeathers until someone smarter than me (yes, that could be just about anyone, thanks very much) pointed out that a sharp L.E. on the tail is just like a sharp L.E. on the wing: it works fine as long as the air is smooth and the angle of attack is zero. But in the turbulent air behind the prop, and whenever you kick the tail down in a turn, that sharp leading edge just causes flow separation starting at 0% of chord and continuing to 100% of chord for all anyone knows.
The tailfeathers on the QM40 Pole Cat, Q500 Bird of Prey, and many other successful designs use a fairly fat, symmetrical airfoil with a rounded leading edge. The Pole Cat tail is nearly a half-inch thick. I'm not sure the exact airfoil is all that important, but I would recommend something that "looks" laminar (narrow but radiused at the front, tapering to a high point at 50-60% of chord) and has a sharp, slightly concave T.E.
That's my 2 cents' worth.
Mr. Error-Foil
I used to use a sharp leading edge on the tailfeathers until someone smarter than me (yes, that could be just about anyone, thanks very much) pointed out that a sharp L.E. on the tail is just like a sharp L.E. on the wing: it works fine as long as the air is smooth and the angle of attack is zero. But in the turbulent air behind the prop, and whenever you kick the tail down in a turn, that sharp leading edge just causes flow separation starting at 0% of chord and continuing to 100% of chord for all anyone knows.
The tailfeathers on the QM40 Pole Cat, Q500 Bird of Prey, and many other successful designs use a fairly fat, symmetrical airfoil with a rounded leading edge. The Pole Cat tail is nearly a half-inch thick. I'm not sure the exact airfoil is all that important, but I would recommend something that "looks" laminar (narrow but radiused at the front, tapering to a high point at 50-60% of chord) and has a sharp, slightly concave T.E.
That's my 2 cents' worth.
Mr. Error-Foil
05-20-2004, 07:06 PM
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RE: Tail Airfoils
I have been using a very sharp edge on my tails, and they are not pitchy.
I will look at that airfoil Michael. I am also thinking of going with Sheeted foam tail.
Duane, I looked at the polecat tail, and it is pretty fat in the center where the stab meets the fuse, but it tapers out as it gets towards the tips to nearly an 1/8". It would be difficult to match that with my crude sanding technique.
I will look at that airfoil Michael. I am also thinking of going with Sheeted foam tail.
Duane, I looked at the polecat tail, and it is pretty fat in the center where the stab meets the fuse, but it tapers out as it gets towards the tips to nearly an 1/8". It would be difficult to match that with my crude sanding technique.
05-20-2004, 09:44 PM
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RE: Tail Airfoils
Dave,
I would guess that your 66-012, or the same thing thinned a little bit, would be a good choice.
I think that some experimenting would show that sharp leading edges are not twitchy (pitchy).
banktoturn
I would guess that your 66-012, or the same thing thinned a little bit, would be a good choice.
I think that some experimenting would show that sharp leading edges are not twitchy (pitchy).
banktoturn
05-20-2004, 11:36 PM
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RE: Tail Airfoils
BankToTurn:
The Vortex uses both the Naca 66-012 on the wing and tail. Not that I want to mess with what works, but that is a tough airfoil to get perfect without using molds and composite construction.
I would like to go with something a little less agressive on the tail.
The Vortex uses both the Naca 66-012 on the wing and tail. Not that I want to mess with what works, but that is a tough airfoil to get perfect without using molds and composite construction.
I would like to go with something a little less agressive on the tail.
05-21-2004, 09:27 AM
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RE: Tail Airfoils
Dave,
I am making the assumption that you could save a little drag by getting a little more laminar flow on the tail. A section like the 66012, with the thick point fairly far back, probably improves your chances of doing that. If you go with that section, but don't get it quite as accurate, I don't think it really costs you anything. The biggest win is probably to use any decent airfoil section, instead of a flat plate with a barely rounded leading edge. It is also a good policy to get the CG as close to neutral as you can, so that loads on the tail are minimized.
banktoturn
I am making the assumption that you could save a little drag by getting a little more laminar flow on the tail. A section like the 66012, with the thick point fairly far back, probably improves your chances of doing that. If you go with that section, but don't get it quite as accurate, I don't think it really costs you anything. The biggest win is probably to use any decent airfoil section, instead of a flat plate with a barely rounded leading edge. It is also a good policy to get the CG as close to neutral as you can, so that loads on the tail are minimized.
banktoturn
05-24-2004, 03:38 PM
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RE: Tail Airfoils
You weren't suppose to see that 
Actually, Pat G. has a CNC foam cutter and has been playing with a sheeted foam core stab. That was one of his first tries at it, and I thought it looked great. Pats was a constant Chord, which makes it much easier to cut, but I would want something tapered a bit more.
Not sure if I would want to build them this way, but it would be a good way to get a consistent, tapered, airfoil in a tail if someone was looking to have a mold made for a compositite tail.
More to come later (hopefully 5 mph)......
Actually, Pat G. has a CNC foam cutter and has been playing with a sheeted foam core stab. That was one of his first tries at it, and I thought it looked great. Pats was a constant Chord, which makes it much easier to cut, but I would want something tapered a bit more.
Not sure if I would want to build them this way, but it would be a good way to get a consistent, tapered, airfoil in a tail if someone was looking to have a mold made for a compositite tail.
More to come later (hopefully 5 mph)......
05-24-2004, 06:06 PM
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RE: Tail Airfoils
Dave,
To taper the stabilizer out toward the tips, or to make a nice wedge shape from the leading edge to the hinge line & back down to a thin trailing edge, a razor planer or very sharp spokeshave is a handy tool.
It takes some fiddling to get the depth of cut just right -- 0.003" or 0.004" is ideal -- but once you do, the balsa will peel off in very pretty, paper-thin curls that will fill up your wastebasket in no time. (Save a few bags of this stuff to help get your fireplace going in the winter.) You can count the number of passes you make with the planer on each side of the slab, so the amount of taper stays even. Get it close with the planer, then use sandpaper from there.
As the formerly rectangular slab of balsa becomes less rectangular, it may become tricky to deal with on a flat workbench. So I pad the workbench with one of those perforated, rubberized sheets they sell at Home Depot and at some grocery stores. I forget the brand name -- Super Grip Sheet or something. When you're sanding, the balsa dust falls through the perforations so it doesn't get in the way as much.
I made a QM40 Swee'Pea tail yesterday using this method, vacuum-bagged it with Mylar and Z-Poxy with 1/2 oz. cloth. The airfoil and surface finish look very much like the Pole Cat tail, weight just 1.3 oz. without the torque wires. I don't think I could do much better if I cut foam cores.
Duane
To taper the stabilizer out toward the tips, or to make a nice wedge shape from the leading edge to the hinge line & back down to a thin trailing edge, a razor planer or very sharp spokeshave is a handy tool.
It takes some fiddling to get the depth of cut just right -- 0.003" or 0.004" is ideal -- but once you do, the balsa will peel off in very pretty, paper-thin curls that will fill up your wastebasket in no time. (Save a few bags of this stuff to help get your fireplace going in the winter.) You can count the number of passes you make with the planer on each side of the slab, so the amount of taper stays even. Get it close with the planer, then use sandpaper from there.
As the formerly rectangular slab of balsa becomes less rectangular, it may become tricky to deal with on a flat workbench. So I pad the workbench with one of those perforated, rubberized sheets they sell at Home Depot and at some grocery stores. I forget the brand name -- Super Grip Sheet or something. When you're sanding, the balsa dust falls through the perforations so it doesn't get in the way as much.
I made a QM40 Swee'Pea tail yesterday using this method, vacuum-bagged it with Mylar and Z-Poxy with 1/2 oz. cloth. The airfoil and surface finish look very much like the Pole Cat tail, weight just 1.3 oz. without the torque wires. I don't think I could do much better if I cut foam cores.
Duane
05-24-2004, 08:03 PM
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RE: Tail Airfoils
After seeing these cores, I think it may be the way to go. I could never get that precision with a razor plane, or sanding block. It sounds like he can put the taper on also (We'll just have to go with two seperate foam cores). The precision of the CNC cutter is pretty impressive.
I have used the Super Grip pads you talk about, and they are the way to go. I wouldn't sand a tail without something underneath and they work well. In a pinch, a stolen hand towel from the linen closet works well also
Speaking of the Polecat, I got a nice coat of paint down on the fuse tonight. Can't wait to fly this thing.
I have used the Super Grip pads you talk about, and they are the way to go. I wouldn't sand a tail without something underneath and they work well. In a pinch, a stolen hand towel from the linen closet works well also
Speaking of the Polecat, I got a nice coat of paint down on the fuse tonight. Can't wait to fly this thing.
05-24-2004, 08:13 PM
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RE: Tail Airfoils
If you need a test bed for the first set of sheeted tail feathers let me know, I think I'll convert my doddger to a v-tail this week for the century race.... I'd hate to bust up the Seeker....
05-24-2004, 09:23 PM
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RE: Tail Airfoils
Don't waste your time with the doddger. Leave the tail as it is.
The Century race is time to dig out he old forgotten racing planes. Still not sure what I'll fly, but it may just be the original Seeker Prototype (about 5 oz. heavy) but flies great...
The Century race is time to dig out he old forgotten racing planes. Still not sure what I'll fly, but it may just be the original Seeker Prototype (about 5 oz. heavy) but flies great...
05-25-2004, 02:27 PM
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RE: Tail Airfoils
Too late, already done..... I was looking for something to mess around with last night and all of the sudden the tail feathers were off and a v-tail on.... I'm not happy unless I'm messing with something.... Better that then my new Seeker. Besides, I'm sure I'll need 2 planes for the century race and the Seeker isn't going to be one of them. I'll probably test it out on Thursday to see if it flies or not.
Besides, I'm sure I'll need 2 planes for the century race and the Seeker isn't going to be one of them. I'll probably test it out on Thursday to see if it flies or not.
