I've been wanting to get into Aerobatics, and I've been looking at the different planes out there, cap 232, edge 540, giles 202, extra 300, etc. At first glance, they all look pretty much alike. Then I've started looking a little closer. Some have straight leading edge and a swept trailing edge. Others have taper wings, and a few even have swept leading edge and straight trailing edge. Verticle and horizontal surfaces are pretty much the same with minor differences.

My question is (because I'm designing my own aerobatic airplane) what are the flight characteristics of these different wing plan forms?

I've been told that the swept leading edge with a straight trailing edge requires fast landings or it will stall. My only experience with this is a .25 Tequila Sunrise. I didn't notice it needing to land all that fast, but it sure was fast on the rolls.

I would also be interested in your experiences with the Tequila Sunrise. I've flown this one about 4 times, wrecked it twice. Engine quit right after take off on one, and the battery quit working (bad wire) on the second. It seemed like it might have been a fun plane if I could have gotten more than 2 good flights with it. I need to fix the fire wall and it will be in airworthy condition again.

Thanks for the input,
Soj

Depends on the type aerobatic style you want.

Straight LE helps with snappy 3D style stuff.

Swept LE helps with straight line tracking and is far preferred for "Pattern" aerobatics.

Thick airfoil again helps slow speed 3D maneuvers. Medium thickness is preferred for pattern as you need some snap, and some drag for sped control on down lines. Thin airfoil is for speed and not great for aerobatics. Then you can get into a bunch of specific airfoil's special characteristics....

A sharp LE tends to cause stalls to happen more suddenly and with less control than a rounded or flat LE (which is becomming common for 3D...) It is possibe to use a sharp LE near root and more troounded out near tips and get almost the same effect as a tiny bit of "washout" upright or inverted (tips stall later in either case.) The side bennefit of this is you can more easilly force the tip-stall because the "washout" is an "aerodynamic illusion" and easilly overcome when trying for a snap. (snap-roll, spin...)

(and we haven't got to TE sweep yet...)

Hmmm, you certainly have given me some food for thought, Yummmy... I was thinking about a double taper, tho my first draft has a straight leading edge and a swept trailing. A friend of mine just wrecked a Cap 232 and gave me the pieces. It should be an fairly easy rebuild, since it is just the nose a little behind the firewall forward on one side that is cruched. It takes a 90 to 1.2 4 stroke, and weighs about 8 to 10 lbs. So many planes, so little time.

Planes to build in order:
Build wing for my Junker Dr-1 the plane I'm
haveing the taxing problems with.
Rebuild Cap 232
Gee BEE Z (from Adrian Paige plans)
Curtis P6E bipe (50% done)
Fokker D-8 my design (it's 50% finished too.)
Fokker Dr1 (1/2a that I want to beef up to .10)
Then I'm designing my own aerobatic plane, and I want to build a FW 109 A or Ta 152 H
CG Gentle Lady

Soj

Your build/rebuild list is almost as long as mine! Not often I see that.

The 1/2 A Dr1 a Guillows kit? Can I get a copy of the plans? I wanna do one with a Norvell .074, 4 ch. Mainly want the wing and fuselage outlines and fuselage formers, and don't want to pay $40 for a kit to toss 90% of the wood.

Done any aero-towing with a glider? (fun stuff! I'm about to try again after appx 15 yrs...)

I got the Dr1 kit for around $21.00 a few years back and never have touched it. I know what you mean about the plans, and just needing the outline. Do you have a cad program? if yes, what type of files can you use? .dgn .dxf? I started drawing my own plans for a DR1 sometime ago, but never finished it. I think I may have the outline of the wings, and fuselage finished. I'll have to open it up and take a look. I do have the plans for a Spad XIII almost finished, in CAD, so it could be printed in almost any scale.

I've never done any rc gliding at all. Well, I say that. I have a wing off a glider that I rubber band to a styrofoam fuselage (the kind you buy for $5.00 at your favorite discount store) The tail feathers are cut, and taped back on with 2" tape. Chuncks of the fuselage were cut out and servos, receiver, and battery are taped into the holes. The gas tank is just taped to the side of the fuselage and a piece of 1/8" ply is glued to the front and a .099 Fugi is on the front. I was using it to teach my son how to fly RC. It turns real slow, is very stable, but will still do a loop, but not a roll. You can use power to get to alt, then glide back down, then power to get to alt, etc. You can get 15 to 20 min. flights on a good with with thermals and only a 2oz. tank.

I'll check on the DR1 plans if your interested in them. The thing I don't like about the kit is the ribs are crossed like an X with an extra rib in the middle. Beefing up the fuselage is easy, but the wings will have to be from scratch. ONe of the hardward stores was selling soom 1/64" plywood for $5.00 / sheet, it was 1'x4', so I bought at least one, and maybe 2 sheets but it has been a while so I cant remember if I got two or not. I know I went back for a second sheet but it might have been all sold out.

enough ramblins.
later,
Soj

If you really wanted a treat, I have several plans that my father built when he was a boy growing up in the 30s and early 40s. One of them has a 24" wing span. I can't remember off the top of my head, but there is a Rear Wind Speedster, Se-5a, French Cauldren, the 24" is a dive bomber from the 30s but I can't remember which one, I still have the engine block with the paper decal of the radial engine and some of the original wheels and props. There are a couple more plans too but I can't remember what they are.

Soj
PS: They are getting in pretty sad shape. I would love to copy them into a cad program before they totally fall apart, but I don't have access to a scanner.

Just a little additional information on wing planforms...

A straight, constant chord "hershy bar" wing will begin to stall at the wing root near the trailing edga and the stall will progress forward and out. This is great for preventing stip stalls, and great for a trainer but not so great for an aerobatic aircraft that needs to do good snap rolls etc, as the stall progression across the wing is fairly slow.

A double tapered or elliptical wing will first begin to stall near the trailing edge in the middle of the wing and progress forward and both inboard and outboard on the wing for a much faster stall break. This provides much better snaps and yet still preserves some aileron control.

A sharply swept wing (think F-100, F-86 etc.) will stall at the tip and the stall will progress inward. This results in an early loss of aileron control and can be rather nasty without some form of flow control such as washout, vortex generators, alternate root and tip airfoil sections etc. A highly swept wing also develops very high drag at high angles of attack. So rolling at low speed in a swept wing aircraft can result in a lot of drag on the downward moving wing as the local AoA increases, this produces large amounts of drag and yaw which causes the upward moving wing to advance and create more lift aggravating the roll/yaw situation. This can create serious low speed handling issues (ever seen a film clip of an F-100 doing a "Saber Dance" down a runway before it crashes and burns).

Generally a slightly swept wing leading edge will unload better and result in better snap rolls. A Smith Miniplane for example with straight leading edges does not snap as well as a Pitts with it's swept upper wing.

The Pitts also uses 2 degrees more incidence on the upper wing to get it to stall first. This allows the aircraft to quickly stall and snap, but also provides continuous aileron conrol on the smaller mostly unstalled "hershy bar" lower wing that is operating at a 2 degree lower AoA. Great design to get the best of both worlds.

In a monoplane a double tapered wing planform potentially offers the most in terms of aerobatic agility and control. Leading edge contour, as indicated above is also very important. Generally a blunt leading edge will handle a higher AoA, and a relatively thick double tapered wing with a "snow cone" type symetrical airfoil can offer a good compromise by delaying the stall and allowing good low speed handling while still allowing rapid stall breaks and good snap characteristics when the wing is pushed or pulled aggressively past the critical AoA.

The tail feathers on full scale aerobatic monoplanes tend to look at lot alike as the requirements for good knife edge flight, rolling circles, torque rolls, etc, pretty much demand it. A big and effective rudder is a must and the vertical positioning to the horizontal stab can have a significant effect on whether the model pitches up or down when rudder is applied during slow rolls, knife edge flight, etc.

On an R/C pattern aircraft, a computer radio can be used to cancel this out so it is a less important consideration in the design. But in a full scale aerobatic aircraft, the pilot has to cancel it out with the stick. So most good full scale aerobatic aircraft have designed this out of the aircraft and most of the current generation of unlimited aerobatic aircraft (including the Pitts S-2C) will go where they are pointed and do it upright or upside down with little or no trim change required. This makes them very good canidates for aerobatic R/C models.