This isn't one of the ten second computer sketches. This shows the delta planform, based loosely on the Rohr delta. It has 200 sq ft of wing area, designated by the red triangle, which is what was used to geometrically calculate the MAC and the CG. The wing loading is around seven pounds per square foot as long as it's not stuffed with fuel for a long trip, and will give a lower landing speed than the Rohr delta and probably the C172 also. This shows the CG at the 25% point, if it needs to be at the 17% it will be more forward, closer to the one in my previous posted drawing. The elevons and trim tabs have been excluded from the area calculations and the MAC calculation in order to provide a good safety margin. The wing span is a little more than 26 feet. The center section is six feet wide.
In the side view the red airfoil shapes show the contours at one foot and two feet from the centerline, showing that the fuselage is airfoil shaped and is an efficient lifting body. The green airfoil shape is the wing root, and the blue outline shows the wing folded in the same manner that the Grumman cats do, for towing on the road.
The things that look like inboard control surfaces on the top view are the trim tabs, which provide the reflex to the wing, and it's an adjustable reflex.
The center section airfoil/fuselage has a sharp leading edge so that it will stall first and tend to drop the nose to prevent too much pitchup at high AOA and high G situations.
Last edited by Starman; October 2nd, 2009 at 01:31 PM. Reason: To switch picture to an attachment
Providing reflex primarily towards the root of the wing does put you at risk of tip stalls. You'll want to reflex your elevons at least as much, and use the inboard sections for just a little trim (if at all). Personally, I'd go for full-span elevons and use either conventional trim tabs or spring trim.
Thanks, will do.
There was a single seat derivative of the Dyke Delta produced in the '80s I think it was called the Delta Stingray. It was designed and built by Mr. Lowell Borchers. It used a single piston engine mounted in the nose and had a single vertical stabiliser. However, the delta planform is akin to the drawing that you have made.
I spoke with Mr. Borchers a few months ago about his aircraft and he indicated that it flew very nicely (after some experimentation which included adding a very small horizontal stab about 3/4 the way up his vertical stab).
I dont believe that he has any of the design paperwork/drawings for his aircraft any more but his experiences with a homebuilt delta may assist you. He has donated his aircraft to his local museum where it is available to be viewed. He was very pleasant to talk to and may be able to give you some useful tips.
All the best with your project.
Another concern with deltas, and one of the reasons I dropped my ideas for one, is where do you put the damn prop? In front (Dyke style) it looks a bit silly, in my opinion; but aft, as you have it drawn, you have major ground clearance issues. Keep in mind that deltas will typically land at significantly higher angles of attack (at least potentially; you might land fast 90% of the time, but sometimes you'll want to land short) than "normal" designs, so you'd be looking for about 9" prop clearance at 30° AoA. And that's not even taking into account extra clearance to prevent the tires from throwing crap into the prop disk...
In order to keep junk out of the prop the main wheels will need to have a wide stance when extended, and maybe put a deflector on the front wheel.
I believe the Dyke Delta gear is designed to place the wing at a positive angle of attack while sitting on the ground for that very reason.
Some VariEze, LongEze/Cozy builders put in a hydraulic nosegear extender so they can board on the groud with the nose low and then raise the nose once they are in. As for the Dyke Delta, I think boarding access may be from the trailing edge and up a wing walk (would require shutting down the engine for safe boarding).
Last edited by bmcj; September 21st, 2009 at 04:44 PM.
I got the idea about the 'kneeling' nose gear from those variEze builders that use the hydraulic nose gear extension while they are in the plane. I think that the Dyke Delta users board over the side, needing a step ladder, except I saw one that had the top of the strake fold out and down and it had a built in step or two. I looked for pictures of it but couldn't find it.
Following is the two possibilities I am considering. The top pic shows conventional trike gear with small safety wheels on the tails. The wing is at one degree of incidence (fuselage has more) and the max rotation on this, assuming the airplane will rise on the long travel gear as it rotates, is 20 degrees, for a total AOA of 21 degrees for takeoff. The lower drawing shows the main gear in the tails with a single retracting gear at the front. The front landing gear on this one is nearly seven feet long and in the raised position the bottom of the cockpit is about six feet in the air and it still has less rotation than the upper one. It seems either one would need to be kneeling because even on the top one the gear is four feet high.
Trade offs for decision on this is the lower one would be less overall labor to build but the upper one looks sexier and more 'threatening' while taxiing. The upper one normally has the prop far from the ground while the lower one has the prop always near the ground, but the lower one has the wheels behind the prop so there is less chance of them throwing things into the prop. I've read that props can suck things off the ground, that they don't need to be thrown by the tires.
So far I'm leaning towards the upper one, which could get by with fixed gear at first.
Last edited by Starman; October 2nd, 2009 at 01:33 PM. Reason: switch picture to an attachment
I'm thinking of using hydraulic or pneumatic gear operation. With pneumatic I can have a tiny air compressor filling a small high pressure tank or a big low pressure tank, and the air pressure could be made to act like a spring.
1) View over the nose while taxiing the second option. Or lack thereof.
2) The prop will, indeed, suck sticks, rocks, dirt, and just about anything else up off the ground even if it's a good foot or so above the dirt. I've seen our towplanes at the soaring club creating little tornadoes of dirt and grit even at fairly low power settings, and they're taildraggers.
3) The nosewheel will throw up rocks, to, so with a pusher such as this one (or any where the lower prop arc is unprotected), you're going to be limited to paved runways at all times, for either of your configurations. That may not be a problem for you, but it should be noted.
"If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them." - Henry David Thoreau
Design Project: Conceptual Design of an "Inexpensive" Single-Seat Motorglider
Discussion Thread for the Project: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider
Having an extra "tailwheel" on the rudders would help protect the prop from hitting the ground at rotation but it could also damage the rudder and the wing it's attached to when that contact occurs.
The alternative would be engine and prop at the front and no tail extending near the ground.
I'm guessing that's more a function of the prop blast being angled downwards in a taildragger? In the conventional gear version of this delta the prop is about three feet off the ground and angled upwards.2) The prop will, indeed, suck sticks, rocks, dirt, and just about anything else up off the ground even if it's a good foot or so above the dirt. I've seen our towplanes at the soaring club creating little tornadoes of dirt and grit even at fairly low power settings, and they're taildraggers.
I hadn't thought about that limitation but if all the other pusher drivers live with it so can I. So many runways are paved that I don't think I will miss using dirt strips.3) The nosewheel will throw up rocks, to, so with a pusher such as this one (or any where the lower prop arc is unprotected), you're going to be limited to paved runways at all times, for either of your configurations. That may not be a problem for you, but it should be noted.
Last edited by Starman; September 22nd, 2009 at 04:02 AM.
During normal landings low aspect ratio planes tend to flatten out and lessen pitch when they get into ground effect, so this will lessen the likelyhood of hitting the tailwheels during landings, but that's just what they are there for anyway, just in case, so they will be built for it. There's always the possibility that some landing somewhere will be hard enough to damage the tail structure, so it will need to have a weaker 'fail' point built in so the damage doesn't get as far as the rear wing connection, which on the tube which holds the tail.
In a hard enough landing the question becomes: Which is the least expensive to damage, the vertical tails or the prop? If the landing is hard enough it could damage both. One my plane I don't think a prop strike would damage the engine because there's going to be a floppy sloppy torsion bar connecting the prop to the engine and I'll be using a car engine. Car engines have crankshafts orders of magnitude stronger than the old antique opposed air cooled airplane engines. Since they are air cooled and the cylinders are so far appart the crankshafts are very big and long, yet in order to be light they are very skinny and wimpy. Just seeing one of those crankshafts lying on a work bench makes you want to run for cover
On the other hand, a two rotor wankel has a crankshaft about a million times stronger, or something.