I have been having day-dreams (starting with an early morning real dream about a week ago) about having my own airplane. Uncle Bob and had been talking about the wingtip vortices issuing off the tips of wings or other sharp discontinuities on the trailing edge of an airfoil. They are visible when the moisture content of the atmosphere is near 100%, especially if the airplane is pulling a few g's. You've probably seen them during the Blue Angels' sharp pull-ups during their aerobatics over the Hydroplane race track.
My ideal airplane will have down-turned wing-tips; it will have its horizontal stabilizer in front instead of the back as in conventional configurations. With the horizontal stabilizer in front, the c.g. will be forward of the center of lift of the main wing. This improves the overall efficiency of the airplane because the horizontal stabilizer will be contributing to lift instead of negative lift and just drag as in the conventional configuration. The horizontal stabilizer will also have its tips turned down.
Now with four tips all pointing downward, my logical conclusion is to put landing gear wheels on each of these extremities; there would be no need to retract these wheels since only the lower half of the wheels are in the "breeze" and their supporting structure is useful airfoils which I will call "winglets".
This airplane will have a tandem seating arrangement, with both fore and aft pilots/passengers having a control stick and adequate view of instrumentation. The fuel (about 50 gallons) would be contained in two tanks located in the lower part of the fuselage more or less below the pilots. Tank switching will be used to manage center of gravity as necessary for landings.
It is my estimate that this airplane, with a 180 hp engine, will fly at about 200 knots (nautical miles per hour) consuming about 5 gallons per hour. (This estimate is an extrapolation from Uncle Bob's Mooney which has the same size engine but a conventional configuration.) This will give it a 9-hour range with an hour of reserve fuel for unexpected weather or diversion to alternate airports. Nine hours in the seat is plenty long enough, I have found -- Uncle Bob and I did a little over 7 hours once and we were both ready to stand on terra firma!
For the past two or three weeks I have been having a very interesting discussion with Uncle Bob via e-mail about wingtip vortices. He hasn't committed to an opinion regarding my configuration. What about the readers of this BLOG? All ideas cheerfully considered (grumble! grumble!! -- not really!).
Friday, May 4, 2007
The Ideal Airplane
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Landing gear on the wingtips sounds cool. I suspect it would require some rather advanced materials?
ReplyDeleteWould you make your wings shaped like a gliding seagull? Their wings must have something close to an optimal shape.
I don't believe special materials should be required. Although the normal (in-flight) wing-loading is spread over the wingspan, placing the concentrated load at the wingtip should not require any change in strength.
ReplyDeleteDuring flight, the wing loading must be designed for about 2.5g (2.5 times the weight of the loaded aircraft). On the ground, the maximum load is only a little over 1g. Provision for the "rough" landing is the only reason for the "little over".
My wing (and forward horizontal stabilizer) shape would be constant chord (very much like the Mooney) but with down-turned "winglets" at the outboard ends (look at a 737 parked at Renton Airport or Portland Int'l and imagine them turned down instead of up).
No, I don't think of the wing shape as being like a seagull or an albatross, although that inspires some interesting thoughts, since these birds are famous for their endurance in flight. The most efficent wing, though would probably be that of the Andean and California Condor who not only soars using updrafts but does so at altitudes over 20,000 feet!
I heard that the main reason they turn winglets up (rather than simply extending the wing horizontally) is to save space. If you're concerned about capturing every bit of lift, then you should extend the wingtips horizontally.
ReplyDeletePutting the landing gear out on the tip of the wing would mean you need to build the entire wing strong enough to support the weight of the fuselage. In contrast, if you place them inboard, or maybe even under the fuselage, then the only part of the wing that needs to be that strong will be right at the connection with the fuselage, and you can build each section outboard of that lighter. I'm maintaining that the wing tip does not carry the entire weight of the airplane, but rather only that portion which is not being supported by the sections of wing inboard from that spot.
Take for example a paddle that I once carved into a shape identical to the one you propose. The tip was so thin that it flexed and would break if I braced it on the ground and put all of my weight on it. However, when I used it in the water, it worked just fine, and the entire length of the paddle blade was capable of supporting my weight.
You're right about the reason for winglets instead of just lengthening the wings: it simplifies the problem of parking at the terminal. The reason the winglets help is because they reduce the severity of the wingtip vortex; this vortex is a waste of energy.
ReplyDeleteBut my proposal is to turn them down instead of up. It is my belief that down-turned winglets would be more effective in reducing the vortex because of the higher pressure under the wing as opposed to over the wing. The down-turned winglet would "trap" the higher pressure air under the wing until the wing was past after which the lift effect is complete.
The tips of constant chord wings would be well able to support the weight of the airplane. The weight would be nominally 1g whereas, during flight, the wings must be able to sustain an airload of 2.5g or more. During flight the lift is distributed over the wingspan. I'll do the Math and give you the equations to prove my point.