Dragonfly Design Contest Build
01-18-2006, 03:06 PM
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Dragonfly Design Contest Build
We are now embarking on another design contest. I figured that since I did not know a lot about these little critter designs, I would pick a parameter and experiment with it. I chose wing aspect ratio. Because I like special and unique a/c, I decided to design a SW racer/combat plane around the U-2 wing. So was born the Dragonfly.
The DF has an AR of 10 and an wing area of 110 sq in. The span is 36 in (using a 3/16" balsa plank) and the length of the fuselage is 28 in. The rtf weight is 8.5 oz.
One of the big difficulties with a high AR SW plane, I think, is the lack of structual rigidity in the wing. I am sure you guys know or can imagine how a sheet wing will twist and flex. Besides posing a possible structual failure problem, the flexing and twisting wing can cause the aerodynamics to go to heck. In an effort to reduce the spanwise flexing, I notched the wing for about 60% of the center portion of the span and added a 1/8" X 1/16" carbon fiber spar. Twist control occurs normally when attaching the wing to the fuselage. Between the spar and the wing attachment, the wing rigidity was improved. But the wing is far from rigid. The wing can still have considerable twist and flex in the outer third or quarter of the span. The movement may ultimately cause failure. Additional wing strengthening is possible, but in an effort to keep the weight down, I chose not to add any more wing structure. I figured the design will be wrung out in the flight test phase. If a failure occurs, then it is back to the drawing board.
I initially planned to power the DF with a product reedy but since I had a good TD sitting around gathering dust, I plan to skip a step and go right to MORE POWER - I love "Tim the Tool Man".
I am using a pt "bubble bottle" tank. Ultimately, assuming the airframe can take it, I will go to an U/C 061AME.
Below are some pictures of the assembly and the finished plane. (Yes Vic, cp's wife happened to be on the East Coast and volunteered to hold my plane). I still need to hook up the ailerons and the elevator. First flight will be in the next week or so.
The DF has an AR of 10 and an wing area of 110 sq in. The span is 36 in (using a 3/16" balsa plank) and the length of the fuselage is 28 in. The rtf weight is 8.5 oz.
One of the big difficulties with a high AR SW plane, I think, is the lack of structual rigidity in the wing. I am sure you guys know or can imagine how a sheet wing will twist and flex. Besides posing a possible structual failure problem, the flexing and twisting wing can cause the aerodynamics to go to heck. In an effort to reduce the spanwise flexing, I notched the wing for about 60% of the center portion of the span and added a 1/8" X 1/16" carbon fiber spar. Twist control occurs normally when attaching the wing to the fuselage. Between the spar and the wing attachment, the wing rigidity was improved. But the wing is far from rigid. The wing can still have considerable twist and flex in the outer third or quarter of the span. The movement may ultimately cause failure. Additional wing strengthening is possible, but in an effort to keep the weight down, I chose not to add any more wing structure. I figured the design will be wrung out in the flight test phase. If a failure occurs, then it is back to the drawing board.
I initially planned to power the DF with a product reedy but since I had a good TD sitting around gathering dust, I plan to skip a step and go right to MORE POWER - I love "Tim the Tool Man".
I am using a pt "bubble bottle" tank. Ultimately, assuming the airframe can take it, I will go to an U/C 061AME.Below are some pictures of the assembly and the finished plane. (Yes Vic, cp's wife happened to be on the East Coast and volunteered to hold my plane). I still need to hook up the ailerons and the elevator. First flight will be in the next week or so.
01-18-2006, 04:52 PM
#2
RE: Dragonfly Design Contest Build
So that's where my wife is! [X(] She goes for that aspect ratio, I guess 
.
If you do manage to snap the wing in half with 1/2A power, you'll one of the very few [I think] who have ever accomplished that. So if a failure occurs, it really isn't a failure, but an acheivement that very few of us [especially the guys who think they're building for .40 sized pylon, instead of 1/2A] have ever done. Remember, [the SWRBA motto] if you don't fold one every now and then, you're building too heavy
.
. If you do manage to snap the wing in half with 1/2A power, you'll one of the very few [I think] who have ever accomplished that. So if a failure occurs, it really isn't a failure, but an acheivement that very few of us [especially the guys who think they're building for .40 sized pylon, instead of 1/2A] have ever done. Remember, [the SWRBA motto] if you don't fold one every now and then, you're building too heavy
.
