Badger
Sep 25, 2004, 11:26 PM
I put together an Aegea from the Phil Barnes wings in the Spring of 2004 to try out the latest Drela airfoils for TD. I now have far too many Drela design based RC sailplanes including 3 Supergees, a Bubble Dancer, a 3m Skydancer and my own design SpinCycles. The Aegea I have came out at 67 ounces ready to fly, so it is pre-ballasted to the mid range of the recommended weight. I have flown it in winds up to 25 mph with only 7 ounces of extra ballast so the speed range is very good at this light weight. To see just how slow a TD plane can fly I decided to build a stretched Aegea to 135" and build it far lighter than the commercial production wings. I also had the chance to observe the performance of the Supra at the 2004 F3J WC flying against some of the world's best pilots and planes and came away with the desire to build one.
Whenever I build a plane, I take shortcuts to ease building and to use the materials/tools I have on hand. Having designed, built and competed with my own composite sailplanes, these choices are simply my own decisions without criticism of the original design choices. On the other hand, I also realize that the changes will mean that the plane will not make the specified weight targets.
These are the changes I chose to make:
1. Planform is a a stretch Aegea, same chords and panel breaks, 135" projected span but with the forward sweep of the Supra.
2. Spar and skin design is my own.
3. Tail design is my own, but moments are retained.
4. Pod and boom fuselage is not a pylon mount, I have a shoulder mount open class pod mold.
5. No RDS.
The center panel has a 1/2" wide spar with full balsa core and the lightweight 1k carbon sleeve. The caps are laminated precured CF strips tapering from 0.124" to 0.062" at the tips. The tip panels have a partial spar 12" long to hold the joiner tubes. The remainder of the tip panel is stressed skin with a unicarbon leading edge and kevlar trailing edge and hinge. I put two 1/8" wide weblets under the top skin only. Joiner rods from 3/8" diameter CF are straight and the joiner boxes give the dihedral at the break of 6 degrees. The center panel is flat.
I tried the integral skin hinge method for the first time and like the results but dislike the extra work. Only the center panel flaps have these, the ailerons use the Barnes skin hinge method and I have faced the aileron gap.
The tail uses the HT series airfoils. The rudder is Kevlar with CF skin spar and the stab is fiberglass because I ran out of Kevlar. I mold my own V-mounts. Pushrods are 0.050 CF rods with bondable Teflon sleeves, run on the outside of the boom. The boom is a tailboom.com 5 layer BD boom that I have stiffened with 1/16" balsa shear webs at the pod end.
Final weight is 55.9 ounces, with nose tooth and heavy nosecone.
Flying
The following is intended for your benefit, learn from my poor decision. On my V-mount the stab is removed by sliding out the pivot pin and detaching the pushrod clevis. This gets to be a pain since you have little room to work between the struts. The specified design is better but I won't make that complex a mold or purchase the part. To make the stab easier to remove, this plane switched to a ball link on a stud. This introduced flexibility into the linkage from the plastic ball cup and more importantly, the pushrod is offset on the control horn allowing it to twist under load. The centering of the stab was solid but there was some springy flex. After two moderate launches, I decided to give the plane a max tension launch into a 10 mph headwind on my competition winch. Right at the top of the launch before the zoom, the stab fluttered and broke the pivot rod.
Slight digression - you can fly an open class sailplane without a stab by rolling inverted and using crow to modulate the pitch attitude. Rudder and ailerons work as normal. I've now done this four times, on a Thermal Eagle where an aileron broke off and took out the stab, a Bird of Prey where the stab fluttered in a dive, a Maestro where the chute hit the tail and this time.
The plane was landed and the tip panels creased slightly from striking the ground first. Other than that, no damage and the plane flew the next day.
I have about 15 hours flight time on the model. What else can you say about a 1100 sq.in. sailplane with radically thin airfoils that weighs 56 ounces? You would expect it to launch hard but suffer in the zoom. You would expect to easily out climb traditional competition designs in thermals. You would think that it would not go upwind at all. Well the last one is not true. After reading earlier posts about the camber setup on the AG4X airfoils and many hours flying my Aegea, I have the 4 flight modes on the wing. Launch is normal. Speed mode is reflex -2 degrees and most of the flying around is in this mode. Thermal mode is 4 degrees of droop and plane slows to jogging speed. I added a reflex speed mode where the flaps are reflexed 4 degrees and the plane moves out much better when flying fast upwind. The plane is completely silent at 50 mph passes so the wing is very clean. I have the plane set up quite stable at 27% of MAC, so all of these trailing edge settings require significant elevator compensation, but the plane flies very well in each configuration.
In summary this is why you build composite planes, to build a design that is cannot be purchased (good luck finding someone to build one for you), that in some ways will outperform anything in the market. Thanks to Dr. Drela for putting out another interesting plane.
Whenever I build a plane, I take shortcuts to ease building and to use the materials/tools I have on hand. Having designed, built and competed with my own composite sailplanes, these choices are simply my own decisions without criticism of the original design choices. On the other hand, I also realize that the changes will mean that the plane will not make the specified weight targets.
These are the changes I chose to make:
1. Planform is a a stretch Aegea, same chords and panel breaks, 135" projected span but with the forward sweep of the Supra.
2. Spar and skin design is my own.
3. Tail design is my own, but moments are retained.
4. Pod and boom fuselage is not a pylon mount, I have a shoulder mount open class pod mold.
5. No RDS.
The center panel has a 1/2" wide spar with full balsa core and the lightweight 1k carbon sleeve. The caps are laminated precured CF strips tapering from 0.124" to 0.062" at the tips. The tip panels have a partial spar 12" long to hold the joiner tubes. The remainder of the tip panel is stressed skin with a unicarbon leading edge and kevlar trailing edge and hinge. I put two 1/8" wide weblets under the top skin only. Joiner rods from 3/8" diameter CF are straight and the joiner boxes give the dihedral at the break of 6 degrees. The center panel is flat.
I tried the integral skin hinge method for the first time and like the results but dislike the extra work. Only the center panel flaps have these, the ailerons use the Barnes skin hinge method and I have faced the aileron gap.
The tail uses the HT series airfoils. The rudder is Kevlar with CF skin spar and the stab is fiberglass because I ran out of Kevlar. I mold my own V-mounts. Pushrods are 0.050 CF rods with bondable Teflon sleeves, run on the outside of the boom. The boom is a tailboom.com 5 layer BD boom that I have stiffened with 1/16" balsa shear webs at the pod end.
Final weight is 55.9 ounces, with nose tooth and heavy nosecone.
Flying
The following is intended for your benefit, learn from my poor decision. On my V-mount the stab is removed by sliding out the pivot pin and detaching the pushrod clevis. This gets to be a pain since you have little room to work between the struts. The specified design is better but I won't make that complex a mold or purchase the part. To make the stab easier to remove, this plane switched to a ball link on a stud. This introduced flexibility into the linkage from the plastic ball cup and more importantly, the pushrod is offset on the control horn allowing it to twist under load. The centering of the stab was solid but there was some springy flex. After two moderate launches, I decided to give the plane a max tension launch into a 10 mph headwind on my competition winch. Right at the top of the launch before the zoom, the stab fluttered and broke the pivot rod.
Slight digression - you can fly an open class sailplane without a stab by rolling inverted and using crow to modulate the pitch attitude. Rudder and ailerons work as normal. I've now done this four times, on a Thermal Eagle where an aileron broke off and took out the stab, a Bird of Prey where the stab fluttered in a dive, a Maestro where the chute hit the tail and this time.
The plane was landed and the tip panels creased slightly from striking the ground first. Other than that, no damage and the plane flew the next day.
I have about 15 hours flight time on the model. What else can you say about a 1100 sq.in. sailplane with radically thin airfoils that weighs 56 ounces? You would expect it to launch hard but suffer in the zoom. You would expect to easily out climb traditional competition designs in thermals. You would think that it would not go upwind at all. Well the last one is not true. After reading earlier posts about the camber setup on the AG4X airfoils and many hours flying my Aegea, I have the 4 flight modes on the wing. Launch is normal. Speed mode is reflex -2 degrees and most of the flying around is in this mode. Thermal mode is 4 degrees of droop and plane slows to jogging speed. I added a reflex speed mode where the flaps are reflexed 4 degrees and the plane moves out much better when flying fast upwind. The plane is completely silent at 50 mph passes so the wing is very clean. I have the plane set up quite stable at 27% of MAC, so all of these trailing edge settings require significant elevator compensation, but the plane flies very well in each configuration.
In summary this is why you build composite planes, to build a design that is cannot be purchased (good luck finding someone to build one for you), that in some ways will outperform anything in the market. Thanks to Dr. Drela for putting out another interesting plane.