Building Tips and technical articles. > Building techniques
Endgame IV Build
Ken Culbertson:
Wing is getting fitted out. Center spar reinforcement assembled. Consists of two laminations of .03 CF Plate over a 1/8" balsa core. This is my new plywood. Considerably stronger Bellcrenk pivot wire (1/8") goes through the center. Plumbing for the motor power cables added and cut the openings for the canard pushrod. Landing gear mounts next. Todays progress was interrupted by the wall mounted hook to hang Endgame III broke and THUD she fell three feet. Saved by the collett. It slipped and let the spinner absorb the shock. Aside from a broken battery limit - no damage!
Ken Culbertson:
Mounted the flap control box and bellcrank. Works great. Absolutely no binding anywhere. Now I have a question. I hesitate to ask it here because I don't think anybody reads the build threads if they are in the building forum but here goes anyway. I have to have trike gear for the twin and I need to place the rear wheels at about 1" behind the CG. I have no clue where the CG should go on a GEO-XL airfoil. I know a million other factors play into the exact position but if I can at least get a ballpark I can bend some wire.
Ken
Larry Renger:
Don’t forget, the canard will require moving the CG forward of a normal configuration.
Make a simple sheet scaled down model and tie some string to the wingtip. Swing it around to get some speed over the surfaces.
Move the CG aft till it flops around and you have discovered the limits. I would guess that 10% chord aft of that would be a good starting place.
Actually, my guess is that airfoil has little to do with stability on a symmetrical airfoil wing. Tail and canard area/moments are the controlling factors. 🤠
Ken Culbertson:
--- Quote from: Larry Renger on May 09, 2024, 08:17:09 AM ---Don’t forget, the canard will require moving the CG forward of a normal configuration.
--- End quote ---
Endgame III eventually had the CG 3/4" forward of it's non-canard but same airframe Endgame II (is there no end to Endgames? Maybe I need a new name!) With the twin canard I am so far out in uncharted waters I can't see the shore anymore. How does double the airflow over the center of the wings with the canard in clean air affect lift is a big one. As far as I can tell, there is not another example of a "stabilator" canard that I can pester the designer for ideas. Had I thought about it more I probably should have gone to a "stabilator" tail as well. Ball links and fiber pushrods make them possible. I tried one many years ago but slop in the controls made it difficult to track properly (nice corners).
My only concern with the CG at this point is where to mount the wing wheels. Two far forward and takeoff and landing get funky, two far aft and I need nose weight. The main spar on the Geo-XL wing (Bob Hunt's Lost Foam Version) appears to be close to where I would put the CG for the initial flight. I will put the main gear 1" behind that and if she doesn't fall on her butt - fly it. Two laps and a loop will tell me where the CG needs to be for trimming.
Thanks for the reply - Ken
Ken Culbertson:
Back to the build. Assembled the main components and resized the pushrods. Found that the Flap gizmo was not giving me enough elevator so I shortened the distance between the levers and now I get 40 degrees with 1 1/2" leadout movement. 40 degrees on a canard is huge so I should be OK even though I had intended my stops to be at 1 1/4" movement each direction. Controls are so loose and slop free with the new ball links Bob Hunt suggested.
I did have to re-do the pushrods to have more thread exposed. These links have about a 1/8" recess before the threads make contact - better but if you have trimmed for the DuBro's you are too short!
Added 5/16" cap strips and wingtips glued on (they fit, imagine that). As soon as I get the gear mounts done the wing gets mounted and I can finally start beefing up the aft wing/fuselage joint and covering up all the false starts that come from composing an airplane vs building from plans HB~>
Ken
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