CG for Elevon Wing Type ?

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aerostadt

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Where should the GG be for an R/C Elevon wing type glider (delta wing) with no motor? This is a parasite glider (4x Orbital Transport) and I do not need to worry about the boost phase of the trajectory. I am wondering where to place the battery. Is there some kind of rule of thumb?
 
If the wing is delta shaped in plan form. start with a CG at 48% of cord. Give it a toss over high grass and adjust the balance from there.

John Boren
 
Thanks for the information, XolveJohn and JumpJet. For the white orbiter I decided to put the 2 cell Lipo battery on a tube coupler and slide it back in the main tube using the idea of trying to get the CG to about 50% of the root chord. After putting everything, electronics, etc. back into the orbiter I closed it up and tried a few test tosses in the back yard. The glides look pretty good. The orbiter comes in at 1 lb and 3 oz, which is pretty light for me. I hope this parasite glider holds up on the launch stresses. If so, it should be a good glider.
 
Looking at my white glider in test tossing more closely, I found that the heavy 2s Lipo battery near the aft end stalled almost immediately. This is very different than my red glider, which does fine with the heavy 2s Lipo battery in the aft end. I consider both gliders to be delta wings, however, the red glider is a half shell with a flat bottom wing and wing tip fins. The white glider has a dihedral wing and a large fixed rudder. So, I put in trimmed coupler tubes in both the aft and forward end of the white glider using velcro strips to position the battery. Since, I have only one 2s Lipo battery left, I used a 1s lipo battery in the forward end of the white glider. Hand tosses show the white glider to glide well with the battery placed in the forward option.

IMG_4448.jpg IMG_4449.jpg IMG_4450.jpg
 
The wingtips and rudder should make no difference in CG requirement, the flat bottom with flat forward fuse should require a more forward cg since you get more lift from the flat forward than from the rounded forward on the white glider but it appears your trailing edges go further back on the red glider so would push the CG back, may be a wash. If your wing planform is identical except for dihedral, the red should have a slightly more forward cg location requirement, have you put them on a balancer and seen where it actually balances with best glide? I would think your red glider is lighter since it has half the body tube and nose cone component, and you have white one with removable tail with couplers that are fully round which also add to tail weight. Point is they aren't identical wing planforms so not surprising the CG is slightly different.
 
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