I revisited this 4" based model the other day, since one of my customers did some exerimenting with my 2.6" based kit to move the CG back from 5/8" to 1 3/4" back from the chine/wing junction, I was hoping I could scale it appropriately on this model which balanced at 1/2" back from the junction and get a longer glide with less drag from up trim and potentially reduce weight. The model is relatively proportional to the small one so was hoping I could go back to 2.5" or a little more back.
On my model the nose cone was hand roto cast and a bit heavy but it balanced fine at the original position without lead and the battery and receiver in the nose cone. To move the CG back I had to move the RX and battery to the back of the model, mounted inside the open end of the model on the foam motor support strips with velcro. I got rid of the servo extensions and cut an inch off the nose cone shoulder to reduce weight as well.
This got my ready to fly weight down to 16.1 oz rtf instead of 17.1. I usually fly this on F-24 or E-20 or F-32 motors with ejection removed. The E-6 is too wimpy for 17 oz. However at 16.1 it would be marginal. One of my customers has built a 1/14 scale B-52 R/C aircraft in nasa colors and is planning on dropping and air starting his X-15 kit he got from me. I wanted to test this so he could reduce weight since he will have to carry onboard ignition ckts. Since he is starting horizontal the E-6 will give a nice long burn and plenty of thrust for a 45 degree climb out.
I started at 2.5" back which should have been slightly conservative, and it boosted slow but fine, but when I clicked in up trim it did a nice slow half flat spin, I figured I was tail heavy and no forward airspeed and too much up trim, so I hit the trim off, to pitch the nose down and get air speed and then remembered I had a middle switch position that had half of the up trim set so tried that, it was better but still too easy to over flare with small inputs.
I landed and put back a quarter ounce into the nose and reduced the up trim to about 1/4" instead of 5/8" and flew it again and it was fine. So I'm now at 2" back from the wing/chine intersection at the leading edge.
Interesting to see how it didn't depart but it was not happy at the first balance/up trim setting... I figured if it would fly stable with this low thrust motor and CG it will be fine with the higher thrust motors I normally use.
