CG on an old CL/FF plan - RC Groups
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Dec 08, 2002, 02:01 PM
EB-66C Team Member
J Morgan's Avatar

CG on an old CL/FF plan

I've built a all blue foam Cessna L-19 from an old Berkeley 1953 Controline/Free Flight plan.
WS: 38.5 " From extended ACE tapered foam wing
Avg Chord: 4 1/2", Middle section 5 1/2"
WA: approx 180 sq. in.
Length: 25"
DX-A with 9-7 prop
AUW with 6-270 ni-cads is 10.2 oz( heavier than I wanted)

Problem: Before I hand launch this beast, I'm a little worried about the CG. The plan shows the CL cg @ 1 1/4" from leading edge ( 23%) and Free Flight @ 2 3/8" from leading edge (43%)
The original plan had a LIFTING stab so I know i can't use the free flight number and the CL seems a too forward.
Should I start at about 30% and hope for the best or what?
Any help would be appreciated, your guess is probably better than mine.
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Dec 08, 2002, 02:23 PM
Ascended Master
Sparky Paul's Avatar
I built that plane, when it was first released as a kit way back when.
I don't recall the specifics, but it fly as a free-flight. Cub .049 power.
A 30% c.g. is probably OK. Don't overdo the elevator travel.
Dec 08, 2002, 06:36 PM
EB-66C Team Member
J Morgan's Avatar
Thanks Sparky, that's what I thought would be a logical approach. I knew I couldn't use the FF CG, I didn't put a lifting stab on it. You're right, Iit was powered by OK Cub .049 or Thimble-Drome .049.
Dec 20, 2002, 09:29 PM
EB-66C Team Member
J Morgan's Avatar
Well, started with a DX-a and CG @ 30%. Kept elevator travel at 1/2" both directions.
First attemt at flight:
Gentle toss and could tell right off it was a little underpowered and it was wallowing from side to side. To far aft on the CG!
Aborted flight and as soon as I tried to level the wings with rudder, tip stalled into the ground. Only from about 5 feet so no damage other than a little tear in the foam around the landing gear wire.
Replaced the DX-a with a M100. Decided to run on 6 cells to minimize weight. Moved the CG to the C/L position which is 23% of wing chord. Little worried about being too far forward but tried it anyway.
Second attempt: Man, this M100 is strong. Rev up and gentle toss. Climbed straight ahead and gain altitude. Flew like it was on rails. First attempt to turn, WOW! Forgot to reduce the rudder throws like I did the elevator. Very carefully turned and did a few circuits. Then scared to land. But it is a happy ending. Landed just fine and now off to the paint shop to detail her. And reduce the rudder movement!
Sparky Paul,
Thanks for the help on reducing the throws. I'm sure it saved me alot of pain.