airbusdrvr

I am in the planning stage of building a Bruce Tharpe Engineering Delta Vortex, http://www.btemodels.com/vortex.html. The fixed gear will be replaced with retracts which means the nose gear will retract into the compartment just aft of the engine bulkhead that was designed for the fuel tank. Using an engine test stand, I confirmed that my engine will run with the fuel tank placed aft of the nose wheel compartment. This location places the tank at or barely forward of the CG instead of the original eight to nine inches forward of the CG. Now my question. CG locations on most kits and ARFs are shown with all equipment installed but no fuel. If the fuel tank is now at the CG location and fuel weight will never affect CG, do I still use the CG location in the plans that assumes the tank is forward of the CG. The recommended tank size for this model is 14oz to 16oz.

combatpigg

My Feedback: (3)

You can't escape the fact that you will have to fly the plane with fuel in the tank. If having fuel in the tank causes the CG to be aft of what is called for, then you will most likely have to move the engine forward to compensate.

wvarn1957

My Feedback: (3)

I have the BTE Delta Vortex with retracts, powered with a YS 61R. The tank is on the CG to allow for installation of the nose wheel retract. Balance it as called for on the plans(21" to 22" from the trailing edge) without fuel and the retracts up. Mine is balanced at the more reaward limit because when the nose gear is down it shifts the balance point foward. How much it shifts is dependent on the size and weight of the nose wheel.

da Rock

Very often, when a tank is placed "on the CG" it's actually not. Most designers consider that the fuel rides around in the back of the tank most of the time. So they usually don't put the center of the tank on the expected CG. It's a bit safer to place it with the center of the tank somewhat forward the expected CG. It often depends on the size of the fuel tank in relationship to the size of the airplane.

airbusdrvr

I sent an e-mail to the designer/owner of the kit, Bruce Tharpe, and received the following reply.

"Use that CG range regardless of fuel tank position. You will have the benefit of no CG shift with fuel burn - nice!
___________________________________
BTE | Bruce Tharpe | Owner "

gcb069

What retracts are you usin?

airbusdrvr

Spring Air Retracts with Robart 3/8" struts.