by Ron Peterka
Scale models often have problems with access to the engines needle valve for adjusting the fuel mixture. Builders of sport models may want to minimize the cutting of cowls, or want to increase the aerodynamics of the cowling. Or, maybe, you are just concerned that reaching in close to a whirling prop is not very safe. Here is the answer -- install a remote needle valve assembly and put that needle valve pretty much where ever you want it.
As this is written there are at least four manufacturers who offer some form of remote needle valve. Varsane Products here in San Marcos, K & B Engines, O.S. Engines, and Bob Violett Models each offer products you can use. Some of the remote valves are designed to offer in-flight mixture adjustment as well as the safety of being away from the prop arc.
Personally, I have used the Varsane and O.S. remote needles. It is easy! For my semi-scale Weddell Williams model I installed the Varsane needle assy. on the firewall with a wire needle extension extending out through the left side of the cowling well behind the prop arc. Fuel is plumbed from the tank to the needle valve and from the needle valve to the fuel fitting on the carburetor. The regular needle valve is adjusted for extreme rich setting. The external end of the engine mounted needle valve can actually be cut off at the carburetor. The remote needle will adjust the high speed fuel mixture! Idle mixture will still have to be set at the carburetor, but this is best done with the engine shut down anyway.
For inflight mixture control a servo is connected to an arm that can richen or lean the mixture with the use of an auxiliary channel on the transmitter. The ducted fan fliers often use this feature to protect their engine if they take off and find the engine is running rich (low power) or lean (burned cylinders). The speed freaks use remote mixture to set the mixture for maximum power during high speed runs and then richening for cool down after the runs.
The only negative I can see is that it take a little more fussing and priming to get the engine running the first flight of the day. Once the fuel line is primed there is little or no difference from the engine mounted needle assembly.