Essentially, as far as the fuel system itself is concerned, it makes almost no difference which side of the engine the needle valve is located. Let me explain why this statement has so many qualifications to it.
For a conventional inverted or upright mounted engine and for a "typical" installation where the pickup tube in the tank is essentially at the same level as the spraybar or the fuel exit into the venturi and consider circular flight where there is a pressure head where the fuel pickup tube is located.
Draw pressure or force diagrams that represent the fuel in the tubing from the the pickup point in the tank to the hole in the spray bar in the venturi. Do this for the case where the needle valve is on the opposite side of the engine from where the fuel pickup tube collects the fuel inside the tank, as in a "typical" wedge tank. This configuration will normally allow the shortest path through the tubing from the pickup point to the spraybar hole.
Now, draw a similar diagram where the needle valve is on the same side of the engine as is the pickup tube in the tank. This configuration will normally require an additional amount of fuel tubing around the crankcase to get to that hole in the spraybar. The pressure head or the difference in the lateral distance from where the fuel enters the pickup tube and the hole in the spraybar is the same. The only difference is that in the one case, the fuel must travel through a bit more tubing, so there is a slight pressure difference because the fuel must travel through a longer piece of fuel line. This pressure difference is probably negligible, at least as far as making any difference on which side of the engine where the needle valve is located. However, if one feels that it is important to keep the fuel line length to a minimum to reduce pressure differential at the ends of that fuel line, then the needle valve should be on the engine opposite where the fuel pick up tube is in the tank. Or another excuse to put the needle valve on the engine opposite of the fuel pickup tube is in the tank will normally allow a "neater" fuel line installation in the nose of the model to avoid the need for the fuel line to wrap around the crankcase of the engine to get to the other side. However, this fuel line wrapped around the crankcase situation can be avoided by simply routing the fuel pickup tube inside the tank to go from the wedge to the opposite side of the tank before it exits the tank, thereby shortening somewhat the total length of the fuel line, albeit still longer than if the needle valve is on the opposite side of where the fuel pickup is. That pickup tube does not have to be straight. The only thing that is really important here is where the end of that pickup tube is to gather the fuel to go to the engine.
Once this is understood, then similar diagrams can be produced for clunk tanks and/or for side mounted engines and/or any combination of all of the above and the same conclusion can be drawn. You can mount the needle valve on either side of the engine. However, if you think it is important to minimize the distance the fuel must travel from the pickup to the venturi, and there are some who think this is an important parameter, then that requirement starts to dictate which side of the engine to mount the needle valve, burnt fingers and/or NV protection notwithstanding.
Keith Trostle
Topic: NV, Which side? Can it be moved? on AT? (Read 1483 times)