Russell,

Since no one to date has responded to your question, I thought I would offer my opinion/experiences with RNV set up, for whatever it's worth.

Allot has been discussed on this subject and, as is the case with most things, a variety of opinions have been expressed.

My experience with RNVs on profile planes has has been this:  The engine run is good until all but the the last ounce or so of fuel has been used up.  the engine then speeds up and slows down repeatedly.  Eight to fifteen laps follow like this before the engine finally stops.  Very annoying and would be disastrous in a competitive situation. It's not very good for the engine either.

By changing the RNV to a standard, through the venturi NVA, the problem ended.  No other changes made.  One lap of increased rpms, a burp or two  and shut down.

I use a Sullivan 4oz. plastic tank.  Sintered bronze clunk with a fill tube from the bottom (inside) of the tank to above the top (outside) and a vent tube from top (inside) to below (outside) the tank.  Maybe a Uniflow tank would act differently.  I can't say because I haven't tried one.  My fuel supply system as described above works very well for me so I see no need to change it.

I haven't tried a RNV on any upright or inverted engines so I can't say how the RNV works on them.  I would speculate that the results might be the same as with a side mount.

I'm sure there are many who have not experienced problems with RNVs.  Perhaps someone who has had good luck with them can offer their advice.

Joe

Not a remote needle valve and not a new idea, The flexible cable is a piece of 1/16 inch cable from the hardware store. knob and connector are home made.  Silver brazed together. Works great and gets your hand away from the prop. Since I made this I discovered that the three inner layers from an old speedometer cable works even better than the 1/16 inch cable. More flexible and designed for torque.

I have flown a G A Special with side mounted LA40 and stock factory remote NVA. Plastic clunk tank. No problems. Perfect run. So far no one has come up with any explanation as to why a remote should run any different from a front mounted needle. I'd be interested to see such an explanation.

I've seen both setups and one of my friends, Roger, can get great runs on remote needles, wired open RC carbs, popsicle sticks for venturis, you name it. I would think that muffler pressure would be of help if a remote needle is used. I'm thinking of the "inventory" of fuel after the needle valve that is being drawn against the restriction of the needle has no head pressure when the fuel pick up in the tank becomes exposed. Adding muffler pressure might be the variable.

Hi. I can't see any reduction in ability to draw fuel. The fuel passes theough the same length of fuel tube, and is metered by a needle valve that is set to deliver the correct amount of fuel in both systems.

Hi. I can't see any reduction in ability to draw fuel. The fuel passes theough the same length of fuel tube, and is metered by a needle valve that is set to deliver the correct amount of fuel in both systems.

At first blush that seems right, but consider what happens with a RNV when air reaches the needle and there remains that inventory of fuel I spoke of earlier. The needle is now metering a much lower viscosity fluid (air) while fuel is still being supplied to the engine.

but consider what happens with a RNV when air reaches the needle and there remains that inventory of fuel I spoke of earlier.

I'm sure air in the system would behave differently, but I guess I'm considering a system that doesn't contain any air.

This question interests me, I/m wondering if it might be one of those folk myths that invade our thinking from time to time, like position of belcrank affects how the plane flies.

I think we need to remember that the fuel is a fluid column. Pressure in a fluid is a constant end to end from basic hydrodynamics.  A needle valve in a system will introduce a restriction in that system but no matter where it is it has the same effect on that system.  The restriction will reduce (regulate) the flow, but will not reduce the pressure.

I feel that if one has problems with a remote needle valve system there is some other related problem other than the location of the valve.  Problems I've had have been air leaks introduced by the design of the needle assy.  Get rid of the leaks, get rid of the problem. 

Hi Don  the ones I have tried had  zero leaks, you need to remember  also what you wrote  above   """"The restriction will reduce (regulate) the flow, but will not reduce the pressure. """
An engine cycling 4-2 is affected  from  not only  pressure but also flow, cut the flow and it can make the motor break much leaner or  quicker  or  longer, increase the flow it can break slower, later or not at all . If it was  only pressure  we  could put the NVAs in the tank or at the front of the tank.  This works very rarely  and  if your  wanting a motor that depends on fast cycling 4-2 it many times ,retards that type of cycling motor run

Regards
Randy

Hello Dick

My point was trying to point out that  there is more happening than just one thing, and that Myself and others have tried the remote NVAs without the results we wanted, and that by moving the needle to the venturie it did  much improve the engine run. I have no reason to want to argue about other things that may or may not be  happening

Regards
Randy

Dick,
I agree with you that once the air hits the needle seat, the low viscosity air will leak past so fast that the engine will or should go pretty rich. However that will last only as long as the amount of fuel in the tubing between the needle and the spraybar. That might be a lap or two, but not much more than that (not the 10 to 15 someone else mentioned that they were seeing.
Otherwise the pressure in the line past the needle will be less simply because the fuel flowing past the needle restriction causes the pressure drop. But other than the effect in the first paragraph, I  have a hard time understanding why a remote should behave different from  the standard. Remember in the standard needle assembly, the fuel between the needle seat and the spraybar opening is also at the same low pressure.