No "BOTH" positions allowed on RV's

[Kevin Horton]

Originally Posted by Toobuilder

I just find it curious that people will categorically rally around the admonition against the use of a BOTH position for low wings (which is OK per FAR 23), but accept passing through OFF when switching tanks.

The current version of FAR 23.951(b) states:

23.951 General.
(b) Each fuel system must be arranged so that?

(1) No fuel pump can draw fuel from more than one tank at a time; or

(2) There are means to prevent introducing air into the system.

These provisions would prohibit fitting an RV with a fuel selector with a BOTH position, if it were a type-certificated aircraft, or a header tank was added from which the BOTH position fed fuel.

[rv7boy]

When this thread started, I didn't imagine it would go on this long. But I'm glad it has, because it has been very educational and interesting.

[Toobuilder]

Originally Posted by Kevin Horton

The current version of FAR 23.951(b) states:.

Yep, saw that. However, the "means" to prevent air from entering the system can be procedural, as they often are to meet FAR 23.

[rvbuilder2002]

Originally Posted by Sam Buchanan

The little red pointer on my fuel valve is primarily for a pilot who isn't familiar with the plane.

As would be a handle that intuitively points at the selected tank.
This is a good thing for day or night, it is just a bit more necessary when in the dark.
A good practice for any situation.... the same reason that as a standard we use engine controls that are identified by different color and shape.
As RV's and other experimentals get embraced more and more by the general aviation world, I think it is a good idea if people built their airplanes mimicking the standards used for Standard Category aircraft.

BTW, Anyone that has an airplane configured with the long part of the handle acting as the pointer, but doesn't like that configuration, there is an alternate handle available form Van's......

Part number FUEL VALVE LEVER
Replacement for stock lever on fuel valves supplied in kits. Keyed so it will work only on valves that use the long arm of the lever as a pointer. Will not work on valves installed prior to 2000 that typically use the small pointer on the lever to indicate the tank in use. Red Anodized finish.

A photo and order info HERE

[airguy]

Originally Posted by rvbuilder2002

As RV's and other experimentals get embraced more and more by the general aviation world, I think it is a good idea if people built their airplanes mimicking the standards used for Standard Category aircraft.

I think a lot of us look at our airplanes as exactly that - OUR airplanes - and we build them the way we want them, thinking we will never ever sell them. I know I certainly am in that camp, and I can't envision a set of circumstances that would result in me selling my toy. The airplane works perfectly fine the way it is with me flying it - but if a third party took over that airplane with its current fuel system configuration, it would not be pretty and I would strongly suggest they rip it out and go back to standard. Modifications to the plans, especially with regard to the fuel system, are not something to be taken lightly.

Scott has a very good valid point about keeping it to the plans.

[David-aviator]

The Vans fuel system is so stone simple, why mess with it?
Its works, leave it alone.

[RV7A Flyer]

Originally Posted by Paul 5r4

I have to side with the OP. Couple of reasons.... 1) He's certainly an expert by most anyone's standards, certainly mine. 2) Why not "build out" any ANY potential gotchas and like he said they'll usually show their ugly head at the worst possible time.

The thought process of know your fuel system is of course important but at the same time, it's not a guarantee. Think of this... during one of the Saturn 5 rocket launches that took us to the moon, one of the main rocket engines shut down. Why, because despite all the checks built in by NASA and the rocket manufacturer they simply had two wires crossed! Their fix was to modify the wires so they would fit only one way thus building out any possible failure modes.

Because I know me, I built my plane as idiot proof as possible! :-)

Actually, it shut down on Apollo 13, the center engine shut down for unknown reasons related to pogoing. NASA has had requirements on sexing connectors forever, so AFAIK that was not why it shut down.

No definitive cause has ever been identified, however.

[Hogdriver]

So, my question is how did you get in the position of one tank is full and the other is empty, with the fuel selector in "BOTH" in the first place. Shouldn't it have fed more or less evenly over the course of time? And, if so, and one tank is sucking air, wouldn't the other not be far behind?

I don't argue that what everyone postulates wouldn't happen, but I'm thinking there must be a few things that have gone wrong before you ever get to that point. What am I missing?

Hogdriver
RV-6 N981

[RV6_flyer]

Originally Posted by Hogdriver

So, my question is how did you get in the position of one tank is full and the other is empty, with the fuel selector in "BOTH" in the first place. Shouldn't it have fed more or less evenly over the course of time? And, if so, and one tank is sucking air, wouldn't the other not be far behind?

I don't argue that what everyone postulates wouldn't happen, but I'm thinking there must be a few things that have gone wrong before you ever get to that point. What am I missing?

Hogdriver
RV-6 N981

Any number it things can cause one tank of two tanks feeding through a both position not feet the same.

IF one vent is plugged or partially plugged, that tank will feed less.
IF there is a restriction in the line, an extra bend or angle fitting in one feed line, a kink on the inside of a bend, a kink anywhere in the line, that will add restriction and feed less than the other tank.

[sailvi767]

Originally Posted by RV6_flyer

Any number it things can cause one tank of two tanks feeding through a both position not feet the same.

IF one vent is plugged or partially plugged, that tank will feed less.
IF there is a restriction in the line, an extra bend or angle fitting in one feed line, a kink on the inside of a bend, a kink anywhere in the line, that will add restriction and feed less than the other tank.

Or not keeping the ball centered in flight!