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Fuel selector

N

nmontei

Member
Ok really dumb question I went flying in a friends RV7 and noticed his fuel selector labeled left, right, both and off, can we drain from both tanks at the same time with the stock set up or does my friend have his selector labeled wrong?

thanks,
Nick
 
nmontei said:
Ok really dumb question I went flying in a friends RV7 and noticed his fuel selector labeled left, right, both and off, can we drain from both tanks at the same time with the stock set up or does my friend have his selector labeled wrong?
Nick
Click to expand...

Normally --- NO!

There has been quite a bit of info on this lately. You should be able to find it with the search function.

L.Adamson
 
Absolutely not in a low wing airplane. If you run a tank dry, you will not be able to get fuel from the other tank, as the pump will not be able to create enough suction to overcome the huge air "leak" now created by the empty tank. This is a critical flight safety item in the RV's. Please call/speak to your friend and make certain that what you saw is correct, and if so, explain to him/her that it needs to be changed before further flight.

Vic
 
I mistakenly believed when I first put fuel in my -7a with standard fuel selector that having the lever hand pointing straight forward, it was in the off position. When I was calibrating the fuel level floats with my EIS, I left the hangar one evening with the selector lever pointing to what I thought was "off" and had one tank filled and the other one empty . Upon arrival the next day, I was stunned to see that I had "lost" half of the fuel in my full tank. Seeing no evidence of it being on the floor, I was perplexed, but quickly reailized what happened when I opened the "empty" tank to find it half full. So, there can be communication between the two tanks with the standard fuel valve under some circumstances. Would I rely on this for a "both" setting? No way.

erich
 
Some low winged..

......airplanes can run both. Matter of fact, my Air Tractor only has on or off....runs on both all the time. The only reason this airplane and the Cessna Agwagons and 'Trucks can, is because the belly is lower than the wing tanks and we have a sump there in both cases so the engine draws from the sump, which is always full.

Regards,
 
operational use of "both"?

This brings up an operational question that I haven't resolved. I have installed tip tanks in my RV 7A. I'm not flying yet, but I realized when doing the boost pump and fuel valve plumbing for my injected lycoming that the middle area between Left and Right was in fact "both".

That got me wondering if it might be good to use the both position when flying with fuel in the tips until they are empty, then reverting to the standard Left and Right. That way I would empty the loads on long moment arms evenly. My problem is not knowing what the control forces would be with uneven fuel in the tips. Am I just over complicating?

Thanks for any input and opinions.

Jeremy Constant
 
NO!!!!

Do not attempt to use a "both" fuel valve on the RV series of aircraft. As Pierre said, the only reason his airplane can do this is because of a sump. This essentially works the same as a "header" tank, if you will. As has been stated before, if one of your tanks runs dry, you will get air into the line and cause the pump to cavitate. Fuel modifications are not something to fool around with unless you REALLY know what you are doing.
 
I have been told that without a common single tank vent,
a slightly uneven tank vent pressure will transfer fuel from
one tank to the other. If the tank is full, you may vent fuel
overboard. I know the above is true in a high wing Luscombe.

The separate vents gives redundancy but you lose the 'both'
function. I also like to know how much flying time I have in
each tank. Although the coiled fuel vent at the wing roots
does seem to have merit, it would be hard to improve on Vans
fuel design.
Tom
 
tomwebster said:
The separate vents gives redundancy but you lose the 'both'
function.
Click to expand...

And for anyone who doesn't know...

Once a tank runs dry for any reason, including roll and yaw; the fuel will just stop flowing altogether ------ if both tanks are connected to a single line at the fuel selector, which then goes to the aux. pump. Which of course, is the RV low wing setup.

edit: Assuming a "both" selector is used

L.Adamson
 
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Tank switch timing

Thanks for the feedback -- I'm happy to go with "both" is a big NO NO. Mel, I hope my question didn't alarm you!:) I will operate the tank switching like any of the low wings I'm familiar with other than the Ercoupe which had a header tank and a fuel valve that was either both or off.

Just for info -- I used the Jon Johanson setup with no modifications. His recommended plumbing is to simply use a fuel line with check valve between the tip tank and the main tank. From the main tank I have the standard Vans plumbing except I used an Andair Fuel Valve. Both tip tanks have their own vents and others have evidence that the pressures between the vents on the tips need to be slightly greater than on the main vents to allow tips to empty completely into the mains in flight. Verifying the balance of the vents will be part of the flight testing.

Can anyone give a guesstimate on an appropriate time for switching tanks, while there's fuel in the tips? Each tip is listed as carrying 12.5 gallons (will verify that during tank capacity/usable fuel checks). So I'll have about 75 lbs out on the tips. Will this be something that just becomes obvious with the need for lateral trim or should I have a proceedure in the checklist for tank switch time with fuel in the tips? I've never flown a C310!

Thanks for your help.

Jeremy
 
Sorry, but sometimes I get alarmed when people talk about trying "new" things with fuel systems. It's so easy to get into trouble. And a lot of uneducated eyes search this forum.
 
Does the Andair fuel valve have the "both" position? I don't want a valve that can be put there.
 
I agree whole heartedly with Mel!!! Do not experiment with fuel systems, unless you are sure of what you are doing. Go with proven designs and systems that have withstood the test of time. There are way too many fuel exhaustion accidents already. Andair has a great fuel valve with R-L-OFF for RVs. I would not recommend one with a BOTH position.

Roberta
 
"both" position

I'm afraid some may have gotten the wrong impression from my initial post. The Andair Fuel selector that I have installed in my injected RV7A has placarded positions for Left, Right and Off, just like Roberta mentions. In my testing/learning about it before I installed it, I discovered that the area between Left and Right in fact feeds from both, (convenient if you want fuel to keep flowing when switching tanks!) but it is not intended to stay in that transitional position. It is purely for switching between Left and Right.

I will use it in the manner intended (just say NO!!!! to Both) and during flight testing will determine an appropriate amount of time before switching tanks while using the fuel in the tips.
Sorry if my posts caused any confusion.

Jeremy
 
Correct me if I'm wrong, but I was under the understanding that the Andair fuel valves are designed so that when you switch tanks, you don't go to the "off" position on one and then arrive at the "on" position on the other. In other words, the valve is closing one side at the same rate it's opening the other, so you don't interrupt fuel flow when you're switching tanks.

The big worry is accidentally arriving in the "off" position either by having a passenger bump the valve handle or by you inadvertently not arriving conclusively at LEFT or RIGHT when you make a change. The design of the Andair valve prevents that from happening.

The Andair valve is a thing of beauty and I'll install another one on my next RV... (can you tell my wife doesn't read this forum?)
 
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