RV-4 Fuel Selector Questions

[Thunda Down Under]

Thanks again Slice, l think I'll try this in the circuit area of my strip and see how it goes.

I had thought of fitting an electric fuel pump on the axillary tank (with in line valve) and just keep topping up the main tank in use.

This would allow the axillary tank to be drained then operate as normal.

I use the extra range to get to (and out) remote areas in central Australia to prospect for gold, so the RV 4 with its low stall and no wheel pants has got all the room for my gear for a few days in the field.
I wonder if anyone over there is doing anything like this, would be good to hear from them.
Thanks again Slice.

[Slice]

Originally Posted by Thunda Down Under

I had thought of fitting an electric fuel pump on the axillary tank (with in line valve) and just keep topping up the main tank in use.

This would allow the axillary tank to be drained then operate as normal.

It is an option. Van's makes a 4 position fuel selector so I opted to feed direct to the engine thus eliminating the need for an additional pump. It also allows me to start feeding from the aux not long after takeoff and being to shift the CG forward again.

Definitely several ways to go about it. Good luck!

[gmcjetpilot]

Originally Posted by riobison

Why not just function the selector, turn it to the fullest tank and leave it there until safely in the air at altitude and then start changing tanks as needed? Thanks Tim

Tim you are thinking correctly. The one basic rule of thumb is have boost pump on and selector to tank with fuel. Period. Switch as you like otherwise. I am NOT a fan of switching tank back and forth right before take-off. I switch to keep tanks fairly balanced on ground or air... and select the proper tank. As long as there is no big difference in fuel level or imbalance either tank, either tank is proper. I don't adhere to absolute fullest tank.

One way to minimize switching:
1) Select "proper tank", typically fullest.
2) start, taxi and run up, do not switch tank
3) boost pump on, take off
4) Airborne (with sufficient altitude) turn boost pump off.
5) As required or desired to keep balance turn boost on and select opposite tank, boost pump off.

I searched the internet for Piper checklist. Piper being low wing is closest thing to the RV. I saw a wide variation.
One says start on fullest. Then before takeoff "select proper tank". I saw "PROPER tank" not fullest several times.
What does that mean? If the tank difference is small use either tank. This is my technique.

Example L tank 65% and R tank 55% entering pattern on R tank. Switching from R tank you were are on last 30 minutes to L tank make sense for 10%?
Now if you screwed up en-route, R tank was 10% and L tank 50% by all means switch to L tank. I would do that on initial descent not pattern.

Unrelated but the Ted Smith Aerostar (Later Piper Aerostar twin engine, mid wing) I flew had wing and aux tanks. It was complicated. Fuel balance and not running the Aux tank dry before wing tanks was critical. The wings were skinny and you could un-port fuel pickup if too low in double cross feed (bypass Aux tank). If you ran the Aux dry before the wing tank you could also starve the engine. There were a few accidents due to fuel mismanagement. RV' have one engine, one selector, one pump and two tanks. Not that hard.

[Yen]

One advantage of having two separate tanks is when you need to sideslip to lose height.
If you are feeding from both tanks you may have no problem, but if your high wing tank is low on fuel you could have starvation.
Even worse is if you have the two separate tanks and run on the low wing tank. I think that put a Bonanza down a couple of weeks ago. He was too high, slipped to get on the glide slope and the engine failed, causing him to undershoot.
I start after I have observed fuel pressure from the pump on one tank, then turn over to the other tank, taxi and do engine run up with pump off, turn pump on and take off. that proves mechanical and auxiliary pump are working on my carbed engine.

[gmcjetpilot]

Originally Posted by Yen

One advantage of having two separate tanks is when you need to sideslip to lose height.

If you are feeding from both tanks you may have no problem, but if your high wing tank is low on fuel you could have starvation.
Even worse is if you have the two separate tanks and run on the low wing tank. I think that put a Bonanza down a couple of weeks ago. He was too high, slipped to get on the glide slope and the engine failed, causing him to undershoot.

I start after I have observed fuel pressure from the pump on one tank, then turn over to the other tank, taxi and do engine run up with pump off, turn pump on and take off. that proves mechanical and auxiliary pump are working on my carbed engine.

Good point. I wounder what level of fuel (emptiness) and slip would un-port the pickup in an RV. Does anyone one to flight test that?

[gjslutz]

On my -4 I have the Johanson tip tanks, they are controlled by an Andair 5 port valve each with it's own line to the valve. I start off on an either main wing tank for T.O. & climb. I then switch to the other wing tank for about 5 min. to make sure it feeds properly. I like to taxi & TO on the climb tank. I will not switch prior to T.O.
Then I go to an tip tank and drain 50% from it then go to the other tip and run it till empty. Then I go back to the first tip and empty it. then I go back to the takeoff & climb tank and empty it.

With 4 tanks on an long trip, I want to know where all my fuel is. I don't need to be guessing where it is. I then run the last tank to my destination and reserve time. a few gallons left in each of the other 3 tanks on an long trip will not work for me.

I have done this with every A/C i have owned. In my -4 It will hold 50 gallons when topped off. With the O-360 with TBI and good altitude @ LOP it has good range. 95% of my flying is with the tips empty for short flights. With my Dynon EMIS I know what I have at all times. when the engine quits, I switch tanks, boost pump on, and keep on going. If I have an PAX, I advise them what is abut to happen. all of my A/C have had fuel totalizers.

Once I empty an tank in flight, the next time I do about 3 or 4 times of running the engine on about 3 seconds each time to purge the air from each tank I ran to empty. I also next flight T.O. on the tank I landed on as there is no air in the lines. The TBI unlike the carb. has no fuel float bowl. I'm the only person to fly my A.C.

[N999BT]

I just upgraded my EFIS, and along with that my checklists. (With my new configuration some stuff just doesn't apply anymore.) I spent a lot of time thinking about fuel and what to do on engine start, taxi, run up, and take off. I have a carburated O-360. I came to the conclusion that the ONLY reason to switch tanks would be if the tank I landed on was less than 1/4 tank, and I would probably get gas if that was the case. If the engine was running fine when I landed, why would I want to change anything? So... I leave the tank selector alone until reaching altitude, then switch tanks every 30 minutes to keep them relatively balanced.

[GHARBEN]

When the electric pump is running, is the carburetor float and needle valve the only control over the fuel? When I bought N12HR the electric pump appeared to flood the carburetor. For that reason I take off without the electric boost pump running. N12HR has a fuel pressure gauge and I can monitor the pressure. I plan to work with the fuel system more since I have a great deal of trouble starting the engine even using the primer.

[FitzRX7]

Originally Posted by GHARBEN

When the electric pump is running, is the carburetor float and needle valve the only control over the fuel? When I bought N12HR the electric pump appeared to flood the carburetor. For that reason I take off without the electric boost pump running. N12HR has a fuel pressure gauge and I can monitor the pressure. I plan to work with the fuel system more since I have a great deal of trouble starting the engine even using the primer.

Not to get entirely off subject, but this sounds what I went through over the last 5 years. If the carb is flooding, do not pass go, do not collect $200, go straight to carb replacement with a factory Marvel carb. I'd have saved so many headaches and close calls. YMMV, but the factory reman carb has been great for me

[Pete O Static]

I'm a big fan of the KISS philosophy. FWIW, I ALWAYS sump and remain on the same tank for start, taxi and takeoff. As soon as I have reached a safe altitude, prior to turning off the fuel pump, I switch tanks. This confirms that the fuel in the newly selected tank is either useable or not before I am well into a X-Country where diversion options may be limited and while I am still within close proximity of the airport. If the fuel in the newly selected tank is not useable for whatever reason I know two things. 1) The tank I just selected from was working and I have enough in it to get back. From then on, I switch back and forth on a 30 minute interval timer. Keeps things in balance and I know that for every tank switch, I have burned about 3.75 gals from the respective tank.