Switching Tanks Technique. How do you do it?

[RV7A Flyer]

Originally Posted by jay bell

As part of testing, I purposely ran each tank dry while 5000' over the airport (separate flights) to check fuel gauge calibration and re-start performance. In level flight, my plane takes about 8 long seconds to recover from fuel starvation without using the auxillery pump, and about 3 seconds to recover with the pump.

Not to necessarily disagree with anything you said, but what part of this portion of your testing required you to do it in flight? Couldn't you have determined the same thing on the ground?

[newt]

I start and taxi on one tank, then change tanks and do run ups and takeoff on the other. I stay on that second tank for 30 mins and switch, then I switch every 60 mins after that.

I have an EI fuel flow meter which flashes a blinking light at me as a reminder every half hour. If I've missed a change and actually need the reminder, I either have a good reason (e.g., unlandable terrain -- do it later) or I chide myself for my lack of discipline.

The actual change: Boost pump on, wait for pressure to increase, switch, count to ten, boost pump off, observe pressure reduce and stabilise. if anything bad happens, I'll switch back and full rich. Hasn't yet.

Andair valve.

I'm intimately aware of how long an aircraft can run on the fuel in the lines and carb bowl. Many years ago, I was in a Glasflugel Libelle, taking the first glider launch after the tow plane had refueled. The tow pilot's routine was to switch the fuel off during shutdown; for some reason he didn't turn it on again for start up.

He had enough fuel in the system to start, taxi from the fuel bunker to my glider, idle while I was being hooked on, and then run at takeoff power for JUST long enough for the glider to become "light" on its wheel... then the engine stopped, and the tug behaved roughly the way a car behaves when the driver jams on the handbrake, while I was 50 metres behind at 30knots with insufficient weight on the wheel for the brake to work.

Somehow I reacted quickly enough to hit full forward stick, full right rudder, and full right aileron while I was pulling the release handle, and initiated a ground loop to avoid ramming the back of the Pawnee. Skidded to a stop sideways about fifty feet starboard of the tow plane, in line with its cockpit.

I think the tow plane ran for over three minutes with the fuel off. Pretty sure I'd have broken both of my legs if my reactions had been just a split second slower.

- mark

[Bugsy]

During phase 1 I flew one tank empty and the other near full with no problem It was a limited maneuvering flight but flew straight with enough trim. Not recommending it, but know that vans design is strong.

[airguy]

Originally Posted by RV7A Flyer

Not to necessarily disagree with anything you said, but what part of this portion of your testing required you to do it in flight? Couldn't you have determined the same thing on the ground?

In-flight restart is going to be completely different from an on-ground restart, this was a valid test point, at least in my opinion.

[Feetwet]

I fly an RV4, generally agree with most comments but have a couple other considerations that I did not see mentioned.

First the aerobatic flop tube. Have one in the left tank, not in the right. Noticed a report of the flop tube hanging up on one individual who ran out of gas with some 3 gallons left in the flop tube tank. Consequently, whenever I'm pushing the fuel on a cross country I run the flop tube tank dry and continue with the right tank. (where I could dump it in somewhere) Even if the flop tube doesn't hang up, it might crack with age and be a problem.

Secondly, I use a 30 minute interval on the switch over. I don't have aileron trim, and the 30 minute interval is enough to let the wing with more fuel in it get heavy enough for me to notice.

Bye the Bye, I have changed out the Van's fuel valve once already - after awhile, when I'd wiggle the old fuel lever a few drops of fuel would appear around the top. Could probably have replaced the packing but easier to just replace.

[Toobuilder]

Originally Posted by Feetwet

I fly an RV4, generally agree with most comments but have a couple other considerations that I did not see mentioned.

First the aerobatic flop tube. Have one in the left tank, not in the right. Noticed a report of the flop tube hanging up on one individual who ran out of gas with some 3 gallons left in the flop tube tank. Consequently, whenever I'm pushing the fuel on a cross country I run the flop tube tank dry and continue with the right tank. (where I could dump it in somewhere) Even if the flop tube doesn't hang up, it might crack with age and be a problem...

Fuel level/flop tube uncertainty was the primary reason that I would run the aerobatic tank dry first on cross country flights with the Hiperbipe. Despite the highly reliable sight tube fuel level indicators, one could never really tell how much time I could get out of that tank. OTOH, the main tank was a hopper style with a bottom feed and would use every drop.