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Unusable fuel

mizer2167

Member
Reading the RV-12 POH, it specifies up to 4 gallons of unusable fuel depending on aircraft orientations like level flight or climb, etc.

Given this, what fuel minimum is everyone using to comply with the VFR reserve?

I've been looking at flying in a -12, but given passenger and baggage weights would be limited to about 15 gallons to not exceed the 1320 lb. GW, so the unusable fuel would make for short durations at ~5 GPH for flight planning, if accurate.
 
The limitation is no take-off with less than 4 gallons. Not no flight with less than 4 gallons.
The reason is that an extended duration steep climb could un-port the fuel outlet of the tank.
If normal flight stays within the pitch attitudes that would be typical, the unusable fuel within the tank is approx zero.
 
The limitation is no take-off with less than 4 gallons. Not no flight with less than 4 gallons.
The reason is that an extended duration steep climb could un-port the fuel outlet of the tank.
If normal flight stays within the pitch attitudes that would be typical, the unusable fuel within the tank is approx zero.

I did read that yes, and apologies if I didn't explain my question fully.

Would this not be a risk in the event of a go-around, thereby needing to limit the fuel to something >4 gallons to meet the minimum and ensure continued engine operation?
 
I target to get gas by 4 to allow for reserve and go around. After 2.5-3 hours I'm ready for a landing break anyway. With reduced speed and fuel capability on long cross countries the 12 requires an extra stop than the other RVs.

Of note too is planning at 4 gallons allows for inaccuracies in fuel usage. My computer and fuel gauge only match on cross countries at cruise power (by design). Normally the computer shows greater fuel usage so it may show less than 4. On the other RVs you have dual tanks so I flew by time 1/2 hour left, hour right, hour left, hour right. That way I knew I had at least a 1/2 hour of fuel left.
 
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I did read that yes, and apologies if I didn't explain my question fully.

Would this not be a risk in the event of a go-around, thereby needing to limit the fuel to something >4 gallons to meet the minimum and ensure continued engine operation?

Most go around's don't require that you climb at Vx (best angle) or even Vy and if it does, not usually for a long duration. If a destination airport would be one of the few exceptions to that, then it would probably prudent to plan for a bit more fuel reserve.

A climb with a pitch attitude of about 8 deg. or less would never un-port the fuel outlet.
 
My personal limit is 5 gallons, but I flew it to 4 before annual to simplify draining the tank for removal at annual. The nice thing is that my fuel level sensor is extremely accurate at low levels.
 
Anyone willing to land with <4gal? Ever?

Yes, I've done it several times with 2 gal showing on D-180 cross checked in flight with Moeller float gage in top of tank. I also have sight gage on side of tank and calibrated stick to dip the tank. Dynon is extremely accurate as all four measures agree especially at the low tank level.

The fuel tank has a baffle around the fuel port which keeps fuel "pooled" and prevents un-porting as Scott mentions in above post. Fuel in tank is 100% usable in level and nose-down flight.
 
baggage floor seems to be about 8 deg. slope up to rear. might be interesting and enlightening to fly the plane with some means of measuring when the nose is up 8 deg. from level.
 
My D180 equipped RV-12 has been displaying inaccurate fuel level for the past several weeks. The Dynon D180 Installation Manual mentions backing up data in case the settings take a vacation. So I decided to do the Fuel Level Calibration again necessitating draining the fuel tank.

I planned a one-hour flight with the 6 gallons visible through sight gage on the side of the tank. I also measured reaming fuel with a calibrated dipstick and confirmed 6 gallons remaining. The flight was timed with the GTX 327 Transponder up-timer and I frequently viewed over my shoulder at the Moeller gage on the top of tank. Upon landing, I drained the remaining fuel (1-3/4 gallon) by powering the Facet electric fuel pump and holding the gascolator drain open. Pouring 2-gallon increments of fuel into the tank and following the Fuel Level Calibration procedure did the trick. Fuel gage once again is extremely accurate.
 
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