Reduced Fuel Capacity when on 29" Tires?

[IainR]

Hi Guys
I recently drained my fuel tank to calibrate a dipstick. I was quite surprised when filling her up again that I only got to 11 Gallons instead of 12. The only reason I can see for this is that I am running 29" Airstreaks which raise the nose quite a bit and possibly tilt the gas tank further back, leaving a unfillable space up front. Has anyone else had this issue?

 

[sj]

Logically, it should make a difference. It sure messes up the sight gauges in 3pt with bigger tires. My belly pod holds 31 gallons, but only when it is on amphibs - otherwise it is somewhat less!

sj

 

[cubdrvr]

I put new markings on my sight gauge with the big tires

 

[skywagon8a]

My belly pod holds 31 gallons, but only when it is on amphibs - otherwise it is somewhat less!

sj

I made some belly tanks from aluminum. They had a vent tube which ran from the tank high spot back up to the top of the filler neck tube. This allowed the air to escape during fueling, thus a full tank. You could look into adding a vent tube to increase your capacity. Or you could install a fuel quick drain valve at the high point in the tank. Leave open when fueling then close it when the fuel splashes out.

 

[Gamagoat]

My Cub has duel markings on each site gauge. Left side is 3-point and right side is level flight. Its a significant difference between the two. Currently I'm on 31's.

 

[BC12D-4-85]

Interesting topic. Anyone found this actual fuel aboard to be a concern later in flight?

Gary

 

[mvivion]

It sounds like the OP is describing a J-3 or other plane with a nose tank, and a wire "gauge". Not sure how you'd deal with that error, other than recalibrate your assumptions of how much fuel remains when the gauge gets to a certain point.

Most of our Cubs had level flight and 3 point markings on the sight gauges. I don't think they were calibrated for bigger tires, but I always assumed there was a bit of error.

A "fudge factor" on fuel remaining (one hour reserve vs 45 minutes, etc) has always been my operating practice, after a really dumb decision early in my career. Nothing bad happened, but I finished a flight with very little fuel remaining, and was really sweating the last half hour......

MTV

 

[Crash Jr.]

The J3 tank can get an air bubble trapped in front of the filler neck when you're on big tires that may sacrifice a gallon of capacity. Whenever I was real hung up on that I would fill the tank then lift the tail to "burp" that bubble and top it off. It's maybe a full gallon in total so I've just given up on it and accepted the loss. With 12 gallons in the wing and 11 in the nose you're still over 4 hours range with a fuel sipping small continental.

 

[cubdrvr]

YEllow marks are 7 & 11 gal w/ 31 tires
at 3 pt gauge shows empty w/ 4 gal

 

[stewartb]

Around here 2 gallons is $13. It sounds like those Bushwheels are saving you money with every fill-up!

 

[hotrod180]

Around here 2 gallons is $13. It sounds like those Bushwheels are saving you money with every fill-up!

 

[courierguy]

This thread made me realize I currently have NO sight gauge markings on my RANS, since I put larger wing tanks in. a while back. I guess I just eyeball it, and go by time of course, but for sure my 3 gallon header tank's sight gauge is marked. I carry so much fuel relative to my burn rate that this works for me. I seem to remember there is a requirement to have a fuel quanity indicator of some sort, my header tank markings are it. I thought of marking the wing tanks FLY, KEEP FLYING, START THINKING ABOUT LANDING, GET THIS THING ON THE GROUND!

 

[IainR]

Thanks very much for the ideas etc.