Hello 175 pilots,
I was wondering why the last 9 gallons will supposedly not flow out of the wing tanks? Have any of you ran a tank until power drop, switched tanks, then measured refill gallons? Rick

The last bit of fuel may not be available in a go around situation due to the angle. If the flight is level the fuel will flow into the inlets.
I do not know this as a personal experience but what I read somewhere.

Clay is right, the last bit of Fuel may not be available at all flight angles. This does not include straight and level or gradual/mild flight angles. I have run a tank almost dry litterally and never a sputter at normal flight attitudes. As long as you have an alternate plan in mind in case of engine failure, I would not be afraid to dip into that last 4.5 gallons. Remember to keep your FAA minimums, though. :-)

Kris

We decided to drain one of our 26 gallon wings tanks and then fill it while stabbing quantity.

To establish the actual amount of fuel that can reach the engine we disconnected the fuel line from the gascolator below the engine. Selected the right fuel tank, and started draining it. Note - we were on level ground.

After 8 or so gallons we had her empty from this point in the fuel system. (we had intentionally ran the tanks down for this test)

Based on the POH, the tanks should hold 26 gallons each side with 4.5 gallons being unuseable.

Once we had drained all the fuel from under the engine we flipped on the master switch to confirm the fuel gauge was at "E". We then stabbed the tank and it was TOTALLY empty. We opened the sample point and only a few drops were drained. All of the capacity drained down to the engine... not exactly what I had expected. I had assumed we would have had a couple of gallons left in the wing.

This phase complete, we pushed the plane to the fuel island and started refilling the tank. We added 4.5 gallons to establish our "unuseable amount" and then stabbed the tank, marked our rod, added 5 gallons, stabbed, marked, added 5 gallons etc... until we were full and had topped off the tank at exactly 26 gallons.

Our results for 7029M 1958 175 with 26 gallon tanks -

4.5 gallons added to reach "zero" amount as per POH = 1 - 1/16" depth
5 gallons above "zero" amount = 2 - 3/8" depth
10 gallons above "zero" amount = 3 - 3/8" depth
15 gallons above "zero" amount = 4 - 3/8" depth
20 gallons above "zero" amount = 5 - 11/16" depth
added last 1.5 gallons to complete top-off to 26 gallons total




Pasted from post in main forums, I agree about the useable fuel changing with flight attitude, but even in '58 the engineers were rather conservative. Maintain those FAA minimums.

Like Kevin said, keep the minimums and stay safe. The fuel pickup in the 175 tanks is towards the rear of the tank slightly forward of the sump drain, it is the only pickup in the tank unlike later models that have a forward and aft pickup in the tank. In a steep decent with low fuel there will be no fuel around the pickups.

There is a project in the works to get an STC to rework the fuel feed system to reconfigure the tanks and get the useable fuel the same as the 172XP (R172), same tanks and same TCDS.

Rick

I ran my right tank dry intentionally one time so I could recalibrate my fuel dip stick (I had two strips within glide + 15gals in the left tank).

The next day I dumped in 4.5gals and marked the dip. At the end I could only get 24.5gals into the wing. I atribute this to my 175 being a taildragger. Anyone else have any comments on fuel capacity for a 175 taildragger?