Thorp Air Command - T18.net

I used PRC Sealants. They are graded by viscosity and time to cure. You will want to use a slow cure for the first layer, then coat the seams with the brushable grade to fill the pinholes. Messy, stinky and NOT fun!

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Bob Highley
N711SH
SN 835
KLAL

Does anyone have a creative way of installing the float switch in the main tank without removing the main/header tank? We just pressure tested the tank and have it re-installed. If you can only install the main tank float switch with the tank out, where did you install it? I wonder if I could modify the current float sending unit and have the float switch installed there, but that may not be possible?

Brent Schultz
N6CM

The float switch can be installed with out removing the tank, but you will have to remove the panel. The key here would be to put the hole for the switch as high as practical on the rear vertical surface of the tank. this would allow for the most fuel to transfer into the tank. That all said, you must be very careful not get junk into the tank from the hole cutting operation. It would also be best to weld the bung hole to the tank in the case of an aluminum tank. My tank is fiber glass so it was much easier. If your floor is not removable, you may want to take this opportunity to convert it.

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Bob Highley
N711SH
SN 835
KLAL

I bought a normally closed alarm switch from Radio Shack. Mounted it on the fuel sending unit support bracket and used heat shrink tubing to attach the magnet to the float swing arm. As Bob pointed out you need to figure out the fuel levels for it to cycle properly. My fuel pumps come on/off at about 7/8 full.

Brent: It sounds like you have the tank installed and you want to replace the sending unit ? I assume you have no cover over the sending unit ? I think I did a measurement (before the windshield was in) from the edge of the top of the dash to the approx. middle of my sending unit . To verify the location I drilled a #52 hole over the location to veryify . Best 1 hour I ever spent putting in that access cover for the fuel sending unit ! >:D I have the solid state fuel probe and so far it has worked as advertised .

RB

Hello Rich! Tank is installed and aircraft has access to sending unit. I also have wing tanks in our new bird, but was trying to dream up a fuel transfer system like Bob Highley. We have tank installed, plumbed, but was looking at how we could dream up a simple fuel transfer from the wings to the main tank. I guess we will just time it and turn on the facet pumps for each tank on trips.

Brent

Sorry Dude...I thought you were talking about the main tank ? You must have a Muey Large Bladder for wing tanks ! If I had to do it over I would just put in the larger main tank . No fuel transfer problems, no additional pumps, no additional valves. Bada Bing, Bada Boom !

RB

I have some more knowledge for the Thorp data bank. On the way out of Chicago, I found that my left Aux tank was leaking into the cockpit when I went to transfer fuel into the main. A small leak, but, none-the-less, disconcerting. As I really didn't have much fuel in there, I shut it off and continued to my fuel stop with the main and what was in the right aux tank. I needed 15 additional gals. to make it home non-stop from the fuel stop, so I topped the right wing tank and got set for the takeoff. I rolled in a bunch of left aileron trim, partial flaps and set the lift off bug (mental) At 85 mph. Takeoff roll was normal heavy weight and I held left aileron as for a x-wind takeoff. Lift off was a non-event except for having to hold left aileron for the climb out. As the speed built, the aileron trim became more effective and the pressure lessened. About 15 minutes into the flight, having turned on the transfer right after takeoff, the autopilot was able to hold wings level and the trim was fully effective after about five gallons were gone.

I offer this not as a standard procedure, but to answer the questions some have had about controllability with trapped fuel in a wing fuel equipped airplane. We had tried this during our test period, but not at the gross weight and density altitude I experienced today. We knew the ailerons could handle the asymmetric load. The airplane could have been landed easily in this configuration.

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Bob Highley
N711SH
SN 835
KLAL

Hey Brent, I too have wing aux tanks. I really like having them. I have tested my aux fuel pump (both wing tanks are pumped through one pump up to the main tank) many times and it pumps 0.5gph. So, I just have to use the clock and a pencil to keep up with it. I use my fuel gauge (in flight) to verify fuel has been added, although the gauge isn't very accurate. I have a red cube fuel flow sensor that is extremely accurate.

If you come up with a better way to verify fuel transfer, let us know. I would be very interested.

I have a float switch in the main tank near the top. It cuts power to the pump relay when the tank nears full and won't let the fuel transfer to a full main.

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Bob Highley
N711SH
SN 835
KLAL

that would be the solution! great idea Bob.

I realize there are those who are convinced that the wing fuel must be pumped into the main. The simplest route however is to install a 3-way selector at the main tank and pull from either the wings or the main. This still retains the original gravity feed (as doe the other method) but eliminates the necessity to remove the fuel tank, install the plumbing required to fill it, float switches etc, individual boost pumps etc. I realize this is a matter of opinion but I dont see the logic in transferring fuel from one tank to another in a small plane like ours, a student/private pilot flying a Cherokee (or RV) can handle switching fuel tanks surely we can as well.

It's dirt simple and it works - sketch attached.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

I needed to have my system fighter pilot simple to operate. Running a tank empty while on the wing and in the weather is one of the situations I wanted to avoid. What ever you do, do NOT have a "both" position. This can un-port the feed when a tank runs dry and you will flame out with trapped fuel in the other tank.

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Bob Highley
N711SH
SN 835
KLAL

I welded an extra bung in my tank at about the half way mark so I could plumb in a line to pump fuel into the tank from an auxiliary source, I have it corked now but would not have to remove the tank to plumb in some aux fuel. My bladder hasn't grown any so I'm still figuring 2.5 hr legs, that seems to be a comfortable amount of Time in the cockpit for me so The main tank does fine at least for now. Dan

Bob or Bill, how much usable fuel is in each wing tank?

I am really torn as to what to do. In perfect world, I would want 4 hours plus 45min IFR reserves. Which would mean a total of about 48 gallons.

However on my recent driving trip from WI to FL and Kentucky Dam, and back to WI, I found that my bladder is only good for about 2 to 2.5 hours.

Dave Read sent me a template for his enlarged main tank, and it is about 40 gallons. Which will still get me over 3 hours with reserves which exceeds my bladder endurance and eliminates the time to construct and cost and complexity of wing tanks and plumbing Etc.

On the other hand, I will be there building the wings up and have perfect opportunity to build the wet wings.

Can pro seal or whatever sealant be left dry for extended periods without drying out and causing leaks? If so then the one time effort to set the wings may be worth it even if only occasionally used. I foresee that most routine daily sort of flights would not need aux fuel. So the wing tanks may realistically only see fuel in them a couple times a year if that. So again it goes back to the question of is the extra work and cost worth it for a couple times a year?

So I really think I'm down to standard tank and wet wings, or the single larger main tank. I just don't know which is the best long term decision.