Thorp Air Command - T18.net

I think the rest of the world has been metric for over 30 years now - 29 gallons = 109.77 litres.

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Fraser MacPhee
N926WM
Serial #279-1
Angel Fire, NM (KAXX)

Willie, i thnk you just hit the nail on the head. The per plans main tank does not have a "neck". It shows a flush cap that extends about .5" below the upper surface of the tank thus preventing a full "top off" and any chance of fuel venting overboard. I suspect those who have venting issues didn't go per plans and installed a neck extending above the tank.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Lee, my tanks fuel cap is exactly as you describe, to a T, ha I kill my self. I fill my tank “past” the bottom of the cap, so in other words well with in a ½ inch of the top of the tank. I know I can get 29 in mine and I’ve had no problems, it will probably crash tomorrow now.
So if some can only get 25 in with out siphoning and some can get 29 in with out siphoning, it’s not a neck problem, it’s a vent problem. I’m guessing when some tanks got built the vent tube was shoved down inside the tank before welding???

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http://www.dixiefriedfabrication.com/

Roger that Lou, you could be on to something there. If there's a neck that allows the fuel level to go above the vent or a vent that sticks down into the tank allowing the same thing you can flood the vent and create a poor mans fuel dump.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

The S-18 has a filler neck and it is considerably higher that the vent. I welded my tank and stuck the vent tube into the tank obviously to far so you are absolutely right Lee. The neck runs up to the skin in front of the windscreen so that neck is probably about and I just guessing about 2" tall I haven't seen it for awhile. The vent being put in the neck will keep the vent always above the fuel thus stop any siphoning that May be occurring now. Dan

I have the tank from CSA that has the flush mount cap on the top skin . Not sure how far the vent tube goes into the tank , but I always try to fill about 1 inch below the top of the tank . About 28 gallons ? On occasion the tank gets "overfilled" as in fuel running out over the top skin . Stupid fuel nozzle didn't shut off in time ! DOH ! Now I test the said nozzle at the start of the fill to see how fast the fuel shuts off . Even with an overflowing tank , I have not had a problem with fuel sucking ! I do use my Facet pump for T/O and landings .

RB

Well, got the tank out, installed the new sender,neoprene gasket under the sender Flange Hi Tacked it all on and safety wired the screws. Moved the vent to the filler neck and run a new piece of vent hose,Gates hose, American Made. While the tank was out did some rudder pedal bushing maint and adjustment. Installed a new fuel hose on the tank valve and reassembled everything back into the Fusealage. At 3.5 Gal the needle on the Guage just moves and that's it, when it says empty it is empty.I will fill the tank in graduations, with the tail up if flying configuration of coarse, and see how everything shakes out on the Guage. I took the time to make a few observations, after 3 years of auto mid grade in the tank, no corrosion,no corrosion on the old sender, none anywhere, Zip. I do cycle my fuel often, I use MMO in it and it doesn't sit in the tank for long periods. In the past 5years I have never drawn any water out of the tank via the gascalator. This was a major undertaking, but I Was able to take a good look at all of it for what it's worth..............Dan

OK Mr. Dan...did you put in an access cover for the sender ? If not you will require a spanking at the next fly in event !

RB

Looks like IM in trouble..........Dan

You will regret until you put the last tank of gas in that AC you didn't put in that little access hole . >:( After all that work to take the tank out and do all the other repairs another 1-2 hours would not have made a difference . I will bring the paddle to the next fly in .

RB

My Stewart Warner fuel sender has been install for 20 years, the only time I removed it was when I added the fuel transfer prox switch, bottom line buy good quality. Remember the fuel sender it only there to tell you still have fuel sloshing in the tank, I fly on time

I flew for 5 years without a fuel level gauge. It did show "0" when the tank was empty.....Anyway, like I said, I flew for 5 years without a fuel gauge and never had issues. I used my watch to keep track of fuel remaining. But, I finally broke down and cut a hole in the top of my fuse and replaced the bad sender. I am very pleased now, but I had a lot of stress about cutting a hole in my plane. I should also say that the first sender (stewart warner) I put in did not work. So I replaced it through my newly cut access panel which made replacement a breeze. I went down to Bass Pro Shop and bought a replacement sender and it works like a charm.

Speaking of venting, ever notice how Tony Bingelis recommended that the vent outlet inside the tank should be at the front? This makes more sense to me, since the only attitude you will see with a full tank is nose up. Also, acceleration tends to move fuel to the back of the tank, causing the fuel to pile up to some degree.

Just sayin'

D

Dick,
The top of our tank is not level with the ground. It is aligned to the boot cowl. Therefore, it slopes down the farther forward you go. So, Bob is right. You need the vent aft. I intend to source a new supplier for fuel necks and move the vent to the neck.
Cubes

Hi Jim
If you're talking about level flight, I agree 100%. I'm talking about takeoff and climb. A full tank and a nose up attitude favors a vent point at the front of the tank, I think. After a few minutes of full-power you would burn enough off the top, though, so it wouldn't matter by the time you leveled off.

I mention it because the airplane that I bought had two known flame-outs on T/O roll. I think this was mostly due to the poor installation of the vent tubing path in the airframe. However, I've always wondered if the aft tank vent location may have been a contributing factor. Both times the tank was brimming full, apparently. ( Needless to say, I fixed the airframe side of the vent. )

Venting to the neck seems reasonable... as does extending the neck into the tank a little.

D