Thorp Air Command - T18.net

O.K. here is what maybe a silly question. Do we need a STC to run auto fuel in the T-18? I'm running a Lyc. O-320-B2B. Header tank gravity feed fuel system. Everything I read talks about certified aircraft & the required STC's. I Don't find anything about Exp. A/C.

Hey Tim - you do not need an STC on an experimental aircraft - run what you wish. Having said that, a couple of things to consider as this is a (pardon the pun) volatile topic amongst us air-nuts.

Make sure your autogas is clean - would recommend filtering before filling the tank.
Ground the container to the plane like you would if you were filling up at the fuel farm.
If your airplane needs liability insurance, they won't pay the claim if they catch you using auto fuel.

Some folks think it's crazy to use auto fuel - I used it on an o-360 with low comp pistons - no trouble - kept the plugs clean. I currently have an O-320 with 8.5-1 pistons (I think) - I run 100LL - I put REM37BY plugs in it - they don't seem to foul near as bad as the 38s or 40s running 100LL.

Personally, I know some local guys who have been running mid grade (87 octane up here in Salt Lake) auto gas with a pinch of MMO in 160 HP O-320s and 180 HP O-360s for many years with no trouble and will never run 100LL if they can help it. I don't quite subscribe to that mentality, but if I had to throw some 91 octane in the tank in a pinch, I wouldn't wring my hands over it either.

Whatever you do, run "clean" gas.

Thanks Fraser. It will be nice not to have to spend that extra $15.00/hour.

I have ran auto gas for a couple years, does keep the plugs clean..........Dan

FWIW...if you have an Air BP gas card you get 5% off per gallon when you you the card at an Air BP pump. On the West Coast I got 100LL for $4.75 gal. I just paid $4.50 gal for 87 unleaded for my Ford. Not worth the 25 cents a gallon to pump into a container then take to my house and then dump it into the A/C. I know, I know...some of you get the unleaded for a song, but I don't pay any hanger rent and I fuel up when I trailer to the airport !

RB
NX115RX

I only run Arco cheapo 87 octane in 7077J with a 0320 a2d (low compression) Plane runs hotter and like crap with 100LL. Try to never run it unless I have to. 160 no problem hours with it. I pump it into my Van and have a lead off of the fuel injector rail that I can open the spigot turn the electric pump on and pump straight into the plane. Easy peasy!

I would like to add a data point;
I recently bought Ed Ulrich's T-18, N883FF.
Ed hadn't flown it in 9 years. It had about 22 gallons of Mogas in it.
The last time he flew it, he secured every switch and the fuel valve. Maybe he knew it was his last flight.
I bought the plane thru his daughter, so I didn't get to meet him, nor pick up any pointers.
I did get a good stack of binders with useful info and about 100 News Letters.
But back to the fuel: it smelled bad, but I'm cheap. So I used the boost pump to decant it into a gas can, and promptly poured it into my nearly empty 1989 Chevy 3/4t pickup truck. This is the base line V-6 model.
It ran poorly, but OK on the flat. Come a hill, it would knock pitilessly, and lost power alarmingly. That 22 gallons seemed to last forever. I didn't dare step down on the gas more that just the smallest amount or it would ping and rattle. Probably got the best gas mileage I ever got.
I worried that the engine was permanently damaged, but finally when it was gone and some average gas was put in, it ran good again.
In an Aircraft it would have been a disaster.
I had to mop the tank out from sediment, including blobs of Fuel Lube which were under the filler cap. I'm not in favor of using Fuel Lube on cap seals any more after seeing the residual blobs in the bottom of the tank. That wouldn't do at all in the tank valve, or on the screen.
So if the fuel smells bad, I wouldn't use it. Maybe 6 months, I'd be worried at a year. Nine Years is redickulous! But it makes a good story.

With that MoGas sittin in there for nine years I would be a little concerned the effect the "bad gas" has had on the hoses, o-rings and the innards of the carburetor...pump plunger etc. I am not a Petro Chemical Engineer, but I would think the stuff breaks down and leaves a "varnish." Sitting for 9 years it would at least require a hose replacement in my book. IMHO. The carb I would be very cautious with and would at least split the bowl and have a look inside.

RB

I ran auto fuel in my 0-290 for 20 years and never had a problem. Engine ran hotter when I put 100LL in it. PA. now has ethanol in all auto fuel so I quit using it.

Jim Hockenbrock
N22JH

I know folks have used auto gas for many years. I just question the fact it has been sitting in the system for 9 years.

RB

Well, not really sitting.
The fuel valve was closed, and the strainer is the kind with a cable operated drain.
So the fuel sytem was drained, or evaporated out.
I rebuilt the fuel strainer drain assy, as it worked once, then the plunger pulled out of the swollen rubber valve tip.
The fuel hoses inspected OK. The Facet fuel pump worked to defuel the tank thru the hoses to the carb fitting.
The carb float valve does not leak, and the engine ground runs perfect, including 2250 RPM static run up.
I haven't flown it yet. The airframe is ready, but I'm refinishing the trailing edge of one prop blade, and I want to drain the carb bowl just to be sure.
Oh, and it's full of 100LL for now. Car gas is now $4.10+ per gallon, I bought avgas for $5.85 Saturday. I think the extra is justified during this period.

If you get an Air BP gas card you can save 5% off the pump price of BP 100LL. That works out to be about 25 cents a gallon ! I am not Scottish, but that's more fuel in the tank !

RB

Just from memory, it seems that most home built aircraft accidents are fuel related. Sometimes it's just running out of fuel, sometimes it can't be determined.
But in the middle, are all manor of problems from vapor lock to hoses failing etc. with handles slipping on selectors, bad gauges, and who knows what?