Thorp Air Command - T18.net

There is a guy on my field who built a seat out of fiberglass. It was a tank. Not sure how much it held, but the actual passenger seat was made to hold fuel inside it.
Cubes

Ya Boy ! Pretty sure the ultra light guys have seats that are also fuel tanks ? Gives new meaning to flaming Arse _ _ le !

RB

My son Peter and 2 friends have Giles G-200 acro planes (Awesome!) which have a fuel bladder in the lower fuselage between the forward seat bulkhead and the wing spar bulkhead. The wing tanks drain into it.
It's a custom made rectangular black rubberized fabric bag that was built to conform to the space. It has a special foam inside that holds the shape and prevents sloshing. It's filled by filling either of the wing tanks. There may be wing isolation valves also, so it's probably vented. It has a cover plate. It's over 20 years old and still looks new, nice & pliable.
This kind of bladder could be adapted to any plane with a space. T-18 could be under the seat, if you don't have 12Volt or high voltage strobe wires near. Under the baggage floor. The wing upper skin could be cut open and a doubler installed so the bladder could be installed, and to fit the cover plate / filler cap. Fuel bladders in Cessna 182 get stuffed in through a pretty small round hole that the filler neck is screwed into.
The leading edge of an outer wing panel has rib bays 15" wide x 15" front x 6" deep. If I don't count the airfoil shape, and consider it a triangle = 675 cubic inches = 2.92 gallons.
The main bays are 24" front to back and 2.75" tall at the rear spar, so I calculate 6.23 gallons. The inboard bay has the aileron bell-crank, so that leaves the outer 3 bays for a max 18 gallons per wing...
I know you will lose some volume to the bladder, But the skins are convex and I didn't calculate the full volume, just the triangles and rectangles.
So there is a way to add fuel quickly without disassembling a wing. Use a long drill bit to drill the inboard wing ribs for press-in bushings and push the aluminum fuel lines through.
http://www.hartwigfuelcell.com/customaircraft.php
Hartwig is an official aircraft PMA. They would understand your placement of fuel suction, vent and drain.

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE

Rich mentioned the gas tank seat:
https://www.leadingedgeairfoils.com/7-6 ... ion-1.html
That = 1 hour additional cruise per seat!
But my T-18 is pretty snug; I wonder if a pair of these would fit? Could I even close the canopy over my head?

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE

Cubes reference to Spankys in the baggage compartment tank just under the turtle deck is a area that would limit the baggage capacity only slightly, should be easy to fill and vent, plus would gravity feed (if you were not planning to feed into the main tank). The only other Thorp with the same wing I have, is said to be in Australia ( 8 Gal's in each wing fillet) you may want to make contact with them.

Phil
118BC

My aux tank is 8 gallons. It is gravity feed and good for about 45 minutes or so (O-360). Although there is a filler cap on top of the turtle deck and just behind the passenger seat, I'm not all that fired up about sticking a fuel hose inside the cockpit. The approved technique is to fill the main tank, then turn the fuel-select lever about halfway between main and aux. Gravity takes over and fuel runs from the main tank to the aux tank. The aux tank has its own vent tube. Since I normally only fly cross-country by myself, I don't have much to put in the baggage compartment, so CG is not an issue. If I'm concerned about that, I can put a small bag in the passenger seat or on the floor in front of the passenger seat. The tank can only be seen by looking up underneath the turtle deck. Baggage volume isn't an issue.

Spanky

We have a Thorpie near Ft. Worth who has an O-320 driving a standard fuselage with Sunderland wings. Has a ten gallons tank in baggage compartment and doesn't like it because it limits the amount of baggage he can carry. He has asked me to build him a couple of drop tanks and we're looking at options.

My Thorp, a wide body, Sunderland wings holds 16 1/2 gallons a side for a total of 62 gallons. I use the wings when traveling and what's good about them is that making a pit stop after 3 1/2 or four hours, I can refuel for the next leg. What's even better is that I have made some pit stops and the airport was either out of fuel or bad pump, making the remaining 34 or so gallons remaining good for a leg to another airport. I once topped off in Perry Foley in Florida and made it all the way home to Ft. Worth because airport near New Orleans didn't have pump in their tank. I landed at home with 15 gallons in the main.

In my opinion, the wet wings, which I've done three airplanes, are the best solution for long range, regardless of standard or Sunderland wings; however, if your airplane is a standard wing type, I would recommend changing the wing joint fittings to the main beam from aluminum, to 4130 type for added strength due to added weight on the outer section. Course, you could wet the center wing section. Either one would hold about 13 gallons each.

_________________
In CowTown USA,
Don D-Day
NX18DD

My 2 cents:
I put 9 gallons of fuel behind my shoulders in the upper part of the baggage compartment. Gravity fed straight into fuel selector, no extra pumps. I have taken my T-18 on two week trips with full camping gear for two and have not had issues with lack of baggage capacity. I pack like a backpacker, light-weight everything, so that helps. And of course, I empty the Aux as soon as I get to cruise altitude. My wife and I easily made it from So Cal to Denver (700+ miles) with fuel to spare (O-320, 180hp, Ellison TBI EFS-4, ElectroAir Electronic Ignition System).

Here are some pics of my 9 gal aux tank, a donated larger upper-baggage aux tank, and a set of 9 gal Outboard Wing tanks for when I build another set of outboard wings. (After previewing -- Pics are reverse order, last loaded show up first.)

-- Tony

Thanks for all the pictures Tony, that's a big help in looking at options/ideas.

I just measured the space under the passenger seat on my T-18. It's 17" x 17" (probably closer to 18x18, but what the heck, we are trying to fit something in there!
Its about 6" deep, if the seat pan does not extend down into the space.
Unfortunately, there are two seat support brackets, a bunch of wires, the transponder antenna and the strobe light power supply taking up the free space.
If I needed the range and was flying solo, I would remove the passenger seat, and install my plywood board I use when working under the panel, then I would seat-belt down a race car fuel cell. I would change the fuel valve under the main tank to a two port valve, and plumb/hose the tank to it.
My plane has electric + mechanical fuel pumps, so no problem pulling the fuel up from the tank. The vent...for temporary, I guess a small hose run aft out the canopy at the back and tape it down.
https://www.summitracing.com/parts/sum-290107/overview/
Link is to a 12 gallon tank that is 16"x17.5" x10" tall, and would fit, but the co-pilot control stick would hit, so would be removed.
I ordered the molded polypropylene 7.6 gallon seat tank, it's supposed to arrive today. Unfortunately, the cockpit frames intrude so the seat probably won't fit. I'll trial fit it next week.

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE

Here are the pictures of a wing tip tanks not completed. You can see the long drill to drill thru the wing ribs for the fuel line . The guy who ordered the set has gone south

Interesting idea James. How much do they hold?
Cubes

The Wing tip tank holds 4,5 US gallon each/ That's 9 gallon the 2 .. The speed has increased due that no trimming needed to fly straight. The modified
wing tips like John Evens build would hold more fuel. For the pick up tube Vans selling it cheap. Its gravity feed to the fuel valve,

Thanks for the pictures James, that looks like a great option to add an extra hours fuel. I'll have to have a chat with a couple of people and see if it's viable from a cost point of view. The hardest part is finding a LAME in Australia who even knows what a Thorp is to get an intellectual conversation out of them.

Thanks everyone for all the ideas/tips etc

Tip tanks appears to be a great retrofit option. And may be simpler to build up front than even wetting the wing (although a lot less capacity than a full wet wing)

One thing that crossed my mind was the addition of at least 30lbs or more weight placed at the extreme end of the spar. What does that additional weight, maybe more importantly, the additional moment may due to the fatigue and/or G loading of the wing? Maybe it is of no concern, but the original design by an aerodynamic and structural enginner John Thorp or Lu Suderland I do not believe included that weight and moment acting through the spar and the connection.

On the other hand, wet wings were not contemplated either and yet that is accepted. I do not know what engineering calcs if any were done for wet wings. However the weight of rhe fuel is distrubuted over the entire D-section, rather than concentrated at the tip.

I am not saying that tip tanks are not viable or safe. I just simply don't know. I hope others who are experienced and knowledgeable here can clear up any concern. If there even is a concern