Wing tank in C/L

[Fred Shattuck]

I have mounted the fuel tank in the wing of my modified Chipmunk, and with any luck will fly it for the first time this weekend. It is mounted behind the spar on the outside wing in the first bay and is about an inch lower than the  carb with an upright engine.  Does anybody have any experience with anything similar? I am worried the fuel lines will be too long. It is pressurized via the muffler from a Super Tigre  61.  The tank is a 6oz clunk with two lines.          Thanks for any input.   Fred

[Terry Bolin]

Fred, I've never done the wing install but I am concerned that you wont get a good run with the tank being that much lower than the venturi. I would use "Large" fuel line going to the carb though....let us know how it works out for you! Post a picture of the plane.
Terry

[Wynn Robins]

more than likely you will have problems - the length of the fuel lines will be an issue - unless you have a pump somewhere in the system - muffler pressure wont aide it that much.  Secondly, with the tank so low, you will have huge issues trying to get consistant runs upright and inverted.

[minnesotamodeler]

What will 6 oz. of fuel located behind the wing spar do to the CG?

[Ray]

It's the vertical orientation of the wing tank that will be the problem for any fuel system that isn't under a HIGH PRESSURE setup.  It may be possible to use a twinned tank arrangement, with a small stunt tank in the normal tank compartment, filled from the wing tank by a pressure line to an RC (Perry) onboard fuel pump, making the location of the main tank irrelevant. 

[Randy Powell]

Paul Walker used a tank mounted in the center of the airplane on his B-17 stunter. 4 engines. But the tank was a bladder under pretty high pressure and each engine had a pressure regulator. Only way to pump fuel from the central tank the engines.

[Ray]

I have mounted the fuel tank in the wing of my modified Chipmunk, and with any luck will fly it for the first time this weekend. It is mounted behind the spar on the outside wing in the first bay and is about an inch lower than the  carb with an upright engine.  Does anybody have any experience with anything similar? I am worried the fuel lines will be too long. It is pressurized via the muffler from a Super Tigre  61.  The tank is a 6oz clunk with two lines.     

Where in Texas are you located, Fred?  There are a lot of experienced model fliers all around the state, due to the (mostly) cooperative weather for flying, I suppose.  You should be taking advantage of that resource to avoid having made what looks to be a series of major mistakes, unless you posted in the wrong forum, and should have been using the "Scale" forum.  But even for that event, a PUMP or crankcase pressure will be needed because of the excessive distance from the needle to the fuel pickup. 

The SIG Chipmunk kit is a medium size model that has a "relatively" thick airfoil, and can use the power of a 46, but your choice of an ST 61 is also not good for aerobatics, although I suppose an ST V60 wouldn't be overdoing it excessively.  The inverted engine arrangement is a well proven setup that places the wing, thrust line, gear drag, vertical CG, and stab location in a most complimentary arrangement that really works.  Changing to an upright engine throws the vertical CG way off if the thrust line is left alone, or throws the relationship of factors (including LG length) out of tune if the thrust line is dropped to keep the vertical CG in a better location. 

[Fred Shattuck]

Ok y'all. First off thanks for the intelligent and enthusiastic help. I had put a heavy tail wheel set up on my chipmunk for better balance and did not consider the weight of the fuel.  The line is brass run diagonally through the fusalage to shorten it.  The mods are very radical. No flaps. The trailing edge is now further back at an angle greater that the angle of the leading edge. The elevator is now full with the vert. stabilizer moved forward and the rudder enlarged slightly, all set up sorta like my big Ringmaster. The fuselage was reconstructed to allow for the wider heavier engine and to eliminate the torsional twist I first experienced. The wing now spans 69 inches, built with top and bottom hardwood spars  and the entire bellcrank area beefed up. I opted for the upright engine simply because I did not like my brother having to use our plug lighter on the bottom. I made an artist's version of the cowling from wood. The front is much shorter now. Hopefully I have the balance close enough that I don't turn it into a red white and blue plow.  What may seem like mistakes to others is simply experimenting to us.  The super mods to my Ringmaster were scoffed by all, but it is the best plane I have seen fly. Full patterns would be hard because of speed, but my lines rarely are slack. If the Chipmunk does it that good, it will be success in my eyes.           My brother flies the begeebers out of his equally rad twister with a 91 KB. You have to see it to believe.   Thanks again.... I love and miss TEXAS, but I love it here in Chapel Hill Tn           FRED

[Paul Taylor]

Fred,
Looks like you are close to Gary Weaver. He too thinks outside the box. Keep on keeping on.

My son Ryan will be at MTSU this time next year and I will be in the poor house.

Paul 

[Just One-eye]

I built my first flying wing combat plane in 1953, and used my K&B 29 on it.  That tank sat in the open atop the motor bearers behind the engine.  A couple of years later, I put a toilet tissue roll inside the wing of a modified Nobody, and used a pen bladder as my tank.  By then, I had two K&B 35s for combat.  The vertical location of that tank would've made no difference, but the engine sat right there against the LE, so there was hardly any "nose" anyway. 

I had gotten tired of digging mud out of the engine's cooling fins from inverted flight too close to the ground, and mounted my Torps sideways.  I was still only about 15 or 16 then, and loved flying very fast with a very highly maneuverable model.  However, when I was a HS sophomore, I acquired a Bill Elliott P40 Black Tiger stunter with a Fox 29 on it and spent the summer of 1956 learning the last AMA pattern before the current one.  I learned to love the sound of a Fox in it 4-2-4 song, and although I still flew faster than modern stunt pilots do now, that was just the way that Don Still was flying, and I saw him doing patterns before I saw George A. 

I tried to fly the same way Don did.  But for pure adrenaline, I stuck to combat planes.  I built a couple of Half- Fasts, then some Quickers.  I bought a Johnson because that was what Riley used on his, and I modified one of my hard tanks into a pressure tank, because that was what Riley suggested.  It was in the wing, and the starting procedure was a lot more difficult than a bladder tank (I was happy when pacifiers became popular later). 

These days, I use the OS 25 FX engines as the closest thing to the Fox 36X BBs and early ST G21-35s, in Arrowplanes somewhat larger than Quickers, but just as fast, and still like flying them, but I use a G21-46 in my Chipmunk.  I have a 4 1/2 Oz tank in it, that I wish held 5 Ounces.  I still have an unbuilt Magnum, for which I've like to have one of ST's V60 engines . .

Good Luck, you'll need it.  Ray is quite correct to predict a poor result from what you've described, however.