Fuel Tank Sizing

Am about to embark on building the fuselage for a JamisonSP and I have two candidate motors in Boxes - A DS.40 and a Fox.40. Can anyone tell me what size fueltanks would be appropriate for either of these two motors?

>Am about to embark on building
>the fuselage for a JamisonSP
>and I have two candidate
>motors in Boxes - A
>DS.40 and a Fox.40. Can
>anyone tell me what size
>fueltanks would be appropriate for
>either of these two motors?

I would guess that they will take around 4-4.5 oz. But just to check, you aren't going to build the tank into the fuse permanently, are you?

I found 3 oz to be adequate for a K&B 40 to make it through the OTS pattern. Second the motion on a removable tank. Consider also, you can always put less fuel in a too-large tank, but you cannot put more fuel in a too-small tank.

RULE of thumb Fox .35 takes 4oz for the PA pattern. Fox .40 should be close to the same. The OTS pattern takes about 4.5 mins to finish. If the plane was one that I was building I would put a 4oz all foward plumbing uniflow tank.

Brooks,

I second both the post by Brett and Scott. Here's what I do now. Make every tank removeable and uniflow plumbed. I put the largest tank in that I can. For example in my All American Sr. I have a 1.75" wide 3.5 ounce tank - the largest that would go into the space in front of the wing and behind the firewall. Normally an OS FP .35 would not make it through the modern pattern on this amount of fuel, but I added one head gasket .005 or .007 and now the engine makes it through both patterns. I have flown the plane in both OTS and Classic. If you want a dual use airplane? Then by all means put the largest tank in that you know will allow a full 5 & 3/4 to 6 & 1/2 minutes of run time. If you use an engine with enough power like a Silver Fox .40, then if the tank is slightly too small, you can detun the engine to extend the run time.

I used a 3 oz tank in the Humongous because that was all there was room for without cutting into the wing. I did have one set of problems. Three of my K&B 40's had the front bearing seal go bad and start pouring fuel out the front end. I couldn't even make it through the horizontal 8's. This happend within one week's time and put me out of the running at one contest. Replacement of the bearings solved the problems. Others have said that the problem was loose shaft fit and that replacing the bearing would not fix the problem, but it did for me.

I ran 4 oz tanks on my Fox 35's and on hot moist days would pull as much as an ounce of fuel out.

Four ounces should suffice. Currell