Allen,
First, I need to explain that I have built a few models for our 1cc multi-engine scale contests here in Tucson. We have two separate events. One is for a "Limited" category which has no flight options, just a requirement to fly 10 laps. The other is the "Unlimited" category which has flight options in addition to the requirement to fly the minimum 10 laps.
I will explain what has worked for me on several of the side mounted multi-engine models that I have built for our 1cc scale contests here. Generally, the tanks are rectangular affairs, no wedge. The fuel pick-up tube is on the bottom of the tank at the rear outside corner. For these small engines, including the Norvel .061's, I have found less than 3/4 oz is needed for the tanks in the "Limited" category, and for the "Unlimited" category, something maybe just more than 1 oz will be plenty to give the laps you would want, some time for maneuvering and if you have throttles to do the touch and go and taxi things and some allowance to get both engines running and still have both engine running at the end of the flight. However, you still might want to "top off" the tanks after both engines are running so both engines will run approximately the same time, particularly for the "Limited" category. More on this later.
These tanks have been set up with uniflow venting. The overflow tube is capped off after filling, but more on that later. The tanks will feed the engine until they are empty. The uniflow vent feed goes into the bottom of the tank on the outside corner in front of the fuel pick up feeding the engine. This has worked for the planes that have throttles as well as the non throttled affairs. When throttled, like on the taxi, the fuel will still at the rear bottom of your tanks and will feed the engines because your C-47 is a tail dragger. I am confident that the uniflow arrangement will do its thing.
My tanks for the "Limited" category are about 3/4" x 1" by 1 1/4" (about 0.6 oz of fuel). For my "Unlimited category, the tanks are .75" x 1 1/4" x 2 1/4" (just over 1 oz of fuel).
It is going to be pretty tight to find a place for your tank between the engine and the leading edge of the wing. I think you will be fine to just mount the tank behind the engine below the wing. The fuel draw should be fine. Plus, there will be less of a problem with fuel siphoning into the engine after you fill it. This arrangement has been used on two of my models where the tank had to go beneath the wing.
What I have done and still be within the rules for profile scale for a radial engine type cowling is to go ahead and make the inside half (the left half of the nacelle) to be scale shape - essentially it will be a half round cross section and the side profile will be in accordance with the profile rule. (In your case, it will still be less than 1" wide.) Then, on the outboard side of the nacelle, you have the engine sticking out with the tank behind and below the engine and wing. The tank is secured to the flat behind the engine with a pair of bolts through small tabs on the tank.
(This uniflow rectangular tank with the pick up on the bottom of the tank arrangement has worked on several of my larger scale models as well.)
One problem with the uniflow tank after you have capped the overflow is that you cannot add fuel after the engine is running to top off the tank to get the run time you might want. If you are using throttles, then the tanks should hold enough to get both engines running, go through your flight routine, and finish your taxi without topping off the tanks before the launch. (With a couple of my "Limited" category models, both engines would start quite easily, so timing was not so much of a problem. When the first engine would stop , the model could remain airborne, but it could be landed and just do a fast taxi until the second engine stopped.)
I thought I might have a problem with my last profile project which had four Cox TD .010 engines mounted upright. This was done for our "Limited" category rules which essentially does not have any flight options, the only requirement is that it be airborne for at least 10 laps. It does not have throttle control, and the tanks were sized to give a run time to give at least the minimum ten laps which met the tanks needed to be topped off just before the launch. (This is because it can be expected that several of the engines will have to run for a period while the other engines are being started which can be kind of tricky with four of these things.) I had the four rectangular uniflow tanks as described above, but did not cap off the overflow tubes. These tanks measure approximately 1/2" x 5/8" x 1 3/16" So, to "top off" the tanks, I just quickly attached a fuel syringe to the overflow vents on each tank, in sequence to each of the tanks, filled them, making sure too much pressure was not applied to flood the engines. And then got along OK by not capping off the overflow. Surprisingly, the engines ran just fine through the flight and stopped within a short period of each other.
I still think the uniflow idea is worthwhile for these small engine wonders.
Now, on two of my models, I have used a circular cross section tank with a clunk pick up, still set up to run as uniflow tanks. The vent is attached to the pick up tube on the clunk weight. In one case, (the Russian Tupolev Tu 95 Bear) this was done to have the tank approximate the scale shape of the nacelle behind the engine. (So, I have a nacelle that sort of resembles the scale shape of the nacelle and still complies with the profile requirement of adhering to the maximum allowable width of the profile nacelle. The side profile shape is still scale. This sort of created a problem that was solved by a tube passing through the length of the tank for the throttle pushrod to get to the engine The rules do not specify what the tank must look like, so it "sort of resembles the shape of the outboard section of the nacelle, at least a lot more closely than a crude looking rectangular object bolted on the side of the nacelle.) But this would not work on your C-47 because of the space you have for the engine and tank, although you could maybe think about a quarter round tank beneath the wing, but I would be concerned with the fuel pick up there, even with a clunk type arrangement. The rectangular tank will "look just fine' because after all, this is "just" a profile and it is partially hidden by the wing. In another one of my models (the Boeing XB-47D), the tanks were made from 1" diameter syringes to fit within the scale 1 3/8 wide nacelles which I think still complied with the profile scale rules since 1 1/2" wide cowls could be used and the rules did not specify what a cowl is or is not. (It got 3rd place in profile scale at the 2000 Nats.) (Whoever thinks that scale profile models are simple should try one.)
Hope this gives you some ideas. through all of this, what I am trying to say is that the rectangular tank with the pick up tube and the uniflow vent on the bottom of the tank has always worked for me.
Keith
We have had a good time with these things here in Arizona.
Topic: Tucson 1/2A boys, help. (Read 1781 times)
