Tank dimensions for profile

[Dennis Toth]

Guys,
Just finishing up an OTS Ringmaster and need to build a tank. In the past I have used the conventional 1" x 2" x X". Reading some articles lately that indicated having the 2" width on a profile might not give a consistent run, even with uniflow, then if it were a little deeper and narrower. Also read that the old Fox Profile style tank (very deep and narrow double vee's) is not consistent either (but I don't think they are uniflow).

So question to the group how deep is too deep? Could you go say 2.5 deep"x 1.25 wide"x X long to keep the same oz. just not have so much of the tank hang outside of the NVA location in the engine? Seems that if the tank is to wide off the mounts to much is outside the NVA even with uniflow.

Best,   DennisT

[Dave Hull]

Dennis,

I see that you didn't get any input yet, so let me provide one example I ran into--although this was with a Mickey .19 Redfin, not a Veco.

I needed all the tank volume I could get, since on this rejuvenated Jr. Flite Streak I was running a rich setting, which flew the plane really well.

The first tank was a stocker:  1-11/16" wide, 1" deep, 1-9/16" long. Standard venting. It ran beautiful, but not nearly long enough. So I needed to try something bigger.

I believe the second tank I tried was an "oval." It was 2-3/16" wide, 1-1/4" deep and 2-1/16" long. Definitely increased the capacity but did not run well on the Jr. Flite Streak, having changed nothing else. Same engine, prop, plug and fuel. Looking at the tank now, it would appear to be plumbed uniflow, so that would be another difference. I did not run pressure on either setup as this was sans muffler.

So I put the "too small tank" back on it and it awaits training flights for some of my buddies who say they want to come out and watch--and maybe try it a little.

What I should do is make a new tank just like the current (small) tank, but stretch it to the max length of the gap, and make the pickup exit the bottom instead of coming out the front where it already interferes with the cylinder. That would add 33% capacity which could get me (optimistically) up to 5 minutes. Might be a good corona-project. One more plane to celebrate test flying when that day comes.

I know I went thru much the same exercise on my first plane, a Lightning Streak. That had an OS 35FP on it, and I don't recall that it ever ran particularly well. I built several tanks one of which was 1-1/2" deep, 2" wide and 2-1/4" long. This is pretty much the dimensions of the Brodak BH-596 3 oz. wide wedge standard vent tank, but I made the wedge sharper and put the lines where they would not interfere with the engine. It was good enough to get me thru about 50 flights and my first two inverted wingover pullouts. But not another flight more....

For the Mickey Redfin, I had the tank centered vertically on the engine centerline. It was fine right there.

Good luck with your project!

The Divot
"Proudly leaving divots on pavement at better parks throughout Southern California"

[Dennis Toth]

Dave,
Thanks for taking the time to post you experience. It is interesting that the wide tank does seem to get some problems even with uniflow. In a full fuse the normal 2" wide tank only pulls away from the point of suction 1" which most engines seem to handle quite well. On a profile the suction point for a standard 2 stroke through the venturi NVA is 1/2"ish off the mounts. Now with the 2" wide tank it has 1 1/2" of fluid moving away from the suction point and that extra 1/2" seems in some engines to cause issues. I had this kind of tank on another Ringmaster, It drove me nuts with setting all over the place. I final got it to work by moving the uniflow vent tube to the free air stream above the fuse off the back engine mount. I took a short piece of stripe brass and soldered a short tube to the end. It was just long enough to raise the tube above the fuse and use the rear mount bolt to hold it pointing into the free air.

Even though that worked I think a narrower tall tank would be better. I have roughed out a tank shape that is about 1 1/2" wide, 2 1/4" tall and 2 1/2" long that I will have a pinched rear outside corner for the fuel pickup and uniflow lines. I'm thinking of putting a small corner baffle just to keep the fuel from sloshing to much. I will still use the uniflow vent into the free air stream as this is always a good thing.

Best,   DennisT

[Tim Wescott]

Clunk tank?  A Hayes 3 ounce is perfect for a Ringmaster with a 20FP; you don't say what engine you're contemplating.

I've had really good luck with mounting tanks inboard on profiles -- it totally eliminates the problem with a "too tall" tank, because instead of the centrifugal force reducing fuel draw, it's increased.

Or a chicken-hopper tank?

[Dennis Toth]

Tim,
I will be using a VECO 19 BB. Dave's experience seem to go along with the idea that a tank can be to wide even if uniflow. Your inboard suggestion also supports this to some extent. I thought about the inboard mount but that messes up the look of the nose.

I've made up a foam block test shape and I think it will work fine, it will be about 1 1/4" to 1 1/2" wide, I need to check the volume. I think I need around 2 3/4 oz. of fuel. I intend to borrow from my electric experience and use Velcro on the fuse/tank side to hold the tank in position (will allow for easy height adjustment) with a couple of J bolts and zip tie to keep it on. I guess I should check if the Velcro is fuel proof (it should be as it is nylon for the most part).

Best,     DennisT