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Engine basics => Engine set up tips => Topic started by: Dennis Toth on August 10, 2013, 06:46:31 AM
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Guys,
I've built several tanks for various ships and started using the GMA pinched corner layout to be able to get more fuel in a given space. Reading several posts on tank setups I was wondering if the pinch corner on uniflow is as consistent as a full wedge? Seems for the first half of the flight it wouldn't matter only near the end when there is room for the fuel to get pushed around in tight maneuvers.
Also are baffles worth putting in? Back in the day we always had baffles but we were running conventional venting. I did build some with uniflow but don't know if it is worth the effort.
Best, DennisT
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I don't think baffles help or hurt. I have the idea, probably self generated, that George Aldrich designed the pinched back tank to manage the leaning out of the engine during the pattern. Maybe it was to hold more fuel, however.
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I'm sure I've seen GMA claimed his tank is uniflow, but it is not what I understand as uniflow. I've also seen that he claimed his tank gives increasing rpm as the tank empties, giving more power towards the end of the pattern, when a bit more power is welcome. This does make sense to me. Maybe that is what George means by uniflow, but it is a bit different from what I understand as uniflow.
I suspect that if you plumbed a GMA tank with conventional uniflow plumbing, it would work quite o.k., - a uniflow as we know it.
I'm not sure about baffles, I always put one in because that's what Bob Palmer said.
Come to think of it, completely rectangular tanks with no wedge or pinch seem to work o.k. with uniflow.
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I'm sure I've seen GMA claimed his tank is uniflow, but it is not what I understand as uniflow. I've also seen that he claimed his tank gives increasing rpm as the tank empties, giving more power towards the end of the pattern, when a bit more power is welcome. This does make sense to me. Maybe that is what George means by uniflow, but it is a bit different from what I understand as uniflow.
I suspect that if you plumbed a GMA tank with conventional uniflow plumbing, it would work quite o.k., - a uniflow as we know it.
I'm not sure about baffles, I always put one in because that's what Bob Palmer said.
Come to think of it, completely rectangular tanks with no wedge or pinch seem to work o.k. with uniflow.
Of course, as shown on the Nobler plans, it gives uniflow for about the first 1/3 of the tank, then leans out afterwards. That's because the vents aren't right up against the inner edge of the tank. The pinch or not pinch or wedge or not wedge doesn't really make that any different. George did not really seem to understand the physics of the tanks and he and I had some very interesting discussions on the topic back on his old RCO forum. He also thought the routing of the plumbing outside the tank was a factor, for instance. It's not, of course.
That having been said, the pinch corner tank works fine and about like any other wedge tank that has a constant width. The very shallow angle of the pinch helps the cutoff, and it cuts off better than the steep angle of a Veco T-21 type. The Kenn Smith tank was an angular version of the same idea that got even more fuel in a given space.
Either type can be vented for uniflow very easily, or made switchable between suction and uniflow per normal practice.
If you make the tank straight off the Nobler plans, two things become apparent - one, it actually ends up with a bit of "reverse taper" because they didn't flare the sides to accommodate the added distance along the wedge, and two - it doesn't fit in the airplane! It's about 1/16 too wide to fit between the doublers, someone didn't measure something right; probably made the fuselage formers a bit too narrow.
I think the tapered wedge tank is even better and that's what I use. If I need more capacity I make it deeper and if necessary make the wedge off-center.
None of them need baffles as far as I can tell. The Veco type may have gotten some advantage from baffles but the real solution is to make the wedge more pronounced. There's a critical angle that I can't recall right now, and the Veco is too flat.
There's really nothing mysterious or interesting about tanks. It's a can with pipes in it and the principles are dead simple. There is some tendency to treat the topic as if voodoo is somehow involved, but it's really as simple as it looks.
Brett
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George told me several times that he did not like uniflow tanks. And then he would tell me how good the Bob Palmer tank ran. At the time neither of us realized that the Palmer tank is uniflow. None of the diagrams I have seen show the overflow capped off, and that confused me. Bob Palmer confirmed the uniflow nature of his tank in an interview published in Stunt News.
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I have used two unusual tanks on my 1/2As.
The first has flat sides with the wedge at the back,not on the side. This was done so that normal tank end caps could be used to make a small capacity tank. The space between the tank caps is 1" for a 1 ounce tank. It seems to work just fine.
The second one is a rectangular tank with a clunk. The weight is a length of copper tube with a wheel collar in the center. This leaves room for the fuel hose on one side, and a narrow pickup end on the other. This type tank holds the maximum fuel for a given space.
Both tanks are Uniflo vented.
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I have used two unusual tanks on my 1/2As.
The first has flat sides with the wedge at the back,not on the side.
The tanks the Mike Mustain made were like that, just a rectangular tank with a point on the back. It wasn't any better than the conventional ones but it worked fine. The explanation for it was one for the ages. I really liked Mike but a physicist he was not.
Brett
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The tanks I use in my NoblARF's are rectangular Kap Pak free flights replumbed and turned into a clunk tank. They hold 5 1/4 oz and run perfectly. No, they are not Uniflo. I do use Muffler pressure.