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Author Topic: Square tanks and uniflow  (Read 1647 times)

Offline Dennis Toth

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Square tanks and uniflow
« on: April 02, 2016, 09:12:32 PM »
Guys,
I'm getting ready to build a new tank and I want to be able to do a reliable command cut off loop to shut off after the pattern is complete. I have used teardrop tanks that never cut off, pinched outside corner that seem similar to the teardrop shape, and also standard wedge tanks. When I was a kid one of the club members made tanks that were just plane rectangles. These worked fine but they were conventional vented. Seems this shape would offer the best shape for cutting off at the end of the flight, however, I don't know how the rectangle shape would work with uniflow venting. Anyone using rectangular tanks on uniflow?

Best,    DennisT
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Offline Chris Wilson

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Re: Square tanks and uniflow
« Reply #1 on: April 04, 2016, 09:18:41 PM »
 This thread looks a bit lonely so ......

Seen plenty of cubic shaped plastic clunk tanks work well as uniflow, and have a friend who uses rectangular tin tanks, uniflow and with a clunk inside.

I have always thought that a good cut off required the fuel pick to be forward of the tank 's back wall so that the cut off loop forces the remaining fuel load  away from the forward placed feed .

So there is far more to it than just the external shape.
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MAAA AUS 73427

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 Nothing in life is so exhilarating as to be shot at without result.  It's not enough that we do our best; sometimes we have to do what's required

Offline Dennis Toth

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Re: Square tanks and uniflow
« Reply #2 on: April 05, 2016, 05:05:25 PM »
Chris,
You make a very good point that I never thought about. I think if the back of the is kicked out with the pickup leaving some room to the tank back I think this should work with any shape. Would think 1/4" - 3/!6" should do it.

Best,    DennisT
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Offline Chris Wilson

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Re: Square tanks and uniflow
« Reply #3 on: April 05, 2016, 08:33:49 PM »
Something else to consider also Dennis (and this was pointed out to me by Brian Eather of stunt fame here in Oz), the fuel's level in steady level flight is not at a perfect 90º tangent to the flight circle but is a few degrees forward because that is the direction of all the forces (discounting gravity of course because of the need to fly inverted without change.)

This is one of the driving reasons to angle the tanks outer wall back when using a rear pickup, to at least match the angle dictated by all the forces.

If you find that hard to believe then just picture what would happen if the model were to escape its lines, would it simply move away from you or would it move away AND forward from the point of release?

The fuels meniscus is always at 90º to its intended direction of travel.
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MAAA AUS 73427

You have enemies? Good. That means you've stood up for something, sometime in your life.
 Nothing in life is so exhilarating as to be shot at without result.  It's not enough that we do our best; sometimes we have to do what's required

Offline Tim Wescott

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Re: Square tanks and uniflow
« Reply #4 on: April 05, 2016, 08:37:19 PM »
I use rectangular metal tanks with uniflow.  But, they don't do cutoff loops.  Instead, they give a very clean, precise cutoff -- clean as in "no warning".  For AMA this is fine, because I just load in enough fuel for a dozen laps after the cloverleaf.  It might be cutting things too fine if you're flying FAI, though.
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AMA 64232

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Offline Dennis Toth

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Re: Square tanks and uniflow
« Reply #5 on: April 07, 2016, 04:31:18 PM »
Tim,
Interesting, how deep are your tanks and how much room do you let from the back of the tank for the pickup and uniflow lines?

Best,   DennisT
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Offline Tim Wescott

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Re: Square tanks and uniflow
« Reply #6 on: April 07, 2016, 05:51:44 PM »
Quote from: Dennis Toth on April 07, 2016, 04:31:18 PM
Tim,
Interesting, how deep are your tanks and how much room do you let from the back of the tank for the pickup and uniflow lines?

Best,   DennisT

I'm currently running one that's 1x2x6 inches.  The uniflow is about 1/2 or 3/4 inch ahead of the back.  The pickup is adjusted so that it rides just barely in front of the back of the tank.

Works great.  It's not the only metal uniflow clunk I've done, but it's the first rectangular one.
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AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

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