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Author Topic: Profile tank position  (Read 1843 times)

Offline Matt Brown

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Profile tank position
« on: September 17, 2018, 03:02:28 PM »
I’m working on a Primary Force, planning on an FP or LA 25. Over the last two years, I’ve seen multiple tank positions on other profiles and not sure which way to go. It seems that inboard mounted klunk tanks go rich after launch and conventional hard tanks mounted outboard lean out. I want to pre-plan the tank mounting such that I have enough vertical adjustment to get the run right as well as a clean mount setup. I’m leaning towards a recessed hard tank but that makes height adjustment difficult.
My biggest thing is I want it right from the beginning so I don’t have to hack on the plane to fix an issue.

Suggestions?
Thanks, Matt
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Offline Dane Martin

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Re: Profile tank position
« Reply #1 on: September 17, 2018, 03:26:14 PM »
I'm currently running an LA 25 in a primary force and started with the fuel tank inboard. I had to lean it out to literally all the rpm it could give before launch. Then it would richen up so much I had to run a 9x6 to keep any airspeed. I switched the fuel tank around, same 4 oz dubro tank, to be on the engine side. Now I get a normal LA25 run on an APC 9x4. I flew it at the Ted Goyet Memorial on 60ft lines and it had power to spare. I'll get pics later if you'd like
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Offline Dane Martin

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Re: Profile tank position
« Reply #2 on: September 17, 2018, 03:28:42 PM »
Oh, the main reason I didn't like it inboard is because; you could always figure out how to peak it out, but there was really no way to know how much it would richen up. Too inconsistent when I travel or weather changes. Just too difficult to predict and tune.
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Offline Matt Brown

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Re: Profile tank position
« Reply #3 on: September 17, 2018, 04:16:21 PM »
Dane, Conventional plumbing and muffler pressure or uniflow plumbing?

Matt
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Offline Dane Martin

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Re: Profile tank position
« Reply #4 on: September 17, 2018, 04:27:54 PM »
Uni-flow, dubro 4oz tank, set up like this
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Offline Steven Kientz

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Re: Profile tank position
« Reply #5 on: September 18, 2018, 03:36:04 PM »
I've seen pics of a tank mounted on a plate that has 2 machine screws holding it to the airframe. The plate is slotted for vertical adjustment. Tank is held to the plate by rubber bands or silicone.
later
Steve
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Offline Tim Wescott

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Re: Profile tank position
« Reply #6 on: September 18, 2018, 04:46:53 PM »
Quote from: Steven Kientz on September 18, 2018, 03:36:04 PM
I've seen pics of a tank mounted on a plate that has 2 machine screws holding it to the airframe. The plate is slotted for vertical adjustment. Tank is held to the plate by rubber bands or silicone.
later
Steve

I prefer four screws, in slots, and zip-ties holding the tank to the tray.  I'm also currently going with 1/32" aluminum with honkin' big lightening holes drilled in it, and the mounting features shaped to tilt the back of the tank to the outboard.

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Offline Matt Brown

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Re: Profile tank position
« Reply #7 on: September 18, 2018, 04:50:14 PM »
Quote from: Tim Wescott on September 18, 2018, 04:46:53 PM
I prefer four screws, in slots, and zip-ties holding the tank to the tray.  I'm also currently going with 1/32" aluminum with honkin' big lightening holes drilled in it, and the mounting features shaped to tilt the back of the tank to the outboard.



Since your tank is inboard and plastic, how consistent and predictable is your engine run? Are you setting it much leaner on the ground to get the inflight setting correct?

Matt
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Offline Tim Wescott

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Re: Profile tank position
« Reply #8 on: September 18, 2018, 05:35:09 PM »
Quote from: Matt Brown on September 18, 2018, 04:50:14 PM
Since your tank is inboard and plastic, how consistent and predictable is your engine run? Are you setting it much leaner on the ground to get the inflight setting correct?

Matt

Engine runs are quite good.  I'm probably setting it a bit leaner on the ground, but not super dry as Dane describes.  It doesn't riches up nearly as much as his setup -- I couldn't tell you why.

I can tell you that my venturi size is tuned for a good run (by piling up layers of nylon mesh onto the venturi -- just enough so you get your desired lap time without running away or getting inconsistent runs), and the system runs on muffler pressure.  I don't think Dane ever said, but if he's not using muffler pressure that would explain a lot.
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Offline Dane Martin

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Re: Profile tank position
« Reply #9 on: September 18, 2018, 06:43:28 PM »
Quote from: Tim Wescott on September 18, 2018, 05:35:09 PM
Engine runs are quite good.  I'm probably setting it a bit leaner on the ground, but not super dry as Dane describes.  It doesn't riches up nearly as much as his setup -- I couldn't tell you why.

  I don't think Dane ever said, but if he's not using muffler pressure that would explain a lot.

Answers to the two questions you've posed,
1) I had my tank on a "table" and the tank stuck out, or inboard another 3/8" or so. So the farther the tank is inboard, the richer it'll want to go in flight.
2) no muffler pressure, suction or uniflow only on mine.

That explains the differences. Also, I have several profiles with the tank inboard which work great like Tim's. But in this exact case, primary force, 25la inboard tank: I didn't like it.
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