Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

One more dumb Magnum R question

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Old 09-07-2005, 03:00 PM
  #1  
MJD
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Default One more dumb Magnum R question

I am wondering whether to install the tank supplied, a 320cc (10 oz) clunk, or to install a Jett 6oz bubbleless tank. The bubbleless tempts me but I am sure that many use the stock tank. Any advice or suggestions one way or t'other?

I am using the Weston .50V1 - what run time could I expect (pinned of course..) on the 6oz versus the 10oz? I am guessing fuel consumption is somewhere approaching the 2oz/minute regime?

Does this aircraft/motor combo act up at all with the standard clunk tank setup?

Thx, maybe I'll finally get it flying this weekend, in which case the subject of next week's question could be "Reparing a Magnum".

Thx

Mike D.

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Old 09-07-2005, 08:38 PM
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Crazy4Flight
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Default RE: One more dumb Magnum R question

I have used the stock tank supplied no problems with Jett.50 [8D]

6oz. tank will give ~ +/-3 minutes of flight time [:@]

A buddy had Weston .50V1 with pipe, stock tank +/- 5 minutes 8x8 APC 21,500 rpm

you may need an ounce of tail weight to balance

Bob brother # 105
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Old 09-07-2005, 08:57 PM
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Ed Smith
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Default RE: One more dumb Magnum R question

The bubbleless tank is the only way to go be it Jett or Tettra. We use this type of tank exclusively in our pylon racing aircraft. It is impossible to get a lean run unless the needle is set that way. There will not be any more bubbles in the fuel. It is not necessary to surround the tank with foam. I hold my tanks in place with velcro, no foam.

You will need a syringe to deflate the bladder and fill the tank. At the end of the run the engine just quits, there will not be much of a warning. Whatever the needle is set to on the ground is pretty much what it will stay at in the air, RIGHT OR WRONG, so be warned.

Ed S
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Old 09-08-2005, 08:35 AM
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Default RE: One more dumb Magnum R question


ORIGINAL: Ed Smith

The bubbleless tank is the only way to go be it Jett or Tettra. We use this type of tank exclusively in our pylon racing aircraft. It is impossible to get a lean run unless the needle is set that way. There will not be any more bubbles in the fuel. It is not necessary to surround the tank with foam. I hold my tanks in place with velcro, no foam.

You will need a syringe to deflate the bladder and fill the tank. At the end of the run the engine just quits, there will not be much of a warning. Whatever the needle is set to on the ground is pretty much what it will stay at in the air, RIGHT OR WRONG, so be warned.

Ed S

Yeah.....
....what he said In the long run, its a good investment, and will avoid nearly all possble fuel system issues.

Nice thing with the bubble-jett or tetra tank, you get to use ALL of fuel in the tank down to the last drop. A 6oz tank will allow you to run the entire 6oz of fuel without worry or a mixture change. On a regular tank, even when filled to the max, you only have 4oz of usable fuel. Below that amount - fuel foam, air in the line from a bouncing clunk, and a blown glow plug (or worse a burnt engine) are waiting for you.

Also, you have the ability to install the tank a little bit further from the engine if desired, and at any angle, sideways, or even backwards (right Ed ). The tank and engine never knows the difference.


Im not entirely sure, but I THINK the 8oz slim jett tank may fit in the Magnum. Can anyone check ? (dimensions of the tank on the jett site). I know the 6 oz tanks all fit.

Bob
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Old 09-08-2005, 09:09 AM
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MJD
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Default RE: One more dumb Magnum R question

Yes please, I'd like to know about the 8oz! Darnit, I only bought 6oz and 8oz short tanks on my last order.

Bob, when you say slim 8oz do you mean the one called "standard"? If so, I am pretty sure it will fit, as it is smaller OD than the short 6oz and it fits, though snughly unless you Dremel out the former a bit.

So from a fuel flow standpoint (Ed and Bob) I am safe to pull the tank rearwards a tad into the radio compartment area to reduce CG shift?

Mike D.
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Old 09-08-2005, 10:03 AM
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Default RE: One more dumb Magnum R question


ORIGINAL: MJD

Yes please, I'd like to know about the 8oz! Darnit, I only bought 6oz and 8oz short tanks on my last order.

Bob, when you say slim 8oz do you mean the one called "standard"? If so, I am pretty sure it will fit, as it is smaller OD than the short 6oz and it fits, though snughly unless you Dremel out the former a bit.

So from a fuel flow standpoint (Ed and Bob) I am safe to pull the tank rearwards a tad into the radio compartment area to reduce CG shift?

Mike D.
Snug with a bubble-tank is not a problem. No worries of foam. Cram it in there. In fact, I have in the past warmed and distorted the tank a bit to make it fit.

The 8oz standard is only 2" in diameter - just a tad bigger than the 6oz (1.9" dia, 5.5 total length) , and its about 3/4" longer at 6.3 total length. So if you have room aft of that tank bulkhead to allow the tank to stick out a bit, go for it

As for tank placement ------



This is (was?) a typical QM40 tank installation. CG type tank located up over the wing. Minimized cg and pitch trim changes (which can drive you nuts) during a heat.

So yes, in most aircraft you can move the tank aft a bit to help avoid a CG change. Just try to keep the center line of the tank in line with the carb (as usual)

Consider this. As the bubble-jett tank (or tetra tank) bladder is collapsed by muffler pressure from the outside of the bag/bladder, the "effective point" of fuel pick up is just inside the stopper of the tank. Fuel is always squeezed toward that tank exit point. You also have move uniform fuel tank pressure (acting on all 'sides' of the fuel), and the fuel system presents no risk of uncovering the fuel pick-up with an attitude change. The fuel is sorta fixed in location - does not slosh around - this helps pressure head issues (or at least mitigates some variables)

So I like to look at it this way...... (over-simplified version)
The stopper location of a bubble-free tank system can be easily located the same distance from the engine that a pick-up clunk would be located on a conventional fuel tank. This is effectively the same fuel draw distance. And..... since there are other good factors working here, it can be even further away than that without any degradation in performance.

On one of my aircraft, I located a 12oz bubble tank just forward of the wing spar (tube socket). Total run length of tubing to the needle valve assembly was 8.5", plus another 3" or so from the needle to the carb. Ran flawlessly. Just an illustration of what can be done.

BTW... the tetra fuel tanks are very good products, and available in various sizes. They are also square, which helps with some installations. Some assembly required. The Bubble-Jett tanks are pre-assembled, and sometimes the round shapes fit better.

Bob
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Old 09-08-2005, 10:07 AM
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daven
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Default RE: One more dumb Magnum R question

Yes you can pull the tank backwards. We are running them on the C.G. of our racers. The backpressure of the exhaust collapses the bladder almost giving you a pressurized fuel system. I have run some pretty long lines on sport planes with very good success.

There are a few different syringes out there, but the Jett Tanker is by far the easiest to use. Pay the money and get the right one.
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Old 09-08-2005, 10:36 AM
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Default RE: One more dumb Magnum R question

Re: Jett Tanker: Got one already, thanks! Nice alternative use of Semco EFD canisters BTW, Dubb - LOL. We use the 6oz Semco canisters here on our EFD's for potting adhesives.

Thank you all for the advice. Sounds like I'll go bubbleless; although I'm sure the stock tank would work okay as noted, I wanted to get familiar with them anyway so here's my excuse to do so. I'll put the 6oz in for this weekend, and order a couple of 8oz for later. I'm sure 3 minute test flights will be enough for now!

Mike D.

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