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Remote tanks?

Old 04-23-2021, 08:05 AM
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H5606
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Default Remote tanks?

Not sure how practical it is to do with .049s but thought I'd ask:

Can you position the fuel tank some distance - say 6" to 7" from the firewall and get a reliable engine run - using either crankcase or pacifier pressure?

Thanks for any thoughts or experiences -
Old 04-23-2021, 12:27 PM
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Pacifier for sure. Even the Little Red Cap would likely be fine. Crankcase pressure might be OK if there are no leaks. Kind of iffy.
Old 04-25-2021, 08:59 AM
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Okay thanks - I've never used pacifiers as fuel bladders and I'd like to try these Little Red Caps.

Optimistic that run times can be several minutes.

While researching these, looks like CEF has good documentation on setups -
Old 05-30-2021, 07:04 AM
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Questions about a balloon tank that is not providing any pressure benefit -

I'm guessing that fluid drag from the wall of the tubing limits suction effectiveness -

What is the longest practical fuel supply tube to the engine using suction alone?

I have doubt but has anyone had success with at least 5.5" length fuel tube on suction or vented suction?
Old 05-30-2021, 02:10 PM
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It would depend on many things like venturi diameter and tank height, if you will fly inverted, if you want an idle. Just try stuff. What's the worst that could happen?
Old 05-30-2021, 03:31 PM
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Cramping laziness but you're right - okay

Old 05-30-2021, 04:21 PM
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Actually I was just thinking about a Chickenhopper tank. Maybe you could put a tank between the motor and tank. Like a large capacity filter, if on suction.
Old 05-31-2021, 06:01 AM
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Default Suction capability?

Originally Posted by aspeed View Post
Actually I was just thinking about a Chickenhopper tank. Maybe you could put a tank between the motor and tank. Like a large capacity filter, if on suction.
I remember looking at doing something like this on an ARF propjet for a .60 at one time - it had a long nose and I wanted to locate the tank close to the CG.

This is what prompted the second series of questions above:

Pond Skipper mentioned this idea and I went so far as to set it up but abandoned the plan before even trying it out, convincing myself that it wouldn't draw under suction alone; I may be my own worst enemy...

The idea is to eliminate launch sag on a pusher arrangement by getting rid of the head pressure surge during the throw to launch which is believed to flood the engine out.

I need to try it or make the move into pressure bladders.


Balloon tank w/ stopper facing fwd and a long feed tube to a reedie in pusher config -

Last edited by H5606; 05-31-2021 at 09:10 AM.
Old 06-04-2021, 06:53 AM
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I dunno. If you accelerate that mass of fuel forward, seems to me it makes no difference whether you have a conventional pickup or that setup - the center of mass of the fuel is in the same place, and the fuel flows from the same point A to B - same elevation change and any surge from head pressure ought to be the same IMHO. I think the path it has to take is academic, except for the additional drag/pressure drop caused by longer tubing. Yes you get pressure drop over a long thin tube - meaning suction will be hampered the longer the line is. And it is not great to begin with. I have had pretty steady engine runs using crankcase pressure on high performance .049 RC models, but not with a reedie, you have some technical challenges there.

Old 06-08-2021, 12:27 PM
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Yeah, you'll need a bladder or pacifier tank to give you the pressure needed to ensure an even run over more than a couple of inches and for when using more than around a half oz. Even the bigger glow engines won't tolerate the tank being more than a couple of inches away from the carb or within a certain size range. I recall from flying .20's and .25's for a lot of years on 4oz tanks that even with the top front of the tank being 1/4" above the needle valve and tucked in tight as I could to the engine that I'd have to land and open the needle about half to 2/3's of the way through the tank to keep peak power.

The good news is that you can easily make a "pen bladder" tank from a piece of thin wall tubing you can find at any fishing store. They sell a black latex thin wall tube. close up the one end with a plug of some sort and some copper wire binding. On the other end make a plug from some fuel tubing and a piece of brass tube to connect to the delivery line. This will be enough pressure that you can get away with a 6 to 7" run as well as run up around 2 to maybe 3 oz. You just need to make the bladder longer so it doesn't try to overfill.

With a tubing bladder what you get is that it first fills and expands into a ball. Then as you continue to fill the ball turns into a wiener. What you want to avoid is overfilling past the point where the long wiener reaches the rear plug. Between the long but not over stretched wiener shape and the final ball the pressure will stay constant. At the end it'll go slobbery rich and then lean out and cut in short order.
Old 06-09-2021, 10:21 AM
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And those needles don't do a bad job of metering pressure flow, in most cases. 049's are definitely not famous for strong suction fuel draw.

I recently decommissioned a Magnum XLS .15 powered model, because despite getting the 3oz tank close as possible to the firewall and with muffler pressure of course, the inch or so separation was enough to cause annoying mixture variations during various aerobatics, enough to take the edge off the fun.

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