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Help with Fuel Tank Choice .051

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Help with Fuel Tank Choice .051

Post  Wiztom on Fri Jul 13, 2018 3:36 pm

Hello,

I am getting down to the finish line with my modified Gullows P-51. It has elevator, rudder and aileron control and no throttle. It has no dihedral. We are going for speed. The model with battery and without fuel weighs 12 oz. It has a 2 Oz tank. The .051 has a Kirn Type needle valve and Norvel Type glow head with K&B long glow plug.
After reading some posts about bladder type fueling vice clunk type, I wandered over to Texas Timers and inquired as to what I would need. They are discouraging me from using a bladder and telling me to stick with suction.
I am looking for some feedback as to the pluses and minuses of each. The the plane will be piloted by my experienced son and yes he will be doing aggressive sport flying, (if it flies at all) https://illiweb.com/fa/i/smiles/icon_biggrin.png

Thanks for any and all feedback.

Hopefully I have attached some photos correctly;


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Re: Help with Fuel Tank Choice .051

Post  1/2A Nut on Fri Jul 13, 2018 4:08 pm

2oz should yield some long flights bit over 12mins. But that
is a lot of fuel weight. Gullows P-51 should stay low weight to
protect the frame from damage. This is not the plane for agressive
flying its all sticks and balsa.

You might want to consider a throttle sleeve to land at will.
You want the fuel tank up close to the engine and you want
the tanks clunk feed line just a bit lower than the NV.

A good 1oz tank such as this one would be recommended:

https://coxengines.ca/1oz-fuel-tank-for-cox-engine-round.html

or this:

https://coxengines.ca/1oz-fuel-tank-for-cox-engine.html
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Re: Help with Fuel Tank Choice .051

Post  balogh on Fri Jul 13, 2018 7:06 pm

As far as I am concerned I prefer balloon tanks to clunk types due to advantages like no need for venting, no fuel foaming, feeding the engine in inverted position without the payload of the clunk, and flexibly occuppying the tank compartment. I personally did not succeed with clunk tanks for my RC planes and have used balloons in my near 10 recent planes. Unless the tank is positioned too far from the engine thus reducing the engine suction and requiring pressurization, I would always go with my balloons.

You mentioned you are going for speed. Then unless you have a Nelson turbo plug you may want to use a insert type glow head or at least a stock high compression COX glow head because the glow plug shown in your pics is a performace robber in TD049...051 engines in my humble opinion and experience.
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Re: Help with Fuel Tank Choice .051

Post  944_Jim on Fri Jul 13, 2018 8:41 pm

Hi Wiztom,
You asked for opinions...you are going to get opinions!

I would bench test the engine with any and all tanks up for consideration. You can play with tank positioning relative to the engine without ever leaving the ground. Of course, it may behave differently than in the air, but you should get close.
Look for my BHM Mosquito in MS thread. Early on I considered tanks mounted above the wing. While bench testing I discovered the engines ran best with the tank centered on the spray bar (height-wise). The reality was when trying to get two difficult engines started, they both flooded out. The fix was shallower tanks just under the wing...but you can read the details there.

You mentioned bladder. Some people consider bladders for pressure fuel systems. What you may mean is a balloon system, whereby the balloon is filled, but not pressurized. This allows a suction-based engine access to ALL of the available fuel down to the last drop. The negative is that balloons wear out, break, and need replacing from time to time. I see Balogh already detailed this one above.

Since the plane is intended for R/C, you could also consider a normal wedge tank...but place the wedge pointed down with the back end lower than the front. The two fill/vent lines would come out the "sides" of the tank. It may be something to consider building a tank shaped to fit in the top of the fuselage, with a wedge to the bottom like the wedge tank I mentioned earlier. Then you could customize the fill/vent lines to come up out of the top of the fuselage. Making a tank isn't too tough (I had to make two matching tanks for the Mossie). This may not work for really agressive flying...back to clunk, bladder, or balloon.

Whatever solution you test, make sure your engine test stand can be moved easily to simulate the plane's flight. The test stand only needs to be no more than a piece of plywood board cut for the engine with a place to strap tanks. Hold the "far end" down with a cinder block. Start the engine and "fly your plane" by holding the the board at various inclinations...pointed up/down...tilt left/right...shake around. Give the engine and tank a chance to prove themselves to you BEFORE you mount them and fly the plane.

Oh, I have to ask. Just how did you color the engine? I have a need to change mine too.

Thanks and good luck! It sure looks good!
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Re: Help with Fuel Tank Choice .051

Post  balogh on Sat Jul 14, 2018 1:20 am

Hi Wiztom,

I got a "noreply" message from you outside this site and I answer you here:

This is the simple setup I use for balloon tanks: I buy a party balloon of the proper shape and size  in any convenience or DIY shop. The good thing is the balloon availability in a wide variety of shapes ranging from bulb to oblong, and sizes between 1/2...3 oz capacity that I typically use in my planes powered by the COX 010-090 engine size range



Unlike with the pressurized bladder tank used in C/L applications, you want the balloon NOT to pressurize the fuel when filled to the required capacity, just to remain slack so that the fuel pressure remains constant from full to empty...this consideration may orient you to select the proper balloon size...

The rubber stopper tucked in the tank throat is available in most hobby shops. These typically have 2 pre-drilled holes for the filling and feed lines and a third "blind" one that is used in clunk tanks for vent lines. I leave this 3rd one blind, or if pre-drilled, fill it with a plastic tube whose outer end is heated to melt then flattened first (= heat-butted in my Hunglish terminology)  to act as a seal.


The balloon throat is tight enough to grab on the stopper fuel-tight even without a quick-tie (you know which plastic tie with ratcheted surface pulled into a no-return head I mean but the English name escapes my mind....) But you may use a quick-tie to make sure  surprises are prevented.

I use repurposed stiff plastic tubes of abt. 1.....1,5 inch length as fuel line and filler line lead-outs from the stopper....old ballpoint pen fills....earbud stems...whatever that resists nitro (these do)..the extension to the stiff tubes inside and outside the tank is normal silicon fuel tube.

The filler tube is plugged with a stiff plastic tube piece with a heat-butted end that serves as a plug..the fuel line connects to a small filter before connecting to the fuel nipple on the carb. The one on the pic is said by my hobbyshop keeper to be used on gas helicopter models...transparent and lighter than the normal aluminum mini-filters sold for glow applications.

You may also want to flush the newly assembled tank with some fuel to make sure no foreign material remains in it before you connect it to the engine.

With regular use i.e. not leaving the tank empty for months between 2 uses - that tends to make the collapsed tank internal surfaces stick together -  the tank will serve you for years without rotting.....My experience....and even if rotten or punctured, you only need to replace the party balloon so buy a few from the same size and shape for a quick replacement in future...

I fuel the tank with a 2 oz syringe I buy in veterinary shops...fill the syringe to almost full (if you need as much fuel), connect the syringe to the fill line, hold the plane in a nose up position to allow air captured in the balloon vent through the filler hose, suck on the balloon by pulling the syringe piston further out until no more air bubbles enter the syringe, then fill the balloon until you see fuel beginning to be forced through the feed line to the carb. This is the point you have just enough but not too much fuel in the tank, i.e. no excessive pressurization.

And again, if you want to beef  that beautiful TD049 up in the nose of the plane, you may want to use the Nelson turboplug sold by www.kittingittogether.com located in Lubbock/Tx just the same state you are in...or the insert type heads sold by COX International and Exmodel engines...or the stock high compression COX head...these all work much better on COX 049 engines than the normal glow plug...just for your consideration

Good luck..
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Re: Help with Fuel Tank Choice .051

Post  1/2A Nut on Sat Jul 14, 2018 9:02 am

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Re: Help with Fuel Tank Choice .051

Post  Wiztom on Sat Jul 14, 2018 9:40 am

944_Jim wrote:Hi Wiztom,
You asked for opinions...you are going to get opinions!

I would bench test the engine with any and all tanks up for consideration. You can play with tank positioning relative to the engine without ever leaving the ground. Of course, it may behave differently than in the air, but you should get close.
Look for my BHM Mosquito in MS thread. Early on I considered tanks mounted above the wing. While bench testing I discovered the engines ran best with the tank centered on the spray bar (height-wise). The reality was when trying to get two difficult engines started, they both flooded out. The fix was shallower tanks just under the wing...but you can read the details there.

You mentioned bladder. Some people consider bladders for pressure fuel systems. What you may mean is a balloon system, whereby the balloon is filled, but not pressurized. This allows a suction-based engine access to ALL of the available fuel down to the last drop. The negative is that balloons wear out, break, and need replacing from time to time. I see Balogh already detailed this one above.

Since the plane is intended for R/C, you could also consider a normal wedge tank...but place the wedge pointed down with the back end lower than the front. The two fill/vent lines would come out the "sides" of the tank. It may be something to consider building a tank shaped to fit in the top of the fuselage, with a wedge to the bottom like the wedge tank I mentioned earlier. Then you could customize the fill/vent lines to come up out of the top of the fuselage. Making a tank isn't too tough (I had to make two matching tanks for the Mossie). This may not work for really agressive flying...back to clunk, bladder, or balloon.

Whatever solution you test, make sure your engine test stand can be moved easily to simulate the plane's flight. The test stand only needs to be no more than a piece of plywood board cut for the engine with a place to strap tanks. Hold the "far end" down with a cinder block. Start the engine and "fly your plane" by holding the the board at various inclinations...pointed up/down...tilt left/right...shake around. Give the engine and tank a chance to prove themselves to you BEFORE you mount them and fly the plane.

Oh, I have to ask. Just how did you color the engine? I have a need to change mine too.

Thanks and good luck! It sure looks good!

I am now realizing that part of my confusion was that I did not realize the difference between balloon tank and bladder tank.
I will experiment.

As mentioned below, I purchased the motor from Jenuine-motor on E-Bay. Its got a polished crank, aluminum carb body, shim and prop plate. Very reasonably priced and it do look marvelous Smile
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