Ed_Moorman

My Feedback: (1)

A good friend of mine, Ugo Ferrari, just filled the nose of his UCD 60-90 with fuel when the fuel tank stopper came out. I have heard of this happening before, but I attributed it to user error, but this time I know Ugo has been flying model airplanes since the 1930s and isn't about to make a rookie mistake like not tightening the tank stopper. I figured a test was in order and I do love a test.

The odd thing was I had just gotten a new Big Stick 40 to replace my old StingRay as a mid-size engine test and break-in plane. All the engines in my previous .46 size test will be flown on it for an air break-in. Last night I e-mailed Ugo that I was tossing the tank because I had heard about the plugs coming out. The next day, his does. Who woulda thunk!

First I inspected the ARF tank and compared the neck where the plug/stopped goes to a Sullivan that I am using for the replacement. The neck might be a little longer on the ARF tank, but that ought to help hold the plug in.

Next, I looked at the plugs. I had the ARF plug, the Sullivan plug and I found a replacement plug for a DuBro tank so I have really good coverage of the rubber plug type tanks.
a. Both the Sullivan and DuBro have outer plastic caps that cover the tank neck. The ARF has a flat metal plate.
b. The inside discs are plastic on the Sullivan and DuBro and flat metal on the ARF.
c. The plugs are white soft rubber on the Sullivan, black soft rubber on the DuBro and a harder rubber on the ARF. The ARF plug is slightly longer, about 1/64 inch, probably to match the longer tank neck. The ARF plug also has chamfered edges on the end inside the tank. These might help with installation, but can they also help the plug come out? The Sullivan and DuBro plugs are squeezy soft and the ARF is fairly hard.

I have attached a photo of the tank with the 3 plug sets and one of the rubber plugs showing the height and chamfer.

Tests:

Test 1. I assembled the ARF tank with its own hardware and snuged the screw down like I normally do. Then I tried to shove it out by forcing it to the side with my thumbs. It popped right out! No good. Bear in mind, this is brand new hardware. No fuel has ever been on it so both the plastic and rubber ought to be grabby, at least I would think so.

Test 2. Next, I assembled the Sullivan hardware and put it in the ARF tank, giving it the same tightness as the ARF hardware. I could not force it out, even with a screw driver. Thinking I may have tightened it more than the ARF hardware, I loosened it a couple of twists. I could raise it a little, but could not get it out.

Test 3. The I assembled the DuBru hardware and put it in the ARF tank. I could not get it out. Apparently the softer rubber expands more, locking the stopper in more tightly than the ARF rubber plug.

Test 4. I assembled a stopper using the DuBro rubber plug and the ARF metal hardware. My thought here was the cap type outer covers helped hold the plug in. The flat metal disc was easier to push on, but I could not get the stopper out. It is looking like the rubber plug is the culprit.

Test 5. Finally, I went back and tried the ARF hardware in the Sullivan tank, figuring the shorter neck on the tank might be helping. It was harder getting the slightly longer ARF hardware out, but I could force it out.

Conclusions: The ARF rubber stopper is the problem. It is too hard to expand well enough to hold in the tank neck. The chamefered edges help the plug on the way out.

Recommendation: You could replace the tank, but many ARFs have the tank compartment sized for this flat-sided, long oval style tank. Replace at least the rubber plug with Sullivan or DuBru soft rubber plugs or get a whole new replacement tank hardware set. Tanks are cheap. If the replacement hardware isn't available, buy a new Sullivan or DuBro and use the hardware. $4-$5 is cheap compared to a nose full of fuel.

Ernie Misner

Your tests are great Ed. I just love it when you have too much time on your hands!....:-)

Ernie

JoeAirPort

My Feedback: (41)

Ed thanks for the info. I'm finding out more and more how important the tank setup is on a plane. It can make the engine run like crap in addition to messing it up with glow fuel. Another thing to do is pull on the tube fittings. They should not slide easily if you push or pull them. If they move easy the stopper is not tight enough (or the stopper is too hard in you UCD's case). Giving things a tug is a good test.

Joe

ShempHoward

My Feedback: (3)

My personal experience with a few Hangar 9 ARFs where the tanks came assembled and already installed in the fuse were that they were nearly always improperly assembled at the point of manufacture. Generally the stopper was loose as the screws were not tightened properly resulting in a fuel soaked fuse within a few flights. Fortunately I learned from the first experience and then always checked future ARF pre-assenbled tanks and found the loose screw syndrome in many of them. Once tightened there were no additional problems.

rajul

My Feedback: (58)

Ed, I replaced all my arf tank stopper with Ernst super stoppers. Thay have anti-warp plastic front/back plates that prevent loosening from vibration and the rubber squeezes just right. Quantum carries them.

Thanks for the thorough evaluation. This is very helpful

rajul

My Feedback: (58)

Ed, I found my original UCD rubber stopper in my scrap box, and it is definitely harder than the dubro and ernst. I kept it just in case I needed it for an emergency, but I just threw it away for good just now

JoeAirPort

My Feedback: (41)

Whoever would think that the stopper material would make it not work? I guess I learned something today. So remember to squeeze those stoppers before you install them!!!

Joe