Twisted Sticks September 2007 Ne

Twisted Sticks September 2007 Newsletter

Hope everybody had a fine Labor Day Weekend.

Well you couldn’t ask for better weather at the beginning of the month or worse these last few weeks. The old saying still holds true if you don’t like the weather in West Michigan, wait a while and it’ll change. Labor day weekend sure looked fine though. Sorry I wasn’t able to make it to the field. My personal life is still undergoing changes – enough said on that.

New members.

Welcome to Jim Wilcox. If I’ve missed a new member please e-mail me and I’ll mention you in the next newsletter. You guys are important to us as you fuel the growth of the club. If anyone wants to email a little about themselves especially their interests and how they got started in the club it would make for some interesting reading and sever to introduce you to the rest of your club mates.

Writer’s Block.

Well guys this letter’s late simply because I could not figure out what to write about. I think in the three years I’ve been writing this I’ve gotten responses from less than five people. It doesn’t make it easy when no one else contributes. You’d think someone would like to publish their new pride and joy or e-mail me the latest dirt on who crashed – it just doesn’t seem to happen. So I thought we would discuss fuel tanks. J

Fuel Tanks.

Height of the tank to carburetor.

The center of the tank should be mounted in line with the spray bar in the carburetor. The spray bar is the bar on the inside of the carb that the needle valve adjusts into or if you have a remote valve it has the fuel line attached to it.

Adjusting the mounting of your fuel tank to the center line will put you at the least risk of; a lean situation or flooding the engine when it is just sitting there, waiting for your turn.

A lot of ARFs simply have their tanks mounted too high. A link to a discussion on RCU

If you mount the engine inverted, I’d strongly suggest lowering the fuel tank so the center of the tank (not the stopper assembly) is slightly below the spray bar. Doing this will prevent fuel from siphoning into the engine and flooding it when the fuel tank is full or dribbling on the setup bench draining the tank. J

If the tank center-line is at the carburetor jet level and you adjust your engine to run a bit rich with the tank half full, your engine will be a bit richer as the tank is full, but will never be lean, even if the engine is run until the tank is near empty.

NOTICE adjusting your engine with a half full fuel tank will prevent it from leaning out when it is near empty. I never have the problem cause the longest I fly is 7 minutes, but I am guilty of adjusting the needles on a full fuel tank. J

A uniflow system uses three lines and will maintain a nearly constant mixture unlike the normal system. A normal system uses a fixed bent pipe mounted so that the outlet is close to the top of the tank. This is then connected to the exhaust nipple. On a uniflow system the muffler nipple is connected to an additional clunk so the exhaust pressure is always under the fuel. The second line uses clunk connected to the carburetor as is normal. The third line is the vent and goes to the top of the tank. It is plugged during flight and unplugged to refuel. You can use either clunk line to fuel the plane. I know it sounds like it shouldn’t work but it does. Here is a link to provide a better understanding. http://www.fraserker.com/heli/uniflow/how_uniflow_works.htm

Tightening the stopper. Don’t be Hercules tighten only so far as to prevent leaking. The tubes can still turn in the stopper and the tank won’t leak. Test it under water by plugging all the lines except the one you blow through while looking for air bubbles.

Bubbles in your fuel can be caused from the tank vibrating against the air frame or a leak in the fuel tubing. If you are building an ARF which doesn’t allow you to use foam padding make sure the tank is fixed against the frame or modify the tank area and use foam padding. Bubbles will cause your mixture to go lean resulting in dead sticks.
1. A couple of drops of Armour All in a gallon of fuel will act as a de-foaming agent reducing bubbles. The down side is that you will get less plug life as it contaminates the glow plug. Barry has used this successfully.
2. A Tetra fuel tank collapses as the fuel is used.
3. Some claim a sintered metal fuel clunk will reduce bubbles. OS makes one. http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXXF25&P=ML as does Dubro for a lot cheaper http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXD741&P=SM

Clunks need to be free to move inside the tank but as close to the rear wall as possible without touching. There was a lot of controversy on RCU about where the fuel in a tank went on a down line, was it to the front or the rear? A member put a tank outside the airplane and videoed it. It goes to the front. Most clunks are not flexible enough to bend toward the front of the fuel tank in these circumstances. So why don’t you run out of fuel? Because the time it takes to auger your plane into the ground is usually longer than the time it takes to run out of fuel left in the lines.