Fussy little details!

I think everyone should have a rigid automaton-like ritual for going flying. Being human, I often do not live up to my beliefs.

I'm flying a Tower 40 glow side mounted with a 3 oz flat tank centered on the engine. The tank has an upper front corner overflow, and the muffler line connects to the unifow a ways back on the top of the tank. I fill the tank through the uniflow. THEN my ritual is to replace the overflow cap. When I do this, a drop or two of fuel squirts out the uniflow tube. I then hook up the muffler line to the uniflow, Choke the engine a couple times, fire it up and go fly.

Today a friend was helping me, and fitting the tubes back on the tank after filling. I didn't pay much (enough) attention. I got a couple of short flights. Mext flight, my friend commented on fuel running out of the muffler. I then realized what was happening. We were attaching the muffler line on first, then putting on the overflow cap. This started fuel siphoning through the uniflow into the muffler. We were loosing an ounce of fuel or more each time.

Point is, I had recognized this as a problem, and developed a ritual to deal with it. As soon as I deviated from the ritual, bad things occurred. Fortunately, I recognized that the engine was running out of fuel before it should and had no problem saving the airplane each time.

Love them rituals!

Rituals, I sacrifice a small goat, but I can see where just swappin the lines might be easier.

Thanks for the tip!!!

Thanks to a tip from Marvin Denny at a recent contest I now plug all tubes (except the feed tube, kinda hard to get to that one ) until I am on the line ready to start. This keeps all the fuel where it is suppose to be, in the tank.....

On a uniflow tank, filled, I plug the uniflow vent tube to keep the fuel from evaporating and crap out of the tank. At one contest, my pit man launched the plane and it flew ok, but when it landed we noticed the plug was still on the uniflow vent!!! BUT, the overflow tube had fallen out of the tank!! Really strange things happen at contests.

On our "Das Ugly Stunter" design, we plumbed the tank so that both the uniflow and overflow tube came out straight up behind the upright mounted engine. We used muffler pressure, and when filling would unplug the overflow and move the tube from the muffler to the overflow tube. Then we would fill the tank until we saw the fuel coming out of the overflow up the tubing. We could usually stop filling before any got to the muffler, but if a little got in the muffler, no problem. It really worked great. There was no spilling, and as soon as we got done filling, we would move the tubes back. No forgetting, either.

>Thanks to a tip from Marvin Denny at a recent contest I now plug all tubes (except the feed tube, kinda hard to get to that one ) until I am on the line ready to start. This keeps all the fuel where it is suppose to be, in the tank

But if it sits in the sun for a while waiting your turn does the fuel in the tank load the venturi? I suppose a solution would be to clamp the fuel feed line if you can get to it.

I usually wind up capping the wrong tube or no cap at all at least once a day anyhow. Sometimes the runs are OK if you cap the uniflow tube, but usually not.

Jim, I have fueled up as many as three flights before my turn, and never had any flooding. I have watched for fuel dripping from the venturi or cowling and never found any. That is in the high heat of Wichita, Dallas, and OK City. I guess that balsa wood is a pretty good insulator from heat. I imagine that if you fueled a couple of hours prior to flight you could lose some fuel from evaporation and expansion. I try to get fueled up about the time the flight before mine is in the hour glass. This procedure is for both my upright (All American Sr and T-Bird I) as well as my inverted engine installations (Nove I, III, IV, and Nobler). My theory is, if air cannot get into the tank, the fuel cannot get out. My BIG problem is forgetting to remove the uniflow cap.

Jim,
A similar thing happened to me at Brodak's a few years ago. I would start the engine, make it to the handle and then it would die. My launcher tried to save it by tilting the airplane up, but didn't make it (chicken hopper style tank). I restarted and made it back to handle and it died again. This time I called an attempt (hard to believe for a beginner at the time) and then figured out that the fuel was dumping to the pickup level through the uniflow vent which was routed to the muffler. Since then, I have been very careful to not let that happen again.

You are right that maintaining a specific routine can be very important. I try to keep things the same in practice as I would during a contest. The other guys I fly with do the same. Keeps those little surprise to a minimum.

This applies to safety as well. A few years back I tried to remove my left thumb with a 3 blade Bolly and a Stalker .51, I attribute it to fatigue. Had to get the last flight in and I tached and needled from in front of the model instead of the side as I normally do. The tach said 8200 steady and I pulled my left hand from the needle through the prop. The rest they say is history.

I've determined that I will stop flying as soon as I hear myself saying "one more flight" like "one-for-the-road".

Develop your routine and practice it consistantly.

We ran into a similar problem when a friend was helping my son Mikey with his old style OS 25 powered Ringmaster. I had forgotten to trim the back of the Taipan prop, the trailing edges of which actually extend behind the thrust face maybe 3/8 inch near the hub. These old style plain bearing engines have the venturi very close to the front. Bill cut himself while adjusting the needle as he was used to other style engines with a longer nose. All in what you are used to. I really felt bad because it was my fault for not being better prepared and because I should have been the one doing the tuning, not that I know anything about CL stunt. I have been bit enough times with these engines on my ignition free flights to know to keep my fingers back.

BTW, are Taipan props still available? The 9-6 seems to work really well for us on the 25. 9-4 too fast, 10-4 too slow, 10-6 too much meat.

John in the PRC

Hi John,

Joe Just AKA Big Country Joe has Taipans from time to time.

I fly FF as well OT and AMA, some of those timer arms were really hard to get to.

>BTW, are Taipan props still available? The 9-6 seems to work really
>well for us on the 25. 9-4 too fast, 10-4 too slow, 10-6 too much
>meat.
>
I never thought that the older OS 25's were "too fast" with 9-4's. Those were my usual for that engine (although not Taipans when I was using that one a lot). A 9-6 made it bog too much in maneuvers, and the prop it was really fast on was an 8-6.

Taipans can be purchased, although they aren't widely available, and only the stiffer, glass-filled composition variety, are imported now.

.
Kiwi

LAST EDITED ON Jul-18-03 AT 10:06 PM (CDT)
 
>BTW, are Taipan props still available?

Try this link:

http://www.hobbyclub.com/framespage.htm

Look under Products and then Accessories. Scroll down to Taipan.I get good service from Alberto, and as many props as we break, the low prices are welcome.

LAST EDITED ON Jul-18-03 AT 03:10 PM (CDT)
 
Anyone who believes that you can get useful pressure out of a device with a big hole in the back of it NEEDS a few rituals. At least the fuel flowing into the muffler stopped the water (burn a gallon of fuel and you get a gallon of water) going the other way.
Come to think of it, if the muffler WAS supplying pressure, how DID the fuel get into the muffler?

Dave, I couldn't agree with you less. To clarify my initial post, the fuel was siphoning out of the tank, to the muffler @ 2 in below, before the engine started. Once the engine started, the muffler pressure was adequate to stop the siphoning and push the fuel back into the tank. Actually not a whole lot more than that. From figures which have been brought up again and again on this board, mufflers furnish pressure equal to about 1/4-1/3 of the pressure necessary to move the fuel into the engine at the spraybar.

An interesting experiment would be to hook the muffler line to the overflow and leave the uniflow uncapped, start the engine and see how far fuel squirts out the uniflow.

Complete oxidation of a gallon of methanol may well produce a gallon of water. Aren't there 4 H's associated with a methanonl molecule? Plus also a bunch of carbon dioxide, of course. My chemistry book is still packed away.

Jim,
Sorry if my humour gets a little distorted at times. I used to have a running battle with the R/C heli people who were determined to use muffler pressure despite the fact that they couldn't make it work due to oil and water contaminating the tank.

This is interesting to think about. Here we are, bubbling hot exhaust gasses, including considerable water vapor, into the tank with muffler pressure. So far as I know no one in the stunt community has given it even a passing thought until you brought it up. This suggests that the effects are so subtile we have not noticed them. This is not to say anything about helicopters, of which I know nothing. But stunt seems to be a different story. I do notice several drops of oil in the muffler when the flight is over.

Stunt models don't use 10 -16 ounce tanks and 25 minute motor runs. Most of the heli people have found that the placement of the pressure nipple on the muffler is critical. They also tend to fit a filter in the pressure line.