Couldn't pass this up: Sukhoi su-31 .40-.46

[19000rpm]

I'd try electrical post terminals with the tubing crimped on and use the post hole as a screw down point.

[Doozer]

Man... the difference in the way it runs is unbelievable. The transition is smooth and without hesitation:



I still have to adjust my throttle servo so I don't need all the trim I had to use, but not tonight. The engine has never felt this smooth and I have to believe it was because of the crappy pipe they try to serve up.  The compression was good. The engine ran like a beast. Oh, and I also changed to a prop nut. I think that looks much better.

[Doozer]

Well hell.... I got to the field, cranked it up and it started missing, I had opened the low needle up some, so I just that that was it. But when I went to lean it out a bit... I noticed air bubbles in the fuel line. I'm not talking one or two bubbles, but more like it was 70/30 fuel/air. It didn't do that yesterday.




So, there are many reasons this can happen:
Fuel line has a hole in it somewhere;
The tank has a hole in it;
The connections were loose;
or, and this is more likely, the pressure/vent line has an issue.

Normally a gas engine doesn't have a pressurized tank because the carbs have pumps, but the carb on this engine does not. After reading many posts and a few forums on the subject, I went to the LHS and picked up new Viton and Tygon and a new 8 oz tank. I can always use the fuel line on my next project so no biggie. I'm starting with the pressure line. If I'm still getting air, I'm replacing the tank. Hopefully its the first thing I replace, but we all know it doesn't work like that. If I don't get this worked out in the next couple of days, I'll put the Sukhoi on the back burner, and start building the Gee Bee.

[akphill]

Change the clunk line inside the tank
Probably has a crack in it next to the out fitting

[Doozer]

After a pressure line change:


I tried to talk over the noise of the engine, didn't work out so well. Basically you can see the bubbles coming from the tank (the line coming from the hole into the fuse) and then into the carb (the line coming from the fuse into the carb; with filter attached). When the I throttle down, the bubbles went away. You could see the air go into the carb, then the RPM's would increase. I'm giving the sponges a try in an hour or so. Well see what happens.

[akphill]

I still think the clunk line needs changing inside the tank or where it comes out of the tank

[Doozer]

Dec 18, 2013 16:40:10 GMT -6 akphill said:

I still think the clunk line needs changing inside the tank or where it comes out of the tank

Can't phil. It's solid one piece. This is the gas tank:
www.jlproducts.net/ProductRotoFlow.html

[Doozer]

I've been messing with this thing the entire day, and I was about ready to rip it all apart, install a new gas tank, line, and a quick fire (fuel balancer/filter)... Then it just popped into my head... "what if it's the Coleman?" I thought "Nah... couldn't be, I had it in the air running on Coleman." But then I thought... it wasn't in the air long. So I said screw it, it's only a couple of bucks and I went and picked up a gallon of 92 (Circle K) for $3.40 and brought it home. Well, I really hate to admit this... but it was the Coleman fuel. It might work ok in the bigger DLE engines, but this little engine hates it. The engine smoothed right out, the bubbles went away and I found the sweet spot on the low needle within minutes.

So.... I'm going to finish out my coleman on my bigger planes. Then its no less than 87 from the pump from now on. I would like to find someone willing to throw some LL100 in a gas can, but I've been told that's a no can do around here... but then again, that was by the guy at my LHS. So, maybe I can find someone willing to give me a break.

I've capped the carb, stuffed paper towels in the muffler tubes and lit some Nag Champa (incense). So far, I only smell the incense, but if stazt mzpseliling ym wezd.....

[Doozer]

I've decided to give up on the hunt for 100LL. I guess you can get it if you know somebody, but if you're just some Joe Blow off the street... no can do... unless of course, you have an airplane. Try to fill up with a gas can... they don't like that. Anyway, I did research on it, and it found out it's really only 96 octane. So, I'll deal with the smell, but to be honest, the smell isn't that bad if you just store it inside. It's when I work on the engine that I'll have to do that outside, and in the winter (not working outside in the summer in Phoenix). I doubt I'll fly during the summer anyway.

It rained most of the day yesterday and through the night, but the clouds are starting to break and I see some sunshine. I'm going to try and get the Sukhoi in the air today if the weather holds up.

[19000rpm]

Good luck with the weather and the flight.

[Doozer]

Dec 21, 2013 6:46:53 GMT -6 19000rpm said:

Good luck with the weather and the flight.

Thanks man. It didn't work out yesterday, but I'm going to try again today. I'm feeling really good about the engine (knocks on wood). I'm going to take out the Cermark Gee Bee too. My oldest son is going to go with me so hopefully I can get him to video (he likes to run out there). I've been eyeballing a Go Pro with the head thinger so I don't have to keep bugging these guys.

If all goes well, I'll start roughing up the covering and give the planes a new look.

[Doozer]

I didn't have a camera man with me because everyone was last minute Christmas shopping :/ , but I am smitten. What a fun plane and a great little engine. I flew through two to tanks each was 20 minutes. I measured and fueled 8oz each time and had an ounce left after each run. I wasn't exactly flying WOT the whole time, but I'd say at least 15 minutes of each run.

The only thing that I could say that I didn't expect, and was kinda/sorta bummed about, was that even though it's has a barrel carburetor like a glow engine, the throttle response is NOT linear. So I'll need to set throttle curves instead of using default (linear) I got to 13K RPMs at half stick. I'm still spinning the 10X6 prop, but I'm propping up to 11X6 next run. I'll probably try the standard 0,10,15,20,25,30,100 to start. I mean its really not that big of a deal, but would have been nice to just gas and go.

Other than that and the gas smell, I had fun. It was extremely satisfying. I'll just take baby wipes to the field to get the gas smell off my hands.

[19000rpm]

Sounds like a great flying day in the Valley of the Sun!

[Doozer]

Ran out of gas against the wind

Fuse and left wing toast, no other damage. I changed my throttle linkage trying to get a more linear response, so I fooled with it on the ground and ran it for a while.  I should have just refilled the tank, but I was being lazy. Kept my timer @ 15 minutes, it ran out of fuel @ 6 minutes.  The wind was blowing it around.  Couldn't save it before this tree got it.

[19000rpm]

Most of my errors can be easily attributed to "pilot laziness" or inattentiveness. Thank god they don't let me ferry people around in a full size.