justinjames09

Hi Guys,

I have a alpha 40 rtf, after the first few flight i notice the engine will lag when at about half throttle. it doesent do it at the first of the flight, just about when the plane gets to half tank. the engine doesnt actually quit just sounds like its going to, i dont give it a chance i just bring it in.
was wondering if its ust a tuning issue. no changes have been made to the settings from stock. any ideas would be much appreciated.

Thanks

Mr67Stang

It is very likely a tunning issue. Unfortunately we can't tell which way you need to go with what you've said. If it's to lean (not enough fuel), the engine will start to get too hot and do what you describe and if it's to rich (too much fuel) it will do what you describe.

At a safe altidude and location that you can perform a dead stick landing from when the engine is lagging, smoothly yet somewhat quickly advance the throttle to full. Observe your exhaust. If you get a more than normal amount of smoke and probably a sputter... it's to rich (turn your needle in, clockwise, two clicks and retest). If it dies without any smoke, it's likely to lean (turn your needle out, counter clockwise 2 clicks and retest).

Aditionally, what does your plane look like after you land. Is it absolutely covered in oil? Is it as dry as a bone in the desert? Do you have a constant yet faint smoke trail behind your plane when flying at higher to full throttle settings? At mid throttle, it is hard to see the smoke.

jetmech05

It is so hard to tell you how to tune an engine..easy to show you. As said above we don't know which way to go, rich or lean. With a new engine and a few flights on it I'll bet you need to tune it. Is there a club near by you can go to for help.

justinjames09

thanks for your post, the plane has oil on the wings and fuse after landing, i know that on the ground i cant go from idle to full open without going very slowly or it will sputter and die.

jester_s1

You likely have a tuning issue given that the plane can't go from idle to full throttle quickly, but the symptom you're describing sounds to me like a tank issue. If the plane flies fine until it gets to half a tank, it's most likely that the fuel line has come loose inside your tank. Either that or it has a split in it that lets it leak air once it's not submerged in fuel anymore.

For your advancing the throttle issue, get the high end set properly which means a 300-400 rpm rich. If you're using the pinch test that will be a barely perceptible increase in rpm when you pinch the line. Then go to idle, and listen for about 30 seconds. If the RPM drops over time, you're too rich. It it increases or the engine suddenly dies at some point, you're too lean. Get that right then recheck that you're still slightly rich on the top. These will give you a preliminary setting that will be close, but may not be exactly right. The next step is to see how the engine behaves when you slam open the throttle. Sputtering indicates that the idle is too rich, while hesitating indicates that it is too lean. Adjust accordingly. Then do the same test the other way- run the engine wide open for 10 seconds and slam the throttle closed. If it dies you're either too lean on the idle or you have your idle set too low. The last test is to check the mix with the nose pointed up. Have the engine at full throttle and hold the plane up. You should hear a slight RPM increase and the engine should hold that increase for 10 seconds or so. If it goes up and then back down you're too lean on the top. Tweak the needle until it does that, then go richer by one click at a time until it holds the rpm increase. Go ahead while you're at it and drop the throttle closed after that 10 second run to see if the engine will die after the lean nose up run. If it does, you need either a richer low end or a higher idle setting.

If you go through all of that, you should get 100% reliability of the engine in all maneuvers and never have to worry about a lean run. Keep a mental note of how the engine reacts to the pinch test after you're all done so you can replicate that same top end mix when the weather at the field is different. If you're inclined to invest in the hobby a bit, a tachometer is a really valuable tool for learning to tune engines. It takes the guess work out of the rpms your getting, letting you repeat your adjustments more precisely. Over time your ear will get tuned to RPM changes so you won't need the tach as much, but even then it's really helpful with a problem engine to be able to put numbers to what you are doing.

Mr67Stang

An oily plane is the norm with glow power so you are most likely safe. Never try to tune it so you do not get oil out of the exhaust. You will be buying a new engine shortly there after. You can lean it a click or two at a time. Unfortunately it is a slow process. Once you get the hang of it and learn the engines you will be able to tune it on the ground. As stated, it is complex to describe it in words and is best done in person. If you needed to tune the "low end" it would have to be done in person as it is far more sensitive.

Do not try to get peak RPM out of it. Just lean it a bit and run the throttle up on it. Repeat the process untill you get a reasonable transition from idle to full throttle. After you get a few engines in your squadron then you can learn to peak an engine.

Luchnia

My Feedback: (21)

Do you have an RC guys in the area that can assist? Maybe a local club? Most groups have someone that is good with the engines or can at least give you some help in getting it going.

jester_s1

If he follows the procedure I gave him he can get max power out of the engine without any worry of damaging it. That's of course assuming the engine is fully run in and in good condition.

justinjames09

thanks for the help guys, i have a few guys who are helping me. the engine is brand new only 3 flights or so, i was thinking it wasnt tuned from the start. i will try your procedure later jester.

rgm762

My Feedback: (4)

our club has one of these that we use as a club trainer, you'll want to get somebody that has expereience with the PTS trainer engine, it has some funny little tricks to it. might try looking in the glow engine forums for some more advice


http://www.rcuniverse.com/forum/m_67...tm.htm#6814279

jester_s1

Glad to help. For a new engine, adjust the "slight rpm increase" with "significant rpm increase" and you'll do fine. Low end tuning on a new engine is pretty much the same, but it's a total waste of time trying to get a perfect idle mix when the engine is still too tight to idle right anyway. At whatever idle speed it will be reliable at though, the same set of tests apply.

Avistarpilot

One way I tune(and probably many others) is after the engine is completely up to temp take it to full throttle. Usually at the "factory recommended" needle setting it is going to be very rich. Close the needle valve a few clicks at a time until you hear a pitch change at WOT. After you do this step a few times take it to idle and check the transition between idle to full throttle. Another trick I do is take a needle nose pliers and with the engine at full throttle, pinch the fuel line for a split second. If you hear a slight RPM rise you know your still safetly rich and can fine tune from there if need be. If it cuts out or there is no RPM change you are lean. I'm pretty sure my .40 LA is slobbery rich but it still runs great and pulls my plane around just fine so I'm leaving it alone.

koastrc

Set up a Alpha this week. It was the Already to fly version. The engine was very rich. After a tank of fuel I studied the set up. The high and low side needles are pre set and have stops. To make the engine run I had to defeat the high side stop. The young man was a bit upset because he figured the thing was ready to fly. No big deal for those that have been around. Other than that little deal the plane is a great deal. I think the plane is as good way to start out, but with help. The Alpha is a good flyer. I would recommend it any version. The Evolution is a find engine if treated right. Like all things in this hobby/sport, it is a time to learn and that time never ends. So to any beginners I say learning is part of aviation. I learn something every trip to the field. Been doing this for a long time. Have fun.