dabigboy

I have a Webra 35 black head (came with the JR Venture CP). For a while I've had a major running issue. At mid-to-high throttle settings, the engine just "bogs down". Tonight I tried zeroing out the needle valves and starting from scratch....I managed to improve my idle a bit, but the mid/high end issue was as bad as ever.

The engine slows randomly, seems like it might be getting rich but I'm not sure (I usually run it rich enough to keep some smoke going, to spare the engine). I can be holding the heli at a hover, not touch the collective, and suddenly the engine just slows down. Similarly, I can be floundering along at lackluster performance unable to take off, and suddenly the engine will speed up and run smoothly again, for a few seconds.

Back when I had spent a lot of time fiddling with mixture settings, I had it where I could pretty much fly the heli, and the slowdowns would only happen for a second or two...but they were very frequent, sometimes forcing me into a descent and brief touchdown. Tonight I couldn't even keep the engine running well enough for sustained hover. Perhaps more tweaking would have brought me back to only intermittent slowdowns, but obviously I still have a problem.

When the engine slows down, it doesn't really sound like a typical rich engine.....it makes a strange popping, almost a metallic sound. In fact, I thought at first that something was loose in the heli and interfering with the mainshaft or clutch, causing RPM/head speed to drop. But I notice when the engine slows down, the heli yaws right a bit, which indicates to me that it is actually not putting out as much torque. Similarly, I get a bit of nose-left when the engine "recovers" itself.

I did have a couple lean shutdowns when I first got the heli (it came with a hopper tank that wasn't working properly, plus I'm new to glow helis). But once I bypassed the hopper tank and made some more adjustments, the engine ran great for quite a while. Perhaps I damaged something on those lean runs?

I've also tried a couple different fuels, currently I'm running Magnum heli fuel, 20% nitro (oil content not specified on the container...hmmm). I did run 20% plane fuel for a bit because the hobby shop I had access to at the time did not have heli fuel....I think the oil content was either 16% or 18% on that stuff. It ran well (this was before all the trouble started).

Any ideas? I like this engine, and I really can't afford to spend $150++ on a new heli engine of some sort, but I'm not getting any flight time.

Matt

Ernie Misner

That is a ringed engine. I have one too. It might have got hot a time or two and lost the tension in the ring or glazed the cylinder over. If a Webra ring can't be found Frank Bowman probably makes one for it.

Keep us posted, Ernie Misner

earlwb

The European engines are designed to run FAI fuel, no nitromethane, so the compression is higher than normal. Thus a engine like that would exhibit those symptoms you mention when using high nitromethane percentage fuel. You likely need to put on some head shims to lower the compression ratio of the engine so you can run the higher nitro glow fuel. Or you use FAI or max of 5% nitromethane glow fuel. Normally the engines imported into the USA had some extra head shims in the box for this purpose, But gray market engines or engines that have passed through several people may not have the extra head shims with them anymore. You can try some 5% nitro glow fuel or FAI fuel and see if it helps or not, before you pull the engine out of the heli to add the head shims to it.

dogshome

These are very resilient and easy handling engines. Only after several tens of hours or so will they wear out. A new ring gives a new lease of life if it's tired.

Not too powerful though and over-pitching will cause pinking and slow-downs. If it's hot and you were giving it some, they will overheat and cut e.g. multiple loops and pitch reversals.

5 or 10% nitro is good. 20% unnecessary.


You should be running with a good cloud of smoke (more with 20%) and the crankcase should be bearable to touch after landing. it sounds like you are running too lean.

Very easy to strip and check. You should have a nice pop in suction with the plug removed. Also no rust and no play in the crank bearings. The bearings are easily replaced and unless the bore has a lip, a new ring should do the job.

Ernie Misner

This 35 was origionally a heli engine.

dogshome

I guessed-so. I had two in my old Raptor. The first one eventually wore out after a lot of use, it gave-in inverted - sagged - and I didn't have enough height (or experience) to reduce pitch and get the revs up again. Just broken blades and bent spindle from memory. Too much play in the bore and past putting in a new ring. It had been slowly declining, but I never really noticed until then (learning to fly helis). Engine very hot.

I replaced it with the same type and the heli was back to normal power. That second one is in a delta now - the heli got totalled in a mid-air with a plane.


bigboy- the metallic popping sound is likely to be pre-ignition. Running too lean! Not enough revs and too much pitch will do that also. What is your hovering pitch (mid stick pitch)? Worn engine (like I had) is also possible.

You have correct size blades and ~5 degrees hovering and ~9 degrees top pitch (12 in hold) ?

Memory kicking in now, they will run 20 or 30% nitro without complaint - but you should see a very smokey trail then. What muffler or tuned pipe do you have?

Enya no3 or OS 8 plugs are good, but I don't think it was too fussy.

Max_Power

Sounds to me like your headspeed is low. Have you checked it? In a heli once you get to the rpm where the clutch is coupled adding a lot of carb opening may just bog the engine, especially as it adds more load to a already lugging engine. Kinda like putting your car in 5th at 25 mph and putting the petal to the floor. You will get more pull with half the throttle. Set your headspeed first....you should be at speed when you are at just a few degrees of pitch.(+1) Are you sure the heli yaws "Right" by the nose? I'm assuming these are clockwise rotating blades? Usually a yaw like that is the product of highly-pitched main blades and a tail rotor not spinning fast enough to overcome it. Higher RPM will equal less main pitch to hover so less torque, and a faster spinning tail rotor that can more easily overcome the torque and yaw effect. Todd

dabigboy

Wow, thanks for the input guys. You've given me some things to think about. It sounds like my engine is definitely getting too hot: if I touch the carb or backplate right after a run, I will burn my finger in a couple seconds. Some of my airplane engines run almost this hot, so I hadn't thought much of it. Thanks for the input on the popping noise...I've never really had an issue with this on planes (I always err on the side of rich), so I really didn't know what to make of it.

On headspeed: I really don't know what I'm getting because I don't have a tach....I should probably get one. The pitch settings are set per the manual from JR: if memory serves me correctly, it calls for 9* at full pitch and 11* in throttle hold. I will double-check everything (perhaps after lots of hours the pitch has drifted), but since it flew great for several months and I haven't adjusted anything, I kinda suspect the pitch settings are not the issue for now. Yes, it yaws right by the nose/clockwise when the engine slows down. The blades do rotate clockwise. Wouldn't tons of engine torque cause the heli to rotate counter-clockwise? I do notice this if I ramp the collective up too fast (especially before I got my gyro dialed in). It seems as though the engine torque is dropping and this causes the nose to swing right because the tail hasn't "caught up" and reduced its pitch enough yet for the lower torque.

It does sound like from what you all are saying that my engine is running lean. This is strange, after I zeroed out the needle valves, it was rich and I had to gradually lean it out just to get the engine to stay running. I also always get a nice plume of smoke. I think I will give 5% fuel a try. Would regular aircraft fuel be ok?

Matt