Lord Mounts revisited!
Please see the original post over on our Manilla Slope Fest thread:

http://www.rcgroups.com/forums/showp...postcount=1062

[QUOTE=Jim.Thompson;12247263...
It is running the best it ever has now with both needles fully closed! ...

The elevators are vibrating at an alarming rate and at a large magnitude; I suspect that this is working the servos hard and draining the batteries....[/QUOTE]

IMHO, having to run any engine with both needles closed does not indicate the problem is fixed. Re the servos jittering seems to me to be either a radio issue or that the spark plug cap is not fully seated. Is it? Probably addressed before, but has this engine ever run correctly with the needles set to nominal positions? What have you done since then to make it not run right?

This all just isn't making sense my friend. Indeed, the servos moving that way is not ok, and indicates some sort of a problem with the ignition system, though I can't say that is the only problem you have. That problem may indeed be only the spark plug cap not on tight. You have to push them on very hard. You should also be running a resistor plug just to be safe.

It sure seems odd that you had it running perfectly on the test stand, and now on the plane it won't. That tells you something right there.

I think it is time to offer a case of XXXX Gold to someone familiar with small engines, and hopefully in aircraft applications, to come spend a couple of hours with you sorting it......

Sorry, but we are trying from here the best we can,
AV8TOR

I don't know if this might be helpful, but it's worth a read:

http://www.rcuniverse.com/forum/gas-...rb-issues.html

AV8TOR

There was a problem with some of the big bore piston and cylinder kits for the 660 having the piston skirt touch the counter weight and also some kits the cylinder flange extension would touch bottom of the seat in the crankcase and hold the cylinder mounting flange off the crankcase.

Maybe this is causing vibration?

There have been SO many changes going on with this project it's difficult to determine what are the problems currently?. Any suggestions are at best a guess because of this, AV8TOR is right in my opinion.
My last suggestion is to obtain good local assistance even if payment is required!

I wish you were right this time Av8tor. Unfortunately, the problem is massive vibration. If my video to computer lead was still functional (I am unable to upload videos currently), I would have taken a video and uploaded it for all to see. I will repeat here: the control surfaces were vibrating through approx 15 mm up and 15 mm down, only the elevators. The ailerons, flaps and throttle servos are not fluctuating. The servos were visibly deflecting by around 5 degrees or more each way trying to hold centre. This results in the high current drain and rapid depletion of the batteries.

No, it was never running perfectly. I must have conveyed the wrong impression about this.
Done that. There have been two engineering professionals who have spent up to 3 hours at a time with me working on it on multiple occasions. All stripped and rebuilt under guidance etc.

Despite all that, every single small problem that has been found, I found myself just by perseverance, asking questions here and on the other thread and reading the answers here, such as yours etc.

I dearly wish it was just a case of "take it to an expert" and all will be quickly and easily solved.

Many thanks again for your comments though! I don't wish to appear unappreciative.

Jim.

I will defer any more answers to this thread until after our coming slope flying festival. This is my #1 flying event of my calendar and I want to have a clear head when preparing my fleet of gliders and sharing the company of the many fellow flying friends who will be there.
I should note that I will take the next month or two to review my options. These include looking a proper engine, short listed is a horizonally opposed twin cylinder 120 cc or thereabouts - DA120 or the like.
I am advised this so called boxer configuration is superior in terms of vibration.
Besides, I am aware that I am beginning to ask far too much from others including you respondents.

My twin cylinder (boxer style) engines are so silky smooth it is amazing.

Vibration as severe as you describe is totally unacceptable and may be contributing to your running/tuning problems. Your prop hub may not be true, or your crank may be bent or twisted.

AV8TOR

That is an encouraging report. In the fullness of time, I might be saving up to buy myself one. Would have to assess the size required, possible the 120 cc DA.
The vibration is most severe at idle. When run up mid to high RPM, it is much less severe and almost acceptable. Accordingly, I have concluded that it is not a balance problem. This may be wrong though.

...

Have you checked/double-checked the spark timing? Rough idle and hard starting can often be caused by the timing being off.

Yes, several times.

Klemm maiden successful.
see: http://www.rcgroups.com/forums/newre...e=1&p=35671075

Some pictures here:http://www.rcgroups.com/forums/showp...postcount=1500

Great job Jim!! How about a flight video??

AV8TOR

Here we go Av8tor: http://www.rcgroups.com/forums/showp...postcount=1543

Some description here: http://www.rcgroups.com/forums/showp...&postcount=778

Very nice flying, and very nicely flown airplane. Congratulations.

Sincerely, Richard

Thanks Richard. I wish it was my flying. It was one of our very experienced fellow mode 2 flyers flying it for me. I was nervous beyond all reason and finally crashed the plane at the end. Full story over on the other thread.
Fortunately, the damage is minor and I have already started to repair it. Building and repairing is good therapy for me, as I am competent at that. Makes me move on psychologically from the crushing feeling following the crash and the feeling of incompetence that comes with it.
One of my buddies will fly the plane for towing next year, I am sure.

The Stihl still has an intermittent miss-fire, mainly at high RPM. It can be heard in the flight video here: https://www.youtube.com/watch?v=wwYrNwiMv2I
I have already reduced the spark gap to .5 mm, as with the recommended .6 mm gap, the engine suffered from high RPM spark breakdown and would not take full throttle at all. There are a number of possibilities I can and will explore when I get the time. I will bench mount the engine again and test until I get it sorted. I am not as rushed now that the plane has been inspected, registered and test flown.
Options include:
1. increase the spark gap up to .55 mm.
2. Decrease the spark gap down from the already .5 mm.
3. Change the plug to a hotter/cooler rated one.
4. Change the CH brand CDI --I have a cheaper Pegasus one from HobbyKing.

Beyond that, I don't know what to do. The battery power supply is 6.6 volt LiFe.
Any other suggestions most welcome.

Jim,

Do you encounter miss fire on the stand when you on the ground on the stand?
Try to do the same test and go to 7.4v. This will put more power out of CDI.
It could be 3 things.
1- the High compression of the engine may kill the spark and the spark will jump to ground in the cap or inside. 7.4v should give more voltage.
2- the spark plug style . With exposed Portelan or NOT. Some times this makes a difference. Gap also need to be right. See if you can find the right gap that Sthill recommends for that engine.
3- Carb adjustment, May act different in flight than on the ground. If the metering diaphragm gets bothered by the air around the hole.
Some people solders a little brass tube on the Metering plate and runs a tygon tubing in to the fuselage .
It could get rich, then high compression will make it misfire.

Those will be my thoughts on this issue.

Adrian

From memory, yes. But will confirm later when I bench mount the engine again. It will be some time before I get to it.
I am pleased that it is safe to do so. I have two 18650 cells which will make up 7.2 volts (Lithium Ion 3.6 volt each). So will try them.
..........................................
I am using the spark plug that you recommended.
We don't think it is a carburettor problem, but will not rule out that possibility. This carb is a WJ57 and has a large rectangular atmospheric pressure sensing orifice (for the metering). Still could be vented to inside fuse like you suggest, but would be a bit complicated.
..................................
Thanks Adrian.

edit: The spark gap recommended for this engine is .5 mm. See attached screenshot of the service manual.

Great job Jim. Very nice plane, and great flying. It's neat to see a low wing plane built as a sport plane/tug instead of a high wing. I like it!

In the first video, I thought I heard some occasional rich misfiring, and was going to suggest a one screwdriver width adjustment leaner on both needles and see how it did. However, if you have tuned back and forth and can't get rid of it, then it probably is the ignition. Shot gun it. Replace the ignition, the sensor, and the spark plug, and bypass the ignition switch and run straight from a known good battery. But please, use a new CH or RCEXL, (or RCEXP), and not the Chinese Pegasus.

Great quality ignitions at both of these places:

http://www.rcextremepower.net/rcxpignitions.html

https://www.ch-ignitions.com/product...ns/single-cdi/

Good luck, you'll get it there.

AV8TOR

Just listened/watched the latest video you posted. It is definitely rich on the low end. The high speed miss is questionable. I would still try a new ignition. If it runs fine on the ground from idle to half throttle, but goes rich in the air, then it is pressurized air in the cowl as described by Adrian. You can plug that Stihl rectangular regulator cover vent with something like epoxy, (I use Seal All), then drill and tap it for a fitting and run a vent line into the fuselage. I do this on all my planes.

If you can't get it to run lean enough to not four stroke while flying at low to mid range power, but still give good throttle response, then try a larger prop. It sounds like your prop unloads quite a bite even in a mild dive, which makes me think you have plenty, if not too much pitch. Try going with a larger diameter. It will load the engine harder, possibly help with leaning the low end/mid range out, and give you a thrust boost as well.

AV8TOR

Thanks for the feedback AV8TOR. I particularly favour a neutral power couple that a low wing model is more likely to have. I don't like the plane pitching up when power is applied requiring constant adjustment. The Klemm is neutral in pitch under all power levels.
Actually, we did not get to do this between flights, as we were all so busy and I was quite stressed just from getting the plane there to get it flying. So, it could still be a mixture problem, even though my first suspicion is a ignition breakdown. We were all content to get the flights in that we did. Must sound strange I know! I did not have enough spare neurons available to attend to this.My budget will not run to the purchase of a second CH ignition system; the international shipping charge on top of the cost of the unit is prohibitive. I can afford to buy one, but not two. Besides, I am hopeful that the Chinese Pegasus will at least show up and eliminate the CH ignition system that I have as being faulty. Also, in the unlikely event it does turn out that the CH CDI is at fault, I don't want another one. I am in correspondence with Adrian currently as you will have read. I plan to try running it at 7.2 volts. I am a bit worried about increasing the voltage though, I have to say. I will bench mount the engine as soon as my replacement props arrive. The first one was broken in the crash.
Also, I am watching and reading about a string of Rxcell ignition problems/failures on the Bull BE124 engine thread with some concern.
Your shotgun method is what I will use.
Thanks again.