Electronic Ignition

Share your thoughts, photos and general help to all builders

Postby Shannon » Mon Apr 20, 2009 7:29 am

Hi Pete,

I've never set the idle on engines that low. We have always used the basic set-up techniques outlined in the old Wajax Pacific (now Wildfire Equipment) Mark 3 portable fire pump manual along with advice given by Peter Corley himself and "Regs" engine service. At one point Reg's was doing a good bit of Lazair engine rebuilding. Some of Reg's engine advice is here in the files section if you haven't already read it.

I would be really careful about any departure from "normal" tuning methods with the engines. I have an idea that low idling engines could be prone to stalling out. There is also some indication that "de-tuning" the low speed setting (and subsequent H adjustments) could shorten engine life as well as make the engines less responsive and reliable. Through the years a lot of guys have got into a lot of trouble by simply doing things a little different than what has proven to work. Just a simple thing like running a bit too much oil can cause problems for example. I've seen very low time engines with hung up carbon fouled rings. The engines ran terrible and were basically brand new.

The amount of thrust generated by engines idling 1900-2000rpms is probably not enough to affect landing distance by any important margin. If it is then the landing area is probably too short for a Lazair regardless of engine idle speed.

I would say that's it fairly unusual for you to be getting well over 6,000 with a standard bore Bi-prop equipped engine. I highly suspect improper mixture assisting the engine to achieve that rpm. You very well may be saving the engine damage to bring the adjustments back in line with what the manual advises. The other slow turning engine may very well be out of timing to only turn up 5600. That engine needs some attention. As you mention normally 5800-5900 is what the engines in good condition are going to produce with Bi-props. Cruise power settings with the 185s/Bi-props are going to be a bit higher than with the Powerbees.
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Postby peter » Mon Apr 20, 2009 9:18 am

Thanks Shannon for putting me strait on the idleing issue...I just never read or heard,...just always assumed, I guess, that the idle speed should be lower....man, that makes me feel better now that I know, thanks to you guys.
I weighed the plane to see the difference between tedlar and fabric ..stits on mine I understand..and it appears to be about 226 lbs....that was stock with wheel pants and with a quarter tank of gas....I also for fun, rigged up the bathroom scales on the tail boom and on gravelly type ground and me..160lbs..and a softish tire it pulled about 95 lbs....the tail wasn't up to flight attitude either....I wanted to check the c of g too ...hang the plane from the boom of my front end loader...but it was too windy....likely ok but just wanted to be sure
Thanks again.....Pete
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Postby JPXman » Mon Apr 20, 2009 1:43 pm

peter

you'd be surprised of the difference from one prop to another.......if you feel like turning some nuts, swap props between the two engines and tune them again and see if the other engine spins up past 6000. if it does, then you need to find a set of bi-props with a little more bite as then it would seem they are too easy for the engine to turn.

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Postby Chappy » Mon Apr 20, 2009 3:11 pm

Peter,

What Tyler says is very true. If you have some well used props on one engine, and some never used on the other. The plastic props get "soft" with lots of use and loose a little bit of "bite". Also, for a short time Ultraflight produced some props made from a different material (Rynite) that was somewhat stiffer than the nylon based ones usually supplied. It produced a prop with a noticeably better thrust (the mold used was the same). If you have a couple of these on one side and the normal prop on the other, you will see a difference in prop loading. The Rynite props look very similar, but when new you could see just enough difference to tell them apart. I would suggest looking at them closely for a slight difference in color and texture. Also, grip a tip and see how much force it takes to deflect it. The Rynite props are noticeably harder to flex. Please be aware that Ultraflight discontinued the Rynite props and returned to the nylon based ones due to a failure rate of around 1% with the Rynite props. But there are probably a bunch of the Rynite ones out there because they did give a little better climb rate and cruise speeds.

There was also an adjustable pitch prop produced by Ultraflight for an extremely short time that had blade failures, but almost none of them got to customers. Getting them back out of the grips of dealers, on the other hand, proved to be a challenge, as the GA props provided a very good boost in performance on the 185's. Dealers had to be threatened with revocation of their dealership agreements to get their return to the factory. A design shortcoming, coupled with poor machining tolerances of the hubs and prop blades, and injection equipment that was borderline capacity all contributed to blade failures right at the hub clamp attachment. Loosing a blade usually meant failure of all the Lord engine mounts. Luckily, no lift struts or pilots were ever severed, but it could have happened!

Also, be aware that with conventional wooden props from different manufacturers with the same specs or markings in pitch, they may not (usually will not) have identical loading and performance. Sometimes, the difference is rather large. Also, wooden props with wide, heavy blades are very hard on the Rotax 185's crankshafts. Later Rotax cranks have a modification that makes them less likely to fail, but if using a wood prop, the Prince P Tip is a good choice as it has lighter blades (and it's a great design too).

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Postby Shannon » Mon Apr 20, 2009 7:59 pm

peter @ Apr 20 2009, 09:18 AM wrote: Thanks Shannon for putting me strait on the idleing issue...I just never read or heard,...just always assumed, I guess, that the idle speed should be lower....man, that makes me feel better now that I know, thanks to you guys.
     I weighed the plane to see the difference between tedlar and fabric ..stits on mine I understand..and it appears to be about 226 lbs....that was stock with wheel pants and with a quarter tank of gas....I also for fun, rigged up the bathroom scales on the tail boom and on gravelly type ground and me..160lbs..and a softish tire it pulled about 95 lbs....the tail wasn't up to flight attitude either....I wanted to check the c of g too ...hang the plane from the boom of my front end loader...but it was too windy....likely ok but just wanted to be sure
     Thanks again.....Pete


Hi Pete, absolutely no problem. Glad to provide you with the information. The good thing is the info is basically straight out the Wajax and Ultraflight assembly manuals so nobody has to take my word for it ! Haa haa !

Several things I think have helped confuse people over the years when it comes to proper idle and tuning on the 185s. The Ultraflight assembly itself states 1000rpm as the desired idle. That is clearly a misprint as it should say 2000rpm. Second there is a obscure reference in some HL carb information that references 1400rpm when the carbs are used on chainsaws or lawnmower engines.

The key thing to remember is this and it's stated in the Series III assembly manual in the "Operating Manual" section. The (L) low speed mixture adjustment controls mixture from 20 to 80% power. When you read this you realize how important it is to have the (L) adjustment set properly. I think some people have the misconception that the (H) adjustment is the most critical adjustment on the carbs. During tuning operations you first get the critical (L) adjustment correct THEN you concentrate on dialing in (H) adjustment. Bottom line is if you must have (L) set correctly first to get (H) tuned in correctly next.

I have scanned the carb tuning page from the assembly manual for your review. Notice the carb tuning instructions are right in line with the information from the Wajax manual.

One thing I wanted to ask is if you were given any history on the engines i.e. last rebuild (if ever), hours on engines, last ring job, have they been bored oversize ?
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Postby peter » Wed Apr 22, 2009 9:35 pm

Tyler...I was wondering too if the rpm difference was in the props, so at your prompting I switched, but there is no change...now I'm wondering if perhaps the seals are leaking....but my motor guy tested them and says they are ok though....When we had the heads and cylinders off in the winter there was no wear at all on the walls and not even enough carbon buildup to require removing....this led us to believe their time was quite low.....I don't recall if I asked Frank specifically about the engines, but my impression was that they are in good condition....no logs or records unfortunatly....It could be as Shannon wondered maybe the one engine was rebored.....You know, there is another thing that has me thinking, and that is the tiny tack itself...It comes up to mid 5000's and then quite quickly gets into the 6000's....I've seen it come close to 7000 when we were tuning the carbs the other day...the engine just doesn't sound like it increases by that much....anyways I'm going to switch tacks tomorrow to see if the difference lies there....It's kind of perplexing......I'll keep you posted
Pete
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Postby Chappy » Wed Apr 22, 2009 10:09 pm

Peter,

I can't remember if this was mentioned, but if the carbs haven’t been rebuilt in a couple years, that might be the problem. The diaphragms get stiff and they can't pump enough gas and mixture adjustment becomes a problem. If you have compression releases, you might have one leaking and perhaps ready to fail. Compare the sparks between the engines. If the weaker engine's spark isn't as "hot" (they should be nice and blue, not wimpy), suspect the condenser. Lots have gone bad. Hard starting (even no starting) and high speed miss result. Head gaskets should not be reused and should only be re-torqued once . Repeatedly re-torquing them can result in cracked heads.

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Postby gdewsbury » Wed Apr 22, 2009 10:33 pm

Peter

I had a tiny tac that seemed to fluctuate sometimes.
Turned out to be a frayed wire at the capacitor connection.
A broken or frayed wire can generate extra radio noise affecting the tac.
Eventually the wire broke and when replaced the tac stopped acting erratic.
Something to check for in the ignition wiring and tac leads.
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Postby JPXman » Thu Apr 23, 2009 2:11 pm

one thing i've overlooked when tuning an engine at WOT (wide open throttle) is the actual control wire. i couldn't figure out why the rpms weren't high at WOT, and after tuning for what seemed like hours, i bumped something while running it and noticed play in the wire - the wire wasn't pulling the carb lever all the way.

so as a final check, take your finger if you can and pull all the way on that carb lever to see if your cable isn't pulling all the way.

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Postby Don » Thu Apr 23, 2009 4:46 pm

Hi Pete,
I start this thead using the Nova modules. In my installation I removed the lighting coil and condenser to mount the module under the flywheel. I also bought a new Tiny Tach and had the same experience as you with the fluxuating readings. I ended up using a hand held to get 5700 rpm's with bi-props. I wondered if there were extra mangets on the flywheel for both balance and auxilary power. With the point system in place the extra electrical pulse wouldn't matter until they initiated the spark. But the electronic might send another pulse when the second set of magnets went past the coil. Just my thought.
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