CDI Ignitions

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Postby pittsnut » Sun Jan 29, 2006 9:48 pm

One more pic

Dale
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Postby lazair3ca » Tue Jan 31, 2006 9:59 am

Shannon,

What static RPM did you have on the engine with bi-props?

The instructions for the CDI mention setting the timing for 0.147" BTDC at 3000 t0 4000 RPM.

I think you should have a solid 5700 to 5800 RPM before adding the P-Tips. What is your recommendation? Will the P-Tips help if you only get 5200 RPM with the bi-props?

My engines are running fine but we are working on another pair.

Cheers,
Bill
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Postby pittsnut » Tue Jan 31, 2006 5:08 pm

Hey Shannon,

O' yes, the carbon "P" tips do look nice, they work well too. Looks like they are turning up good rpms, need to adjust the engines a bit, my 2 do not work exactly the same, within 100 rpms, they run around 4900.

Thanks for the great pics.

Later

Dale
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Postby lazair3ca » Wed Feb 01, 2006 6:03 am

Shannon,

I have been adjusting the idle down to 2000 RPM. The engines just seem to run smoother with the CDI. It may be just perception but I think the vibration is less. I have adjusted the carbs in the past by ear but now we both have tachs so we can see what is happening.

One engine runs a little faster (10%) than the other. So we have been looking at the slow one. Cleaning the muffler, checking the timing, de-carboning it. We noticed a little blow-by on the piston which may be due to wear.

This engine sounds like it has a megaphone attached at bout 4600 RPM. It does not have a tuned pipe. George is checking the props now. The front prop of biblades has more pitch at the tip than the one behind. So George will chang ethe prop and try it again later today.

Thanks for your support.
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Postby Shannon » Wed Feb 01, 2006 11:29 am

Keep after it and you will discover the source(s) of the problem.

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Postby rayjb60 » Wed Feb 01, 2006 4:46 pm

Hi Shannon,

About the lower idle with CDI.

Whats happening is that with the points system, the strength of the spark is a function of the rotor speed......slower speed equal weaker spark to some degree.

I have actually seen the difference with the plugs out and pulling the engine over.

The spark was small and weak.

Once I switched to CDI the spark is as strong at idle as at full speed....again with the plugs off and pulling the engine over like before I got a big strong spark.....it was a huge difference and very easy to see....I wish I'd mpeg'd it so you guys could see what Im talking about.

So since the spark is so energetic at low speed you get a reliable ignition at slower speeds as well when the points version would start to sputter and stop.

Because of that you can simply reduce the low end limit screw and mixture screw to reduce your rpms to what ever you feel comfortable with.

In fact I noticed that when I throttle down to idle for landing approach, the prop acts noticibly like an airbrake and brings you down at a nice descent rate...which I found quite nice since Im used to spoilers on Gliders for landing path control, I simply played the throttle to bring her down exactly where I want.

Nice short landing roll even without brakes, with the lower idle...I think I was getting about 1800 rpm idle if I remember correctly.

CDI means you KNOW your engine will run until the fuel is gone.....even if it is out of tune.....it makes a huge difference.

Case in point: When I first installed the CDI with the old flywheel it was 50 degrees off in the timing and the engine STILL ran....although it had a fierce kick on starting, but still idled fine.

Once I put the new flywheel on that came with it, I gained some top end rpm and it started much more gently.

I cant say enough good about the CDI its probably the single more worthy mod you can perform to improve reliability, safety and stop having to mess with the engine constantly.

A number of us have made the conversion and there is nothing but rave reviews about it.

The main benefits are:

- Very Reliable and lower Idle.
- Easier starting.
- Maybe a hundred RPM more top end.
- NO ignition maintenance required.
- Peace of mind due to reliability....no engine failures due to fouled points


Ray
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Postby rayjb60 » Wed Feb 01, 2006 5:06 pm

Im a little surprised at the lower rpm with the P-tips......if it was a regular tiped prop, I'd say cut the overall diameter down by an inch or two to get the Rotax 185 rpm's up into its strongest power band around 5700.

At 5200 or worse 4900 it sounds like the engine is over proped a bit and you had better watch for overheating if your running full throttle a lot.

I wonder if P-tips can be had at a smaller diameter and same pitch?

The prop2006 says your getting only ~6 hp at 4900 rpm.....thats a lot less than the 9hp the 185 is normally capable of.

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Postby lazair3ca » Thu Feb 02, 2006 9:17 am

This thread is really interesting.
I would like to add some observations:
1. We did not seem to increase the peak RPMs when we converted to CDI.
2. Starting spark is strong and starting is easier than before.
3. I can start my points R185s on the first pull if everything is setup right, Prime etc. So the points can work as well as the CDI but they can and will wear or get coated with oil and develope a film (oxidation) if they are not run regularly.
4. The CDI timing can be adjusted just like the points but it means taking the engine off and adjusting the position of the plate. A strobe is necessary.
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Postby lazair3ca » Thu Feb 02, 2006 9:34 am

This post may belong in the "are there any Rotax 185 Experts here" thread but it does involve CDI. So here it is:

Ihope I'm not stealing George's thunder but you may find this interesting.

George replaced the Bi-props on his engine with two bi-props we picked up last week.

The engine picked up 400 RPM. We could see a warp in the front blade. The warp gave one blade more pitch than the other half of the prop. I will try to include a picture later. The engine RPM increased from 5150-5250 with a muffler to 5840 RPM without a muffler and back to 5560 when the cleaner muffler was add to the engine.

Question is: Is 300 RPM loss typical when using the muffler? I have not tuned the engine since the prop was changed so we may get some RPMs back.

The right engine had a stubby intack stack. George replaced it and picked up a 200 RPM.

Atmoshperic conditions were not the same both days and the engines have not been tuned for Maximum RPMs but the results so far are encouraging. The aircraft should perform a lot better with the engines running in the 5600-5700 RPM range.
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Postby rayjb60 » Thu Feb 02, 2006 4:01 pm

Thats good information Shannon!

Perhaps that explains why my one engine runs a hundred rpm faster than the other.

I did not realize that the LOW screw contributed a bit to the high end as well.

Looks like a bit of a trade off of low end idle set too low will steal a bit from the high end.

Your engine runs nice and strong.....how many hours have you got on it?

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