CDI Ignitions

[pittsnut]

[lazair3ca]

[pittsnut]

[lazair3ca]

[Shannon]

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

Shannon

[rayjb60]

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

[rayjb60]

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.

Ray

[lazair3ca]

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.

[lazair3ca]

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.

[rayjb60]