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Engine RPM

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skylane812(at)hotmail.com
Guest

Posted: Thu Feb 21, 2008 6:39 am Post subject: Engine RPM

I have a Kitfox S-7 with a Rotax 912ULS w/o the airbox.  My static RPM has always been 4700 or less even though the engine runs very smooth and tops out at 5800rpm.  I have tried numerous pitch settings on my Powerfin prop to get these numbers.  My worry is that my mag drop has always been 380 or so per side even though all the other numbers are within specs.  The performance is great with about 150 ft takeoff and 105mph at 5200 rpm.  I took a half inch off the prop and it helped a little.  Any ideas will be greatly appreciated.    RichClimb to the top of the charts! Play the word scramble challenge with star power. Play now!  [quote][b]

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Thu Feb 21, 2008 7:58 am Post subject: Re: Engine RPM

What rpm are you doing the mag check at? The higher the rpm when you do a mag check the higher the mag drop. My CT drops approximately 

70-80 rpm at 3500rpm. Mag check should not drop more than 300 rpm on either ignition and no more than 115rpm between ignition systems A & B.



With that prop pitch setting to achieve 5800 rpm I bet you climb very well and take off is short. Unless you have a reason to be that high you might want to consider adding some pitch back into the prop to bring it down a little (around 5500, which is continuous WOT rpm). It will still run and perform well. Only 5 min. run time on anything over 5500. The higher rpm if not needed for a special duty will just be a little harder on the engine as you accumulate higher engine time.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

Rich L

Joined: 23 Feb 2008
Posts: 63
Location: North Idaho

Posted: Sat Feb 23, 2008 3:42 am Post subject: Re: Engine RPM

My problem with the mag drop is finally fixed.  The Rotax specs say the mag drop should not be over 300 with 120 difference.  Mine has been over 400 since day one and I have tried almost everything.  Sent queries out to numerous sites asking for a fix and nobody came up with anything worthwhile till I went to a Rotax troubleshooting sight which listed about 10 things it could be.  I tried each one for the past months but didn't do the ignition because I couldn't see it with the engine mounted.  Today I used an inspection mirror and set the spacing on the trigger coils which make up the ignition system.  My mag drop is now 110 per side and 10 difference.  I went flying tonight and the EGT's, CHT's are all even and the engine is even smoother.  I still take off in 150 feet and the RPM is about the same.

ami(at)MCFADYEAN.FREESERV
Guest

Posted: Sat Feb 23, 2008 4:04 am Post subject: Engine RPM

Did you find the trigger coil gaps too tight of too loose?



Duncan McF

do not archive

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Rich L

Joined: 23 Feb 2008
Posts: 63
Location: North Idaho

Posted: Sat Feb 23, 2008 4:58 am Post subject: Re: Engine RPM

They were to wide, about .020.  I set them all to .015 per the maintenance manual. I also noticed that when you tighten them, they open up if you don't hold down on them with the feeler gage in place.  Even more fun when trying to get to them on a mounted engine.

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sat Feb 23, 2008 7:08 am Post subject: Re: Engine RPM

Rich,



Is this a 912ULS? About how old is the engine and how many hours? I would be really curious on how those even got out of adjustment.

Those are rarely ever an issue. Usually the coil is either good or bad, but not just out of adjustment. The trigger coils tend to last the life of the engine. (1500 hr. TBO)



There are a few diagnostic things to check to see if your ignition problem is on the trigger coil side, the ignition modules or from the modules up to the plugs.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

Rich L

Joined: 23 Feb 2008
Posts: 63
Location: North Idaho

Posted: Sat Feb 23, 2008 8:54 am Post subject: Re: Engine RPM

Its a long story but when I bought the engine, the ignition cabling had been installed by the previous owner.  I was the first one to run it.

Rich L

Joined: 23 Feb 2008
Posts: 63
Location: North Idaho

Posted: Sat Feb 23, 2008 1:28 pm Post subject: Re: Engine RPM

Roger,



I have the 912ULS w/o an airbox so less than 100hp.  I have adjusted the prop where I like it now. The s-7 flys at 115mph at 5300 rpm just fine.  My question is, I only get about 4600 rpm at initial ground role with full throttle. Climb out is 4800 and it will still go to 5600 on cruise.  It gets off in less than 200 feet but do you think I am lugging down the engine?  I plan to get the airbox later.



Rich

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sat Feb 23, 2008 2:57 pm Post subject: Re: Engine RPM

Hi Rich,



It sounds like you have it set up just fine. The rpm on roll out and takeoff are normal. It varies a little from plane to plane because of different variables.

No one gets 100hp so don't worry about about that part too much. My engine rpm's are very much like yours.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

Rich L

Joined: 23 Feb 2008
Posts: 63
Location: North Idaho

Posted: Sat Feb 23, 2008 6:58 pm Post subject: Re: Engine RPM

Roger,



Thanks for the expert input.  I had my s-7 DAR'ed in August and have 90 hours on it but have not found a lot of information on what I have done with the 912uls and s=7 till now.



regards

Rich

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sat Feb 23, 2008 8:16 pm Post subject: Re: Engine RPM

Hi Rich,



You can find all the manuals for any Rotax 912 or 2 stroke on the Rotax or Kodiak website under tech info. They can all be downloaded and printed for a book for easy reference. All the bulletins or AD's can be found there ,too. They are now putting out videos on some of the line maint. items. (i.e. carb balancing)

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

JOE RONCO

Joined: 04 Aug 2007
Posts: 31
Location: CENTENNIAL COLORADO

Posted: Sun Feb 24, 2008 12:09 pm Post subject: Engine RPM

And don't forget the Rotax tuned exhaust if you don't already have it. It is

also required with the airbox to get the published 100 HP (at) 5,800 RPM.



Joe R



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