Engine Run-Up

[Newkentboy]

I have a 2019 CTSW with a 912is. When I do my run up to 3200 rpm at the end of the runway, first Lane B, then back to A+B, then checking Lane A, then back to A+B, I seldom see any drop in the rpm. The Lane A lights on the Lane B check, but doesn’t go out when back to A+B. The Lane B light comes on when I move the key to Lane A and the Lane A warning light stays on. When I switch back to A+B, the Lane B light goes off, but the Lane A light remains illuminated. Only when I then switch back to Lane B key position once again and then back to A+B will the Lane A light go off. Everything else seems fine. Am I doing something incorrectly? Thanks.

[shiny.ice]

I have somewhat similar behavior on my CTLS with the iS. Lane lights will remain on if I do the B-both-A-both test like on a magneto engine. So my procedure is to test B, then A, then both. You shouldn’t have much drop when running on a single lane, 20rpm is common in my experience on the CT and other 912iSes.

 

[Newkentboy]

41 minutes ago, Roger Lee said:

Go from both lanes A&B to just B and let it sit for about 10 seconds and let it stabilize. The B light will come on. Then go directly to Lane A and allow it 10 seconds to stabilize and Lane B light should go out and you have now checked for the mag drop. Now go back to lane B and let Lane A light go out and let it sit for 10 seconds and stabilize and then finally back to A&B. You check each lane and allow a short time for the two computers (Lane A&B) to switch and stabilize before turning the key again. This is not like a carb engine that you only see mag drop on each ignition instantly. The 912iS engine has two computers Lane A&B and the mag check is different and you must allow the computers to swap and settle for a few moments.

Interesting. Thanks.

[Blueyonder]

Hi everyone.

I found that Roger's suggestion / procedure works well. What I find interesting, at least in a CTLSi sport is that as you go fro Both, to either A or B the RPM goes up by about 100 and as you return to Both it remains high, i.e. Set 4000>10sec>B=4100>10sec>A=4100>10sec>A&B=4100 and remains, at times it may be 150RPM increase but there is always a very close RPM between A and B.

The main point, as Roger mentioned, is to wait between key switching. If you go B wait 5 sec, go A wait 10, go to B wait 10 and then A&B also works but it always give you the increase in RPM.

Is that typical? A couple of them that I used dis the same, which is not typical if you are used to other acft like the C172...

The main problem, in the POH, see list below, is that they do not caution to wait between switching positions, otherwise that procedure also works, except for the drop.

>>...

Throttle 4000 rpm

LANE B check Max. drop 180 rpm, LANE A light flashes.

Both LANES Check, both lights off

LANE A check Max. drop 180 rpm. max. diff. to B 120 rpm, LANE B light flashes.

Both LANES Check, both lights off

....<<

[Blueyonder]

Hi Roger and everyone.

I agree, my question is why FD warns us about a drop and there is actual increase? It does sound like it's typical, at least from what I've seen but is it and overcompensation?

A safety procedure? What is the logic behind it? I know that they can set it it up to do any thing they want, but the question is Why?

[Bill3558]

Rotax class at Lockwood suggested not messing with it.  If lane lights go out at start up, you’re good to go. 
I will go through the procedure about every 10th start.