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georg.stiller(at)arcor.de
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 Posted: Sun Jan 23, 2011 8:39 am Post subject: drop of rpm on take off |
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Hi,
I started this thread on January, 4. I should like to thank for the advise and report on my findings:
I changed the needle in the carb from pos. 3 to 4 and made some testflights at 5 - 6 centigrade below zero with carb heat pulled. There was no trouble, no rpm drop anymore. Power output is okay. Carb heat is nearly ineffective, however, as I checked the temperature in the air box with a digital thermometer and there was virtually no difference with or without carb heat.
So the needle position obviously fixed the problem.
I have now a little problem with the warm start of the engine. Seems to be running somewhat rich, a little bit of grey smoke from the exaust when the engine catches.
Thanks again!
Regards, Georg
Kitfox, Rotax 912
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Sun Jan 23, 2011 9:21 am Post subject: Re: drop of rpm on take off |
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Make sure your idle rpm is set to only 1700-1800, not more it may be hard to start and less it may be hard to start. No throttle on start up is normal. Once in a while a 10% throttle opening can help if your normal rpm is a little too low, but no more than 10%. Make sure that both choke/enricher circuits open fully and not one more or less than the other. Try one or two different start up procedures and I'm sure one will work.
Starting is also tied to poor carb balance so make sure they are set.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Sun Jan 23, 2011 4:11 pm Post subject: drop of rpm on take off |
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I'm now installing a 912 to replace a 582. On the 582 I intentionally set
the idle very low so the plane wouldn't drift on touchdown. Once on the
ground I had to add throttle to keep 1800 rpm. Is this used with the 912?
Noel
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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Sun Jan 23, 2011 4:48 pm Post subject: Re: drop of rpm on take off |
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Hi Noel,
You' re going to like your 912.
1800 rpm is not enough to keep you flying and might extend a glide
50', maybe. I have a plane that has a 14:1 glide ratio and can land in 1K feet easily with 2800 rpm. I will use 2700-2800 rpm for all flap settings on normal landings or I can land at idle. It can make a world of difference carrying a little rpm to touch.
The rest of this post is on my soapbox and not aimed at anyone single person.
If someone can't put their plane down with 1800-2000 idle rpm then they should look at their landing technique and try a few changes. Remember the stick controls speed and throttle altitude. So what ever the rpm pulling back the stick to your desired speed works just fine. Yes I know up to a point it makes a difference, but not at rpms at or below 2000 rpm. Landing with rpm will also give you better control surface authority just before touch down. The controls won't feel mushy and give good solid input. If you can't hit a target landing spot at 1600 rpm then you can't hit it at 2800 rpm and either way that just means more focused practice. RPM doesn't decide where or when the wheels or floats touchdown, you do in your setup and execution of the landing. I can hit my spot at 1700 or 3000 rpm on landing and I can touch down at the same speed.
Purposely setting an idle rpm so you may loose the engine is, in my opinion, the wrong way to set up your aircraft. It isn't good for the engine or the pilot as some day it may cost you.
The more distractions you throw into a landing the more chance of making a mistake some day. It only takes a second for a normal landing to mess up, keep throwing distractions in your execution and sooner or later you may not be jolly on the spot with a correction.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Sun Jan 23, 2011 4:48 pm Post subject: Re: drop of rpm on take off |
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Hi All,
Here is a link to the ROAN website to watch a fairly new Rotax engine tips video. It covers things like start up, carb sync, prop balance, shut down and proper engine rpm, ect. This video gives proper idle speed. This video is in conjunction with "Service Letter" 0912-016.
For those who have argued about idle speed for the 912ULS 100 HP I hope this will clear up any low rpm idle issues. It not only talks about it, but you can see it on the instrument panel. The 912UL with only a 9.0:1 compression can do 1500 idle rpm, but the 912ULS at 10.5:1 compression has too much compression and beats up the engine/gearbox, not to mention the chance of loosing an engine at a 1500 idle approach. Be kind to your engine, it's the only thing that keeps you off the ground and out of the tress.
The video will tell you to keep rpms at 1800 + rpm and higher depending on the phase of the engine run. Running a 9121ULS at rpms of 1500-1700 is not good for your engine as we have discussed here before. This is in writing now and I hope alleviates some of the confusion from other sources.
http://rotax-owner.c...ning&Itemid=174
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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AmphibFlyer
Joined: 29 Dec 2009
Posts: 25
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