Kitfox Aircraft Stick and Rudder Stein Air Grove Aircraft TCW Technologies Dynon Avionics AeroLED MGL Avionics Leading Edge Airfoils Desser EarthX Batteries Garmin G3X Touch
Page 3 of 4 FirstFirst 1234 LastLast
Results 21 to 30 of 36

Thread: Cruise rpm

  1. #21
    Banned
    Join Date
    Jul 2008
    Location
    Miami, Florida
    Posts
    5

    Default Re: Cruise rpm

    There seems to be a wives tale going around about not cruising below 5000 RPM which I beleive to be FALSE I cruise my Rotax 912-S at 4200 RPM all the time, it reduces noise and fuel usage is much lower, and the engine seems very happy with almost 300 hours of this. I have read the Rotax manuals looking for limitations, and there are limitations on cruise RPM. There are RPM limitations listed, such as not idling below 1800 RPM, and 5500 maximum continuous RPM, so obviously thy did not just forget this issue, but there is NOTHING saying not to cruise below 5000 RPM. So it seems some guys have just " Invented ", or heard from someone else thier own limitation and pass it on as fact. Ever seen the AirCam twin engine Plane ??? That plane has two 912-S on them and they cruise them at very low RPM using about 3 1/2 gallons per hour per side as normal cruise procedure, Lockwood sells that plane...

    My guess is that someone very correctly said not to have a high throttle setting and then pitch the prop to below 5000 RPM cruise, that would be lugging the engine, which would be very bad. Some simple minds probably just understood " Dont cruise below 5000 RPM " and spread it around, which is why there I think there is so much misunderstanding about this among the Rotax community. You should NEVER prop your engine to the point where it is lugging at low RPM and high throttle, This is very bad... If you have the prop pitch set correctly, and you pull the power back to a fuel saving, less stressful less than 5000 RPM cruise, I do not see a problem.

    Rotax centers do not always get it right either, you may get a different stroy from every guy you talk to, guys that work at Rotax Centers could very well be subject to the same type of misconceptions as everyone else. Until I hear it DIRECTLY from the Rotax engineers, and they have had 20 years to put this limitation into the manual if it were important, I will continue to cruise below 5000 RPM and a low throttle setting.

    The above is just what I have found out based on hearing the same garbage and researching it as much as possible over the years. So the above is just my OPINION. Just as guys that try to add thier own limitations to the Rotax manual are merely stating opinion, which I beleive to be with good intentions, but misguided.

    Mike
    Last edited by JetPilot; 10-13-2010 at 07:10 PM.

  2. #22
    Senior Member HighWing's Avatar
    Join Date
    May 2009
    Location
    Goodyear, AZ
    Posts
    1,743

    Default Re: Cruise rpm

    I love these discussions especially the part about any differing opinions being garbage. Well, this "simple mind" got his caution about cruising below 5000 rpm from Eric Tucker who used to be a regular at the Kitfox factory fly-ins. This was a long time ago for the guys only having 300 hours on their engines and in a time when we got to rub shoulders from time to time with the experts. Maybe things have changed, but for me, until I see or hear something specifically negating what we were told then, I plan on sticking with that advice. To each his own,though, it's only money.

    Lowell

  3. #23
    Banned
    Join Date
    Jul 2008
    Location
    Miami, Florida
    Posts
    5

    Default Re: Cruise rpm

    Quote Originally Posted by HighWing View Post
    Well, this "simple mind" got his caution about cruising below 5000 rpm from Eric Tucker who used to be a regular at the Kitfox factory fly-ins.

    Lowell
    The fact that Rotax puts NO SUCH LIMITATION in the manual is pretty good evidence.

    Rotax has a warning about low RPM idling.
    A limitation on maximum RPM.
    A limitation on Continuous RPM.

    The LACK of any limitation by Rotax on cruising below 5000 RPM tells me a lot, there is no limitation. This is just an example of the kind of way down the chain type information that spreads misconceptions. Lowell, did you ever do the excercise where you get a bunch of people in a circle, and start out with one person telling the next a simple fact, and on down the line. By the time it gets to the last person there is none of the truth left, what you get is total garbage. So I will take it straight from Rotax, not made up limitation some guy that said something at a fly in, and got passed down the line etc. etc....

    So we are supposed to assume, that Eric Tucker got his information direct from a good source like the Rotax Factory ( I doubt it ) Or that that he did not misunderstand it. And that you totally understood what this guy was saying, and did not misunderstand it, etc. etc. Throwing names around does not produce any evidence on this subject at all. My guess is that somewhere along the line, some simple mind misunderstood the bad idea of running high throttle settings while lugging the engine down to less than 5000 RPM in cruise with an overpitched prop.

    So we are all supposed to beleive 5 th hand information at best, and ignore the very obvious lack of any such limitation in the Rotax manual, even when Rotax went to the trouble to publish sevearl types of RPM limitations ( Rotax obviously did not just forget to put RPM limitations in the maunal ).

    You have zero facts, and zero logic, you just quote some 5th hand information to support your post. This is the type of information I would NEVER listen do. I operate my Rotax 912 on facts, and good information according to the Rotax manual and their service bullitens. I do not operate my engine based on 5th hand wivestails as Lowell would have us do.

    Mike
    Last edited by JetPilot; 10-14-2010 at 05:59 PM.

  4. #24
    Banned
    Join Date
    Jul 2008
    Location
    Miami, Florida
    Posts
    5

    Default Re: Cruise rpm

    The AirCam kit is sold by Lockwood Aviation, a Rotax service center. It is standard practice to cruise the Rotax 912-S on these planes at around 4000 RPM. Lockwood, Rotax, nor anyone else have given any warnings or limitations about cruising with the Rotax 912-S below 5000 RPM on these planes... Why ??? Because there is no limitation against it.

    Just another nail in the coffin of the made up 5000 RPM Cruise limitation of the 912-S engine...

    http://www.clamarfloats.com/downloads/0709_feature.pdf

    http://www.kitplanes.com/issues/pdfs/0806-2230.pdf

    Above are a couple of examples of the 4000 ish cruise RPM's used in these planes, there are many more available if you do your research...

    Lowell, I will give you a good peice of advice, do not beleive everything you hear at arishows


    Mike
    Last edited by JetPilot; 10-14-2010 at 06:28 PM.

  5. #25
    84KF
    Guest

    Default Re: Cruise rpm

    "I cruise my Rotax 912-S at 4200 RPM all the time, it reduces noise and fuel usage is much lower, and the engine seems very happy ...."


    Same here...912UL w/ Warp Dr. 4200-4800, and she just purrs right along happy and smooth. Sure, I may not be tooling along at 100mph+, but I get where I want to go eventually, and I don't feel like I beat the heck out of the engine gettin' there.

  6. #26
    Senior Member HighWing's Avatar
    Join Date
    May 2009
    Location
    Goodyear, AZ
    Posts
    1,743

    Default Re: Cruise rpm

    "So we are supposed to assume, that Eric Tucker got his information direct from a good source like the Rotax Factory ( I doubt it ) Or that that he did not misunderstand it."

    Do I have to be the one who tells our resident expert who Eric Tucker is?

  7. #27
    Banned
    Join Date
    Jul 2008
    Location
    Miami, Florida
    Posts
    5

    Default Re: Cruise rpm

    Quote Originally Posted by HighWing View Post
    "So we are supposed to assume, that Eric Tucker got his information direct from a good source like the Rotax Factory ( I doubt it ) Or that that he did not misunderstand it."

    Do I have to be the one who tells our resident expert who Eric Tucker is?
    I know who Eric Tucker is, and he does NOT work for the Rotax Factory. Like I say, you can get as many different opinions from Rotax Centers as you like. The ONLY thing that counts is what Rotax says. Rotax is very specific and publishes the care and limitations of thier engines, so I just do not buy it when you want to " Invent " a new limitation.

    I have not seen Eric Tucker post here, or write anything on this issue. Even if he did, it would just be another opinion until something came from Rotax. He is Human and capable of error, or even simple miscommunication to the point that Lowell misunderstoood something

    I genreally discount people that claim to speak for God. I also have a hard time lisening to a guy that claims to speak for Eric Tucker on this issue.

    Mike
    Last edited by JetPilot; 10-14-2010 at 07:26 PM.

  8. #28
    Banned
    Join Date
    Jul 2008
    Location
    Miami, Florida
    Posts
    5

    Default Re: Cruise rpm

    Since this is becomming a discussion, I did my research on this. First, after a pretty good search, there are ZERO publications limiting cruise of 912 engines below 5000 RPM. Second, there are several covering many RPM's, INCLUDING crusing below 5000 RPM. Here it is straight from the Rotax operators manual:

    http://www.rotax-aircraft-engines.co...kus/d04670.pdf

    Page 5-3 Revision April 01 2010

    " RUN THE ENGINE ACCORDANCE WITH THE FOLLOWING TABLE "

    They list RPM's of

    5800 RPM
    5500 RPM
    5000 RPM
    4800 RPM
    4300 RPM

    The graphs on the previous pages cover the full RPM range from 2500 to 5800 RPM.

    There is a service letter Rotax SL-912-016 that warns against " HIGH ENGINE LOAD WITH LOW RPM " and a couple other things.

    http://www.rotax-aircraft-engines.co...kus/d04670.pdf

    http://www.rotax-aircraft-engines.co...kus/d04645.pdf

    Everything in these recent Rotax publications agrees with what I said in my first post.

    Mike
    Last edited by JetPilot; 10-14-2010 at 08:05 PM.

  9. #29
    Senior Member av8rps's Avatar
    Join Date
    Oct 2009
    Location
    Junction City, WI
    Posts
    680

    Default Re: Cruise rpm

    Below are a couple pictures of my flight last weekend to Osh SPB (80 miles from my house). One shows my panel which shows my cruise power setting and my IAS and GPS groundspeed.

    It was a near calm wind day and was just beautiful flying. My Kitfox is a Model IV-1200 on Aerocet amphib floats. It weighs 776 lbs empty, and that day I had 20 gallons of fuel, 15 lbs of baggage, and my 185 lbs. It powered by a 81 hp 912ul and I use an IVO in flight adjustable 3 blade 68" ultralight prop.

    The IVO IFA is used primarily to give me improved out of the water takeoff performance by allowing a full 5800 rpm on takeoff. Fwiw, during straight and level flight if I adjust the prop for maximum pitch, I get 5400-5500 rpm with wide open throttle.

    If you look at the panel picture you will see I have my engine set to a cruise setting of 4800 rpm, with a couple of inches of throttle left. At these settings I am seeing 100 mph IAS while showing 103 mph groundspeed (in very calm wind at 2000 ft msl).

    If I am willing to run the throttle right against the panel and adjust my prop to max pitch (5400-5500 rpm), I will see my top speed of 118-124 mph tas depending on load and temps. And I've verified these numbers many times - they're real. And remember - this is on floats. l'd anticipate a 5-7 mph increase in speed if I replaced the floats with standard wheel gear. Besides the 175 lbs of weight I would lose, I'd see a serious amount of drag reduction (both from the floats and the AOA).

    Now some may think the only way to get good speeds like mine is if you have an IFA prop. But after playing with my prop for hundreds of hours now, I found that if I adjusted my prop to simulate a fixed pitch, setting it to give me 5400 rpm with wide open throttle straight and level, that I would still have an acceptable climb rate and takeoff. Granted, my little amphib gets off the water much better if I can get max rpm on takeoff, but even if I don't change the pitch for takeoff it is quite acceptable. Even with fixed pitch setting it provides better performance than the average amphib. So if I had to fly a Kitfox as an LSA, I wouldn't be heartbroken to not have the IFA part of the IVO. My kitfox would still fly just great.

    On the subject of low rpm...I fly my Kitfox regularly in the low 4000 rpm range when I am just loitering around the neighborhood. From memory I recall my cruise speed to be around 80 mph at 4200 rpm. There again, I can tweak my prop for best operation (so as not to lug the engine or to run it too lightly loaded - fwiw I do have a manifold pressure gauge).

    I've even flown my Kitfox (on floats) as low as 3400 rpm, indicating 63 mph with partial flaps. Fuel burn is right around 1 gallon per hour at those settings, and as long as the airplane is light and it's not overly warm outside, it will fly all day long at that speed and rpm setting and will have no trouble maintaining altitude. If I ever find myself nearly out of fuel those are the settings I will use to get me to my fuel stop. 63 mpg isn't bad for an airplane, much less an amphibious floatplane.

    I do believe the IFA is very advantageous if you like to operate regularly at low rpms like I do, as you can make sure you are not lugging the engine at those low power settings. But overall I feel the 912ul can handle lower rpms, you just have to get to know what speeds your particular engine runs best at. And that's more of a feeling than it is a specific rpm or speed imho.

    Paul S
    Central Wisconsin
    Attached Images Attached Images

  10. #30
    Administrator DesertFox4's Avatar
    Join Date
    Aug 2008
    Location
    Arizona
    Posts
    3,563

    Default Re: Cruise rpm

    Good stuff Paul. Love your little amphib. Sorry I didn't get over to see you when I was at Osh. My only regret. Next time for sure.


    DesertFox4
    Admin.
    7 Super Sport
    912 ULS Tri-gear


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •