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Rotax 912 80HP Idle RPM
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SkySteve

Joined: 16 Dec 2007
Posts: 94
Location: Huntsville, UT

Posted: Wed Mar 12, 2008 1:52 pm Post subject: Rotax 912 80HP Idle RPM

At what RPM do you set your 80 HP Rotax 912 when the throttle is pulled all the way back (and the engine will still run)?  I understand Rotax suggests 2,000 to 2,500 RPM at idle, but I'm referring to when the throttle is all the way back and you are about to land, without killing the engine, or when you want to taxi slowly?

_________________
Steve Wilson
Huntsville, UT
Kitfox Model 1- 85DD
912A / 3 Blade Warp Drive
Convertible Nosewheel & Tailwheel

kerrjohna(at)comcast.net
Guest

Posted: Wed Mar 12, 2008 2:57 pm Post subject: Rotax 912 80HP Idle RPM

mine is set at about 1800 rpm for LGU.  Should be about the same for Morgan.  The key is as slow as possible without excessive shaking and clatter from the impulse washers.

  

 John Kerr

  

 [quote]-------------- Original message -------------- 

From: "SkySteve" <Wilson(at)REinfo.org> 



 	  Quote: 	
		   --> Kitfox-List message posted by: "SkySteve" 

 

 At what RPM do you set your 80 HP Rotax 912 when the throttle is pulled all the 

 way back (and the engine will still run)? I understand Rotax suggests 2,000 to 

 2,500 RPM at idle, but I'm referring to when the throttle is all the way back 

 and you are about to land, without killing the engine, or when you want to taxi 

 slowly? 

 

 -------- 

 Steve Wilson 

 Huntsville, UT 

 Kitfox I-IV 85DD 

 912A / 3 Blade Warp Drive 

 Convertable Nosewheel & Tailwheel 

 

 

 

 

 Read this topic online here: 

 

 http://forums.matronics.com/viewtopic.php?p=169388#169388 

 

   

&  ====== ================================= 
	


[quote] 

 

 [b]

SkySteve

Joined: 16 Dec 2007
Posts: 94
Location: Huntsville, UT

Posted: Wed Mar 12, 2008 3:16 pm Post subject: Re: Rotax 912 80HP Idle RPM

Thanks, John.  I currently have mine set at 1800 RPM also, but it really taxis fast and would like to be able to slow down without riding the brakes.

_________________
Steve Wilson
Huntsville, UT
Kitfox Model 1- 85DD
912A / 3 Blade Warp Drive
Convertible Nosewheel & Tailwheel

Jim Shumaker

Joined: 09 Jan 2006
Posts: 106

Posted: Wed Mar 12, 2008 6:14 pm Post subject: Rotax 912 80HP Idle RPM

My idle is set to be able to get as low as 1500.  This is only used for landing.  The minimum rpm while landing will still be about 2000 rpm until touchdown.  Then the engine will slow down to 1500 if I don't bring in a little throttle.  Sure helps on short landings.  The latest from Rotax is that the minimum rpm should be set for the needs of the aircraft and the mission which can vary from 1400 to 2000 rpm.  I always taxi between 1800 and 2000 because that is smoother.  But do have to ride the brakes a bit.

  

 Jim Shumaker

 ---

_________________
Jim Shumaker

SkySteve

Joined: 16 Dec 2007
Posts: 94
Location: Huntsville, UT

Posted: Wed Mar 12, 2008 6:50 pm Post subject: Re: Rotax 912 80HP Idle RPM

Thanks, Jim. I think I'll back mine down a bit and try it.

_________________
Steve Wilson
Huntsville, UT
Kitfox Model 1- 85DD
912A / 3 Blade Warp Drive
Convertible Nosewheel & Tailwheel

Sbennett3(at)aol.com
Guest

Posted: Wed Mar 12, 2008 6:54 pm Post subject: Rotax 912 80HP Idle RPM

I can pull my throttle on a short final where the  prop will keep the engine idling. If I don't add throttle after my wheels touch  the engine will die. I feel THAT is perfect control. Steve  Bennett



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  [quote][b]

kerrjohna(at)comcast.net
Guest

Posted: Thu Mar 13, 2008 6:24 am Post subject: Rotax 912 80HP Idle RPM

Steve, I keep just a little brake on but in checking this week, there is still a lot of pad left after 775 hours.  mostly just polishing the rotors.  coming to logan sometime?

  

  ures N  [quote][b]

SkySteve

Joined: 16 Dec 2007
Posts: 94
Location: Huntsville, UT

Posted: Thu Mar 13, 2008 8:09 am Post subject: Re: Rotax 912 80HP Idle RPM

John, 

Yes on the coming to LGU.  Johnny O and I have discussed it several times.  Thinking of coming to one of your Saturday morning breakfasts in the near future.  It's snowing here today and looks like it will be thru the weekend.  Understand you and I are in the same business (which sucks right now).  Would love to meet you.  In fact, maybe you, John and I should meet for breakfast or lunch at OGD soon (or even somewhere in BMC).

_________________
Steve Wilson
Huntsville, UT
Kitfox Model 1- 85DD
912A / 3 Blade Warp Drive
Convertible Nosewheel & Tailwheel

pulsair(at)mindspring.com
Guest

Posted: Thu Mar 13, 2008 1:53 pm Post subject: Rotax 912 80HP Idle RPM

Steve,

When my throttle is against the stops on short final I'm at 2,000 RPM. Once 

I touch down and tap the brakes I keep it at 2,000 RPM. Anything less then 

that I hear the dog ears/legs (whatever) slapping in the gear box. Jeff 

Classic IV

---

kerrjohna(at)comcast.net
Guest

Posted: Thu Mar 13, 2008 2:09 pm Post subject: Rotax 912 80HP Idle RPM

our monthly breakfasts are 8-10 on the second Saturday of each month.  come on down

  

 J

  

 [quote]-------------- Original message -------------- 

From: "SkySteve" <Wilson(at)REinfo.org> 



[quote] --> Kitfox-List message posted by: "SkySteve" 

 

 John, 

 Yes on the coming to LGU. Johnny O and I have discussed it several times. 

 Thinking of coming to one of your Saturday morning breakfasts in the near 

 future. It's snowing here today and looks like it will be thru the weekend. 

 Understand you and I are in the same business (which sucks right now). Would 

 love to meet you. In fact, maybe you, John and I should meet for breakfast or 

 lunch at OGD soon (or even somewhere in BMC). 

 

 -------- 

 Steve Wilson 

 Huntsville, UT 

 Kitfox I-IV 85DD 

 912A / 3 Blade Warp Drive 

 Convertable Nosewheel & Tailwheel 

 

 

 

 

&gt  ; Read  gt; _-   	  Quote: 	
		  [b]

Don G

Joined: 10 Jan 2006
Posts: 156
Location: Central Illinois

Posted: Mon Mar 17, 2008 7:29 pm Post subject: Re: Rotax 912 80HP Idle RPM

I have found that If I have the prop set..(taper tip warp) at a good cruise pitch, and the wide open rpms in flight will just touch redline, that at Rotaxs Recommended min idle speed I have a heck of a time getting the Plane to land...makes it a tremendous floater.  I either have to take some pitch out of the prop to get good landings, or reduce the idle speed to 1500, at which It begins to get rough.

_________________
Don G.
Central Illinois
Kitfox IV Speedster
Luscombe 8A
RV9A

Catz631(at)aol.com
Guest

Posted: Tue Mar 18, 2008 4:54 am Post subject: Rotax 912 80HP Idle RPM

Don, Don't feel like the 'Lone Ranger" I too have been having fits landing my Kitfox like a normal taildragger.In fact when I first bought the plane the engine quit on me three times on final (3 different flights) and the airplane landed very nicely. Well, like a dummy I adjusted the idle back up so it wouldn't happen again and like you, it wouldn't land cause you can't get the power back far enough! So now I have it adjusted as it was and make the rpm part of my landing scan. As the former owner said it's called "slip and plop" Nature of the  beast I guess. (with a Rotax 912 anyway-weird engine)

                                               Dick Maddux

                                               Fox4-1200

                                               Rotax 912UL



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  [quote][b]

kmamjones(at)comcast.net
Guest

Posted: Tue Mar 18, 2008 8:34 am Post subject: Rotax 912 80HP Idle RPM

I'm confused about this subject.  I'm a Series 7 builder. I have a  912S not yet installed. I thought I was building a STOL aircraft that could land  short. I knew the engine idle speed was high, but I thought the gear box reduced  the prop speed so that it was not providing thrust at idle speed.  These  messages suggest that is not correct.  Do I have to change to another  engine to get STOL landings?

  

 Ken Jones

 Waynesboro, PA

 Series 7 builder

  

 [quote]   ---

Don G

Joined: 10 Jan 2006
Posts: 156
Location: Central Illinois

Posted: Tue Mar 18, 2008 10:03 am Post subject: Re: Rotax 912 80HP Idle RPM

Ken,

I dont think so...

Now, I am a long way from an "expert"...so take this as just one fellas experience, and not necessarily the norm..and I have never riddin in a series 7...only the 4's and older.



Airplanes flight characteristic's are equal to the sum of a list of compromises.

ON this particular subject...some of the things I can think of on the list are:

Cruise speed...vs Landing speed



IN other words...set the prop for maximum cruise potential,(max pitch) and even with the gearbox slowing it down when it is at Rotaxs recommended Idle speed of 2000 rpms or thereabout...it still it putting out a fair amount of thrust...so Landing short requires alot of pilot technique.

This was Dick was referring to in the previous post with the "slip and plop" description...I liked that alot...he means crab/slip it in with a high drag attitude to help slow it down quickly and then plop it in..



or...lower the min throttle setting to less than Rotax's min recommendation, and get familiar with the chattering of the gearbox that this high idle speed is supposed to prevent. This way you can keep one hand on the throttle and when you bring it in...bring the rpms down real low....just so you loose that residual thrust from the prop....and when you get the airplane on the ground...ride the brakes and push the throttle back up to get out of your engines particular "gearbox chatter" rpm range



or.. compromise on the fast cruise and lessen the pitch of the prop so that there is no thrust or very little at 1900 or 2000 rpms,,,and land it without the either of the extra techniques referred to above required.



OR...since you are building...install an airbrake like a F-86 or a tomcat and use it on landing....(this actually might be more viable than comical after considering)



After streamlining the struts...really tweaking the rigging and getting the wings set "just right"...running the prop pitch up to where the engine wont redline until after about a minute of so at wide open throttle...my Speedster flys so dang fast I cant hardly tell people about it because they just don't believe it...Not that this near sonic speed matters to me that much, but I do like the super economical cruise ...with the engine down around 4700 or so, 3.5 to 3.7gph on the fuel flow.. and the airspeed over 100



I personally think you have made a good choice..but when you think about it....making the best Short landings in ANY aircraft is all about pilot technique.



And remember this...I could be wrong.....

_________________
Don G.
Central Illinois
Kitfox IV Speedster
Luscombe 8A
RV9A

Last edited by Don G on Tue Mar 18, 2008 10:11 am; edited 2 times in total

clint_bazzill(at)hotmail.
Guest

Posted: Tue Mar 18, 2008 10:04 am Post subject: Rotax 912 80HP Idle RPM

The kitfox is STOL because of light wing loading and lots of power to weight.  Its not like an airplane with big wing flaps that allows you to put you self behind the power curve and adjust your glide by power.  The Kitfox glides very well, kind of like landing a C 150 with no flaps.  A completely different approach (No Pun) to the technique to landing, doing a lot of slipping.  I have had the engine stop on landing a couple times, trying to get the airplane to slow down.  Practice landings with a kitfox over a 50 foot obstacle and this will help a lot.  My 2 cents worth.  Clint

 From: kmamjones(at)comcast.net

To: kitfox-list(at)matronics.com

Subject: Re: Rotax 912 80HP Idle RPM

Date: Tue, 18 Mar 2008 12:27:28 -0400

     [quote] I'm confused about this subject.  I'm a Series 7 builder. I have a 912S not yet installed. I thought I was building a STOL aircraft that could land short. I knew the engine idle speed was high, but I thought the gear box reduced the prop speed so that it was not providing thrust at idle speed.  These messages suggest that is not correct.  Do I have to change to another engine to get STOL landings?

 Ken Jones

 Waynesboro, PA

 Series 7 builder

 [quote] ---

Fox5flyer
Guest

Posted: Tue Mar 18, 2008 10:51 am Post subject: Rotax 912 80HP Idle RPM

Ken, as was previously posted, the recommended idle speed is around  2000rpm, the same for my Subaru setup.  The only reason for the high idle  rpm is to smooth out the tortional vibration pulses from the prop and keep the  gearbox from hammering for long periods.  However, landing rpms are much  different and can be easily backed off to 1500 or less (about 500 prop rpm  depending on ratio) to get a slow prop speed for short final and landing  only.  One poster said his engine kept dying at the lower rpms, but I  believe that he might be dealing with a mixture problem, probably too  rich that is causing the engine to die at the lower rpm.  The Kitfox,  whether a model 1 or 7 is a good short field airplane, but prop speed is  important so that excessive float isn't encountered.  I idle mine about  2200rpm, but the idle stop is set for 1400 for landing.  The 912 shouldn't  be very much different and I'm sure others will chime in soon with their  setups.

 The 912S is a good package, and probably the best choice out there for  the Kitfox.  What probably keeps most people from going with it is only the  price.

 Deke Morisse

Mikado Michigan

S5/Subaru/CAP 355+ TT

"The aim of an  argument or discussion should not be victory, but progress."

- Joseph  Joubert

  

 ---

Fox5flyer
Guest

Posted: Tue Mar 18, 2008 10:56 am Post subject: Rotax 912 80HP Idle RPM

I like Jeff's idea about using the F4 drag chute...

do not archive



 	  Quote: 	
		   OR...since you are building...install an airbrake like a F-86 or a tomcat 

 and use it on landing....(this actually might be more viable than comical 

 after considering)

 --------

 Don G.

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Tue Mar 18, 2008 11:04 am Post subject: Rotax 912 80HP Idle RPM

At 09:27 AM 3/18/2008, you wrote:

 	  Quote: 	
		  I thought I was building a STOL aircraft that could land short. . . 

. Do I have to change to another engine to get STOL landings?


	


         First, there is no problem with the 912. Most Kitfoxes have 

them and some of the ones that do can land reliably in less than 

100'. That said, my Kitfox IV with a 582 is a very difficult plane to 

land short. Minimum sink is at 50 mph indicated. (This from my gross 

weight flight test data.) At that weight my stall is 40-45 mph 

indicated. Thus, unlike a full-flaps Cessna the only way to really 

increase sink is to point it down hill and go fast, (lots of drag,) 

or to slip like mad. Unfortunately, in either case you end up fast in 

the flare and you float. (I haven't the courage to slip close to 

stall speed near the ground.) So how do these guys land short?

         First they drag it in as low and slow as they dare. (Speed 

is based on gust factor, etc.) When I say low, I mean 2-3 feet over 

the terrain. When they get near the threshold they pull power and 

simultaneously rotate. Ideally the mains touch the ground with little 

vertical velocity just as the wings stall. When the mains touch they 

push a little and brake hard. Then begins the game of braking as hard 

as you can without nosing over while using elevator to control 

attitude. Initially you push forward on the stick to plant the tires 

(reduce AoA) to get traction. Then as you mash the brakes you pull 

the stick back, maintaining attitude. You apply as much brake as the 

elevator will stand. As the plane slows and before the elevator 

looses effectiveness you reduce the braking just enough to get the 

tail to drop. This moves the CG back and puts more down-force on the 

tires. (Don't do it too soon or the wing's lift will offset your 

gains.) Ideally the tailwheel kisses the ground just as you stop. All 

of this happens in about 3-5 seconds.

         Compare this with the trike 152. Full flaps, 5mph over 

stall, (I think about 50,) and the plane's sinking like a rock. Just 

before touchdown you rotate to buffet. (You do this to mitigate the 

impact a little, but mostly to keep the nose wheel from hitting too 

hard.) The impact is incredible, but the spring gear soaks it up. 

Upon impact pull full back stick and full brakes. (No skidding.) 

Doing this you can land a 150 incredibly short. (I don't remember the 

numbers, but it was impressive, something like 100'.) More 

importantly just about anybody can do it. I learned during PPL 

training. Compare this to a couple hundred hours in the Kitfox and I 

still can't land short EVERY TIME.

Guy Buchanan

San Diego, CA

K-IV 1200 / 582-C / Warp / 100% done, thanks mostly to Bob Ducar.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

wingnut

Joined: 11 Jan 2006
Posts: 356

Posted: Tue Mar 18, 2008 11:51 am Post subject: Re: Rotax 912 80HP Idle RPM

 	  Quote: 	
		  So how do these guys land short? First they drag it in as low and slow as they dare. (Speed is based on gust factor, etc.) When I say low, I mean 2-3 feet over the terrain. When they get near the threshold they pull power and simultaneously rotate. 	




This seems to me like a great example of why I think you have to be real careful about making generalizations based on personal experience. From this description, my model IV is a completely different animal. Like most of the people on this thread, I had to tweak my idle setting to get it low enough to limit excessive float on flare. But, now that I have it dialed in, itâ€™s not an issue at all. Not to say that I land short reliably but I blame that on my piloting skills. I say this because I have managed to land quite short on occasion with nothing more than setting up the approach well and managing my air speed properly.

_________________
Luis Rodriguez
Model IV 1200
Rotax 912UL
Flying Weekly
Laurens, SC (34A)

kmamjones(at)comcast.net
Guest

Posted: Tue Mar 18, 2008 4:22 pm Post subject: Rotax 912 80HP Idle RPM

Thanks for your input guys.  The conclusion I've reached, as Dick  Maddux said, the 912 is a weird engine. I find it hard to understand that the  engineers would design an aircraft engine that cannot idle on a landing  approach with no added thrust.  If I remember right all the  Lycomings I used to fly would idle so slow the props would actually create a  little drag. I'm really annoyed with myself that I didn't think to research this  subject more before I made the engine purchase decision.  Yet we all know  there are a lot of new light sport aircraft on the market using the Rotax 912  engines. So I wonder if I'm being overly concerned. Is this really an important  issue? Do all the new light sport's have this problem?  I've been planning  on taking a biannual flight review next month.  I think I'll make sure to  do it on a light sport using the Rotax 912 to see for myself.

  

 In any case the conclusion seems to be that the only way to achieve  low approach speeds with a Rotax 912 is to slip hard or accept gearbox  chatter at low idle settings during the approach.

  

 Ken Jones

 Series 7 builder

 [quote]   ---

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