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Bob Griffin

Joined: 22 Jan 2006
Posts: 34
Location: Slingerlands,NY

Posted: Mon Feb 20, 2006 3:49 am Post subject: rpm

Goodmorning guys, I was wondering what rpm most are running their 100 hp rotaxes in cruise?  Is 4800 ok or should it be higher?

 Bob Griffin

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Fly Safe
Bob Griffin
Slingerlands, NY

DandP(at)qx.net
Guest

Posted: Mon Feb 20, 2006 5:02 am Post subject: rpm

Hi Bob,

  

 I cruise about 5000-5100 in my Zenith 701, I now have a little over 200  hours on the engine and just finished the annual in early January.  The  engine inspection revealed no wear and everything checked within  required/recommended tolerances.  I also fly a Remos G3 and normally cruise  at 4800-4900 unless at altitude (above 8,000').  It has about 275 hours on  it.  Since it is not my aircraft I have not performed any detailed  inspections, but is smooth and seems perfect.  Both of these engines are  912S.

  

 Dan Yeast

 [quote]   ---

j.piepers(at)prevalent.nl
Guest

Posted: Mon Feb 20, 2006 5:37 am Post subject: rpm

Bob,



I fly regularly on aircraft with 912 and 912S engines and always run

them between 5000 and 5200 rpm and they seem to like it. Also have some

time (150hrs) on a 914 turbo engine with a constant speed prop and that

too ran on 5000 with no problems at all.



John Piepers

Netherlands



 	  Quote: 	
		   -----Oorspronkelijk bericht-----

 Van: owner-rotaxengines-list-server(at)matronics.com 

 [mailto:owner-rotaxengines-list-server(at)matronics.com] Namens 

 Airgriff2(at)aol.com

 Verzonden: maandag 20 februari 2006 12:48

 Aan: rotaxengines-list(at)matronics.com

 Onderwerp: rpm

 

 

 Goodmorning guys, I was wondering what rpm most are running 

 their 100 hp 

 rotaxes in cruise?  Is 4800 ok or should it be higher?

 Bob Griffin

David X

Joined: 10 Jan 2006
Posts: 154
Location: Princeton, NJ, USA

Posted: Tue Feb 21, 2006 7:08 am Post subject: Re: rpm

5150 is where it seems to like it. The operators manual concurs.

_________________
Zodiac 601 XL - CZAW Built - Rotax 912S
DO NOT ARCHIVE

ami(at)MCFADYEAN.FREESERV
Guest

Posted: Tue Feb 21, 2006 1:35 pm Post subject: rpm

David,

Where specifically does it say that? I can't find that in owner's, 

installation or maintenance manuals.



Duncan Mcf.

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David X

Joined: 10 Jan 2006
Posts: 154
Location: Princeton, NJ, USA

Posted: Tue Feb 21, 2006 5:40 pm Post subject: Re: rpm

Look in Chapter 10 - Operating instructions. I have revision 3, July 01/2004. Look specifically at page 10-7 and 10-8 at the power curves and engine power settings table.



Max cruise power = 5500

75% power = 5000



The above figures are probably based on a standard day. Power decreases with altitude or decrease in density altitude, so it would make sense that you would increase RPM a little at altitude to maintain the same sea-level power. Also, the power curve reveals that maximum torque is at about 5150 RPM, which is the happy medium between power and economy.



At some point, you begin to split hairs.

_________________
Zodiac 601 XL - CZAW Built - Rotax 912S
DO NOT ARCHIVE

ami(at)MCFADYEAN.FREESERV
Guest

Posted: Wed Feb 22, 2006 12:53 pm Post subject: rpm

OK.

Now I understand where you're coming from; I'd expected to see an explicit 

reference in the manual.



Duncan Mcf

---

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Sun Feb 26, 2006 3:48 pm Post subject: Re: rpm

So does that mean that using a lower RPM like 4800 on a 912-S for cruise is bad ?????

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"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

Gilles.Thesee(at)ac-greno
Guest

Posted: Sun Feb 26, 2006 3:56 pm Post subject: rpm

JetPilot a écrit :



 	  Quote: 	
		  



So does that mean that using a lower RPM like 4800 on a 912-S for cruise is bad ?????



  




	


Hi JetPilot,



Better follow the engine manufacturer recommendations.

You may wish to download the Operator's Manual. All the tables are in it.

As a rule, to insure the best specific consumption, you run at the 

highest manifold pressure, and the lowest RPM compatible with engine 

reliability. 4800 RPM seems quite right for circa 65-75% power.



Regards,

Gilles Thesee

Grenoble, France

http://contrails.free.fr

ami(at)MCFADYEAN.FREESERV
Guest

Posted: Sun Feb 26, 2006 3:56 pm Post subject: rpm

Why would reducing both mechanical stress and thermal stress be bad?



Duncan Mcf.

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David X

Joined: 10 Jan 2006
Posts: 154
Location: Princeton, NJ, USA

Posted: Sun Feb 26, 2006 5:02 pm Post subject: Re: rpm

The only "bad" RPM settings that are evident from available documentation/bulletins are exceeding 5500 for more than 5 minutes, or running below 2000 RPM for extended periods; which may cause gear box "chatter".



Max cruise power will give you most speed, 65% power will give you better economy and range, 75% power will give you the happy medium between speed and economy.



I really don't know if running an engine mostly at 65% power vs. 75% will make it last longer or not. Theoretically, perhaps. I think the greater factors to long life have to do with running MOGAS instead of AVGAS, changing the oil every 50 hours instead of every 100, keeping the carbs tuned, keeping the fliters and plugs clean etc.



Maybe someone who has worn out a few Rotax 912 might have more authoritative opinion.

_________________
Zodiac 601 XL - CZAW Built - Rotax 912S
DO NOT ARCHIVE

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon Feb 27, 2006 4:49 am Post subject: Re: rpm

The stresses on the crankshaft, connecting rods, pistons, piston pins etc. vary with the square of the rpm. This is the case for all parts subject to reciprocating motion, therefore it also applies to valves and pushrods, etc. The Rotax 912 series engine are strong enough to run continuosly at 5,500 rpm. The TBO (I believe) assumes continuous running at that speed but it may assume some lesser percentage power. In any case, lowering the stresses in the engine will increase its life dramatically assuming you take care of all the things already mentioned. 



When I fly with my Ultralight friends at UL speeds (around 65 mph) my 912 is turning around 3,000 rpm and burning way less than 2 gph.



Thom in Buffalo

do not archive

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Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

nyterminat(at)aol.com
Guest

Posted: Mon Feb 27, 2006 3:31 pm Post subject: rpm

 Dave

  

 Are you using Mogas in your 912S? I thought the 912S required premimum unleaded? I would love to fill up at the pump instead of using gas jugs.

  

 Bob Spudis

 N701ZX/912S

 

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jean-paul.roy4(at)tlb.sym
Guest

Posted: Mon Feb 27, 2006 4:05 pm Post subject: rpm

Premium unleaded is still Mogas, not  Avgas.

  

 Jean-Paul

 do not archive

 [quote]   ---

David X

Joined: 10 Jan 2006
Posts: 154
Location: Princeton, NJ, USA

Posted: Mon Feb 27, 2006 5:13 pm Post subject: Re: rpm

It will burn either MOGAS (automobile unleaded gasoline) or AVGAS (low lead aircraft fuel) but you have to change the oil every 25 to 30 hours and clean the lead from the spark plugs about as often. Appearantly, AVGAS gives the rotax the engine the equivilent of clogged arteries over time. :(



Most my flights are less than 4 hours round trip, so I manage to run MOGAS most of the time. On longer trips, I have no choice but to run AVGAS. It's not a big deal to run AVGAS once in a while ... just have to change the oil more often.



If you do run AVGAS, you're supposed to use a particular oil. There's a good article here if you haven't seen it: http://www.rotaxservice.com/rotax_tips/rotax_feed4.htm 



Regards

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Zodiac 601 XL - CZAW Built - Rotax 912S
DO NOT ARCHIVE

nyterminat(at)aol.com
Guest

Posted: Tue Feb 28, 2006 2:56 pm Post subject: rpm

 Dave

  

 What grade fuel are you using? The MOGAS at our airport is only 87 octane, my understanding is that premium unleaded is recommended. I am running the Mobile One Synthetic which is not recommended for AVGAS. I was wondering whether 87 octane would be OK.

  

 Bob Spudis

 N701ZX  do not archive

 

--

David X

Joined: 10 Jan 2006
Posts: 154
Location: Princeton, NJ, USA

Posted: Tue Feb 28, 2006 6:19 pm Post subject: Re: rpm

For the 912, 87 octane is the minimum required. If that's what you are flying, then it's convenient for you at your airfield ... but I'd use 89 octane instead just to avoid engine knock on hot days or risk losing the octane as the fuel sits in the tanks for too long.



For the 912S, 91 octane is the minimum required. That's what I fly, and I usually bring 20 gallons in 5 gallon cans in the back of my truck.  It's a habit now. I usually go to Sonoco because I can get 93 or 94 octane. AVGAS is $4.00 at my field, MOGAS is $2.40 ... so I'm motivated to put up with a little hassle to save $48 on two 15 gallon tank fulls ... and it's better for my engine too.



The down side to MOGAS is that it will begin to lose it's octane rating after about 3 weeks. It will also start to leave a sort of varnish behind if left for about 6 weeks (unless you put in some fuel preservative). This is not a problem with AVGAS.



If you fly about once a week (or more) and your flights are at least an hour long ... then MOGAS is a better way to go. If you fly once a month (or so) then you're better off burning AVGAS and changing out the oil every 35 hours (or so) and cleaning the plugs when you change the oil. 



There is also a lead scavanger additive that you could try if you burn AVGAS. I use it in my CH2000 (which has a Lycoming in it) and it really does work. I take some with me in my Zodiac when I know I'll be flying where there is only AVGAS. The plugs are cleaner and the deposits that are there on the plugs are easier to clean off.



The additive is called TCP and you can get it at Aircraft Spruce: http://www.aircraftspruce.com/catalog/appages/alcortcp.php 



Hope this helps.

_________________
Zodiac 601 XL - CZAW Built - Rotax 912S
DO NOT ARCHIVE

goodings(at)yorku.ca
Guest

Posted: Wed Mar 01, 2006 7:06 am Post subject: RPM

There is a possible concern about using Sunoco 94 octane mogas.  It is my

understanding that the high octane is achieved at least in part by the

addition of ethanol (ethyl alcohol) to gasoline of lower octane rating.

Aircarft engines in general, and Rotax engines in particular, are not

equipped to handle ethanol.  The combustion of the fuel is not the

problem.  Ethanol is a good solvent, and the gaskets, O-rings, etc. in

aircraft engines do not stand up to ethanol.  I listened to a lecture by a

fuel additives expert from one of the oil companies a couple of weeks ago

who made the case that ethanol in aircraft engines is deadly.  It is

fairly easy to test for the presence of ethanol in gasoline.  Put some

gasoline in a clear test tube-type container.  Add an approximately equal

quantity of water.  They separate, water layer on the bottom.  Mark The

dividing line.  Shake it up thoroughly.  If the water-layer fraction has

increased, the fuel contains ethanol, because ethanol dissolves in water,

but gasoline does not.



John Goodings, C-FGPJ, CH601HD with R912S, Waterloo and Toronto.

David X

Joined: 10 Jan 2006
Posts: 154
Location: Princeton, NJ, USA

Posted: Wed Mar 01, 2006 10:34 am Post subject: Re: rpm

A very good point and an oft raised one in various forums.



Can you provide evidence for your statement: "Aircarft engines in general, and Rotax engines in particular, are not equipped to handle ethanol." If you can point to something other than antidotal opinions, I - for one - would be very grateful.



I'm aware of Rotax service bulletins that warn against ethanol (more than 5%) for the two-stroke engines. This makes sense because the fuel is also used to lubricate the engine. The ethanol will compete with the lubricant. Unfortunately, the news spreads like a rumor and grows to include all Rotax engines.



The issue is quite different in regard to the 4-stroke Rotax engines. There are no FAA regs or Rotax service bulletins that disallow ethanol in MOGAS for the Rotax 9xx series engines, despite the fact that ethanol has been used in MOGAS for many years both in the US and Canada.



I've heard this very question asked at Rotax seminars at Oshkosh and again at Sun 'N Fun. The unwavering answer is that the engines have no problem with the new fuels containing up to 10% ethanol. The only concern is the fuel hoses and connectors. Certain materials used in poorer quality connectors or fuel lines may swell or soften with higher levels of ethanol. A good neoprene or buna-N rubber fuel line and brass connectors are preferred.



By the way, the o-rings you spoke of are neoprene.

_________________
Zodiac 601 XL - CZAW Built - Rotax 912S
DO NOT ARCHIVE

nyterminat(at)aol.com
Guest

Posted: Wed Mar 01, 2006 2:45 pm Post subject: rpm

 Dave

 Thanks for the reply. That is what I thought. I have been also carrying around 20 gals in 5 gal jugs and have been using 93 octane in my 912S. It sure would have been easier to pull up to the pump for the 87 octane mogas. I did not realize that the mogas lost it's octane so fast, I am very suprised at that. 

  

 Bob Spudis

 N701ZX /912S

 

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