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Why exactly shouldn't you run a 914 without a prop?
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rparigoris

Joined: 24 Nov 2009
Posts: 792

Posted: Mon Apr 12, 2010 7:51 pm Post subject: Why exactly shouldn't you run a 914 without a prop?

I have read in the past you shouldn't run a 91X without a prop. Why exactly is that?

Here's a guy running a 914 without a prop, seems at low idle without flywheel effect it isn't quite as happy as with a prop, but just a little higher it seems pretty happy.

http://www.youtube.com/watch?v=uksKDll6n7M

Ron Parigoris

Thom Riddle

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

Posted: Tue Apr 13, 2010 3:13 am Post subject: Re: Why exactly shouldn't you run a 914 without a prop?

The primary reason is that with too much throttle and it could very easily over-rev. As this video shows, if you make sure that the throttle is limited, it can be done. 



Keep in mind that the spring pulls the throttle to wide open in normal configuration. The spring can be hooked to the other side of the throttle arm to pull it closed. If I felt a need to run one without a prop that is what I would do.

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Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Tue Apr 13, 2010 5:23 am Post subject: Re: Why exactly shouldn't you run a 914 without a prop?

It's an absolute no no to run the 912 or 914 with no prop. It can over speed at a very small throttle setting  and you won't be able to react in time to save your engine. Prop it and be happy to know it's the right thing to do.

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cicrn(at)telus.net
Guest

Posted: Tue Apr 13, 2010 12:06 pm Post subject: Why exactly shouldn't you run a 914 without a prop?

Years ago, I ran a two stroke (503 w 'A' Box) for a few minutes  

without a prop. About 20 hours later during a gearbox oil change, I  

noticed lots metal stuck to the magnetic drain plug. I flew for a  

couple more hours and changed the oil again. Lots more metal debris.  

I ended up dismantling the gearbox and found that there was evidence  

of the hard surface coming off of the gears. The subsequent rebuild  

was expensive. Coincidence? I think it was a direct result of running  

it without a propeller.

YMMV



Joe



On 13-Apr-10, at 12:15 PM, rparigoris wrote:



 	  Quote: 	
		   

 <rparigor(at)suffolk.lib.ny.us>



 Hi Rick

 Thx. for the reply.

 "Regardless of what someone else has done, or gotten away with, the  

 engine is designed to run with a prop. Why would you want to risk  

 it to run it without one?"

 At the moment I have no need to run without a prop, but got to  

 wondering. I have run plenty of motorcycles and cars that

 are a lot hotter tune than a 914 and have yet to over rev one in  

 neutral.

 Easy to over rev, not very hard to keep within limits. If I ever  

 had a need to run without a prop would keep kill switch close at  

 hand. Running without

 prop is a lot safer if you needed to check something, like  

 intermittent

 miss where you could observe one of those transparent spark plugs like

 Bing sells? Had a nagging charge problem that would allow you to  

 have a volt meter hooked up and aggressively wiggle and polk at  

 connections? Wanted to check exhaust for leaking by blocking  

 exhaust pipe and listening? If you had a nagging coolant or fuel or  

 oil leak that only dripped with engine running? Start up I think  

 can be a bit harder without flywheel which could stress spraigue I  

 imagine, but sure do like the idea of keeping ones self at less  

 risk compared to performing mentioned checks with spinning prop  

 close by.

 Ron Parigoris





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=294086#294086

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Tue Apr 13, 2010 3:06 pm Post subject: Re: Why exactly shouldn't you run a 914 without a prop?

[quote="cicrn(at)telus.net"]Years ago, I ran a two stroke (503 w 'A' Box) for a few minutes  

without a prop. About 20 hours later during a gearbox oil change, I  

noticed lots metal stuck to the magnetic drain plug. I flew for a  

couple more hours and changed the oil again. Lots more metal debris.  

I ended up dismantling the gearbox and found that there was evidence  

of the hard surface coming off of the gears. The subsequent rebuild  

was expensive. Coincidence? I think it was a direct result of running  

it without a propeller.

YMMV



Joe



On 13-Apr-10, at 12:15 PM, rparigoris wrote:



 	  Quote: 	
		   

 <rparigor>



 Hi Rick

 Thx. for the reply.

 "Regardless of what someone else has done, or gotten away with, the  

 engine is designed to run with a prop. Why would you want to risk  

 it to run it without one?"

 At the moment I have no need to run without a prop, but got to  

 wondering. I have run plenty of motorcycles and cars that

 are a lot hotter tune than a 914 and have yet to over rev one in  

 neutral.

 Easy to over rev, not very hard to keep within limits. If I ever  

 had a need to run without a prop would keep kill switch close at  

 hand. Running without

 prop is a lot safer if you needed to check something, like  

 intermittent

 miss where you could observe one of those transparent spark plugs like

 Bing sells? Had a nagging charge problem that would allow you to  

 have a volt meter hooked up and aggressively wiggle and polk at  

 connections? Wanted to check exhaust for leaking by blocking  

 exhaust pipe and listening? If you had a nagging coolant or fuel or  

 oil leak that only dripped with engine running? Start up I think  

 can be a bit harder without flywheel which could stress spraigue I  

 imagine, but sure do like the idea of keeping ones self at less  

 risk compared to performing mentioned checks with spinning prop  

 close by.

 Ron Parigoris

	




No no no...  Trust me, the hammering the gears get _with_ a prop attached is way worse than the little bit of lash they get running free.....



The real hazard, as Roger and others have said is overrevving. Even at a typical idle speed, the load a prop puts on the engine is considerable, so the throttles are open a surprising amount even at idle. If you remove the prop without also reducing the idle throttle setting, it'll likely spin up and overrev....



For example, the 503 dual carb needs the slides completely bottomed out to idle with no load and even then the lowest it'll go is about 1800 rpm.....

But it idles perfectly at 1800 rpm with no load and I'd assume the flywheel in the 912 series would be plenty for it to idle without a load

__IF__

the throttles were closed enough....



Still I agree, don't try this at home! 



LS

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AmphibFlyer

Joined: 29 Dec 2009
Posts: 25

Posted: Wed Apr 14, 2010 5:32 am Post subject: Re: Why exactly shouldn't you run a 914 without a prop?

 	  rparigoris wrote: 	
		  I have read in the past you shouldn't run a 91X without a prop. Why exactly is that?

Here's a guy running a 914 without a prop, seems at low idle without flywheel effect it isn't quite as happy as with a prop, but just a little higher it seems pretty happy.

http://www.youtube.com/watch?v=uksKDll6n7M

Ron Parigoris 	




That's Russ Garner, a friend of mine. The reason Rotax says not to run their engines without a prop is that they attach the carb springs to keep the throttles wide open unless something pulls them closed.  Russ has the springs on the other way (which is standard for all SeaReys), so the engine idles very nicely until you open the throttles manually. I ran that very engine three days ago myself with no prop and it idled perfectly smoothly.

blackmore(at)platinum.ca
Guest

Posted: Thu Apr 15, 2010 6:07 am Post subject: Why exactly shouldn't you run a 914 without a prop?

scottmschmidt(at)yahoo.co
Guest

Posted: Thu Apr 15, 2010 9:51 am Post subject: Why exactly shouldn't you run a 914 without a prop?

I just joined this group so I can start learning about the Rotax.  Just started an RV-12. 



I may have missed something discussed earlier about this thread, but why would you ever run this motor before mounting it on the plane with a prop?

What is the advantage of running it without a propeller?  When I built my RV-10 I had to be very careful not to bet my CHT's over 200 during my 3 test runs before the first flight.  I just made sure the mag and ignition system worked, the oil pressure was up and the prop cycled.  But I don't know the break-in procedures for the 912 yet so that is why I am asking. 



Thanks. 

 

Scott Schmidtscottmschmidt(at)yahoo.com



From: lucien <lstavenhagen(at)hotmail.com>

To: rotaxengines-list(at)matronics.com

Sent: Thu, April 15, 2010 7:46:16 AM

Subject: Re: Why exactly shouldn't you run a 914 without a prop?



 --> RotaxEngines-List message posted by: "lucien" <lstavenhagen(at)hotmail.com (lstavenhagen(at)hotmail.com)>

Gilles.Thesee(at)ac-greno wrote:

 	  Quote: 	
		   AmphibFlyer a ï¿½crit :

 How do you qualify a "perfectly smooth" idle ?

 My engine also idles perfectly smoothly (with a prop attached, though) 

 between 1100 and 1800 rpm, and yet Rotax advises against idling below 

 1400 rpm, due to stress and chatter in the reduction gear, which to date 

 I have never been able to detect.

 

 


	




Like you said, tho, that doesn't mean everything is necessarily ok and there won't be long-term problems. 

In fact, I was in a nasty thread a while back on another group where someone was advocating a shutdown procedure that introduced the possible hazard of running the engine below the specified minimum if it weren't carried out just exactly  right. The claim was that it came from Eric Tucker or something like that but was otherwise backed up with nothing else but that heresay. 

My contention is, at 20 large (and continuing to go up) a pop, the 912 is a poor platform for testing these oddball procedures gotten off the Internet or somewhere, unless you really have a lot of money to burn.



As for running the 912 series without a prop, it's also very likely that not a lot of field testing has been done with the 912 in that particular configuration .



So basically, these oddball ideas are done at one's own risk, both financially and in terms of support from Rotax and dealers, etc. On something relatively inexpensive like an auto or motorcycle engine you're not likely to be out a whole lot of cash if something breaks, but not with our 912's. 



Let's be careful out there,



LS



--------

LS

Titan II SS





Read this topic online  here:



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rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Fri Apr 16, 2010 3:50 am Post subject: Why exactly shouldn't you run a 914 without a prop?

Guys and gals, I know it's been said before, but, again, how about just because, for 99% of 914 installers it's a bad idea because it will void your warranty and the good folks at Rotax who have put over a quarter century into refining the 912 / 914 series say it's not a good idea. As Brian Carpenter of Rainbow Aviation said to our LSARM class many moons ago, "They (Rotax) have a hundred or so white coated engineers running around who are paid to figure out this stuff, what chance do you think you have of finding something they haven't". When Ron Pagoris first asked this question of the group, my response was, "Why would you want to?". Ron came up with a list of reasons that centered around his dislike for working around a spinning propeller. I can appreciate that, for sure. I didn't respond because I didn't know if it would have made any difference to the discussion and I respected his reasoning.

 However, with a few days reflection, I did come up with a few ideas that addressed his concerns.

Intermittent coolant, fuel or oil leaks.....use fluorescent dyes. I'm doing that right now in my 582 to track down a pesky coolant leak. $20 for the blacklight and $5 for the dye and I've eliminated the need to work around a spinning prop.

 Intermittent ignition problems.....use a spark plug tester, oscilloscope, ohm meter, well, you get the idea. You may have to spin the prop, but you can at least get away from it.

Ron, I know I haven't addressed all your issues here, sorry, I'm an AR deleter of posts and just right now too lazy to go to the forum to back track.

 Last, and I think this is the big one, simply use a club prop and a cage around it. Now, I'm quite sure this isn't in most tool kits, it isn't in mine, although if needed I have the equipment to make both in a few days. 

 Last fall our EAA chapter was lucky enough to have some of the volunteers from Bomber Force bring out one of Doc's R-3350's mounted on a test stand to do a night time run up of that big radial engine for us. The B-29 runs a 16' (4.88 m) prop which would have required a massive test stand. Instead they have a 3' (.9 m) club prop. With it they were able to run the engine all the way to take off power without damage. On the other end of the scale, when my friend Dave worked for Cascade Ultralights he used a 2' (.6 m) wooden club prop to do break in and diagnostic work on the 250cc Zenoah's.

 My point is that there are work arounds for darn near every situation you can come up with that don't require running any engine against the advice of its manufacturer.

Just a thought.

 Rick Girard





  [quote][b]

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Dick Maddux

Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl

Posted: Fri Apr 16, 2010 4:40 am Post subject: Why exactly shouldn't you run a 914 without a prop?

Ron,

  Now you see what you did ? You should spank yourself for starting this thread !

                                                    Dick Maddux

                                                    Milton,Fl

  [quote][b]

rparigoris

Joined: 24 Nov 2009
Posts: 792

Posted: Fri Apr 16, 2010 5:38 pm Post subject: Re: Why exactly shouldn't you run a 914 without a prop?

Hmmm

True not a 91X, but these guys decided to take the prop load off engine below 2500RPM:

http://www.rotaxparts.net/Scripts/prodView.asp?idProduct=1210

Ron Parigoris

occom

Joined: 26 Aug 2006
Posts: 404

Posted: Sat Apr 17, 2010 3:15 am Post subject: Why exactly shouldn't you run a 914 without a prop?

That unit is possible because of the design of the "C" box. It does allow 

for the smooth idle of the engine, but the 912 doesn't suffer terribly from 

that problem. Of interest is the statement about shock loads in the small 

info blurb. I do not regard the prop on the gearbox as a contributor to a 

smooth and continuous idle as some others do. I see it is a large inertia 

load, contributing to load spikes and gearbox shocks. It isn't a problem 

because Rotax designed for it obviously, but observation says it doesn't 

make things smoother. There is a similar clutch engagement type device on 

one of the Subaru conversion engines, not sure which one. I wonder how badly 

the freewheeling prop will contribute to drag in the case that the engine 

stops and the clutch disengages, can the freewheeling prop overspeed itself, 

etc.



---

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Sat Apr 17, 2010 4:47 am Post subject: Why exactly shouldn't you run a 914 without a prop?

I have thousands  of Rotax powered hours. Clutches on C box are just not 

that exicting to me. It an attribute when on floats  for docking but the 

cons out weight any advantage.



suberu are a heavy engine, they wok ok but the weight disadvantage

is a real drawback.



lots of rotax powered flicks heres   http://www.youtube.com/user/kitfoxflyer

---

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lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Sat Apr 17, 2010 4:50 am Post subject: Re: Why exactly shouldn't you run a 914 without a prop?

 	  occom wrote: 	
		  That unit is possible because of the design of the "C" box. It does allow 

for the smooth idle of the engine, but the 912 doesn't suffer terribly from 

that problem. Of interest is the statement about shock loads in the small 

info blurb. I do not regard the prop on the gearbox as a contributor to a 

smooth and continuous idle as some others do. I see it is a large inertia 

load, contributing to load spikes and gearbox shocks. It isn't a problem 

because Rotax designed for it obviously, but observation says it doesn't 

make things smoother. There is a similar clutch engagement type device on 

one of the Subaru conversion engines, not sure which one. I wonder how badly 

the freewheeling prop will contribute to drag in the case that the engine 

stops and the clutch disengages, can the freewheeling prop overspeed itself, 

etc.



--- 	




For what it's worth, my Kolb FSII ran a 503 equipped with the RK-400 clutch. I finally had to stop talking about when I was on the Kolb list because several of its most prominent members just couldn't resist telling me over and over what a useless device it was, even tho they never used one and despite my repeating my positive experience with its use.



The truth is, the 503 idles much _more_ smoothly disengaged from the prop with the clutch than it does with a normal gearbox/prop. However, when you add the clutch you also readjust the idle speed and you also don't have the overspeeding hazard in any case (you still have the prop!).



As for the performance in the air, that's a whole 'nother topic.



Finally, I also wish there was a similar device for the 912 series. I'd add it in about 2 seconds 



LS

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lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Sat Apr 17, 2010 5:30 am Post subject: Re: Why exactly shouldn't you run a 914 without a prop?

 	  dave wrote: 	
		  I have thousands  of Rotax powered hours. Clutches on C box are just not 

that exicting to me. It an attribute when on floats  for docking but the 

cons out weight any advantage.



--- 	




Not meaning to keep pouring 100LL on this, but...  What would those cons be?



LS

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dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Sat Apr 17, 2010 6:20 am Post subject: Why exactly shouldn't you run a 914 without a prop?

Not able to hand prop

extra parts that "could " give troubles



giant airbrake

---

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Sat Apr 17, 2010 6:22 am Post subject: Why exactly shouldn't you run a 914 without a prop?

try this with a clutch



http://www.youtube.com/watch?v=osZC56FyM6o

---

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Sat Apr 17, 2010 7:06 am Post subject: Re: Why exactly shouldn't you run a 914 without a prop?

 	  dave wrote: 	
		  Not able to hand prop

extra parts that "could " give troubles



giant airbrake

--- 	




Er, that hardly qualifies as a large set of cons outweighing the (much larger) set of pros of using the RK-400 clutch. 



Like I said, most of the folks who go on about how worthless the clutch is have very little, if any, time on a clutch-equipped engine/airplane.



No hand propping is a good try, but I'm not too convinced - the Rotax 2-strokes come with an excellent pull-rope starting system that is very reliable and gives little trouble. Even if, say the rope pulls out of the handle, the pull start is easily fixable in the field with a few hand tools you can keep in your flight bag. So it'd be rare indeed that you'd have to resort to hand starting (a very dangerous proposition on many pusher designs anyway).

If you put a mag-end electric start on Rotax 2-stroke, you get what you deserve anyway. At that point you should have gone with the E box which addresses that concern already.



I totally don't buy the extra-trouble argument. The RK-400 is a very well designed, heavy-duty item that lasts simply forever. On my FSII, the original engine was starting to wear out (at about 400 hours) before even a few _thousandths_ had been worn off the original set of shoes (I still have them out in the hangar in fact).  The RK-400 was tested on the 618 and couldn't be made to slip or otherwise give any trouble at all even on that huge monster. 



The giant airbrake argument is another I get all the time from folks who don't run the clutch. They don't realize, for example, that when the clutch is disengaged in the air (engine-idle), the plane flies _exactly_ as it would with the engine off. So you can _exactly_ replicate the engine off situation in your emergency procedure practice without having to shut the engine down. This makes getting familiar with the engine-off glide much safer to practice - i.e. if you really do happen to screw up an approach during practice you're not in a real emergency if you can't get the cold engine started again.



So on that day when the engine actually does stop for real, you're not dangerously trying to stretch a glide you've hardly ever practiced in the case of a fixed prop. Instead, it's exactly the same condition you've already practiced a million times before, greatly increasing your chances of a successful descent and landing.



Sorry, don't buy this one either 



LS

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occom

Joined: 26 Aug 2006
Posts: 404

Posted: Sat Apr 17, 2010 8:40 am Post subject: Why exactly shouldn't you run a 914 without a prop?

Lucien, this is extraordinarily interesting to me. I have always understood 

that when the engine is stopped, the prop will accelerate wildly and 

generate a huge drag effect. Are you saying that this is not the case? I am 

very interested in what is observed and not conceived. Please feel free to 

email off list if you care to.



BTW the "E" box is not a candidate for the clutch as you would be unable to 

start the engine, I'm sure you already knew that but you made such a case 

for it with the electric start that I thought someone might not be aware.



---

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Sat Apr 17, 2010 9:16 am Post subject: Re: Why exactly shouldn't you run a 914 without a prop?

 	  occom wrote: 	
		  Lucien, this is extraordinarily interesting to me. I have always understood 

that when the engine is stopped, the prop will accelerate wildly and 

generate a huge drag effect. Are you saying that this is not the case? I am 

very interested in what is observed and not conceived. Please feel free to 

email off list if you care to.

	




"accelerate wildly" is of course silly and not the case, no. It does windmill in the relative wind but the magnitude of the drag effect is also usually overblown, again by folks who've never flown a clutch equipped plane. On my FSII, for example, the drag added by my 68" WD 3 blade freewheeling wasn't too much more than the added drag of the 66" TPI 2 blade stopped on a dead engine on a friend mine's FSII. My glide ratio was a little worse than his, but not the "drag chute" myth spread by the guys who don't use a clutch.



They also don't understand that the drag that does get added can actually be useful (i.e. if you need extra drag such as when high/hot on final).

 	  Quote: 	
		  



BTW the "E" box is not a candidate for the clutch as you would be unable to 

start the engine, I'm sure you already knew that but you made such a case 

for it with the electric start that I thought someone might not be aware.



--- 	




No, I was talking about the concern that you couldn't hand prop. My point was the E box kills two birds with one stone there - you have the prop fixed to the crankshaft for hand propping if desired and you can also retain the pull start on the mag end in case of an electrical problem.



LS

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