---------------------------------------------------------- RotaxEngines-List Digest Archive --- Total Messages Posted Tue 04/13/10: 7 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:14 AM - Re: Why exactly shouldn't you run a 914 without a prop? (Thom Riddle) 2. 06:24 AM - Re: Why exactly shouldn't you run a 914 without a prop? (Roger Lee) 3. 07:54 AM - Re: Why exactly shouldn't you run a 914 without a prop? (Richard Girard) 4. 11:16 AM - Re: Why exactly shouldn't you run a 914 without a prop? (rparigoris) 5. 01:00 PM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Gilles Thesee) 6. 01:06 PM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Joe Harrington) 7. 04:08 PM - Re: Why exactly shouldn't you run a 914 without a prop? (lucien) ________________________________ Message 1 _____________________________________ Time: 04:14:39 AM PST US Subject: RotaxEngines-List: Re: Why exactly shouldn't you run a 914 without a prop? From: "Thom Riddle" 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. -------- Thom Riddle Buffalo, NY Kolb Slingshot SS-021 Jabiru 2200A #1574 Tennessee Prop 64x32 An ounce of action is worth a ton of theory. - Friedrich Engels Read this topic online here: http://forums.matronics.com/viewtopic.php?p=294055#294055 ________________________________ Message 2 _____________________________________ Time: 06:24:11 AM PST US Subject: RotaxEngines-List: Re: Why exactly shouldn't you run a 914 without a prop? From: "Roger Lee" 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. -------- Roger Lee Tucson, Az. Light Sport Repairman - Maintenance Rated Rotax Repair Center 520-574-1080 Read this topic online here: http://forums.matronics.com/viewtopic.php?p=294062#294062 ________________________________ Message 3 _____________________________________ Time: 07:54:27 AM PST US Subject: Re: RotaxEngines-List: Why exactly shouldn't you run a 914 without a prop? From: Richard Girard 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? Rick Girard On Mon, Apr 12, 2010 at 10:51 PM, rparigoris wrote: > rparigor@suffolk.lib.ny.us> > > 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 > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=294046#294046 > > ________________________________ Message 4 _____________________________________ Time: 11:16:32 AM PST US Subject: RotaxEngines-List: Re: Why exactly shouldn't you run a 914 without a prop? From: "rparigoris" 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 ________________________________ Message 5 _____________________________________ Time: 01:00:22 PM PST US From: Gilles Thesee Subject: Re: RotaxEngines-List: Re: Why exactly shouldn't you run a 914 without a prop? Hi Ron, Please allow me to chime in. > 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. > Cars and motorcycles are *designed* to run in neutral. They have carefully designed flywheels, bobweights, balance masses to dampen out torque vibrations. Aero engines rely on a prop with specific inertia range to achieve the same goal. Just think of the press fitted crank, timing gear, reduction gear. > 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. > Treating such an expensive piece of hardware the way the manufacturer forbids is not necessarily the best way to ensure reliability. As for the simple troubleshooting you describe - not likely to be needed in a properly assembled homebuilt- chock the airplane, inspect the engine, run it up, stop it, re-inspect, that's all. Best regards, -- Gilles http://contrails.free.fr ________________________________ Message 6 _____________________________________ Time: 01:06:46 PM PST US From: Joe Harrington Subject: Re: RotaxEngines-List: Re: 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: > > > 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 > > ________________________________ Message 7 _____________________________________ Time: 04:08:00 PM PST US Subject: RotaxEngines-List: Re: Why exactly shouldn't you run a 914 without a prop? From: "lucien" [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: > > > > 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 -------- LS Titan II SS Read this topic online here: http://forums.matronics.com/viewtopic.php?p=294117#294117 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message rotaxengines-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/RotaxEngines-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/rotaxengines-list Browse Digests http://www.matronics.com/digest/rotaxengines-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.