Today's Message Index:
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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
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| 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.
--------
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
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| 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.
--------
Roger Lee
Tucson, Az.
Light Sport Repairman - Maintenance Rated
Rotax Repair Center
520-574-1080
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| Subject: | Re: Why exactly shouldn't you run a 914 without a |
prop?
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 <rparigor@suffolk.lib.ny.us>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
>
>
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| Subject: | Re: Why exactly shouldn't you run a 914 without a prop? |
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
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| Subject: | 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
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| Subject: | 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:
> <rparigor@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
>
>
Message 7
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| 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:
>
>
>
> 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
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