Today's Message Index:
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1. 03:07 AM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Dave G)
2. 03:52 AM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Gilles Thesee)
3. 04:50 AM - Why exactly shouldn't you run a 914 without a prop? (Richard Girard)
4. 05:40 AM - Re: Why exactly shouldn't you run a 914 without a prop? (Catz631@aol.com)
5. 01:04 PM - Re: Rotax 912/914 Mechanical Fuel injection (Catz631@aol.com)
6. 01:11 PM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Dave G)
7. 06:39 PM - Re: Why exactly shouldn't you run a 914 without a prop? (rparigoris)
8. 06:55 PM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Gilles Thesee)
Message 1
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| Subject: | Re: Why exactly shouldn't you run a 914 without |
a prop?
Hello Gilles, no, I would not. Is there some particular point that you feel
is important that you would like to make? I can think of a couple of things
with running the engine without a prop that may or may not be issues. The
crank and gearbox suffering damage from torsional stress spikes or gearbox
chatter would not be areas I would be concerned about. However BRP's
cautions are centered around over revving.
I am somewhat curious to hear why you think extraordinary force spikes will
present themselves in the situation discussed, low rpm, low throttle
openings, no gearbox load. I don't require or demand any proof to back up
your thoughts.
----- Original Message -----
From: "Gilles Thesee" <Gilles.Thesee@ac-grenoble.fr>
> Dave,
>
> Would you care to share with us the physics beyond your opinion ?
> I'm surprised that you make a point of over reving though this situation
> can be easily controlled by careful use of the throttle, as has already
> been pointed out. Whereas you seem to dismiss torsional vibrations which
> need lots of experimenting to take care of.
>
Message 2
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| Subject: | Re: Why exactly shouldn't you run a 914 without |
a prop?
Dave G a crit :
> Is there some particular point that you feel is important that you
> would like to make? I can think of a couple of things with running the
> engine without a prop that may or may not be issues. The crank and
> gearbox suffering damage from torsional stress spikes or gearbox
> chatter would not be areas I would be concerned about. However BRP's
> cautions are centered around over revving.
My point is, in stating that overreving is the only damage induced by
running without a prop, one might lure the beginner into thinking that
since the revs can be easily controlled, there is no danger in running
the engine with no prop.
>
> I am somewhat curious to hear why you think extraordinary force spikes
> will present themselves in the situation discussed, low rpm, low
> throttle openings, no gearbox load. I don't require or demand any
> proof to back up your thoughts.
A reciprocating engine can be considered as a mass-spring system with
wildly variable torque inputs. Any change to the masses or inertia in
the system will dramatically change the vibration modes, and induce
torque spikes or reversals well outside what the system has been
designed and tested for. The torque input variations are comparatively
higher at low RPM.
I feel it important to determine whether the "no problems running with
no prop" opinion is supported by facts and real knowledge, or just beliefs.
Best regards,
--
Gilles
http://contrails.free.fr
Message 3
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| 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
Message 4
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| Subject: | Re: 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
Message 5
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| Subject: | Re: Rotax 912/914 Mechanical Fuel injection |
Here is some more gouge (Navy term) on the Fuel injection:
. HP increase of 8-10%
. no more carb sync
. throttle and manual mixture control
. all mechanical, no electrical
. compatible with avgas,auto fuel and alcohol blends
. precise metering under all conditions
. price is $3600
Airflow Performance Inc. Spartanburg,SC phone: 864-576-4512
I also looked at the "Billet Pump" which is a super deluxe replacement for
the 912/914 fuel pump. Now this is really well built. When my pump heads
south, I will definitely buy this unit! No "Mickey mouse" here it is really a
nice unit. The 912 unit retails for $368, the 914$396. This is from Corbi Air
Inc. ph: 877-267-2424.
These were two of the more interesting things I saw at Lakeland. I did see
a Titan T-51 go into a tomato field. It was a shame. He made a low pass and
it sounded real nice. He circled to do another pass and instead descended
into a tomato field. He had it on the road next to the field put hit sand and
went belly down in the field. No one was hurt but sure whacked a beautiful
3/4 scale metal mustang. Apparently, according to the write up in the paper,
he switched fuel tanks. Moral: don't do it at low altitude!
That's all for now
Dick Maddux
Fox 4
Milton,Fl
Message 6
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| Subject: | Re: Why exactly shouldn't you run a 914 without |
a prop?
I don't believe I did state that overrevving is the only damage. I think
that I pointed out that Rotax identifies overrevving as a distinct
possibility that will likely result in damage. I did point out that
overrevving can occur very quickly. They identify no other potential
problems.
Thanks for your thoughts on low rpm running and the mass-spring concept,
something to consider for sure.
My major "belief" in the matter is that it's best to follow the
manufacturers recommendations unless you have some very good reason to
disregard them, in which case you are now forging your own trail and should
be comfortable with any consequences that follow. On the other hand without
the trail blazers, we would never make any progress.
----- Original Message -----
From: "Gilles Thesee" <Gilles.Thesee@ac-grenoble.fr>
> My point is, in stating that overreving is the only damage induced by
> running without a prop, one might lure the beginner into thinking that
> since the revs can be easily controlled, there is no danger in running the
> engine with no prop.
>
>> I am somewhat curious to hear why you think extraordinary force spikes
>> will present themselves in the situation discussed, low rpm, low throttle
>> openings, no gearbox load. I don't require or demand any proof to back up
>> your thoughts.
> A reciprocating engine can be considered as a mass-spring system with
> wildly variable torque inputs. Any change to the masses or inertia in the
> system will dramatically change the vibration modes, and induce torque
> spikes or reversals well outside what the system has been designed and
> tested for. The torque input variations are comparatively higher at low
> RPM.
>
> I feel it important to determine whether the "no problems running with no
> prop" opinion is supported by facts and real knowledge, or just beliefs.
>
> Best regards,
> --
> Gilles
> http://contrails.free.fr
>
>
>
Message 7
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| 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
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=294497#294497
Message 8
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| Subject: | Re: Why exactly shouldn't you run a 914 without |
a prop?
rparigoris a crit :
>
> 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
>
Hi Ron,
Yes, they sell this device for the 2-strokes. Far less expensive, and
far less reliable than the 91x.
Now if you were asking about starting your Rotax with no prop, I would
strongly advise against it.
But are you really asking ?
Best regards,
--
Gilles
http://contrails.free.fr
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