Today's Message Index:
----------------------
1. 04:15 AM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Dave G)
2. 05:47 AM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Dave Fisher)
3. 05:51 AM - Re: Why exactly shouldn't you run a 914 without a prop? (lucien)
4. 06:30 AM - Re: Why exactly shouldn't you run a 914 without a prop? (lucien)
5. 06:39 AM - Re: Why exactly shouldn't you run a 914 without a prop? (AmphibFlyer)
6. 07:20 AM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Dave Fisher)
7. 07:22 AM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Dave Fisher)
8. 08:07 AM - Re: Why exactly shouldn't you run a 914 without a prop? (lucien)
9. 09:40 AM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Dave G)
10. 09:52 AM - 914 Fuel Flow (h&jeuropa)
11. 10:16 AM - Re: Why exactly shouldn't you run a 914 without a prop? (lucien)
12. 11:04 AM - Re: 914 Fuel Flow (Mike Parkin)
13. 01:01 PM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Dave Fisher)
14. 01:23 PM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Richard Girard)
15. 02:34 PM - Re: 914 Fuel Flow (Michael Grass)
16. 07:20 PM - Re: 914 Fuel Flow (Gilles Thesee)
17. 07:44 PM - Re: Re: Why exactly shouldn't you run a 914 without a prop? (Gilles Thesee)
18. 09:28 PM - Re: Why exactly shouldn't you run a 914 without a prop? (rparigoris)
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| Subject: | Re: 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.
----- Original Message -----
From: "rparigoris" <rparigor@suffolk.lib.ny.us>
Sent: Friday, April 16, 2010 10:38 PM
Subject: RotaxEngines-List: Re: Why exactly shouldn't you run a 914 without
a prop?
> <rparigor@suffolk.lib.ny.us>
>
> 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
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| Subject: | Re: 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
----- Original Message -----
From: "Dave G" <occom@ns.sympatico.ca>
Sent: Saturday, April 17, 2010 7:13 AM
Subject: Re: RotaxEngines-List: Re: 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.
>
> ----- Original Message -----
> From: "rparigoris" <rparigor@suffolk.lib.ny.us>
> To: <rotaxengines-list@matronics.com>
> Sent: Friday, April 16, 2010 10:38 PM
> Subject: RotaxEngines-List: Re: Why exactly shouldn't you run a 914
> without a prop?
>
>
>> <rparigor@suffolk.lib.ny.us>
>>
>> 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
>
>
>
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| 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
--------
LS
Titan II SS
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=294520#294520
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| 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
--------
LS
Titan II SS
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=294522#294522
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| Subject: | Re: Why exactly shouldn't you run a 914 without a prop? |
flyadive(at)gmail.com wrote:
> It never ceases to amaze me .... 1.5 Million Years to evolve from
> Neanderthal to Modern Man.
> ...
> What the hell does it prove if YOU can get a ROTAX to run without a prop?
> Ya want a pat on the back - - - OK, Here it is. Pat - Pat.
> Now, give every one your N-Number and Serial Number of the engine so
> they know to stay
> away from them when you go to sell.
>
> Barry
>
Dear Barry:
If you want information, please try to be civil. If you want to be abusive, go
find a cave and make up stories for the Neanderthals there, who might be entertained.
Science requires light, not fantasy or invective.
I posted the information that Russ Garner has run a Rotax 914 without a prop in
order to let the the h. Sapiens here know that is it possible, even though Rotax
advises against it in several documents. Whether it is advisable to run the
engine without a prop, I can't say--can only report that Russ has run that particular
engine for several hours with no apparent damage.
The engine has a flywheel; that is clear if you look at the Illustrated Parts Manual,
which is available online. Let's please stick to what we observe and can
verify, and not cloud the picture with untested hypotheses.
=Don
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=294525#294525
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| Subject: | Re: Why exactly shouldn't you run a 914 without |
a prop?
Not able to hand prop
extra parts that "could " give troubles
giant airbrake
----- Original Message -----
From: "lucien" <lstavenhagen@hotmail.com>
Sent: Saturday, April 17, 2010 9:30 AM
Subject: RotaxEngines-List: Re: Why exactly shouldn't you run a 914 without
a prop?
> <lstavenhagen@hotmail.com>
>
>
> 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
>
> --------
> LS
> Titan II SS
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=294522#294522
>
>
>
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| Subject: | Re: Why exactly shouldn't you run a 914 without |
a prop?
try this with a clutch
http://www.youtube.com/watch?v=osZC56FyM6o
----- Original Message -----
From: "lucien" <lstavenhagen@hotmail.com>
Sent: Saturday, April 17, 2010 9:30 AM
Subject: RotaxEngines-List: Re: Why exactly shouldn't you run a 914 without
a prop?
> <lstavenhagen@hotmail.com>
>
>
> 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
>
> --------
> LS
> Titan II SS
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=294522#294522
>
>
>
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| 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
--------
LS
Titan II SS
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=294535#294535
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| Subject: | Re: 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.
----- Original Message -----
From: "lucien" <lstavenhagen@hotmail.com>
>> 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.
>
> 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
>
> --------
> LS
> Titan II SS
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=294535#294535
>
>
>
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We are finally starting to fly cross country and use cruise power settings. We
have a 914 with intercooler and Airmaster constant speed prop in our Europa.
When using 75% power per section 10.1.1.1 (5000 rpm 31 in Hg) we see fuel flow
of 7.5 gph. Our EGTs are about 1450. The spark plugs have a nice tan color
to them. The fuel consumption graph (fig. 11) suggests fuel flow should be
about 5.5 gph.
If we throttle back to 5000 rpm, 29 in Hg, fuel flow drops to 6 gph. Not sure
where this setting puts us on the consumption graph!
What fuel flow do others see? What power settings do others use?
Is our mixture too rich and is that adjusted by changing the position of the needles
in the carbs? Dean at Lockwood said don't change anything, mostly because
the plug colors are correct.
Thanks
Jim & Heather
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=294545#294545
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| 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).
>
>
> 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
--------
LS
Titan II SS
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=294551#294551
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Hi Jim & Heather,
My Europa 914/Airmaster (monowheel) seems pretty close to the 5.5 gph in the
cruise. I normally cruise on fuel flow (generally 19 litres/hr) which gives
about 130 knots indicated, a little faster when lightweight. 7.5 gph equates
to 28 litres/hour which seems very high. Perhaps your fuel flow instrument
needs calibrating. Measuring actual fuel usage over time may help.
Regards,
Mike
Do not archive
-----Original Message-----
From: owner-rotaxengines-list-server@matronics.com
[mailto:owner-rotaxengines-list-server@matronics.com] On Behalf Of
h&jeuropa
Sent: 17 April 2010 17:52
Subject: RotaxEngines-List: 914 Fuel Flow
We are finally starting to fly cross country and use cruise power settings.
We have a 914 with intercooler and Airmaster constant speed prop in our
Europa. When using 75% power per section 10.1.1.1 (5000 rpm 31 in Hg) we
see fuel flow of 7.5 gph. Our EGTs are about 1450. The spark plugs have a
nice tan color to them. The fuel consumption graph (fig. 11) suggests fuel
flow should be about 5.5 gph.
If we throttle back to 5000 rpm, 29 in Hg, fuel flow drops to 6 gph. Not
sure where this setting puts us on the consumption graph!
What fuel flow do others see? What power settings do others use?
Is our mixture too rich and is that adjusted by changing the position of the
needles in the carbs? Dean at Lockwood said don't change anything, mostly
because the plug colors are correct.
Thanks
Jim & Heather
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=294545#294545
Checked by AVG - www.avg.com
07:31:00
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| Subject: | Re: Why exactly shouldn't you run a 914 without |
a prop?
lucien.
many rotax powered planes do not have pull starts and you could never start
since there is not room for one.
if they got c box and electric starst you would need to pull the engine on a
Kitfox to get to the pull start.
I have E box on mine, battery dead no problem. wing the prop.
I have no use for a clutch but I don;t have one to brag about.
You have one and have good luck, will you still like once it gone ?
Dave
----- Original Message -----
From: "lucien" <lstavenhagen@hotmail.com>
Sent: Saturday, April 17, 2010 11:06 AM
Subject: RotaxEngines-List: Re: Why exactly shouldn't you run a 914 without
a prop?
> <lstavenhagen@hotmail.com>
>
>
> 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
>
> --------
> LS
> Titan II SS
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=294535#294535
>
>
>
Message 14
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| Subject: | Re: Why exactly shouldn't you run a 914 without |
a prop?
Well, I ran the Rice King for about 50 hours and I didn't find it the
panacea you want to make it, but then I don't run a sea plane or a tow
plane. It DID reduce the glide of my Kolb Mk III to somewhere between 1 to 1
and 2 to 1. As long as I did my approaches with the engine at 3000 RPM it
made no difference. If I chopped the throttle I got Space Shuttle descents.
I traded it for flight time at Wallaby Ranch and went back to stock. I've
had engine outs twice since and with the prop stopped it still has about
twice the glide it had with the RK.
Rick Girard
On Sat, Apr 17, 2010 at 12:16 PM, lucien <lstavenhagen@hotmail.com> wrote:
> lstavenhagen@hotmail.com>
>
>
> 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).
>
> >
> >
> > 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
>
> --------
> LS
> Titan II SS
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=294551#294551
>
>
Message 15
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| Subject: | Re: 914 Fuel Flow |
Jim, Heather,
Might a silly question but worthwhile to check. Did you check the return
fuel flow meter that it is indeed working and the setup in your display unit
to display the differential value?
Just a thought.
Michael Grass
A266
----- Original Message -----
From: "h&jeuropa" <butcher43@att.net>
Sent: 2010-04-17 12:52
Subject: RotaxEngines-List: 914 Fuel Flow
> <butcher43@att.net>
>
> We are finally starting to fly cross country and use cruise power
> settings. We have a 914 with intercooler and Airmaster constant speed
> prop in our Europa. When using 75% power per section 10.1.1.1 (5000 rpm
> 31 in Hg) we see fuel flow of 7.5 gph. Our EGTs are about 1450. The
> spark plugs have a nice tan color to them. The fuel consumption graph
> (fig. 11) suggests fuel flow should be about 5.5 gph.
>
> If we throttle back to 5000 rpm, 29 in Hg, fuel flow drops to 6 gph. Not
> sure where this setting puts us on the consumption graph!
>
> What fuel flow do others see? What power settings do others use?
>
> Is our mixture too rich and is that adjusted by changing the position of
> the needles in the carbs? Dean at Lockwood said don't change anything,
> mostly because the plug colors are correct.
>
> Thanks
>
> Jim & Heather
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=294545#294545
>
>
>
Message 16
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| Subject: | Re: 914 Fuel Flow |
h&jeuropa a crit :
> What fuel flow do others see? What power settings do others use?
>
Our fuel flow reads 21-22 L/h at 75 % (31/5000) and about 33-34 l/h at
115 % (39.9/5800) at takeoff.
> Is our mixture too rich and is that adjusted by changing the position of the
needles in the carbs? Dean at Lockwood said don't change anything, mostly because
the plug colors are correct.
Check the instrument : feed and return turbines, K-factor, etc.
Best regards,
--
Gilles
http://contrails.free.fr
Message 17
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| Subject: | Re: Why exactly shouldn't you run a 914 without |
a prop?
> The engine has a flywheel; that is clear if you look at the Illustrated Parts
Manual, which is available online.
Don,
A flywheel has a *large diameter* and a heavy rim to provide inertia to
the rotating crank.
The part you are referring to is the magneto/alternator rotor, which
mainly consists of a *small diameter* aluminum rim with magnet inserts.
Of course it looks a little like a miniature flywheel, and it has its
own inertia, but it can't compare with that of the prop for the role of
engine flywheel. Measuring its moment of inertia should be a
straightforward operation.
You'll find a picture of the Rotax alternator here
http://contrails.free.fr/elec_ducati.php.
While conducting some in-depth investigations about this particular part
of the engine, I became fairly acquainted with its role and features,
hence what I suggested.
Best regards,
--
Gilles
http://contrails.free.fr
>
Message 18
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| Subject: | Re: Why exactly shouldn't you run a 914 without a prop? |
Hi Gilles
"A flywheel has a *large diameter* and a heavy rim to provide inertia to
the rotating crank.
The part you are referring to is the magneto/alternator rotor, which
mainly consists of a *small diameter* aluminum rim with magnet inserts.
Of course it looks a little like a miniature flywheel, and it has its
own inertia, but it can't compare with that of the prop for the role of
engine flywheel."
I think somewhere somehow we should break down flywheel effect into two categories
that are not the same. First off is needed flywheel to allow motor to run.
Gilles the Rotax 914 is much closer to a motorcycle engine than a traditional
cont. or lyc. or in many ways an auto engine. Many motorcycles have a similar
in size of rotax 914 flywheel and they run just fine. Too light and if you miss
a gear you can easily over rev in a split second, but none the less they run
fine. Running a 914 without a prop should be at low power output. This low
torque is nothing compared to running motor with a load.
Now for prop flywheel effect. This is a major engineering problem. Unlike the limited
weight of a flywheel on a car or motorcycle, the prop is a huge flywheel.
With this huge flywheel effect it does not want to accelerate or decelerate
too quickly. Now with the 91X engines you have a crankshaft, that twice per revolution
gets hit with the torque blow of two connecting rods trying to accelerate
the crankshaft. BTW this could be another discussion but connecting rods
are more rotational weight than reciprocating, in other words they too act for
most part act like a flywheel, not reciprocating weight like pistons moving
up and down. OK back on thought, now you have a crankshaft when cylinders are
expelling some BTUs that is in constant state of accelerating and decelerating.
Now if you have a flywheel mass like the prop that does not feel too much like
speeding up or decelerating as quickly as the crankshaft, enormous stress is
burdening the gearbox. Cessna had a big bore motor that they tuned for making
good torque/ thus higher horsepower compared to direct drive low revving cousin
and put a redrive gearbox to keep prop tip speed down. The gearboxes tore
themselves up, never did they figure how to get them last a long time. Rotax addresses
problem by momentarily absorbing some of the connecting rods hitting
acceleration, and subsequently releasing when crank begins to slow down. I will
give a quick description. If we had a helical set of gears, when you begin to
load that set of gears you will also begin to create thrust (sideway) loads.
Now if we did our homework and put a spring to absorb sideways loading, there
would be some give in the gearbox to prevent tremendous loading of gears, then
when crankshaft began to slow, the spring would put back some energy. Well that
is pretty close how Rotax gearbox works. They have dogs which are mini ramps
that when the prop begins to load will create a sideways force, this force
is absorbed by kind of sorta Belleville style spring washers. Now when crank gets
hit by!
connect
ing rods and forced to accelerate and the prop which will not accelerate anywhere
near as fast as the crank and total rotating mass of engine, in fact this pulse
of acceleration is absorbed by spring washers, and when engine begins to
decelerate then energy will be released, in other words the prop can remain at
a constant RPM where it is most happy and the engine can have crank accelerating
and decelerating twice per revolution and not rip up the gearbox. Without
the dogs/spring set up the gears would take the brunt because the prop would
actually hold back the crank acceleration.
Now to hopeful put this to rest, if you take off flywheel mass of a rotating prop,
not only is the flywheel effect gone, but there is no load on the prop shaft.
You can do anything you want with motor and you are not going to hurt the
gearbox/dogs. The spring washers will never get side loaded because there is no
load. I think there is a bit more rotational weight but it would be like a clutch/transmission
of a motorcycle turning when in neutral
I absolute agree that figuring out ramp angle of dogs and spring tension of spring
washers is an engineering challenge and there are many factors to get it right,
but take prop off and there is not much loading of gearbox at all.
Now if you all of a sudden increase output of motor like turbo charging of a 912S,
lets all of a sudden put in a hotter cam where it now is happy at a cruise
of 6000RPM instead of 5000RPM and wanted to use a much heavier constant speed
prop to absorb the 190HP and hold up without not breaking, you may want to from
an engineering point of view revisit strength of crankshaft (perhaps welding
bits together) and ability of gears to hold up, probably needs slipper clutch
redesign, dog redesign, spring washer recalculation and prop shaft and bearing
strengthening. Taking prop off goes the other way and takes load off of gearbox.
I forget precise numbers, but think at 1400 RPM load on gearbox is like 10 times
as much compared to 5000RPMs.
BTW if you really want to challenge the gearbox of a 914, after you just sinked
the carbs forget to connect the cross tube connecting the starboard to port bank
manifold. A Europa did just that and the shaking was so violent it broke the
motor mount! Europa has since incorporated a mod to strengthen.
To close, I don't really have a need to run without a prop but want to understand
my options.
Ron Parigoris
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=294621#294621
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