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Best RPM for takeoff with IVO prop and 912ULS

 
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wingnut



Joined: 11 Jan 2006
Posts: 356

PostPosted: Wed Jan 11, 2006 1:23 pm    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote


Hello. I'm a new owner of a Model IV 1200 with a 912UL and an IVO prop. The checklist that came with the airplane instructs me to set the prop pitch for takeoff at 5200RPM. According to the published specs for the 912UL, peak power is made at 5800 for two minutes then 5400 continuous. Shouldn't I set the prop pitch for peak power?
Finding the best setting for cuise is another area of confusion. I'm assuming that, since the RPM is adjustable with pitch that I need to look at the manifold pressure to set for 80% power. Then it's just a matter of tweaking the pitch for max speed right? So what manifold pressure constitues 80% power?


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PostPosted: Wed Jan 11, 2006 8:26 pm    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote


At 01:23 PM 1/11/2006, you wrote:
Quote:
Hello. I'm a new owner of a Model IV 1200 with a 912UL and an IVO prop.
The checklist that came with the airplane instructs me to set the prop
pitch for takeoff at 5200RPM. According to the published specs for the
912UL, peak power is made at 5800 for two minutes then 5400 continuous.
Shouldn't I set the prop pitch for peak power?

In the true tradition of the Internet I'll offer an opinion even though I
don't know what I'm talking about. If I remember correctly, the IVO is an
electrically adjustable, but not constant speed, prop. I'm guessing, then,
that 5200 is the static RPM that will get you 5800, or thereabouts, at Vy.
Regarding your question about how to set power: a very useful equation
someone once offered was that the aircraft velocity was proportional to the
cube root of the power. Thus, if you know your maximum velocity at maximum
power, you can find 80% power by adjusting power until you achieve 93% of
that maximum velocity value. (0.93 is the cube root of 0.8.)
Guy Buchanan
K-IV 1200 / 582 / 99.9% done, thanks mostly to Bob Ducar.


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wingnut



Joined: 11 Jan 2006
Posts: 356

PostPosted: Thu Jan 12, 2006 6:07 am    Post subject: Re: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

After further research on the internet, I finally found where I can download the operators manual for the 912UL. For those of you that don't know (being optimistic here and assuming I wasn't the only one), you can download the opertors manual for every rotax motor made at http://ww.rotax-aircraft-engines.com. It comes up in german but there's a link at the bottom for the english version.

If you've purchased a used, rotax powered airplane that didn't come with the manual, then this download is a must. It answered all my questions and a few I didn't know I needed to ask.

For the reccord, the manual has a nifty chart listing the reccomended power and rpm settings for a 912UL with a variable pitch prop.

There's one bit that I picked up that seems too good to be true. According to the manual, if I set the prop pitch to keep rpm to 5400, then there's no time limit for full throttle operation. I'd been told that full throttle should be limited. I wasn't sure about duration so I'd developed the habbit of pulling back to 5000 after the cross wind turn. Consequently, it was taking me forever to get to cruise altitude. If I'm interpreting the manual correctly, I can keep full power all the way up. Even at 5200rpm, that's better than 1000fpm solo. WOOHOO!

This is fantastic news. It's going to make for a whole different experience in the climb.


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PostPosted: Thu Jan 12, 2006 8:38 am    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

The recommendation for 5200 RPM is static, i.e., while the plane is
not moving. When you accelerate to normal flight speeds the RPM will
rise to approximately red line RPM (5800).

Mike G.
N728KF


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wingnut



Joined: 11 Jan 2006
Posts: 356

PostPosted: Thu Jan 12, 2006 9:21 am    Post subject: Re: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

That makes alot more sense. Unfortunately, my brakes are not strong enough to hold the plane in position at full throttle so I resorted to tweeking the pitch for 5200 on the upwind climb.

If 5200 static = 5800 at cruise, should I be seeing something like 5500 in the climb?

Any feedback on my interpretation of the opertors manual? Can I realy set the pitch for 5400 and leave the throttle in for the duration of the climb?


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PostPosted: Thu Jan 12, 2006 9:55 am    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

Yes you can..

Another area for manuals.. http://www.kodiakbs.com/tiintro.htm

Those with Rotax engines should also take a look at R.O.A.N.
http://www.rotax-owner.com/index.htm

Have a Safe New Year !!
John & Debra McBean
www.sportplanellc.com
"The Sky is not the Limit... It's a Playground"

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PostPosted: Thu Jan 12, 2006 9:55 am    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

Where are you located and what is the field elevation at you airport ? Full
power static RPM (on the brakes) will typically be about 200-500 rpm lower
then the desired max rpm for takeoff... setting the prop at the 5200 rpm
static should give you an approximate 5400 when climbing out but will push
up to 5500 - 5800 with full power level flight. It is referred to as
"UNLOADING" the prop.

Manifold pressure... You are correct.. 80% would be determined with MP.
Standard pressure is 29.92".. 80 % would be 24"... Rule of thumb.. you'll
loose an inch of manifold pressure per thousand feet... so in theory at 6000
feet full throttle will give you 80%.
Have a Safe New Year !!
John & Debra McBean
www.sportplanellc.com
"The Sky is not the Limit... It's a Playground"

--


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wingnut



Joined: 11 Jan 2006
Posts: 356

PostPosted: Thu Jan 12, 2006 10:45 am    Post subject: Re: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

Quote:
Standard pressure is 29.92".. 80 % would be 24"


According to the operator manual, 75% power is obtained at 27.2" and 5000 RPM for the 912UL. Could it be that power doesn't scale linearly with pressure? Am I missing something?

The airplane is based at 34A (Laurens, SC). Elevation is 697 ft.

I'm hoping to get comfortable enough with short field operations one day to bring it home to my 1000ft turf field.


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PostPosted: Thu Jan 12, 2006 1:02 pm    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

The Rotax is RPM limited.. So, If you had a prop that would deliver 5800 RPM
at full power level flight.. Then following the 912 power curve 75% power
would be at approx 5000 RPM which would result in a 27.2" MP at sea level
pressure. I had some numbers somewhere from test flights.. but they were
with the 912S.. I'll see if I can find them...
Have a Safe New Year !!
John & Debra McBean
www.sportplanellc.com
"The Sky is not the Limit... It's a Playground"

--


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Jim Shumaker



Joined: 09 Jan 2006
Posts: 106

PostPosted: Thu Jan 12, 2006 9:07 pm    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

Wingnut,

The Rotax 912ul is rated 100% (5500 rpm) power for continous operation. It can be run to 5800 rpm for 3 minutes of takeoff power. So if your engine is warm, 140 degrees F, then you can climb for 3 minutes at 5800 rpm and then reduce the power to 5500 rpm and fly till the tanks run almost dry. You must reduce power to 3500 for a minimum time to cool the engine (30 seconds or more if my memory is correct) and then you may shut it off.

The Minimum recommended rpm is 5000 for continuous cruise.

You have an adjustable pitch prop so you should be able to get great performance. Keep in mind that running high throttle settings and lowering the rpm is harder on the engine than running high rpms at low throttle settings. That is, 5500 rpm and a low throttle setting is better than 5000 rpm with the throttle more open.

Rotax also recommends that if you should run the engine above 5800 rpm that you make a logbook entry....yep, that is all...just a logbook entry.

I do not always follow these recomendations to the letter. Last week I flew formation with some overweight ultralights. They topped out at 65 mph. My climb rpm was 4600 rpm I have a ground adjustable fixed pitch. Normally my long descent rpm. Cruise was about 3900 rpm, my normal final approach rpm, and during the low level pass over the airfield I had to land to give them room to get ahead of me.



wingnut <wingnut(at)spamarrest.com> wrote:


That makes alot more sense. Unfortunately, my brakes are not strong enough to hold the plane in position at full throttle so I resorted to tweeking the pitch for 5200 on the upwind climb.

If 5200 static = 5800 at cruise, should I be seeing something like 5500 in the climb?

Any feedback on my interpretation of the opertors manual? Can I realy set the pitch for 5400 and leave the throttle in for the duration of the climb?


Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=3313#3313


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PostPosted: Fri Jan 13, 2006 5:25 am    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

I have the same configuration as you do. Just put an IVO Medium on the
plane last summer. I turned the adjustment 2.5 turns towards fine pitch,
and that gave me 5800 RPM at best climb. I was used to flying on floats,
and when the new prop went on I had re-configured for wheels. After a bit
I found I preferred to have a less ballistic departure so I did not scare
the crap out of my passengers, so I increased the pitch somewhat in favour
of a better cruise. I am now about 1/2 run to fine from neutral. I now
have something like 5500 at best climb, and I get a cruise of 100 mph.

Yes..you can operate at 5400 rpm continuous. In fact, I have been told
that the 912 series was designed to turn, and running it at rpms like 4800
rpm was not good for it. I typically run it at 5200 in cruise.

There is a good reference card you can get from a dealer in Quebec Canada.
He has a card that shows all the operating ranges. He bases the power
settings on RPM and manifold pressure vs RPM alone. I have a MP guage in
my plane, and find it quite helpful.

I am looking at getting the in flight adjustable option soon. Best of
both worlds.

Are you running an IVO Medium or the Ultalight version. If the
latter..then the turns I quoted will be different.

Gary Walsh
KF IV Anphib 912S
C-GOOT
www.decisionlabs.com/kitfox

do not archive


Guy Buchanan <bnn(at)nethere.com>
Sent by: owner-kitfox-list-server(at)matronics.com
01/11/2006 11:09 PM
Please respond to kitfox-list

To: kitfox-list(at)matronics.com
cc:
Subject: Re: Best RPM for takeoff with IVO
prop and 912ULS


At 01:23 PM 1/11/2006, you wrote:
Quote:
Hello. I'm a new owner of a Model IV 1200 with a 912UL and an IVO prop.
The checklist that came with the airplane instructs me to set the prop
pitch for takeoff at 5200RPM. According to the published specs for the
912UL, peak power is made at 5800 for two minutes then 5400 continuous.
Shouldn't I set the prop pitch for peak power?

In the true tradition of the Internet I'll offer an opinion even though I
don't know what I'm talking about. If I remember correctly, the IVO is an
electrically adjustable, but not constant speed, prop. I'm guessing, then,

that 5200 is the static RPM that will get you 5800, or thereabouts, at Vy.

Regarding your question about how to set power: a very useful equation
someone once offered was that the aircraft velocity was proportional to
the
cube root of the power. Thus, if you know your maximum velocity at maximum

power, you can find 80% power by adjusting power until you achieve 93% of
that maximum velocity value. (0.93 is the cube root of 0.8.)
Guy Buchanan
K-IV 1200 / 582 / 99.9% done, thanks mostly to Bob Ducar.


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PostPosted: Fri Jan 13, 2006 5:25 am    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

Sorry...in my last email I mean to provide the links for the Rotax 912
series quick in cockpit reference card for operating parameters. Here is
where you can find the source for these.

http://www.rotaxservice.com/rotax_tips/rotax_age.htm
http://www.rotaxservice.com/rotax_tips/rotax_vibration.htm
Gary Walsh
KF IV Anphib 912S
C-GOOT
www.decisionlabs.com/kitfox

do not archive


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wingnut



Joined: 11 Jan 2006
Posts: 356

PostPosted: Fri Jan 13, 2006 7:17 am    Post subject: Re: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

I don't really know which IVO prop I have (medium vs ultralight). Is there an easy way to tell?

It sounds like the adjustment on your prop is mechanical. Mine is electric. Push up on the toggle switch to decrease pitch push down to increase.

I don't really like the set up because there's no feedback for the current position of the prop except for the RPM. Adjusting for proper pitch is tedious affair where you tap, tap, tap on the switch and watch the rpm move. There’s no way to know if the pitch motor has hit the stop except that the RPM has stopped moving.

I imagine that I will become more comfortable with the prop as I gain experience with the setup but I would have much preferred something like the GSC, GTA prop that is adjusted with a vernier cable.


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PostPosted: Fri Jan 13, 2006 9:21 am    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

Not too tedious.. While doing your run-up try setting the RPM at 4000 and
the MP for 22" for your mag check... That will give you a pretty close
setting for max takeoff RPM... Like anything new, it does take some time to
adapt.. With well over 300 hours behind the Ultralight IVO now it has become
very quick and easy to adjust.

The easiest way to tell is measure the chord of the blade.. the ultralight
is approx 3" The Medium is a little wider...

Have a Safe New Year !!
John & Debra McBean
www.sportplanellc.com
"The Sky is not the Limit... It's a Playground"

--


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PostPosted: Fri Jan 13, 2006 9:35 am    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

While on the subject of IVO props, a friend with a Kitfox V/Subaru combination. The prop came to him as part of used package of parts. It is a very heavy prop to my way of thinking. Probably 5" chord. Is there an IVO Magnum?

In any case, the prop seems so heavy that in order to approach recommended rpms he has to reduce the pitch to the point that full power will only net him about 90 mph. Seems to me he needs to prop down, but how far?

John Kerr

-------------- Original message --------------
From: "jdmcbean" <jdmcbean(at)cableone.net>

[quote]

Not too tedious.. While doing your run-up try setting the RPM at 4000 and
the MP for 22" for your mag check... That will give you a pretty close
setting for max takeoff RPM... Like anything new, it does take some time to
adapt.. With well over 300 hours behind the Ultralight IVO now it has become
very quick and easy to adjust.

The easiest way to tell is measure the chord of the blade.. the ultralight
is approx 3" The Medium is a little wider...

Have a Safe New Year !!
John & Debra McBean
www.sportplanellc.com
"The Sky is not the Limit... It's a Playground"

--


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PostPosted: Fri Jan 13, 2006 10:33 am    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

John,
There is a Medium and a Magnum... The medium has about a 4" to 4.5" chord
depending on where you measure... Which Soob is it ? If over 100hp I don't
think I would go below the Medium...

Have a Safe New Year !!
John & Debra McBean
www.sportplanellc.com
"The Sky is not the Limit... It's a Playground"

--


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PostPosted: Sat Jan 14, 2006 9:41 am    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

Quote:
It sounds like the adjustment on your prop is mechanical. Mine is
electric. Push up on the toggle switch to decrease pitch push down
to increase.

A lot of the advice you've been receiving has assumed that you had a
ground-adjustable prop. With a ground-adjustable you have to
compromise between best takeoff & climb performance against best
cruise performance.

If you have an in-flight adjustable prop you don't have to
compromise! Push the switch to move towards flat pitch (higher RPM)
during your runup. When you takeoff push the throttle in and use the
switch to get full takeoff power (maybe a little shy of 5800 RPM).
As you accelerate the RPM will rise--if it gets to or past 5800 then
move the the switch the other way to pull it back down to 5800 or a
little less. Within 5 minutes use the switch again to bring the RPM
down to 5500. If you maintain full throttle the entire time you'll
get your best climb performance.

Mike G.
N728KF


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PostPosted: Sat Jan 14, 2006 11:18 am    Post subject: Best RPM for takeoff with IVO prop and 912ULS Reply with quote

Gary,
Is the reference card on the website? I couldn't find them.

It does sound like something of value.

Thanks,
Randy - Series 5/7 912S

.
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