Today's Message Index:
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1. 05:42 AM - Re: Disappointment in Rotax 9 series (Thom Riddle)
2. 06:09 AM - Re: Disappointment in Rotax 9 series (rampil)
3. 07:18 AM - Re: Disappointment in Rotax 9 series (Thom Riddle)
4. 10:31 AM - Re: Re: Disappointment in Rotax 9 series (Steve Hagar)
5. 10:35 AM - Disappointment in Rotax 9 series (D Wysong)
6. 01:38 PM - Re: Disappointment in Rotax 9 series (rampil)
7. 01:56 PM - Re: Disappointment in Rotax 9 series (rampil)
8. 02:20 PM - Re: Re: Disappointment in Rotax 9 series (Gilles Thesee)
9. 02:24 PM - Re: Disappointment in Rotax 9 series (jetboy)
10. 02:47 PM - Re: Disappointment in Rotax 9 series (rampil)
11. 03:39 PM - Re: Re: Disappointment in Rotax 9 series (Gilles Thesee)
12. 04:46 PM - Re: Disappointment in Rotax 9 series (Ivan)
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| Subject: | Re: Disappointment in Rotax 9 series |
rampil,
I do not know where you got your data but attached is a snapshot of the cover page
from my Katana Manual and the page with the performance and fuel consumption
table data.
See attachments.
As you can see there is nothing indicating a variance in fuel flow AT A CONSTANT
POWER SETTING regardless of variations in altitude.
Per my training, knowledge and experience, fuel flow is a nearly linear function
of power being produced, regardless of altitude at which it is being produced.
I have never had a fuel flow meter on any of the airplanes I've owned with
the 912 series engine but have flown a good bit of cross country time in them
at known power settings at widely varying altitudes, and the fuel required to
fill the tank after these flights has always been within 1/2 gallon of my projections
based on time and power setting during these long continuous power flights
at varying altitudes. Also, the EGTs on my 912 read pretty constant at a
constant power setting at varying altitudes.
Thom Riddle
Retired Mechanical Engineer
FAA Certificated Powerplant Mechanic
http://riddletr.googlepages.com/a%26pmechanix
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=163281#163281
Attachments:
http://forums.matronics.com//files/da20cruisedata_729.jpg
http://forums.matronics.com//files/katanaafmcover_116.jpg
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| Subject: | Re: Disappointment in Rotax 9 series |
Hi Tom,
Again, the data was for the DV-20-100 912S3
not the DA-20 912.
Yes my DA-20 manual looks the same (I have about 150 hours in them)
but the manual does not specify what altitude the measurement was
made, and since my time was in a rental, I did not bother to try.
Re the DA-20 manual, certainly you dont believe the carbs compensated
up to the max altitude of 13000? Nobody I spoke every claim claimed
they compensated for altitude over 8000, including Eric Tucker who
I spoke to at Oshkosh 2005 at some length when he was hanging out at
the CPS booth.
Unrepentant Electrical Engineer
AME Eastern Region
--------
Ira N224XS
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| Subject: | Re: Disappointment in Rotax 9 series |
rampil,
I appreciate your bringing this increased fuel flow with increased altitude data
to us. It was news to me and a bit of a surprise. The good news is that at higher
altitudes you get higher TAS with a given power setting, which helps compensate
for the increased fuel flow.
If my current airplane were certificated experimental I would be tempted to try
the adjustable mixture control (HACman) that you mentioned. But then again, most
of my current flying is at low altitudes so it might not be an economical
solution for me anyway. I'm happy that I can run methanol free 87 octane autogas
in our 912UL and burn between 4.0-4.2 gph at 75% power.
I still like the 912 series better than any other engine I've flown with.
--------
Thom Riddle
N221FA Allegro 2000 912UL
N197BG FS1/447
--------------------
Believe nothing, no matter where you read it or who has said it, not even if I
have said it, unless it agrees with your own reason and your own common sense.
- Buddha
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| Subject: | Re: Disappointment in Rotax 9 series |
The carbs on my Europa are almost indistinguishable from the carbs on my
old BMW pushrod motorcycle. So there should be no moaning and groaning
that you are not getting "altitude compensating" carbs. What you have are
"constant velocity" motorcycle carbs. Those diaphrams on top of the slides
keep you from opening up the bores too much for the mass of air that can
flow through them and get a relatively good mixture. Supposedly to give
you better or smoother throttle response when cranking it on a motorcycle.
As noted before fuel consumption is directly related to hp produced.
Leanable carbs only reduce fuel consumption by allowing you to keep the
gas/air (oxygen) ratio proper (stoiciometric?). You can keep the throttle
wide open. What you probably get with the bings is the fact at altitude
the mass of air going through at altitude will not allow the diaphrams to
pull the slides up all the way even though the throttle is opened up fully.
The 914 shouldn't care as it should think it is at sea level to 16K I
believe.
Steve Hagar
A143
Mesa AZ
> [Original Message]
> From: Thom Riddle <riddletr@gmail.com>
> To: <rotaxengines-list@matronics.com>
> Date: 2/10/2008 8:21:21 AMa
> Subject: RotaxEngines-List: Re: Disappointment in Rotax 9 series
>
<riddletr@gmail.com>
>
> rampil,
>
> I appreciate your bringing this increased fuel flow with increased
altitude data to us. It was news to me and a bit of a surprise. The good
news is that at higher altitudes you get higher TAS with a given power
setting, which helps compensate for the increased fuel flow.
>
> If my current airplane were certificated experimental I would be tempted
to try the adjustable mixture control (HACman) that you mentioned. But then
again, most of my current flying is at low altitudes so it might not be an
economical solution for me anyway. I'm happy that I can run methanol free
87 octane autogas in our 912UL and burn between 4.0-4.2 gph at 75% power.
>
> I still like the 912 series better than any other engine I've flown with.
>
> --------
> Thom Riddle
> N221FA Allegro 2000 912UL
> N197BG FS1/447
> --------------------
> Believe nothing, no matter where you read it or who has said it, not even
if I have said it, unless it agrees with your own reason and your own
common sense.
> - Buddha
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=163287#163287
>
>
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| Subject: | Disappointment in Rotax 9 series |
>
> Has anyone performed actual, careful engine performance flight
> test. I'd like to, but my new EFIS has the output of my FloScan
> bouncing all over creation to the point where it is unusable.
>
Hello Ira. We saw the same erratic behavior out of our FloScan and EFIS
(MGL RDAC-X). The solution was to pull the signal line (white wire) up
through a resistor to clean up the signal. I'll send you a sketch of the
schematic if you're interested.
D
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| Subject: | Re: Disappointment in Rotax 9 series |
Hi D,
Thanks for the offer. Supposedly the EFIS I have has a 10k ohm
pullup to the 5v rail internally. A pullup makes sense when the
optical transistor inside the Floscan does not generator enough
voltage swing on it's collector. I don't think that is the problem in my
case, but I will check the waveform with my scope.
I think my problem is that the company has a strange idea of how
much digital filtering (smoothing after conversion from pulse interval
to flowrate) they do to this particular signal.
--------
Ira N224XS
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| Subject: | Re: Disappointment in Rotax 9 series |
Steve,
I think we both know what a carb is supposed to do.
You are just off track when you compare aircraft to motorcycle
applications. I cant think of the last time I gunned my rotax throttle
at the stop line ;-)
The constant "depression" in Euro-speak or constant pressure in USA
English is in fact supposed to provide altitude compensation, the goal
in the case of the Rotax, to run just rich of peak at all altitudes.
This is the stated and advertised goal of using the Bing 64 instead
of a single conventional carb.
What is in fact happening is that the engine IN FACT is running richer
and richer with DA when it should should reduce fuel flow to match the
reduced air mass charge.
As for increased TAS with DA, well you don't need a Rotax for that!
A rubber band motor will do exactly the same thing!
--------
Ira N224XS
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| Subject: | Re: Disappointment in Rotax 9 series |
rampil a crit :
>
> Hi Gilles,
>
> I think you are an experienced thoughtful guy, but what does it mean
> to have an opinion on these carburetors . On the other hand, what you told Ivan
is absolutely
> true from my hands on experience with both engines,
>
> We are not talking about health food nonsense or placebo. We must talk
> engineering, these are deterministic systems, they either work
> or they do not work.
>
> The DATA says they do not work, in fact, they perform WORSE
> than just leaving full rich on a Lycoming.
>
> I may well be wrong due to lack of sufficient data, but the DATA
> so far says the 912S3 is CONTRACOMPENSATING.
>
Ira,
Not sure what your point is, but what I'do first is double check the
printed data.
Especially when they seem indicate something contrary to engine physics.
> Please explain to me my error. Opinions can not count
>
I may have missed something, but could you provide a link to this
particular manual ?
> Well, unless someone can prove the following data wrong now, this
> Altitude compensation is a complete crock.
I'd say it the other way "unless you can prove our engines and carbs are
wrong, these data you're referring to are not reliable".
Best regards,
--
Gilles
http://contrails.free.fr
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| Subject: | Re: Disappointment in Rotax 9 series |
I would like to add here that although the carbs used on the 912 are similar to
those on the Jabiru, the Jabiru ones now have a much different profile needle
which gives the standard Continental / Lycoming aero engine profile of leaner
mixture below 75% power and progressively richer above 75%. This saves 1 or
2 litres/hr of fuel flow over the original needle profile. Above 8,000 feet the
needle should not be able to enrich the mixture even at full throttle setting
although I have not tested this recently. they wont be able to compensate above
this altitude however the Jabiru needle keeps a much leaner mixture due to
the different taper.
You might consider purchasing more appropriate needles for the 912.
Downloading the latest Jabiru SB-18 gives good guidance.
Ralph
Gilles.Thesee(at)ac-greno wrote:
> Ivan a crit :
>
> > I have owned a 912UL for about 4 years and definitely it does not have
> > an altitude compensating carburetor. As I go up in altitude I must
> > allow for increased fuel usage. As I go from 2000 ft to 9500 ft I
> > increase my fuel consumption by 20%. This makes sense to me since I
> > am burning richer as I go up in altitude. The new LSA's have the Bing
> > compensating carburetor and thus no mixture control.
> >
> > My Jabiru engine has the Bing compensating carburetor. As I go up in
> > altitude I dont see much change in my EGT because in stead of the
> > engine running richer, the carburetor compensates to keep the mixture
> > the same as evidenced by a contant EGT. So I know for a fact that the
> > Bing compensating carburetor works well as stated. I dont know why
> > Rotax states the fuel cosumption is increasing with altitude. My
> > engine does the opposite and I run most efficiently at high altitude
> > on my cross countries.
> >
> >
> >
>
> Ivan,
>
> Would you care to elaborate on the "compensating" and "non compensating"
> carbs ?
> As far as I could see, there is no particular difference between the
> Bings 64 on the Rotax, and the Bing 64 on the Jabiru. Also, except for
> the particular engine jetting, there is no apparent technical difference
> between the carbs in each engine documentation : the Jabiru manual shows
> the same picture as the Rotax.
>
> In my opinion, the Bing carb provide *some degree* of altitude
> compensation due to the constant vacuum design.
>
> Best regards,
> --
> Gilles
> http://contrails.free.fr
--------
Ralph - CH701 / 2200a
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| Subject: | Re: Disappointment in Rotax 9 series |
Gilles,
I wish it were so simple as to have wrong data.
Here is the URL you seek for your own official copy straight
from Austria.
http://www.diamond-air.at/dv20_afm_bas+M52087573ab0.html
I refer you to page 73 in the PDF corresponding to page 5-04 on paper.
--------
Ira N224XS
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| Subject: | Re: Disappointment in Rotax 9 series |
rampil a crit :
> I wish it were so simple as to have wrong data.
>
Ira,
Had a look at the manual.
Concentrated on the 75 % power numbers. The 8000 ft numbers are in close
agreement with every other 100 hp Jabiru/Rotax engine : in the 22-23
L/hr ballpark. At this altitude, 75 % power is obtained with full
throttle and max allowable RPM. Nothing wrong with those data.
Now at lower altitudes, one can choose between different MP/RPM
combinations. The lower the RPM and the higher the MP, the lower the
fuel burn for a given % output. So it is normal to burn *less* at those
settings. Any atmospheric engine behaves like that.
So I'd rather say : at lower altitudes it is possible to burn slightly
less fuel for a given % output. At 1000 ft you also can use the 8000 ft
settings. You'll burn a little more fuel because you'll be at part throttle.
But at 75 % any atmospheric 100 hp engine will burn about 22-24 L/hr at
8000 ft : Lyc, Conti, Rotax, Jabiru or whatever.
At 75 %, our 914 (same carbs) burns around 22 L/hr.
Best regards,
--
Gilles
http://contrails.free.fr
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| Subject: | Re: Disappointment in Rotax 9 series |
Gilles
Supposedly the "altitude compensating carburetor" is one that self
compensates for changes in atmospheric pressure and adjusts the fuel flow
accordingly. Thus even without a mixture control as you go up in altitude
with a constant power setting the carburetor compensates and decreases the
fuel flow, thus giving the engine less fuel when there is less oxygen and
thus doesnt let the mixture get rich but keeps it about constant. This has
been my finding on my Jabiru 3300 since the EGT(a measure of mixture) stays
about the same as my altitude is increasing. There is a little error due to
different temperatures from day to day which thus a colder day with the same
barametric pressure can lean out the mixture slightly as evidenced by
slightly higher EGT's for that day. The carburetor ONLY compensates for air
pressure and not air temperature(which indirectly may affect pressure.)
And that is the way I see it as evidenced by by EGT probes. My fuel usage
is basically constant at about 5.1 gal/h on cruise at 75% power (2850 RPM)
on my 120hp engine.
Hope this lightens things rather than confues them,
Ivan
Phoenix, AZ
----- Original Message -----
From: "Gilles Thesee" <Gilles.Thesee@ac-grenoble.fr>
Sent: Saturday, February 09, 2008 2:43 PM
Subject: Re: RotaxEngines-List: Disappointment in Rotax 9 series
<Gilles.Thesee@ac-grenoble.fr>
Ivan a crit :
> I have owned a 912UL for about 4 years and definitely it does not have an
> altitude compensating carburetor. As I go up in altitude I must allow for
> increased fuel usage. As I go from 2000 ft to 9500 ft I increase my fuel
> consumption by 20%. This makes sense to me since I am burning richer as I
> go up in altitude. The new LSA's have the Bing compensating carburetor
> and thus no mixture control.
> My Jabiru engine has the Bing compensating carburetor. As I go up in
> altitude I dont see much change in my EGT because in stead of the engine
> running richer, the carburetor compensates to keep the mixture the same
> as evidenced by a contant EGT. So I know for a fact that the Bing
> compensating carburetor works well as stated. I dont know why Rotax
> states the fuel cosumption is increasing with altitude. My engine does
> the opposite and I run most efficiently at high altitude on my cross
> countries.
>
Ivan,
Would you care to elaborate on the "compensating" and "non compensating"
carbs ?
As far as I could see, there is no particular difference between the
Bings 64 on the Rotax, and the Bing 64 on the Jabiru. Also, except for
the particular engine jetting, there is no apparent technical difference
between the carbs in each engine documentation : the Jabiru manual shows
the same picture as the Rotax.
In my opinion, the Bing carb provide *some degree* of altitude
compensation due to the constant vacuum design.
Best regards,
--
Gilles
http://contrails.free.fr
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