Needle position

[Angelitomon]

Hi; I have always though that the rotax engine lost all the power above 7500/ 8500 ft not to say above. I would like to know what position, from the four we have, the needle for the mixture in the carburators you are using.

 

Here in Spain most of the engines I see have it in position Nmr 2 ( low rich) and I have seen looking around internet that it should be in position 3 ( not to Lean).

 

Thank you

 

Angel

[Roger Lee]

Hi Angel,

 

Most Rotax 912ULS (100 hp) and the 912UL (80 hp) engines have the carb clip in position #3. They are numbered with #1 at the top of the needle and #4 at the bottom. The #2 position is leaner than the #3. If you live at high altitudes and fly at really high altitudes then #2 might be ok, but that will also raise all your temps in the lower altitudes. We all use #3 and it works for everything all the way up to normal flight altitudes. (2K-12K msl) It will still work up to FL18, but will be very rich there. I just did a little experiment with mine since we get hot in Tucson, AZ. I used position #4 all summer. Lowered all my temps across the board. I just changed it back to position #3 because of the cooler day time winter temps and we are going to Page, AZ where it is a lot cooler and much higher altitudes than my normal.

[coppercity]

Mine is also at position 3 and have not had any trouble at altitudes from sea level to 15000 ft. I think I will let Roger set mine to position 4 in the summer, just to try to reduce the temps during all the pattern work my airplane gets.

 

Regards

Eric

[Angelitomon]

Hi Roger:

Thank you very much for your rapid respond. I had it all wrong. I thought that the numbers started from dow to up. Then mine must be ok. The thing is that I ussually fly at 6500/9500Ft and I notice a very big reduction of power above 7000ft and Im looking and thinking all the time how to tune everything to work better.

 

Have any of you get to know any one who installed a tuned exhaust? I have been thinking in installing one for a time know but don´t know anyon who has. Take a look at this web " love4aviation.com" they advertise one.

 

Another question is about the K&N air filter. Would the CTLS use the one that you posted in the forum?

 

Thank you

 

Angel

[Tom Baker]

Angel, over here the CTLS comes with a K&N filter. I would think your did too. Tom

[Jeremy MacGregor]

Hey guys,

Roger is right Rotax recommends leaving the 912ULS position at #3 which is the second notch from the point. Some people have experimented with dropping it down a clip which does lean the mixture in the 1/8-3/4 throttle range. Dropping the clip will give you a little bit better fuel economy but the trade off is that it can result in higher than normal and sometimes over spec mag drops. If you run your engine at 4000 static and do you mag test and you get more than a 250rpm drop than that position is too lean for the conditions you are flying in. Now this does of course depend on altitude and chances are its going to be leanest on the ground since the air is only getting thinner as you ascend. For the most part the factory says don't bother messing with it but as long as your EGTs stay with in range (not exceeding 1580 F ) then you don't really have to worry about doing any sort of damage to the engine. This clip position should not effect the engine at its 85-100% power range but seeing how we are all flying with fixed pitch props we spend more time using our needle jet metering than we do on main metering. If your starting to miss on climb out on a rather cool day ie. under 60F then go back to the factory sepcs. The carbs are jetted for standard conditions at 1000MSL not sea level.

[Ed Cesnalis]

Hi Roger:

Thank you very much for your rapid respond. I had it all wrong. I thought that the numbers started from dow to up. Then mine must be ok. The thing is that I ussually fly at 6500/9500Ft and I notice a very big reduction of power above 7000ft and Im looking and thinking all the time how to tune everything to work better.

 

...

 

 

Angel,

 

best performance for normally aspirated engines is 7,500'. at that altitude you are at 75% power at WOT if your prop is pitched for performance. this altitude gives you best performance by blending available power and (reduced) drag (due to thinner air at altitude).

 

a little above 10,000' you go below 70% horse power and the available power fails to compensate for reduced drag.

 

in other words reduced performance above 7,500' is to be expected to the point (15,000' approx) where climb performance is eliminated and cruise is near stall.

[Tony & Rose]

Yep, where those two meet, where I come from, is referred to as the 'coffin-corner'.

[Angelitomon]

Yeah CT, thats where I ussually look for cruising Alt . I allways, while traveling, try to stay in the 5500/8500 Da. I actually have in my CTLS a constant speed prop (Airmaster 68') . Another thing that bother me is the accuracy of Rotax performance charts. I have made a table with MP settings with diferent power settings and RPM and they dont work that well specially if a fly with a 65% power at 4800Rpm. The fuel flow is about 2 litres more than it must be. At 75% and 5000Rpm it runs ok but with 1 ltrs more than what the table says. Have you made this calculations for your engine?

another question looking to improve performance is about the prop size. Those of you that have a warp drive in your Ct, what size, type and performance are you getting? As I said above, I have an Airmaster 68' tapered in my CTLS. Im very happy with it. I have it for 250hrs now and it works perfect. The doubt I have is if is would be better to have a prop a litle smaller like 65' in order to improve cruise speed. I would get a litle less climb maybe.

just another thought.

Another thing is .... Have any of you tried a vortex generators in your Ct? I have a set ready to install from stolspeed and would like to know if any of you have installed to get vectors about positioning and results.

Thank you all again

Angel