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CTLSi power setting table & RPM


Jnowak

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Posted

Hello there,

I wondered whether anyone would have power setting table for CTLSi? There is one in Rotax Operator's Manual (chapter 5, Performance data) but I am not sure it applies to all aircraft with this engine. The table does not show what the power setting at different altitudes is - I might think that ECU does the job but I am not sure. I have also another question to someone with more expertise on this engine. I have access to a rented plane and occasionally I see that RPM gets unstable. It oscillates up to +/- 200 RPM at and above 4500. It gets stabilised after some workout with MP and/or RPM but I am not sure it is normal. I spoke to Rotax - they exchanged MP sensors and things got better (they were worse before). Thanks in advance.

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Posted

Not sure this answers your question, but the 912iS Supplement (11) to the CTLS POH gives no new performance data.  Section 5 just says that all performance data provided in the basic POH for the carburated engine apply conservatively to the fuel injected engine.    I have not experienced the RPM fluctuation you describe although it is quite possible I'm just not being as attentive as you to it.  What make of plane are you flying?

Posted

... I get 3.4gph and 120kts true at around 5000 most of the time in calm winds...

 

At 3.4 gph you are clearly cruising in econo mode, or what ever they call that gas saving throttle range.  There is no free lunch, your TAS is probably lower than 120kts at that setting, have another look.

Posted

MovingOn: actually, flying slower does save fuel. Remember that drag is a squared function. Induced drag drops at higher speed, and parasitic (form) drag increase. The best distance airspeed is where these two are the lowest.

 

Drag_Curve_2.jpg

 

However, this is a pretty slow airspeed, as it is right around best glide ratio. What may be of more interest to you is "Carson's Number", which is efficient cruise. It's basically speed divided by fuel consumption per hour, whereas economy cruise is distance divided by fuel per hour.

 

http://www.nar-associates.com/technical-flying/efficiency/efficiency_wide_screen.pdf

Posted

To further complicate matters...

 

...you have to figure in some increased maintenance.

 

Why?

 

If you're making trips of a set length, and by going more slowly it takes you longer, each trip will add just a bit more to the hobbs than if you went faster.

 

So, if you change oil every 50 hours, that 50 hours will come up after fewer trips.

 

Not arguing against efficiency - I always operated my Cirrus LOP, giving up about 10k to save at least 4 gph.

 

There's no right and wrong here.

Posted

Fast Eddie:

Most people use carson's number, because it's a good balance. Also, if you use a lycoming or continental, with a few exceptions with the high powered engines, you actually lower your maintenance by flying at economy cruise. If you rent by hobbs though, screw it, firewall it.

Rotax engines supposedly does not like really low engine power, because the gearbox wear increases. I believe it is due to gear lash, and a question of how well oil film can cushion the impulses. At high engine power, there is so much load on the prop that it helps hold oil in place between the teeth, so there is less tooth against tooth. Low settings however, the impulses are further apart, so it is a little more springy on tooth contact.

Posted

Rotax engines supposedly does not like really low engine power, because the gearbox wear increases. I believe it is due to gear lash, and a question of how well oil film can cushion the impulses. At high engine power, there is so much load on the prop that it helps hold oil in place between the teeth, so there is less tooth against tooth. Low settings however, the impulses are further apart, so it is a little more springy on tooth contact.

From what I understand gearbox issues only come into play below 1800rpm, which is lower than anybody can idle in the air. Folks like Roger Lee that advise against long cruises below 5000rpm usually point to harmonics in the engine itself at lower rpm that while not immediately damaging might have long term effects out near TBO and beyond. Of course, there is plenty of debate on that around here...

Posted

Flying at something less than full power may give you a little better fuel efficiency and therefore a little more range. 

 

When I rent a plane I never fly at max power. 

Posted

CT,  the 912i is that fuel efficient.  The 120kt cruise (and GS around 105 to 115 dependent on wind) is about as fast as I need to go most of the time.  And yes, I get 3.4 to 3.5gph.  Its not about saving fuel, its about flying plenty fast enough, all the guages in the green, the engine humming along happy and sounding good, and getting there and back with plenty of fuel to spare...

 

 

This is one of those stick and rudder moments that Eddie is talking about.  It is hard to take your claim of 120kts true air speed at 3 1/2 gph seriously when you translate the performance to "GS around 105 to 115 dependent on wind"  Where did the other 10kts go?

 

If your cruise is 120kts true then your average ground speed in cruise will be very close to 120kts.  With a head wind your ground speed goes down but with the tail wind on the way back your ground speed goes up to average your 120kts true airspeed.  Crosswind cost you a small penalty so all in all you have a small penalty.

Posted

CT,  the 912i is that fuel efficient.  The 120kt cruise (and GS around 105 to 115 dependent on wind) is about as fast as I need to go most of the time.  And yes, I get 3.4 to 3.5gph.  Its not about saving fuel, its about flying plenty fast enough, all the guages in the green, the engine humming along happy and sounding good, and getting there and back with plenty of fuel to spare.

 

Econo mode?  Sometimes I hop around at 4200 RPM, about 90kts TAS, and the fuel burn is about 2.2 gph.  I also buy my own mogas as I mentioned under a bulk card often getting fuel at about $3.25 a gallon. 

 

MovingOn: Sure its a $180k craft after taxes, so what?  If you wanna blow money wasting fuel, go for it, no one really cares.

 

No CT is going to get 120kt true at less than 5000rpm.  Your fuel burn might be right, but not the speed; at 5000rpm according to the manual you are making 68hp.  I don't think anybody here really believes that any CT will go 120kt true airspeed in level flight on less than 68hp.

Posted

This is one of those stick and rudder moments that Eddie is talking about.  It is hard to take your claim of 120kts true air speed at 3 1/2 gph seriously when you translate the performance to "GS around 105 to 115 dependent on wind"  Where did the other 10kts go?

 

If your cruise is 120kts true then your average ground speed in cruise will be very close to 120kts.  With a head wind your ground speed goes up but with the tail wind on the way back your ground speed goes up to average your 120kts true airspeed.  Crosswind cost you a small penalty so all in all you have a small penalty.

 

Yes!  And 110-115 knots correlates very closely with what other CT owners see at ~5000rpm. 

Posted

If headwind:

 

GS = TAS + tailwind component of wind

 

If tailwind

 

GS = TAS - headwind component

Something is mislabeled here or I'm reading it wrong.

Posted

Okay, tried to be nice. ... All you do is carp and whine and attack me.  

 

To be fair, you kinda started it :P. The reputation will follow you for a little while.

 

 

Yes!  And 110-115 knots correlates very closely with what other CT owners see at ~5000rpm. 

 

I feel like this is a little low on RPM... I need to do a flight test again!

Posted

Okay, tried to be nice. But you goofs want to keep playing games. GS is TAS plus-minus wind. I own and have read Stick And Rudder too. You guys are a laugh. All you do is carp and whine and attack me.

 

I know a lot of you guys are just old and cranky because you lost your medicals and have to settle for being sport pilots now and fly old used LSAs and kit planes with steam guages and day flying. But it doesnt negate the superior aspects of the 912i, and the advancements in the all digital cockpit that comes with the CTLSi.

 

Still chuckling. Sick and Rudder? More like old bitter guys clogging up the skies is closer to the truth.

CTLSi,

I got to fly one of my friends "kit planes" last weekend while I was in Arizona on business and it was a pretty nice ride. Of course it was 1. All metal 2.Had steam gauges and 3. Old non fuel injected engine. So I doubt it would have impressed you.

My hope is that if and when you become a pilot (seems to me you should have had it by now based on prior comments)that you look for ways to experience other forms of flying in different aircraft. There's nothing wrong with taking off, hitting the autopilot and viewing a video on your ipad while your state of art aircraft takes care of all things related to monitoring essential systems and gets you to the downwind at your destination where you fly it onto the runway and feel you are a master of all things aviation as you taxi to the FBO. I'm not sure if I consider that enjoyable.

 

I really look forward to meeting you one day and discussing our mutual love of flying!

 

 

My numbers are almost exactly the same as Andy's

post-456-0-82915100-1392612454_thumb.jpg

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