Prop pitch -again

[Roger Lee]

The rub is there are variables to interpret and apply to the different engines and the info isn't always separated for each engine in the manual. Case in point the 1400 minimum rpm it recommends. It shows it for both engine, but definitely isn't for the ULS. You certainly can run 5500 rpm all day long if you choose because it was designed to handle that.

[Ed Cesnalis]

CT, I have been crusing at 8500 most of the time. The last time i opened it all the way up, the tach went into the yellow so i backed it off, it can run at 5500 at about 90% throttle it seems. Remember, like you, there is little moisture right now, so density altitude is only about a K higher on most days.

 

I am going out today for some cross-wind landings. I will try a wide open throttle today.

 

You are permitted 5,800 for 5 min. Sounds as though you are really flat, too flat for my carbed 912. If I had your FI I would consider flatter than I currently run so that I could take more advantage of the economy you have available.

 

Thanks

[Ed Cesnalis]

So you also think I should cruise at 5500 and not lower? I would probably be at a 4.5 gph but be booking at around 120kt true (given no cross or headwind).

 

I think you need to consider prop pitch, RPM and throttle setting. 5,500 seems to be the best RPM but its somewhat of a Rotax secret. You want to cruise below 92% throttle to be in eonco mode and you want your pitch to permit both at the same time.

 

5,500 @ 9,500 @ 91% throttle would be a great setting but it would limit your top speed and permit you to overspeed at highest throttle settings.

5,500 @ 9,500 @ WOT would give you top performance for altitude but limit economy.

5,200 @ 9,500 @ 91% would be focused on economy cruising at altitude.

 

See what your starting point is ( current WOT RPM ) and then decide what your target is ( speed vs economy ) and see how far off or on your pitch is.

 

BTW winds only effect your ground speed not your true air speed or your indicated speed.

[Roger Lee]

CTLSi,

 

You shouldn't have any issues idling that engine at 1700-1800. We can and your engine is smoother. If it runs rough down at idle something needs to be looked at.

From what I was taught in the Rotax fuel injected engine class you should be in a nice rpm range between 5100-5500 for cruise rpm provided you can get 5500-5650 WOT. These rpms will also put you down in your economy cruise rpms below 92%. At around 5100 you should be around 3.6- 3.8 gph. Above that rpm I don't have any real life numbers to give you yet.

 

Ed,

I don't think he needs to run 5500 all the time. I would bet the majority of us cruise around 5100-5300 with a few lower and a few higher. You end up at higher settings because you're not a flat lander like the rest of us.

 

Remember there are no secret societies or inner circle secrets.

[Ed Cesnalis]

I didn't say he needs 5,500 all the time, even when he asked I said he should learn his pitch and I gave 3 options as examples.

 

His needs due to where he lives are similar to mine. I bet he simply needs to open his throttle a bit and burn a little more fuel and go a little faster but who knows till you check WOT RPM?

 

rpm range between 5100-5500 for cruise rpm provided you can get 5500-5650 WOT. These rpms will also put you down in your economy cruise rpms below 92%

 

There is some overlap there, if you can get 5,500 and cruise at 5,500 you are 100% not 92%

[Roger Lee]

CTLSi,

 

Isn't 1800 the bottom of the green idle arc before the yellow starts? Even with that we set our idles like yours can be down between 1700-1800 to reduce to a good idle for landing. That said none of us should just sit and idle down at the 1700 area. All our engines will idle smoother at 2000+

[Roger Lee]

I meant warm engine idle. All of us have rough engines when cold with low rpm. Mine rpm arc changes on my Dynon too. I usually warm up at 2200-2300 rpm until I get to my 120F oil temp operating lower limit.

[FlyingMonkey]

My engine usually will not idle below 1900 when cold, but once warm will idle at 1700-1800. 1800 is the top of the yellow on my tach, and it's dead accurate for chatter, any rpm below that and the gearbox noise is audible. If I start to hear chatter I just add a little throttle to idle above the yellow on the ground. It sounds like CTLSi's engine may be set with a little too much RPM for idle, unless the gearbox or something else is different on an LSi. OTOH, I have found that a little higher idle can give a little cushion on landing that can make thing smoother, especially when just learning to land the thing. When I had my idle reset lower my landings immediately got worse until I adjusted to the change.