NEUFORM Prop Pitch

[Roger Lee]

Hi CTfarmer,

As for that Rotax article, who do you think wrote it?  

 

 

I have flown all rpms starting at 5200 rpm and increasing to 5800 rpm on the Rotax with 10 different props. Interpreting graphs is one thing, doing it for real and flying side by side 3 other identical aircraft is another.

I still maintain that a prop pitch setup to achieve 5600-5700 rpm is the best balance point between cruise, climb and fuel economy. 5500 WOT is not as good as 5650. Some may like 5600 over 5700 rpm and that part is a personal preference item.

After setting up 75+ LSA aircraft with a new prop pitch this has been pretty much proven out over the last 8+ years. Setting your individual WOT rpm still should take into consideration your specific flying needs. (i.e. setup at your average altitude, do you fly heavy most of the time, airport elevation, short field operations,  ect...)

Remember Rotax basis all their numbers on you being able to achieve 5800 WOT, even at take-off. We have to also remember not to compare our ground adjustable numbers with the in flight adjustable group.

 

 

 

Hi Eddie,

"I can see the engine idling faster with no prop, but why would it overspeed with the idle speed properly set on the carbs? I just can't see enough fuel making it past the carbs at idle to take the engine to redline."

 

 

I have never started a Rotax without the prop because I took them at their word when they said it could cause damage. From what I have been told, without the prop for resistance just a bump of the throttle may cause it to over rev.

 

You'll have to questions Rotax's statement, I'm just repeating what is taught and in print.

​This is in the manual to never do and talked about in classes.

[Ed Cesnalis]

What good is the available RPM above 5,500?

• Improved initial climb.
• Improved speed/climb available at higher altitudes
• More cruise time can be spent leaned as opposed full rich
• Less likely to 'lug' the engine (high power setting at too low RPM)

Lower RPM for overspeeding margin isn't needed, exceeding 5,500 isn't over speeding until 5 minutes.  I used to change my pitch twice a year so I was almost always WOT @ 5,500 and accidental overspeeding has never been an issue, I can hear it in an instant.

[IrishAl]

I believe you.

But why?

Similar engines of all descriptions are routinely started in neutral, and hence with little or no resistance.

I can see the engine idling faster with no prop, but why would it overspeed with the idle speed properly set on the carbs? I just can't see enough fuel making it past the carbs at idle to take the engine to redline. 

 

Eddie.

I suspect it's because 'Engines of all descriptions' have flywheels which create acceleration/deceleration resistance (inertia) as well as smoothing out power pulses.  In aero engines, the propeller acts as the flywheel (it's inherent inertia plus drag).  If you remove the prop, all the energy produced by the engine goes into the crank and the pistons, which will then be much more prone to overspeed at the slightest blip of the throttle. 

So, in theory, I think you're right: if you started it and kept it at idle, it probably wouldn't overspeed.