Question about the MAP limits in SB-912-079 R1

RW

"For the moment don't worry about static trust, that can vary a lot due to the different aircraft or prop being used". 

My appologies in advance - an amature should not contradict an expert. I disagree with the above statement.

It seems to me that for anyone attempting to set the prop pitch from scratch, the only safe way is to go for 5200 rpm Static @ WOT.

This  gives the pilot confidence that the setting is conservative, little chance of an engine overspeed/underspeed.

The aircraft can now be tested, performance noted and adjustments , as per your advice above, can then be made according to airframe characteristics and mission intention.

Sean Griffin wrote:

Sean,  E prop is an extreme in that it does not follow the standard idea of a fixed prop. E prop and only a very small number of flex type blade props and not the same as a rigid prop blade.   I know of many engine prop combinations that have to have a 4500 to 4700 static to get them to unload to 5200 in climb.   On average more slippery aircraft will unload significantly after leaving the runway.  

The important thing is that the prop has to act as a governor when in WOT level flight.  In the event of a linkage problem the system is designed to go to full open.  To be sure you do not just blow up the engine the prop has to control the RPM.  I am sure that everyone who is switching to an E prop is most likely aware of the quirks it has be hunting prop loading due to its design.  

Cheers

Murray Parr wrote:

Sean Griffin wrote:

RW

"For the moment don't worry about static trust, that can vary a lot due to the different aircraft or prop being used". 

My appologies in advance - an amature should not contradict an expert. I disagree with the above statement.

It seems to me that for anyone attempting to set the prop pitch from scratch, the only safe way is to go for 5200 rpm Static @ WOT.

That doesn't work for me. My example below shows exactly why Rotax has that view on this.

The E-Prop ground adjustable Prop I have is set to 5650RPM static. As soon as it starts rolling down the runway, it loads up and quickly drops to 5100RPM 

By the time I get airborne, it runs around 5200RPM on climb out. It doesn't unload much from there until i get faster than 100 kts IAS, then it starts unloading and gets right back to 5650 at WOT cruise speed of 130 Kts IAS

So, it really does matter on a lot of variables and different combinations. For example, if my plane was only capable of 100 KTS it would be WOT at 5200 RPM in cruise with 5650 static set and I would likely have to set static to 5800 or higher in that scenario.

Murray,

I deliberatly did not mention props that automatically change pitch/flex in flight (Roger L covered this in his comments).

You & I have talked about this - I believe your observation was/is to stick rigidly to the manufactures set up instructions.

Flexing props are still very much the exception to standard practise.😈

Rotax Wizard, thanks for your response.  

Fortunately in my case Van’s Aircraft provides a recommended propeller pitch my Sensenich ground adjustable propeller on my 912 ULS in my RV-12. This provides a great starting point.  

It fully makes sense that the propeller should be pitched to run at or slightly above the maximum continuous operating rpm when operating at WOT during cruise.  Also, that this is complicated by the impact of different environmental conditions (i.e., altitude, barometric pressure, temperature, etc.) and that the faster one operates the engine the easier it is to overspeed it when pitching the nose of the airplane down. 

This how I previously pitched my propeller.  

So, what about my MAP being above the RON 95 (i.e., 91 AKI) line shown in figure 1 of this Service Bulletin only during takeoff roll and initial climb?  Does this limit apply to my fixed pitch application?

I ask because it determines if I can switch from 100LL to 91 AKI unleaded.

Thanks. 

Brett