New Rotax Service Letter

[Roger Lee]

New Rotax Service Letter

 

 

http://legacy.rotaxowner.com/si_tb_info/serviceletter/sl-912-016-r1.pdf

[gbigs]

Key Takeaways:

 

ROTAX strongly recommends the installation of a manifold absolute pressure gauge.

 

Fixed pitched propellers should be set so that the take off rpm is above 5200 rpm (WOT).

 

Engine speed over 5500 rpm is restricted to 5 min maximum.

 

Continuous use of engine speed below 5200 rpm with WOT should be avoided (can cruise below 5200, just not with full throttle).

[Anticept]

Nice that it's all that in writing.

[Rich]

Thanks Roger,

I was able to download your link for my files.

When I tried to download from original on my android, it took me to AvWeb, constantly.

[Roger Lee]

Nothing has changed. A service letter is for information distribution and or clarification. 

 

 

You guys are forgetting that some of this and items in the manuals is written for an in flight adjustable prop and for 3 different engines.

 

Manifold gauge is only worth while for the in flight adjustable prop. The 5200 rpm at climb WOT will put most over 5800 rpm WOT in level flight.

 

Some common sense and being able to know how to interpret these things to YOUR SPECIFIC should be considered. Not everything here is an absolute.

[ct9000]

Roger with all due respect , the use of  manifold pressure is quite important . Firstly it will educate the pilot about the real altitude especially when you get up a bit . Many would not realise that you cannot get more than 27 inches except at low levels on a day of low pressure so full throttle is still ok at say 5000 . All the parameters fit together if you have the info . I think that is why Rotax recommend a manifold pressure gauge . Lets face it these engines are very hard to hurt if you stick to the guidelines .  

[Roger Lee]

With a ground adjustable prop the manifold pressure will always be 1-1.5" lower than ambient. You have no control over it other than adjusting rpm. The MAP with Rotax is setup for in flight adjustable props and turbos. Most Rotax 912 engines since 1990 don't even have a MAP gauge. We fly by rpm and most seem to cruise around 5100-5300 rpm on the average. Some higher some lower, but they don't use the manifold pressure.

In all the Rotax classes I have been to this question comes up quite frequently and the answer I gave is what is given.

 

What control over it do you have with a fixed pitch prop and keep in mind the rpm Rotax wants you to fly at.

 

 

If you want to fly at 5200 rpm in cruise how do you set the manifold pressure on a 912ULS or UL with a fixed pitch prop?

[ct9000]

Sorry if you took offence , but like you have said if you pitch for cruise RPM , on climb it will be too low . My point is that the low RPM is still ok at full throttle because you often cant get more than 27 inches anyway except at low levels and then it is not for long . Having the gauge is a good educational tool . It would be great if you guys could have CS props or at least inflight adjustable the extra performance is significant .

[Roger Lee]

I never take offense so please don't give it a thought. It's just people debating a subject. There may be a right or wrong answer and maybe it's just preferences. Either way I'm good.

 

I fully agree that a CS prop setup is the way to go and Rotax writes most of its specs for that, but unfortunately here in the US we are stuck with either fixed pitch (non adjustable) or ground adjustable. So we have to pick an all around balanced rpm which is best determined at WOT in level flight at that persons average altitude which helps us in the entire flight envelope. Because of this we don't get to pick a manifold pressure. We pick an rpm and just live with whatever the manifold pressure is. That's why in the US we tend to only talk about rpm vs manifold pressure. Now the guys that have a CS on a certified Rotax aircraft or a turbo they certainly need to use the manifold.