Need some advice

Hi Paul

First, glad it seems to be working now.

Just to clear up gear ratios.  The 2.27 ratio was common up to about 1999.  After this point they changed to 2.43.  There was a great deal of benefit to lower the ratio as it allows for a longer propeller to be used to achieve better performance.  You can check what you have by counting how many turns on the flywheel to the prop.  I doubt if you have any engine made after 1999 that it has anything but a 2.43.  

The peak torque is always 5200 (5252 to be exact) and the latest SB in performance will show the best way to set up a constant speed by RPM (crank) vs manifold reading (MAP) This is the correct way for a constant or inflight adjustable prop on the Rotax.  Given the Rotax is a geared engine you can't just apply the same technique as from a direct drive type.  The danger area is when you are making adjustments and it is important to apply the principles set out in the SB for this. 

SB-912-079

Cheers

Rotax Wizard wrote:

Hi Paul

First, glad it seems to be working now.

Just to clear up gear ratios.  The 2.27 ratio was common up to about 1999.  After this point they changed to 2.43.  There was a great deal of benefit to lower the ratio as it allows for a longer propeller to be used to achieve better performance.  You can check what you have by counting how many turns on the flywheel to the prop.  I doubt if you have any engine made after 1999 that it has anything but a 2.43.  

The peak torque is always 5200 (5252 to be exact) and the latest SB in performance will show the best way to set up a constant speed by RPM (crank) vs manifold reading (MAP) This is the correct way for a constant or inflight adjustable prop on the Rotax.  Given the Rotax is a geared engine you can't just apply the same technique as from a direct drive type.  The danger area is when you are making adjustments and it is important to apply the principles set out in the SB for this. 

SB-912-079

Cheers

I have seen those charts, but I honestly don't understand them because I cannot figure out how I could even get close to those manifold pressures.   

Are those numbers showing the absolute maximum manifold pressure as I understand it?  We barely see anything over 25 inHg here when engines are running, and our aerodrome is sitting at 880 ASL so when they are flying at altitude 23 is tough to achieve.

Obviously, it would be ideal to run at a lower RPM setting and better throttle as well to benefit from the improved efficiency over the older more antiquated direct drive aircraft engines, so maybe if I can find a way to prove I am not getting detonation at that range we can run your recommended settings, I can move to that and back to our MOGAS which was proven as a RON 98 by way of fuel analysis 

Paul...right at the top it states it is absolute pressure.  We always use this for pressure.  

Detonation is not just overload of the engine it can also be exhaust backpressure, high intake manifold temperatures and other things.  The Tecnam P2006 twin generally has issues as a training platform but almost never has detonation issues in normal use.  The take-away from that is what conditions are different while doing training?  Items like shutting off ignition in flight for example (single engine?) When you switch it back on the soft start will not advance the timing for some 5 to 8 seconds, it will be running at 3 degrees after TDC until it advances.  Exhaust systems can fail internally or just have excessive restriction.  That one is not hard to check, it is shown in the installation manual and should be easy to exclude that as a contributor to detonation.  

Be very careful with fuels, make sure that the winter fuel is never used in summer conditions.  The  Reid Vapor pressure limits are very different.  (winter fuel can be as much as double the RVP of summer) 

My last comment is related to RPM, this engine loves RPM.  You only have a 61MM stroke, less than 3 inch.  The gearbox you should think of as a torque multiplier.  The dwell at TDC is extremely small and as such we never want to find the engine way below the powercurve.  it will love you with a little bit of RPM rather than ask it to lug the prop over the peak pressure point of 5200.  

I am speaking of my opinions, some can argue the points.  I only really work on Rotax.  I did all my private pilot behind Lyc engines of all types and a few Contis.

Cheers