M.A.P.

We had almost the same conversation in April 2023! Your initial post was about oil temperature but it broadened onto how the Airmaster prop should be set.

I guess I was focussed on the oil temperature problem and its apparent relationship with the engine load/pitch settings. The oil temperature issue has been solved by a rethink/positioning of the radiators, increased airflow and larger oil cooler.

My interest now is around the small difference between Rotax "book" figures for RPM/MAP and my actual figures. 

Is this small difference something I should be addressing?

What if any implications might there be for living with the difference (ie making no adjustment)?

Sean, I'm afraid I literally cannot understand your question in the original post of this thread. I can only think that there is something amiss with your Airmaster controller, or those figures are derived using manual control in an illogical way.

I really tried to make my response as clear as I could but we don't seem to be on the same wavelength. Please read it again, also the Airmaster manual about setting up.

Let me try one other way. Look at the curves on P7 of SL-912-016R2. My interpretation of those curves is this (and maybe I'm wrong!)

The orange line shows you the maximum MAP you can use at different RPM with WOT with Mogas 98 or Avgas (100/94/91, any of them) without causing detonation (pre-ignition, knocking, same thing)

The blue line ditto but using 95 Mogas.

The yellow line shows the MAP you will get at WOT fully loaded at various rpm under ISA atmospheric conditions. (Where the orange line is above this, I don't know whether those measurements were on high pressure days, or with boost,,or what. I think they confuse matters!)

The blue and orange lines assume you are using a prop set to fully load the engine so that the rpm will go no higher at WOT than the point they have recorded. In other words, a variable pitch prop that you can vary during the test. The point they are measuring is the onset of detonation. (I don't know how they detect it, it doesn't matter. Trust them.)

The blue and orange lines are operational limit points to avoid risk of damage from detonation. There is nothing on this page that gives you recommended operating points.

So lets assume I have my Airmaster in cruise setting, which maintains 5000rpm by controlling prop pitch automatically. At WOT, in conditions near ISA, I should see nearly 29" MAP. Well I've said in practice I see around 28" on the gauge, so near enough. If I'm on 98RON fuel, that's OK (but I wouldn't actually do it as it feels harsh.) If I'm on 95RON fuel it's not OK, the MAP is too high, I must reduce it to max 27". How? By closing the throttle a bit. The controller will keep rpm the same by reducing pitch.

As I said before, in practice I can close the throttle at 5000rpm cruise setting until MAP is about 20" before the prop has reached the fine stop and then if I close further the rpm will reduce.

So your statements about the rpm/MAP combinations you get and slight differences from Rotax puzzle me, bluntly I think they are meaningless. It's all within your control. You set the rpm to what you choose and then vary the MAP with the throttle to what you choose. You have to judge it, Rotax don't tell you. They only tell you the max continuous and max short term permitted rpm, and the max MAP at WOT at different rpm. The rest is up to you.

The "penny may have dropped" - I have been trying to replicate my Cessna Constant Speed training, from about 30 years ago. If I remember correctly (???) the idea was to obtain a "square" reading of RPM/MAP,  as in 2200 RPM/22"' MAP. I do realise that the old style square setting does not apply to the higher revving Rotax but have confused myself over the semi automatic Airmaster verses the full pilot control of the LyCon system.

I have not found the Airmaster Operators Manual to be user friendly - in short it confuses me. I think may have to go back to school.

The only time I routinely operate my engine at WOT is;

 - Take-Off, with Airmaster in TO setting, RPM goes to 5750

 - Climb Out, RPM 5450. At other times ie when I initiate Climb from Cruise, I usually limit it to 5300 rpm.

In Cruise, I look for a fuel flow (still fine tuning the settings) of around 13-14L/hr (or better), so 5000-5200 rpm which gives a MAP of around 26-27"

"The pitch range is limited by microswitches not mechanical stops. These must be adjusted to suit the aircraft, they are not factory preset."

I have not adjusted my pitch stops/micro switches (semantics) they are as the factory set them. While they can be adjusted, I am quite happy, at the moment, with the factory settings - In Cruise @ WOT 5450rpm, my Sonex is doing 147 knots Indicated (TAS 153 knots) @ 3000ft. This is far too exciting, hence my preference for 5000-5200 rpm at 130-133 knots.

No, sorry, still don't follow. I think maybe there's confusion between different ways of operating the Airmaster.

Are you using the "hold" mode, where you set rpm with the rocker switch and the controller then holds that rpm when you change throttle? See section 10.4.6 on p56. If you are, the figures you've given are more plausible, but what's the point? So much easier to make use of the three preset speeds! Alternatively you could be using manual mode but then you'll be fiddling all the time juggling rpm and pitch and MAP. That really doesn't make sense.

You really do need to check the setting of the adjustable pitch stops i.e. the microswitches. This is a matter of safety not convenience. See p35 section 8.3 and 8.4. It is most unlikely that their ex factory settings will happen to suit your aircraft.

The stops have to be set to ensure that if the prop fails fully coarse you can still climb away from a baulked landing, and that if the prop fails fully fine, you cannot overspeed the engine during takeoff.

I do agree the manual is not the easiest to understand on some topics.