M.A.P.

Hi Sean,

I do not think you will need to adjust any settings in your controller. I suspect the reason that Airmaster suggests checking the configuration of the controller is that your letter is not clear as to whether or not you have altered the controller configuration, The suggestion may have been made to eliminate one of the possible variables, but as long as you've not previously modified the controller settings yourself, it's probably not absolutely necessary.

From everything you've said, I agree with Mike that adjusting the coarse adjustable pitch stop (switch) in the prop hub is the most likely solution to your question. The setting of the propeller pitch limits is a trial and error process requiring several test flights, as laid out in sections 8.3.2 to 8.3.4 of the Airmaster manual. It's very possible that in an airframe with as wide a range of airspeeds as yours the final coarse pitch limit setting will be somewhat of a compromise between safety and performance, but where that compromise lies is ultimately your choice.

Mike/Tim,

Gentlemen / Scholars both.

Airmaster have also advised course pitch adjustment . A ++ to both of you.

To assist the not so bright,they have sent (pdf) coloured diagrams/instructions, which are a major step up in clarity, from the Operator's Manual.

Airmaster advisor -

"My suggestion is to adjust the Coarse cam 2 turns Anti Clockwise (as seen from front ) then re-check in flight.  If you continue to see the COARSE Led turn green the adjust another 2 turns ACW."

Assuming the high winds we have been experiencing abate (my Sonex lives outside) Tomorrow, I will act on yours & Airmaster advice and enjoy a day of adjustments.

Let you know how it all goes.

PS Neither you or Airmaster have answered this question:

How will adjusting the prop, Auto Cruise, to go to 5000-5200 rpm, effect max speed in level flight? ie with a limit of say 5200 rpm, will I get the current 147 knots? ( This is a question about pilot in flight, cruise speed options, after setting the prop).

I presume, that if a diffrent setting, to Auto Cruise 5200 rpm, is desired (eg 5400 rpm) I would turn Auto select switch to Hold and adjust pitch with the Manual switch? then adjust power to desired MAP?

Hi Sean,

I'll have a stab at answering that question, although I'm very much not an expert and this answer is a is a bit of a guess: The Rotax performance graphs show a a peak in the torque curve at about 5100 RPM and a continuous positive gradient for the power curve. Any reduction in RPM from maximum power will naturally reduce your airspeed at WOT (less power available) however the engine will be producing that reduced power more efficiently (closer to peak torque) resulting in a potential reduction in fuel consumption at WOT.

In answer to your second question: Yes, when the controller is in AUTO/HOLD mode, you can use the manual control switch to select any engine speed you like within the programmed limits. (between 4000 RPM and 5700 RPM for the factory settings) The controller will then continue to regulate prop pitch to maintain that engine speed. (This of course only applies as long as the prop pitch required to maintain that engine speed is within the range of the pitch limits. I know I'm stating the obvious there, but I don't like to give an incomplete answer.)

Oh God the bloody forum just lost a lengthy reply! I'll try to do it shorter.

Yes!! Adjust the prop. Before you start, don't just use the short instructions - RTFM and take it in properly!

Adjusting may take several iterations and most of the day. They say you must replace the spinner for every test flight.

When you think you've finished - you MUST do the safety test of climbing away from a baulked landing with the prop stuck fully coarse. Shouldn't be a problem for your a/c but do it. I don't know about Oz, in UK you wouldn't get a permit without that done (at max weight too.)

After adjustment, you won't get 5200 in auto cruise even at WOT. You'll get 5000. So maybe you won't achieve 147kts. So what? Switch to auto climb which is 5400rpm (you can use it in level flight, it's just an rpm setting!) and you assuredly will.

You'd never want to use WOT at 5000 anyway, it feels horrible and increases big end and piston ring loadings etc. More rpm is kinder to the engine at those power levels.

Yes you can set 5200 on auto hold if you want but what's the point? Maybe 5200 would be slightly more fuel efficient for the engine than 5400 - but what about the prop? Do we know what rpm that prefers?

I agree 100% with Tim's words above.

Mike

Hi Gents,

My commiserations Tim - I too have lost so many carefully worded responses, I now copy what I have written BEFORE I click on Post Reply. For the most part the loss is on the first response of the day (after logging in), I have never failed to get through on the second go/ copy.

All good advice.

Tim

"After adjustment, you won't get 5200 in auto cruise even at WOT. You'll get 5000."

How so? Surly I can adjust, within reason, for whatever rpm I choose (4800 -5500 rpm). Seems to me that in cruise 5100-5200 rpm is about where the Rotax (torque) would like to be. My last  aircraft, Zephyr/Rotax 912ULS/Fiti prop(ground adjust), was sweet as a nut, in cruise, at 5200 rpm, averaging under 13l/hr.

Yes I understand that I am adjusting for a Max Cruise RPM - irrespective of power/throttle (as indicated by MAP) - I just wondered what might be the effect of increased/decreased power on speed, at the new setting. 

What's so special about 5000 rpm?

"..............but what about the prop? Do we know what rpm that prefers?"

Good point - will ask  my Airmaster contact .