The big problem on constant speed units is to get them stable. Arplast
developed one for their VP prop but I believe it tended to hunt. Too many
variables perhaps. When the pitch changes for example the load on the
engine changes so the mixture changes so the output changes so the prop is
no longer set as it thought it was and so on.
Arplast are looking at a new idea.
The MT controller appears to work satisfactorily suggesting that the
solution does exist.
Jerry
----------
> From: Miles McCallum <milesm@avnet.co.uk>
> Subject: Electric CSU laws
> Date: 13 April 1998 11:28
>
> Here's a poser: I've got a friend working on an electronic constant speed
> unit for NSI VP props.
>
> It will work just like a standard CSU when switched on (off will revert
to
> manual blade pitch control) but it is possible to add some features to
> reduce pilot workload and/or save his bacon when he/she cocks it up
> -typically opening the throttle before increasing the rpm, sending MP
into
> the detonation zone.
>
> 914's are protected (MP is limited according to rpm via electronic
> wastegate control) but 912's and other engines are not.
>
> We have decided to stick to a relatively simple system on cost grounds
> -meaning inputs will be limited to throttle position, rpm, and perhaps
> manifold pressure for unsophisticated (!) engines.
>
> The question is, what laws govern CSU behavior?
>
> My preference (at the moment) is a very simple system: -"manual" constant
> speed setting via a switch on the throttle (just like a prop lever) and
two
> trip switches at, say, the 20% and 90% throttle positions that will reset
> the target rpm to max -so that pushing the throttle forwards will
> automatically fine off the prop to reduce the chance of detonation, and
> pulling the throttle right back will prepare you for a go-around, and put
> the prop in air-brake mode.
>
> It is possible to get more or less sophisticated than this. Any ideas?
>
> Miles
>
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