Re: Rules of thumb...

On Monday 20 Jun 2005 19:52, Andy Ross wrote:
> Lee Elliott wrote:
> > does anyone know of any rule-of-thumb method for determining
> > the most efficient cruise speed of a propeller?
>
> Propeller efficiency curves are pretty flat.  For lightplanes,
> you should probably pick a specified cruise speed/rpm from a
> POH.  For props with a wider range of use, pick something from
> the middle.
>
> Generally, especially with constant speed propellers, it
> shouldn't matter much.
>
> Andy

I'm still trying to get the TU-114 I've been working on to behave 
credibly and playing with the cruise-speed is the most recent 
thing I've tried.  I found that by lowering it from the typical 
cruise speed of 431kt @ 36000ft to 300kt @ 1000ft has improved 
the take-offs no end and it's also allowed me to reduce the 
camber on the wing which was causing sudden pitch-downs at low 
altitude/low weights/high-speeds.

However, I've not been able to get a config working if I specify 
a condition lever anywhere and I imagine that this points to a 
serious problem in the config.

I'm also not clear on how the prop-pitch and condition levers are 
used together.  I understand, I think, the prop-pitch control 
but I'm still confused by the condition control and how constant 
speed props fit into the equation - there seem to be three 
variable factors here, with control over pitch and condition, 
and the CS prop taking care of itself.

I was given max and cruise prop rpms and I can control the actual 
rpm to match these numbers by using the pitch control but this 
doesn't seem right to me.

LeeE

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