Re: YASim Propeller rpm

On Monday 18 April 2005 21:18, Jim Wilson wrote:
> > From: Lee Elliott
> >
> > Hello all,
> >
> > I'm trying to work out the right prop rpm figures for the
> > TU-114 - the airliner version of the TU-95 'Bear' - and I've
> > arrived at a figure of around 494 rpm for the cruise
> > setting.  I'm also using a value of 958 for the takeoff-rpm,
> > which I calculated at 150 kts and 0 ft.
> >
> > This is based on 3.2m radius props and a cruise speed of 475
> > kts at around 30000 ft.
>
> Off the top of my head...that'd be about 20m circumference,
> which at 1000rpm would be 20km per minute.  Since an airliner
> does about 15km per minute.  I think that'd be a bit over the
> speed of sound...depending on altitude.
>
> > Could someone check my maths and confirm that these figures
> > are about right i.e. the prop tips staying sub-sonic?
> >
> > While I can get the config to solve with these rpm values
> > the stand alone YASim solver seems to go into a loop if I
> > include the min-rpm & max-rpm tags.  Is this likely to be
> > due to me trying to use impossible numbers in the config or
> > is this a problem within the solver?
>
> Not sure.  Just make sure if you are using a ratio that you
> scale everything that needs to be.

Thanks for that Jim.

I think I've got a much better understanding of constant-speed 
props now and realise that I should be using the low value i.e. 
around 494 rpm for both the take-off and cruise settings, the 
turbine speed staying pretty much constant.  Heh - I didn't 
realise how little I knew about turbo-prop engines.

What I'm trying to find out now is the high-altitude power of the 
engine.  I've got a basic rating for the engines but I assume 
that's at sea level.  I'm also assuming that the engine will 
produce less power at high altitude but I don't know the factor 
or what a reasonable ball-park figure would be.

Still, things are starting to make some sense.

LeeE

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