Re: Prop mass and bsfc figures for YASim

On Monday 07 February 2005 18:53, Andy Ross wrote:
> Jim Wilson wrote:
> > When I use this things do not come out right...or at least
> > the way the p51d is configured.  No where have I been able
> > to find a referece to kg-m being as an moi, but that is what
> > the YASim doc asks for.
> >
> > Maybe Andy will see this and clarify.
>
> A 2D moment of inertia about a point is a mass times a moment
> arm.  In YASim's units, that's a kg-m.
>
> I think the issue of that formula came up on the list once
> before. I'm not sure sure where the numbers in it are coming
> from.  If you assume that a propeller is a "stick" (i.e. has
> the same linear density along its length) then the MOI
> equation has a much simpler form:
>
>   mass * radius / 2
>
> That is, just integrate density*distance from distance=zero to
> R, and remember that density*R is just the mass of the prop. 
> Note that the term for the number of blades drops out
> entirely.  A prop of the same mass and radius has an MOI
> independent of the number of blades.
>
> Real propellers aren't sticks, of course (I'd guess they're
> heavier towards the center, leading to a result somewhat less
> than this equation gives you).  But this should get you into
> the right ballpark presuming you can get a good value for the
> prop's mass.
>
> Maybe the posted equation is tuned for a particular prop
> design and doesn't apply well to other types?
>
> Andy

There's nothing special about the SR45 prop design that I'm aware 
of.  I've not seen any references to any trick stuff wrt the 
SR45 props so afaik it's all pretty standard late 40s/early 50s 
turbo-prop stuff.

However, I'm also working on a TU-114 and I imagine that the 
props on that may be a little bit out of the ordinary, bearing 
in mind the top speed that that TU-95s & TU-114s achieved (I 
believe that this 'family' of a/c still hold the speed record 
for prop powered a/c).

LeeE

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