Re: Prop mass and bsfc figures for YASim Prop MoI Formula

----- Original Message ----- 
From: "Jim Wilson" <[email protected]>
To: <[email protected]>
Sent: Monday, February 07, 2005 8:19 PM
Subject: Re: [Flightgear-flightmodel] Prop mass and bsfc figures for YASim


>> -----Original Message-----
>> From: Andy Ross <[email protected]>
>>
>> Jim Wilson wrote:
>> > When I use this things do not come out right...or at least the way
>>
>> 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.
>> Maybe the posted equation is tuned for a particular prop design and
>> doesn\'t apply well to other types?
>>
>
> This makes sense.  Thank you.  It has been a while, so who knows. My
> notes just mention
> the source of the info.  I am assuming now you are suggesting that we
> should apply the   weight of the prop in kg to the above simplified 
> formula to get a
> starting number.  Might   be a good note to add to the YASim doc.

> Jim


    Try this:  Prop MoI ~ (0.6 * Prop_Weight(lb) * Dia(ft)^2)/386   sl-ft^2 
[My Formula]

    Thats weight of the blades, less hub.

    Convert to MKS if necessary.

    Ron



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