Re: Prop mass and bsfc figures for YASim
Andy Ross <[email protected]>
| Newsgroups | gmane.games.flightgear.flightmodel |
|---|---|
| Message-ID | <[email protected]> |
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 _______________________________________________ Flightgear-flightmodel mailing list [email protected] http://mail.flightgear.org/mailman/listinfo/flightgear-flightmodel 2f585eeea02e2c79d7b1d8c4963bae2d