Re: Prop mass and bsfc figures for YASim
Jim Wilson <[email protected]>
| Newsgroups | gmane.games.flightgear.flightmodel |
|---|---|
| Message-ID | <[email protected]> |
> -----Original Message----- > From: Andy Ross <[email protected]> > Sent: Monday, 7. Feb 2005 13:53 -0500 > To: Flight dynamics model discussions <[email protected]> > Subject: Re: [Flightgear-flightmodel] Prop mass and bsfc figures for YASim > > 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? > 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. What sort of effect would this setting have on YASim specificly? Would this be limited to things like the speed at which RPM increases/decreases? Should I worry about trying to find a better number for the P-51D? Thanks, Jim _______________________________________________ Flightgear-flightmodel mailing list [email protected] http://mail.flightgear.org/mailman/listinfo/flightgear-flightmodel 2f585eeea02e2c79d7b1d8c4963bae2d