Re: Prop mass and bsfc figures for YASim
Andy Ross <[email protected]>
| Newsgroups | gmane.games.flightgear.flightmodel |
|---|---|
| Message-ID | <[email protected]> |
Lee Elliott wrote: > 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. Even changing the material the prop is made out of would throw the posted equation off. It has a diameter^5 term in there, which looks really weird to me. Diameter cubed goes with mass, if the prop is a solid wood or metal. And you get another linear factor in there due to the fact that it's a moment arm. But the last one? Dunno. Likewise, the number 8.2 appears in there for no reason that I can see. Add to that the fact that it depends on the number of blades* and I'm honestly befuddled; I have no idea what it's trying to do. * Here's a gedankenexperiment to prove that's wacky: take a propeller and carefully slice the blades lengthwise into two pieces. Rotate them 90 degrees, so you now have a four bladed prop. Have you changed the MOI? Clearly not, although this equation says that you have doubled it. I'd suggest starting with the "stick" equation I showed earlier. It's based on pretty easily verified high school physics, and doesn't have any magic numbers at all. It will always give you something usable, provided you have the prop mass handy. Andy _______________________________________________ Flightgear-flightmodel mailing list [email protected] http://mail.flightgear.org/mailman/listinfo/flightgear-flightmodel 2f585eeea02e2c79d7b1d8c4963bae2d