In 1987 I wrote an article showing how to generate the centerline for a helical pitch distributuion on a cylindrical or conical form. Saw little use for it as it lacked the stiffness of the 3D shell with the helical form.
Also included an equation for camber useful for selecting the form:
Camber = Chord / 4 Diameter
Don Lindley raked me over the coals for not saying it was an approximation, but he liked the 2D of the cylinder for flaring on LPP.
The article included an isometric view of different pitches. It appeared in the Phoenix MAC newsletter & I think Model Builder picked it up. Home fire wiped out any copies I may have had.
Is very simple. Y-axis = Pitch/ 2 pi X-axis = Prop Radius ( 0, 25%, 50%, 75%, 100% )
Connect apex to all Radii to show all angles.
Center the form Dia on the apex and the intersection w/angle lines shows where Centerline goes. Centerline is curved in scimitar fashion and results in interesting design.
Helical forms are so easy with hot wire foam or fanned strips + an undercamber form & is my preference.
Jim Richmond used the same helical form for all his props, including Atrium Insect (AROG) and Starwalker (90 cm F1D).
He moved the small blade closer to the hub to get more twist. Seemed to work as both set records.
Good luck,
H
Received on Sat Mar 05 2011 - 00:48:25 CET
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:46 CET