I have never covered an indoor propeller with film but it seems to me that if you want a frame to hold the film whilst covering a helical propeller that the most effective (and probably the simplest) thing would be a ‘skeleton’ pitch block. The picture below is from an article I wrote for the 2012 Symposium. It shews a pitch block before the sheet top has been added. The thing on top is a roll of sandpaper for smoothing the edges. If the roll is slid along the two side curves it also keeps in contact with the straight center spine; therefore if covering film is spread over the curved sides it should settle in a smooth helical sheet.
Of course, the center spine will not be needed on a frame. Also, if you are looking for a light frame the curved sides need not be made from sheet balsa but could just be laminated around a former, like one does with a wing tip. By the way I should mention that the curves on both sides are the same but one is turned end-for-end.
As I mentioned in the Sympo paper, if anyone wants a spreadsheet to calculate the ordinates for the side curves for a range of pitches, diameters and blade widths, just ask.
John Barker - England
From: Indoor_Construction_at_yahoogroups.com [mailto:Indoor_Construction_at_yahoogroups.com] On Behalf Of Tapio Linkosalo
Sent: 22 February 2014 16:10
To: Indoor_Construction_at_yahoogroups.com
Subject: Re: [Indoor_Construction] RE: Prop covering jig
I have tied a depron frame, twisted in the pitch of the prop, but it
seems to me that the film gets a little loose in the middle, and the
result is not too good. So my latest props I covered the same way as
have done my wing and tails; smooth the film onto a clean piece of
newspaper, and "roll" the inverted part over the film. With prop blades,
you need to start from the root, and cut the lifting edge loose while
rotating the blade over the film, but going a little at a time and
moving the blade so that film keeps tight resulted in the neatest prop
covering I have done so far... Also crumbling the film first helps some.
-Tapio-
- application/x-ygp-stripped attachment: stored
Received on Sat Feb 22 2014 - 13:08:34 CET