Re: Re: Re-Pitching the Ikara Prop

From: Bill Gowen <b.gowen_at_earthlink.net>
Date: Tue, 13 Nov 2007 19:38:20 -0500

There are a number of reasons to use a Harlan bearing or a bent wire pigtail bearing. If you'll take a stock Ikara prop and it's hanger, you can get maybe 5 degrees of movement in the prop relative to the thrust centerline. If you have any out of balance of pitch or mass or tracking, the slop in the bearing will magnify the effect, causing the very type of misbehavior that you have described. A properly set up thrust bearing supports the prop shaft in 2 places and allows close to zero movement of the shaft relative to the thrust centerline. My guess is that there is also less friction in a machined aluminum bearing than in a plastic one.

The reason for using the Harlan penny plane bearing is because the penny plan has the split rear shaft ("pigtail") support that allows the prop to be removed. As I understand the SO bearing, it does not allow prop changing. Please correct me if I'm wrong about that. The Geauga bearing has the same problem if I remember correctly.

The prop is glued to the shaft for the same reason that you use the better bearing. If there is free play between the prop and shaft, then you can't expect to get an accurate and equal setting for the pitch and tracking, and any out-of-balance situation will be magnified.

  ----- Original Message -----
  From: calgoddard
  To: Indoor_Construction_at_yahoogroups.com
  Sent: Tuesday, November 13, 2007 6:10 PM
  Subject: [Indoor_Construction] Re: Re-Pitching the Ikara Prop


  Bill:

  As usual, thanks for your expertise.

  Can you describe why you like the Harlan bearing insead of the
  standard Ikara thrust bearing? The latter allows you to quickly
  change props onthe Ikara prop hanger.

  I have Harlan's metal thrust bearings that are already sized for
  the .020 prop shaft. He calls them his Science Olympiad bearings.
  So there is no need for delicate drilling. But thanks for the info
  on drill sizes. That may yet come in handy.

  When you glue the shaft to the Ikara prop with CA, how do you know
  it is perfectly perpendicular to the prop spars? There is a tiny
  amount of slop there, but I suppose it makes little difference if
  the prop is vertical at the time. Why do you glue the prop shaft to
  the prop anyway?

  One year our team used special prop bearings that were machined by
  Geauga. They were really neat, but you couldn't swap out props very
  easily and you had to make sure you used a tiny rubber motor to keep
  the motor shaft pulled back during transport.

  Thanks Bill.



   

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Received on Tue Nov 13 2007 - 16:38:26 CET