Yes, I'm familiar with the PVHC prop blanks. What you describe would have a
pitch of 8.64" and P/D of 1.57, which is good for this plane. You can get a
more precise figure by measuring the thickness of the block from the front
face to the rear face, most easily measured right across the blank at the
centerline, and the width of the blade chord at the tip. The ratio of the
thickness to the chord is the sine of the blade angle at the tip. From that may be
calculated the blade angle, then calculate the tangent of that angle. The
tangent times pi is the P/D and that times the diameter is the pitch.
Make a full size drawing of the prop so you can reproduce it if necessary.
It is cut from a rectangular block. The side view is a rectangle. The front
and end views will show the outlines of the rectangle with the two parallel
lines denoting the edges of the blank. You can use a plastic prop as a
pattern for the blade outline and airfoil. There are several guides to prop
carving on the Internet. Most of the cutting has been done, only final shaping
and finishing is necessary. Be careful about drilling the hole, get it
centered and perpendicular to the block. Some like to cover their prop with tissue,
others use polish.
On the plan that I have, with the correct 16" wingspan, the motor stick is
9&13/16" long, so I can't see how you could have got the rear hook at 11.5".
The plan shows it just ahead of the tailplane, which is fine.
There are three things I would suggest you work on. Get it to fly in the
largest circles you can safely fit into the space, with the wings as level as
possible. Try different wing positions, glide test with motor on but with
ballast to replace prop to find the lowest rate of descent, or power test with
about 70% of winds, to get the quickest climb from floor level to eye level,
and note the CG position on the wing chord. Try different motor thicknesses,
wind to at least 90%. When you change motors, move the wing to get the CG in
the same relative position as shown in the earlier tests. On each flight,
record turns put in, turns left on landing, how close to ceiling. Not getting
to ceiling suggests too thin a motor. Having many turns left on landing
suggests too thin a motor. Hitting ceiling suggests too thick a motor. Running
out of turns midair suggests too thick a motor. A different prop might work
better, but the rules limit your prop selection.
Bob is right, the rules are too restrictive. But those are the rules and if
other guys are getting two minutes, you should be able to also.
Gary
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Received on Fri Nov 03 2006 - 14:57:19 CET
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:44 CET