Jim, go to http://genie.rchomepage.com/ and get into File 2. I've been using
these light stabs (1 oz. for the pair) on my big Genie for 12 years or so
and now on the smaller Genie Pro and LT/S versions. Although costing but a
couple of bucks to make they work very well and I've never had one break.
Chris Boultinghouse, while doing a Genie build for RCSD magazine did a
simple little modification with a strand of CF on top and bottom of the hard
balsa spars. He says the stabs are even stronger. This might be advisable
for 2 man F3J type launches.
In truth, I just looked at a picture of the stabs on the Icon and then
brewed up the built-up version. I arbitrarily made the hard balsa spars 12"
long. With the balsa cap at the root and the tip piece, the finished chord
is about 12-1/2". The root chord is 4-1/2". The area is just 7.7% of the
wing area of the big Genie and something more than that for the other
smaller wing area ships. I've never bothered to figure the %. For reasons of
scale, I assume, less % area is needed on larger ships. I can easily fly
inverted with the big Genie, do tight loops, dive it and tuck under and come
out level. There is plenty of pitch authority on landing approach at lower
speeds, too.
Sorry, I can't give you a bunch of formulas for % of area on different sized
ships with varying tail moment arms. I just try stuff out to see what
happens. It's easy and inexpensive with a simple built-up stab design.
My opinion, based on experience, is that stabs on RC sailplanes can be a lot
smaller than typically used for ample pitch control and, if smaller, they
weigh less to assist in balancing out.
----- Original Message -----
From: "jrmaclean" <[EMAIL PROTECTED]>
To: <soaring@airage.com>
Sent: Monday, May 08, 2006 6:27 PM
Subject: [RCSE] Design question - how large to make stabs?
Soaring Friends, My TD ship of choice is Compulsion by Fred Sage usually
with a 126 inch wing. I have had good success with this plane and managed
to stock up a few as bargains came available. Some time back there was a
comment that the stab was a bit small. Fred agreed and started to produce
a larger stab with a light layup to compensate. Unfortunately, mine
warped. Fred promised to fix but I was deliquent and events overcame Fred.
I then went to some lighter, built-up stabs which were somewhat larger in
area. I very much liked the way the plane flew with this setup.
Unfortunately, the stresses were too high during launch and I had some
very exciting landings with shredded stab halves! So what to do now? Any
thoughts on the following: sources for straight, tough, light replacement
stabs. How big in area and chord should they be? Characteristics of
oversize / undersize stabilizers on the aircraft handling?
Many thanks for helpful suggestions. Jim MacLean
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