1-34 Rudder

This is a pretty amusing conversation from an engineering
point of view - lots of opinions and a smattering of
facts - some of them even true!

Vertical tail volume is in fact the appropriate design
paramerter for determining static directional stability
for any aircraft. A longer moment arm and/or a larger
surface area (fin plus rudder) will increase stability.
Gliders have long tail booms because you get a better
drag tradeoff by making the boom longer than by making
the fin bigger. In addition, gilders generally need
more tail volume because their high aspect ratios generate
considerable adverse yaw. I have not looked at the
Genesis planform in detail, but I suspect (as has been
already observed) that it has a longer tail arm than
at first appears because of the forward sweep and wide
root chord. Even so, that vertical stab looks pretty
puny so I'd be curious to hear if it has the 'cha-chas'.

In terms of yaw authority (responsiveness), the size
of the rudder relative to the tail volume and yawing
inertia of the aircraft is the relevant attribute to
consider (airfoil matters too). By deflecting the rudder
you generate a sideways lift vector that creates a
yawing moment proportional to the tail arm. This moment
has to overcome the yawing inertia of the aircraft
to yield a yaw rate. The yaw rate (plus any dihedral)
will pickup the outside wing, which is why you often
lead a bit with rudder when initiating a turn, or to
pick up the inside wing when recovering from a turning
stall.

I flew a 1-34 for a few years before transitioning
to glass long ago. I don't particularly remember it
being underdamped in yaw, but I do remember it being
slow to enter a turn. I suspect the issue is that
it has a relatively small rudder and a lot of yaw inertia
(those wings are HEAVY). I also remember the ailerons
being quite stiff. I built up good biceps by the end
of the season.



At 19:48 15 February 2004, Dave Nadler Yo wrote:
Roy - beg to differ - the 1-34 has inadequate yaw stability.
If you hold neutral rudder at moderate cruise speed
in any
turbulence, it often does a very notable cha-cha in
yaw.
Not as bad as some V-tail Bonanzas, but to me uncomfortable.
OK, find cha-cha in your textbooks...
Best Regards, Dave

Roy Bourgeois wrote in message news:...
I think that the difference is that my original post
focused on 'rudder
response' and others are focusing on 'yaw stability'
- which are different
and somewhat opposite. The 1-34 is quite stabile
in yaw but as Doug noted
in his first post, it's response (time to desired
effect) to your stepping
on the pedal is pretty bad. I flew several 1-34s
about 250 hours (and
still occasionally). It doesn't have a problem with
adverse yaw in a
turn. But when you step on the pedal (say, to begin
a slip) - nothing much
happens (compared to other gliders). I was suggesting
to Doug (and still
believe) that the lack of rudder 'response' is a function
of the
extraordinary fuselage length and that he would need
a much bigger rudder
to solve that problem.

Now - if somebody will show me how to make my Nimbus
3 do ANYTHING
responsively - I'll be eternally grateful

Roy