Rudder Cable Systems Used in Modern Sailplanes

On 15/05/2012 23:41, Dan wrote:
On May 15, 6:33 am, wrote:
What would be the consequence of removing the springs from the rudder pedals?

I used to fly competition aerobatics in a Pitts S-1S I built. I
became worried about rudder return springs in that airplane for the
same reasons. Eventually I removed the springs and I actually liked
the feel of the rudder much better.

Dan
ASW 20
WO

Might be fine in your Pitts but my memory is that the ASW20 manual made
a special point about NOT using lower strength rudder springs. I also
remember them as the strongest I've come across in the dozen or so
gliders I've worked on.

GC

On May 15, 10:05*am, GC wrote:
On 15/05/2012 23:41, Dan wrote:

On May 15, 6:33 am, wrote:
What would be the consequence of removing the springs from the rudder pedals?

I used to fly competition aerobatics in a Pitts S-1S I built. *I
became worried about rudder return springs in that airplane for the
same reasons. *Eventually I removed the springs and I actually liked
the feel of the rudder much better.

Dan
ASW 20
WO

Might be fine in your Pitts but my memory is that the ASW20 manual made
a special point about NOT using lower strength rudder springs. *I also
remember them as the strongest I've come across in the dozen or so
gliders I've worked on.

GC

Spring strength may be a requirement to control/dampen flutter...
Control dynamics are not something to play with lighly!

Cheers,


Derek

At 18:05 15 May 2012, Derek Mackie wrote:
On May 15, 10:05=A0am, GC wrote:
On 15/05/2012 23:41, Dan wrote:

On May 15, 6:33 am, wrote:
What would be the consequence of removing the springs from the
rudder
=
pedals?

I used to fly competition aerobatics in a Pitts S-1S I built. =A0I
became worried about rudder return springs in that airplane for the
same reasons. =A0Eventually I removed the springs and I actually
liked
the feel of the rudder much better.

Dan
ASW 20
WO

Might be fine in your Pitts but my memory is that the ASW20 manual made
a special point about NOT using lower strength rudder springs. =A0I
also
remember them as the strongest I've come across in the dozen or so
gliders I've worked on.

GC

Spring strength may be a requirement to control/dampen flutter...
Control dynamics are not something to play with lighly!

Cheers,


Derek

Ah! you have illuminated a point about rudder flutter.
In 1972 the bank bought me a kestrel 19 for an important comp.
I discovered in the precontest flying that it was prone to rudder flutter
well below rough air speed, quickly damped by pushing on both pedals, but
it gave one pause when aiming for the start line.
3 years later I acquired same kestrel in pieces after a syndicate had bent
it. On inspecting the fuselage layup, I found that this
was orthogonal to, not 45 deg to the Cl. Hence the rudder flutter
, fuselage lacked torsional rigidity. The repair was acording to factory
specs, but I did add mass balance to the rudder at the TOP.
Test flights showed the flutter speed had moved up above the
roughair speed; much better.
Now I understand why cables in PE tubing are much safer.
JMF

This may be faulty memory, but I seem to recall that the Open
Cirrus used a pushrod rudder drive with cable drive from pedals
to just behind the seat; early ones suffered from rudder flutter
and a hydraulic damper was fitted to the system. Subsequent
Schemmp-Hirth designs ran the rudder cables all the way to the
rear fuselage, and the guide tubes were slightly waved to
increase friction for rudder damping.

Ah! you have illuminated a point about rudder flutter.
In 1972 the bank bought me a kestrel 19 for an important
comp.
I discovered in the precontest flying that it was prone to rudder
flutte
well below rough air speed, quickly damped by pushing on
both pedals, bu
it gave one pause when aiming for the start line.
3 years later I acquired same kestrel in pieces after a
syndicate had ben
it. On inspecting the fuselage layup, I found that this
was orthogonal to, not 45 deg to the Cl. Hence the rudder
flutter
, fuselage lacked torsional rigidity. The repair was acording to
factor
specs, but I did add mass balance to the rudder at the TOP.
Test flights showed the flutter speed had moved up above the
roughair speed; much better.
Now I understand why cables in PE tubing are much safer.
JM

On May 15, 3:10*pm, John Firth wrote:
On inspecting the fuselage layup, I found that this was orthogonal to, not 45 deg to the Cl...

Interesting! Do you mean that there were no +/-45 plies, or just that
they weren't all +/-45?

Thanks, Bob K.