Hands off thermalling

On 22 Apr 2004 11:16:50 -0700, (Andy Durbin)
wrote:

John Jones wrote in message ...
How many gliders can be trimmed for hands off thermalling?

An instructor showed me, with spoilers open and proper
trim, the glider will stabilize in a slow descending
turn. Claimed it was good for getting out of a cloud.

Neat, but would not want to thermal with the spoilers
open.

My ASW 19b and ASW 28 will thermal hands off for several turns. Only
works for smooth thermals not the more typical rowdy tight cores of a
strong Arizona day.

The full airbrake, hands and feet off controls, descent is known as
the benign spiral. Does not work in all gliders so try it before you
use it in a real descent emergency.

Indeed. I found out that the ASW-20 has a 20 second phugoid when
trimmed at 50 kts, clean at zero flap. I didn't notice the height
variation, but the speed excursion is +/- 5 kts and its stable - once
the phugoid is established in smooth air it doesn't increase or damp
out over about 10 cycles. I haven't tried other trim speeds and was
using my feet gently to stay straight, so I don't know if a spiral
would have developed or what happens at other trim settings

I must try the benign spiral next time I'm out with height to spare.
What sort of speed is recommended?

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

Jim Vincent wrote:

You're talking about two totally different things here. One is thermalling,
the other is the benign spiral mode (what your instuctor did with you....good
instructor!).

The way I teach the benign spiral is trim for 60 kts and don't touch the stick.
The plane will speed up and slow down and turn, but should always stay within
limits. As you said, it is useful if caught in cloud. Spoilers deployed is a
new one to me.

My experience, and that of many others, is the having spoilers deployed
is crucial to the benign spiral mode. Some gliders can't manage it, even
with the spoilers open. What glider are you teaching this in?

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

My experience, and that of many others, is the having spoilers deployed
is crucial to the benign spiral mode

You're correct, Eric. The maneuver should be taught in both configs to
determine the characteristics.

Jim Vincent
CFIG
N483SZ
illspam

"John Jones" wrote in message
...
How many gliders can be trimmed for hands off thermalling?

An instructor showed me, with spoilers open and proper
trim, the glider will stabilize in a slow descending
turn. Claimed it was good for getting out of a cloud.

Neat, but would not want to thermal with the spoilers
open.


Open Cirrus, no problemo

(Doug Taylor) wrote in message . com...
During Gary Osoba's first flight in the SparrowHawk, he flew for 10
minutes hands off, including entering and centering two thermals.

Also in the SparrowHawk, I find it easiest to use the pee-bag while in
a thermal, as long as it is a nice big smooth one.

Yeah. Those small, textured bags can be a real distraction ;-).

Mike

illspam (Jim Vincent) wrote in message ...
My experience, and that of many others, is the having spoilers deployed
is crucial to the benign spiral mode

You're correct, Eric. The maneuver should be taught in both configs to
determine the characteristics.

Jim Vincent
CFIG
N483SZ
illspam

The whole point of the benign spiral is to make an emergency descent
in non visual conditions. Emphasis on descent. Full airbrakes, gear
down, hands AND feet off controls. I can see absolutely no point in
doing this with airbrakes closed.


Andy

John Jones wrote in message ...
How many gliders can be trimmed for hands off thermalling?



LS4
-Dan

The aerodynamics of this are interesting.

The most likely reason that a glider exhibits the spiral stability to fly
thermals hands-off is that once it is set up to fly coordinated circles and
the controls released, the controls have just enough friction to keep the
aileron and rudder controls where they were - just a bit of outside aileron
and rudder. If you lube the controls, you may lose the hands-off
thermalling capability.

The other possibility is that the inner and outer wings are flying on
opposite sides of the polar curve with the outer wing on the high speed
side of the polar and the inner wing on the slower side. Discontinuities in
the polar due to separation bubbles may play a part too.

A perfectly symmetrical glider with a perfectly smooth polar and
frictionless controls SHOULD develop a spiral dive from a hands off turn.

Bill Daniels


"Buck Wild" wrote in message
om...
John Jones wrote in message
...
How many gliders can be trimmed for hands off thermalling?



LS4
-Dan

mike fadden wrote:
(Doug Taylor) wrote in message . com...
Also in the SparrowHawk, I find it easiest to use the pee-bag while in
a thermal, as long as it is a nice big smooth one.

Yeah. Those small, textured bags can be a real distraction ;-).
ROFLMAO. I KNEW someone was gonna catch that one...
--

------------+
Mark Boyd
Avenal, California, USA

On Fri, 23 Apr 2004 20:14:02 GMT, "Bill Daniels"
wrote:


A perfectly symmetrical glider with a perfectly smooth polar and
frictionless controls SHOULD develop a spiral dive from a hands off turn.

How does this explain the behaviour of non-radio-controlled model
gloiders that return to level flight anytime? They are built perfectly
symmetrical, have a smooth polar and no controls at all...


Bye
Andreas