Hands off thermalling

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...

They have a lot more dihedral or polyhedral to help them return to level
flight.

Interestingly, a well trimmed hand launch free flight glider will climb almost
straight up, "flop" into a glide without stalling, and then start turning in a
stable, constant circle. Great fun!

Jim Vincent
CFIG
N483SZ
illspam

At 12:18 24 April 2004, Andreas Maurer wrote:
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


My hand-launced gliders are built with crossed controls,
which produces this effect. A slight amount of rudder
into the turn keeps it going. A slight amount of opposite
aileron keeps it from overbanking. A slight amount
of up elevator lifts the nose. Just enough weight on
the nose keeps it from making phugoids. Just enough
dihedral helps it right itself. It is not the most
effective climbing setup possible, but it produces
stability much like a sailboat with the tiller down,
the main sheet slack, and the jib tied across to the
opposite side.

It requires experimentation to get it right and they
have to be built for a left-handed or right-handed
person. It must turn to the left for a right-hander
and vice versa.

"Bill Daniels" wrote in message news:eOeic.21511$GR.2890579@attbi_s01...
The aerodynamics of this are interesting.


I was taught (and that was long enough ago for it to have passed from
fashion, apparently) that shallow, medium, and steeply banked turns
were defined by the control inputs required to maintain them, to which
the actual angles of bank are merely incidental. Shallow turns
require pro-turn aileron to maintain the angle of bank. Steep turns
require anti-turn aileron to preclude over-banking. As in level
flight, medium turns balance the converging lift vectors of wing
dihedral and require no control displacement whatever to maintain
angle of bank. This isn't to say that medium turns are stable, only
that at some particular angle of bank all lateral forces produced by a
wing with dihedral will balance about the c.g..

From an instructional standpoint, it's easy to demonstrate and serves
as a graphic intro to the subjects of stability and control. One
caution: Dont add this to the student's plate before he's in the
habit of (I mean "really learned") to manuever by applying whatever
force, rate and displacement of controls may be necessary to achieve
the desired result. This is one of those things that can get a
student to thinking too much and (except possibly for spin recoverier)
I've never seen anybody's flying improved by watching their hands and
feet while maneuvering.

Cheers,
Eric

On Sat, 24 Apr 2004 14:04:11 +0200, Andreas Maurer
wrote:

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...

Free Flight gliders - at least in the F1A class, which I fly - are not
aerodynamically symmetrical: There is always more wash in on the inner
wing in the turn and the rudder is set into the turn, giving a
crossed-controls effect. Without the differential wash-in most designs
will have nasty spiralling tendencies.

The flight regime is somewhat different, too. The model is trimmed at
min. sink (about 8-10 kts) and is flying in a still air circle that
requires 40 - 60 seconds to complete. That's a 30 - 40 m diameter
circle being made by a 2.5 m span model, which is a relatively much
larger circle than we tend to use in our sailplanes and yet is small
enough to fit easily inside a thermal column.


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

Also, adding stab tilt helps the free flight glider turn towards the high side.

All these are tweaked in until the glider performs as desired. I also fly
Jet-X gliders, little free flight gliders with a small rocket engine attached
that burn for about 10 seconds. If done right, a thing of beauty. If not, they
loop like mad or auger in dramatically. Always fun.

My hand-launced gliders are built with crossed controls,
which produces this effect. A slight amount of rudder
into the turn keeps it going. A slight amount of opposite
aileron keeps it from overbanking. A slight amount
of up elevator lifts the nose. Just enough weight on
the nose keeps it from making phugoids. Just enough
dihedral helps it right itself.



Jim Vincent
CFIG
N483SZ
illspam