Benign Spirals
Martin John Gregory
vaguely remember reading something along these lines, though I can't find
the reference. The article was talking aout what your glider would do if
you let go of the controls. A `nicely` configured glider will end up in a
stable spiral dive below Vne, wheras a `nasty` one may exceed Vne.
That is as far as my recollection of that article goes - I can't remember
what the assumptions about trim and airbrake settings were. If any one
else knows more about this I'd be interested!
Martin.
Joshua Koslov
Regarding the BSM (Benign Spiral Mode):
I think this first appeared in Soaring magazine around 1980 or so, by Jim
Nash-Webber of MITSA. My recollection is that one holds full brakes/spoilers.
Don't remember the trim recommendation. Try it in the clear before using to
descend through clouds! I think Martin is correct that it is glider-dependent...
--Josh Koslov
PP-G, Ham NG2V
Charlie Stone 4915162
>In article 1mc4i...@flash.pax.tpa.com.au, mgre...@flash.pax.tpa.com.au (Martin John Gregory) writes:
>> A while back someone posted an enquiry as to what benign spirals are. I
>> vaguely remember reading something along these lines, though I can't find
>> the reference. The article was talking aout what your glider would do if
>> you let go of the controls. A `nicely` configured glider will end up in a
>> stable spiral dive below Vne, wheras a `nasty` one may exceed Vne.
My recollection of this was that you pulled out full dive brake, took your
hands and feet off the controls and waited until the desired amount of
height had been lost. When tried in a Blanik L13 it seemed to be a stable
way of descending. I can remember trying it myself a long time ago, but as
I was more interested in gaining height than losing it, I am sure that I
didn't give it much of a trial. I think that speed limiting brakes would
be a pre requisite and obviously the response would be aircraft dependent.
Charlie Stone.
Michael Peters
In article 1mc4i...@flash.pax.tpa.com.au, mgre...@flash.pax.tpa.com.au (Martin John Gregory) writes:
> A while back someone posted an enquiry as to what benign spirals are. I
> vaguely remember reading something along these lines, though I can't find
> the reference. The article was talking aout what your glider would do if
> you let go of the controls. A `nicely` configured glider will end up in a
> stable spiral dive below Vne, wheras a `nasty` one may exceed Vne.
>
> what the assumptions about trim and airbrake settings were. If any one
> else knows more about this I'd be interested!
>
> Martin.
Back when I was a student, my instuctor had me take the 2-33's trim and
put it in the full aft position (nose up pitch) and just let go of the
controls. The benign spiral got quite steep at times and he commented on
that. He suggested that it was a good way to get out of a cloud, if one
accidently got sucked up in one.
I think individual aircraft will definitely react differently, probably
even different 2-33's, so give it a try before relying on it.
--
Michael Peters
WIN Management Services
Michael...@wtcd.DaytonOH.NCR.COM
...!uunet!ncrcom!wtcp!wtcd!mpeters
Mark Milbourne
cst...@nodecg.ncc.telecomwa.oz.au (Charlie Stone 4915162) wrote:
>My recollection of this was that you pulled out full dive brake, took your
>hands and feet off the controls and waited until the desired amount of
Last summer I was up in our club's Grob 103 with a fellow club member
who has a lot of hours in both gliders and powered A/C. I recall that
he mentioned to me that it would do a benign spiral if you released
the controls and pulled full spoilers and full rearward trim.
Mark Milbourne
milb...@esvax.dnet.dupont.com
--
Paul Raveling
After doing (or trying) benign spirals in a reasonable number
of G103's I'd say most do them well, but there's a fair bit of
variation among individual specimens. My technique is generally
to trim to 45 knots, which isn't full aft trim if I'm flying solo,
then apply full dive brakes and release the controls.
Most settle into a nice benign spiral after a few phugoid
oscillations and stabilize at about 55 knots. One wouldn't spiral,
it just flew on more-or-less straight ahead; one did a spiral
that was trying to become a graveyard spiral before I stopped it.
"Your milage may vary" based on CG location, wing loading, and
a few more subtle factors.
I think the biggest factor for G103's that aren't well-behaved
in benign spirals is aft CG. If I fly one solo without ballast
I'm within 1/2 inch of the aft limit, and some particular airframes
that I've flown have behaved as if their positive pitch stability
isn't really positive, not only in a spiral but also in
straight-ahead hands-off phugoid oscillations. In most cases
though G103's do a very nice benign spiral.
------------------
Paul Raveling
Rave...@Unify.com
David C. Rolley
my reference material.
The folowing came from:
"Transition to Gliders, A Flight Training Handbook for Power Pilots"
by Thomas L. Knauff. It is quoted without permission.
"Some gliders are more stable than others. It has been
discovered that some gliders become especially stable
when their dive brakes are opened."
"With the dive brakes open and your hands off of the
controls, the glider will typically enter a slow sprial.
It may oscillate a bit, the speed may vary as well as the
bank angle, but amazingly, the speed never becomes very
high, nor does it stall; the bank angle may vary, but
never becomes very steep. The glider simply decends with
safe oscillations. This is the benign sprial. You should
become familiar with the sailplane you fly in this mode,
for it could save your life."
... (examples of when you would use the benign sprial,
such as being trapped on top, deleted) ...
"The first step is to point the glider into the wind.
This has no aerodynamic reason, but will simply allow you
to perhaps come down over familiar terrain. If you were
pointed downwind, you might exit the clouds miles
downwind of where you began."
"The second step is to open the dive brakes. This
provides the drag necessary to cause the glider to be
more stable and fly at a safe speed."
"Third, you should trim the sailplane for a slow speed -
say 45 - 50 knots."
"Fourth - and this can be the hard part - you must take
your hands and feet off of the controls. (Except to
maintain full open dive brakes.)"
"During the time you are in the clouds, there will be
false sensations that will convince you that you are
turning one way or another. It is way difficult to
overcome the desire to manually control the glider. You
must not touch the controls until you leave the cloud and
can see the ground."
"Obviously, the first time you try the benign sprial mode
should not be the occasion of your first emergency
descent. On a clear day you should take your sailplane
to a high altitude and try the benign sprial mode while
descending. After several attempts, you will gain
confidence in the maneuver in case you ever need it."
"WARNING: Not all sailplanes are stable in this mode.
Sailplanes with all-flying tails or with flaps only for
glide path control, probably will not perform a safe
benign sprial. Even different sailplanes of the same
type may react differently with different weights or
center of gravity locations."
"Try entering the benign sprial from different attitudes.
From a steep turn, pull the dive brakes on, set the trim
and let go of the controls to see what happens. I have
done this from spins and sprial dives, and other pilots
have told me that they have enter the benign sprial from
inverted flight!.... and it worked! Before tryting any new
maneuver, it would be wise to first try it with a flight
instructor in a two-place sailplane."
end of quote
Tom's comment about a sailplane with flaps only for glide
path control holds true for my Concept 70. The trim system
can NOT trim the sailplane to a speed above a stall with
full flaps and when the flaps are reduced to a setting
which allows me to trim to 50 knots, there is not enough drag
to keep the speed below the flap extension speed. So it
is not one of the tools in my bag of tricks that I save
for for a rainy day.
I have tried the benign sprial in a SGS 1-34 and
it seems to work as Tom describes, but that bird has
speed limiting dive brakes so the usefulness of the
maneuver in that case could be questioned.
Hope the above is helpful.
Dave Rolley Concept 70 "Y7"
___|___
--------------------( )--------------------
"
Nothing compares with being 100 miles out without an engine.
Unless it's making it back from 100 miles out, without an engine.