"Hands off" decent from altitude with spoilers?

[MHende6388]

I was taught during wave training that all sailplanes, properly trimmed, when
you let go of the controls, will seek a gentle banked circle to one direction
and maintain that attitude, even in light turbulence.

There must be great variation from one a/c to the next with varied CG and trim
settings.

What experiences have others had and with which makes and models?

Thanks,

Michael

[Kevin Anderson]

Michael,

You were taught WRONG. Not all gliders will do a benign spiral. Some
models will not do this at all and will gather speed and get you into
trouble.

The benign spiral is performed by trimming for best L/D, pulling full
spoilers and taking hands and feet off of the controls while holding the
spoilers on.

The Schweizer 1-26, and the Blanik L-23 are a couple of models that will in
general perform a benign spiral well.

This is NOT a maneuver that you want to test when you suddenly get trapped
in cloud at wave camp. This is something that you want to practice in the
blue with the ship that you fly. Different models of the same ship will
behave differently. Our club 1-26 performed about a 20 - 30 degree bank and
would settle on a airspeed of 60 after a couple of oscillations. My present
bird will only very slightly bank, but settles on the same airspeed.

Harry Senn saved my bacon by teaching me about the benign spiral when I was
flying our club 1-26 at my first competition. I went on to purchase my
first bird a 1-26B from him and have taken it to wave camp 3 years. Last
year I put myself into a stupid position running about 9 miles up the face
of long wave cloud at Petersburg WV. I slowly gained altitude and found
myself on top. I was constantly watching the blue hole, but you would be
amazed at how quick they close. I dove to get through the hole as it was
closing just in time to go into the cloud. I had practiced the manuver in
the blue and was comfortable with it. The only thing that bothered me was
just how thick the cloud ended up being. I was quite fortunate in two ways.
One because Harry had taught me about the benign spiral, and two because the
cloud did not go all the way to the ground.

Practice this manuver in the ships you fly. It is very useful if it works
in the ship that you are flying, and is even more useful if you get stupid
like I did one day and put yourself into the position where you have to use
it.

Kevin



MHende6388 > wrote in message
...
> I was taught during wave training that all sailplanes, properly trimmed,
when
> you let go of the controls, will seek a gentle banked circle to one
direction
> and maintain that attitude, even in light turbulence.
>
> There must be great variation from one a/c to the next with varied CG and
trim
> settings.
>
> What experiences have others had and with which makes and models?
>
> Thanks,
>
> Michael

[Pete Brown]

Michael:

What you are talking about is generally referred to as
benign spiral descent mode. It may allow you to get down
through the clouds if you are trapped above them in wave.

Here's what you do.

1. Point glider into wind
2. Open dive brakes
3. Trim for slow flight
4. Hands and feet OFF controls and stay OFF until VFR.

This procedure is not be suitable for stabilator aircraft or
aircraft with flaps only for glide slope control. I also
wouldn't try it unless you know you are within the CG envelope.

We did this in a number of aircraft, including a Blanik L-13
and found that the nose would bob a bit and the aircraft
would eventually enter a spiral but the airspeed would
remain in a safe range and the turn would not tighten beyond
a certain degree of bank. It would oscillate in pitch and
roll but ours would stay well within safe limits.

However, yours may act differently. Before you have to use
this in a an emergency mode, try it in your own aircraft in
good weather with lots of altitude to see what your glider
does. It should not exceed 30 deg. in pitch or 60 deg in
roll. Try it first from level flight and then from steeper
turns and see what happens.

It may be a lifesaver sometime and its fun to try in good
weather.

Pete




MHende6388 wrote:

> I was taught during wave training that all sailplanes, properly trimmed, when
> you let go of the controls, will seek a gentle banked circle to one direction
> and maintain that attitude, even in light turbulence.
>
> There must be great variation from one a/c to the next with varied CG and trim
> settings.
>
> What experiences have others had and with which makes and models?
>
> Thanks,
>
> Michael

--

Peter D. Brown
http://home.gci.net/~pdb/
http://groups.yahoo.com/group/akmtnsoaring/

[Bill Daniels]

I have also tried this with several gliders. The IS28B2 Lark was the most
interesting. As long as the CG was near the middle of the allowable range,
it would circle first to the right reaching about a 45 degree bank in
several turns and then reversing the turn direction and going to 45 degrees
the other way for a while before reversing direction yet again. This
circling to the right and then to the left would continue until the pilot
took control.

I have no idea why it would do that but it was interesting to watch.

Bill Daniels

"Pete Brown" > wrote in message
...
> Michael:
>
> What you are talking about is generally referred to as
> benign spiral descent mode. It may allow you to get down
> through the clouds if you are trapped above them in wave.
>
> Here's what you do.
>
> 1. Point glider into wind
> 2. Open dive brakes
> 3. Trim for slow flight
> 4. Hands and feet OFF controls and stay OFF until VFR.
>
> This procedure is not be suitable for stabilator aircraft or
> aircraft with flaps only for glide slope control. I also
> wouldn't try it unless you know you are within the CG envelope.
>
> We did this in a number of aircraft, including a Blanik L-13
> and found that the nose would bob a bit and the aircraft
> would eventually enter a spiral but the airspeed would
> remain in a safe range and the turn would not tighten beyond
> a certain degree of bank. It would oscillate in pitch and
> roll but ours would stay well within safe limits.
>
> However, yours may act differently. Before you have to use
> this in a an emergency mode, try it in your own aircraft in
> good weather with lots of altitude to see what your glider
> does. It should not exceed 30 deg. in pitch or 60 deg in
> roll. Try it first from level flight and then from steeper
> turns and see what happens.
>
> It may be a lifesaver sometime and its fun to try in good
> weather.
>
> Pete
>
>
>
>
> MHende6388 wrote:
>
> > I was taught during wave training that all sailplanes, properly trimmed,
when
> > you let go of the controls, will seek a gentle banked circle to one
direction
> > and maintain that attitude, even in light turbulence.
> >
> > There must be great variation from one a/c to the next with varied CG
and trim
> > settings.
> >
> > What experiences have others had and with which makes and models?
> >
> > Thanks,
> >
> > Michael
>
> --
>
> Peter D. Brown
> http://home.gci.net/~pdb/
> http://groups.yahoo.com/group/akmtnsoaring/
>
>
>

[Bruce Hoult]

In article >,
(MHende6388) wrote:

> I was taught during wave training that all sailplanes, properly trimmed, when
> you let go of the controls, will seek a gentle banked circle to one direction
> and maintain that attitude, even in light turbulence.
>
> There must be great variation from one a/c to the next with varied CG and trim
> settings.

Pretty much *any* aircraft should do this, not only gliders. The only
requirements are that a) the airframe not be *too* out of whack, and b)
there being sufficient drag available to allow a reasonable nose-down
attitude without a large speed increase.

The key is that the hands-off roll rate is probably non-zero, and that
would eventually turn you upside down. A significant nose-down attitude
allows roll rate to be coupled into turn rate and the whole thing
stabilizes when the degrees per second of turn matches the degrees per
second of roll.

So trim for a slowish speed (trim right back unless that is going to
stall you) and put out all the drag you can manage: spoilers, wheel,
flaps.

Preferably try it in the aircraft you fly before you actually need it.

-- Bruce

[Robert Ehrlich]

Bruce Hoult wrote:
>
> In article >,
> (MHende6388) wrote:
>
> > I was taught during wave training that all sailplanes, properly trimmed, when
> > you let go of the controls, will seek a gentle banked circle to one direction
> > and maintain that attitude, even in light turbulence.
> >
> > There must be great variation from one a/c to the next with varied CG and trim
> > settings.
>
> Pretty much *any* aircraft should do this, not only gliders. The only
> requirements are that a) the airframe not be *too* out of whack, and b)
> there being sufficient drag available to allow a reasonable nose-down
> attitude without a large speed increase.
>
> The key is that the hands-off roll rate is probably non-zero, and that
> would eventually turn you upside down. A significant nose-down attitude
> allows roll rate to be coupled into turn rate and the whole thing
> stabilizes when the degrees per second of turn matches the degrees per
> second of roll.
>
> So trim for a slowish speed (trim right back unless that is going to
> stall you) and put out all the drag you can manage: spoilers, wheel,
> flaps.
>
> Preferably try it in the aircraft you fly before you actually need it.
>
> -- Bruce

Beside providing drag, spoilers or airbrakes, as opposite to some others drag
sources like the wheel, as they are far from the longitudinal axis, provide
a mean of countering and damping yaw movements, as soon as there is some yaw,
the difference of drag on both sides tend to cancel it. With some dihedral,
which converts slip into roll, this will cancel the spiral instability that
most gliders exhibit in sleek configuration. The best ones for this should
be gliders with air brakes extending far from fuselage and appreciable dihedral.
The LS4 comes in my mind as such an example.

BTW I wonder why the standard procedure, as it was also taught to me, is to
let go the controls rather than block them in the approriate position, i.e
neutral for ailerons and rudder, trimmed position for elevator. This should
provide a better damping of oscillations than free controls. Maybe the idea
is that it would be to difficult to resist to do some blind corrections, which
would probably be in the wrong direction. Any opinion on the subject?

[henell]

GDay,
Have been in that position in an L13 (Blanik) in lee wave, climbed to
top of the roll cloud 10000 amsl, foehn gap about 150 metres wide. Wind
stopped. Foehn gap closed. Cloud base 2000 agl. Had sighted ground and
knew position relative to known hills. Extended brakes fully, trimmed
for 30 deg down and popped out the bottom with no fuss.
Very forgiving aeroplane the Blanik. Can verify previous reference to
speed of closure of gap.
Cheers
Henell


--
henell
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