bildan wrote:
On Sep 11, 12:01 am, Bruce wrote:
vaughn wrote:
"Mike the Strike" wrote in message
...
I do know of one where the spoiler handle on a Grob 103
broke after they had been deployed and jammed full open, resulting in
an off-field landing.
And I know of a case where just one spoiler deployed on a glider. Causes a
nasty uncommanded roll. The only solution (once you figure out what is
going on) is to close the spoilers and proceed without them.
Vaughn
Single spoiler deployment has caused at least one fatal accident.

If a linkage fails resulting in asymmetric airbrake deployment it is
possible to run out of options very quickly.

My thoughts are that you need to open the brakes to balance the drag and
lift asymmetry. Then you can fly the aircraft through the resulting
descending roll and recover. Depending on your height and speed it may
be quite pressing to land, it may also be quite pressing to reduce speed...
However - if this happens in a high energy state (where else?) you may
already have a lot of yaw and roll inertia by the time you get the other
airbrake open. Especially on a long winged open class ship there may
just not be enough control authority left, and if you are very fast
and/or very close to the ground the options are limited.

To overcome the differential lift caused by the yaw you may need full
rudder.
To limit the speed and avoid terrain you may need large elevator deflection.
To reverse the roll and return to level flight you almost certainly will
need full aileron.

You are unlikely to find such a high G, rolling pull up close to , or
over Vne with airbrakes deployed in the manual.

There is a reason for that "max manoeuvre speed" entry...

A little math says that at 250km/h and 300m (~1000")AGL a 30 degree
descent angle will give you less than 8 seconds to avoid terrain.

40 years ago I was involved in building and testing a glider with
spoilers for roll control instead of ailerons. Preliminary flight
tests were done on normal gliders rigged to permit one spoiler to be
deployed at a time.

The first thing we learned is that spoilers don't do what they are
generally thought to do.

The results of asymmetrical spoiler deployment vary dramatically with
airspeed since drag increases with the square of airspeed but lift
which is 'spoiled' pretty much remains constant with airspeed. (Any
lift reduction is transient since the glider quickly re-establishes
equilibrium at one G flight where lift =weight.)

The bottom line was that below some airspeed like 50kts, weak roll
(~10% of aileron authority) was the dominate result and above that
powerful yaw was the dominate result. We found it best to regard
differential spoilers as yaw control devices. Thus the concept of
roll spoilers was a failure.

In one iteration, spoilers were rigged to the pedals with the normal
rudder fixed in neutral. With yaw spoilers, ailerons and elevator, we
had a remarkably agile glider - albeit not a particularly efficient
one.

So, the accidental deployment of one spoiler will result in powerful
yaw not roll which leads me to the subject of using one in a slip.

Al relatively low speed I would expect this to be reasonably controllable.

It would be interesting to test this at high speed - the yaw will be
severe at full open, the secondary effect of that yaw will be a roll in
the direction of the open spoiler. The uncoordinated flight is going to
increase drag significantly, and the glider will start to descend.
In the case of an open class/long winged glider the roll may exceed
aileron authority if this happens at high speed.
Even with 15m wingspan you are going to need significant control input
on the ailerons.

a glider one quickly finds the limit is available rudder
authority. With full rudder one can use only about 15 degrees of bank
while maintain a straight track. However, with one spoiler deployed,
the pilot has far more 'rudder' authority in the direction of the open
spoiler and a far steeper bank can be used. This results in an
incredibly steep approach.

This situation is 'dangerous' only to the extent the pilot doesn't
understand how to control his partially disabled aircraft.

Full control input on an already stressed airframe at speeds above max
manoeuvring speed is not advisable - but may be the only option available.

The only incident I know of the glider ended up in tiny pieces of carbon.