http://www.jaa.nl/section1/jars/445499.pdf

JAR 22.73 Descent, high speed
It must be shown that the sailplane with the
airbrakes extended, will not exceed VNE in a
dive at an angle to the horizon of:
(a) 45° when the sailplane is approved for
cloud flying and/or aerobatics when certificated
in the Aerobatic or Utility Category;
(b) [in other cases
(i) 30°
(ii) less than 30° when a rate of
descent of more than 30 m/s can be achieved].

Don't know how many sailplanes may be built to para b. Guess I assumed all
JAR22 aircraft were designed to para a standards.

I believe this resulted from the supposedly demonstrated difficulty in
maintaining a vertical descent, even in cloud, as a result of some empirical
testing about 40 years ago. At least that's what I recall from
conversations in the '70s.

If you want vertical limiting airbrakes, I know where you can buy a
Schweizer 1-34;^)

Frank Whiteley

"Arnold Pieper" wrote in message
om...
The glider won't stay at 90 degrees nose down like I said. As it
accelerate
it will bring the nose up.
That in itself is no guarantee you won't reach VNE before long, of course,
so you have to control the recovery.
Avoid reaching VNE by deploying the airbrakes if you see the speed
increasing too fast, as I said, controlling the dive.
That is always better than trying to bend the wings by pulling too many
Gs.
Your attitude will be at 45 degrees or less in a matter of seconds, and at
that attitude, the airbrakes will prevent the overspeed or at least
minimize
the condition (if they were deployed too late).

You can go over VNE if you don't deploy the airbrakes and just try to
"G-load" your way out of such a high-speed dive,and that's the condition
in
which you overstress the structure, produce internal cracks, bend or
damage
some of the hardware in the control system.
That's the reason you should watch the airspeed and deploy the airbrakes
in
time (before reaching VNE).

Don't be affraid to open the airbrakes at high speed, believe me, the
manufacturer is just a little smarter than that.
You have to be careful at high speed just because they tend to jump out
more
easily, so, have a firm hand on it.

Real aerobatic training (as opposed to some occasional loops) will clarify
a
lot of this.


"Todd Pattist" wrote in message
...
"Arnold Pieper" wrote:

Maybe true if "near vertical", however, staying at a near vertical dive
is
something that requires a conscient effort.
The glider won't just stay there on its own.
To remain in a 90 degree vertical dive requires a significant amount of
forward stick force and concentration.
As speed increases, the nose will come up (away from vertical) even if
you
don't want it to, and even with full forward trim, it would still
require
an
honest push on the stick to maintain that attitude.

All of this is true, but it's not relevant to whether the
airbrakes of a modern glider are speed limiting. They
aren't. There are lots of initial conditions that will
exceed Vne with the brakes out.

If you're recovering from an unusual attitude that puts you in a near
vertical dive, just don't sweat it.
Open the airbrakes and slowly pull out of the dive. There is no need to
overstress.

There is also no guarantee that you will not exceed Vne or
that your final speed will be lower than someone who applies
a higher AOA with it's higher G-load and reduces the descent
angle more quickly.

If you want to feel safer, go for aerobatic training.
You will see that you can actually dive 90 degrees down and recover
without
exceeding VNE, without using the airbrakes and not getting even close
to
G
limits.

I do loops often. Slow and vertical is far different from
fast and vertical.


Todd Pattist - "WH" Ventus C
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