How Low to Spin??

At 14:48 01 September 2004, Chip Bearden wrote:
There's a somewhat separate question of what the right
contents for
the procedures and checklists should be!

With apologies to pilots whose memories never fail
even under stress,
I'm one of those guys who does use a very detailed
written checklist.
Chewing gum isn't on it but things like food, drinking
water, reading
glasses, and landout jacket are. But I don't wait until
I'm #1 on the
takeoff line to use it.

etcetera


It's fun to scoff about obsessive/compulsive types
reaching for their
checklist and pencil during a spin recovery. But
I'll continue to
use my written checklist before every flight, as I
noted in the safety
talk I gave at this year's U.S. Standard Class Nationals.

Chip Bearden


At the World Gliding Championships many years ago,
I crewed for a guy who presented my fellow crewman
and I with a checklist containing 19 items regarding
the setting up of the glider ready for him to fly.
After about two days of practice we added two extra
items. #0 get rid of pilot, #20 ensure pilot in glider
before launching. We got on just fine after that (and
it was always just how he wanted it).

"Ian Johnston" wrote in message news:cCUlhtvFIYkV-pn2-uRi7CmzCveOr@localhost...
On Tue, 31 Aug 2004 18:19:55 UTC, (Tom Seim)
wrote:

: 2. An immediate check of each control linkage after hookup.

Which I always get someone else to do.

I have mixed feelings about this. Nobody knows your glider as well as
you do (save, perhaps, by someone flying-or flown-the identical
model). I certainly am not going to trust my life to someone who is
unfamiliar with my glider.

Additionally, flying a motorglider, I am often times the only one at
the airport, so I have to do the complete assembly unaided.

It wouldn't hurt to have someone else review the assembled glider
after you had done all of your own checks, however.

BTW: I check my Hottellier connections by simultaneously pressing on
the release plunger and pulling on the rod. Of course, the connection
has to be safetied first. I know of accidents where the connection was
only part way on, passed a PCC, only to come off in (attempted)
flight.

Tom

Bill,

Can't say I agree, but at least from my point of view, you are erring
on the side of safety.

Here is a simple argument that I have backed up with experiment in
many types of gliders. An aircraft that is capable of spinning during
a stall while aileron and rudder are held neutral (and within
published cg limits) is inherently unsafe. This means that such a
glider flown into a strong, turbulent wind gradient 50 feet above the
ground is likely to autorotate. Since recovery from an insipient spin
requires much more altitude than a straight ahead stall, there is a
very good chance that such a glider would see very few flights before
being retired.

I have proven to myself many times that stalling a glider without
abusing the controls results not in a spin but a spiral dive. While we
can all point to experiences of having a wing drop and losing control
in a stall, I doubt very seriously that any of us were holding
coordinated controls throughout the stall break. It takes a very
determined effort not to move the stick throughout the stall and
self-recovery.

Here's another argument. The vertical stabilizer provides a great deal
of yaw stability, even at very low speeds. To start autorotation, you
need a source of drag at the tip greater than the normal differential
to be expected resulting from span effect in a turn. That we don't
kill ourselves everytime the glider approaches stall is testament to
the stability provided by the tail. That we occasionally do screw
gliders into the ground makes me think that the cause lies more in the
way we are applying the controls under stress than any inherent
tendency of the glider snap into a spin at the least external
provocation. Yes, outside factors can influence how the glider flies,
but I think they do more damage by causing pilots to react in
unacceptable ways.

Go back and read through my reports on control use during stall in my
Ventus. What it drives home in my mind is that spins are the result of
control abuse. You're right, don't stall land you won't spin. But it's
just as right to say that a stall needn't develop into a spin so long
as the controls are not abused.

I'd always assumed there were two factors in choosing a pattern speed.
First, safety, thus the +5 for turbulence. The other was to place the
glider at best speed to fly. That way if you have to put the spoilers
away, you are guaranteed to cover the maximum distance. If I recall,
the simple formula for best speed was best l/d speed plus 1/2 the
headwind. Don't recall the second ever being explained though. Just
seemed to fit.

Could be. I think the approach speed in my flight manual
is several knots below best L/D. I'll have to double-check.
Of course at my home airport (Minden), there's hardly
ever less than 15 knots of wind in the afternoon...

...egads, maybe I'm flying too slow!!!

9B

At 18:24 01 September 2004, Chris Ocallaghan wrote:
I'd always assumed there were two factors in choosing
a pattern speed.
First, safety, thus the +5 for turbulence. The other
was to place the
glider at best speed to fly. That way if you have to
put the spoilers
away, you are guaranteed to cover the maximum distance.
If I recall,
the simple formula for best speed was best l/d speed
plus 1/2 the
headwind. Don't recall the second ever being explained
though. Just
seemed to fit.

"Chris OCallaghan" wrote in message
om...
I'd always assumed there were two factors in choosing a pattern speed.
First, safety, thus the +5 for turbulence. The other was to place the
glider at best speed to fly. That way if you have to put the spoilers
away, you are guaranteed to cover the maximum distance. If I recall,
the simple formula for best speed was best l/d speed plus 1/2 the
headwind. Don't recall the second ever being explained though. Just
seemed to fit.

up to plus 15 knots is currently being taught around here

gust fronts and micro bursts make 30-50knot gusts relatively common during
summer afternoons here if there's over-development

two years ago we had a member landout in 70+mph cold front winds roaring in
from the north. in some places along the front the winds exceeded 90mph.
the pilot got about 8 miles in 7000ft to a landing about 4 miles south of
the gliderport. he stayed in the glider, flying it on the ground until
someone walked out and phoned for help.

at the time I was playing father/son softball with my boy scout troop about
30 miles southeast of the landout location. large chunks of trees started
flying by almost immediately as the winds hit

we knew the front was coming, but no clue of the strong conditions. we
usually expect some dust, but this was very different

frank whiteley
colorado

That's nonsense. Spin/autrotation is all about one wing (partially) stalled,
and the other not. It's not about drag.

--
Bert Willing

ASW20 "TW"


"Chris OCallaghan" a écrit dans le message de
m...

Here's another argument. The vertical stabilizer provides a great deal
of yaw stability, even at very low speeds. To start autorotation, you
need a source of drag at the tip greater than the normal differential
to be expected resulting from span effect in a turn. That we don't

the simple formula for best speed was best l/d speed plus 1/2 the
headwind. Don't recall the second ever being explained though. Just
seemed to fit.

Not a formula but a rule of thumb that's pretty close - judging by a
number of polars I've looked at. The following article is very
simplistic but was written for a student who had trouble grasping the
concept of needing to stay upwind of the field in strong conditions:
http://home.comcast.net/~verhulst/GB.../headwind.html

Tony

Uh, Bert, what happens when a wing stalls? Lift decreases... drag
increases. Something needs to start the spin. Could that be... a
force? I suppose we could call it something other than drag. Gremlins
maybe?

Let's see, perhaps I can offer another explanation. Non-symmetrical,
differential lift across the wingspan produces roll. Non-symmetrical,
differential drag along the wingspan produces yaw (adverse yaw when
actuating the ailerons, for example). The vertical stablizer and
rudder are there to provide stability and yaw authority to counteract
the aileron drag effect (as well as the destabilizing effect of the
fuselage forward of the cg). If the stall (or partial stall) produced
no drag, the glider would simply roll. There would be no yawing
motion. And thus, no spin! (But lots of rolling.) Here's another way
to think about it... if you had an infinitely large vertical
stabilizer (that is, infinite directional stability), would it be
possible to spin? Since the infinitely large tail would produce an
infinitely large counterforce to any adverse yaw, then a spin is not
possible. What's the practical substitute for an infinitely (or very)
large vertical stabilizer? A moveable rudder.

It's all about the flippers, man.

And from a practical standpoint, spins are all about the drag. And
even though a partially stalled wing will display adverse yaw with
neutral control surfaces, so long as you don't move the flippers, the
vertical stabilizer will keep you from spinning. As noted before, I
prove this to myself with every modern model of glider I fly. But if
you move those flippers in an uncoordinated fashion, baby, all bets
are off!

Piggott: "Drag from the badly stalled, falling wing, pulls the glider
down into a steep spiral and the autorotation is speeded up."

There's a graceful way out of your dilemma... we could discuss the
torques brought into play by the rolling motion of a partially stalled
wing. That will introduce a rotation about the yaw axis (the
aerodynamicist's definition of autorotation), but you'll need to prove
to me that it alone is sufficient to overpower the vertical
stabilizer, even at very low airspeeds and relatively high rates of
roll. Since the vast majority of modern aircraft need an additional
yawing moment to enter a spin (pro rudder, counter aileron), it's
going to be a tough sell. But I'd be interested to see you work
through the problem.

Maybe we'll both learn something new.



"Bert Willing" wrote in message ...
That's nonsense. Spin/autrotation is all about one wing (partially) stalled,
and the other not. It's not about drag.

--
Bert Willing

ASW20 "TW"


"Chris OCallaghan" a écrit dans le message de
m...

Here's another argument. The vertical stabilizer provides a great deal
of yaw stability, even at very low speeds. To start autorotation, you
need a source of drag at the tip greater than the normal differential
to be expected resulting from span effect in a turn. That we don't

BTW,

I thought I'd add that "autorotation" is why highly controllable, low
stability aircraft can be spun with ailerons held into the direction
of spin. If you can roll fast enough with stick well back, the
resulting torque about the yaw access is sufficient to overpower a too
small vertical stabilizer (in designs where stability is sacrificed
for greater controlability). But this does not describe a modern,
certified glider. And, after all, we're looking for practical
knowledge we can take into the air. But I remain interested in whether
you can demonstrate that rolling torque alone will make the glider
spin. If it can't, then we can focus on other sources of adverse yaw
that contribute to the autorotation. If it can, then we'd all best be
looking for a new, safer passtime, like freeclimbing solo.

But hey! I'm making your argument for you.

Bert, this could really be fun. Fire away, please!