Glider Tail Stall

To add to the confusion:

Many modern gliders are elevator limited - full aft stick just won't
result in enough AOA to stall the wing. Nothing to do with the tail
being stalled. In fact, it's "lifting" just fine, just in the "down"
direction (which could be up if you are at the top of a loop). If the
tail did actually stall, you would get a brisk nose down pitch rate, I
would think! It would be almost the same as the horizontal tail
falling off. Think about it....

Also, the tail on modern gliders do not always push "down". Depends
on speed, AOA, G-load, CG location, flap position, etc. You have to
look at the entire lifting contributions of all the parts of the
glider. Stability is due more to decalage. Look it up.

It's amazing how little most pilots know about how their aircraft
really work....including yours truly!

Kirk
66

Just remembered that there is a good discussion about glider-induced
towplane tailstalls - both horizontal and vertical - in the BGA
towplane manual. The rudder one kinda sounds like fun, actually, as
long as I had a parachute and lots of altitude!

Sorry, no link, I'll try to find it and post later.

kirk
66

On Feb 20, 10:15*am, jcarlyle wrote:
Bumper, Toad - thanks. Sorry for my confusion about pitch direction -
you're right, it would pitch down. The recovery with a tail stall,
though, is to pull back on the stick, not push forward. That's why I'm
worried about differentiating a tail stall from a wing stall.

Bill, please see comments embedded in your reply.

I think the others made the essential point that the video subject was
a special situation where ice on the tail leading edge led to a
separation bubble on the lower surface with flow re-attaching aft of
the hinge line. The re-attached flow was sucking the elevator down
(nose down) so the pilots were advised to pull back to counter this
force to retain control of their aircraft.

The violent pitch down was due to this effect. The video also talked
about non-linear elevator effects which could lead to PIO's

As for the tail/wing stall discussion, unless you've flown a glider
with yarn tufts on the wing and tail, this is hard to visualize.

Yes, of course, the wing is designed to stall at the root first. In
fact, unless there is a very effective root fillet, there will be some
root flow separation visible at any AOA.

In every case I know of, the yarn tufts show full flow separation on
both upper and lower surfaces of the tail when as nose 'breaks'
suggesting a wing 'stall' to the pilot. At the same time the wing
tufts show attached flow over the majority of the wing which is why
the ailerons work as expected. You can say the tail just loses
effectiveness or you can call it a tail stall - the distinction isn't
really important.