Tim Taylor wrote:

So here is the issue. You are high on final and full spoilers aren't
enough; what do you do?

List of options so far:

1. Slip
2. "S" turns
3. Dive until intercepting normal angle for spoilers
4. Dive until near the ground, then decelerate
5. Slow down until intercepting normal angle for spoilers
6. 360 degree turn

Unfortunately I still don't have good data for what happens to the
polar as speed increases with the spoilers open. Condor was a good
suggestion, and I am working to see if I can get meaningful data from
it.

John Cochrane brought the discussion back to the real point which is
what would you use in the real world? It is interesting but not that
useful to discuss how you do this at your home airport with 2500 to
9000 feet of runway and know precisely the field elevation. When your
aircraft and your own safety are on the line in a real off-field, what
are you going to do?
Is there really a need
to be on the ground 10 seconds faster than using some of the other
techniques? Maybe only if a severe thunderstorm is approaching and
you must be on the ground now.

Fast approaching weather is a good reason for an "expedited landing",
and besides thunderstorms, there gust fronts, snow, rain, and blowing
dust. And also other reasons: there are a dozen gliders approaching at
high speed to finish a contest task; you want to land before sunset and
are still high; you want to land before the tow plane so you don't
interfere with the next tow (or have the next tow interfere with your
landing); airplanes are holding their takeoff until you land; to fit in
between the four airplanes circulating in the pattern doing incessant
touch and go's; getting out of the way before the skydivers exit the
jump plane. I've done it for all those reasons.

Regardless of the need to get down quickly, Option 3, as I use it, is
something I do on final after a normal pattern entry. It's not a "get
down quicker" technique.

snip

It is true that sink rate goes up with speed, but the
actual decent angle does not go up nearly as much. For my Ventus B at
45 knots descent rate is 122 ft/min while at 135 knots it is 894 ft/
min, but actual loss per nautical mile is 163 ft/ktm verses 397 ft/
ktm.

This is not a good comparison, because these numbers are for a "clean"
glider, where the major drag at 45 knots is *induced* drag (which
reduces as speed increases), at 135 knots the major drag is *parasitic*,
and you've gone to negative flaps to reduce drag!

With the gear and spoilers out, landing flap selected, the drag will
increase more rapidly with speed than for your example, as the drag is
significantly parasitic to begin with.

The other thing we don't mention is the average pilot going to
handle the decision making process better at higher speeds and less
time? At stable speeds it takes about 11 seconds to lose 300 feet at
135 knots with the spoilers out verses 22 seconds at 45 knots.

These numbers way off: the Ventus (spoilers out) has a 800 fpm sink rate
at 45 knots (seems too high), and it is only 1600 fpm at 135 knots
(seems too low)? Three times the speed and only double the descent rate?
Even clean, the descent rate increased a factor of 7.


Ok, lets try a hypothetical (well maybe not, been there done that ;-)
off-field landing.

snip


Slip?

Yes, when I had the Std Cirrus (I practiced slips a lot, because it has
poor spoilers); no, with the ASW 20 C (slips work fine, however); maybe,
in my ASH 26 E (I don't practice them much).

"S" turns?

Never, at that altitude.

Dive until intercepting normal angle for spoilers?

Yes, in Ka-6E (got to love those divebrakes!); Yes, in the ASW 20 C (got
to love those 40 deg landing flaps!); yes, in the ASH 26 E.

Dive until near the ground, and then decelerate?

No, Std Cirrus; no, Ka-6e (it will be on glide path well before it gets
near the ground); probably won't need to with the 20 C; might be what
happens with the ASH 26 E, with it's 8.3 psf wing loading.

Slow down until intercepting normal angle for spoilers?

Never.

360 degree turn?

Never.

snip
Dive until intercepting normal angle for spoilers?

Maybe, but can you dive, lose the altitude, decelerate and get it on
the ground for a tail wheel first, full stall landing?

As others have pointed out - bad idea. I might be able to manage it the
Ka-6e with it's huge spoilers and light wing loading (5 psf); the
Cirrus, 20, and 26 would be put on the ground as soon as possible with
full air and wheel brakes and some forward stick to give maximum
traction. I think the 20 would stop the soonest of these three.

snip

Summary
Each situation is different, but I think we should focus on teaching
techniques that are robust and give that average pilot the best
opportunity to have a good outcome in an off-field landing. I know of
very few off-field landings that start at 1000 feet at the end of down
wind.

The off-field landing "technique" of turning final at 800' instead of
400' is "robust", in my opinion, and should be one of the things we
teach. A lot (majority?) of bad outcomes during an off-airport landing
have "too low" when starting the landing pattern as a major factor.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org