Are 'Single 180 Turn From Downwind to Final' and 'Stall-spin on Turnfrom Base to Final' mutually exclusive?

Le vendredi 29 juillet 2016 16:33:21 UTC+2, a écritÂ*:
The majority of gliders are more stall and spin resistant at medium to steeper banks than at shallower bank angles. (This is aerodynamically different than most airplanes).

I'm sure you can elaborate on this...

Some of the reasons for standard patterns rather than 180:
- it's what other traffic at airports expects. It's what most instructors checking you out on their planes, airports, BFRs, or FAA examiners expect.
- it gives you good time to look from base to see if there is other traffic on final
- many stall spin accidents come from overshooting base to final, then ham-handed corrections. That's more likely from a 180
- many off field accidents come from being too close to the field. planning a 180 puts you close automatically
- less adjustment room if things go wrong.
- A test: try doing your no-spoiler approach that way.

John Cochrane BB

On 7/29/2016 8:33 AM, wrote:

Turning flight presents a more dynamic visual picture then straight flight.
Most normally equipped humans are better at assessing and reacting to the
changing energy state of the glider (relative to landing area & speed) as
well as detecting conflicting traffic and other hazards during wings level
straight flight than during turning flight. This may be due to the less
dynamic visual presentation in straight flight. This is especially true
while under stress.

Hey Matt, howzis for a data point? The 2nd-most-stressful landing approach I
ever made (microburst [just like #1 & #3] - not recommended for the
faint-hearted!) was done in the Zuni to a (shortish, with drop-off to an
arroyo at the threshold) prairie runway on which I'd never before landed (Owl
Canyon's SE one), from a close-in circling approach, with zero flaps until
v-e-r-y short final, begun from overhead the field at ~3,000' agl and
completed with (essentially) only a 270-degree turn from crosswind to final.
Gives me the mild shakes just recalling it!

Judging the "lower altitude bits" angle of bank was trivially easy compared to
deciding when to steepen the "downwind" portion of the turn into the "downwind
to final" portion. Why? The breathtaking descent rate (estimated later at
~3,000 fpm) "visually overwhelmed" the normally-to-be-expected sight picture
for "normal conditions." How bad was it? It nearly gave me heart failure, when
- for a brief, "I didn't, did I?!?" moment on downwind - the *vertical* ground
rush (contrasted with the downwind's seemingly-absent, more expected,
*horizontal* rush/related rapid progress over the ground) made it seem as if
I'd turned the wrong way onto downwind. I knew I hadn't, but it alarmed me so
much I "wasted" a few moments looking back over my left shoulder just to see
if there was still dust blowing from the SE immediately off the east end of
the target runway. (If I'd turned upwind rather than downwind, a serious
accident would likely have been in my immediate future.) The microburst
downwind sight picture and "over the ground feel" was more akin to what you'd
expect from turning downwind the wrong way on a "normally breezy day...i.e.
agonizingly slow progress over the ground in conjunction with a dismal
L/D....sort of like flying through molasses in terms of "expected downwind
progress." Despite trying to make a conservatively judged approach - e.g. not
planning a base much beyond the approach threshold, etc. - for a while it was
looking as if base would be made entirely within the shortish (2,000'?) runway
length...and crosswind had been at midfield!

As it was, I straightened up on final *maybe* 300' beyond the lip of the
dropoff (quite possibly less...no one on the ground saw the approach to share
their estimates), but I was too focused on judging final approach to give that
estimate much attention. Thermalling-flaps-only until past the threshold lip,
and still several hundred feet aloft; down and stopped well before midfield
after not using the wheel brake (trying to minimize the walking retrieve -
stress removed, we humans revert quickly to "energy saving mode," ha ha!).

I'd reckon prolly 95-98% of my attention throughout the approach was devoted
to "getting the approach path correct" with the remainder being "the usual"
airspeed/coordination cross-checks. There was very little "waiting for the
situation to develop" aspect to this approach, as is typically the case in
more routine patterns. Thanks to the sink rate, things developed "all too
quickly!" as in from 3,000'agl atop midfield. followed by two quick,
thermalling-flaps-only, 360s and on the ground. The first 360 was to clear the
pattern, positively locate a 1-36 I'd figured would opt to land before I did
(he turned out to be clueless, afterward, but got away with it just fine!),
and indubitably verify ground winds (as in "Where in heck is the center of the
downburst?), the second one was the pattern itself.

I don't remember my target pattern airspeed, but it likely wasn't all that
much higher than normal, because throughout, the air - other than being
abbie-normally descendant - was astoundingly smooth, so the primary airspeed
tasks seemed likely to be "only" retaining sufficient energy to deal with
low-level shear while not "overdoing" things. Control wasn't an issue (not the
case with #1 alluded to earlier, and to a lesser extent, #3).
- - - - - -

While it is true that many of you normally performing well trained pilots
can safely fly all kinds of approaches, common sense suggests training and
establishing flying habits that are more likely to result in safe outcomes
when normal conditions and normal performance deteriorates.

I agree with your general sentiment, but would add that "actual reality" is
the ultimate arbiter of "what must be done" in every landing pattern. Under
the above conditions, I doubt I could have pulled off "a full rectangular
pattern" that wouldn't have terrified me even more than the one performed, due
to the (almost certainly likely) need to turn final well within the runway
western/downwind boundary, and (at some point) to be facing a rapidly
decreasing headwind...my overshoot concerns weren't far behind my undershoot
concerns. As with undershooting, the overshooting options on that runway are
nonexistent, short of barbed-wire fence/railway
embankment/fence-in-borrow-trench/interstate highway/fence/etc., or, (major
yikes) trying to convert to a howling crosswind landing to the south on open
prairie. I dunno if the preceding explanation makes sense, but under the
circumstances and at the time, an "analog" circling pattern seemed more
amenable to fine-tuned approach adjustments than did a "digital" rectangular
pattern, while also likely maximizing runway ahead without wasting runway behind.

I didn't "originally plan on" a circling pattern, it simply seemed the best
and most natural of the available options...and worked superbly.
- - - - - -

The fact that we are still debating these things in 2016 makes me want to
beat my head against the canopy.

Aw, c'mon - please don't. The latest scientific evidence suggests doing so can
be harmful to canopies: plastic and cranial (and, the latter's contents)! A
baseline landing pattern standard is a great thing for many reasons...but I
see no fundamental harm in assessing why (and why not) it may not be the cat's
meow for *all* circumstances. You DO want your students to retain, and further
develop, their critical thinking skills, right?

Bob W.

We [British] divide the downwind to base turn into two approximately 45 degrees turns, to insert a 'diagonal leg'.

I'm going to give this a try. I don't like the "wait until the touchdown point is 45 degrees behind you before turning base" part of the square pattern training...I can't see the touchdown point then. This BGA method seems like better training for XC outlandings than a square pattern

Sorry to be so flip with my first response, however subjects like this keep coming up. Bottom line - there is a best practice technique for most tasks. Many of these best practices are designed to result in the safest methods.

From this "best practice" there develops alternative methods. Some of these other methods are for good reason, but they do not supplant the reasons for the best practice method.

This is a big subject, and I have submitted a lengthy article regarding landings for publishing in Soaring Magazine - probably after the first of the year.

Gather your stones for throwing.

Tom Knauff

Whatever method you use, if you don't make a controlled arrival to the ground, you still broke something.
Even a "normal day at normal field" can bring surprises..........
Have a plan, make adjustments as required......
Don't break the glider, you won't likely break yourself.

On Thursday, July 28, 2016 at 5:43:41 PM UTC-4, wrote:
Sorry to be so flip with my first response, however subjects like this keep coming up.

I tried the 'Inverted Flight Landing Pattern' and I DID NOT LIKE IT.

Looking forward to your article on landings.

Another advantage of a standard-ish circuit, is that the focus is on preparing for the final turn -- you aim to have your final turn completed at a safe height (and speed) in a reasonable place.

There's no reason you can't do this in a 180 deg turn too, but my guess it that it somewhat reduces this focus if it's not trained well. It could potentially have you focusing on your reference point too early, flying more cramped-in circuits as a result?

my $.02:

First, the beauty of the 360 "Overhead" pattern is that it makes it really easy to fly exactly the same pattern at ANY airfield. As long as you come up initial at the same speed, and pitch out at the same bank angle, you will end up at the same place on downwind (adjusted for x-wind, of course). The, you just configure, motor to the perch, and roll into your easy 180 turn to line up on final. Done well, it's one of the most satisfying maneuvers in aviation.

And it has the advantage of being a really quick way to enter the pattern, slow down, and land - useful for towplanes.

BUT - it's meant for relatively fast movers with bigger turn radius's; works fine in a Pawnee at 120 mph, no so good in a J-3 at 65 mph, and not at all in most gliders (yes I've tried).

So, for gliders, all that is really useable is the second half - the continuous 180 degree turn to final. As others mention, that is not what is normally taught, and has some limitations that need to be taken into consideration; the main one is that it has to be done from a low downwind, and it happens fast.

And that is why I think it is actually a useful skill to practice: If you end up low and tight, you should be able to fly a safe 180 (or 270, or 90) pattern and land out of it - because you don't have the option of going around!

Just realize that most other traffic will not be expecting it and fly accordingly.

In regards to you question about the military's track record - I don't have numbers but would bet an expensive bottle of whiskey that it's a LOT better than that of GA - after all a military pilot is better trained, flies more often, gets lots of check rides, etc. That being said, modern military jets are more susceptible to high-sink rate problems in the pattern that stall/spins; look up almost any T-38 accident and getting low and slow on final will pop up often. For a supersonic jet, it is really a dog when slow!

Kirk
66

On 7/29/2016 1:10 PM, kirk.stant wrote:

Snip...
So, for gliders, all that is really useable is the second half - the
continuous 180 degree turn to final. As others mention, that is not what is
normally taught, and has some limitations that need to be taken into
consideration; the main one is that it has to be done from a low downwind,
and it happens fast.

I don't comprehend why a circle-from-downwind-to-final landing pattern in a
glider "...has to be done from a low downwind, and it happens fast." I
understand it CAN be done that way, but not why it MUST be done that way.

If Joe Glider Pilot is aiming to produce a threshold landing directly from the
180-degree turn, I suppose an overall lower flight path compared to the case
where he seeks to achieve the same "no straight final leg" threshold landing
directly from the base-to final turn would be the case, simply because the
latter/"tangencies-to-the-circle" flight path pattern would be longer due to
the "uncut corners," and hence the "rectangular path" pattern has greater
distance over which spoilers can be modulated. (The preceding scenario assumes
a "normal downwind offset distance;" the closer in the final, the less
additional distance flown, of course.) But if the goal is "simply" to hit a
pre-selected landing spot on a runway, he can also do "the circling thing" to
final, rolling out short-of and "normally above" the runway onto his final
approach path...which is what all of my "circling patterns" sought to achieve.
IOW, my circling-to-final in the HP allowed me to be able to use less bank
angle-per-unit-time (aka lower roll rate/stick forces) to a high, straight,
final approach path; I wasn't trying to emulate Joe Carrier Pilot in any way
beyond borrowing his 180-degree downwind-to-final turn. Likewise, the
microburst-influenced "fully circling pattern" described in another post, in
actuality, by design, resulted in a (very) short straight final.

Tangentially and as noted elsewhere, for whatever reason, I found no
difference in difficulty judging "howzitgoing" with respect to my glider's
status "in the descent cone" whether circling from downwind to final or using
separate, distinct, 90-degree turns to get there...if anything, the circle
seemed "more natural" to me..but then I preferred playing outfield to infield
as a kid! Either way, every pattern's goal: to arrive on a straight final
"somewhere on the high side" of my ship's theoretical descent cone.

Back to my original puzzlement...am I correct in believing "military approved"
circling approaches essentially do NOT include "a straight final" portion,
a-la the "immediately before touchdown" curving flight path understandably
employed by (e.g.) Pitts biplane pilots as a means of retaining over-the-nose
vision for as long as possible until the runway edges appear on either side of
the nose?

And that is why I think it is actually a useful skill to practice: If you
end up low and tight, you should be able to fly a safe 180 (or 270, or 90)
pattern and land out of it - because you don't have the option of going
around!

"Roger that!" on the go-around-impossible bit. (No mulligans in sailplane
landing patterns!) When I blundered into the sport, the concept of being
unable to "re-do a poor pattern" by going around was a
new/completely-foreign/ignorantly-scary concept to my "power-polluted" (in the
reading sense of things) brain. Upon becoming "stick-time/usefully familiar"
with the flight physics of sport sailplanes, the no-go-around reality quickly
mentally-morphed into "entirely normal and not a big deal"...so long as
reasonable and continuing assessment of "minding the approach store" was part
of the piloting package. It was immediately clear to me "an easily repeatable"
landing pattern was the primary tool in minding the store.

And "Roger that!" on being able to safely do (or more accurately, salvage, if
previous inattention/screwups have contributed, sardonic chuckle) low
patterns. Following "licensure," safely expanding one's flight envelope surely
is the name of the aviation game! So - where do I go to practice departures
from controlled flight *in* my landing pattern?

Bob W.