Spin

"Mark James Boyd" wrote in message
news:4023fa90$1@darkstar...
Arnold Pieper wrote:
I've done quite a few turns with level wings and using rudder
to turn below 2 feet. I've done it both on the takeoff
roll (to line up from being way off) behind the towplane, and
after landing to line up with the takeoff runway (about
120 degrees left).

In the first case I probably should have simply released immediately.
In the second case I should have stopped straight ahead.
Not because this was necessary (it wasn't, since de facto
everything worked out fine) but because it would
be better practice for flying a higher performance glider,
where both of these circumstances could possibly create a
ground loop.

The competition pilots stay REAL straight at low airspeeds.
I suspect a few ground loops have convinced them not to
put in adverse yaw (and rudder to turn) during taxi.


Sometimes you have no choice. I had a tow pilot suddenly brake to a halt
just as I lifted off. My choice was to try a flat turn and risk a ground
loop or hit the tug. My wheel brake was useless for the task of stopping
short of the tug and anyway, my wheel wasn't on the runway. Fortunately, I
succeeded in turning the Lark 45 degrees before touchdown using rudder
only - and avoiding a groundloop. (Then I had an eyeball to eyeball talk
with the tug pilot.)

Bill Daniels

On 2/6/04 1:22 PM, in article 4023f76a$1@darkstar, "Mark James Boyd"
wrote:


I've wondered why airliners don't have some spot on the
ground (GPS) some distance down the runway, and abort
at that spot if they haven't reached a certain airspeed.
Seems simpler than doing all them calculamications for
wind, density altitude, etc. which may have changed since
you did them. Why not observe instead of predicting?

We can't afford not to do both, Mark. The calculations would still be
required in every case, making the "spot" different for each takeoff.

Airlines conduct operations on many different runways under all conditions
of weather, ambient lighting, loading, runway slope, braking coefficients,
etc., and many of these factors will vary from flight to flight even at the
same field, on the same day, in the same aircraft. In some cases a crew
member may fly in as many as three or four variations of a single type
(e.g., DC-9-10, DC-9-30, DC-9-40, DC-9-50), with a significant range of
performance and handling characteristics, within the same 24-hour period. I
think you can see that calculations for each flight with go/no-go decisions
made according to predetermined speeds for the anticipated conditions, with
adjustments when conditions change (there's your "observation") is the only
way we can safely operate.

With hundreds, or thousands, of pilots on the roster, and scores or hundreds
of destinations across the country and around the world, the idea of trying
to train every pilot to the visual cues at every runway would leave the
training department using far more assets than the revenue side of the
operation could likely produce.

I'd much prefer to make split-second decisions based upon the well
understood performance of the aircraft, than on the often vague cues
provided by the environment in which we operate the aircraft. In contrast to
the typical sailplane flight, we operate big fast moving machines often
under conditions in which I would prefer not to have to walk to my car, let
alone drive it to the airport.

If visual cues are to comprise the primary reference for takeoff
performance, by all means let it be at 30 to 50 mph in a 1-26 or in a
Pawnee, on a sunny day from 2500 feet of grass, where I am familiar with
every bump and soft spot, and not from the cockpit of a 180,000 lb
(relatively light, at that) Boeing 757 on a snowy February night from 6500
feet of wet runway at Midway, on the south side of Chicago.

Flying sailplanes well, I suspect, will be complicated enough.


-----
Jack
-----

Bill Daniels wrote:
Mark, I think Janos was talking about winch launch. The land ahead/turn
height for winch launch depends greatly on the winch site although at 25% of
the altitude expected without a wire break, say 500 feet or 150 meters, a
landing straight ahead on the runway should be possible. The ideal,
available at most sites, is an overlap between the two options where a 360
degree turn with a landing into the wind can be made from 300 feet AGL and a
straight ahead landing can be successful at 450 feet.

Aha! An excellent point. I hadn't considered the advantages of
the steep climb from ground-launch and the increased options it
provides. Thanks for pointing this out (since ground-launch is
rare in this part of the gliding community i.e. west coast USA).

In fact, he did exactly what you said can't be done. He had some help
from the main gear, which touched the runway several times assiting
his skidding turn. If memory serves, he wound up pretty much where he
started, pointing in the opposite direction. There were many, many
witnesses. What parts I didn't see while running, I had recounted to
me in excrutiating detail, mainly because it was my glider. (The pilot
of the 20F, by the way, nearly hit my other glider, a parked Pegase.
The only two French gliders on the airport. Proof again that like
seeks like.)

Better, I think, to start with observed facts rather than to try to
deduce them.

As for owning two French gliders, you are welcome to exercise your
powers of induction.

Jack wrote:
On 2/6/04 1:22 PM, in article 4023f76a$1@darkstar, "Mark James Boyd"
wrote:

I've wondered why airliners don't have some spot on the
ground (GPS) some distance down the runway, and abort
at that spot if they haven't reached a certain airspeed.
Seems simpler than doing all them calculamications for
wind, density altitude, etc. which may have changed since
you did them. Why not observe instead of predicting?

We can't afford not to do both, Mark. The calculations would still be
required in every case, making the "spot" different for each takeoff.

OK, then both. From my point of view, however, if I had to choose
between 1. point on the ground and ASI and timing to acceleration vs.
2. just look at the engine gauges and interpret them, I'd take #1
first.

http://www.avweb.com/news/safety/182403-1.html

Airlines conduct operations on many different runways under all conditions
of weather, ambient lighting, loading, runway slope, braking coefficients,
etc., and many of these factors will vary from flight to flight even at the
same field, on the same day, in the same aircraft. In some cases a crew
member may fly in as many as three or four variations of a single type
(e.g., DC-9-10, DC-9-30, DC-9-40, DC-9-50), with a significant range of
performance and handling characteristics, within the same 24-hour period. I
think you can see that calculations for each flight with go/no-go decisions
made according to predetermined speeds for the anticipated conditions, with
adjustments when conditions change (there's your "observation") is the only
way we can safely operate.

Yep. So add in a calculation for time to airspeed. And add in
a calculation for ground distance to airspeed. If one detects
that the acceleration and airspeed aren't coming up at that point,
abort the takeoff (presumably that point is calculated to be
the point of safe abort).

The simplicity of this is one doesn't need to deal with the complexity
of diagnosing what CAUSED the lack of acceleration. Was it the
RPM or the EPR that was wrong? Is it the RPM or that the prop is
worn thin? Did I leave the hand brake on for takeoff? Is the
nosewheel flat? Did they put a second passenger in the glider and
now it's too heavy? So many factors (some known, some not).
I prefer simplicity...

Of course the simple answer is just to have much more power
available than you could possibly need (RJs with 8000fpm climb,
a nice 400hp stearman) so really I'm talking about using this
as a tool to provide the same level of safety with less training
and less cost, rather than improving safety...

With hundreds, or thousands, of pilots on the roster, and scores or hundreds
of destinations across the country and around the world, the idea of trying
to train every pilot to the visual cues at every runway would leave the
training department using far more assets than the revenue side of the
operation could likely produce.

Umm...I didn't say anything yet about visual cues. GPS, a stopwatch,
and marking the point when the takeoff roll starts. For jets,
an automated calculation and "low acceleration" warning
light.

For towplanes, probably a visual cue is easier, though,
and simpler than for an airline, because one tows off the same field
again and again. Another possibility is to simply walk the
field (or taxi up the taxiway) with the GPS and measure the
visual cue distance and the safe takeoff runway.
I've used GPS to measure a short strip before and declined to
takeoff there. Useful things, these little gadgets. Better than
my golfing range estimating eyeball...

If I towed out of a farm field or a "new to me" airstrip, and
I had some questions about whether I could make it over the
power lines, I might use this technique as an "extra tool in my bag"
to improve my confidence and capability. How much does the 1" thick
soft dirt slow me down? Am I light enough on fuel? I can do all
the calculations, but it's never the things I know that hurt me,
it's the things I don't know that I don't know...


If visual cues are to comprise the primary reference for takeoff
performance, by all means let it be at 30 to 50 mph in a 1-26 or in a
Pawnee, on a sunny day from 2500 feet of grass, where I am familiar with
every bump and soft spot, and not from the cockpit of a 180,000 lb
(relatively light, at that) Boeing 757 on a snowy February night from 6500
feet of wet runway at Midway, on the south side of Chicago.
-----
Jack
-----


The last time I even dreamed that an airline pilot looked out
the window was at Ontario in low overcast when the tower called

"Delta XYZ traffic 2 O'clock 1 mile below you an experimental
with no transponder tight left base will pass behind you..."

And a real nervous co-pilot "XYZ looking for traffic"

....and I suspect a few expletives from the captain
"Who lets a f***ing no-squawk ragwing fly around in OUR
go***mn airport?"

Again, for any airline guys, I wouldn't DREAM of asking you
to look outside the cockpit for a visual cue of anything.
(Now, now, don't get yer panties in a bunch, I'm jus'
hasslin' ya, with yer umpteen item checklists, and yer
bells and whistles, and yer big cozy pilot chairs, and
yer Datsun 280Z's :PPP)

For you guys, I just thought maybe a nice shiny new
"acceleration" computer might be an extra takeoff tool... :P
Something to go with the pre-calculated trim settings and
"gee ya almost hit the tail" printouts?

But you are right, perhaps try it a while in the pawnee towing
an extra heavy ballasted two seat glider a few times first
and see how it affects the rotation point, and then
come up with some takeoff abort scenarios, and see how
much runway you REALLY have.

I actually really also liked the discussion about how longer
towropes allow an abort where the glider doesn't ram into the
back of the tug, too...

Bill Daniels wrote:

Sometimes you have no choice. I had a tow pilot suddenly brake to a halt
just as I lifted off. My choice was to try a flat turn and risk a ground
loop or hit the tug. My wheel brake was useless for the task of stopping
short of the tug and anyway, my wheel wasn't on the runway. Fortunately, I
succeeded in turning the Lark 45 degrees before touchdown using rudder
only - and avoiding a groundloop. (Then I had an eyeball to eyeball talk
with the tug pilot.)

Bill Daniels

A real good reason to use a little longer rope, eh?
I'm glad you weren't hurt, and I hope you got a good reason and
a beer from the tuggie.

I must say though, when I was taught to aerotow, and to drive a tug,
both instructors said "you don't owe a damn thing to the other guy.
If you have a problem, you release immediately and save your own
arse."

Don't get me wrong, release and potential release at rotation
is one of my greatest fears (it's happened to me a few times,
never initiated by me on purpose). But it is so scary
I didn't even practice a tuggie abort while actually hooked up
during any of my training...

Even if I rehearsed this one on the ground first, I'd still be
pretty apprehensive of practicing this abnormal procedure...

Bill Daniels wrote:

A longer rope will just move the tug further down the runway where he has
even less room. I'm pretty comfortable with 250 foot ropes.

Yes, I really meant longer "within reason." I'm really just saying
even as a tug pilot I'd rather have a 250 foot rope and less
runway in front of me, than the extra 150 feet in front of me and
some guy on a 100 foot rope, if I had to abort. I can't imagine
anyone could abort takeoff and release successfully with a 100
foot towrope without scraping metal...I wouldn't even consider
practicing this as an abnormal during training...

A tuggie
always has the right to abort a takeoff roll any time being on the ground
will be preferable to being in the air. What I would like is a review of
the runway abort procedures. As far as I know, the following is not in the
"How to be a Tuggie" comic book.

The first step is for the tug to release the rope - that gives the glider
pilot the unmistakable sign that this is an abort. Just as in the air, the
tug must turn left and the glider right. There may be room to leave the
runway completely or just move as far to the edge as safety allows. If
there are runway lights, there may be clearance for the tug wing to pass
over them - use all the room available. The tug should try to maintain
speed and not brake until reaching the departure end of the runway or when
it's clear that a collision is not possible.

Again, you see why I like winch launch.

Bill Daniels


Bill,

excellent review. Just as with power training, aborts are
too rarely discussed or trained, IMHO.

I'd add the one point from our local tuggie/CFI, that if a certain
tire flattens, the tuggie may not be able to abort to the "correct"
side. I guess this is rare, but has happened to him...

"Mark James Boyd" wrote in message
news:40252327$1@darkstar...

I actually really also liked the discussion about how longer
towropes allow an abort where the glider doesn't ram into the
back of the tug, too...

A longer rope will just move the tug further down the runway where he has
even less room. I'm pretty comfortable with 250 foot ropes. A tuggie
always has the right to abort a takeoff roll any time being on the ground
will be preferable to being in the air. What I would like is a review of
the runway abort procedures. As far as I know, the following is not in the
"How to be a Tuggie" comic book.

The first step is for the tug to release the rope - that gives the glider
pilot the unmistakable sign that this is an abort. Just as in the air, the
tug must turn left and the glider right. There may be room to leave the
runway completely or just move as far to the edge as safety allows. If
there are runway lights, there may be clearance for the tug wing to pass
over them - use all the room available. The tug should try to maintain
speed and not brake until reaching the departure end of the runway or when
it's clear that a collision is not possible.

Again, you see why I like winch launch.

Bill Daniels

On 7 Feb 2004 09:40:55 -0700, (Mark James Boyd)
wrote:

Yep. So add in a calculation for time to airspeed. And add in
a calculation for ground distance to airspeed. If one detects
that the acceleration and airspeed aren't coming up at that point,
abort the takeoff (presumably that point is calculated to be
the point of safe abort).

Add a little data about brake authority (wet runway, maximum wheel
brake temperatures depending on OAT), wind conditions, flap setting
(affects acceleration due to drag), and you get the complex scheme
that is being used today.

FYI: In the early days of jet aviation the pilots of the B-47 bomber
indeed used a stop watch. If a certain speed was not achieved after a
certain time, the takeoff was aborted.

Bye
Andreas

Did some simple calculations to get an idea of what caused the spin of
the DG500.
If the glider flew initially with an IAS of 100km/h and had a headwind
of say 25 km/h then its speed relative to the ground is 75km/h. If
after making the 180° turn back to the airfield the glider flew again
with an IAS of 100km/h but now with a tailwind of 25km/h, then its
speed relative to the ground is 125km/h. This means that during the
180° turn the glider had to be accellerated from 75km/h to 125km/h
relative to the ground.

For a banking angle of 45° and an IAS of 100km/h one finds from simple
mathematics that a 180° turn takes 8.9 secs when properly flown. The
forward accellaration of the glider during the 180° turn must then be
(125-75)/(3.6)/8.9=1.56m/s2 to come out at the same speed of 100km/h.
Suppose the mass of the glider (including the pilot) is 650kg, then
the force needed to accelarate the glider with 1.56m/s2 is 650x1.56 =
1014kgm/s2 or 1014N.

Where does this force come from. Indeed, from gravity. The glider must
pitch down to keep its IAS up. With a glider mass of 650kg, its weight
is 650x9.8=6370N. The pitch down angle must then be
arc(sin)1014/6370=9.2°. Add to this a normal glide angle of 1.4° (for
a glide ratio of 40), then the total pitch down angle during the 180°
turn of the DG500 should have been over 10°.

If the pilot does not move his stick quite a bit forward to achieve
this relative large pitch angle, the glider will loose its IAS, then
stall and spin. This looks to me what happened unfortunately with the
DG500 at Magdenburg.

Karel, NL