Safety of winch launch vrs. aero tow?

As long as we're sitting around the campfire and also to show you I can
go both ways, I 'member a time only a couple of years ago that I
experienced the dreaded aerotow line break at 200 ft and 60 kt over the
outbound fence.

I looked out front and it wasn't too exiting, so I gingerly turned
ninety to the left and the scenery looked some better, but not the
greatest, so I REALlY gingerly gave it another ninety to the left and
was really impressed this time as I found I was perfectly lined up with
the takeoff runway. And I recall I hadn't lost too much of my original
60 kt. Will wonders never cease!!

I thought "OK now God, you've made it possible for me to do this little
magic trick perfectly the first time I tried it in front of all my
friends and hangar bums, give me your hand again and let's try just one
more."

So I pulled spoilers, checked gear down and rolled up to my exact
takeoff spot.

And as I popped the canopy, my good friend who shall remain nameless,
said "S--t!, you've gone and lost us another Tost ring, somebody go back
to the hangar and see if they can find another tow rope". It was his
turn to tow, so I pushed back. Nobody else said a word.

Safety lecture from a dummy follows:

I don't remember to this day why I ninetied to the left. During the
previous year's biannual when Juan Batch pulled the plug on me over his
outbound fence, turning right was the correct choice because in that
direction lay the wind, which blows one back over the airport. This
improves the scenery like you wouldn't believe.

When I tried the trick for real solo, the wind lay to my left. I'd like
to think it was instinct. But I believe it was a coin toss.

Anyway, thank God. And Juan.

It Depends

BJ






Bob Johnson wrote:

Hi Bill --

I 'member my O-Nine Two oil field piano wire breaking at the half way
point during a tow in Roy Schlemeyer's old SGS 2-22. I yelled "Oh, line
break" or something to that effect and recall the glider innards debris
collected since the last ice age floating up and dancing before my eyes
as I dumped the stick full forward. Was it half a second before I
reacted? Can't believe I waited that long. And when the astronauts tell
you that zero-g is exhilarating, believe it.

Luckily, I had been well briefed by Roy as to what to expect. It has
been theorized that some people are "allergic" to zero-g and they
instinctively jerk the stick full back instead of push full forward.
Unfortunately, this is the last mistake they ever make and we can no
longer interview them as to why they did this.

There, we're back to the original question, "Is winch launch safer than
aerotow?" The answer? -- scroll down

IT DEPENDS!

Thanks and good to hear from you again.

BJ



Bill Daniels wrote:

"Bob Johnson" wrote in message
...
Eggert --

Those are really good numbers for your winch.

With V8 300 HP (GMC 454 c.i., 7.4 L), and 5000 ft (1550 m) Plasma line
laid out, we are getting the rule of thumb 1/3 cable length releases of
1700 ft (525 m). This is into 10-15 kt wind. Much over that, we leave
the Blanik in the barn!

BJ
Midland, Texas

Bob, When winching, the wind is your friend. Quitting at 15 knots is not
necessary. I have winched into 35 knots and higher winds and the results
are spectacular. Each 10 knots of headwind is the equivalent of about 40
additional HP.

The thing that often severely limits the altitude gained is a slow pitch-up
profile at the start of the launch. The final height achieved is largely
determined by the profile flown in the first few seconds of the launch.

Now, as everyone has pointed out, you need to be careful here. Safety at
the start of the climb is a combination of airspeed, altitude and attitude.
The more you have of the first, the faster you can get the second two and
the higher you will get.

I've done calculations, simulator runs (X-Plane) and flight test to prove
the following point. If you have 60 knots in a glider with a stalling
airspeed of 40 knots, you can be in full climb attitude at zero altitude and
still have a large safety margin. Practice this way - at several thousand
feet AGL, zoom the glider into a 50 degree nose-up attitude. As the
airspeed decays to 60 knots, yell "WIRE BREAK", delay 0.5 seconds
(simulating reaction time) and pitch forward at zero G. Watch the airspeed
and altitude, you'll see what I mean. (For winch CFI-G's, this is a great
way to teach how to handle wire breaks.)

If you have (or simulate) a wire break at this point and start a zero G
pitch over after a .5 second delay, the minimum airspeed during the
parabolic ballistic trajectory will be about 50 - 55 knots when the glider
reaches apogee at an altitude of about 100 feet AGL. So there you are at
100 feet and 55 knots in a normal gliding attitude - not exactly a
problematic situation, just land straight ahead. The reason this works is
that the glider's induced drag at zero G is minimal so the airspeed decay is
mainly just due to gravity and the glider follows a parabolic trajectory
until the pilot re-establishes one G at the normal glide attitude.

I need to repeat that I am not advocating a rocket blast-off kind of climb
profile but a smooth transition into the full climb without undue delay
equipped with a full understanding of the safety margins.

Bill Daniels