Safety of winch launch vrs. aero tow?

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