Is 34 mph fast to a motorcyclist? Hardly.
How about for a guy on a skateboard? Yeah. He is hauling a**.
Then, how fast is 34 mph to a hang glider pilot?
This is the indicated airspeed Jim had when he touched down on the grassy field.
The true ground speed, of course, would be 34 mph minus the headwind on the field, but for the purpose of the example I am using zero headwind.
I came across an accident report from 1978 about a young British pilot, John Randall, 19, who launched his Chargus Midas Super E off a hill in Wales in turbulent conditions.
Witnesses saw the inexperienced pilot fall prey to Pilot Induced Oscillation (PIO) and execute a series of whipstalls of increasing severity until the glider entered a tailslide, then tucked at 60 meters, snapping both leading edges.
Randall hit the ground at an estimated 50 feet per second.
He died of his injuries before he reached the hospital.
50 fps is exactly 34 mph.
Using the mass of the previous example, the kinetic energy at impact was 138,720.
This is exactly 8 times the kinetic energy of a 12 mph landing.
It is really disturbing to realize that the small increase of only 4 mph added twice the kinetic energy of a 12 mph landing to the already fearsome 30 mph kinetic energy total.
This is why we land hang gliders as slowly as possible.
A slow speed whack or ground loop resulting in little (bent downtube) or no damage is really no big deal compared to a high speed landing accident.
In a high speed landing accident, where the glider is turned off course by a gust or thermal popping off and strikes a bush, rock or other unyielding object with the base tube, the nose rotates down and digs into the ground, the pilot flies forward into the keel and the entire aircraft balls up with a tremendous noise.
Sometimes the energy absorbed by the failing airframe saps away enough kinetic energy to allow the pilot to survive.
Other times, not.
This brings me to the rather murky area in aviation of good ideas vs. seemingly good ideas that don't really pan out.
There may not be any appropriately direct comparisons but the sad story of my friend John Hudson comes to mind.
John was a driving force behind bringing the British team to the Owens Valley Competitions in the early years of cross country.
Later on, he left hang gliding to build ultralights and founded Mainair Sports.
He built the highest quality aircraft he could conceive of and his models became very popular.
Then his customers started getting killed on them.
Then his friend and main test pilot died on one.
Then John was killed on a prototype, all within a year, I think.
Somewhere in that, a good idea turned bad.
You can't always recognize the cause but the funerals kinda spoil everything.
Me, I like simple hang gliders.
Light hang gliders.
I don't like hanging stuff on them.
I want them to fly fast in the air and I want them to slow down, way down, when I land.
I want to step onto the ground like getting off a bus.
The Factorial of RiskIn addition to luck, and perhaps a great deal of it, I feel I owe my survival to a concept I've always called
The Factorial of Risk.Factorials work like this: 5!=5x4x3x2x1=120
Say you can identify a number of things that can go wrong in a flight.
For a hang glider, you take off. That's one thing that can go wrong.
You fly around. Hopefully, you don't fly into something. That would be another thing that can go wrong. That's two.
You land. There is something else that can go wrong. That's three.
The
Factorial of Risk would be 3!=3x2x1=6
If you're dumb enough to fly a paraglider, the risk increases.
You take off. That's one. But as you prepare to take off, you're facing backwards and can't see what's going on behind you: the direction you are about to be going. There could be a dust devil or hang glider crossing your path, so that's two. And you don't have an airframe so your canopy can collapse in turbulence below minimum reserve deployment altitude as you gain height. That's three.
You fly around. That's four. But your airfoil has almost no kinetic energy or momentum so it can go bonkers in turbulence. That's five.
Now as you descend towards landing, you pass below minimum reserve deployment height again. That's six.
Then you land. That's seven. Your factorial of risk is 7!=7x6x5x4x3x1=5,040. That is a lot more than 6.
No, it doesn't mean paragliders are 830 times more dangerous than hang gliders.
But it means something.
Now think about all the things that can go wrong with towing hang gliders. You get a Factorial of Risk right up there with paragliding.
Every time you add a critical part to your hang glider, that thing has the potential to fail or cause unexpected problems.
Remember what happened at Jean Lake. The tow line snagged on an exterior wheel and two people died.
Each wheel added risk and the failure occurred in the air where wheels are not even useful.
I'm not trying to make a particular point about wheels.
There is no question they make tandem flights safer.
I'm saying that anything you attach to your hang glider adds a level of risk.
For instance, I built a locking sail tensioning lever and mounted to to the right downtube of my Moyes Meteor.
I thought it was pretty trick. It worked great.
Until I was circling in a thermal next to a 3,000 foot cliff and my Sport Keller zipper cord caught in it.
It put me in a spiral dive with my weight forward. I almost hit the cliff!
That lever added to my
Factorial of Risk.
Hang gliders are simple aircraft.
That's what makes them safe.
When you veer away from that, you head into dangerous waters.
by Frank Colver » Mon Jan 29, 2018 8:05 am 
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