Peter's probably declared victory and left at this point - leaving the usual pile of inconvenient and embarrassing unanswered questions behind him - but there's a lot more fun to be had at his expense here. And where there's fun to be had...
Peter Birren
Skyting Criteria
These are Donnell Hewett's original 12 elements of a good tow system. They are as viable today as they were in the early 80's when he wrote them.
Group 1 – Accurate simulation
In order for an artificial gravity to accurately simulate natural gravity, it must have the same characteristics as natural gravity, namely (1) constant in direction, (2) constant in magnitude, (3) distributed the same as gravity and (4) acting only through the center-of-mass of each component.
#01: CONSTANT DIRECTION
The direction of the towing force must remain essentially constant throughout every phase of the towed flight. (Length of the tow line must be long compared to the transverse motion of the glider... the faster the glider climbs and maneuvers, the longer tow line needed... 500 feet or longer.)
#02: CONSTANT TENSION
The tension in the tow line must remain essentially constant throughout every phase of the towed flight. (Some tension regulation device must be used... +/- 15 pounds during every phase of tow. Settings should reflect a "comfortable" flight and "reasonable" climb rate.)
#03: C-M (Center of Mass)
DISTRIBUTION The towing force must be distributed between the components of the flying system proportionally to the masses of the respective components. (Pilot and glider move in relation to each other and the tow force needs to be evenly distributed. 2:1 bridle is quite effective at this – 2/3 force on the pilot, 1/3 force on the glider.)
#04: CM ATTACHMENTS
The tow line/bridle must be attached as closely to the effective center-of-mass of each of the components and must not be allowed to touch any other part of the flying system. (Violations of this produce lockouts, adverse yaw and other loss of control problems.)
Group 2 – Safe transition
Any system must be able to handle: deviations from the ideal case; pilot release; excessive tow forces; learning.
#05: GRADUAL TRANSITIONS
The transition to and from tow, as well as any variations while on tow, must be gradual in nature. (Use of a long line that has sufficient stretch – but not too much stretch or driving will be difficult. 3/16" – 1/4" hollow braided polypropylene, polyethylene or nylon are used successfully.)
#06: RELIABLE RELEASES
The release devices and their activation methods must be sturdy, rapid and reliable. (Release activation MUST be readily accessible to the pilot regardless of where his hands are or where his body has shifted. Only single-point release systems should be used.)
#07: INFALLIBLE WEAK LINK
The system must include a weak link which will infallibly and automatically release the glider from tow whenever the tow line tension exceeds the limit for safe operation. (There is always the possibility something unexpected can happen. Breaking point should be appropriate for the weight and experience of the pilot, not to exceed 1G – sum of all towed parts.)
#08: SAFE LEARNING METHOD
The system must include a method for safely learning to use it by gradually advancing from one level of experience to the next. (NEVER try 2 new things at once. NEVER allow yourself to be pushed beyond your personal comfort level. NEVER exceed the limits of your equipment and skills. NEVER go more than twice as high, fast, far, etc., as previously mastered. Learn in smooth air before transitioning to rougher air.)
Group 3 – Practical implementation
Perhaps obvious, but safety should never be taken for granted.
#09: ADEQUATE POWER
The system must contain a source of power adequate to maintain a safe mode of flight while under tow.
#10: CAPABLE CREW
The system must be operated by a crew which is adequate in number and competent in ability to see that it functions properly. (Driver, spotter, launch assistant, pilot.)
#11: RELIABLE COMMUNICATIONS
The system must provide a means whereby the pilot can reliably communicate to the rest of the crew. (Anything longer that 500 feet of tow line requires a radio – minimum from pilot to driver – for pilot-in-command. Everyone must agree on what signals or commands that will be used.)
#12: SUITABLE ENVIRONMENT
The system must be operated only within the environment and under the conditions for which it was designed.
Zack C - 2011/04/15
After over a hundred each of hill/mountain launches, aerotows, and surface tows, I feel that platform launching is the safest way to get a hang glider into the air.
Zack's got that absolutely right - the way they do it at his Hearne home site anyway.
1. He uses a bridle effectively connected only to his hips.
2. He starts prone with both hands on the basetube and stays that way.
2. He lets the truck power him up to a steady 25 or 30 mph airspeed before allowing the glider to become airborne.
3. He instantly blasts up from virtually on top of the winch through the kill zone with a high sustained rate of climb under high tension transmitted through a spectra towline using a weak link over twice his flying weight and a three-string release ready to blow himself off under full tension in an instant if necessary.
...
01. His effective towline length is close to zero at the most dangerous point of the operation - five hundred feet under the minimum Skyting Criteria requirement. Are we seeing platform launchers getting majorly int*rcoursed up just off the truck because of that flagrant violation?
02. Let's move Zack from the runway at Hearne to the dry lakebed outside of Vegas (where Todd Jones shows us all how to use a hook knife to best effect...
http://www.youtube.com/watch?v=mJGUJO5BjnA...to supplement his very very reliable bent pin release) so the truck can operate in an extra dimension. If Zack gets blown or rolled to the left should the truck move to the left to help him out - the way a tug does for an aerotower - or continue straight ahead so as not to violate the constant direction mandate?
03. On one of my early platform launches there was a lot of wind as we rolled up to launch airspeed and about a half a second after I pulled the pin there suddenly wasn't and I found myself looking straight ahead at the license plate for a while. Would it have been OK for the driver to really crank up the tension to get me climbing or would he have been limited to giving me an extra fifteen pounds to stay in compliance?
04. Shouldn't Zack be using a two to one bridle so that two thirds of the tow tension is routed to his hips and one third is routed to the center of mass of the glider to make himself lockout and adverse yaw proof?
05. Instead of blasting off at 25 or 30 miles per hour shouldn't he be eeeasing the glider into the air a little over stall speed and graaadually increasing his airspeed and climb rate for a nice smooooth transition to tow?
06. What if he locks out because he wasn't using a center of mass bridle system? Should he blow tow immediately or wait a while to stay in compliance with the gradual transition from tow mandate?
07. Why is he using spectra instead of a nice stretchy poly or - even better - nylon? Wouldn't that help a lot with smoothing out the tension fluctuations in rough air. Hey, Dead-Eye Mike! You got an opinion on this issue?
08. We can't give Zack a button under his finger so in an emergency he could blow the three-string release/bridle assembly off his hips with both hands still on the basetube and without doing an unplanned semi-loop because:
-a) That would add complexity to the system and complexity is ALWAYS BAD.
-b) It might not work.
-c) Zack wouldn't use it 'cause he'd hafta check the battery level every Friday evening and run a wire up his sleeve when suiting up. And he's got enough hassle already locking his carabiner, checking his parachute pins, and buckling his helmet.
-d) The rule says the release "MUST be readily accessible to the pilot regardless of where his hands are or where his body has shifted", his three-string fulfills that requirement just fine, and that's plenty good enough.
-e) If he were really concerned about safety he'd be using a maximum one G weak link which would infallibly and automatically release the glider from tow whenever the towline tension exceeded the limit for safe operation.
-f) He's got a radio he can use without taking his hands off the basetube so he can phone his spotter to start getting busy with that machete.
NEVER go more than twice as high, fast, far, etc., as previously mastered.
09. Is that how you learned to tow, Zack? "OK, you did fine at twenty miles per hour at five feet for a hundred yards. Let's try forty at ten for two hundred this time and see how it goes."
The system must be operated by a crew which is adequate in number and competent in ability to see that it functions properly. (Driver, spotter, launch assistant, pilot.)
10. OK class, let's see a show of hands...
Jim Rooney - 2007/08/01
Whatever's going on back there, I can fix it by giving you the rope.
It's more of this crappy argument that being on tow is somehow safer than being off tow.
How many of you would feel great being low, rolled, and partially stalled with that guy on the other end of the line?
William Olive - 2008/12/24
I've seen a few given the rope by alert tug pilots, early on when things were going wrong, but way before it got really ugly. Invariably the HG pilot thinks "What the hell, I would have got that back. Now I've got a bent upright."
The next one to come up to the tuggie and say "Thanks for saving my life." will be the first.
Any takers for Billo?
I want a good driver and a launch assistant who at least understands about ten or fifteen words of English but I'll take care of the piloting myself, thank you very much. I don't want anybody NEAR the other end of MY rope - especially if he has something sharp in one of his hands - and I don't want the idiot tug driver even thinking about the release lever unless HIS situation is being compromised.
Bill Bryden - 1999/06
During the tug's roll-out for the second launch attempt, the tug pilot observed the glider clear the runway dust and then begin a left bank with no immediate correction. At that point he noticed the launch cart was hanging below the glider and immediately released his end of the 240 foot towline. The tug never left the ground and tug pilot watched the glider continue a hard bank to the left achieving an altitude of approximately 25 feet. Impact was on the left wing and then the nose of the glider. Rob was killed immediately from severe neck and head trauma.
And and I've never been behind a tug whose situation was being compromised by me.
The system must provide a means whereby the pilot can reliably communicate to the rest of the crew.
Why?
Zack DOES use a radio but ONLY to call for tension adjustment at high altitude when the line diameter on the drum is nearing minimum and safety has long before ceased being an issue. Once the glider has started rolling what needs to be said on the radio that's gonna affect the operation in a positive manner?
The system must be operated only within the environment and under the conditions for which it was designed.
Can you predict that the environment and conditions will be benign and stable enough that you can dumb down your design...
Peter Birren - 2008/10/27
Imagine if you will, just coming off the cart and center punching a thermal which takes you instantly straight up while the tug is still on the ground. Know what happens? VERY high towline forces and an over-the-top lockout. You'll have both hands on the basetube pulling it well past your knees but the glider doesn't come down and still the weaklink doesn't break (.8G). So you pull whatever release you have but the one hand still on the basetube isn't enough to hold the nose down and you pop up and over into an unplanned semi-loop. Been there, done that... at maybe 200 feet agl.
...the way Peter does so that it doesn't really need to be able to handle a worst case scenario?
Peter Birren - 2011/11/29
So why haven't you re-written them, correcting the physics professors obvious errors?
Most of this stuff is CLUELESS. Donnell was an isolated Rogallo standard pilot with about three hours airtime, a hundred flights, and a Hang One rating when he cooked most of this stuff up. He didn't look at how sailplanes were operating, assumed that everybody who was frame towing had everything else wrong too, ignored the parallel development and superior advancements from the Norfolk (England) Hang Gliding Club people (Brooks and Lake Bridles), got the physics catastrophically wrong, and either ignored or attempted to shoehorn into place by any means possible any data that contradicted his models and assumptions.
Today there are ZILLIONS of aerotow launches of high performance gliders.
01. NOBODY uses a two to one "center of mass" bridle. The pilot typically tows with shoulder only attachments with nothing going anywhere NEAR his center of mass and NOTHING AT ALL going to the glider.
02. NOBODY foot launches. Everybody gets on a cart, prones out, puts his hands on the basetube, builds up a lot of excess speed, blasts off, and pulls in and waits for the Dragonfly to get airborne. People who make "gradual transitions to tow" are likely to get their freakin' necks broken.
03. The smart ones - like Steve Kinsley and the Russians - have release actuators in their teeth so they don't hafta do unplanned semi-loops when they release like the idiots do (sometimes surviving from two hundred feet and sometimes dying of massive head trauma from one hundred feet).
04. They don't do gradual transitions from tow when the s*** hits the fan because if they did they'd have been dead five seconds ago. They don't even do gradual transitions from tow when the s*** ISN'T hitting the fan.
05. The off the scale stupid ones use weak links...
http://www.youtube.com/watch?v=bTa6XL16i0U...which infallibly and automatically release the glider from tow whenever the tow line tension exceeds the limit for safe operation.
06. The halfway intelligent ones don't use weak links.
07. The smart ones use one and a half to two G weak links.
08. They don't use tension controlling devices or gauges, they have NO FREAKIN' CLUE what their tensions are, and their tensions are all over the map in the violent thermal conditions in which they most like to fly.
10. They don't use minimum 500 foot nylon towlines. They use maximum 250 foot spectra towlines.
11. They don't do "constant direction". If the tug finds a thermal it immediately banks on its ear to hook it and the glider immediately banks on its ear to follow. If the glider gets kicked to the side the tug moves to get back in front of it.
12. They don't talk to each other on radios. They watch each other and use common sense.
13. Except for takeoff and waveoff they don't even use hand signals. They use plane signals - fer instance, the glider being low is a signal to the tug to gas it and dive.
According to Donnell's assumptions, prediction, criteria the smart one point aerotowers would all be dead after two or three tows in smooth conditions at best. And, in reality, even the ones using Straub/Rooney links, releases, and bridles usually survive a couple of dozen.
REAL WORLD safe aerotowing criteria for based on REAL physics and common sense?
1. Use a one to one bridle or, if you're feeling a little lucky, a one point.
2. NEVER foot launch.
3. "Never take your hands off the bar." - Tom Peghiny
4. "The greatest dangers are a rope break or a premature release." - Richard Johnson
5. "A bad flyer won't hurt a pin man but a bad pin man can kill a flyer." - Bill Bennett
6. Elasticity is a four letter word.
7. Any talking you need to do, do it before any engines are started.
8. If you're gonna do something stupid, do it over two hundred feet minimum.
9. If you see a USHGA Safety Award or Instructor of the Year Certificate hanging on the wall in the office, leave the glider strapped to the racks, get back in the car, and drive somewhere else.
Home
I second that 
Put up or shut up. We shouldn't have to listen to an admitted drunk 
