Bob,
Re: missing release
bobk
2011/05/13 13:13:54 UTC
Cutting it a bit close aren't you? 41 seconds earlier and you coulda brought the apocalypse down on all of our heads.
Since your current browser has trouble uploading images, I've taken the liberty of posting them here.
I can do 'em anywhere just by logging on with the other Mac - just thought I'd save the bandwidth. But, what the hell, as long as you've got them up and side by side...
I REALLY like the twin barrels over the three-string.
The ONLY advantage that the three-string configuration has is that there's ZERO possibility of a bridle wrap 'cause the release is upwind of the bridle.
1. But if you put releases on bridle ends you double their capacities ('cause they're only feeling (a bit more than) half the towline tension).
2. Even with only half the load on one a barrel release kicks a three-string's a** with respect to slack line performance.
3. With proper design, the bridle wrap issue is virtually zero - and you've got another release to deal with it anyway.
4. There are, for all practical purposes, zero abrasion/wear issues associated with towing and actuation.
5. The mechanisms are simpler and cheaper.
6. The load is always distributed equally between the two anchor points (tow loops on the harness). (With that three string configuration you could get the full load going to just one tow loop through just one bridle half.)
Zack,
I don't know and I don't know if anyone does.
I'm kinda surprised and disappointed.
I'd love to know what the actual tensions are (not just at launch but through the whole tow)...
1. Get Sam to bring his 200 pound scale next time - if you don't have one.
2. Tie it to a trailer hitch and simulate a launch.
3. I think you can get pretty close to what's going on at altitude just by doing the math for the reduced spool diameter and throwing a few more pounds in to account for the line that's being lifted.
...though I don't think it's all that important in the end.
1. The flight park a**holes have gotten off a few zillion tows having no freakin' clue what the tension of the line is. Likewise with respect to the strength of their (our) weak links.
2. I asked Sunny what the towline tension was, he told me he was tired of not being able to answer that question and asked me to get some numbers.
I rigged a cylinder and got some numbers for me on my HPAT 158 (320 pounds, VG on) behind a 914 Dragonfly - vanilla and turbocharger kicked in (125 and 155 pounds). But for the last couple years before the sonsabitches kicked me out they could never be bothered to let me go up four hundred feet on a tandem to get another really useful data point. With those weight, glide ratio, and climb rate numbers I coulda made some pretty good predictions for other gliders.
Michael Derry - 2001/10/02
The climb rate for the 914 is mind blowing !!!!!!!! I wonder how much extra tension is pulling the hang glider say in KG's?
Tracy Tillman - 2001/10/02
I don't know--there is some.
Stupid useless bastards.
(And instead we gotta deliberately release from the bottom and jam the bridle to see what happens to a Falcon when you tow it from the keel.)
No one suggested it could cause a decrease.
It's confusing 'cause TO COMPENSATE for the line drag and what it's doing to the glider you've gotta INCREASE the tension at the truck.
I'm having a hard time wrapping my brain around this.
Me too. Try this...
Choo-choo train. Locomotive, a thousand horsepower, a hundred empty boxcars, a caboose, a hundred miles of straight track in Kansas, no wind.
Most of what the engine is working against is the aerodynamic drag of each and every boxcar - and the caboose.
There's a zillion pounds of loading on the coupling between the engine and the first boxcar. But at (call it) twenty miles per hour you could probably hold the caboose to the last boxcar yourself without being torn in half.
That's essentially what's going on with the drag and tension with respect to the towline. It just gets confusing 'cause the towline drag is so negligible compared to that big min sink / high angle of attack drag generating caboose you're trying to move up a two thousand foot mountain with ever increasing train length.
In the end I think it's a bit academic since other factors appear to affect tension a lot more.
It's hugely academic. But knowledge is power and that's all you're got going for you against tug drivers.
Be that as it may, there is a wealth of excellent information on this thread. Thanks.
Delighted. But if you need a little entertainment to break up the tedium check out the Julia Kucherenko thread. They totally skipped releases and wheels and are now discussing the best ways to administer CPR. Somebody please let Bill Bryden know about it.
Sam,
I think the line that failed on my release is the same size as your last loop that engages the tow line on Zack's release.
Me too. Which would make it 205 leechline.
I'm thinking that two knots came untied with the increased forces/tension.
I'm thinking that that's about the looniest configuration anyone's concocted in a very long time.
1. You can't get to it when you need to.
2. The bridle is high stretch.
3. It uses an unbent bent pin.
4. When you blow - or lose - the weak link you lose the release.
5. The weak link is half as strong as it should be so you're pretty much guaranteed to lose the release. (So he can sell lots of them?)
6. The weak link is a U which appears to be tied to the bridle apex with two Bowlines. It should be a loop formed with a Fisherman's Knot. Bowlines are OK as long as they're under uninterrupted loads - otherwise they're a real bad idea. People die when things connecting gliders to winches come undone.
7. There's a length of leechline connecting the release to the bridle (in addition to the weak link) which, as far as I can tell, serves no function whatsoever. It just blows after (or possibly before) the weak link does.
Reconfigure your remaining release so's it looks like Zack's.
On -windy- days while on tow, the rope is at ~45* angle.
The rope and glider can't differentiate (head)wind from truck and winch generated no wind airspeed. If the winch is turning the same RPMs (read the truck is maintaining the same airspeed) the angle's gonna be the same.
When the vehicle slows or even stops, and you are still climbing, flight path has to be in an arc.
You can't predict what the flight path of a climbing glider's gonna be with a payout winch. It can be an arc curving forward or aft, a straight line straight up or angled forward or aft, or just about anything else the driver, pilot, and wind wanna make it.
At the top of the tow/arc, if the spool is not turning, and you are still climbing, at some point you will be climbing/flying farther away from the vehicle/winch. Like going into orbit.
No. As long as the spool is stopped (and the line is tight) you're in static tow mode and there is absolutely nothing you can do to change your distance from the vehicle. If you're lined up and climbing you WILL be describing an arc - relative to the vehicle.
That would cause a spike in line tension.
No, the tension's not gonna spike unless unless there's something going on with the gas pedal, basetube, gradient, or thermal activity.
But then why won't the winch spool out?
You know you've got drum inertia combined with the issue of the rotor being harder to break away from the brake pressure than keep turning under the brake pressure.
Thanks
And thanks for participating.