[JoeF]

so I've been thinking of how we could have a "universal" set of big wheels available that could quickly be attached to any guest glider.

Right on. Two wraps of Velcro of two wraps each?

=================================

Thanks for link and name brianscharp .
Tad collected some important whack incidents there.
Serious matter.

[JoeF]

WindSwitchAndSlightMissRunWouldBeCostly.JPG (46.09 KiB) Viewed 4236 times

Slight surprise of wind switch or surprise helicity and a costly whack could occur even on a groomed grass field.

When will the day come when it will be cool to have a good Safe-Splat handy and ready
adequate to meet many surfaces?

[reluctantsparrow]

Did a test this morning. I chose to test a simple Bungee restraint system and the device failed (allowed way too much forward swing) but the testing rig worked pretty good. Test was done with only 60 pounds of sand and the result is so violent I am seriously humbled that some of our much heavier bodies have survived these sudden stops and less surprised now so many have been injured..


Next time I will shift the camera a bit forward but this was obviously a fail. Bungee used was one of those short shock cord used to restrain horses in horse trailers.....I am going to test more of the ideas we have all shared but I am starting with ideas that should result in no damage to the test vehicle.....the idea about using the rear wires to provide a fairly sudden stop may cause the rear wires to fail and that would put a stop to all the fun so I used a bungee for the first go round.

[Bill Cummings]

Good test Jim,
I clicked on the actual Youtube link where I could select the slow motion tool.
I set it at .25 and watched the stop many times.
I think I'm seeing the yellow rope - the stopping rope- stretch about six inches from where it comes to final rest.
I don't know how much that elasticity will affect the results. I think it does have at least some mitigating factor.
I don't know how much the zip line will also mitigate the nose over results but I suspect it will somewhat.
I can't think of a way yet to adjust for those elastic forces. Or if it is necessary to do so.

With the lower wire restraint to the harness if there is a failure I believe it will most likely be the keel tube kinking down and slightly to left or right with the kink just ahead of the anchor bolt for the rear keel wires. (The kink will jump up and the very tail end will go down.)
The reason for left or right is because the king post rear wire is right on line with the keel tube.
I broke tested a keel by launching from a moving boat with the keel tied to the boat.
The rope to the keel was right behind the rear anchor bolt but the keel kinked 3 to 4 inches ahead of the anchor bolt when everything went south.

[JoeF]

RS001.JPG (59.12 KiB) Viewed 4219 times

[reluctantsparrow]

Ah! Point taken Joe. Next test I will fold the shock cord onto itself and lengthen the non-stretching portion to allow half the stretch as in the previous test to see Where the pilots head ends up .
the Bar mounted half way down the rear wires is a short piece of downtube with slots cut lengthwise at each end...dipped in iiquid rubber to soften the edges..the tube fit neatly over two copper ground clamps on the rear wires as suggested by Bill. This did not cause any rear wire failure and the short DT length handled the load just fine as well.
so I guess this first test was not a total flop. Always something to be learned eh?

[Bill Cummings]

Ah! Point taken Joe. Next test I will fold the shock cord onto itself and lengthen the non-stretching portion to allow half the stretch as in the previous test to see Where the pilots head ends up .
the Bar mounted half way down the rear wires is a short piece of downtube with slots cut lengthwise at each end...dipped in iiquid rubber to soften the edges..the tube fit neatly over two copper ground clamps on the rear wires as suggested by Bill. This did not cause any rear wire failure and the short DT length handled the load just fine as well.
so I guess this first test was not a total flop. Always something to be learned eh?

I suggest you check your rubber dipped down tube each test for remaining rubber.
And thimble deformation of the lower rear wires.

[reluctantsparrow]

the pulleys are fried. They were plastic. got em at a yard sale for a buck each...going to emai a zipline outfit for better pulleys.
They have to replace pulleys every year and might give them away for non-life threatening experiments.....
But I did get one more test in today.
Shortened the bungee, and in slow motion I must say.....the pilot swings forward to the extent of stretch available...but NOT up into the keel....when the rear leash goes tight the pilots body appears to stop all upward movement.
but....new pulleys....a faster crash speed.....more weight in the harness....and check thimbles and tube for wear....later...RS

[Bill Cummings]

Wow Jim,
You are really closing in on the best safe splat so far for HG.
So it looks like the leash goes tight and then there is some stretch happening -- is that right? Edit yes I see that there is.
I would figure that with more weight more stretch will occur. What would you estimate the max effective speed should be planned for - for a realistic or at least average crash?

[reluctantsparrow]

Wow Jim,
You are really closing in on the best safe splat so far for HG.
So it looks like the leash goes tight and then there is some stretch happening -- is that right? Edit yes I see that there is.
I would figure that with more weight more stretch will occur. What would you estimate the max effective speed should be planned for - for a realistic or at least average crash?

All the stretching takes place below the no-whack bar.....a solid line runs from the rear flying wire junction to just below the no-whack bar where a shock cord is installed long enough to allow a pilot to fully stuff the bar before going taught.
the shock cord is a simple stabilizing leash for horses (for use in horse trailers) I bought for 18 dollars at the local feed shop. It is 22 inches long and doubled up for the second test.

Max effective speed? NO idea. Better pulleys, more weight, and SOMETHING to measure g load....
If a simple bungee and a bar really would do the job...how cool is that?
But you know and I know.....no one is going to fly with this set up...maybe one or two out of twenty pilots....
Can i tell you a little secret? I am not too impressed by the hang gliding community at large...I am really not...you guys I like. you guys are smart..like Frank...Frank is smart...BiG WHEELS!....DUH!
But how many pilots fly with them?...no...they like the teeny tiny hard plastic wheels that are NOT adequate for the terrain they fly over.
I know a great guy who is in a wheelchair right now that 12 inch wheels would have probably prevented....it happened at a comp...a blown launch...and the terrain below launch is perfect for 12 inch wheels but not small hard plastic do nothing wheels......
The guy was a great pilot and his glider never got flying....full speed run....glider het out ahead of you....we all know what happened next....and yet....go to a comp today at Chelan this year and count how many 12 inch wheels you see on launch......yeah, right...

That is why I say most pilots are not going to use this device Bill, but when it gets all sorted out I sure the hell will.
a properly designed device mounted to a properly reinforced glider chassis should provide the same crash protection as a fricken Airbag on a car....or better.....our harnesses hold our bodies and distribute Gs much better than a seat belt does....and we have twelve inches of travel to play with behind us! TWELVE INCHES!!!
thats a LOT...most airbags on cars dont give you twelve inches of protection and they are slamming you in the face when they do it...not pulling from behind like we are....
heck...properly designed? properly tested and mounted to a properly reinforced giider?
I think a high speed crash in a hang glider could someday become safer than a high speed crash in an automobile.
And I still bet no one flies with them if they dont have to.