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ian9toes
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 Posted: Sat Nov 05, 2011 2:47 pm Post subject: |
 #21 |
| Dan Harding wrote: |
| After some more thought and another look at the pic, it sems to me that the G-force is not straight down through the keel, if it had been, the bolt should not have bent and only the keel would have been damaged, just sayin. |
Yeah definitely, while pitching up on a loop my weight would be pulling down from behind. Which is why I think it is possible that the keel gave way first or maybe the keel was already damaged. Something worth inspecting if you engage in aerobatics.
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ian9toes
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| Posted: Sat Nov 05, 2011 2:53 pm Post subject: |
#22 |
| Hangskier wrote: |
To me the keel does not look like the weak point. Looks like the bolt bending caused the keel to break.
Wonder how many hrs the glider has on it and how many loops. Wonder if the bolt was replaced after so many hrs or loops if this would have still happened.
I see the nut on the dd has been removed a few times.
Wonder in GA or helos, is there any bolts that get more stress than others that are replaced at a certain number of hrs?
What about the Dragon Fly (they get a lot of stress), are there any bolts that are replace at certain number of hrs?
Are AN bolts of the same size have the same strength? Don't think a larger bolt would be the answer due to that would require a larger hole and weaken the keel.
These are a few questions that pop into my mind.
Thanks for sharing. |
To answer your questions on the gliders back ground. I bought it with about 200 hrs on it then proceeded to learn how to loop on it, and have done dozens of loops/big winovers on it. Not all my maneouvres have been smooth either. I never thought to check there.
I believe a bigger bolt would be a good idea. Yes a bigger hole would weaken the keel, but it is also sleeved there as well.
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ian9toes
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| Posted: Sat Nov 05, 2011 2:55 pm Post subject: |
#23 |
| Dan Harding wrote: |
| From the pics, it appears that the keel is sleeved in that area, maybe a bigger dia.bolt with a saddle that spreads the load out fore and aft over a longer area would suffice. |
I think that's pretty much all it needs, as long as the saddle is strong enough, I would like see a longer dingle-dangle base also.
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ian9toes
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| Posted: Sat Nov 05, 2011 2:57 pm Post subject: |
#24 |
| Cloudhopper wrote: |
If you had separated from your wing on that pull-up, how would you have fared in a free-fall deployment? Did you have enough altitude to get your laundry out? You DO know how close you came from blowing through that keel, don't you?
Tom |
So you reckon I could have easily seperated?
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ian9toes
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| Posted: Sat Nov 05, 2011 3:01 pm Post subject: |
#25 |
| jjcote wrote: |
| Dan Harding wrote: |
| After some more thought and another look at the pic, it sems to me that the G-force is not straight down through the keel, if it had been, the bolt should not have bent and only the keel would have been damaged, just sayin. |
Well, no, you wouldn't expect it to be, would you? It should only be straight down at one pitch position, probably at trim, or close to it. If he were pulled in for speed, there would be a forward component to the force on that bolt.
The longer fore/aft that the "saddle" on top of the keel extends, the smaller the force on the end of it. I'd be inclined to replace that piece with a homemade one (maybe machined out of aluminum?) that's maybe 10 cm long, to keep this from happening again.
What does the other side of the keel look like? Did the nut make a dent there as well? |
No there is no dent on the other side.
Someone else asked if the bolt was a bit loose, I don't know for sure. But I guess if it was I would have noticed everytime I move my dingle-dangle into postion, it would have felt sloppy, so I'm gunna say to the best of my knowledge it wasn't loose.
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srskypuppy
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Joined: 01 Jun 2008
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Location: Brisbane, California
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| Posted: Sat Nov 05, 2011 3:27 pm Post subject: |
#26 |
Here is an interesting reply from a long time aero buddy of mine:
"I suspect that the keel and bolt were possibly weakened previously through landings.
Good flare, stick the keel, and if the pilot doesn't stand up the body weight jerks down hard on the hang point.
I tore the kingpost off my Xtralite by doing a big, high flare, stuck the keel in the ground and before my feet could reach the ground my weight ripped the kingpost off, wrecking the keel just like those photos.
That's the only way I can see enough lateral load to do that kind of damage."
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Andrew Vanis
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| Posted: Sat Nov 05, 2011 3:42 pm Post subject: |
#27 |
guess you could always sleeve with a solid piece of plastic rather than just another alum tube. Easier than making up a special saddle.
It would be interesting to see where the next weakest point would be. |
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ksykes
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| Posted: Sat Nov 05, 2011 3:50 pm Post subject: |
#28 |
| Quote: |
| I don't want to disreguard the fact I have, and posibly did just recently push out too rapidly, but the gliders are rated for 6g's and I've gotten away with it before. I believe it is very possible that the keel was already weakened from previous abrupt maneouvres, and therefore a better design in this area would do heaps for my safety. |
I am not a looper, but if someone of Jonny's caliber has watched you loop and has concerns, I'd be looking at how I loop vs. reinforcing the keel.
Just my 2 pence. |
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ian9toes
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Location: Gold Coast
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| Posted: Sat Nov 05, 2011 4:30 pm Post subject: |
#29 |
| srskypuppy wrote: |
Here is an interesting reply from a long time aero buddy of mine:
"I suspect that the keel and bolt were possibly weakened previously through landings.
Good flare, stick the keel, and if the pilot doesn't stand up the body weight jerks down hard on the hang point.
I tore the kingpost off my Xtralite by doing a big, high flare, stuck the keel in the ground and before my feet could reach the ground my weight ripped the kingpost off, wrecking the keel just like those photos.
That's the only way I can see enough lateral load to do that kind of damage." |
Very interesting, I hadn't considered that before.
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ian9toes
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| Posted: Sat Nov 05, 2011 4:31 pm Post subject: |
#30 |
| ksykes wrote: |
| Quote: |
| I don't want to disreguard the fact I have, and posibly did just recently push out too rapidly, but the gliders are rated for 6g's and I've gotten away with it before. I believe it is very possible that the keel was already weakened from previous abrupt maneouvres, and therefore a better design in this area would do heaps for my safety. |
I am not a looper, but if someone of Jonny's caliber has watched you loop and has concerns, I'd be looking at how I loop vs. reinforcing the keel.
Just my 2 pence. |
I will be looking at both.
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Last edited by ian9toes on Sat Nov 05, 2011 4:41 pm; edited 1 time in total |
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AIRTHUG
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Location: Point of the Mountain, Draper, UT
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| Posted: Sat Nov 05, 2011 4:35 pm Post subject: |
#31 |
I have a few thoughts I would like to add to this discussion.
First, I'll point out that a while back I sent Ian similar correspondence as Jonny Jr sent. It was about the time Ian picked up that glider and started getting very upside down very quickly... and posted video of some slowburgers.
If Jonny Jr saw you in action, fairly recently, and sent that message- perhaps you should heed his warning. Notice that he didn't outright say DON'T LOOP... he said perhaps YOU should stop looping. Hard to hear, I'm sure... but like I told you when we exchanged PM's, doing steep aerobatics properly (and as safely as possible) requires MUCH practice and preparation. And most of all, it requires patience... which your lack of is why I contacted you initially.
IN RESPONSE TO THIS RECENT INCIDENT:
I agree, based on the pictures, that the damage on the keel was caused by the saddle... AFTER the bolt bent, which allowed the saddle to cut into the keel like that.
I do not think the CG adjustment holes were the issue, since even with the damage to the keel, there was enough strength for you to continue flying without things folding up. And yes, if the keel broke all the way through, you would have separated... no doubt about it. The keel was obviously strong enough, as it kept you alive!
If anything WASN'T strong enough, you should FIRST be talking about the saddle. If it were one piece, rather than a metal piece on top of a plastic piece, the bold could not bend where it did. Or a stronger bolt... but I personally woudln't want bigger diameter holes through the keel. The holes in the keel and the saddle should really keep that bolt in line, without slack it shouldn't be able to bend at all.
BUT- since there are LOTS of people flying Airborne Climax gliders out there, and this is possibly the first of these failures... perhaps you should be looking INWARD for the problem. See Jonny's note...
Nothing is unbreakable... and gliders are not designed for, or tested to, the speeds or forces we hit when looping.
AND NO, YOUR GLIDER ISN'T CERTIFIED FOR 6G's. I don't know where the "-4/+6 G" idea came from, but it ain't true. At least not for HGMA certification here in the U.S. There's actually NO G rating at all.
Since you admittedly did it wrong, and have many other times, and you haven't broken anything until now... you pretty much prove your glider is STRONGER than 'strong enough'. You just found how far is too far, or how many times is too many times, going too far...
Higher speeds and bank angles require much more responsibility... saying parts of the glider aren't strong enough because YOU pitched out too hard (again) isn't where it's at.
Open your eyes... you're lucky to be alive.
Your glider SAVED you, when you tried to kill yourself. (Not the other way around, the glider didn't try to kill you)
I'm sorry for the harsh words... but I hope this gets through to you. I wish you the best, and many fun and SAFE flights to come.
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ian9toes
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| Posted: Sat Nov 05, 2011 4:36 pm Post subject: |
#32 |
| Andrew Vanis wrote: |
guess you could always sleeve with a solid piece of plastic rather than just another alum tube. Easier than making up a special saddle.
It would be interesting to see where the next weakest point would be. |
That's not a bad idea. My only concern is that if you make one piece of something extra strong, right beside that becomes a weak point, weaker than if you hadn't beefed up the piece right next to it. But definitely a worthy of consideration, given that the weak point of a keel would normaly be in the middle, and the hang point is right next to the uprights. I think this idea has a lot of merit. What does everyone else think?
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AIRTHUG
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| Posted: Sat Nov 05, 2011 4:37 pm Post subject: |
#33 |
| srskypuppy wrote: |
Here is an interesting reply from a long time aero buddy of mine:
"I suspect that the keel and bolt were possibly weakened previously through landings.
Good flare, stick the keel, and if the pilot doesn't stand up the body weight jerks down hard on the hang point.
I tore the kingpost off my Xtralite by doing a big, high flare, stuck the keel in the ground and before my feet could reach the ground my weight ripped the kingpost off, wrecking the keel just like those photos.
That's the only way I can see enough lateral load to do that kind of damage." |
I very much respect the pilot that posted that response (quoted above) to the aero list.... and after reading it, I have to agree completely.
The fact that he has personal experience with very similar damage proves the theory is sound.
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fakeDecoy
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| Posted: Sat Nov 05, 2011 4:57 pm Post subject: |
#34 |
I'm no engineer, but I don't see a few G's bending an aircraft bolt that way. I would think something had to have been bending before that, due to a shock load of several Gs. Like the base bar or wheels of a loaded glider hitting the ground hard, or a hard recovery in the air from zero G, or even just a dumbass hang check.
Used topless gliders can be friggin dangerous. And I don't mean hangidling.org dangerous, I mean real-life dangerous.
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Paul H
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| Posted: Sat Nov 05, 2011 5:14 pm Post subject: |
#35 |
It would be an interesting experiment to test that out. 3 G's with a pilot hook-in weight of 250 lbs would give a loading of 750 lbs, 4 G's would be 1000 lbs. It would be easy enough to find out if that size (diameter and length) bolt would survive it or not. Fasten the threaded end in something solid and drop the load fastened at the head end. I'm pretty sure it would fail at 4 and very possibly at 3.
| fakeDecoy wrote: |
I'm no engineer, but I don't see a few G's bending an aircraft bolt that way. I would think something had to have been bending before that, due to a shock load of several Gs. Like the base bar or wheels of a loaded glider hitting the ground hard, or a hard recovery in the air from zero G, or even just a dumbass hang check.
Used topless gliders can be friggin dangerous. And I don't mean hangidling.org dangerous, I mean real-life dangerous. |
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ian9toes
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| Posted: Sat Nov 05, 2011 5:31 pm Post subject: |
#36 |
AIRTHUG, thanks for your input. Yes I can be a bit short on patience, and I don't always fly on a regular basis, but tend to go out and throw it around as though I have been flying regularly.
| Quote: |
| saying parts of the glider aren't strong enough because YOU pitched out too hard (again) isn't where it's at. |
Maybe so, but if I've indentified a weak spot that can be redisigned, I'd be stupid not to.
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AIRTHUG
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| Posted: Sat Nov 05, 2011 5:39 pm Post subject: |
#37 |
You identified the weak spot all right... it wears a harness and hangs between the uprights.
Reinforce the keel, saddle, bolt all you want... if it's not that, something else will fail.
Learn to do it WITHOUT failing a perfectly strong aircraft. Other people do it fine on that very same glider. Google Adam Parer for one...
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Hangskier
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| Posted: Sat Nov 05, 2011 6:00 pm Post subject: |
#38 |
| ian9toes wrote: |
To answer your questions on the gliders back ground. I bought it with about 200 hrs on it then proceeded to learn how to loop on it, and have done dozens of loops/big winovers on it. Not all my maneouvres have been smooth either. I never thought to check there.
I believe a bigger bolt would be a good idea. Yes a bigger hole would weaken the keel, but it is also sleeved there as well. |
Pilot error or bolt fatigue ........ 200 hrs when you bought it and......previous owner did what, 1000 9G Loops...Do you even know? I assume you bought this from a friend that stored the glider at your house and you saw each take off, flight, loop, and landing?
Dude, you are looping a previous owned glider and a couple experienced aero pilots say you have bad form and you are thinking of design flaw. As Ryan said...your are lucky the glider saved you.
Just my 2 cents from maybe a less experienced pilot. |
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jjcote
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| Posted: Sat Nov 05, 2011 6:55 pm Post subject: |
#39 |
Has anybody else had a failure of this nature? Or have you done something with the glider that nobody else has?
(Having looked at the pictures and thought about it some more, I take back what I said about replacing the part. Making a new one is doable, but not easy -- however, I think the part that's there should be adequate for the situations that the glider should probably be exposed to.)
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aeroexperiments
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| Posted: Sat Nov 05, 2011 7:01 pm Post subject: |
#40 |
| Hangskier wrote: |
Dude, you are looping a previous owned glider and a couple experienced aero pilots say you have bad form and you are thinking of design flaw. As Ryan said...your are lucky the glider saved you.
Just my 2 cents from maybe a less experienced pilot. |
Wake up and smell the coffee, it's hang gliding, aerobatic hang gliding to be specific, a sport with inherently narrow margins, or less. A few months ago I was teaching myself loops in a sailplane made in about 1975 with no worries, yeah I got a little neutral/ negative and the dust fell out of the tailcone and got into my eyes, wah wah wah. I didn't fall into the keel, or break anything.
Back to hang gliding-- If the aerobatic gods intimate that you don't have the right juju you should probably listen, whether you believe it or not, whether they can explain precisely what your problem is or not, the margins in this sport being as narrow as they are...
PS there may be a few others interested in whatever engineering fix you come up with, others who have never passed the acid test of getting a thumbs-up looking cool looping in front of one of the aerobatic gods, so please pass it on...
Steve |
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