["I bought it with 200 hrs on it and proceeded to learn how to loop on it."]
["I never thought to check there."]
The damage area is not difficult to inspect.
How many of us are flying a glider that we have never thoroughly pre-flighted?
I hope the number is much lower than I suspect.
I was at a flying site where a glider in the set-up area was flipped by a dust devil, No damage noticeable and pilot was going to fly.
Someone insisted he do a pre-flight and upon doing so found a severely broken (near the nose) leading edge.
Ian I believe if you continue to fly this way you are living on borrowed time
I know of more than one pilot who refused to admit he was acting carelessly and is no longer with us.
Please give some serious thought to your safety and that of those around you.
at the pull up of a loop you can high speed stall the glider and put many g's on the air frame.I kept breaking batten tips on my stealth 2 and i could not figure out how i was doing this.After watching someone on a topless do a proper loop i realized i was washing out all my energy on the maneuver at the pull up.A very slow over the top would always be the result.I built the titanium keel for just this reason.If your bar slips out of your hands or the vg cleat lets your vg loose in the middle of a maneuver(this happened to me) you might want a little more insurance to keep your bird together.We all blow maneuvers,i just want the odds stacked in my favor. _________________ self appointed defenders of truth and grammar.
at the pull up of a loop you can high speed stall the glider and put many g's on the air frame.I kept breaking batten tips on my stealth 2 and i could not figure out how i was doing this.After watching someone on a topless do a proper loop i realized i was washing out all my energy on the maneuver at the pull up.A very slow over the top would always be the result.I built the titanium keel for just this reason.If your bar slips out of your hands or the vg cleat lets your vg loose in the middle of a maneuver(this happened to me) you might want a little more insurance to keep your bird together.We all blow maneuvers,i just want the odds stacked in my favor.
G'day Noman. Nice to get a non judgemental post, after all I only posted in the interest of educating/warning/passing on my experience. It's not like I shot someone.
I was a little slow at the top of my loop, but wonder if I washed out some of my energy because when the bolt bent this would have increased my pull-up. I like your idea of a titanium keel (how much did that cost?), why not stack the odds in your favour. I always fly with a aerobatic specific harness, so if I'm ever slow at the top of a maneouvre I can ball up and encourage the nose to come down first. I also always fly with very sticky silicone coated box-handling gloves to aid in holding onto the bar should things go south. I too want to stack the odds in my favour, and I will be making this part of my glider stronger as I feel I can do so with no real significant increase in weight to my glider.
The way the base of the dingle-dangle is now it wouldn't take much movement of the hang strap in order for the line of force to be directly over the edge of the base. By making this base longer say 100-150 mm, the line of force will always be somewhere in the middle of the base. And like you said Noman why not stack the odds in my favour, so if I do pull up too quickly again it will take more force to break the next weak link, hopefully I'll never find the next weak link. But with one identified, and able to be rectified I'd be crazy not to.
To those who seem to be a bit negative, I don't intent to keep overstressing my glider, and has anyone else ever really thought of checking that bolt, or replacing on a schedule. I have had the frame out of my glider for full inspection once too. And I also keep physically strong, so that I can control the rate of push out over the dive recovery. I do take this aerobatic stuff a little bit serious.
Perhaps I should be in the market for a whole new glider, anyone want to buy a cheap preloved C4 _________________ C4 13, KTM 300 2-stroke.
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.
The -4/+6 G idea come from reading manufactures documentation. Go on to the airborne website and see pictures of how they are testing one glider for the 6G test.
The images show the 6G ultimate load we are applying. Each sewn tube is 5 kg of steel ball bearings. We apply the weight inside the undersurface and then the top surface to get the correct load distribution.
It looks to me like you have made some mistakes, "i know i do", the point to this post is to steer you toward "learning" from them, and not repeating them. If you are intent on doing loops, try to get to a class or seminare, Check all hardware, tubing, sail, cables twice before attempting the "gyrations" ,,,maybe hang with the guys that are doing loops and aerobatics successfully.
So that is another 2 cents worth, and Good Luck. _________________ U.S.H.G.A. # 20275
Perfect example of finding the weak point of a systems design. You can correct this one and if you keep pushing the limits you will find the next one. Fly within the manufactures recommendations and chances of a structural failure are slim to none. Exceed them and roll the dice.
Here is a quick and dirty CAD model of what I thought might work.
I am not sure if this apperatus has to swivel in the yaw direction.
Just an Idea, I do not have the dimensions to make a real model
that could be machined.
This approach would need to be subjected to finite element analysis,
to make sure that the keel would hold up.
The machining would have to be refined for weight reduction/ cost.
Edit: no good read on!
Last edited by Phoenix on Tue Nov 08, 2011 10:47 am; edited 2 times in total
The damage to the keel was caused by the sharp edge of the aluminum pedestal.
If this had been a single piece, incorporating the plastic saddle, it may have caused less damage. I'll CAD up a model, and see what you think.
That would be great, does that mean I could take the CAD file to an engineering place and get it made up? I am also going to email airborne tonight, and see what sugestions they have. I also think a bigger bolt wouldn't hurt. I believe the redesign should have a bigger bolt with 150 mm atleast wide dingle-dangle base. So atleast the edge taking the weight is not sitting over an adjustment hole.
My old man just happened to be up here visiting at the time. He reckons the dingle-dangle shouldn't be so high off the keel, is there a definite need for it to be so high? It looks as though it could be a bit lower and still have room to move, but I'm sure they would have experimented with that. Anyway I think it would be easier to lengthen the effort arm (dingle-dangle base) than to shorten the load arm (distance off keel). Maybe the effort and load are the other way around depending on your perspective
Does anyone think there was much risk of going through the keel, my old man reckons with the dingle-dangle being so close to where it connects to the base bar uprights that it would have been very strong there?
Thanks for all your input, I appreciate your comments.
A bigger bolt may do more harm than good. I have thought about some other
ways this could be configured, but it would be nice to have at least some
of the dimensions. I know quite a few places to get it made, but its really a job
for the manufacturers engineering team.
The height of the "sea-saw" above the keel acts as a longer pendulum, decreasing pitch force. Lowering it would not be good.
Repeated loading band unloading of the plastic saddle, may cause it to
deform permanently, allowing the bolt to be loose. Getting rid of that,
just puts the force directly on the keel, so it must flex.
Don't loose sight of the fact that it was the rapid acceleration of your weight,
that bent the bolt.
The slo-mo of his loops demonstrates perfect control of speed all the way through and they are just as beautiful to watch in real life.
Jonny's advice is worth listening to in terms of taking a bit of a step back, but there was a very interesting thread on this list some time ago about looping a glider, to which both Adam (AP on this forum) and Aaron Swepston contributed valuable information in terms of how to build up to loops (slowly and patiently, very slowly and patiently ). I've never been able to use the search function in this forum but perhaps someone else remembers the thread and can link.
I've flown with you Ian and know that you have a huge amount of natural talent - a few years ago Easterly Plumbing and I saw that you could stick the SS on very small spot landings when you were over our way. Most people's skills advance more slowly so there's time for the understanding to develop at a rate commensurate with technique. However, for someone with a bucket of natural talent whose skills grow so quickly, as yours clearly had, sometimes the technical understanding of what you're doing can lag behind. So for example, you could stick the glider on the spot, but couldn't yet identify what spot was the best/safest or why/why not (the effects of rotor, slope, wind direction etc).
For slow learners like me without an ounce of natural talent , the reverse is true
In any case this misalignment isn't a bad thing at all if you're aware of it because you can then make a concerted effort to advance that component of your flying, and you have terrifically skilled pilots in your local club who can mentor you.
I strongly agree with the replies that suggest you shouldn't be looking to strengthen the glider to compensate for deficiencies in your technique, but rather that you work on your technique by taking a step or two back.
Hopefully you'll be able to demonstrate some beautiful loops high over Tunkallilla next time you're down our way and I look forward to flying with you again soon! _________________ Cheers from Down Under
Falcon1 170, Fun 190, Malibu 188, Malibu 166, Shark 144, Litesport3, Adv, GT, SSO
Thanks Helen you are too kind. I'm planning on heading down your way around Christmas time again too. Its funny I've looped in NSW, QLD, and WA but never in SA, everytime I'm down there I'm just too keen to fly the floater close to the ground.
And I do intend to improve my technique, AND strengthen any areas that can be done so easily and thus increase the safety margin at both ends of the spectrum. Probably my biggest down fall is my patience like you said, I only had about 130 hrs before I did my first loop, and that was after taking about 10 years off and putting 10 or so hrs on the glider I did it on.
To the negative people, call me crazy, call me an idiot, but 100 years from now everyone on this forum will be just as dead as me, whether they looped or not. Before you start putting me down, I started this thread for some constructive ideas. And to benefit you guys.
And again for your benefit. Here is what Ricky Duncan had to say.
Thanks for the EMail. I have read a couple of EMails from the Canungra club regarding this incident.
You suggest that the glider should be "strengthened especially for aerobatics, or should I say for someone still learning to be smooth with aerobatics." The reports indicate that your loops are very poorly executed with rapid pitch up.
I think you should seriously review what you are doing because it is obvious that you are very lucky not to have had a catastrophic structural failure. Sure you can strengthen the keel but what is the next component nearing its yield point. Downtubes, side wires, cross bars etc etc
If you want to persist with aerobatics, which is dangerous you should consider doing a course and learn how to do them as well as possible to minimise the already high risk activity.
Sorry if I sound negative but I've seen gliders break from being overloaded on numerous occasions. This is with experienced aero pilots. You mention that not only are you inexperienced but you have not flown a lot recently.
We cannot give advice on "strengthening" of components for aerobatics because the certification requirements do not investigate loads outside the envelope and we therefore do not have data on hand to try to figure out what loads you are putting on the glider.
Ricky said "The reports indicate that your loops are very poorly executed with rapid pitch up."
Maybe some of my loops have been poorly executed, but here is another comment I got after my first video. "As for the loop vid, it looks good, really good for the time you have." That was a comment by Mitch Mcaleer.
I'm sure not all of my loops have been smooth, but I think the comment of very poorly executed as a general rule is a bit of an exageration. Have a look and make your own judgement. Mostly wingovers in this vid, but there's a wingover into a double loop at 2:30.
You know, I haven't really seen any "negative people" on this thread. I've seen instead a bunch of folks concerned for your safety and for your life. You might do well to listen a bit more to the "negativity" and not dig your heels in so much. Just my two cents.
those pull ups are violent.It took allot of time and watching mitch before i started doing smooth loops.As soon as you start coming out of a steep dive the control bar wants to rip out of your hands and i used to just let it out at the rate it want ted to come out.Now i resist and it gets me over the top with way more speed.ian thanks for posting this stuff.Im glad the old keel held up. _________________ self appointed defenders of truth and grammar.
I think you hit on a key point when you mentioned making the base larger so that that the line of tension from the bolt head on down through the hang strap passes well within the perimeter of the base, not outside of the base.
It seems foolish not to fix a known weak point of a design regardless of whether the aerobatic experts are ever damaging this part of the glider, or not.
Thanks for sharing both your experiences and your thoughts on a possible fix to the weak point.
If anyone else out there damages a glider in aero maneuver I sure hope they share too. It's less helpful to hear from the experts that they are not damaging their gliders in their maneuvers, unless they are also able to share precisely why and how. Aerobatic hang gliding is a bit of a "black box" and some of the forces and dynamics are not fully known to anyone, in my opinion, so we all have lots to learn.
Remember it is from the analysis of the failed maneuvers/ damaged parts, not the successful maneuvers/ undamaged parts, that we can learn the most.
i just like to say well done to ian for the open and honest way he has posted this information and responded to all replies with a degree of humility.
i think people hoped you may be more forthcoming with admitance of a problem and agree with their suggested actions.
but i say to onto them dont worry he has herd you. looking within is hard and often happens in private even when not displayed in public.
think back not that long ago, i remember a thread a year or so ago on here involving many current members about which were the best knee pads to buy. back then i thought hmm not the real issue here perhaps we might want to look at our landings. it was they who were then not keen to listen, and in defence of my slander all manour of reasoning was offered, like a demanding site, or better to be prepared etc. in the end we can only suggest ideas and people will only listen to what fits in their own personal schema.
one thing i really liked from that thread which is sort of fitting here (cant remember who said it) was something of hazard or threat management.
1. dont do it
2. if not do it a safer way
3. if not put procedure in place to minimise risk i.e checks.
4. finally accept it and issue protective equipment.
so i guess knee pads and re designing your keel, is in both cases, jumping straight to step 4. _________________ fly2 tandem (aerowtow training)
falcon 2 and 3 195
aeros Target 16
wills wing eagle 180
Airwave Sportster (L)158
Other favourites flown but not owened
Airwave Xtreme (topless), aeros discuss
There is SO much that can be said about this topic, and so little time and space for it. :-) First of all, thanks Steve for forwarding my note about the possibility of the damage being initiated by landing loads. I was at a marching band parade my daughter was in when I read the initial note, and had to reply with my phone, then yesterday was spent flying (woo hoo!), but now I have a keyboard to respond myself.
Like Steve said, I really did do even worse damage to my Xtralite keel, which had to be removed, cut apart and repaired in the Telluride LZ, following a landing after an aero round. I suppose that event could have been seen as an aero failure had it been a dingle dangle instead of a kingpost hang system, but when the kingpost gets torn off it's easy to know just when it happens. The Xtralites always had an Xtra-long keel too, so a really solid flare always ended up with the keel banging the ground first, and since my harness kept me from reaching my feet to the ground with the glider stood up vertically on its keel, I'd end up losing grip on the downtubes sometimes, or breaking the keel if I held on to the downtubes too firmly when the keel struck the ground. Most sites were nice enough to have soft ground for the keel to bury itself into, enough for my feet to reach the ground. Eventually, I cut 8 inches off the length of the keel and that solved the problem completely.
But seeing that photo of the damage to the keel from the dingle dangle bending back just didn't jive with what I would expect from an aero induced load. I always try to look at things as numbers, if I can. I have a couple of G meters that I have used now and then to get an idea of what loads I pull in loops. For me, 4 G's is pretty standard for most of my loops. I have done some nasty hard pullups by accident, way back when, and saw as high as 10.5 G's (no s***), complete with face bashing on the basetube and the complete inability to hold the basetube anywhere normal, it was yanked out to full arm extension. Long time ago, but that set the upper extreme for any loops I have done. I've seen as high as 6 in fairly hard, unusually hard pull ups, but still manageable loops. So I figure it's not unreasonable to assume people that do lousy loops, with too much or too strong of a pull up would see 6-7 G's. If you use that number, multiply the pilot weight by that, say if the pilot is hooking in at 200 pounds, you'd be seeing 1,400 pounds on the hang strap.
Then, consider the angle that that load would be pulling on the hang point, whether a kingpost or dingle dangle. On a nice, normal loop, the peak load happens with the bar further back, without "push-out", so like maybe just in form trim position, mid chest. If you blow one bad, do one of the scary "positive pitch divergency" style pull ups, that load would probably be peaking with the bar around face level or a bit out from that. So considering a normal peak load and an extreme peak load, and looking at the angle the hang point would be at the keel when pushed out to those degrees gives you an idea of load compared with angle of that load. I'll post some photos showing angle on my own glider, and anyone else can do he same, so we would have an idea whether that angle is sufficient to cause an in air failure like this one. I suspect not, but that's just me.
A reasonably easy onset of load in looping is only going to peak at whatever it peaks at, from 4 -6 or 7 G's usually. A landing where the pilot sticks the keel will peak a G load far in excess of 10 G's as a sudden, sharp, shock load. Plus, a nose high flare will put the hang strap at close to a parallel angle to the keel, the most advantageous angle possible for both creating a strong enough load and a right enough angle to rip the dingle dangle backwards.
Oh, P.S., about that flare thing. All you have to do to load the hang point and the keel up dramatically is to do a nose high flare, and when the keel hits the ground, absorb the drop shock with you legs. Squatting down fast, like if it's a decent enough flare that you can't really stand it up and have to let your legs collapse a bit, that will nail a ton of force straight down, parallel to the keel, on your hang point. Good reason to do more squats, get stronger legs, and don't fall down on a good flare. :-)