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HangDiver
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Joined: 06 Nov 2007
Posts: 2085
Location: Salida, Villa Grove, Colorado
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Wingspan34
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Joined: 14 Mar 2007
Posts: 5652
Location: Central NY
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 Posted: Sat Nov 24, 2007 4:25 pm Post subject: |
 #2 |
I'm not afraid of tumbling*, but those articles were very informative and enlightening. Some of the information is very simple, almost common sense. But some of what you might think you should do, is actually just the opposite from what is actually best. (i.e. pulling in in a "tuck" situation - is best!)
And, anyone with an older glider should read the second article, in particular. In fact, I need to check my own sail height at my sprongs since my glider's sail is nearly 6 years old. Sail shrinkage (and its results) is not something to ignore.
* Not because it's not scary, but because it is very rare. |
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franklingrx
3 thumbs up
Joined: 06 Sep 2007
Posts: 396
Location: Maui/Florida
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| Posted: Sat Nov 24, 2007 5:55 pm Post subject: |
#3 |
On a flight in 98, admittedly rough air, I went over the falls straight ahead, in my K5, not with any particularly pitching moment, but a little. I pulled in hard, but the glider kept nosing over, the bar was very light, but it seemed like I had more than an adequate amount of airspeed. Finally the sail "caught" as I was pointed straight at the ground (maybe beyond) and going pretty fast. I returned to normal flying, but not until I had lost a lot of altitude. I flew on out to the lz, but was very nervous the whole time.
I had been over the falls plenty of times, but not with glider behavior like that. I was a bit freaked and didn't fly for a few months, but after reading the Meier article, by chance, I pulled out my manual, which described the method for measuring the position of my trailing edge relative to the keel. The trailing edge was 3-4 inches low!!!! I called airwave and they said shrinkage! I fixed it by adding shims to the luff wires, so I could take them out, if the sail stretched back out. The glider flew normally after that.
It's not one of those things that is well documented, but should probably be part of all training programs, like other basic glider inspection-maintenance routines.
Bob Franklin |
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Vrezh
2 thumbs up
Joined: 19 Nov 2006
Posts: 367
Location: Los Angeles
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| Posted: Sat Nov 24, 2007 8:00 pm Post subject: |
#4 |
Glad you broth up the subject.
Most pilots pay attention to the shape of their gliders only after a mishap of a some sort.
But it changes because of the materials and stress.
SS and lower to mid end intermediate gliders won't show a noticeable change in their behavior or stability.
It is a good idea to check your glider every season for the planform, airfoil and stability deviations. Especially high performance gliders.
Vrezh. |
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Nibs
3 thumbs up
Joined: 29 Dec 2006
Posts: 2612
Location: Atlanta, GA
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| Posted: Sun Nov 25, 2007 6:44 am Post subject: |
#5 |
Great collection of articles. Thanks for posting that!  |
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spekkinout
3 thumbs up
Joined: 29 Jun 2007
Posts: 593
Location: BC Canada
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| Posted: Sun Nov 25, 2007 7:49 am Post subject: |
#6 |
| franklingrx wrote: |
On a flight in 98, admittedly rough air, I went over the falls straight ahead, in my K5, not with any particularly pitching moment, but a little. I pulled in hard, but the glider kept nosing over, the bar was very light, but it seemed like I had more than an adequate amount of airspeed. Finally the sail "caught" as I was pointed straight at the ground (maybe beyond) and going pretty fast. I returned to normal flying, but not until I had lost a lot of altitude. I flew on out to the lz, but was very nervous the whole time.
I had been over the falls plenty of times, but not with glider behavior like that. I was a bit freaked and didn't fly for a few months, but after reading the Meier article, by chance, I pulled out my manual, which described the method for measuring the position of my trailing edge relative to the keel. The trailing edge was 3-4 inches low!!!! I called airwave and they said shrinkage! I fixed it by adding shims to the luff wires, so I could take them out, if the sail stretched back out. The glider flew normally after that.
It's not one of those things that is well documented, but should probably be part of all training programs, like other basic glider inspection-maintenance routines.
Bob Franklin |
Pecofly had this exact same issue with a Klassic, said it didn't feel right in the air and felt like it might tuck or not recover from a dive. We measured the trailing edge at the keel and found it several inches low too. Strangely, the glider had been flying fine before that, but this might have been at the start of a new season, I don't recall. I would have thought this would be a progressive thing happening over time, not one flight it's fine and the next it's not. That made me think something inside the kingpost to do with the VG compensation system may have broken. It just seemed that the several inches low was too excessive to be explained by sail shrinkage or stretch, but maybe not.
This was one of his (many) backup gliders, so he just put it away and pulled another one out of the quiver, I don't think it's ever been fixed or looked into further. Might be worth another look, Pecofly, that glider is otherwise in immaculate shape!  |
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sg
3 thumbs up
Joined: 17 Jul 2006
Posts: 11030
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| Posted: Sun Nov 25, 2007 8:32 am Post subject: |
#7 |
I wonder if sail shrinkage could have a similar effect on topless gliders with sprogs inside the sails.
_________________
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Aeros Stealth III 142
| Thomas Jefferson wrote: |
| All tyranny needs to gain a foothold is for people of good conscience to remain silent. |
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franklingrx
3 thumbs up
Joined: 06 Sep 2007
Posts: 396
Location: Maui/Florida
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| Posted: Sun Nov 25, 2007 10:07 am Post subject: |
#8 |
| spekkinout wrote: |
Strangely, the glider had been flying fine before that, but this might have been at the start of a new season, I don't recall. I would have thought this would be a progressive thing happening over time, not one flight it's fine and the next it's not. |
I can't remember how long it had been since I had flown that glider, but it could have been 3-6 months... My flying has always been on again off again, and I often go 6-8 months without flying and then it's just about every day for months. Work deadlines come and go.
I remember at the time, it didn't seem unusual that this would have been noticed suddenly, so it was probably just after a layoff... plus, this was a ratty day, and most of the flying on maui is not that rough. |
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