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Bertram
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PostPosted: Sat Feb 20, 2010 11:23 am    Post subject: HG design and landing characteristics (flare in nil wind) Reply with quote #1   
I'm wondering, why most modern high performance HGs are so much easier to flare in nil wind conditions compared to the (very) old kingposted high performance HGs (e.g. the WW HPAT 158; at least my painful experience).

The only main difference I know of is the further rearward apex of the control frame, which I can't believe is the only reason for easier flaring authority and the not so tight flaring window of modern gliders.

Does anyone know more about it?

Cheers, Bertram
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bobk
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PostPosted: Sat Feb 20, 2010 11:37 am    Post subject: Glider or Pilot? Reply with quote #2   
Are you sure you just haven't become a much better pilot over the years? Smile

Actually, I'm sure gliders have improved in many ways, but I didn't want to overlook the fact that our perceptions do change with time.

Good luck with the topic!!

Bob Kuczewski

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jimrooney
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PostPosted: Sat Feb 20, 2010 1:00 pm    Post subject: Reply with quote #3   
There are lots of things for sure, but the apex change was quite significant.

As the story goes from Paris... he came up with it while working at Wills Wing.
It's a leaver arm issue. If the apex is in front of the hang strap, then you're trying to lift yourself with the keel (counterproductive)
If it's behind the hang strap, you're rotating the keel... much much easier.

We've modified old KPL Stealths in this manner, moving the apex behind the hang point. Huge difference.

Jim
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ChattaroyMan
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PostPosted: Sat Feb 20, 2010 1:10 pm    Post subject: Reply with quote #4   
jimrooney wrote:
It's a leaver arm issue. If the apex is in front of the hang strap, then you're trying to lift yourself with the keel (counterproductive)
If it's behind the hang strap, you're rotating the keel... much much easier.

We've modified old KPL Stealths in this manner, moving the apex behind the hang point. Huge difference.

Jim


good idea Ahhh.... Now I get it. I was wondering why I was seeing the hang loop so far in front of the control bar @ the keel in modern gliders. I just figured it was due to the geometry for folding up the glider or other similar reason.

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peanuts
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PostPosted: Sat Feb 20, 2010 1:17 pm    Post subject: Reply with quote #5   
hangy-down straps above the keel aka kingpost hang probably don't hurt none neither
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Bertram
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PostPosted: Sun Feb 21, 2010 12:54 am    Post subject: Reply with quote #6   
Thanks, Jim!

I suspect too much washout at the wingtips also to be detrimental since they are still producing lift after the wing's middle section has already stalled during the flare. Because their lift is acting behind the hang point this might aggravate the tendency of the glider to punch its nose into the ground. On the other hand the flare window is probably not that tight with more washout.

Did anyone play around with wingtip tuning and can report on its effect on flaring characteristics in nil wind?

Bertram

@ChattaroyMan
Apex further back is more of a problem for riging and tensioning a glider in strong winds laying flat on the ground, since the bottom side wires do get too short. That's why the WW XC (and the RamAir) had these apex sliding rails on the keel. Many modern gliders can't be rigged flat on the ground any more.
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jimrooney
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PostPosted: Sun Feb 21, 2010 1:02 am    Post subject: Reply with quote #7   
Wing twist has a direct effect on the "flare window" as you say.
It is exactly as you describe it... the more twist, the more the tips are fighting you when you "flare"

Yup, you can directly test this if you like.
Do be careful to only try this in very smooth conditions, big field, big approach, etc....
Land full VG.
It will be the most crisp flare you'll ever do.

It will be this way because much of the twist of the glider will be gone so the tips will stall very closely to when the root stalls. It will be very easy to stall the entire wing... which is actually what you're trying to do when you "flare".

Please do not however try to pull off a late flare with full VG. You will pound the hell out of your glider.

Jim
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NMERider
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PostPosted: Sun Feb 21, 2010 7:15 am    Post subject: Reply with quote #8   
Interesting thread! I was gone from the sport when the control bar apex was moved aft. I imagined it was to make it easier to balance the glider on one's shoulders. I never thought about the increased effective reach it gives your arms for flaring when they're held high on the uprights.
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remmoore
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PostPosted: Sun Feb 21, 2010 8:17 am    Post subject: Reply with quote #9   
"(e.g. the WW HPAT 158; at least my painful experience)."
Yeah, the HPAT specifically had quite the reputation as a crater-maker, at least in my neck of the woods. I never flew one, but I know WW's subsequent Ram-Air and XC gliders were somewhat better.

RM
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fakeDecoy
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PostPosted: Sun Feb 21, 2010 8:30 am    Post subject: Reply with quote #10   
With the HPAT, the issue is the downtubes are farther forward than other gliders, so they're farther away from your CG and your reach is shorter. In nil wind you have to put your hands near the apex of the downtubes to flare. It results in a slow flare cuz you don't have much leverage.
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Bertram
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PostPosted: Sun Feb 21, 2010 10:39 am    Post subject: Reply with quote #11   
Hi Jim,

when you say flaring with VG full on gets "crispier", do you also mean flaring is getting easier for the average pilot (ignoring now all other associated handling aspects of the glider with little wing twist).
Or does the flare window get that tight, that it's more difficult to know when to flare and you miss out on all that "crispness"?

Thanks, Bertram
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ksykes
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PostPosted: Sun Feb 21, 2010 11:00 am    Post subject: Reply with quote #12   
Here's another way to think about it, without directly answering your question. If it's windy and turbulent, use less VG when landing for control authority. Flaring is much easier with a headwind. If there is little or no wind, use a bit more VG to "crisp" up the flare. The best way to think abou the difference is that if you are a bit early with the VG a bit tighter, you can get the glider to stall "more" as the stall will be across more of the wing. But as Jim said, it's less forgiving of being late.

I generally use 0 to 1/4 VG in windy landings (0 if it's rodeo air, 1/4 if its windy but smooth) and 1/4 to 1/3 in nil wind, smooth.

If you use too much VG and a wing get's popped, it can be a real fight to get it back on line, hence Jim's advice about doing a full VG landing in no wind, and a big, forgiving field. Also remember you will retain more energy and glide farther on Full VG and that your stall speed will be higher.
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Paul H
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PostPosted: Sun Feb 21, 2010 5:17 pm    Post subject: Reply with quote #13   
Most gliders have very little bar pressure with the VG pulled tight so there is basically no resistance when you flare for landing. You push up and the nose goes right up.

Bertram wrote:
Hi Jim,

when you say flaring with VG full on gets "crispier", do you also mean flaring is getting easier for the average pilot (ignoring now all other associated handling aspects of the glider with little wing twist).
Or does the flare window get that tight, that it's more difficult to know when to flare and you miss out on all that "crispness"?

Thanks, Bertram

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johnpeace
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PostPosted: Sun Feb 21, 2010 5:22 pm    Post subject: Reply with quote #14   
The shorter chords and higher aspect ratios of todays gliders make a pretty significant difference in flare characteristic too, I would think.
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Bertram
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PostPosted: Mon Feb 22, 2010 11:00 am    Post subject: Reply with quote #15   
My pretty old HPAT had short chords and a high aspect ratio and was a pig to land in nil wind.
Don't think chord length and aspect ratio have a big impact on flare characteristics (and it would also mean that beginner HGs would have a huge disadvantage here).
Though I find it hard to believe, I think that - as Jim and others confirmed - it's predominantly just the apex thing with the aditional reach it gives the pilot for flaring.
Could imagine that the heavy weight (mass inertia) of the first topless gliders might have been the reason, why many 1st generation topless gliders had a bad reputation for landing characteristics (well, doesn't really apply for the heavy WW Fusion)?
Mass inertia might also be the reason, why rigid wing pilots usually "run" their nil wind landings. Just guessing.
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Jason
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PostPosted: Mon Feb 22, 2010 11:03 am    Post subject: Reply with quote #16   
johnpeace wrote:
The shorter chords and higher aspect ratios of todays gliders make a pretty significant difference in flare characteristic too, I would think.


my sensor is easier (force wise)to flare then my tandem falcon
same goes for the t2s I've flown


granted the consequences for missing it are higher, but the forces are much less when you reduce the chord/increase the aspect ratio

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Bertram
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PostPosted: Mon Feb 22, 2010 11:24 am    Post subject: Reply with quote #17   
Yes, I agree that you should need less force with less chord length.
But I doubt whether that makes flaring easier (not force-wise). At least a long chord doesn't spoil easy flaring control of beginner HGs.
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remmoore
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PostPosted: Mon Feb 22, 2010 11:35 am    Post subject: Reply with quote #18   
"Mass inertia might also be the reason, why rigid wing pilots usually "run" their nil wind landings. Just guessing."

Nah, it's just a decision they've decided to make. I can snap off a nil-wind/no-stepper in my ATOS VX, and strive to do that on every landing. Not always successful, though, and will sometimes need a couple of steps. It's no harder to do a no-stepper on a rigid than any hi-perf flex, IMO.

RM
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johnpeace
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PostPosted: Mon Feb 22, 2010 11:45 am    Post subject: Reply with quote #19   
Bertram wrote:
Yes, I agree that you should need less force with less chord length.
But I doubt whether that makes flaring easier (not force-wise). At least a long chord doesn't spoil easy flaring control of beginner HGs.


From my experience, especially with the Sensor, it's not so much the force required as it is the duration of time in which it happens.

With the longer chorded/lower aspect ratio wings, the duration of the flare is quite a bit longer. You spend all this time floating above the ground, pushing against the downtubes while they push back at you. I never liked that period of time and the process of the flare felt too gradual and progressive to me.

On the Sensor, (highest aspect ration/shortest chord I have experience on) it was different. You round out, wait for the glider to slow to the point that pitch feedback is perfectly neutral, then push. The wing goes straight up instantaneously. It just snaps to a stop.

I guess it's a matter of preference, I like the immediate, snappy flare better than the progressive, time-to-think-about-what-I'm-doing flare.

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HangDiver
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PostPosted: Mon Feb 22, 2010 12:45 pm    Post subject: Reply with quote #20   
Like NME I too was (pleasantly) surprised when I returned to the sport by how easy today's gliders are to land. I sometimes wonder when I think of a former flying buddy who is no longer with us due to a bad landing, if things would have been different if gliders were easier to land years ago.
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