. . . The airflow the wing experiences is down and forward, . . .
Slight correction. The airflow the wing experienced was UP(ward) and from the LE to Trailing edge (i.e., front to back, or moving backward) over the wing.
The motion the wing experienced was down and forward.
And, as I detailed in my post, the most critical aspect of a null wind launch is accelerating the wing to the point of minimal air speed. And AOA in this process requires an unusual balance. Hence the added danger.
I would add the following, considering your essentially correct reply:
The critical thing with a null wind launch is that lowering your nose angle to what may be considered to be a "perfect" AOA (for an ordinary, higher wind launch) will, in fact, tend to generate an excess forward thrust vector leading the glider to out accelerate the pilot BEFORE minimal air speed is achieved. This leading, of course, to a nasty down hill WHACK.
To do a null wind launch expertly - or, at least, well - you must maintain an AOA which does not generate typical (or significant) forward forces - because doing so will lead the wing to exceed your human ability to keep up with it.
The best course in a null wind situation is to adjust the AOA so that the forces generated by the wing pull only (or almost so) upwards. (This may NOT be the situation you normally want your glider to be in during the "average" positive up slope airflow launch.)
Meanwhile, the pilot and gravity can take care of accelerating the glider forward to the point at which the positive airflow over the wing produces adequate lift to allow the pilot/wing to become airborne. The glider is likely to be in mush mode or near it (particularly an intermediate or advanced wing!), but the alternative (holding a more typical AOA at the beginning of the launch run) is, I repeat, for the glider to over speed the pilot, and consequently end up nosing in violently.
What I'm saying may seem to contradict my earlier statement (in my previous post) about flying slow close to the ground. However, I still emphasize that ZERO wind launches ARE more dangerous. That's why, as a pilot who began flying nearly 35 years ago, I seriously avoid them.
For any students, or prospective students, reading this -
Training gliders are designed to fly and stall at slower speeds. They are often much lighter than intermediate and advanced wings and the pilot's personal equipment (usually a very minimal harness and helmet for students) is up to 15 pounds lighter than that of an experienced pilot. For these reasons instructors very often can and do teach in calm, or near calm, wind conditions.
Wingspan, everything you said makes alot of sense to me. That I can understand totally thanks. And horizon? I don't think I have ever worried about that when I set my AoA. I set it based on the amount of wind I have to work with,and what i'm launching off. Wingspan is right about the higher performance wing being harder to launch IMO. I would not sweat the launch as much with my Eagle I had, but this was my first time with this U-2. And I want to be able to do one. And running hard was on the brain during launch. And Ryan, that last pic of those three, really gave me perspective on how close I was to clearing that barbed wire fence at the bottom Cuz during a launch like that, you are gonna want to push out if you get to the bottom, and pray you have airspeed cause that fence will get you,and introduce you to Mr. Rockpile,hard as f***. Well, I can now say I did one, and probably might do a couple more, but I'm not going to make a regular thing. But again, thanks for the discussion and your thoughts guys. _________________ Always a student.
"The mountain doesn't care what that card in your wallet says." - Bruce Stobbe
that last pic of those three, really gave me perspective on how close I was to clearing that barbed wire fence at the bottom
I have to admit I didn't know there was a barbed wire fence at the bottom
Here's a clip of me launching from Camel's for a morning sled... it's probably not as steep as the McClure launch in the video, but it's probably higher altitude...
There is a bush that sticks up at the bottom, which is why I pop the nose up at the end of the run... but that only works if you have enough airspeed/energy built up from the initial run...
Here's an example of what I use and I often drop the nose a little lower before I start my run. Letting the wing get ahead of you is not caused by having too steep an AOA, it's caused by not holding and balancing the glider correctly.
The last two posts with the pictures especially Ron's picture diagram was freaking cool!!! I was having a hard time seeing what you guys were seeing. Now I get it. I'm a little slow but the more I read what you all are posting....well, I'm getting it. Thanks.
Michael Owens, H-2 _________________ H-3, TUR, 360, ACP
Here's an example of what I use and I often drop the nose a little lower before I start my run. Letting the wing get ahead of you is not caused by having too steep an AOA, it's caused by not holding and balancing the glider correctly.
There's a difference between a shallow slope and even moderate slope launch as compared to the Slide launch. I've been to Slide and although the wind was blowing down and I couldn't fly it, one brief look at the site and it is obvious that it's just shy of being a cliff launch. On a calm wind moderate slope launch holding an excessively low AOA can cause the glider to over speed the pilot. I've seen it and experienced it.
Also, I've seen pilots in situations (typically very steep or cliff launches) where they can't get the nose any lower because the base tube is pulled against their ankles and still the glider is producing tremendous amounts of lift. In that case, it could be argued that it was simply impossible for the pilots to hold and balance the glider "correctly" considering the upward direction of the wind. But I've most often seen this when the wind was quite strong.
BTW - In my experience, ". . . not holding and balancing the glider correctly." can certainly involve having too "steep" (or too shallow) of an AOA. Another kind of bad launch can also involve having too high an AOA. So, many poor launches involve improper "holding and balancing" techniques.
Paul H wrote:
Here's an example of what I use and I often drop the nose a little lower before I start my run. Letting the wing get ahead of you is not caused by having too steep an AOA, it's caused by not holding and balancing the glider correctly.
If you look closely at the picture you can see some tape on the sail undersurface of the right wingtip. The guardrail can really suck at times. Those posts are sharp and sometimes you can't keep the wingtip from making some contact when you climb over it on a windy day.
noman3 wrote:
Paul H wrote:
Here's an example of what I use and I often drop the nose a little lower before I start my run. Letting the wing get ahead of you is not caused by having too steep an AOA, it's caused by not holding and balancing the glider correctly.
i hate climbing over that guard rail.
_________________ Paul H
U2 160 USHPA # 51178 KE7VOG
H4, FL, AT, PL, FSL, RLF, TUR, X-C, CL, AWCL, 360, HA,
USN ret. A & P mechanic
Last edited by Paul H on Thu Jan 21, 2010 8:39 am; edited 1 time in total
I do understand the differences between the different slopes, I was using this as an easy to see example of AOA. Having the glider get ahead of you on a moderate slope is more of the pilot not having an aggressive run while not holding the glider correctly (leaning too far forward). The only pilots who should ever have a problem with the control bar hitting their ankles are those who are vertically challenged. Lean over, grab the down tubes low enough so that the harness straps will be tight when you stand up with the glider, and the control bar shouldn't be a factor. One thing I think is very important for pilots especially those with the height issues is to not stand on launch holding the glider up for long periods of time. The pilot should be able to pick the glider up and within a few seconds tell if the conditions are right to launch. Too many pilots just stand there and then end up getting tired which contributes to a bad launch.
JMHOYMMV
Wingspan34 wrote:
Paul,
There's a difference between a shallow slope and even moderate slope launch as compared to the Slide launch. I've been to Slide and although the wind was blowing down and I couldn't fly it, one brief look at the site and it is obvious that it's just shy of being a cliff launch. On a calm wind moderate slope launch holding an excessively low AOA can cause the glider to over speed the pilot. I've seen it and experienced it.
Also, I've seen pilots in situations (typically very steep or cliff launches) where they can't get the nose any lower because the base tube is pulled against their ankles and still the glider is producing tremendous amounts of lift. In that case, it could be argued that it was simply impossible for the pilots to hold and balance the glider "correctly" considering the upward direction of the wind. But I've most often seen this when the wind was quite strong.
BTW - In my experience, ". . . not holding and balancing the glider correctly." can certainly involve having too "steep" (or too shallow) of an AOA. Another kind of bad launch can also involve having too high an AOA. So, many poor launches involve improper "holding and balancing" techniques.
Paul H wrote:
Here's an example of what I use and I often drop the nose a little lower before I start my run. Letting the wing get ahead of you is not caused by having too steep an AOA, it's caused by not holding and balancing the glider correctly.
_________________ Paul H
U2 160 USHPA # 51178 KE7VOG
H4, FL, AT, PL, FSL, RLF, TUR, X-C, CL, AWCL, 360, HA,
USN ret. A & P mechanic
If you look closely at the picture you can see some tape on the sail undersurface of the right wingtip. The guardrail can really suck at times. Those posts are sharp and sometimes you can't keep the wingtip from making some contact when you climb over it on a windy day.
The Nevada Department of Transportation specifically prohibits us from attaching anything to the guardrail. They don't even want us to tie streamers onto the snow markers that stick up from the rail. We could put something there temporarily while we launch, but then someone would have to remove it afterwards. We don't always have a driver so we wouldn't be able to just leave it there until we do a vehicle retrieve.
gasdive wrote:
Paul H wrote:
If you look closely at the picture you can see some tape on the sail undersurface of the right wingtip. The guardrail can really suck at times. Those posts are sharp and sometimes you can't keep the wingtip from making some contact when you climb over it on a windy day.
So why not attach some padding to the guardrail?
=
_________________ Paul H
U2 160 USHPA # 51178 KE7VOG
H4, FL, AT, PL, FSL, RLF, TUR, X-C, CL, AWCL, 360, HA,
USN ret. A & P mechanic
Ryan, I see your lower angle of attack. I also see your kite not flying for a while too-as can be seen by your hangstrap swinging side to side and the metallic clanking of your frame not yet loaded as you run way further down the hill-ears don't lie. And then you pop your nose way more than dreamers ever does at liftoff when it seems like you just barely loaded the wing before doing so. Yes dreams AOA is higher at the first few steps but not nearly so half way through his run as his wing automatically lowers to find its trim.
sorry but not a great example of superior performance Although I would,not say it was bad, as you say dreamers was. However both launches are close to the limits, as the terrain and lack of wind dictates it so.
Ryan, I see your lower angle of attack. I also see your kite not flying for a while too-as can be seen by your hangstrap swinging side to side and the metallic clanking of your frame not yet loaded as you run way further down the hill-ears don't lie. And then you pop your nose way more than dreamers ever does at liftoff when it seems like you just barely loaded the wing before doing so. Yes dreams AOA is higher at the first few steps but not nearly so half way through his run as his wing automatically lowers to find its trim.
sorry but not a great example of superior performance Although I would,not say it was bad, as you say dreamers was. However both launches are close to the limits, as the terrain and lack of wind dictates it so.
Thanks Gluesniffer, but if Ryan thinks it's bad then it's bad. Otherwise he would not have gone through so much trouble to prove it. Now that I think about it, the only way to go from this point is up. The more you fly, the better you get, the more you fly the better you get. _________________ Always a student.
"The mountain doesn't care what that card in your wallet says." - Bruce Stobbe
Ryan, I see your lower angle of attack. I also see your kite not flying for a while too-as can be seen by your hangstrap swinging side to side and the metallic clanking of your frame not yet loaded as you run way further down the hill-ears don't lie. And then you pop your nose way more than dreamers ever does at liftoff when it seems like you just barely loaded the wing before doing so. Yes dreams AOA is higher at the first few steps but not nearly so half way through his run as his wing automatically lowers to find its trim.
I already commented that I wanted to pick up plenty of speed so I could pop over the bush at the bottom, hence the 'nose pop'. 'Popping the nose' is generally a term reserved for unintentionally raising the angle of attack... by the time I push out and pop over that bush, I'm FLYING... that's just an abrupt pitch input.
It's really besides the point, except that when I asked the glider to pitch up, I had the wing flying, and it responded. When Day pushed out, the glider continued to mush a bit before flying away. Airspeed = energy... I had it, Day didn't have enough to be 'safe' if something unexpected were to come along.
As for how far I ran, remember this was mid summer at 8,000 ft msl, on a launch that isn't as steep as the one Day launched... _________________ Ryan Voight
BLOG: www.AIRTHUG.com
VIDEOS: http://vimeo.com/AIRTHUG
Thanks Gluesniffer, but if Ryan thinks it's bad then it's bad. Otherwise he would not have gone through so much trouble to prove it.
I didn't say it's bad! I just said it could have been better, and explained how/why. Everyone posting that it was perfect isn't doing you any favors... launches could always be better and safer (myself included, I know that!) _________________ Ryan Voight
BLOG: www.AIRTHUG.com
VIDEOS: http://vimeo.com/AIRTHUG
I understand why not have the nose too high, but too low seems just as bad. Low AoA would not load the hang strap. No load on the hang strap means (to me) no roll control in a weightshift aircraft. Your only roll control would come from forces exerted by your upper arms which in my experience aren't strong enough to control the glider. Just lifting the glider with your arms to tighten the strap won't cut it, there has to be actual load, weight if you will.
I look at newbies in strong wind struggle for control of the glider, fighting to bring the nose down, wrestling with the uprights, banging tips on the ground and eventually standing on the bar to right the glider.
I can (and have) just stood next to them with a glider flying above me, calm, stable, and with the nose higher and *no hands* on the controls.
In a no wind launch I try to replicate that. The glider flying above me as I run to create the wind. Gentle inputs keep it flying just where and how I want it. I build up speed and the glider builds up lift letting me run faster and faster as I take longer and longer steps. All the while tiny gentle inputs, or often no inputs at all, keep it flying straight. As it starts to lift me I gently pull in, keep moon walking till eventually it pulls me into the air despite being pulled well in.
I can't come anywhere near running fast enough to fly without the glider carrying some or most of my weight. It can't do that without the nose being up a bit. Still pulled in from trim, but I can't run at 20 km/h carrying a 30 kg glider over my head. Siht, I can't run at 20 km/h *without* a glider.
Having said that I haven't tried it with a topless. I can't imagine that it would be much different in that respect to the GTR or for that matter, a standard...
Ryan, do you recall if there was any wind during that video or was the air calm? BTW: Do you have other training videos you've created? _________________ Wingless
H2 - FL CL FSL
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Cuz during a launch like that, you are gonna want to push out if you get to the bottom, and pray you have airspeed cause that fence will get you,and introduce you to Mr. Rockpile,hard as f***. Well, I can now say I did one, and probably might do a couple more, but I'm not going to make a regular thing. But again, thanks for the discussion and your thoughts guys.
I'm a little slow but the more I read what you all are posting....well, I'm getting it. Thanks.
Although I would,not say it was bad, as you say dreamers was. However both launches are close to the limits, as the terrain and lack of wind dictates it so.