it would be interesting to go up in smooth air with a camera running and a GPS receiver recording and compare the results of gradual and abrupt lockouts with a one and a half G weak link.
Yeah, actually we are looking for a device that can measure and record instant tow forces during a tow and different configuration. I'd like to see the cinetic of increasing force during a lockout. But commercial instruments I saw are for big industry and not cheap..
ATGuideline
Releases
(..)
Actuation sequence
(..)
Tug Release
If the situation is not time critical continue the climb to a safe altitude if necessary, signal the tug to release, and drop the tow line after actuating the secondary release.
How do you signal the tug to release ? didn't read anything and know nothing about that..
I used a hydraulic cylinder - which I describe in Mousetraps - at the end of the towline and rigged a release in front of it so it came down with me after I stowed it.
It doesn't record but you can just read the gauge as you're flying.
You don't really need any numbers other than steady climb because anything else doesn't really mean anything. If the glider wants to he can attain zero tension, the weak link determines the maximum, and anything in between is possible.
I can tell you that the needle swings up very dramatically when your pushing out and drops likewise when you're pulling it.
If you decide to get a cylinder, talk to me. I have two (very nice) assemblies and I'd like to get rid of one. You can see one installed in my load tester at:
It's really fun to look at it - especially if you've really wanted to know the numbers for fifteen years. Don't stare at the gauge. If you do for more than about three or four seconds you won't be able to find the tug when you look up again. Just take quick glances when everything's lined up.
How do you signal the tug to release ?
In the US when people's Lockout Mountain Flight Park releases don't work they usually just roll hard one way or the other and slam back into the runway. Even if he doesn't release before impact it's a no brainer that the Greenspot will blow and he can return to the flight line for the next glider.
The Federal Aviation Administration's Glider Flying Handbook gives the signal for a sailplane unable to release as:
Glider moves to left side of towplane and rocks wings.
I suspect that's international but that wouldn't be a great idea for a hang glider either.
We have no standardized signal but if - for some unimaginably bizarre reason - I wanted the towline, I would duplicate the tug's signal for release: wave my left arm up and down - and hope he could see it in the mirror.
...until the nose heading the ground at small angle of attack ?
I didn't read that one very carefully either.
If you're heading toward the ground after a lockout it's because you have a HIGH angle of attack and the glider's diving to get it back down to something low enough to start using again. When the angle of attack is low it will be pulling out of the dive.
You say that just before the wl failure, in a lock-out situation, the angle of attack is high ?..
But..
In an engaged lock-out, does the glider still flies or becomes mainly a drag device ?
If it still flies, fast in a turn (rolling+yawing), the tow line (almost normal to the glider's plane) is like a big ballast. So why the angle of attack couldn't be acute ?..
You often use the Pagen story:
I hung on and resisted the tendency to roll to the side with as strong a roll input as I could, given that the bar was at my knees. I didn't want to release, because I was so close to the ground and I knew that the glider would be in a compromised attitude. In addition, there were hangars and trees on the left, which is the way the glider was tending. By the time we gained about 60 feet I could no longer hold the glider centered--I was probably at a 20-degree bank--so I quickly released before the lockout to the side progressed. The glider instantly whipped to the side in a wingover maneuver.
I'm confused with the wing over reaction rather than the stall predicted if he was at high angle of attack..
I'm ready to be wrong, no worries..
I did imagine a theoric (and psychedelic) tow configuration in which the glider, hardly banked, would spin and drawing a twist like a spring behind the tug and around its horizontal track. It should flies in a permanent turn by correcting the weight force action by pulling/relax to sink/climb respectively with the pilot over/below the wing in the upper/lower half of the turn respectively..
What could we learn from that ?.. a new way to exit a lock-out at safe altitude ?
Yeah, the angle of attack is high in a lockout. The glider's turning away from the towline and the towline's pointing in the direction of the relative wind.
The glider's still flying but it is rapidly becoming a drag device and making the tug unhappy.
Yeah, the towline's becoming a lot less like an engine delivering thrust and a lot more like ballast and raising the stall speed.
But the better lined up the glider is the more acute the angle of attack is (and, of course, the worse the less).
I'm confused with the wing over reaction...
For a wingover you first pull in for a low angle of attack / high airspeed / dive.
Then you roll and push out hard. High angle of attack / decreasing airspeed / climb / turn / increased G loading.
When you come out of a wingover the glider falls, you stuff the bar, you wait for the glider to regain airspeed, and you better be high enough for that to happen.
Even on a normal tow when you're climbing under normal tension if you hit the release things get very very quiet for a few seconds until the nose drops and the glider recovers airspeed.
In a lockout the tow tension is acting to both increase your load and accelerate you into a high angle of attack turn. On an aerotow with the tug needing to keep going straight and the glider on a short towline that situation isn't going to continue for very long before either somebody releases or something breaks...
And then the glider will be working for a while on converting a high angle of attack to a low angle of attack.
Again, I have a real hard time getting my head wrapped around the physics/aerodynamics of lockouts but I think I'm still on solid ground.
After the 1996 season took out my longtime student/friend while another instructor was scooter towing him and two high profile people from this region tip stalled and died behind a tug Dennis Pagen published a pretty good vector analysis of a lockout in the 1996/10 issue of the magazine. I always have to reread it to understand it but I think he's got everything right - except for the crap about stuff contacting the wires or downtubes.
Say the word and I'll e-mail you a pdf copy of the issue - 33.3 megs.
I'm ready to be wrong...
Me too.
And, while it's good to understand the physics of what's going on, fortunately, we don't really have to. We know:
- how to react to them up high
- that we can't survive them down low
- how to:
-- prevent them from happening down low
-- equip to substantially lower the definition of high
The spring track...
I have heard a couple accounts of hang gliders being barrel rolled on aerotow. But I think I'll stay with the conventional approach while others work some of the bugs out of the other technique.
Unresponsive... Slow or partially stalled - requiring a lot of muscle and time to start getting the glider to do what you want it to.
An Extra 330 has a massive and powerful elevator and can be stalled at just about any speed. So what is the stall speed of this airplane? Do you see why "stall speed" is confusing to me? I'm not saying this is relevant to towing gliders, just something to think about.
It's confusing to me too and I'm on the edge of my confidence - but I think what's going on there is...
- The massive and powerful elevator allows the plane to pull up with lotsa Gs.
- It weighs a lot more when it pulls up with lotsa Gs.
- When it weighs a lot more it stalls at a lot higher airspeed.
Say the word and I'll e-mail you a pdf copy of the issue - 33.3 megs.
Please..
The spring track...
I have heard a couple accounts of hang gliders being barrel rolled on aerotow.
they did it, really !!?
a tight towline makes the glider heavier
When it weighs a lot more it stalls at a lot higher airspeed.
but we can push the bar further away than in free flight, that could be confused..
why ?
the angle of attack is high in a lockout. The glider's turning away from the towline and the towline's pointing in the direction of the relative wind.
I thought the speed of the turn changed that
The glider's still flying but it is rapidly becoming a drag device and making the tug unhappy.
DRAG
If the glider flies during a lockout its speed increase under new G and Fd increase proportionally with v².
If the glider was turned into a new "drag device", Cd ans A increase badly
a mixture of both ?
