XC TrikerAir Creation Tanarg 80hp BioniX 15M
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~ 166 Airports, Fields, or off road (4 Countries- hopefully more soon :)
If you put all your airports/off airports on SkyVector, you can make a cool map of the places you've been. These are mine:
In North American Continent (US, Mex, Canada, Hawaii)
In AUSTRALIA (MegaFauna 2014, etc)
ALL (get's a little crowded in this view)
Keel-fixed versus keel free: Spectrum 144: self-sustaining yaw-roll oscillations
Categories: Trike Talk, Equipment, Training / Learning to Fly a Trike, Hang Gliders
Comments (20)Normal glider configuration (keel able to move along cross bar)
Comments
Slo-motion version of above:
Keel temporarily fixed tight to crossbar:
From Oz Report v17, #240
There is much more trailing-edge movement in keel-free case-- naturally. Allowing greater "shedding" of the loads imposed by aerodynamic damping in roll, and much greater roll rates.
(link to thread on fixing keel to crossbar: http://ozreport.com/forum/viewtopic.php?t=34422 )
Once I got the oscillation going, I did my best to hold myself completely fixed on the bar. I don't believe that the slight movement of my body that you see especially in the keel-free case, where the oscillation was so large and involved lots of slip and sideforce, was significantly driving the oscillation. Occasionally you can see me give a significant input in which case the oscillation has damped out for some reason and I am getting it restarted.
Commentary:
Oscillations involving roll, yaw, and pitch. After some control inputs to initiate the oscillation, pilot is holding body fixed in center of base bar as much as possible, with bar well pulled-in. (Arms fully extended, but pilot is not tucked head-down or knees-over bar into extreme dive, which actually would yield a steep dive without these oscillations.)
The pilot's body does move a bit, especially in the test with the keel free to move, where the roll was so dramatic and the resulting adverse yaw and aerodynamic sideforce on the wing was significant. Even as the pilot's hands grip the base bar tightly, his CG is slightly aft of his hands and tends to swing in the same direction that a slip-skid ball would deflect-- in the "upwind" direction, as signalled by the yaw strings. The pilot's arms and hands are not in a good position to generate a great deal of yaw torque and completely prevent his body from twisting. This creates a slight movement of the hang strap. On the whole I believe the effect of this is negligible: a similar maneuver where the pilot pulled in the bar but tried to let himself move freely from side to side on the bar, yielded essentially the very same results. The glider's roll dynamics are dominated by the wing's powerful anhedral response to sideslip, not by very small movements of the pilot's body. To the extent that the pilot fixes himself in place on the base bar, he lowers the CG of the whole system and this shifts the glider's "effective dihedral" to be slightly less negative. To the extent that the pilot swings freely, he pulls the keel to the side during sideslip, which has the opposite effect. In either case, the glider's "effective dihedral" is still strongly negative at this low angle-of-attack that results from the bar being well pulled-in.
Even in the test where the keel is fixed relative to the crossbar, note that the wing does have some flexibility to distort under load and shed some of the loads imposed by aerodynamic damping in roll. Watch the trailing edges carefully. This flexibility helps to increase the roll rate. The keel pocket on the Spectrum is a very tight sleeve, and the changes in trailing edge shape are not the result of the keel pocket shifting from side to side. A glider with a looser keel pocket would should much more flexibility in the trailing edge, even if the keel were not free to move relative to the crossbar.
In the test where the keel is free to move, note how much the trailing edges move, as the wing "unloads" some of the aerodynamic damping force created by the rolling motion. This allows for a much greater roll rate, which in turns increases the bank angle, slip angle, and pitch excursions that we see in the oscillation.
Note the yaw string deflections. Their deflections are almost synchronized to the roll rate, deflecting toward the rising wing, but with a slight lag-- lagging by 1/8 or less of the complete oscillation cycle.
As the roll rate slows, the yaw strings are still strongly deflected. When the direction of roll reverses, the yaw strings are still slightly deflected from the previous rolling motion. At the instant the direction of roll reverses, the yaw strings are still deflected toward the wing that was formerly rising, which is still the high wing.
(This is much more visible when the video is watched at 1/10 speed or slower!)
With the bar pulled in, the glider's "effective dihedral" is strongly negative-- anhedral dominates over sweep. When there is a sideways component in the airflow, anhedral creates an "upwind" roll torque. At the moment that the direction of roll reverses, with the yaw strings still deflected toward the high wing, this "upwind" roll torque will tend to keep increasing the bank angle. Therefore, the aircraft's yaw/ slip dynamics cannot be responsible for the reversal in roll direction. '
This is very different from a classic "Dutch roll" oscillation, in an aircraft with enough sweep or dihedral to have significant positive "effective dihedral" at the angle-of-attack of interest.
What is responsible for the reversal in roll direction? I believe a strong rolling-out torque is generated by the fact that the wingtips are negatively lifting, and the outboard or high wingtip is moving at a higher airspeed than the inboard or low wingtip.
A related observation-- when we fly in a constant-banked turn and then pull in the bar while exerting no roll torque on the bar, the glider will roll into a turn in the opposite direction. Again, when we pull in the bar, I believe a strong rolling-out torque is generated by the fact that the wingtips are negatively lifting, and the outboard or high wingtip is moving at a higher airspeed than the inboard or low wingtip.
It's a dihedral-like effect, tending to roll the glider toward wings-level, but it responds to yaw rate, not sideslip angle.
A wing with less washout could not show these dynamics.
On the other hand, once the direction of roll has reversed, the glider's yaw/ slip dynamics are surely helping the glider reach and sustain a high roll rate. The interaction between aerodynamic adverse yaw and yaw rotational inertia probably causes the nose to swing "too far" toward the rising wing compared to what we would see if the aircraft had less yaw inertia, and then stay strongly deflected toward the rising wing for some seconds after the maximum roll rate has passed. The resulting "upwind" roll torque created by anhedral, acting to roll the glider toward the descending wing, helps sustain a high roll rate longer into the oscillation than would otherwise be the case. Decreasing the aerodynamic adverse yaw torque associated with rolling would certainly decrease the peak roll rate that we see in this oscillation. Decreasing the aircraft's yaw rotational inertia might also decrease the peak roll rate that we see in this oscillation.
A related observation: adding a vertical fin to the keel greatly diminishes the oscillation that we are seeing in this video.
Maybe this helps explain why pulling in helps in exiting a spiral dive:
""A related observation-- when we fly in a constant-banked turn and then pull in the bar while exerting no roll torque on the bar, the glider will roll into a turn in the opposite direction. Again, when we pull in the bar, I believe a strong rolling-out torque is generated by the fact that the wingtips are negatively lifting, and the outboard or high wingtip is moving at a higher airspeed than the inboard or low wingtip."
Many trike wings when flown fast have a tendency to tip walk...which is something I hate in a wing, and one of the main things I like about Gibbo's wings...excellent directional stability throughout the speed range.
Thanks CBurg, good input. Sometimes wing walking and PIOs at speed are hard to differentiate or part of the same spectrum of tendency from easy to PIO if you're not careful, to tip walking on it's own even with good technique. Have you flown HG as well?
Started HG in 1977. Many wings tip walk at speed...I don't like that. Sweep, Span, Nose Angle, Wash-out, Planform and loading are all determinants.
@Cburg, Wow, 1977 !! "When Sex was safe and hang gliding was dangerous!!!"
I started around 1999, the bugs (unrecoverable dives, non-standardized training, parachutes as routine, etc) had been worked out by then. Had a few flights years before 1999, and lots of begging as a kid living near Torrey Pines.
The scary part was the old towing methods...no weak links, release failures, rope connected to the control bar, rope breaks=tumbles, and...LOCKOUTS....the only thing that ever put me in the hospital in 40 years of flying everything.
I've done hundreds of Aerowtows (many at Wallaby, some behind Dragonfly's, Trikes & a Kolb) & I LOVE IT !!! Was very happy to introduce Ken ( @Knussear ) to it this year when he picked up his previously-loved Tanarg, & @JamrCrow . I did one day of winch towing, and that was a blast as well. Never truck towed, though been there on the truck-- still a little butt-clenchy for me just to watch it !! ;) For some reason last night I was semi-awake dreaming about towing, and the various releases- chest, handlebar, tug, weak-links x 3-- somehow I was dreaming not about getting "locked out" in a turn, but getting locked into a dive with a crashing tug, all the releases failing and having to go for my hook knife (it worked). I woke and thought how ridiculous that would be, that all would fail, and all the weak links-- much, much safer now-- thank you for being part of the development team. I have had so much fun towing in the relative safety we now enjoy.
Until Donnell Hewett Physics professor in Kerrville Texas invented “Skyting” all towing was attached to the glider. Professor Hewett dragged the rest of the towing community kicking and screaming to a pilot attached method. Now the only way it’s done. He was banned from the Hang Gliding Magazine because his ideas were “too dangerous”. Of course he was absolutely correct…
Now towing is safe and fun…and lockout are almost unheard of and easily avoided and mitigated…compared to glider attached methods of old.
Cburg i remember the old towing methods.never liked the setup so i never did it? First the problem was lockout and then they started useing a saftey quick release.i never liked that idea iether because anytime you used it was in high angle of attack in which if you were out of configuration and hit the panic button the resulting stall was fatal. Killed my friend jim malek. So cburg correct me if iam wrong as i had little exsperience other than watching and making the decision it wasnt for me. So now iam seeing the newer methods are vastly improved and i dont know much about them iether.so what kind of saftey records are the new methods holding? Xc isint the pulling in on the bar in a spiral
Dive just widening the arc of the circle causing the stalled side of the wing to fly again regaining roll authority.enough to snap out of it and gradually reduce the resulting climb and speed? Hope iam not sounding stupid here i cant see the videos iether but from what i think youre saying is that a free floating crossbar and a looser keel pocket when pulling in on the bar has a more natural ability to turn out of the dive rather than say a hp rigid wing with less free float and tighter keel pocket.just trying to understand.cburg would you add a little to how they are ataching tow to the pilot instead of the glider i didnt know they were doing that iether.what makes that safer?
Gosh between Wallaby and Quest, and a few other big operations they must have loged 100's of thousands of safe tows. The methods have evolved some over the years but all involve pilot attachment...unlike the old days.
Take a look at the above two HG parks and you can see the current methods. Many Youtube clips too. Very safe and easy.
Hey W.E. all that technical speak above about the wings wasn't me-- that was copy paste from the video author. I think you're right about pulling in widening the arc of the turn and getting the inside wing flying again/better (increase lift of the lower/inside wing).
The style of towing they do most at Wallaby is called "center of mass towing." A V-Bridle attaches from the pilot's chest (with a weak link and backup release there), then up to the keel at the main release via a weaklink as well (at an adjustable point somewhere between the crossbar and the nose). That "V" of bridle is hooked to the tow line, which is hooked to the tug via a release / weaklink on the tug pilot's end as well.
A lockout (think of flying one of your old bat kites on a string when it did that nose down dive thing, and the harder you pulled the string the harder it would dive) is less likely to occur. If a lockout did occur one of the 3 weaklinks should automatically, with no pilot input, break before a serious turn / forces were applied (in fact the weaklink is just barely strong enough to overcome the static tow force when beginning to roll). The pilot and the tug can both release with a quick motion on their end as well. The HG pilot also has a backup release on the chest, and the last ditch hook knife.
Tow cart advances were a big deal as well. Basically, suffice it to say that Janet did a whole bunch of towing at Wallaby and thought it was super fun. She loved their operation because they were so safety conscious as well. If you went to Wallaby, you would have no fear, and we wouldn't be able to keep you off the flight line, drooling also from a permanent grin.
Let me change that to, "WHEN you go to Wallaby ..." Ken ( @Knussear )& I do have it on our bucket list to fly all the way out there, and it will be sooner than later. We could use a driver possibly, or just a passenger.
The link to Wallaby is ... Wallaby.com http://www.wallaby.com/
They have a section on aerotowing there, but it is just a couple paragraphs for Wuffos- no details-- but they do have a very good primer available in their office in person.
There is this tour of Wallaby page:
http://www.wallaby.com/take_a_tour.php
W.E. let me add a bit to what XC said since I have done scores of tows at Highland Aerosports and Wallabys. The way releases are setup now days it is quite safe. Multiple weak links and either end can release at a moments notice. It is a fantastic way to get airborne in the flat lands. I have never felt in imminent danger aerotowing. Actually for me one of the biggest frustrations was periodic weak link breaks when nothing out of the ordinary is going on. Weak link breaks at low altitude can be a surprise but you are taught to immediately and instinctively react and you just quickly set up for a landing. And no you are not typically at a high AoA even right after getting airborne so even with a surprise weak link break you should never be forced into a stall because you automatically react by pulling the bar in a bit. Hope this is helpful.
Yeah, what UL said !!! ;) Three additional points:
1) With aerotowing the towline is pulling you UP!!! (not down like winch / truck- though safety has greatly advanced there too).
2) The HG will get airborne before the tug-- this means that
A) the HG can afford to stay on the cart a little longer (gain more airspeed / control / power before take off)
B) The HG HAS to immediately pull in ALWAYS on takeoff (after dropping the weight of the cart (or partial weight to prevent zooming) AND if the HG didn't pull in s/he would zoom way higher than the tug which is still gaining airspeed and not OFF yet-- otherwise the HG would pull the tug's tail up, making the tug want to nose down somewhat on take off. So, it is just natural that you are pretty well pulled in on takeoff, and well above stall speed and in control.
3) Finally, with aerotowing the HG pilot decides when to start rolling, and exactly when s/he will release the cart (I usually take the front of the cart 2 feet up in the air with me).
oh & 4) You can tow directly into the wind (from a huge multi-runway open area like Wallaby) to a greater extent than truck towing from a road (but same as from a lake bed), or from a winch where the other end of the line is staked to a pulley in the ground.
But, with the distant pulley on the winch, the winch operator is sitting right beside the HG on takeoff and can see and hear everything and adjust (hydraulically) or dump all power IMMEDIATELY-- and you get to run with winch towing, which I actually really find a fun challenge.
Hey thanks all when i stoped hang gliding . I asumed the sport was as it was . Then one day i picked up a lesure aviation magazine and saw all the trikes bam .wow how things had advanced.then i had rememberd a guy i mete at a hotel who hand a glider on top of his car. He said he had been hang gliding a couple of years. I told him that i had been flying hang gliders scince 1979. He had told me that he was traveling around the country doing towing.
I told him wow do you know how dangerous that is. He looked at me kinda funny .and now i see why.little did i know that they had greatly improved towing. Thanks all for the update. I almost did a baloon drop once at the alb int baloon fiesta but we got shut out due to windy conditions and thats another ball game.i also remember my boss larry newman in the first trans atlantic double eagle baloon crossing the atlantic had a oly hang glider atached to the gondola.he was going to crawl down the gondola hook in and land in his hang glider in france but due to loss of alt the had to let it go into the ocean before having to ditch into the atlantic. So somewhere there is a brand new hg at the bottom of the ocean for someone to find many years from now. Towing sounds awesome but
I feel with my soaring trike ive got the best of the flying world! Its just so convienient to just take off and climb to altitude in nice air and turn off the motor.
Note that pilot attached methods (only some of which are actual center of mass towing concept invented by Donnell Hewett) have an adverse yaw force imposed when you shift to the sides. Trikes do the same thing. That's when vectored thrust has benefits...no imposed adverse yaw forces from (aero) tow lines or engine thrust lines.
You want to go right...you shift right...but that creates a left yawing force...which the wing overcomes but causes a control lag.
Regarding Pilot attached towing, some are pilot attached only, some 1-to-1 with the keel, some 2-to-1 one with the keel. The center of mass is between the pilot and the wing...but you can tow pilot only, or even keel only (it's been done) but the various brides attempt to get the tow force somewhere near the center of mass...it's better. Although every possible permutation has been tried over the past 50 years of towing.
HI did alot of sailplane towing behind a stearman in the 70s. It looks to me that aerotowing in a hang glider is fundamentaly simular. The hang glider lifts off first then remains at a fixed point above the tow planes trailing edge wash. And their now towing hang gliders by the center of mass.very cool! Its such a sad thing when i look back at a few friends who paid the price of developing a safe working system.i try to self anilize my reasoning skills and decicion processes.back in the late 70s and 80s i remember looking at towing but my instinks told me it just didnt look safe. Safety is everyones responsability but must always be applied to self. Learn to trust youre instinks if something dosent look or feel rite it probably isint.the current modes of towing look so vastly improved.
Thanks to all those smart guys who step out against the norm and costantly figure out safer methoeds.back then
Leaps were made in blood by a few who dared to test the limits by proving that it could be done but at a cost. I remember in the 80s when hang gliding had to reevaluate itself for the sake of the sport. Ive always thought that triking and hangliding were not cousins but blood brothers. So many improvements have been made in the way we do research and development those people deserve a big thank you?
Getting too low on aerotow
Certainly have had extreme towing experiences in Australia. Video of aerowtow gone wrong:
The student on tow
Thu, Dec 19 2013, 7:00:04 pm AUSEST
Couldn't find the release
http://ozreport.com/17.249#4
Followup response from the Pilot himself, below. I think this speaks to the general safety of modern aerotowing-- this new student made several mistakes, including reducing the safety of the weaklink by 50%. In addition, my shoulder release is VERY easy to find, and Ken @Knussear who's a new aerotow student will verify that the primary release for students is a lever (brake handle) release at the corner bracket of the basetube. All you have to do is a quick Karate chop to the corner bracket and you're off the hook. finally, the tow pilot wasn't paying attention here. Even through all of this, the outcome was good.
Oz Report, Dec 19 2013, 7:00:04
Couldn't find the release
I was the pilot in the 'lockout'.
Firstly, as it was my first aerotow without an instructor present and my first aerotow in 12 months since the aerotow course, I probably should have had a tow in calm conditions early morning or in the evening to familiarize myself again.
Secondly, as I had watched two weaklinks break before me, I made a bad decision to strengthen mine from the standard 1G to 1.5G. As you might have guessed, I changed it back for the next tow.
Thirdly, because there was a ground marshal with a radio, I, for some reason, deliberately chose not to lock-on my radio during the tow. My radio PTT switch is on my left shoulder and I have to take a hand off the control bar in order to operate it. Things got busy very quickly and I didn't get to communicate with the tug pilot (who didn't see what happened to me) when I needed to.
However, my main problem, which no one has alluded to because it is not obvious from the camera angle, is that when I wanted to release I couldn't see the release line. The release was tied high on my right shoulder strap and in theory all I had to do if I couldn't see it was to locate it by feel and pull it. However in such a situation (and I have gone over the video which was filmed in 30 frames per sec), things were happening literally frame by frame, there is no time to work out whether the release is on the right shoulder or the left shoulder and then start feeling for it. I didn't end up releasing before the (previously strengthened) weak link broke.
My towing inexperience caused me some indecision when the trike rose quickly in a thermal. This doesn't seem to show well on the video, but I remember the trike shooting up above my horizon reference. My indecision was because in all my previous tows it has been an effort in my slow glider to stay down at the tug level and not get above it, being below it was a novelty, forgot all about prop wash.
As I watched two other pilots being towed up before my next tow, I also remembered the short positive weight shift inputs that I had been taught but had also forgotten about on that tow.
The glider had popped no.3 + no.4 batten tips on both sides and both no.2 +no.3 undersurface battens had come out on both sides, so I guess the wing had been working hard.
The next tow was good and at all times I knew exactly where the tow release was!!
Lockouts on the old control bar towing were much more radical...and were before the days of any weak links. Scary stuff those lock-outs...especially if the release failed. Much easier to avoid nowadays, but still possible.