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Wing-Over - Response to potential frontals with Bagheeras (initiated by Les Sharp) on Asia PG mailing list
by Gabriel Jebb (E-mail) , 2000/3/19
Les, Could be... but it could also be a few other things. I have spent a lot of time on a Bagheera and haven't noticed it as a problem. I like to do really big wing-overs and frequently watch my wing from tip to tip just to see where the loading is on the wing. I suspect I would have noticed and saw these small frontal closures as you describe. I have a feeling that the real answer would be the pilots themselves and how they were flying the Bag's. If you tell me who the guy was I can give you more definite word on the pilot vs. wing issue since I know the Marshall boys real well... One of the things that I did notice about the Bag was what seemed like a lot of tension in the leading edge of the wing, which protects it from a lot of symmetric collapses, and helps speed the process of asymmetric recovery. It also gives the canopy a better shape and allows it to maintain a cleaner airfoil by reducing the flutter you get in the leading edge. It also helps keep the canopy from ballooning especially when giving a lot of brake input. I am going to make a guess that these guys were giving a lot of brake, not using a ton of body, and not giving enough outside brake during the dive after turning past the apex of the wing-over. Without going through the very specific details of properly executing a wing-over we should examine a couple of the basics.
First off a let me say this can be a potentially dangerous maneuver and a lot of pilots get hurt when learning the timing and mechanics of a wing-over... so remember altitude is your friend. Please don't try this on your landing approach, or straight off launch because you want to impress the guys. I always hesitate to explain these kind of things because I feel it promotes the idea of doing them to the pilot. At the same time, if you are going to give it a go... better to know the right way to do it.
Okay wing-over mechanics, then where I suspect the guys are going wrong. This maneuver takes a lot of practice because the timing is counter intuitive. That's what most guys don't understand, they try to do it by feel which is wrong... unless you know the timing. Okay I am flying straight away from a cliff, hill, mountain, whatever, and I want to do big wing-overs. I first have to pick a point I can center myself on. Often people do asymmetric wing-overs because they will apply more brake or lean on one side than the other. I have my point and I am ready to go. BTW, this is how I do big wing-overs, I recommend we start on small ones. I will start my wing-over by turning to the right. Okay, I take a deep breath and relax... I crank the right brake hard and fast letting my left brake up almost totally. Just the lightest amount of pressure in the outside wing, so we don't turn negative from a collapse on the outside. This throws my body to the right side of the wing, which I want to accentuate as much as possible. This also makes that initial turn and dive with my glider. My glider is picking up speed and my body is also building up potential energy. Now I look up at the outside (left) side of my wing, because I want to try and keep my head centered throughout the wing-over. Lot's of guys lean their head to the right, which does two things. Number one it gives them the false impression that the are doing big maneuvers because their head is leaning with their body, so the are not seeing the horizon straight. This will make a bank angle of 30deg seem like 130deg. Secondly, they can't see if the outside wing tip is about to collapse. I am looking up and waiting till the wing reaches the peak of it's bank angle. Then I give a little bit more right brake to turn the canopy from perpendicular to the ground to facing the ground. This is just a little extra pop with the right brake that angles the glider so that it is facing and flying down.
Now my canopy is flying downwards fast, but my body is not positioned straight with it. I have a lot of energy built up with my body but I can't use it yet. At just about the point I see the outside wing tip collapse, right after I pass the apex of the wing-over and have the wing slanted down facing the ground. I have to give my outside wing tip brake hard and fast (my left brake) to keep tension in the canopy (like a big pop), to slow my canopy down for a second so that my body can pass through and we have the extra speed and energy that my body has created. This pop will also get the canopy set for the hard left brake which I am about to do. Both hands raise a bit for a split second. Now I have to know my wing to do this and just before the wing starts to return the energy in straight and level flight, which it will seek to do, I have to drive the left brake down hard and fast, also throwing my body into the left side of the harness. Again I want to look up to make sure that the outside wing (now the right side) stays pressurized. Also look at your right hand for a split second and make sure that you have raised it up. A lot of guys get so excited, after the first turn they forget to raise the initiating break, which slows the wing down because we are increasing our drag. It also reduces our bank angle a lot. From this point, it is just the same as a right turn wing-over
Now recommendations and tips on wing-overs... after coming out of that second turn, in this scenario the left turn... check your center point on the horizon and make sure you are still centered. Make sure that at no point during the wing-over do you hang onto the risers. I have seen guys do this and go from wing-over to spin. Always look at the canopy outside tip when you are learning the timing, because it is not natural. Most guys initiate the next turn, when the canopy is at the apex. This can be very dangerous and will usually result in a side slip with a huge outside collapse. Don't forget to pop the outside brake once the canopy has passed the apex. This will slow the glider for just long enough for your body to swing through instead of fall through which most people do and screws up the wing-over momentum. When you start with wing-overs don't do more than four in a row... as a beginner you will loose your equilibrium and start to get a little confused with out understanding why. Also try not to practice for more than 10-15minutes in a row as a beginner, because I guarantee in a few weeks you will be banking over 90 and this will also distort your equilibrium. The constant rush and drain of blood to and from the head also adds to dizziness, which can be very dangerous. Lastly, please, please, please don't do this close to the ground. When you are learning the mechanics of it, you will have a lot of outside collapses, because your timing is off, you don't give a hard enough pop, or an inside collapse, because you tried to give brake when the canopy was at the apex instead of past it... so you side slip. All of these can result in huge problems including spin, flat spin, cravatte, and pilot falling into lines. So give yourself plenty of space. Of all the maneuvers I see guys get hurt performing spirals and wing-overs lead the pack by a huge margin. I guarantee that while you are learning you will have some big collapses and you may need some time to recover. So Marshall guys probably did two or three things wrong. Not giving a little extra pop to get the glider turned downward after the Apex. This will often result in a collapse on the inside wing as the pilot falls downward past the glider, sometimes the wing will automatically try to return to equilibrium and level flight and will turn past the apex with the energy it has built from a previous wing-over, especially if the body is leaning into it. This could result in temporary loss of pressure along the leading edge as the wing charges downward and the pilots body is not yet on the same path. This leads to the second more likely occurrence, which is that the pilot did not apply enough outside break pressure after turning past the apex, to slow the glider momentarily as the pilots body regains downward momentum. This outside break and inside break will pull the tips back slightly as the pilot's body catches up with the glider, which keeps the leading edge solid. Without this pressure, big frontal collapses are a possibility... or little ones as the Marshall guys may have demonstrated. Finally, they could have been using a ton of brake without much body involvement, which means they have to keep slowing their glider, then letting it shoot forward, without having drastic changes in their cg which would have kept the wing much more solid and efficient. These of course are just a couple of theories and I could probably come up with a few more. Tough to do without having seen it first hand. I don't believe that these wing-over frontals where a result of a design flaw in the camber area, pressure center of the Bag. I tend to think it was more of a pilot error, or timing problem. Hope this helps, would love any feedback.
Gabriel Jebb, Director / Flight Instructor, Philippines Sky Sports, Inc. , +63 (2) 825-7756