Ready to Launch!
02/12/08 16:51 Filed in: Launching Techniques
Welcome to the Soaring Stuff blog. What a bizarre word that is... Blog. It almost sounds like something that my Scotish ancestors might have eaten, that was cobbled together from various inedible portions of various inedible animals. Yccchhhhhh!
Anyway, this is the "launch" of the Soaring Stuff blog, so what better subject to deal with than launching.... a sailplane that is. Obviously, all soaring flights start with a launch, and for purposes of thermal duration flying, the higher the better. Unless you are just practicing spot landings, you'll probably want to get your bird as high in the air as possible. It just increases the odds that you'll come in contact with rising air ... either a thermal, or some sort of wave lift.
So how do we maximize our launches? Step one is to make sure that we have the tow hook placed in the optimum position. If your tow hook is too far forward, the winch or high start line will tend to pull the nose of your sailplane downward. All aircraft rotate in the pitch axis around that all important center of gravity (or "C.G.")
If the towhook is forward of the C.G., then the aircraft will pivot forward in a "nose down" direction, and you won't get much of a launch.
So... the natural thing to do is move the tow hook rearward and all will be right with the world, Right? CRUNCH! If the tow hook gets too far aft, everything gets really squirrelly. Your normally well behaved sailplane will suddenly take on a mind of its own, and try to twist, roll, stall, and do anything it can think of to evade the tow line. If you are lucky, your bird will just pop off the tow line... usually very quickly and dramatically. If you aren't so lucky, it will stay attached to the line, and attempt to smash itself into the ground.
So how do we determine a safe place for the tow hook before disaster strikes? One key (pardon the pun!) for checking this out is in your pocket. Pull out your key ring, and hang your sailplane by the tow hook, upside down from that steel ring that holds your house and Maserati keys together. A properly placed towhook will hang your sailplane almost level.... but without the plane trying to fall off onto the ground. If your fuselage is hanging really hard, tail down, then the tow hook is too far forward. If the hook is trying its best to slide off and drop your bird on the ground, then the hook is too far aft. Adjust it as necessary to achieve this slightly tail down attitude and you should be good to go for that first launch.
DISCLAIMER - Fuselage thickness (the distance from the belly of the plane up to the wing) can have a significant effect on this tow hook placement. Visually, from the side, it may look like the hook is right under the C.G. on the wing. But when the glider rotates on tow, the effective hook placement may be a lot further back than you want. This is particularly an issue with big, fat, round old time scale fuselages like on a KA-6 or a Minimoa. This is why many scale sailplane flyers use a double line "bridle" that attaches to hooks on the underside of the wing. This takes the fuselage thickness "out of the equation" for launching.
So once you have your tow hook positioned properly, what else can you do to maximize launch height? One thing that really helps is to THROW your sailplane at an upward angle. This may sound silly to even mention, but many folks just give their plane a limp wristed toss... or no toss at all, and let the plane stagger and shudder out of their hand until it reaches flying speed. If you give the plane a good, hard, aggressive toss upwards, it is immediately at flying speed, and headed towards a release high in the sky.
If you find yourself having to hold a bunch of "Up" elevator to keep the plane tracking upward at a good angle, it is an indication that your towhook is too far forward. Move it forward 1/8 of an inch or so... and try again. Obviously, this is where those nice, extruded aluminum channel tow hook mounts come in to play.
(But make darned sure that the hook is LOCKED into position. You really don't want it moving on its own. Some folks use an extra screw and nut ahead of the actual threaded tow hook for some added security.)
When you have mastered these basics of getting high... err.... ah... launching effectively, then you can start playing with the big kids. Having a variable camber wing (ie: having flaps... or adjustable, droopable ailerons) will provide a bunch more lift on launch. But this requires a fair bit of skill, as you want to get that camber back to normal as the plane comes off the top of the launch. And for REALLY spectacular launches, you can do a Zoom launch. This is where you build up a lot of tension (and potential energy) by stretching the towline, and then doing a shallow dive at the top of the launch to reduce the grip of the towline on the sailplane.. and then ZOOOOOMING up into the air as much as 200 to 300 feet above the point of release. This is the technique that the championship level pilots use to get every inch of altitude. It is also the technique that the wannabe's use to lose a couple of hundred feet that they could have had if they had just done a normal, non-screwed up launch. Yep... it's all about that dreaded "P" word.
Practice! Flying and practicing will do more for your flying skill than any amount of reading that you can do..... but hey, reading this certainly beats watching another episode of "The Bachelor", doesn't it?
See you in the next blog article!
-Taylor
Anyway, this is the "launch" of the Soaring Stuff blog, so what better subject to deal with than launching.... a sailplane that is. Obviously, all soaring flights start with a launch, and for purposes of thermal duration flying, the higher the better. Unless you are just practicing spot landings, you'll probably want to get your bird as high in the air as possible. It just increases the odds that you'll come in contact with rising air ... either a thermal, or some sort of wave lift.
So how do we maximize our launches? Step one is to make sure that we have the tow hook placed in the optimum position. If your tow hook is too far forward, the winch or high start line will tend to pull the nose of your sailplane downward. All aircraft rotate in the pitch axis around that all important center of gravity (or "C.G.")
If the towhook is forward of the C.G., then the aircraft will pivot forward in a "nose down" direction, and you won't get much of a launch.
So... the natural thing to do is move the tow hook rearward and all will be right with the world, Right? CRUNCH! If the tow hook gets too far aft, everything gets really squirrelly. Your normally well behaved sailplane will suddenly take on a mind of its own, and try to twist, roll, stall, and do anything it can think of to evade the tow line. If you are lucky, your bird will just pop off the tow line... usually very quickly and dramatically. If you aren't so lucky, it will stay attached to the line, and attempt to smash itself into the ground.
So how do we determine a safe place for the tow hook before disaster strikes? One key (pardon the pun!) for checking this out is in your pocket. Pull out your key ring, and hang your sailplane by the tow hook, upside down from that steel ring that holds your house and Maserati keys together. A properly placed towhook will hang your sailplane almost level.... but without the plane trying to fall off onto the ground. If your fuselage is hanging really hard, tail down, then the tow hook is too far forward. If the hook is trying its best to slide off and drop your bird on the ground, then the hook is too far aft. Adjust it as necessary to achieve this slightly tail down attitude and you should be good to go for that first launch.
DISCLAIMER - Fuselage thickness (the distance from the belly of the plane up to the wing) can have a significant effect on this tow hook placement. Visually, from the side, it may look like the hook is right under the C.G. on the wing. But when the glider rotates on tow, the effective hook placement may be a lot further back than you want. This is particularly an issue with big, fat, round old time scale fuselages like on a KA-6 or a Minimoa. This is why many scale sailplane flyers use a double line "bridle" that attaches to hooks on the underside of the wing. This takes the fuselage thickness "out of the equation" for launching.
So once you have your tow hook positioned properly, what else can you do to maximize launch height? One thing that really helps is to THROW your sailplane at an upward angle. This may sound silly to even mention, but many folks just give their plane a limp wristed toss... or no toss at all, and let the plane stagger and shudder out of their hand until it reaches flying speed. If you give the plane a good, hard, aggressive toss upwards, it is immediately at flying speed, and headed towards a release high in the sky.
If you find yourself having to hold a bunch of "Up" elevator to keep the plane tracking upward at a good angle, it is an indication that your towhook is too far forward. Move it forward 1/8 of an inch or so... and try again. Obviously, this is where those nice, extruded aluminum channel tow hook mounts come in to play.
(But make darned sure that the hook is LOCKED into position. You really don't want it moving on its own. Some folks use an extra screw and nut ahead of the actual threaded tow hook for some added security.)
When you have mastered these basics of getting high... err.... ah... launching effectively, then you can start playing with the big kids. Having a variable camber wing (ie: having flaps... or adjustable, droopable ailerons) will provide a bunch more lift on launch. But this requires a fair bit of skill, as you want to get that camber back to normal as the plane comes off the top of the launch. And for REALLY spectacular launches, you can do a Zoom launch. This is where you build up a lot of tension (and potential energy) by stretching the towline, and then doing a shallow dive at the top of the launch to reduce the grip of the towline on the sailplane.. and then ZOOOOOMING up into the air as much as 200 to 300 feet above the point of release. This is the technique that the championship level pilots use to get every inch of altitude. It is also the technique that the wannabe's use to lose a couple of hundred feet that they could have had if they had just done a normal, non-screwed up launch. Yep... it's all about that dreaded "P" word.
Practice! Flying and practicing will do more for your flying skill than any amount of reading that you can do..... but hey, reading this certainly beats watching another episode of "The Bachelor", doesn't it?
See you in the next blog article!
-Taylor