Future Aviation Events

[mrsteven]

pitch meaning twist. Are you launching with your plane level to the ground, twisted to have a pitch...
Usually you treat the horizon as 0 degrees so your 160 (from ground) would be 70 degree from the horizon

[jander14indoor]

<SNIP>Lol sorry. Well its my own design. I only fly it indoors and it does loops any way you throw it by hand or launcher. Launcher is a wooden Y. rubber size is 1/8th i believe and it is about 30 cm. tilt of wings is hardly any about even. Stretch hardly changes anything on this glider. It doesnt go up to the cieling it goes straight into a loop and then half way through the 2nd one it lands on its back and sinks. When it is hand launched it goes up even if i throw it straight and it does a loop and then always fails in the 2nd loop. It falls on its back and then goes down.
I hope thats all that is needed sorry I have so many questions. Thanks alot though

OK, that's more useful.

I'm guessing when you throw by hand you throw hard. What happens when you just give it a gentle level push? Maybe from a ladder or a few steps up on a bleacher. Before you spend too much time on the rest of why I think you are looping, try that kind of gentle launch and let us know what happens. If you don't get a nice glide, let us know what is happening so we can diagnose those problems first. If you aren't gliding right, fixing the launch is a waist of time.

I THINK I know what's happening. One of the challenges of glider is that they fly in two very different speed ranges.
- When launched they go very fast. When gliding they SHOULD go very slow.
- The problem is, you spend most of the time at the slow gliding speed where its essential that the lift just match the weight of your glider. During launch you are going much faster so have MUCH more lift.
- As a result, your glider keeps trying to pitch the nose up, more and more eventually looping if you have enough power. You can get enough power from the catapult or hard hand launches.

Two things are done to tame this. One design, the other is technique.
- Design first. Two things pitch the nose up, excess lift, and nose up moment from the horizontal stab (if the stab is flat, you get this by having a negative incidence, ie the leading edge points down with respect to the trailing edge). The lift you can't stop, you'll need it in the glide. The stab you can manage. To fly stable, you must have SOME nose up pitch. How much depends on where the center of gravity is. The problem with too much nose up from the stab is back to speed again. A little at slow speed becomes a lot at high speed. Look back up the string to where we were talking about incidence. Most catapult launch gliders have 0-0 incidence for just this reason. So you DON'T get a lot of added nose up at high speed from the stab. You then trim for a nice glide by adjusting cg. Look at the Simple Simon design on the AMA site referenced above in this string. If you study it carefully you'll note the wing and horizontal stab are both parallel. This is a critical feature.
- Technique second. You CAN'T stop the excess lift from the wing on high speed launch. If you launch wings level you WILL loop. So, what do you do. Launch with the wings tilted to the right (assuming a right hand design). This will turn the loop into a steep spiral climb. The trick is to figure out how much tilt and nose up to spiral once or twice to the ceiling where you want the glider to roll out and start gliding. I can't tell you the exact answers because it depends on too many things. You'll just have to try a bunch of things yourself. till you find the right one. I might suggest you try to launch with your 10 to 20 degrees short of vertical and wings tilted at 45 degrees to the right unless you are launching a design recommends a different starting point.

Hope that helps, keep asking questions. Just give us more detail when you do.

Jeff Anderson
Livonia, MI

[jander14indoor]

Hmm, seeing some more problems with terms. The orientation of a plane (glider) through the air are typically described by the terms roll, pitch and yaw. Look those up so you can have a better understanding, but briefly.

Think of the plane flying straight and level. Roll is the wings twisting right and left around an imaginary line along the fuselage, parallel to the ground. Right wing drops as left wing rises and vice versa. Pitch is the plane spinning around a line drawn from tip to tip of the wings, perpendicular to the roll axis and parallel to the ground. The nose moves or pitches up and tail moves down and vice versa. Yaw, a little harder to see, but important. Here you draw a line perpendicular to the first two axis which means its perpendicular to the ground or a vertical line. Yaw is the plan moving around this axis the tip of the fuselage swinging right or left and the tail vice versa of course. By convention (and for good physical reasons) we typically draw these imaginary lines through the center of gravity.

Think of an x-y-z coordinate system.

Now, here comes the tricky part because I described these axis with reference to the ground. Well, that was just for convenience of explanation. In reality, these axis stay locked to the plane! Roll is always the wings spinning around the fuselage, whatever orientation the plane is in.

OK, so back to the launch description using the correct terms. You want to launch the glider with the rubber band about 70 to 80 degrees up from horizontal and the nose of the glider pitched up the same. you want to roll the wings from level to the right about 45 degrees for a starting point.

Jeff Anderson
Livonia, MI

[science8]

I was so excited my glider went in a circle the first time and now it only does loops

[scioly1195]

Could someone please explain the dime rule to me?
I literally attached a chapstick cap to my glider, but I'm starting to doubt whether that's the point of the rule.

Also, where should the CG be for a good glider?

[jander14indoor]

The point of the 'dime' rule or Chapstick cap is to have a safely blunt point on the tip of the glider. The rules writers are concerned about the safety of an overly heavy glider launched by an oversized rubber band injuring another competitor, tournament staff or audience.

No we do NOT mean for you to glue a cap onto the glider it is just stealing an approach to ensure a blunt tip used by the bottle rocket team that seemed to work well.

The rules committee meets Sunday after the National Tournament to finalize the draft that then goes through an extensive checking process before being finalized and published next fall. There could be many iterations before then and you are not safe assuming even us rules writers know how it will come out till you see it published.

SO.... don't worry about it for your trials and prep work this summer. Just make your tips blunt and friendly and your gliders light.

As to cg, of course, that depends on your wing and horizontal stab details. You can get some sense by looking at the glider designs on the AMA glider site referenced above. Expect a good working cg to be somewhere around 50% of the wing chord measured from the leading edge.

[chalker7]

The point of the 'dime' rule or Chapstick cap is to have a safely blunt point on the tip of the glider. The rules writers are concerned about the safety of an overly heavy glider launched by an oversized rubber band injuring another competitor, tournament staff or audience.

No we do NOT mean for you to glue a cap onto the glider it is just stealing an approach to ensure a blunt tip used by the bottle rocket team that seemed to work well.

The rules committee meets Sunday after the National Tournament to finalize the draft that then goes through an extensive checking process before being finalized and published next fall. There could be many iterations before then and you are not safe assuming even us rules writers know how it will come out till you see it published.

SO.... don't worry about it for your trials and prep work this summer. Just make your tips blunt and friendly and your gliders light.

This is all true, but if you're competing this weekend it's good to note that a Chapstick cap is not larger than a dime (as required by the rules.)

[calliekernick]

I interpreted the rule as dealing only with the bluntness. I thought as long as the edge of the fuselage is as curved as a dime, it would be valid under the rules. Does the rule mean that it has to be physically larger than a dime?

[chalker7]

I interpreted the rule as dealing only with the bluntness. I thought as long as the edge of the fuselage is as curved as a dime, it would be valid under the rules. Does the rule mean that it has to be physically larger than a dime?

This is neither a place for official clarifications, nor am I running gliders on Saturday, but if I were, I would be checking to see if the blunt tip of the fuselage had a radius larger than a dime.

[science8]

Places in nationals?