Elastic Launched Gliders B

[AirplaneMan]

Ok so I had a few good flights when I increased the incidence, but then the glider crashed and when I rebuilt it, I put less rudder.
Now the glider seems to be flying only straight, although when I bend the fin with my hand, it temporarily helps the glider to turn.
Also, sometimes I notice flights where I will launch the glider, and then it goes up, but then immediately flies towards the ground, but not at a complete 90 degree angle. It's more like a 45 degree angle, but either way the glider crashes to the ground. Why is this happening?
Also, my glider is now like 3.8 grams because of all the repairs. The center of gravity is a little bit ahead of the wood and flap joint. The stabilizer is not tilted at all, and I have been using a pretty steep launch angle (60-80 degrees).
The bank angle is maybe 45-60 degrees. The incidence is about 1 degree I think. It is possible the one flap is more bent than the other (the one on the left might be a little more stiffer than the right, but if it is there's a very small difference)
The glider is still flying really fast. It's supposed to have a slow glide, but it seems like it's flying too fast and that's reducing my flight time. How can I slow it down?
Thanks, AirplaneMan

[Maxout]

Now the glider seems to be flying only straight, although when I bend the fin with my hand, it temporarily helps the glider to turn.
Also, sometimes I notice flights where I will launch the glider, and then it goes up, but then immediately flies towards the ground, but not at a complete 90 degree angle. It's more like a 45 degree angle, but either way the glider crashes to the ground. Why is this happening?

Ok, you need more stab incidence before you do anything else. Bent the trailing edge of the stab up until the model recovers into a level glide. If it stalls afterwards, add clay to the nose until that goes away. After that, you can add more rudder trim. If this causes the model to roll too hard in the direction of the rudder trim on launch, grab the wing on the side it's rolling toward and twist it right next to the fuselage so that the leading edge is higher than the trailing edge. Don't worry of the wood starts cracking, you can just seal it with a little CA glue. This will likely induce a glide stall and require a touch more clay on the nose.

[bjt4888]

Airplaneman,

Good job supplying additional detail. I like Josh’s suggestion of additional decalage angle. Does the FF glider have a wing mount that is taped to the fuselage? If so, another way to increase decalage is to remove the front piece of tape and insert a shim between the mount and fuselage and use a new piece of tape to secure again.

Remember that a shim of 1/64” increases wing incidence 0.3 degrees. For most ELG’s, this is a significant change. I’ve even used little pieces of playing card as shims as they are about .01” thick. Please describe “goes up and immediately flies toward the ground” in more detail. I’m assuming that the glider is banking this entire time. If it’s banking and turning into the ground and the right wing never levels out, you could try less bank angle in the launch. If that doesn’t help, a little extra flap deflection on the right side might help.

You could also try a shallower launch inclination angle to possibly get a better look at the flying characteristics.

Flappers fly best if the flaps are equal in deflection and stiffness. Did you sand the flaps when you constructed (not all foam is designed to be sanded, just wondering). If you did sand, and the flaps are unequal in stiffness, sand the stiffer one a little more till they are better matched. You mention, “one flap is more bent than the other”. By how much? I’m not sure how much flap deflection the FF kit recommends, butif the flaps are soft, we have used as much as 3/16” with a high degree of success. I would think that 1/8” flap deflection would be the minimum you want. Measure settings like this using the fuselage top or bottom edge as a reference point.

Good

[AirplaneMan]

So both flaps are about evenly deflected and both have about the same thickness, although I checked and the right flap is a tiny tiny bit less thicker than the left flap.
Also, the glider is meant to turn left for a counter-clockwise circle.

I tried increasing the incidence a lot and I had to also add more clay to compensate for that. But this same situation seems to occur. The glider goes up and then immediately flies towards the ground. What I mean by that is that the glider goes up, then after reaching its maximum height, it slightly turns to the left and flies downwards at a 45 degree angle. It doesn't dive at a 90 degree angle; it's almost as if it's a glide, but the glider loses altitude very quickly and hits the ground.

Anyway, at first increasing the incidence was indeed working, but then in 1 flight the situation described above occurred, and some parts broke so I had to make some minor repairs. After that, I tried again but then the same situation as described above occurred. However, I'm not sure if that happened because the incidence was wrong or because I put too much clay on the nose. Sadly, I couldn't continue testing because the basketball team needed to use the gym.
Is there anything I can do to fix the issue (the one describe in the 2nd paragraph)?

[bjt4888]

Airplaneman,

Sounds like you’re launching too steep. Try starting with about 30 degrees inclination and moderate power and increase inclination about five degrees each subsequent flight till you find the inclination that the glider likes.

Before this flying though, reset the CG per plan by taking off clay from the nose and remove all incidence shims. Be sure that flap deflection (amount flaps are dropped down) is at least 1/8” and even. Hand glide the glider gently aiming at a point on the floor about 50 ft away releasing smoothly so the the airplane flies out of your hand. If the airplane dives, add a 1/64” shim. Repeat till the glide is smooth and flat. This hand gliding is trickier than it sounds. Most of my students release the glider slightly nose up when learning this skill. Slightly nose produces a stall every time, but not a real stall, a stall due to improper alignment during test gliding. Many students I coach need dozens of hand glide practices before they can do this properly.

With the design CG and a flat test glide, the next step is to throw the glider a little harder in a test glide. The glider should glide mostly flat, gently climbing into the smooth left turn. If it dives or stalls, one more shim change is probably necessary.

Now your ready to start flying per the above with shallower launch angle.

As an event supervisor, I’ve seen quite a few FF gliders flying well. I’m sure you’ll get there. Let us know how things go.

Brian T

[fifty_missions]

I tried increasing the incidence a lot and I had to also add more clay to compensate for that. But this same situation seems to occur. The glider goes up and then immediately flies towards the ground. What I mean by that is that the glider goes up, then after reaching its maximum height, it slightly turns to the left and flies downwards at a 45 degree angle. It doesn't dive at a 90 degree angle; it's almost as if it's a glide, but the glider loses altitude very quickly and hits the ground.

Airplaneman-
Gliders are tougher to trim then Wright Stuff. See my list below-

If the glider ROLLS Left, points its nose down, then the left (Port) wing needs more positive incidence. That is, the leading edge needs to be higher than the right (Starboard) wing.

1) Technique #1, Turn model upside down and bend the port wing's leading edge up a couple of degrees. It the wing cracks, drop some CA in the crack.

2) Technique #2, crack the port wing's wing root at the leading edge and lift it a degree and glue in place.

3) If the glider enters transition, note if the orbit is left or right. I suspect a left hand orbit. If the glider is stalling, add clay to reduce the stall.

4) If the glider has a slight diving flight, remove some clay.

Report on these changes and I can offer more suggestions.

Regards,
50 Missions

[fifty_missions]

One lore thing.... Important.... BANK the glider on launch.

50 Missions

[builderguy135]

Any tips on how to reduce drag to get to a cat II ceiling? I was far from being able to get to the 35' at Cornell invy and I don't know how I can get my plane to climb higher without something breaking.

[bjt4888]

Builder,

Very stiff and light fuselage, wing and stabilizer. Usually accomplished by use of very good quality wood and judicious use of carbon. See Designs by: Stan Buddenbohm and Kurt Krempertz on the AMA Glider website and Bill Gowens design on Hip Pocket Aero website. All good AMA Category II gliders easily fly to the 15 meter ceiling limit.

I use Bill’s design with Stan’s Littl Sweep glider fuselage for up to 65 ft ceiling. Once you have a good airplane, to get to a tall ceiling may require a thicker rubber loop and a good bit of stretch on the rubber.

Brian T

[bjt4888]

One more note. If you have a glider design that won’t climb high, it’s probably not a drag issue, it’s more likely that something is flexing that shouldn’t be. Hence the recommendation for good wood and carbon.

Actually, with the right design and very good wood, carbon on the wing shouldn’t be necessary on anything except the fuselage to get 35 ft high. If your wing wood is marginal, add carbon.