Elastic Launched Gliders B

coachchuckaahs
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Re: Elastic Launched Gliders B

Postby coachchuckaahs » November 26th, 2018, 7:16 am

We had a similar problem with one glider. We played with flaps for awhile, but did not find the issue. Finally we put a different wing on the fuselage (taped on), and it did the same thing, while that wing was fine on its own fuse. Therefore, we cut the stab off and put on a new stab and fin, problem gone.

Whatever was not straight was subtle. Small errors on the tail group can cause big issues.

I would certainly look at flaps for differential flex, and look for wing warp. But if you have more than one plane (you should), try mix/match parts for diagnostic reasons.

Coach Chuck

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Re: Elastic Launched Gliders B

Postby WafflesareReal » December 3rd, 2018, 2:54 pm

My glider keeps turning when I do not want it to. Please help me.

Thanks.

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Re: Elastic Launched Gliders B

Postby bjt4888 » December 3rd, 2018, 3:14 pm

Waffles,

Unwanted turn can come from a number of sources, including: rudder offset, one wing heavier than the other, warped wings, warped fuselage, stabilizer tilt, etc.

Please describe your glider in detail (ex. Kit or from a particular published plan, or self designed 1/16” sheet rectangular 3” width wing with 15” x 3/32” thick x 1/4” deep tapered to 1/8” at the tail fuselage and ... dimensions for the stabilizer and rudder, and weighs...grams).

Also please describe the turn. Is it hooking on launch? Turning too tight of a circle in glide?

Also please describe your launch device and launch details (ex. Launcher 6” x 3/16” wood dowel with 6” loop of tan sis rubber; launched at 45 degree angle with 10 degrees of bank in a 25 ft. Ceiling site and launched to about 20 ft.).

With this info, I can provide some specific suggestions.

Brian T
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Re: Elastic Launched Gliders B

Postby falcon1236912 » December 4th, 2018, 7:03 am

What times have people been getting with the FF kit?

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Re: Elastic Launched Gliders B

Postby bjt4888 » December 4th, 2018, 9:31 am

Falcon,

As the FF kit is very similar to gliders that my students built for Division C in 2013 and 2014, and as the wing loading is very similar in this year’s rules as compared to 2014 (this year = .125 g/square inch of projected wing area vs. 2014 = .115 g/sq in), the FF glider should be capable of 1.1 to 1.15 seconds of duration for each foot of launch altitude if built accurately to minimum weight of 3.5 grams and trimmed to transition without loss of altitude.

My and 2014 students flew 27.5 - 28.5 seconds at a launch height of 25 ft (their gym ceiling was 27 ft). Based upon past results, these flight times should probably be competitive to win at any State Championship and at Nationals.

Brian T

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Re: Elastic Launched Gliders B

Postby prd06 » December 13th, 2018, 2:24 pm

Hi I'm having an issue with my glider transitioning from the launch to the glide.
The glider does not have flaps and is made entirely of balsa. It has dihedral in the wing and stabilizer (no rudder/fin) When I just threw it, it glided pretty smoothly and was turning, but in the launch, it went straight up, then the glider suddenly pitched down and nose-dived into the floor. Does anyone know what is causing this? Do I need to launch it a certain way, or change the wing incidence, or change the surface area of the wing?

Thanks.

bjt4888
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Re: Elastic Launched Gliders B

Postby bjt4888 » December 13th, 2018, 3:14 pm

Prd06,

Why no fin? The fin provides an important element of yaw stability that balances the wing dihedral lateral area.

What is the current incidence setting of the wing and stabilizer?

What is the current center of gravity location?

If you provide more details about your airplane design and specifications, I can give better feedback.

Two launch angles are critical; the inclination angle and the bank angle. Usually, a glider that is designed to turn in right circles needs to be banked to the right anywhere between 5 and maybe 30 degrees. Start with low power launches with moderate (maybe 30 degrees) inclination angle and maybe 5 degrees of bank. Starting this way should allow you to evaluate the first flight and determine if more or less bank is needed. More is needed if the airplane noses up into a stall and dives to the floor. Less is needed of the glider hooks hard to the right.

Once you have determined a pretty good bank angle, add more power and increase inclination angle to maybe 35 degrees or 40 degrees. As power is added, slight changes to bank angle might be necessary.

Add more power gradually. Our first flights transition at about 10 ft. Second flights maybe 15 ft. 3rd flight 20 ft. Etc. till your at just below the ceiling.

Brian T
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IvanGe
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Re: Elastic Launched Gliders B

Postby IvanGe » December 15th, 2018, 8:08 pm

I was testing my gliders in the gym today and it was getting launched and then semi-nosediving for around 5-6 feet before transitioning into a glide. However, once it starts gliding it glides nicely and it doesn't dip or stall. I wonder if it is the degree of the angle that I am launching it at or if the center of gravity is too forward. The other thing I was thinking about was moving the vertical stabilizer to a less of an angle. Anyone have any suggestions?
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Re: Elastic Launched Gliders B

Postby bjt4888 » December 16th, 2018, 5:56 am

Ivan,

What is the inclination angle and bank angle of your launch? By “nose diving” are you referring to a sharp hooking at the top of the climb that results in loss of altitude? If so, reduce the bank angle by a few degrees. Make this change gradually as inadequate bank can result in a hard stall and straight in nose dive to the floor.

More details about your glider and your launch would allow me to give better advice.

Brian T


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