Elastic Launched Glider B

[bjt4888]

How to calculate the area of wing if it has flaps? Including flaps or not?

Thanks,

Nathan

Nathan,

Yes, include flaps. Most successful glider wings are essentially 1/2 ellipse shaped. Area of a 1/2 ellipse, of course is "(radius 1 x radius 2 x 3.14)/2".

Also, for the sake of simplicity, I typically use "flat span" wing area, which is different than projected wing area (multiplier is the cosine of the dihedral angle).

Brian T

[maxvadas]

I have been having trouble with my transition. The glide is extraordinary, but the transition at the top isn't great. The plane looks like it will transition well, but then it dips down and loses about five feet before it finally snaps into its good glide. Any tips?

[bjt4888]

I have been having trouble with my transition. The glide is extraordinary, but the transition at the top isn't great. The plane looks like it will transition well, but then it dips down and loses about five feet before it finally snaps into its good glide. Any tips?

Max,

What glider design are you using? If a kit, I know the specs. If not a kit, please supply all measurements and details (ex. Wing span and chord, wing shape, wing dihedral, flap deflection amount, flap size, nose length, tail moment arm length, stabilizer span and chord and shape, fin width and height and shape, fuselage material, wing incidence (shimmed detachable wing?, unshimmed? Not adjustable?), stabilizer incidence (if any) and is any carbon used to stiffen fuselage, wing or other parts. What does your glider weigh? What is your launch inclination angle and bank angle? How high is the launch height? What are your flight times (knowing this helps the analysis).

Knowing the bone details, I can offer very specific feedback.

Brian T

[bjt4888]

Not “bone details”. Typo. Should have been “above details “

[maxvadas]

I am using a 2020 freedom flight kid

Thanks,
Max

[maxvadas]

Launch angle up is around 70 degrees, my plane turns right, the bank angle is 0 degrees but if I try to bank it to the right a little more it just rolls over, weight is about 4.2 grams, launch height is around 22 feet and the time is consistently around 17 seconds

Thanks,
Max

[bjt4888]

Launch angle up is around 70 degrees, my plane turns right, the bank angle is 0 degrees but if I try to bank it to the right a little more it just rolls over, weight is about 4.2 grams, launch height is around 22 feet and the time is consistently around 17 seconds

Thanks,
Max

Max,

God job supplying details. How much are your flaps deflected, or curved downwards? Have you verified that the deflection of the right flap is exactly the same as the right flap? How much right deflection is bent or set into the rudder? Do you have any incidence shims under the front edge or back edge of the wing attachment? Where is the balance point (center of gravity) in inches from the leading edge of the wing?

Brian T

[maxvadas]

Brian,



On both of my flaps, the trailing, middle edges of the foam are about an inch lower than the trailing middle edges of the balsa wings, I don’t really know how to explain the deflection of my rudder, but I’ll try. The very bottom of the balsa leading edge is 4 mm from the carbon, and the bottom of the trailing edge of the foam is 6 mm from the carbon rod. I don’t have any incidence shims, and the CG is pretty much exactly where the foam meets the balsa at the middle of the wings.

Thanks,
Max

[bjt4888]

Brian,



On both of my flaps, the trailing, middle edges of the foam are about an inch lower than the trailing middle edges of the balsa wings, I don’t really know how to explain the deflection of my rudder, but I’ll try. The very bottom of the balsa leading edge is 4 mm from the carbon, and the bottom of the trailing edge of the foam is 6 mm from the carbon rod. I don’t have any incidence shims, and the CG is pretty much exactly where the foam meets the balsa at the middle of the wings.

Thanks,
Max

Max,

Good job with additional detail. Please remind me of the wing chord dimension (width of the wing). Is it 3” so that the balsa forward portion of the wing is 1.5” width and the flaps 1.5” width also?

Flap deflection of about an inch sounds like a lot. Typical for a 3” chord wing would be 3/16” to 5/16”. We measure this deflection with a ruler using a reference point that is parallel to the forward portion of the wing, like the fuselage top or bottom edge (depending upon design).

A lighter glider will always transition better than a heavier glider. If it possible to build another copy of the glider using lighter wood (possibly with carbon reinforcement, if necessary) or, sand the wing thinner (see my instructions for building the 2014 flapper in Hip Pocket Aero/Science Olympiad topic) etc. the closer your glider is to 3.0 grams (as long as each component is adequately stiff) the better it will transition.

Possible solutions to transition issues would be:

1. Add 1/100” shim (small shim cut from a playing card or card stock business card would work) between the leading edge of the wing mount and the fuselage and then tape the wing mount back in place. Test with low power, moderate inclination, and 20 or 30 degrees of bank after a change like this and gradually find the new optimal bank and inclination angles in successive flights as you increase power.

2. Steeper launch angle. This is risky as you might get a hard stall and nose down dive.

3. Build lighter.

Brian T

[maxvadas]

Brian,

Thank you so much for the advice! I tried the shin today and it worked great! I got about 24 seconds in my gym so that was a improvement of 7 seconds. Much appreciated.

Max