Elastic Launched Gliders B

[AdiMohapatra77]

Is the protege glider better than the guru glider?

[Hartman]

Thanks, Brian, but I think I have it mostly figured out. However, one more question I have is on storing my glider. Every time I take it out again for the next practice, it seems different from last time. I've been thinking that it could be the cold temperatures that are changing my glider whenever I bring it into the car and drive over to the gym. Is it true that this could be happening?

[bjt4888]

Hartman,

Good job. It is one of the complexities of a flapper glider that the flap curve “relaxes” in storage; even for one day. I measure and reset flaps every time I fly.

If built from good quality wood and stored in a moderate humidity, nothing else should change much unless stored for a number of months. Cold temperature in the drive to the gym is not a problem.

Good luck in your remaining competitions.

Brian T

[builderguy135]

Does anyone know where I can buy less than 5#/ft^3 wood?

[bjt4888]

Builderguy,

If you pay the up charge to Specialized Balsa for specific density and order 5-6 lb cu ft, you can inspect the sheets of wood by holding up to a light source and cut your parts from the clearest sections of the sheet. These sections of the sheet will likely be in the 4-5 lb cu ft range.

Maybe you’ve already seen this, but it is usually true that very light wood is sometimes “punky” and doesn’t have much structural integrity. You can fix this by strategically adding thin strips or threads of carbon. 1k carbon tow thread, applied with thinned duco cement only adds about .005 g/inch.

Also, if you are shooting for larger wing area very light wings, light foam for flaps is not a bad idea. Very light foam is roughly equivalent to 3 lb cu ft balsa.

Brian T

[bjt4888]

Builderguy,

Pictures and description of my version of a medium weight glider with foam flaps are near the bottom of this Hip Pocket Forum thread:

http://www.hippocketaeronautics.com/hpa ... ic=16492.0

Sorry, i May have posted this previously.

Brian T

[bjt4888]

Sorry, “medium weight” for AMA competition is 2.0 grams.

[builderguy135]

Builderguy,

If you pay the up charge to Specialized Balsa for specific density and order 5-6 lb cu ft, you can inspect the sheets of wood by holding up to a light source and cut your parts from the clearest sections of the sheet. These sections of the sheet will likely be in the 4-5 lb cu ft range.

Maybe you’ve already seen this, but it is usually true that very light wood is sometimes “punky” and doesn’t have much structural integrity. You can fix this by strategically adding thin strips or threads of carbon. 1k carbon tow thread, applied with thinned duco cement only adds about .005 g/inch.

Also, if you are shooting for larger wing area very light wings, light foam for flaps is not a bad idea. Very light foam is roughly equivalent to 3 lb cu ft balsa.

Brian T

Thanks. I already used foam to make the glider lighter. What would be the benefits of using lighter wood anyways?

[bjt4888]

Builderguy,

I only use lighter wood if I need to in order to get down to the weight minimum. Very light wood almost always requires use of various types of carbon application, which increases build time.

You will see that my design from 2014 uses carbon on the fuselage. This allowed us to get the fuselage weight down to 0.65 g and still be very stiff. This light weight fuselage allowed the design to use slightly heavier 6.0 lb cu ft for the wing, which, if selected carefully for grain and stiffness, is stiff enough to resist over flexing without using carbon. So, the two component wood densities and weights are selected in concert with each other.

Stabilizer and fin wood for my designs is always “super quality” 5.5 lb cu ft, or less, c-grain. Some of this stabilizer wood that I let my students use has been in my collection for more than 30 years.

Brian T

[builderguy135]

Builderguy,

I only use lighter wood if I need to in order to get down to the weight minimum. Very light wood almost always requires use of various types of carbon application, which increases build time.

You will see that my design from 2014 uses carbon on the fuselage. This allowed us to get the fuselage weight down to 0.65 g and still be very stiff. This light weight fuselage allowed the design to use slightly heavier 6.0 lb cu ft for the wing, which, if selected carefully for grain and stiffness, is stiff enough to resist over flexing without using carbon. So, the two component wood densities and weights are selected in concert with each other.

Stabilizer and fin wood for my designs is always “super quality” 5.5 lb cu ft, or less, c-grain. Some of this stabilizer wood that I let my students use has been in my collection for more than 30 years.

Brian T

Thanks for the help!