Glider Design Project Information
MATERIALS: Each student will be issued the following materials:
1/16” x 4” x 18” balsa sheet, 3/16” x 1/2” x 18 balsa stick, clay ballast
DESIGN CONSTRAINTS
 Your glider must be constructed only from your issued balsa (one sheet and one stick)
 Wing span
18 in, ballasted gross weight 1 oz, Vtrim 25 ft/s
 The spreadsheet does not account for control surface stall. Therefore, it is very
important to avoid lift coefficients above stall. As a rule of thumb, keep CL for the wing
and horizontal stabilizer below 0.5.
 Other design constraints are contained in the spreadsheet, beginning with cell Q32.
These constraints are meant to ensure your design is reasonable and has a chance of
performing well.
 No cells on the left side of the design worksheet (columns A through L) may be red
(indicating you have violated a design constraint) at your design’s maximum range
velocity. Cells may be red at your design’s maximum endurance velocity. Exceptions
may be approved by your instructor once he/she has determined your design is
reasonable.
GLIDER HINTS AND GUIDANCE
1. You could have the best design in the world, but if you don’t build it right, it won’t fly well.
2. You can design a conventional (rear tail) or canard glider (rear wing). The canard design
seems to have fewer problems with spiraling. Regardless, the wing span and the fuselage
should each be around 15 inches. Adjust wing and tail location forward and aft as
appropriate. Wing root chord should be at least 2.5 inches to prevent stalling due to low
Reynolds number.
3. Wing dihedral (less than 6 degrees) helps roll stability and wing sweep (less than 20
degrees) helps yaw (directional) stability. Directional stability is also function of tail size and
distance from center of gravity. A larger horizontal tail size has a significant impact on pitch
stability. Tail dihedral is not very useful and is difficult to implement.
4. |CN/CL| ratio needs to be between 1/3 and 2/3. If it’s too high, increase CL by increasing
the wing dihedral (). Increasing wing sweep (LE) should also help. If the ratio is too low,
increase CN by increasing the size of the vertical tail or moving it farther away from the nose
of the aircraft. You want the value to be closer to 1/3 to avoid the spiral mode.
5. Make sure the Vtrim you input in cell K21 is the same value the spreadsheet calculates in cell
E39. This value changes every time an adjustment to the glider design is made.
6. The L/D ratio should be as high as possible, but if it’s too high (more than about 12), they
could be designing a glider that’s unrealistic. Just look at the design, and something may jump
out at you.
7. Be sure the angle of attack () isn’t too high… anything more than about 10 degrees or so.
They may have to redesign the entire glider to make this one work. This could also be the
result of a too small a horizontal tail. If the tail is small, the incidence angle must be high,
which causes the trim angle of attack to increase.
8. Be sure the tail incidence angle (it) isn’t too high... anything more that about 10 degrees or
so. If it is, they need a bigger horizontal tail. Their L/D ratio may decrease, but the glider
won’t be stable without a decent tail!
9. When you are satisfied with your glider’s layout, evaluate its stability and glide
performance. Investigate different combinations of parameters to optimize L/D while
satisfying stability constraints. Refer to the following table for stability guidelines:
STABILITY
TYPE
PRIMARY
CONTRIBUTOR
DESIGN PARAMETER
SUGGESTED RANGE
TO INCREASE
DESIGN PARAMETER
Longitudinal
(pitch)
Wing
&
Horizontal Tail
0.01 < SM < 0.20



add ballast to nose
move wing or tail aft
make horizontal tail larger
Directional
(yaw)
Vertical Tail
0.001/° < CN < 0.003/°



make vertical tail larger
move tail aft
sweep wings aft
Dir/Lat ratio
(yaw/roll)
Wing / Vertical Tail
1/3 < |CN / CL| < 2/3


decrease wing dihedral
make vertical tail larger
10. You must be able to cut your glider from the 4”-x-18” sheet of balsa wood. Before you cut,
sketch each component (scale: each block is one inch square) on the diagram below:
11. Do not glue the horizontal tail to the fuselage but to use rubber bands and wooden wedges
to attach the tail so that you can adjust the tail incidence angle on fly-off day. However, it may
be beneficial to glue the horizontal tail to the fuselage at an incidence angle at which the glider
seems to fly well, and then adjust the speed by adding/subtracting ballast.