The documentation for the 1st version can be found here.
My Goals for this project:
Improve the controls
Increase the wing-span
Reduce the drag
Improve the picture quality of the onboard DVR, e.g., Vibration-isolation, and keep the prop out of the FOV.
Use the Smart Tunnel to test and improve the design before the test flight.
The embedded elevator and rudder controls design
The upgraded parts
A solid model of the original passive glider model
Rudder push-rod design
Elevator direct-drive control
What I will do:
Test the performance of the original airfoil of the Fox-Glider
Choose an airfoil shape for the extended wing section.
Test the final wing (original + extended part) if the design increased the total wing performance (L/D, Cl/Cd)
Constraints:
The airfoil cord should be 90mm
Normal flight speed will be ~10m/s. Hence, Low-Re# of 60K to 100K and probably high AoA ~7deg.
The mounting angle of the new wing section should be aerodynamically matched to the original wing section.
The pitch moment should be less than the elevator surface's maximum torque.
I estimate that the upgraded model will weigh around 160[gr].
The airfoils that might work for this project are:
Trainer60
SG6043
SG6041
SD7037D
SA7036
SA2035
Avistar
BW-3
Geo417A
PT-40
Givens:
Re = V*L / u link
Lift = 0.5*p*Cl*V^2*A link
Re - Reynolds number
Lift - The lift force of the wing [N]
p - Fluid (air) density [Kg / m^3] = 1.225 kg/m3 @300K -< 25DegC
Cl - Lift coefficaint (from airfoil datasheet or wind-tunnel measurements)
A - Wing area [m^2]
V - Air velocity [m/s]
L - Referance lenght (airfoil cord) [m]
u - Fluid (air) kinematic viscosity = 1.57e-5[m^2/s] @300K -> ~25DegC
Model weight = 0.16[Kg]
Cruising speed = 10[m/s]
Wing area = 0.6*0.09 -> A=0.054[m^2]
Re = (10 * 0.09) / (1.57*10^-5) -> Re=57K (For normal flight)
0.16*9.8 < 0.5 * 1.225 * Cl * (10^2) * 0.054 -> Cl > 0.47 @10[m/s] Re=57K (Normal flight)
0.16*9.8 < 0.5 * 1.225 * Cl * (7^2) * 0.054 -> Cl > 0.94 @7[m/s] Re=40K (Slow flight)
0.16*9.8 < 0.5 * 1.225 * Cl * (6^2) * 0.054 -> Cl > 1.3 @6[m/s] Re=34K (Landing)
0.16*9.8 < 0.5 * 1.225 * Cl * (5^2) * 0.054 -> Cl > 1.8 @5[m/s] Re=28K (Maybe possible with flaps)
After examining the results, I narrowed down the airfoil list to two:
SG6043 - Good for high lift force at cruise speed of >10[m/s]
Geo417A - Good for high lift force at slow speed of <10[m/s]
Dimensions: 160x80mm
Current weight is less then 14g
+-6.4deg control surface deflection
I did not want to cut the original body yet, so I made a mockup just to connect the tail section and to install it inside the wind-tunnel. I kept a distance of 270mm between the elevator and C.G - like in the oreginal model.
The mockup is installed inside the wind-tunnel
+-6.4deg produces ~+-9[N*mm]. Similar to 3.4[gr] weight placed at the tail (9000/270/9.8 = 3.4[gr])
+-6.4deg produces ~+-23[N*mm]. Similar to 8.6[gr] weight placed at the tail (23000/270/9.8 = 8.6[gr])