PART 6: PARACHUTE SPECIFICATIONS AND PERFORMANCE:




The modified Aerotech Astrobee D rocket kits uses a Paratech Parachutes 6 foot diameter cross chute with an arm to witdth length (W/L) ratio of 3:1. The surface area for this parachute is:

So = [ (2) (Dc) (W) - (W) ^2 ] = [ (2) (6) (2) - (2)^2 ] = [ 24 -4 ] = 20 ft^2

W/L = arm width to length ratio (ft): (6 ft / 3 ) = value of 2 ft for cross arm width (W)
W = cross chute arm width (ft)
Dc = constructed parachute diameter

Cross Chute Drag Coefficient (Cd) = 0.85

Material = 1.1 oz/yd^2 F-111 ripstop nylon (fabric strength = 42 lb/in^2 and tear strength = 5 lb)
Suspension Lines = 80 lb dacron line
Parachute Bridle = 1/2 inch 550 lb kevlar tape and 3/16 in 400 lb flat braided dacron line
Hardware = No. 4 Rapide Links at 400 lb working load
Skirt Tape Reinforcements = 200 lb nylon
Number of Lines = 16
Max Design Load = 832 lb = [ (80-lb x 16 lines) (0.65 loss factor for of 35% for line knot at each end ]
Working Load = 400 lb
Safety Factor = 3

Payload Weight = 8.5 oz (0.53 lb) for IAX-96 accelerometer board, 2 9-V batteries and mounting hardware.
Cross Chute Weight = 5.9 oz (0.37 lb) includes two no. 4 rapide links and 5 ft dacron bridle.
Total Rocket Weight = 3.7 to 4.0 lb (with motor, parachute and payload)

Parachute Descent Rate For Listed Max Weight:
(nominal projection for sea level standard day conditions)

Vt = [ (2)(W) / (Cd)(rho)(So) ] ^1/2 = [ (2)(4.5) / (0.85)(0.00237689)(20)^1/2 = 14.1 ft/sec (9.6 mph)


Vt = terminal velocity (ft/sec)
W = weight (lb)
Dc = constructed parachute diamter (ft)
rho = 0.00238689 slugs/ft^3 (standard day conditions at sea level; 59 degrees F and seal level altitude)
So = parachute surface area (ft^2)

Note: Values for atmospheric density (rho) based on altitude are obtained from the 1976 U.S. Standard Atmosphere Tables.


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