TM 10-1670-287-23&P
0003 00
MC-4 RAM AIR FREE-FALL PERSONNEL PARACHUTE SYSTEM
THEORY OF OPERATION
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MC-4 RAM AIR FREE-FALL PERSONNEL PARACHUTE SYSTEM THEORY OF OPERATION
The MC-4 parachute system is a dual parachute system with similar main and reserve canopies. Both
parachutes are located on the back of the parachutist leaving the front clear for mounting additional
equipment or instrumentation. The principles used in its construction allow it to have high forward speed,
a 3 to 1 glide ratio, and excellent maneuverability. In an emergency, the ram air system uses a single
point canopy release to jettison the main canopy and deploy the reserve canopy. The reserve parachute
uses a free bag deployment system, a high drag pilot chute, and an 18-foot bridle line with deployment
assist pockets; each designed to increase the reliability of the reserve parachute in an emergency.
1. Canopy. The ram air canopy incorporates spanwise construction. By running fabric from side-to-side
instead of from front-to-rear, the size of each cell is not limited to the width of the cloth. This method
of construction results in a decrease in weight and bulk and a higher level of safety. 13-airfoil section
ribs dividing the canopy into 7 cells attach the upper and lower surfaces of the canopy. Each rib has
three (3) elliptical crossports cut into it. These crossports allow air to flow spanwise through the
canopy to equalize parachute pressurization. During descent, air enters the cell openings at the
leading edge, pressurizing each cell and giving the canopy its shape and glide characteristics. A
glide ratio of 3-feet of lateral movement to 1-foot of the descent is obtained. The rate of descent is
determined by the suspended weight as well as the angle of the parachute with respect to the ground
and distance that the trailing edge is pulled down. The parachute is controlled and maneuvered by
using trim tabs and control lines. The canopy has two control lines that connect to five (5) cascaded
lines attached to the trailing edge of the outer cells. By pulling on either the right or left control line,
the canopy will turn in that direction. By pulling down on both control lines simultaneously, the rate of
descent and the forward speed are decreased. Trim tabs are used to change the glide angle of the
MC-4 canopy.
2. Slider. A slider is used with the ram air parachute system to reef the opening of the canopy and
reduce opening loads. This allows for a more controlled opening of the canopy. During packing, the
slider is placed at the lower surface of the canopy. During opening, the slider controls the drag area
of the parachute as it slides down the suspension lines.
3. Stabilizer Panels. During parachute descent, turbulent air can be produced at each side of the
canopy, creating instability. The addition of stabilizer panels to each side helps reduce turbulent
airflow, thus stabilizing the canopy.
4. Deployment Brakes. Without deployment brakes, the parachute deployment becomes unreliable.
Deployment brakes lock down the trailing edge of the parachute using the control lines during
deployment. They are set by pulling each control line down through the guide ring and locking each
in place by using the appropriate toggle. The control line remains locked in place until manually
released by the parachutist after deployment.
