Air Data Probes and Sensors for Small- and Mid-Sized Aircraft
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Trailing Bomb Usage Note

This information is provided only for the purpose of communicating how a specific customer uses a trailing bomb. It is not a recommendation from SpaceAge Control. The flight test engineering for a trailing bomb use must be performed by the user and the user is solely responsible for all flight test engineering activities regarding trailing bombs.

The trailing bomb is mainly used for rotary wing aircraft and very seldom for fixed wing aircraft. A trailing bomb flight is considered hazardous and safety is critical. It requires a chase aircraft at all times and the there must be a cut or quick disconnect feature.

For deployment, the trailing bomb is attached to the aircraft on a 70-foot line (eye-to-eye on the steel cable). The 70-foot dimension is a critical dimension and it is used in all applications. With the aircraft on the ground, a technician stands out to the side of the aircraft and holds the trailing bomb. As the aircraft lifts off the technician walks towards the aircraft until the aircraft has reached sufficient height to where the technician is directly under the aircraft and the trailing bomb is supported off the ground. This is all monitored and controlled by the chase aircraft.

The procedure for landing is just the opposite. Again, controlled by the chase aircraft, the helicopter hovers over the runway with the bomb suspended. The technician walks out and catches the bomb. Then, as the helicopter descends, the technician walks away from (to the side) the helicopter, keeping the line taut and off the ground. The technician uses heavy rubber gloves to prevent electrocution by static electricity.

Stainless steel cable (3/16-inch diameter, 7 x 19 strands, 4200-lb minimum tensile strength) is used. The pressure tube is a Eastman 33P, semi-rigid black polyflow tubing with a 3/16-inch inside diameter. The cable and tubing are tied together every 6 inches with standard waxed tie string lacing. The last 6 feet of the assembly are wrapped with electrical tape for extra protection from the aircraft's wheels and skids.

A cable cut feature (quick release) is a must. Due to the length required for the cable, there is a potential for the cable assembly to get tied up in the tail rotor. If that happens you can imagine the problems it creates. In flight, the primary area of drag is the triangular-shaped cable/tube assembly (cross section). The trailing bomb itself creates very little drag. Under certain conditions, the trailing bomb can lift up and get tangled with the tail rotor. That is why the chase aircraft is required to monitor this situation. If the trailing bomb gets within 10 feet of the rotor, the aircraft first slows down a couple knots. If that does not resolve the situation, the chase aircraft will issue a command to cut the trailing bomb at which point the trailing bomb is cut loose.

The cut (or quick release) feature is for the steel cable only. The pressure tubes are a slip fit only at the aircraft so that when the cable is cut the drag on the assembly will pull the pressure tubes off. Originally, a seat belt latch was used for the cut feature. Now, an aluminum block assembly with a tooling pin release is used. The pin's spring is rather strong and requires a good firm tug to release, preventing it from releasing on accident.

Maintenance involves two primary items. First, ensure the pressure transducers are maintained in calibration before each flight. Because these flights can be dangerous, you want to ensure you get good data the first time. Second, inspect the cable and tubing assembly carefully for damage. Any damage is unacceptable. The slightest nick in a pressure line can have severe effects on the performance. The stainless steel cable should be replaced if broken strands are found. Repairs are not made on damaged items -- the item are replaced. Again, the flights are too critical to take unnecessary risks.

100800 Trailing Bomb Resources

100800 trailing bomb
Page last modified on 2006-11-25 15:30
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SpaceAge Control, Inc.
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38850 20th Street East • Palmdale, CA 93550 USA
661-273-3000 • Fax: 661-273-4240 • email@spaceagecontrol.com
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