Recovery System Design

DESIGN OF A PARACHUTE RECOVERY AND LANDING SYSTEM

This chapter deals with the design of a parachute recovery and landing attenuation system for a military reconnaissance drone. The prime emphasis in the design of this system is on undamaged recovery of the drone from the total flight performance envelope during the development and test phase, on undamaged recovery after a completed mission during military operations, and on multiple use of the recovery system. An engineering team conducts performance and system analyses and chooses what recovery concept to use, what types of parachutes to select for high-speed deceleration and for final recovery, and what impact-attenuation system is best for the particular application. This chapter covers the selection process for concepts and components. Different engineers may make different selections based on experiences with particular types of parachutes or deployment concepts; experience is always a viable reason for selecting a particular approach. However, using the selection criteria shown in Figure 2-6. the designer must put reliability of operation, undamaged recovery, reusability of the landing system, and minimum weight and volume at the top of the list of requirements.

7.1 REQUIREMENTS

7.1.1 System Requirements

An unmanned air vehicle used for military reconnaissance must be recovered after a completed mission in rough terrain, undamaged and ready for multiple reuse. The recovery system must be able to 1. Recover the air vehicle after the completed mission when the vehicle has landed in rough terrain at altitudes from sea level to 5000 feet. 2. Recover the drone during the engineering test phase from all controlled and uncontrolled flight conditions. 3. Serve as a range-safety device to prevent the air vehicle from leaving the boundaries of the test range.

The air vehicle has a takeoff weight of 7200 pounds and a landing weight, after the i completed mission, of 4800 pounds. Undamaged landing shall be possible in rough terrain with rocks up to 8 inches in diameter. Replacement parts and refurbishment cost shall be kept to a minimum.

7.1.2 Requirements for Normal Operation

Drone weight at recovery after completed mission		Wd = 4800 lb
Recovery velocity		vo = 150 to 200 KEAS
Minimum recovery altitude		Ho = 2000 ft above ground level (AGL)
Maximum ground level		H = 5000 ft
Maximum allowable total parachute force		Fo = 16,000 lb
Maximum allowable impact deceleration at landing		a = 9.0 g's

7.1.3 Requirements for Emergency Operation

Emergency operation includes recovery during the test phase from takeoff to landing and also includes recovery for range-safety reasons.

Drone weight at takeoff .................................. Wdma = 7200 lb

Maximum recovery velocity at mean sea level (MSL) ................................... vo = 490 KEAS

Maximum recovery velocity at 38,000 to 50,000 ft altitude ........................................ vo = 1.5 Mach

Maximum dynamic pressure .............................. qmm = 812 lb/ft2

Maximum allowable parachute force ........................ F0 = 22,000 lb

7.1.4 Requirements Analysis

Three primary requirements pace the design of the recovery system:

1. The drone must be able to land in rocky but level terrain without damage.

2. Refurbishment cost and time shall be kept to a minimum.

3. Recovery must be possible from all flight conditions during the flight test phase, including cases where the out-of-control drone flies off the range.

7.2 LANDING ANALYSIS AND IMPACT-ATTENUATION SYSTEM

7.2.1 Landing Analysis

Three known recovery concepts prevent damage during landing in rocky terrain:

1. Midair retrieval.

2. Dual air bags or dual frangibles.

3. Retrorockets combined with small, nondeflatable air bags.

The need for retrieval helicopters or retrieval aircraft makes Method 1, midair retrieval, impractical. The other two methods are affected by the deceleration distance required to meet the 9-g limit.

In section 6.8 of this manual, the required deceleration distance(s) is determined to be

$s={\frac {{V_{e_{1}}}^{2}-{V_{e_{2}}}^{2}}{2g(n\eta -1)}}$

where

${V_{e_{1}}}$ = velocity of the drone descending on the parachute (rate of descent), ft/s

$V_{e_{2}}$ = permissible impact velocity, ft/s

$g$ = acceleration of gravity, ft/s2

$\eta$ = effectiveness of the impact attenuation system used, dimensionless

$n$ = allowable impact deceleration, ratio $n={\frac {a}{g}}$