Design calculations 2 . . . . indicate that this method of sampling is feasible, but a major disadvantage is the inefficient use of the rocket's potential energy to overcome friction in the flow of air over the canopy. This reduces the energy available to force air through the collector scoop and creates the need for a pump or blower in addition to the parachute to process the required amount of air. Rotorchute Sampler. was studied, In view of the shortcomings in the parachute method, the rotorchute method of sampling A schematic diagram of a rotorchute is given in Figure 1. vice which operates like a gliding helicopter or Autogiro, The rotary motion of the blades can be used to power impactors which sweep the particulate matter from the air. These impactors can be mounted underthe blades, within the blades, or they may protrude from the nose cone separately. stability to the rotorchute in flight. A rotorchute is a rotating bladed de- The rocket motor case provides some The general operation for this device would include firing the rocket vehicle with sampler to the maximum altitude desired. The blades would then extend and the sampling would take place during the drop to the lower level of altitude desired. The impactors would then retract and the blades or a small parachute would return the entire device back to earth. To illustrate the feasibility of the rotorchute for upper atmosphere sampling, the theory of operation and sample design calculations for a practical rotorchute were investigated. In the example used, a gross weight of 100 pounds is assumed for the burned-out rocket motor plus payload at the start of sampling, and the impactors were assumed to be mounted on brackets below the blades. taken to represent a reasonable maximum in collector area, A 5-bladed device with 5 impactors per blade was Since a rocket plus nose cone having a 100-pound burnout weight will generally be about 17 feet long, the blades are taken to be 14 feet long. Particles as small as 0.01 micron in diameter are to be removed from the air with better than 80 percent efficiency. is collected in descending from 200,000 to 100,000 feet. ft. The sample The density of collected particles is taken as 128 Ib/cu Calculations give a simplified relation for the rate of descent of a rotorchute with forward motion as We V¥ = 13 R 1/2 p. 1/2 or” oO — (1) p Particle Collecting Methods Five methods of collecting particles have been analyzed for use with either the parachute or rotorchute 2,3 se ge . : . : : samplers. ’ Of these, three are by precipitation-thermal, electrostatic, and centrifugal; one is by filtration, and one is by impaction. Since the impaction technique is the most practical of these to use with the rotorchute, it is the only one described in detail here. The impactor should be designed so that the minimum size of particle is removed from the air stream at maximum efficiency while processing the maximum air volume. Work by Stern, et al,* has indicated that a focusing array impactor gives collection efficiency at low values of the inertia parameter, K, k_ Ke ppd 2 defined by Vv P Pp (2) 9uL The collection efficiency versus inertia parameters, as given by Stern, is shown in Figure 2. This graph was computed by Stern using an electrical analogue technique employing an electrolytic tank and an analogue computer to determine the particle trajectories in the vicinity of the impactor surface. The focusing array, because 103