10-04-2017, 09:12 PM
RAM-AIR PARACHUTE DESIGN
[attachment=565]
INTRODUCTION
Accurate delivery of a payload by parachute is a requirement in both the space and military fields.
The cost savings available from the recovery and re-use of expensive space vehicle elements provides an incentive
to develop systems capable of allowing recovery to land sites 1. Clearly, recovery to land engenders safety risks to
population and property. Re-entry trajectories can only place recovered hardware at the position for initiation of
the recovery system within certain tolerances. The recovery system must therefore have sufficient gliding
capability and wind penetration to reach the designated landing site. It should also be able to achieve low vertical
and horizontal velocity at landing to minimise the potential for damage to the payload. The only option for land
recovery is a high reliability guided gliding parachute recovery system.
AERODYNAMIC CHARACTERISTICS OF RAM-AIR WINGS
General
Once inflated a ram-air parachute is essentially a low aspect wing and thus conventional wing theory is applicable.
While CFD Navier Stokes and vortex panel methods can give accurate predictions of the performance of ram-air
wings, a simpler approach is adopted here in order to bring out clearly the influence of the various parameters on
wing performance.
Two dimensional flow around the ram-air wing section
Before embarking on the analysis of the ram-air wing, it is useful to consider the two-dimensional flow around the
wing section at various angles of incidence. The flow pattern can be determined using a vortex singularity
method 3. The canopy is modelled by a vortex sheet placed to coincide with the physical location of the canopy.
The strength of the sheet is determined by the application of velocity boundary conditions. The sheet strength is
then used to determine the pressure distribution and circulation, and hence lift coefficient. By varying the angle of
incidence, the lift curve slope dCL/da, and the incidence angle for zero lift aZL, are found.
[attachment=565]
INTRODUCTION
Accurate delivery of a payload by parachute is a requirement in both the space and military fields.
The cost savings available from the recovery and re-use of expensive space vehicle elements provides an incentive
to develop systems capable of allowing recovery to land sites 1. Clearly, recovery to land engenders safety risks to
population and property. Re-entry trajectories can only place recovered hardware at the position for initiation of
the recovery system within certain tolerances. The recovery system must therefore have sufficient gliding
capability and wind penetration to reach the designated landing site. It should also be able to achieve low vertical
and horizontal velocity at landing to minimise the potential for damage to the payload. The only option for land
recovery is a high reliability guided gliding parachute recovery system.
AERODYNAMIC CHARACTERISTICS OF RAM-AIR WINGS
General
Once inflated a ram-air parachute is essentially a low aspect wing and thus conventional wing theory is applicable.
While CFD Navier Stokes and vortex panel methods can give accurate predictions of the performance of ram-air
wings, a simpler approach is adopted here in order to bring out clearly the influence of the various parameters on
wing performance.
Two dimensional flow around the ram-air wing section
Before embarking on the analysis of the ram-air wing, it is useful to consider the two-dimensional flow around the
wing section at various angles of incidence. The flow pattern can be determined using a vortex singularity
method 3. The canopy is modelled by a vortex sheet placed to coincide with the physical location of the canopy.
The strength of the sheet is determined by the application of velocity boundary conditions. The sheet strength is
then used to determine the pressure distribution and circulation, and hence lift coefficient. By varying the angle of
incidence, the lift curve slope dCL/da, and the incidence angle for zero lift aZL, are found.