• Created by Unknown User (mzhengxi@mit.edu), last modified by Unknown User (lcbjorns@mit.edu) on Jan 18, 2021 22:24

Parachute Vocabulary

Quick overview of different aspects of a parachute and the correlating vocabulary terms:

TermDefinition
Canopy
  • cloth surface that inflates to a developed aerodynamic shape to provide the lift, drag, and stability needed to meet performance requirements
  • can be modified with different geometries
Confluence Point
  • point of convergence of all suspension lines of a parachute
Crown Area
  • region of the canopy above the major diameter of the inflated shape
Gore
  •  material of canopy between radials

Radials

  • provide structural continuity across the canopy from the vent to the suspension lines
  • load bearing member
Skirt
  • portion extending below the major diameter of the inflated canopy shape to the leading edge of the canopy
Suspension Lines
  • length = distance from the canopy skirt to the confluence point
Vent
  • small circular opening at the center of the crown or side of parachute
  • simplifies fabrication and provides flow-through relief to initial surge of air at start of inflation
  • vent porosity plays large role in determining inflation time and structural loads

 

Image from the Advisory Group for Aerospace Research & Development (AGARD).

https://apps.dtic.mil/dtic/tr/fulltext/u2/a246343.pdf

 

Geometry Characteristics

Images from the Advisory Group for Aerospace Research & Development (AGARD).

https://apps.dtic.mil/dtic/tr/fulltext/u2/a246343.pdf

 

 

Design Trends

High Drag Coefficient is produced by...

  • Decreasing the porosity, which also produces a less stable parachute and a higher opening force.
  • Conical, multi-conical, quarter-spherical canopy shapes.
  • Long suspension lines because they increase the inflated diameter.

 

Drag coefficients, canopy area ratio, diameter ratio as a function of suspension line ratio...

 

Images from the Advisory Group for Aerospace Research & Development (AGARD).

https://apps.dtic.mil/dtic/tr/fulltext/u2/a246343.pdf

 

 

S_o = canopy surface area including the vent area and all openings and slots in canopy, ft^2

C_D_o = parachute drag coefficient related to canopy surface area, dimensionless

 

x_o and x_p are interchangeable in this directory.

 

Other Considerations

Material considerations:

  • as porosity increases, drag coefficient decreases
  • low porosity yields a faster inflation time and generates a higher opening shock

Design considerations:

  • orifice coefficient
  • vent hoop: single vs double
  • larger parachutes = lower porosity

 

Geometries Compared

This section will cover different parachute designs that are relevant to our use case of the Phoenix drogue. Note: there are many other main types of parachutes that are not included here because their use cases were not appropriate for the Phoenix drogue goal.

Parachute TypeAdvantagesDisadvantagesRanking for Phoenix
Cross
  • low-cost replacement for the ringslot parachute
  • stable, design decreases oscillation
  • meant too be used more for aircraft, stabilization and slowing down of mines
3

Disk-band-gap

  • verified inflation and drag performance for M = 0.05 - 2.7
  • good inflation at low dynamic pressure
  • good stability
  • lower mass than conical ribbon
  • general application = supersonic drogue
  • good for main parachute, not really drogue
2
Hemisflo Ribbon
  • good for supersonic deployment up to Mach 3.0
  • useful for drogue application at supersonic speeds
  • hemisflo experiences less flutter and breathing of parachute
  • good performance at higher dynamic pressures
  • Phoenix drogue will not be deployed supersonically, so this is not needed
4
Conical Ribbon
  • good drogue deployment at speeds of M < 1.5
  • good structural integrity
  • stable
  • Apollo and Mercury drogues
  • might be hard to manufacture
1
Guide Surface
  • good damping characteristics
  • pressure distribution independent of oscillation angle
    • high stability
  • low drag - used for stabilizing payload that is supposed to fall quickly
6
Ringslot
  • useful for decelerating object with large wake behind it
  • more useful for aircraft
5
Ballute
  • optimal for use at high altitudes
  • can withstand supersonic velocities
  • generates a high amount of drag for its mass
  • not useful, not really seen in industry since Goodyear
  • has not been tested that much
7


Common Problems and Solutions

ProblemSolution
Skirt inversionreefing
Parachute skirt damagereinforcement, reefing, choice of material
No inflationreduce canopy porosity near vent
Flutter of canopydue to supersonic deployment, keep supersonic consideration in mind during design

Sources

https://apps.dtic.mil/dtic/tr/fulltext/u2/a246343.pdf

https://www.eucass.eu/doi/EUCASS2019-0411.pdf

Presentation by Lindsey (for reference): https://docs.google.com/presentation/d/15pSj0BIAoheozw1xzQbNt7CpkSzQ688wtMqQf2JNJUU/edit?usp=sharing

 

 

 

 

 

 

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