A short history of the PRG The first parachute inflation studies by Potvin began in 1994

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1 Development of a New Parachute Inflation Modeling Computer Program PIMS - Parachute Inflation Modeling Suite Gary Peek & Jean Potvin Parks College Parachute Research Group Parks College of Engineering, Aviation and Technology Saint Louis University, St. Louis MO Contact: peek@industrologic.com potvinj@slu.edu

2 A short history of the PRG The first parachute inflation studies by Potvin began in 1994

3 A short history of the PRG, cont d Peek has been studying the fall rate of skydivers since 1990, with a Barograph he designed

4 A short history of the PRG, cont d Peek and Potvin had infrequent contact until 1996 when they finally discussed their individual research efforts. "We should be working together!", they realized. In 1996 Peek and Potvin formed the PCPRG, created and began publishing some of their research. Their areas of expertise complemented each other.

5 A short history of the PRG, cont d Peek and Potvin combined their expertise in their first project: the measurement of riser force on a skydiving rig

6 A short history of the PRG, cont d Second team project Computer simulation of the drag force on sport ram-air air parachutes & comparison with test jump data (slider-descent descent stage) (Test drops carried out with funding from Performance Designs)

7 How to do a computer simulation of inflation? Simple model example: S(t)C (t)= 6 = = ½SC 2 D At +B Drag F D V (inflation part) Post-inflation deceleration model dl Steady descent Jagged line = experimental data

8 Why create PIMS? Pims arose from the lessons learned from these early efforts - Initial inflation simulation software of Potvin was ackward to use: written in FORTRAN; command line input; the code was linear; output t was only ASCII; graphing not a result of the computer run itself - The comparison of the computer simulations with test jump data was a very labor-intensive process; this can be a handicap given that for a given parachute design and set of drop/jump conditions, the inflation force evolution will change on a drop-to-drop basis. A large number of computer simulations were therefore needed more labor! - Peek and Potvin decided to write a totally new software inflation package - This effort involved the support of the US Army

9 What is PIMS? PIMS: Parachute Inflation Modeling Suite Development has been funded since 2001 by the US Army: Natick Soldier Center & Yuma Proving Ground R&D effort involves: software development validation - collection of inflation data from test drops Commercial version may be available ~

10 What does PIMS provide? Easy input via GUI Immediate graphing during the simulations Output also yields an ASCII simulation data files for detailed graphing using Excel or other spreadsheet programs

11 PIMS was written in Power Basic Why Power Basic? Peek had already used it for Industrologic application software and found it very good Other programming languages were expensive even for "academic" versions - Neither Peek nor Potvin had any experience with Visual Fortran

12 Characteristics of Power Basic Requires knowledge and use of Windows Application Programming Interface (API) Generates a single executable file (.EXE) No DLL files necessary No installation program necessary Executable is very small - PIMS.EXE is only 350K bytes! (including embedded graphics) Executable is very fast t( (calculations l and graphing almost ti instantaneous) t And last but not least- Source code syntax of Basic and Fortran are very close! - Combining Potvin's simulation code in Fortran with Peek's GUI in PowerBasic took only about 2 hours for the first version - Syntax was similar enough that Potvin abandoned the Fortran and started making changes to the Basic code in later versions

13 What does PIMS calculate? Basic output drag force speed drag area ballistic trajectory angle deceleration modulus Input inflation models parachute design characteristics drops conditions (altitude, acft speed, payload weight,etc)

14 Current and future parachutes type modeled by PIMS Parachute types (current version V3.0) Flat circular types (USAF C-9, USA T-10, etc.) Skirt-reefed reefed flat circular types Drive-slotted hemispherical types (USA MC1-1C, 1C, Crossbow, Pioneer K22, Phantom, etc.) Ring-slotted hemispherical types Unreefed ram-air air parafoil types (no slider) Parachute types and computational models (future versions) Ram-air air parafoils reefed with sliders (next version V3.1!) Round types with sliders Skirt reefed ring-slotted hemispherical types Supersonic inflation Fabric and line elasticity during inflation

15 Other important features Not a based on Computational Fluid Dynamics (CFD); rather uses the Newtonian equation of motions of the parachute-payload payload system and those of sub-components (canopy skirt, slider, etc.) Pims includes eight different inflations models Choice of gravitational constant (wanna jump on Mars or on Titan?) Tracks payload trajectory prior to parachute deployment Includes the simulation of the snatch force Includes a special model for the deceleration of the system after inflation (but prior to steady descent)

16 Pims does have some restrictions.. Input, output, and calculations in American Standard Units only Pims simulates parachute events that only involve subsonic airflows about the parachute Except for the snatch force simulation, Pims does not model the elastic properties of the canopy fabric and suspension lines (feature to be included in a future version) The inflation models do not include the occasional (and hard to predict) shedding of vortices from the canopy However Pims yields the correct - overall shape of a riser-load vs. time curve - temporal width of the curve (i.e. inflation duration) - maximum value of the force sustained

17 pre-inflation processor - cubical container input? pre-inflation processor bypass; user inputs angle & speed Windows GUI *.mdl text file pre-inflation processor - palletized container? snatch force sim Snatch bypass? Round, wing or cruciform (low mass ratio) inflation model Two-phase model V3.0 upgrade Round, wing or cruciform (high mass ratio) inflation model Two-phase model V3.0 upgrade General (Pflanz) inflation model Lingard s inflation models: C-9 canopy or GQ Aeroconical 1000 canopy Drive-slotted rounds Low and high-mass ratio V3.0 upgrade PIMS V2.0, V2.1, V3.0 PIMS V1.0? User option post-inflation deceleration model output Windows: graphs and simulation data menu *.txt text file

18 Running Pims yields a graph and a menu

19 Sample menu functions: choosing the models

20 Sample menu functions: Parachute input parameters e

21 Sample menu functions: Other input parameters

22 Sample menu functions: Windows graphic output

23 Sample menu functions: Input file definition and use The mdl file stores all input and Pims settings of a particular run

24 Time,Speed 0.01, , , Sample menu functions: Output file definition and use , , , , , , , , , , , , , , , , , , , Th ttfil t l t dt j t tf hi The txt file stores selected trajectory ouput for graphing with spreadsheet program (Excel for example)

25 Parachute type = round, for low mass ratio Sample menu functions: Diagnostic output file Deployment phase (pre-processor) Duration of deployment (seconds) = 1.5 Total simulation time (seconds) = 2 Iteration interval (seconds) =.01 Air density (slugs/feet cubed) =.0023 Aircraft speed (TAS in feet/second) = 160 Payload weight (pounds on Earth)= 110 Mass (slugs) = Acceleration of gravity (feet/seconds squared) = Trajectory angle (degrees, 90=horizontal) = 90 Payload surface area of one CUBE face (feet squared) = 4 Angle of attack mode= CUBE Wedge first with uplift, optimal lift area Payload surface area adjusted for angle of attack = 4 Initial payload py box drag coefficient upon leaving aircraft= 7.5 Steady state payload box drag coefficient (constant) = 1.12 Deployment duration (seconds) = 1.5 Payload size equivalent disk drag diameter (feet) = Terminal velocity of payload without parachute (feet/second) = The load decelerates TPhase1 (seconds) = 0 Pre-processor beta (only when motion flag=1) = Ratio of speed after Tphase1/Aircraft speed (correct only when load accelerates) = Snatch simulation Number of suspension lines = 28 Suspension line length (ft) = 14 Approx. payload drag area (sqf) = 4 Approx. chute initial drag area (sqf) = 16 Parachute weight (lb) = 5 Payload weight (lb) = 105 Spring force exponent = 3 Lines' breaking strength (lb) = 400 Percentage line elongation at breaking point = 20 Initial load-chute speed difference (fps) = 5 Snatch dynamics time scale (sec) = E-2 Payload drag dynamic time scale (sec) = Duration of snatch simulation (sec) = E-2 Maximum line tension generated = Inflation phase Steady state drag coefficient of parachute = 1.44 Round parachute constructed diameter (feet) = 14 Parachute flat surface area (square feet) = Ratio of projected mouth length-scale to (inflated) projected diameter =.2 Initial instant velocity (at line stretch or after snatch) (feet/second) = Parachute/payload descent terminal velocity (feet/second) = Initial trajectory angle (in degrees, 90=horizontal) = Steady state drag area of open parachute (feet/second) = Filling time (seconds) = Extra inflation simulation was carried out (peak force was not reached by filling time) Time peak drag (seconds) = Peak drag (pounds) = mass ratio = Cd-adjusted mass ratio = Froude number (using g =32.17) = Ballistic parameter = Ck-Factor (from raw sim data) = Post-inflation phase Post-inflation motion = deceleration Post-inflation beta =

26 Examples of Pims runs and comparison with test drop data

27 Introductory remarks The user must be knowledgable about inflation in general; in particular he/she must be aware that inflation duration depend on many factors of equal importance, such as: Parachute designs characteristics Payload characteristics Deployment method used The user must be aware of the variability of inflation characteristics on a drop-to-drop or jump-to-jump basis. It is necessary to perform repeat test drops and repeat PIMS runs in order to completely understand the inflation properties p of a given parachute design The user must know the limits of the various models being used in PIMS

28 Example: Round parachute type US. Army T-10C Red-dotted original model for round chutes Blue line upgraded model: Phase 1 cigar/light bulb expansion Phase 2 skirt/hem spreading

29 Example: Round parachute type - Half-scale USAF C-9 Thick red line = Pims V3.0 Thin blue and purple lines = Pims V2.1 In both versions 2 & 3, the end of the snatch phase needs improvement Versions 2 and 3 can t reproduce this shoulder

30 Example: Round parachute type US Army MC1-1C1C Red line unslotted round chute model Green line drive-dlotted round chute model

31 Example: Round parachute type US Army MC1-1C1C

32 Example: Round parachute type with drive slots - Security Crossbow

33 Example: Ram-air air type without slider symmetrical opening ( the cells of the right side of the span open at the time as the cells on the other side) The match is pretty good

34 Example: Ram-air air type without slider asymetrical opening ( the cells of one side of the span open before the cells on the other side) The match is not so good

35 To be included in V3.1: Ram-air air type with slider The smooth curve on the graph represents the slider-descent descent phase A model of the early pressurization phase -i.e. prior to slider-descent- is now being tested

36 Pims run demonstration

37 Questions?