Parachute Research, from Computer Simulations to Uses in the Field

Transcription

1 Parachute Research, from Computer Simulations to Uses in the Field Gary Peek & Jean Potvin Parks College Parachute Research Group Contact:

2 Overview 1. Truncated Cone Decelerator (TCD) a parachute for wind-drift studies 2. New parafoil inflation module for the PIMS inflation simulation platform 3. & 4. New parachute engineering inflation calculators: PIFCALC OSCALC FREE PROGRAMS!!!

3 1.Truncated Cone Decelerator (or TCD)

4 Why use TCDs? They are inefficient decelerators! Being streamlined aft, their C D is very low, much smaller in fact than for a low-porosity hemispherical type parachute Need a lot surface area to generate as much drag TCD vs. cross chute: both have the same drag area!!!

5 BUT Their lateral drag area is much larger very little glide if any Their reaction time to wind changes would be shorter TCD s would be ideal for wind column studies that use an instrumented payload under parachute and drifting freely with the wind

6 Slow winds round loops Fast winds tight loops Windpack: milk crate shown in previous slide

7 How to build a TCD? There are many ways to do this One example: Two-gore design with four suspension lines Isosceles triangles Lines are attached at points a, b, c, d Single confluence point for suspension lines Lower, down-pointing triangle to ensure equal tension on suspension lines (which are of equal length)

8 Experimental study of inflation and steady descent

9 Parachutes that we have built and tested: Sub-scale : B = 5.50 ft and H = 8.0 ft; variable vent height VHT; four suspension lines; total parachute-payload payload weight = 4.1 lb; i.e. the vent was gradually increased and parachute re-droppped Full-scale : B =10.66ft and H = 16.0ft; VHT = 26.7in; VHT/H = 13%; eight suspension lines; total parachute-payload payload weight = 18.0 lb VHT

10 Instrumentation rate of descent sensor load cells on risers on board data acquisition system Drop conditions ~ AGL over Vandalia IL (534 ft MSL field elev.) sub-scale: scale: dropped by parachutist under sport ramair canopy; fall rate study only; repeated drops, with increasing vent area full-scale: dropped from Cessna 120mph indicated inflation and fall rate study

11 Sub-scale parachute VHT (in) VHT/H % (see figure 5) VHT/H (%) S V /S P (%) S V /S T (%) Fall rate (ft/sec) ±2ft/sec S TF (ft 2 W = 4.1 lbs C D0 Rates of descent (steady state) No-vent Smaller C D Largest C D Note the low C D compared to the value of a low- porosity round chute C D ~ 0.7 All sub-scale drops performed during the same day Widest vent Smaller C D Table 3.1 Fall rates measured on the sub-scale TCD. The values of the drag coefficient are computed with the total fabric surface area S TF. Full scale VHT/H= 14% 17-20fps

12 Typical inflation load evolutions Inflation duration according to video Compare with typical sport ram-airair canopy

13 2. New parafoil inflation module for the PIMS p inflation simulation platform

14 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 ~ 2007

15 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

16 What does PIMS calculate? Basic output drag force speed drag area other parachute-payload payload trajectory parameters Input inflation models parachute design characteristics drops conditions (altitude, acft speed, payload weight,etc)

17 Current and future parachutes type modeled by PIMS Parachute types (current version V3.2) Flat low-porosity circular types (USAF C-9, USA T-10, etc.) & cruciforms (less than 4:1 AR) - with or without permanent reefing - with skirt disreefing (currently under development Ring-slotted hemispherical types Unreefed ram-air air parafoil types (no slider empirical modeling) Ram-air air parafoils reefed with sliders today s talk

18 Current and future parachutes type modeled by PIMS (cont d) Future developments Round types with sliders Skirt reefed and unreefed ring-slotted hemispherical types Fabric and line elasticity during inflation Alternate inflation modes for parafoils

19 Other important features Not a based on Computational Fluid Dynamics (CFD); PIMS uses the Newtonian equation of motions (i.e. trajectory-based) of the parachute-payload payload system and those of sub-components (canopy skirt, slider, etc.) 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)

20 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) 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

21 Input & pre-processingprocessing Inflation sim Output

22 Slider-reefed reefed parafoil model Today s y talk

23 Running the inflation model for manned slider-reefed reefed parafoils Next slide

24 Pims input Construction characteristics known n accurately Characteristics known, but with some uncertainty Characteristics known empirically (jump-to-jump change)

25 A sample run (PD Sabre 150 parachute)

26 Slider-reefed reefed parafoil inflation computer model

27 The sim model incorporates four of the eight stages that characterize inflation: Container bag extracted by pilot chute (deployment) Suspension lines unstow first (deployment) Canopy pulled out of bag (deployment) Center cell(s) pressurization (inflation phase 1) Outboard cells pressurization and expansion (inflation phase 2) Slider descent (inflation phase 3) Post-inflation (no lift - very approximate!) Flight (steady state)

28 Important note: the model assumes a specific series of inflation events Center cell(s) pressurization outboard cells pressurization slider descent But other inflation modes can occur for example: - Bottom-skin opening where the bottom surface of the wing is spread out by the relative wind prior to cell inflation; ; occurs with unreefed parafoils, line dumps, displaced sliders, etc. - Reverse pressurization when the outboard cells inflate before the center cells - Inflation with line twists - Df Deformed canopies iflti inflating with ithli line-overs, other malfunctions - etc.

29 Center cell(s) pressurization (Inflation phase 1) All photos by Gary Peek, except for photo on left

30 Outboard cells pressurization and expansion (Inflation phase 2) All photos by Gary Peek

31 Slider descent (Inflation phase 3) All photos by Gary Peek

32 Dynamics of slider-reefed reefed parafoil inflation Drag area evolution during center cell(s) inflation (i.e. 1 st phase of slider up stage) Underlying principle: Unconstrained inflation of the center cells - cells inflate without external pressure applied on the walls - air flow enters at a speed equal to that of the parachute-payload system

33 Drag area evolution during outboard cell(s) inflation (i.e. 2 nd phase of slider-up stage) Underlying principle: constrained cell inflation of the outboard cells - outboard cell llinflate, but against the external pressure that keep the outboard cells folded; this leads to an increase of pressure inside the cells - the net air flow into the cells is slowed down because of internal pressure build-up, intermittent inlet width expansion/reduction, and canopy surging Not modeled here: 1) actual chaotic opening/closing of the inlets; 2) air actually being exhaled and inhaled due to canopy surging gback-and forth. PIMS models inflation according to an average in-flow.

34 Outboard cell pressurization cont d Constrained cell inflation Center cells Outboard cells slider

35 PIMS keeps track of the forces applied on the slider; the slider-up stage ends when the net force on the slider points down Note: too large values of slider surface area and/or too large values of the coefficient of friction do lead to PIMS predicting a NO-OPENING (i.e. no slider descent) situation v : Fsliderdrag = ρ( Σ slider + Σ slider extra ) V ( t) ( 1 μ ) F = ρσ() t V () t sin Ω() t cos Ω() t linedrive W = m g slider slider 2 2 s

36 Next comes slider descent We use dimensional analysis to derive a relation between the change of the parachute s drag area and the force differential sustained by the slider: 2 d Σ ( t ) 2 2 = KipmV () t dt v Σ ( t ) = F 112. L L end final span chord K ipm LspanLchord L ( extra span ~ ρ Σ slider + Σ slider ) () t ( 3 Δ ρlchord + mcanopy ) L extra susplines L + Σ sliderspan slider Φ < Δ() t >

37 One missing element in the slider descent model No lift force included! Model will miss canopy surging and dancing that may occur especially with de-tuned canopies This shouldn t too much of big v deal for tuned canopies

38 Validation Data from over 60 test jumps performed in by JP and GP Activity funded by the BLM smokejumpers Some drops supported in equipment by Performance Designs Inc. (PD) Data is in the public domain (some has been published in the past) US. Navy/China Lake (inflation for MC-5 canopy)

39 Measurements of riser force and fall rate

40 Available inflation data: F D (t) Free fall speed prior to deployment Test jumper event switch (marks slider descent on the F D data) Repeat jumps with same parachute configuration and freefall profile Many different canopy shape (3) and sizes (4) Different slider sizes (2 per canopy) Different brake setting during inflation (i.e. tuned and de-tumed ) (2) Different slider weights (2) With or without bottom skin venting (on BLM Trilobe)

41 Parachutes tested: PD Sabre 120 PD Sabre 150 PD Stilletto 150 PD Sabre 230 BLM Goliath (i.e. MC-4 with smaller slider) BLM Trilobe (standard & with bottom skin vents)

42 Theory meets experiment - PD Sabre standard Not as good - no lift incl. in model; surge or wake re-contact missed Slider descent Very good validation of slider descent model!

43 Theory meets experiment - PD Sabre standard Good validation of models for phases 1 and 2 (i.e. slider-up stage) Slider descent

44 Theory meets experiment - PD Sabre standard Good match: not typical Slider descent Typical: PIMS misses the lift force being generated at the end of inflation

45 PD Sabre 150 shallow brakes a de-tuned canopy w/r to factory standard (less trailing edge cupping during inflation) Surging/dancing

46 PD Sabre 230 standard Very nice validation of the phase 1 and 2 models! slider descent not as good here missing lift in the model? Not a very good match; Typical of a surging canopy

47 PD Stiletto 150 standard semi-elliptical elliptical canopy

48 BLM Trilobe canopy Note the two oversized cells Surge alert!

49 BLM Goliath (MC-4 with smaller slider)

50 Some conclusions about the validation of the inflation model PIMS is sensitive on how a given canopy is balanced or tuned, i.e. whether the brakes are stowed at a point that minimize surging (canopy flight) during inflation PIMS does not work well in cases where the canopy surges back- and-forth during inflation (i.e. tries to fly). PIMS has been quite qood at reproducing about 80 85% of the repeated jumps for each tuned canopy that were tested

51 Some conclusions about the validation of the inflation model (cont d) PIMS does not include lift production at the end of inflation and it shows The simulations are very sensitive to the mean opened inlet area - an input parameter Remember: PIMS has a prescribed inflation sequence (center cell infl.; then outboard cell infl.; then slider descent); not all inflation sequences may be correclty simulated

52 Some conclusions about the validation of the inflation model (cont d) Canopies using Spectra lines needed an input value of the friction coefficient near ~ for PIMS to work well Canopies using Dacron (braided) nylon lines, which are much larger involved an input friction coefficient ~ 0.4

53 Introduction to slider engineering using PIMS V3.1

54 Sabre 150 slider engineering: Replace PD standard slider (2.42x1.59 sqf) with Gary Peek slider (2.67x2.42 sqf) Same PIMS runs, but with differing slider dimensions

55 3. PIFCALC Parachute Inflation Force Calculator

56 Free download at pcprg com/pifprog htm Windows- executable file Complete user s manual OR see us after the talk we have it on a thumb drive

57 Parachute Inflation Force Calculator What is it? It is a program for skydivers that estimates the maximum (drag) force F max generated during parachute inflation Uses inputs that are straightforward to obtain Calculation applies only to these parachute designs: - low ow-porosity hemisphericals - parafoils (unreefed, line-reefed, slider-reefed reefed) - parachutes must be inflating while in an vertical trajectory Is it based on F = m a F 2WV V gt 2WV i final i final max = 1 + = 1 + gt V i V i gt V V i 2 W Pronounced as PIF CALC

58 PIFCALC features; restrictions Features Run on the Microsoft Windows operating system Inputs can be made using either metric or ASU units Instant processing speed Restrictions OSCALC is not a true predictor of opening shock since it requires the use of the inflation time t fill i.e. an actual inflation performance variable; but t fill can be obtained from the video of the opening - PIFCALC is video-based - Applies to manned parachutes; can t be used to study the inflation forces sustained by drogues and pilot chutes Earth-bound jumps; deployment altitudes below 39,000ft MSL Answer could be inaccurate for BASE jumps (b/c of low deploy speeds) or hop n pop jumps (b/c of non-vertical trajectories)

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60 Questions so far?

61 4. OSCALC Opening Shock Calculator

62 Free download at /oscp og. t Windows- executable file Complete user s manual

63 Opening Shock CALCulator What is it? It is an engineer s program that estimates the maximum (drag) force F max generated during parachute inflation Uses inputs that are straightforward to obtain Calculation applies to any parachute design and reefing type: - low- and high-porosity hemisphericals (unreefed, reefed, dis-reefing) - parafoils (unreefed, line-reefed, slider-reefed reefed) -in fact, anything that can be used as a parachute Is it based on an equation commonly used in parachute engineering Pronounced as O - S S CALC

64 OSCALC other features; restrictions Features Run on the Microsoft Windows operating system Inputs can be made using any unit system Instant processing speed Restrictions Restricted to parachutes attached to unpowered payloads (no motors but gravity is OK); ; there is no guarantee that OSCALC will produce, for example, an accurate calculation of the maximum force sustained by a parachute deploying while connected to an ejection seat that is being propelled by a rocket OSCALC is not a true predictor of opening shock since it requires the use of the inflation time t fill (n fill ), an actual inflation performance variable; but there is a lot of n fill -data in the public domain already; otherwise measuring t fill from video is a straightforward task

65 What applications is it most useful for? F max -estimation at the DZ, right after a test: OSCALC provides the means for calculating F max, based solely on the basic canopy dimensions & drag properties, payload weight, deployment conditions and video of the inflation process (for inflation time info). This tool should be very useful during those tests where the payload is not equipped with load cells or accelerometers. Provides a good guess for F max, even for new parachute and reefing designs, including designs that have not yet been documented in the public domain

66 What applications is it most useful for? cont d Sanity -check for developers of computer simulations of the inflation process Calculation of F max sustained during inflation scenarios that are not covered by computer simulations of inflation such as PIMS, FSI/CFD, Sandia model, etc.; for example: malfunctions, mis-stagedstaged openings, etc. Again, all one needs here is video to get the inflation time information

67 Figure 3.1 Default calculation lation and windows displayed at the beginning an OSCALC session

68 Opening Shock Factor Unreefed or permanently reefed hemispherical e canopies es( (low-and high-porosity) os (compiled by Wolf [3]) C k at R m = 0 is called C X in Knacke [1] Drogues and pilot chutes; All chutes deployed in wind tunnels Personnel and cargo airdrop parachute low altitudes

69 ρ m V stretch C D 0 S 0? See Fig. 3.3 below n fill t fill?? See Fig 3.4 below R m n gen fill Figure 3.2 Basic input and output of OSCALC. The color coding for this figure is as follows: Calculated versus inputs. F max Upper F max Lower F max C k Upper C k Lower C k

70 Original graph from: D. Wolf - paper AIAA ; colored data points collected by GP and JP n gen fill 4 fill Long Non-Dimensional Filling Time Upper bound Full-scale TCD (Deep cone) Unreefed C-9 Lower bound Reefed C-9 (24%) T-10C R m -value of system MC1-1C Half-scale C-9; Reefed at 16% Aeroconical/steerable National Phantom Aeroconical/steerable GQ Security Crossbow

71 Original graph from: D. Wolf - paper AIAA ; colored data points collected by GP and JP 1 n fill gen < 4 Short Long Non-Dimensional Non-Dimensional fill Filling Filling Time Time Aeroconical/steerable GQ Security Crossbow Aeroconical/steerable Pioneer K22 Aeroconical/steerable National Phantom Half-scale C-9 - unreefed Parafoil - ParaFlite Strato Cloud no slider Parafoil - Precision Aero Falcon 175 no slider

72 6E 6. Examples (from the user s manual) 6.1 Unreefed low-porosity hemispherical canopy ( Default case) 6.2 Permanently reefed high-porosity hemispherical canopy, deployed at high altitude and at low mass ratio 6.3 Un-reefed parafoil vs. dis-reefing parafoil Disreefing Dis-reefing hemispherical canopy Next two slides 6.5 Parachute cluster (unreefed) 6.6 What to do with a new design that is not documented in the World s database on inflation time and opening shock factor

73 6.3 Un-reefed parafoil vs. dis-reefing parafoil Part 1 - Consider the example of a 250ft 2 parafoil that is not equipped with a slider; this parafoil has no reefing whatsoever. In this example the values of S 0 is computed from the product of wing chord times span. ρ = sl/ft 3 deployment at 5000ft MSL m = 6.21 sl (corresponding to 200 lbs on Earth) V stretch = 130 ft/sec C D0 = during inflation the parafoil looks like a flat plate S 0 = 250 ft 2 n fill fill = 2 no reefing - see table, section 2 OSCALC gives: R m = 1.27 and n gen fill = 1.13 User should choose the Short Inflation Time graph User would pick C k = 0.6 with ~ 0.9 and ~ 0.3 as bounds The result is F max = 2535 lbs with 3802 lbs and 1267 lbs as bounds

74 Part 2 - Consider the same 250ft 2 parafoil but equipped with a slider. Assume the same payload and dd deployment conditions. The only difference is the non-dimensional filling time which is increased (sliders do that). ρ = sl/ft 3 deployment at 5000ft MSL m = 6.21 sl (corresponding to 200 lbs on Earth) V stretch = 130 ft/sec C D0 = during inflation the parafoil looks like a flat plate S 0 = 250 ft 2 n fill = 14 See table, section 2 old 1980 s 7-cell design (they are in the n fill ~ range with the 1990 s and 2000 s designs) OSCALC gives: R m = 1.27 and n gen fill = 7.89 User should choose the Long Inflation Time graph User would pick C k = 0.2 with ~ 0.3 and ~ 0.1 as bounds The result is F max = 845 lbs with 1267 lbs and 422 lbs as bounds. Compare with the no-slider case: F max = 2535 lbs, with 3802 lbs and 1267 lbs as bounds. QUITE A REDUCTION OF OPENING SHOCK!

75 Questions?

76 Trilobe/Windpack drift speed vs. altitude Smooth curve is that of a polynomial function that parametrizes the wind column Wind profile (Trilobe drift) - NWV y = x x x x x x Vns Vew Poly. (Vns) Poly. (Vew) Horiz compon nent (m/s) y = -9628x x x x x x MSL altitude (m/1000)

77 Differences in fall rates attributable to: Wind gusting near the ground VSI calibration vs. atm pressure of the day will change with changing weather

78 Some inflation properties (full-scale article) filling time (non-dimensional): n fill ~ n fill = V stretch H t fill D 0 (cone height, not base diameter) mass ratio: R m ~ 0.83 R = m gρ W total ( SC ) 1. 5 D steady typical peak load ~ 4G V stretch ~ 110ft/sec opening shock factor: C k ~ 0.12 C k = ρ( SC D 2F max steady ) V 2 stretch

79 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

80 Figuring out the inflation phases is important: Force evolution curve is more realistic Most importantly, knowing the phases allows a decent calculation of the descent speed prior to slider descent, when F max occurs for most low mass ratio cases Vl Values chosen for the best match

81 Slider-up phase net force on the slider points upwards Slider-descent phase net force on the slider points downwards

82 Input parameter variations PD Sabre 150 (standard brake setting) Sab150 22a Sab150 22b Sab150 22c Sab a Sab150 23b Sab150 25a Sab150 25b Mean wing chord thickness (ft) Static friction coefficient Mean outboard inlet area during slider-up phase (sqf) Ratio of final to- steady-state (projected) drag area Canopy spreading rate constant (K) Fraction of mean inlet area for center cell opening V stretch (ft/sec) 170 (barograph) (barograph) 160 (barograph) Clear and Clear and Freefall Freefall Freefall Remarks pull jump pull jump jump jump jump

83 MC-4 slider engineering

84 MC-4 Slider engineering

85 But changing slider dimensions only is not entirely consistent: the value of K ipm may change too (constant in slider descent phase) the value of the (mean) inlet opening during phase 1 will change too how much? Not clear how much, but we can do a sensitivity study 2 d Σ () t 2 2 = KipmV () t dt Σ ( t ) = F. L L end 112 final span chord

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89 Slider engineering can be performed in a systematic way: by running PIMS over a range of those empirical parameters by starting from a database of validated PIMS runs performed with similar canopies

90 Parachute Inflation Force Calculator What is it? It is a program for skydivers that estimates the maximum (drag) force F max generated during parachute inflation Uses inputs that are straightforward to obtain Calculation applies only to these parachute designs: - low-porosity hemisphericals - parafoils (unreefed, line-reefed, slider-reefed reefed) - parachutes must tb be inflating while in an vertical trajectory t Is it based on an equation commonly used in parachute engineering: PIFCALC computes this number Hard-coded; value obtained from a well-known principle of physics F max = 1 2 ρv stretch SC 2 D sd C k Pronounced as PIF CALC From the inputs of the problem

91 Opening Shock CALCulator What is it? It is an engineer s program that estimates the maximum (drag) force F max generated during parachute inflation Uses inputs that are straightforward to obtain Calculation applies to any parachute design and reefing type: - low- and high-porosity hemisphericals (unreefed, reefed, dis-reefing) - parafoils (unreefed, line-reefed, slider-reefed reefed) - in fact, anything that t can be used as a parachute Is it based on an equation commonly used in parachute engineering: OSCALC computes this number From graph in pop-under/over window F max = 1 2 ρv stretch SC 2 D sd C k Pronounced as O - S S CALC From the inputs of the problem

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