OSCALC – Opening Shock Calculator Version 1.01 User`s manual
Contents
1. scare uU 1 4 m scale Example 2 comparison of the filling time of a given ow porosity canopy involved in unreefed inflation versus dis reef inflation from a very small reefing ratio 20 disreef mouth unreef m 292i 0 29 unree Do 56 Filling time and deployment strategy latter See next slide Ngu Will vary depending on whether the parachute is deployed in more drop to drop variations with the former approach than with the a cross wind or facing the wind Typically will be larger and with n cross wind deployments the canopy mouth is kept shut for a while longer during the early stages of inflation Facing the wind 2 7 AIR VEHICLE p DEPLOYMENT Pd gt m Cross wind 9 deployments e Data by GP and JP 10 full scale C 9 water tunnel models v wind tunnel 6 v Heinrich 3 cross wind Drop to drop variations during test drops from n 5 to 7 facing the wind deployments Filling Time amp Figure by Desabrais amp Li i eng 10 10 109 10 107 108 105 10 10 10 Relative Stiffness Index C 58 Other dependences Dependence on mass ratio example 11 Ry 0 0501 5 68 USAF C2. CONSTRUCTED SHAPE INFLATED ORAG OPENING FORCE AVERAGE GENERAL TYPE D ANGLE APPLICATION PROFLE e INF MASS FLAT FIST 0 45 0 DROGUE RIBBON 1 00 0 67 1 05 DESCENT 0 50 3 DECLERATION gt OBSOLETE CONICAL 0 95 0 50 0 DESCENT RIBBON Q 0 70 TO 1 05 DECELERATION i l 0 97 0 55 3 1 lt lt 20 CONICAL 0 55 1 05 0 DROGUE RIBBON gt 097 0 70 TO TO DESCENT IVARIED POROSITY 30 t ION VA OSITY I REL EFT f RIBBON i 00 SUPERSONIC s IHEMISFLO 0 62 0 62 t p 1 30 10cM 30 RINGSLOT j 0 57 L EXTRACTION s 0 1 05 DECELERATION be 0 70 0 65 5 0 1 M lt 0 9 RINGSAIL dim 0 75 5 DESCENT 0 84 0 69 TO 1 10 TO M 0 5 r 0 85 10 DISC GAP BAND fo uu PE 052 10 073 0 65 1 30 M lt 0 5 D 0 58 15 70 Figure 6 5 Using reference 1 to determine the drag area of a permanently reefed canopy Note using this curve for the ribbon chute of figures 6 4 above and 6 6 below may be an approximation since the two chutes may not be exactly the same RATIO i HEEFING Sla C55 FIGURE 5 71 Reefing Ratio Versus Reefmg I Ane Kati Conical Ribbon Parachute Tested in Aurcral
3. 4 Final Inputs P drag fiom nee AEA The entries resulted in the generalized inflation time being 0 651 but this result must be greater than or egual to 1 0 to allow the use of either graph See user s manual about the strategy that deals ir 4 Final Inputs Lower bc 83 OSCALC warning message Warning clicking the Calculate Final button before clicking the In this example the mass was changed from 6 21 to 6 followed by the clicking of the Calculate Final button To clear the warning message click OK then click Calculate Initial Atmospheric density at deployment altitude 0 002 Total mass i200 from Knacke 1 or other sources Steady descent drag coefficient n 75 Warning Hominal surface area C Drag area from knovdedge Weight used Atmosphere density dunng de One or more Initial Inputs may have changed Please click the Calculate Initial button once more 2 Intermediate Results Massralio 3198 amp Final Results Average maxinum force Generalized mag 1663 2 Upper bound of Force Graph Choice 2661 12 Long time Lower bound of force 78 17 2 Calculate Initial Calculate Final Descent fall rate Nominal surface area Mon dimensional inflation time Actual inflation time r 4 Final Inputs Aver
4. 1 n n 0 if fill D stretcht n n fill fill 1 2 F SC p Both 1 and D are defined on next slide 21 Filling time or inflation time DEFINITION e At high amp dimensional time interval elapsed between line stretch and the moment when the canopy reaches its designed steady state diameter for the first time as the parachute often times over inflates e At low amp dimensional time interval elapsed between line stretch and the moment when the canopy reaches its maximum extension D nominal canopy diameter hemisphericals 48 12 with S total canopy surface area inlcuding the area of the vents and all other openings 1 e D diameter of circle of same area as wing span X chord parafoils 22 There is a lot of data on non dimensional filling time nj for details see Section 4 below Note that can be obtained from the analysis of the video of the inflation process is then calculated using this value of as well as the value of D and an estimate of V peren 23 How is inflation time used in C K graphs One chooses the right eraph according to the value of the generalized filling time see next two slides the colored data points were collected by GP and JP More details can be found in reference 4 gt 4 the user chooses the graph formely associated with un reefed and reef
5. v wind tunnel 6 Heinrich 3 tee eee he Te CR RRR Ee Se RHEE LL Lb 1 a 2 2 1011 107 10 108 107 10 105 10 Relative Stiffness Index C 10 10 53 remarks depends on how wide canopy mouth is opened at beginning of the inflation process oftentimes a random process due to the canopy being in a limp state i e non tension bearing as it is exposed to the wind Sometimes such mouth state is determined by design payload width reefing etc Check out the following formula which follows from this definition of the filling time Fill time Needed air to fill canopy volume air speed X mouth opened area which together with the definition of n implies V tofill S netmouth Do init ng 54 V tofill S netmouth Do init ng Note In most cases the to fill volume V is impossible to calculate priori because of porosity no one can track accurately the air that goes in and then later leaves The formula is more useful in studies where the scaling properties of V gy are known eventhough its precise value is not see examples on next the slide 99 V tofill S netmouth Do init Here how the mouth state is determined by design N fill Example 1 comparison of the filling time between a full scale and a half scale canopy hooked to the same i e unscaled payload container
6. 33 OSCALC short inflation time graph showing defaults Original graph extracted from Wolf D paper 4 99 1782 Ss 5 7 1 Initial inputs 3 t Almosphenc at deployment altitude 0 002 10 Tels mass 621 Estimated fall rate at line stretch 1 i 2 1 Drag aea from Knacke 1 or other sources amp UPRER Steady descent_DO 1forpmaok 075 AVERA Nominal surface area e160 L LOWER OU sane Se EDU 1 TTD Ta nh Weight used 2000 Descent rate Nominal surface area 550 Average opening shock Factor 025 Upper bound of opening shock factor 0 4 Lower bound of opening shock Factor 01 Figure 3 1 Default calculation and windows displayed at the beginning an OSCALC session 34 How to run OSCALC Cont d This window is the Default window the graph shows how the values of were picked given the mass ratio and inflation time that resulted from the default input values The Default case is discussed further in Section 6 example 6 1 Click on the graph to see it completely click on the program window to return to the program The correspondence between the input output shown on the main window and the variables discussed in this manual is shown in figures 3 2 3 3 and 3 4 below Note about the Default graph the graph will be repla
7. 10 10 INVERSEMASS RATIO Aeroconical steerable National Phantom 4 Aeroconical steerable GQ Security Crossbow 29 3 How to run OSCALC 30 3 How to OSCALC The logic flow is as follows Parts 1 amp 2 Input amp intermediate calculation User enters the values of p V User enters engineering data that yields a calculation stretch and m User enters Cp and S or of Cp namely S weight atmospheric density and OSCALC computes 5 4 measured steady descent speed OSCALC computes 5 User enters User enters g 9py OSCALC computes gy OSCALC computes the values of and ny Parts3 4 amp 5 31 Parts 3 4 amp 5 Choice of proper graph input of C final calculation Parts 1 amp 2 User chooses either the high or 2 graph of C vs R based on the computed value of n P From the graph the user picks the average value of C as well as its upper and lower bounds User enters those three values of C into OSCALC OSCALC computes F ax and its upper and lower bounds 32 How to run OSCALC e Copy named OSCALC exe in a directory of your choice OSCALC does not require any input files nor does it generate any ouput files Run OSCALC exe The main window appears with one graph tucked under see figure 3 1 below These instructions apply both to V1 0 and V1 01
8. 4 Potvin J On Opening Shock Factor Mass Ratio Universality To appear in Journal of Aircraft 2006 Copies of manuscript available on request 5 Potvin J and Peek G Parachute Inflation I General Phenomenoloy lecture delivered at the 2006 H G Heinrich Parachute Systems Short Course May 15 19 2006 copies available on request 13 What are values of C Originally defined as C PT 2 Y rein js Over years values of C for different parachute systems have been collected by many authors see references 1 3 t was found that this C data show distinct trends when plotted against the mass ratio R 2 cos total mass of the payload parachute system 14 Opening Shock Factor Unreefed permanently reefed hemispherical canopies low and high porosity compiled by Wolf 3 C at KR 0 is called in Knacke 1 OPENING FORCE FACTOR Ck 2 0 2 0 1 7 Drogues and pilot chutes All chutes deployed in wind tunnels x 4 F amp F BEC i p MASS RATIO EWING DATA FW DROGUE LARGE MAIM SANDIA PILOT SANDIA WF ORBITER WT PETE 2 vc p 109240 1015 Personnel and cargo airdrop parachute applications 40 low altitudes 15 Opening Shock Factor dis reefing hemispherical canopies low and high porosity co
9. Warning this is not always true See Knacke s description of the lead lag phenomenon Figure 6 10 Assumptions used to compute the non dimensional inflation time of a cluster 80 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 The momentum impulse theorem discussed in section 2 guarantees that the C data of the new parachute will duplicate the trend shown in the C graphs as long as its generalized filling time is such that n p 2 Coming up with an educated guess of the filling inflation time may be possible for example by using the values of documented parachute systems that are similar or by guessing filling times values that could single out worse case scenarios i e the largest realistic values of Fax Better filling time information will be obtained after the video of the first flight is analyzed 81 7 OSCALC error warning messages 82 7 OSCALC error warning messages So far there are only two built in warning error messages n 75 OSCalc Warning E One mare Initial Inputs may have changed Please click the Calculate Initial button ance mare OK 19 des we 7 13 11 ledge am 1 or other sources am kn with cases where it is smaller than 1 0 a 616 0 1
10. di lor 13 4 Foot L rameter Tow lest 71 Figure 6 6 Choosing non dimensional filling time using reference 1 Various Parachute Types Canopy fill constant n Parachute type Disreef Unreefed opening 3 opening opening Solid flat circular ID 8 Extended skirt 10 4 5 10 Extended skirt full 7 12 Cross ID 11 7 Ribbon 6 14 Ringslot ID 14 Ringsail 2 7 Ribless guide surface 4 6 Insufficient data available for meaningful evaluation 72 6 3 Un reefed parafoil vs dis reefing parafoil Part 1 Consider the example of a 250ft parafoil that is not equipped with a slider this parafoil has no reefing whatsoever In this example the values of S is computed from the product of wing chord times span p 0 002 sl ft deployment at 5000ft MSL 6 21 sl corresponding to 200 Ibs on Earth V seren 130 ft sec C 1 0 during inflation the parafoil looks like a flat plate S 250 ft Nay 2 no reefing see table section 2 OSCALC gives 1 27 and ny 1 13 User should choose the Short Inflation Time graph User would pick 0 6 with 0 9 and 0 3 as bounds The result is F 2535 105 with 3802 Ibs and 1267 Ibs as bounds 73 6 3 Un reefed parafoil vs dis reefing parafoil Part 2 Consider the same 250ft parafoil but equipped with a slider Assume the same payload and deployment conditions The only difference is the non dimensional filling tim
11. 62 to be entered in OSCALC together with S 6 see figure 6 2 Nyy 0 5 x 6 3 See figure 6 10 OSCALC gives 8 73 and nf 2 15 User should choose the Short Inflation Time graph User would pick C 0 1 with 0 2 and 0 05 as bounds The result is F 77 872lbs with 155 744lbs and 38 936lbs as bounds 78 Figure 6 9 Net drag coefficient of a parachute cluster w r to the drag coefficient of the member parachute 4 making up the cluster oc DRAG COEFFICENT RATIO COMPOSITE DATA FROM DIFFERENT SOURCES 100 FT D G 11A l D 1 0 REF 2 2 C 100 FT D FLAT V lt 25 FTS REF 5 50 100FT D FLAT V 25 30 FTS REF 5 50 88 1 FT D RINGSAIL I D 1 40 REF 5 50 85 6 FT D MODIF RS l D 1 44 REF 5 50 128 9 FT Dj RINGSAIL I D 1 15 RF 5 50 X 1 25 FT D RIBBON NO RISER REF 5 165 1 25 FT D RIBBON LONG RISER REF 5 165 NUMBER OF PARACHUTES FIGURE 5 110 Drag Loss in Parachute Clusters 79 Since the inflation time of cluster inflation time of each parachute of the cluster then 4 cluster 4 cluster chute chute V t n D N D stretch fill fill 0 fill 0 1 chute 5 0 chute 1 4 cluster __ 1 chute fill fill ll 4 cluster 4 S 0 It is assumed here that all the parachutes of the cluster inflate at the Same time and with the same inflation time
12. 75 Figure 6 7 Using reference 1 to determine the drag area of a permanently reefed canopy 5 6 C551 REEFING RATIO Fu P punn 0 1 0 2 0 3 0 4 LINE RATIO FIGURE 5 72 Reefing Ratio Versus Reefing Line Ratio for Circular Flat Conical Tricankcal and Extended Skirt Parachu BEES TYPE TEST 0 7 76 Figure 6 8 Choosing non dimensional filling time Various Parachute Types ode EN n r rsonule type Diarest Y Urrested ml 5 open Solid flat circular Extended skirt 1096 Extended skirt full 12 Cross 11 7 Ribbon 14 Ringslot 14 Ringsail 7 Ribless guide surface 4 6 insufficient data available for meaningful evaluation Df unreef n fn What to do Used simple estimate discussed in section 4 limited to very low reefing ratios and low porosity canopies mouth unreef 29 0 29 D Cr f 6 5 Parachute cluster unreefed Consider a cluster of four 100ft flat circular canopies p 0 002 sl ft deployment at 5000ft MSL 622 sl corresponding to 20 000 165 on Earth V etch 290 ft sec 5 chute 75 unreefed value reference 1 see figure 6 1 So 4 x x 100ft 4 31 400 We need the drag coefficient of the cluster use figure 6 9 SC po 0 83 C S 0 83 x 0 75 x 31 400ft 19 5478 So Cpo 41451 0 83 Cpo s 0
13. 9 low porosity flat circular Yes that makes sense should be smaller if the parachute payload moves at constant speed compared to the same system undergoing a deceleration in other words the air in flux is larger with the former than with the latter In the small regime the dependence may not be as dramatic Dependence on relative stiffness important issue when working with small amp sub scale models 0 064 pV 0 064 n fill 1 3 5 5 D stretch 1 0 Tunnel data by Heinrich and also By Johari and Desabrais 8 Filling Time t 10 10 10 10 107 108 10 10 102 Relative Stiffness Index C 59 5 Some tricks to estimate fall speed at line stretch 60 5 Some tricks to estimate fall speed at line stretch V parachute payload fall rate the beginning of inflation e Most often raf Depends on deployment strategy 2W Vstretch drogue VA P S drogue D After long stabilized freefall Deployment by static line and for a mostly pre inflation horizontal trajectory 1 dim const acceleration V kinematics n At ast AX acft payload distance At deployment duration 61 Deployment static line and for mostly vertical pre inflation trajectory Adjust FUDGE to match mean flight angle hori P Verretch vertical P seen on video payload EM drag stowing down V stretch _ ho
14. Calculate Initial Calculate Final Help buttons E Help 4 Final inputs Average opening shock factor n25 Upper bound of opening shock factor 04 Lower bound of opening shock factor 01 40 4 More information on filling time 41 The following references contain experimental data inflation time of several types of parachutes References 1 and 2 previously mentioned also contain inflation time data 42 4 References on inflation time 6 Lee C K Modeling of Parachute Opening an Experimental Investigation Journal of Aircraft 26 444 451 1989 7 Cruz J R Kandis M and Witkowski A Opening Loads Analyses for Various Disk Gap Band Parachutes paper 2003 2131 17thAIAA Aerodynamic Decelerator Systems Technology Conference and Seminar Monterey CA May 19 22 2003 8 Johari H and Desabrais K J Stiffness Scaling for Solid Cloth Parachutes Journal of Aircraft 40 pp 631 637 2003 9 Berndt J and DeWeese J H A Filling Time Prediction Approach for Solid Cloth Type Parachute Canopies 2nd AIAA Aerodynamic Decelerator Systems Technology Conference Houston TX September 7 9 1966 pp 17 32 10 Wolf D A Simplified Dynamic Model of Parachute Inflation Journal of Aircraft 11 No 1 pp 28 33 1974 43 4 References on inflation time cont d 11 Lingard J S Semi empirical Theory to Pred
15. Descent Characteristics of Truncated Cone Decelerators paper 2005 1620 18th Aerodynamic Decelerator Systems Conference and Seminar Munich Germany May 23 26 2005 45 The following tables summarize some of data found in these references Please go to the references to get the details on the parachute construction dimensions payload characteristics and drop conditions 46 Low and high porosity hemisphericals see Knacke 1 Various Parachute Types Canopy fill constant n Parachute type Disreef Unreefed opening opening Solid flat circular 8 Extended skirt 1096 us 10 Extended skirt full 7 12 Cross ID 11 7 Ribbon 6 14 Ringslot ID 14 Ringsail 2 7 Ribless guide surface 4 6 aiD Insufficient data available for meaningful evaluation 47 Note about previous Table de AM Why the differences in n between reefed opening disreef opening and unreefed opening Relative to unreefed opening opening involves a canopy mouth which over time does not open as widely should be larger longer inflation time However can be shorter as well with parachutes reefed by very short reefing lines small reefing ratios result in inflated canopy volumes that are smaller than the inflated volumes of the unreefed configurations disreefed opening needs a smaller amount of air to fill the canopy from its initial state i e inflated but reef
16. Manual revised 07 17 06 OSCALC Opening Shock Calculator Version 1 01 User s manual Gary Peek amp Jean Potvin Parks College Parachute Research Group Saint Louis University St Louis MO Contact peek industrologic com 800 435 1975 potvinj slu edu 314 977 8424 Contents Acknowledgment Warning Disclaimer What is OSCALC Basic input data How to run OSCALC More information on inflation time some tricks to estimate the fall speed at line stretch Examples OSCALC error warning messages Concluding remarks OQ Un bh N Acknowledgment OSCALC was developped under US Army Natick contract W9124R 06 P 1068 The authors would like to thank Dr Dean F Wolf for allowing the display of his two C amp graphs in this program They would like to thank also the Natick Soldier Center U S Army RDECOM Airdrop Aerial Delivery Directorate Airdrop Technology Team for their continued support of this project Version Tracker This manual covers the use of both OSCALC V1 0 and V1 01 Version 1 01 is the same as version of V1 0 except for slightly modified input box titles Warning Disclaimer OSCALC provides the means to estimate the value of the maximum drag generated during parachute inflation based on inputs provided by the user The authors and their governmental funding agency cannot make any claim on the accuracy of the results 1 What is OSCALC 1 Opening Shock CALCulat
17. SCALC uses following approximation for calculating the value of 7 If R gt 0 10 then 7 0 5 If R lt 0 01 then 1 7 0 2 If 0 01 lt R lt 0 10 then 0 5 0 2 2 e NOTE The integral is one of the factors that generates the scatter in the two graphs OSCALC does not computes but accounts for it through C lower and upper bounds that must be entered C ym TT 407 k n En fill fill m x SC p sa 2 recap The value of determine which one of two C vs R graphs to use From the chosen graph the value of C of its lower bound and of its upper bound are obtained by spotting the value of the system under consideration see next slide for example F 18 finally calculated from this data and from the other basic inputs SC y p and V setn its upper and lower bounds are estimated as well using the upper and lower bounds of C Note Section 7 explains what to do when nj lt 1 2 ax EV Y sc 5 28 Original graph from D Wolf paper 99 1702 colored data points collected by GP and JP OPENING FORCE FACTOR Ck 0 5 0 0 10749 10739 KNACKE EWING DATA FWC DROGUE LARGE MAIN SANDIA BOMB SRB PILOT SANDIA WT ORBITER WT Full scale TCD Deep cone Unreefed C 9 Reefed C 9 24 T 10C MC1 1C Half scale C 9 Reefed at 16 w r T 10 2
18. age opening shock factor 0 25 Upper bound of opening shock factor 4 84 OSCALC error message Error Considering a case where the generalized filling time is less than unity am 1 or other sources Lower be drag E BE area The entries resulted in the generalized inflation time being 0 651 but this result must be greater than or equal to 1 0 to allow the use Pali of either graph See user s manual about the strategy that deals with cases where is smaller than 1 0 Cal am kn sity d 2 grea See next page 85 The case of very small filling time This error message is triggered whenever ng lt 1 The problem is that neither graph apply to this case If this value is not the result of a typing error the user may consider using the Momentum Impulse Theorem in tandem with OSCALC 1 Run OSCALC for the same type of parachute and reefing but with canopy diameters atmospheric density and payload weight that is characterized by the same R and a larger n thereby obtaining a C alt alternate 2 Use the formula below to estimate the C of the actual system n alt C actual __ C alt fil actual fill 86 8 Concluding remarks This is the OSCALC Version 1 0 family Future versions will provide updated C g
19. ations of drag force evolution would be most desirable i e models sought to provide both and outputs depending on the actual design and constuction of the parachute and on the actual drop conditions Will such models ever replace OSCALC Even with these detailed simulation tools being around OSCALC will still be useful in particular for calculating F sustained during inflation scenarios that are not covered by the detailed models for example malfunctions mis staged inflation or inflation sequences that begin with unusual canopy shapes Long live OSCALC 99 Please send all questions to Gary Peek amp Jean Potvin Parks College Parachute Research Group C O Dr J Potvin Physics Department Saint Louis University 3450 Lindell blvd St Louis MO 63103 Contact peek industrologic com 800 435 1975 potvinj slu edu 314 977 8424 90
20. ced by the same graph but without comments whenever the Short Inflation Time radio button is clicked Exit OSCALC and start a new session if there is a need to look at the original Default graph again 35 1 Irutial laput r z Intermediate 1 5 Final Results p Atmospheric density at deployment altitude 0 002 Mass ratio 3 198 Average maximum force Total mass 21 Generalized 3 305 73s 1553 2 1 Inflation time Upper bound of force 2661 12 Upper Lower bound of force V fall rate at line stretch 20 0 3 Graph Choice f Drag area from Knacke 1 other sources Long inflation time C pp steady descent DU 1 for parafoils 0 75 665 28 Lower S 0 surface area 616 0 C Drag area from steady descent data rounds only Calculate Initial f Weight used 2100 0 Calculate Final See Atmospheric density during descent 0 00237 Fig 3 3 S Descent Fall rate ET below Maominal surface area 61 6 0 4 Final Inputs Ex Q Average opening shock Factor 0 25 k Nan Non dimensional inflation tine 6 0 Upper bound of opening shock factor 0 4 k Actual inflation time 1 63 Lower bound of opening shock factor 0 1 1 owe hin See Fig 3 4 Figure 3 2 Basic input and output of OSCALC The color coding for this figure is as follows Calculated versus input 36 Again note
21. data in 1 Initial inputs click Calculate Initial button After looking at the values of RX and in 2 Intermediate results click the relevant graph in 3 Graph choice in order to find and its bounds enter these values in 4 Final inputs Then click the Calculate Final button and look at the calculated force in 5 Final results Figure 3 5 Parts 3 4 and 5 of an OSCALC run Lower bound of opening shock factor o1 _ 015 2 Inbermediale results 5 Final results Massralio 3198 Average maximum force Generalized Song 1 2 inflation lire E Upper bound ol force 3 Graph choice DEETT M ou ides Lower bound of force 555 28 Short inflation time Cakulete inii Calculate Final 4 Fra Average opening shock tector 825 Upper bound of opening shock factor 0 4 39 Note the button Print sends to printer an image of worksheet but not of the graph Note the button Help generates a window that shows copyright information a list of suggested units an acknowledgement and limited information on the program Pele 2 Intermediate results 5 Final results Massratie 3198 Average maximum force Generalized ax ar SRS 3 909 1653 2 m Upper bound of force 3 Graph choice ERGO Lower bound of force 55528 Figure 3 6 The Print and Short inflation time
22. e which is increased sliders do that p 0 002 sl ft deployment at 5000ft MSL 6 21 sl corresponding to 200 Ibs on Earth V seren 130 ft sec C 1 0 during inflation the parafoil looks like a flat plate S 250 ft Nay 14 See table section 2 old 1980 s 7 cell design they in 15 25 range with the 1990 s and 2000 s designs OSCALC gives 1 27 and 7 89 User should choose the Long Inflation Time graph User would pick C 0 2 with 0 3 and 0 1 as bounds The result is 7 845 Ibs with 1267 lbs and 422 lbs as bounds QUITE REDUCTION OF OPENING SHOCK 74 6 4 Dis reefing hemispherical canopy Consider a 20 reefed USAF C 9 canopy which has been falling steadily in its reefed configuration until reefing line cutter activation at 5000ft MSL p 0 002 8 cutter activation at 5000ft MSL 6 21 sl corresponding to 200 Ibs on Earth V stretch V 40 3 ft sec using reefing drag area data of figure 6 7 to compute the fall rate prior to dis reefing inflation Cpo 0 75 unreefed value from reference 1 see figure 6 1 S 616 ft calculated from S 28 1 2 4 Ngu 0 3 x 6 1 8 See figure 6 8 OSCALC gives 3 19 and 1 17 User should choose the Short Inflation Time graph User would pick C 0 3 with 0 5 and 0 15 as bounds The result is 225 Ibs with 375 Ibs and 113 lbs as bounds
23. ed to it final state i e fully opened should be smaller shorter inflation time 48 Total weight Reefing ney References deploy altitude V Deep Cone 18165 700ft MSL No reefing Cone height 110ft sec 16 00ft Cone base 10 66ft D 32 72ft hypothenuse of half cone init See reference 18 calculation based on D 49 Parafoils Total weight deploy altitude V init Parafoil 160lbs 7008 MSL Paraflite Strato 105ft sec Cloud chord 10 08ft span 19 16 Parafoil 2001 4000ft MSL PD Stiletto150 160 170fUsec skydiving elliptical 1990 s design 9 cells 150ft factory configuration Parafoil 2001 4000ft MSL PD Sabre150 160 170ft sec skydiving elliptical 1990 s design 9 cells 150ft factory configuration Reefing Slider sail free Slider sail free 16 20 Typical drop to drop variations 10 19 Typical drop to drop variations References Note with slider reefed systems will depend on the actual dimensions of canopy rigging angle brake setting inlet canopy and slider design and dimensions 50 5 Size Parafoil Paraflite MT 1X skydiving recta ngular 1980 s design 7 cells 370ft factory configuration Parafoil No data 1980 s design for personnel applications Parafoil No data 1980 s designfor personnel applications Total we
24. ed in Wolf s compilation If 1 lt 4 the user chooses the graph formely associated with dis reefing in Wolf s compilation Note The half scale C 9 unreefed data shown on the small 7 graph characterized a parachute system with unusually large riser separation which yielded unusually shorter filling times 24 Original graph from D Wolf paper 99 1702 colored data points collected by GP and JP OPENING FORCE FACTOR Ck KNACKE EWING DATA FWE DROGUE LARGE MAIN SANDIA BOMB SRB PILOT SANDIA WT ORBITER WT Full scale TCD Deep cone Unreefed C 9 Reefed C 9 24 T 10C MC1 1C Half scale C 9 Reefed at 16 0 0 107 9 10730 10 26 INVERSEMASS RATIO Rm Aeroconical steerable National Phantom 4 Aeroconical steerable GQ Security Crossbow 25 Original graph from D Wolf paper 99 1702 colored data points collected by GP and JP EWING DATA LARGE MAIN SANDIA WT OPENING FORCE FACTOR Ck 0 0 LE 10 40 10 2 10 28 a I 10 s INVERSE MASS RATIO 4 Aeroconical steerable GQ Security Crossbow A A ical steerable Pi K2 Parafoil ParaFlite Strato Cloud no slider eroconical steerable Pioneer Half scale C 9 unreefed Parafoil Precision Aero Falcon 175 no slider 0 Aeroconical steerable National Phantom NOTE O
25. ict Load time History of an Inflating Parachute AIAA 84 0814 8th Aerodynamic Decelerator and Balloon Technology Conference 1984 Hyannis MA April 2 4 1984 12 Lee C K Experimental Investigation of Full Scale and Model Parachute Opening paper 84 0820 8th Aerodynamic Decelerator and Balloon Technology Conference 1984 Hyannis MA April 2 4 1984 13 Lee C K Lanza J and Buckley J Experimental Investigation of Clustered Parachute Inflation paper 97 1478 I4thAIAA Aerodynamic Decelerator Systems Technology Conference and Seminar San Francisco CA May 19 22 1997 14 Lingard S J Ram Air Parachute Design ALAA Aerodynamic Decelerator Systems Technology Seminar May 1995 63 pp Unpublished 44 4 References on inflation time cont d 15 Barnard G A The Effect of Extreme Altitude of Parachute Filling Distance 93 1207 12th Aerodynamic Decelerator Systems Technology Conference and Seminar RAeS AIAA London England May 10 13 1993 16 Heinrich H G The Opening Time of Parachutes Under Infinite Mass Conditions AIAA 68 12 3rd AIAA Aerodynamic Decelerator Systems Technology Conference El Centro CA September 23 25 1968 17 Heinrich H G The Opening Time of Parachutes Under Infinite Mass Conditions Journal of Aircraft 6 No 3 pp 268 272 1969 18 J Potvin and G E Peek Inflation and Steady
26. ight altitude 12 19 Typical drop to drop variations V init 274 360158 10 000ft MSL 270 3 10ft sec Slider both sail free and pilot chute controlled Slider sail free Reference 14 Reference 14 Note on slider reefed systems suspension line abrasion can significantly increase the value of to values well exceeding 20 51 Remarks These tables show that depends on canopy design and reefing BUT n5 also depends on how wide the canopy mouth is opened at the beginning of the inflation process time of line stretch in many cases wide mouth lots of air gulped in fast fast inflation low value of N siu narrow mouth air entering at a slower rate slow inflation large value of N fiu The actual amount of opened mouth area is often and strongly determined by the way the parachute gets out of its container bag and aligns into the wind depends on what happened during deployment Expect to see drop to drop variations of n py next slide 52 Drop to drop variations during test drops from n 5 to 7 Figure by Desabrais Johari 8 Filling Time 10 o h a 1 0 ga ooo gt de 2826 0000090090090 20 0000000990909 0 water tunnel models
27. ion time for a C 9 type canopy low porosity hemispherical canopy 67 5 5 004 LOWER BOUND al ENING Snore FACTOR ior ine INVERSE MASS RATIO Rm X DEFAULT CALCULATION Parafoil Strate Cloud m dide Half scale C uraesfed Parafeil Precision Aere Faken 175 sider Average opening shock factor Upper bound of opening shock factor 0 4 Lower bound of opening shock factor 0 1 Figure 6 3 Chosen graph and C values for the Default case 6 2 Permanently reefed high porosity hemispherical canopy deployed at high altitude and at low mass ratio This example would be typical of 28ft diameter ribbon type canopy reefed at 20 0 001 sl ft deployment at 27 000ft MSL m 62 1 sl corresponding to 2000 Ibs on Earth V 200 ft sec typical if launched from cargo flying 130K TSI Cpo 0 38 unreefed from reference 1 see figure 6 4 S 616 ft calculated from S 28 1 2 4 9 SC 0 27 x 0 38 x 616ft 63 2ft see figure 6 5 10 See figure 6 6 OSCALC gives 0 008 and n 5 14 27 User should choose the Long Inflation Time graph User would pick C 1 25 with 1 50 and 1 00 as bounds The result is F 3465 Ibs with 4158 Ibs and 2772 lbs as bounds 69 Figure 6 4 Knacke 1 Tables 5 1 5 4
28. ke 1 Tables 5 1 5 4 Figure below is from Table 5 1 CONSTRUCTED SHAPE INFLATED DRAG OPENING mS SHAPE COEF FORCE apts ip GENERAL TYPE D D C COEF ANGLE VES 2 Cy OSCILLATION APPLICATION D RANGE NE MASS DEGREES EE 0 67 10 DESCENT FLAT 1 00 TO 1 7 BSOLET CIRCULAR iA TO OBSOLETE 0 93 0 75 10 CONICAL 0 70 1 8 TO M lt 0 5 0 90 0 75 10 DESCENT BICONICAL TO 0 70 18 TO M 05 KD 0 95 0 92 30 FEN 0 90 0 80 10 DESCENT TRICONICAL TO 0 70 TO 18 M 0 5 POLYCONICAL oss 0 96 Es EXTENDED 0 66 0 78 10 DESCENT SKIRT 0 86 TO TO 1 4 M lt 0 5 10 FLAT 0 70 0 87 15 0 81 0 66 0 75 10 DESCENT SKIRT TO TO TO 14 TO M 0 5 14 3 FULL 0 85 0 70 0 90 15 66 10 t2 a09vansesaedioaesoseceousvesedeseseseaeseconto t9tottoetott water tunnel models Nue v wind tunnel 6 poU Heinrich 3 Drop to drop 2 MN variations during test drops from n 5 to Ney 7 facing the wind deployments SO ESS SFOS SHS SSOSSESSE HSA Filling Time Figure by Desabrais amp Johari 8 1 i i 10 107 109 10 107 108 105 104 10 102 Relative Stiffness Index C Figure 6 2 Choosing the non dimensional inflat
29. mpiled by Wolt 3 7 EWING BATA FWCDROGUE LARGE MAIN BANDIA BOMB ok x SANDIA ORBITER WT FETE DTZ OPENING FORCE FACTOR Ck 0 0 271 Se ES kirj o 8 T F 1074 nr 10774 18 THE MASS RATIO Em C data Figure extracted from the USAF parachute design guide reference 2 Opening Load Factor Opening Load Factor il Eee IL TUNI LAU js DH SU p EUN S LL Stage 1 or 2 F 0 n Borat dum HS ur t0 23 58710 Ratio Averaged Composite Data From Many Sources SE IS ended Zi O O Rested Ref 217 g ec Vi d Dik Gap Band Ret 378 S Fier Cireular Cluster of 3 T 206 100 Fr 1 eer Mas Ratio Fin bh Selected Parachute C Avg Diseeef to Full and Non Reefed 17 Figure 6 25 Parachute Opening Load Factor Vs Mass Ratio Some important questions about 1 Why is the value of C for unreefed permanent reefing C vs K graph different from that of the dis reefing graph 2 These graphs were built out of the data collected on hemispherical parachutes what about the C data of parafoils slider reefed parachutes and other parachute and reefing types Would those data fit in the same two graphs Answers 1 Filling
30. or What is it It is a simple program that estimates the maximum drag force aa generated during parachute inflation Uses inputs that are straightforward to obtain Calculation applies to parachute design and reefing type low and high porosity hemisphericals unreefed reefed dis reefing parafoils unreefed line reefed slider reefed in fact anything that can be used as a parachute Is it based on an equation commonly used in parachute engineering OSCALC computes this number From graph 1 pop under over window 4 2 F max LWV orerch scp e 4 From inputs of problem tPronounced as O S CALC 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 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 being connected to an ejection seat propelled by a rocket OSCALC is not a true predictor of opening shock since it requires the use of fc which is an actual inflation performance variable but there is a lot of n data in the public domain already otherwise measuring from video is a straightforward task What applica
31. raphs that include data points of parachute drops carried out more recently These updates should close gaps on the plots This new data could also help create a new graph for the case n lt 1 Remember the data scatter on the graphs is not due to lack of knowledge or measurement errors but rather to 1 the integral changing with flight angle at the same value of R 2 being defined over a range of values for each graph and 3 the drop to drop variations associated with both and n More details on all this can be found in reference 4 8 e is not a true predictor of opening shock since it requires use of fc which is an actual inflation performance variable OSCALC is not a design tool either with regards to changing the dimensions of sub components For example changing slider size on a parafoil will be reflected in a change in But even if the designer knew how to predict this change of ti OSCALC may still give the same the new tay involves the same C R graph One way out of this problem especially if tau is known is to use the equation I shown on slide 20 and discussed in details in ref 4 m fill Note that OSCALC can be of some use to the designer if the overall size and porosity of the canopy payload weight deployment altitude and or pre inflation fall speed are changed 88 Design is where detailed simul
32. riz F UDGE Vacft horizontal motion of payload over time Do Vstretch _ vertical 448 Lstaticline 7 Lsusplines Vertical acceleration dominated by gravity 62 6 Examples 6 Examples 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 6 4 Dis reefing hemispherical canopy 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 64 6 1 Unreefed low porosity hemispherical canopy Default case This example would be typical of the USAF C 9 canopy a flat circular canopy made of low permeability fabric This canopy has no drive slots just a small vent at the apex p 0 002 sl ft deployment at 5000ft MSL 6 21 sl corresponding to 200 105 on Earth V sern 120 ft sec C 0 75 from reference 1 see figure 6 1 S 616 ft calculated from S 28ft 7 4 6 See figure 6 2 OSCALC gives 3 19 and nf 3 91 User should choose the Short Inflation Time graph User would pick C 0 25 with 0 4 and 0 1 as bounds See figures 3 1 and 6 3 The result is 1663 2 Ibs with 2661 1 Ibs and 665 3 Ibs as bounds 65 Figure 6 1 Where to get steady state drag coefficient data Go to Knac
33. s seconds kilograms and Newtons The examples of Section 6 show how to enter OSCALC inputs using American Standard Units 10 2 Basic input data 2 Basic input data SCp m e V sern parachute payload fall rate at line stretch or at the moment of first air for canopy first deployments or whenever the canopy is stretched and its mouth opened or wing inlets opened e Atmopsheric density at deployment altitude SC Drag area of the fully opened canopy during steady descent For hemispherical canopies 5 Cpo Sp Cp x with S being to total canopy area including vents area 1 For parafoils 5 Cpo Sy 1 0 X wing chord X wing span For a cluster of hemispherical canopies see example 6 5 in Section 6 below e C Opening shock factor What are the values of 12 Basic references about Opening Shock Factor 1 T W Knacke Parachute Recovery Systems Design Manual Para Publishing Santa Barbara CA 1992 2 Ewing E G Bixby W and Knacke W Recovery Systems Design guide pp 254 257 report AFFL TR 78 151 Submitted to Air Force Flight Dynamics Laboratory AF Wright Aeronautical Laboratories Wright Patterson Air Forced Base December 1978 Unpublished 3 Wolf D Opening Shock AIAA 99 1702 15 CEAS AIAA Aerodynamic Decelerator Systems Technology Conference Toulouse France 8 11 June 1999
34. that user can either enter the values of Cp and and have OSCALC compute the value of 5 Cpo S in the case of parafoils enter 7 amp S chord span enter proprietary engineering data related to the steady descent of the canopy in order for OSCALC to compute Cp and SC y Cp S note W and can be different from the values of m g and p used for the calculation of F Note this alternative applies only to hemispherical parachutes Just click the relevant radio button Drag area fram Knacke 1 other sources only one button can be clicked ee descent C_DO 1 for parafois 075 during the same run Nominal surface area 616 0 Drag area fram steady descent data rounds only IW Weight used W d 200 0 d T m Atmospheric density during descent Psa 9 00237 P a SV Descent fall rate ian Nominal surface area S 0 Figure 3 3 Drag area options 37 e Note also that user can either enter the values of Nn or enter the dimensional inflation time bin as measured on video OSCALC will then compute Just click the relevant radio button only one button can be clicked during the same run PN EI dut an Maon dimensianal inflation time 7 0 pper b fill Actual inflation time f fill fill stretcht 0 D d AS Figure 3 4 Inflation time options 38 After entering input
35. time or inflation time is the key concept 2 Yes these two graphs can accommodate the C data of any parachute and reefing dis reefing type 18 Back to college physics Momentum Impulse Theorem details in reference 4 integral version of F ma f f mV mV impulse cos O t dt Ii j E a nv my Lh pv Ck w cos O t dt A T ax Fog f b Fi lt SRS 1 4 sg SS NS X NS I p Drag integral area under the curve SS ty 19 Solve the momentum impulse equation to get General Result Reflects gt directly See ref 4 Mass ratio en 1 oy yr Generalized filling time 1 2 GC psa Standard filling time f V v a cos 1 dt V horizontal vertical 20 0 4 0 5 high R amp 0 2 0 4 low R C R n gen m fil The Momentum Impulse Theorem confirms the importance of the mass ratio R in determining the value of The Theorem also makes clear that the inflation time or filling time is another crutial ingredient OSCALC uses three different concepts of filling time Actual inflation time has dimensions of time Standard non dimensional filling time has no dimensions Generalized non dimensional filling time 7 has no dimensions
36. tions is it most useful for F estimation at the DZ right after a test OSCALC provides the means for calculating based solely on the basic canopy dimensions amp drag properties payload weight deployment conditions and video of the inflation process for inflation time info The tool should be very useful during those tests where the payload is not equipped with load cells or accelerometers designs including designs that have not yet been documented in the public domain see Section 6 6 for suggestions e Provides a good guess for even for new parachute and reefing What applications is it most useful for cont d Sanity check for developers of computer simulations of the inflation process e Calculation of 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 staged openings etc all one needs here is video to get the inflation time information What is unit system of OSCALC No physical constants are being used explicitly the only dimensional equation is F Verrete SCp Most variables are used in non dimensional form ratios Input values can be entered in any units as long as they are balanced and consistent We recommend using either eAmerican Standard Units based on feet seconds slugs and pounds or Metric Units based on meter
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