Testing Without Load Cells - Can Opening Shock Be Estimated From Video Data Only?

Transcription

1 Testng Wthout Load Cells - Can Openng Shock Be Estmated From deo Data Only? Paper AIAA Gary Peek & Jean Potvn Physcs Department, Sant Lous Unversty, St. Lous MO Contact: peek@ndustrologc.com potvnj@slu.edu Talk presented at the 19 th AIAA Aerodynamc Decelerator Systems Conerence, Wllamburg, A 22-24, 2007

2 Work unded by Natck Solder Center (Natck, MA U.S. Army contract W9124R-06-P-1068

3 Executve Summary The maxmum drag orce generated by an nlatng parachute can be estmated va these two ormulas: Horzontal trajectores 2m Fmax 1 ( t t descent ertcal trajectores (downwards F max ( t 2m t 1 descent + g ( t t Note the dependence on (t t nlaton duraton (obtaned rom vdeo Such estmate wll work wth most parachute and reeng types Works only or slow-descendng parachute-payload systems (.e. descent < 30t/sec Paper shows the large database that was used to check the range o valdty

4 Executve Summary NOT DISCUSSED IN THIS TALK OR PAPER: The maxmum drag orce generated by an nlatng parachute used at nnte-mass condtons (.e. low mass ratos/wnd tunnels,etc., can be estmated va ths ormula: F U max ck U 20 ck (Horzontal trajectores ρ ( SC 2( t D sd t 3 / 2 For both low- and hgh porosty hemsphercals - unreeed More detals can be ound n: Unversalty Consderatons or Graphng Parachute Openng Shock Factor ersus Mass Rato "; JOA, 44, No. 2, pp , Paper-copy avalable on request.

5 Why s ths a bg deal? The value o the maxmum drag orce s a standard measurement durng the testng phase o most parachute systems (nvolvng load cells and/or accelerometers But what about ndng out durng servce use, say ater unusual deployments and/or unusually hard openngs? Typcally such parachutes are not equpped wth orce-measurng devces. The method dscussed here proposes an estmate, based on general deployment and parachute characterstcs AND on nlaton duraton, whch obtaned rom the vdeo coverage o the openng

6 Man ngredent the Momentum-Impulse Theorem Integraton o Newton s 2 nd law o moton m m = F ( t dt + W cos θ ( t dt D Momentum change Parachute drag Gravtatonal o parachute-payload mpulse mpulse = descent end o nlaton = descent the begnnng o nlaton lne stretch θ(t = lght angle The MI-theorem has been used extensvely to study the maxmum orce on many types o systems. See reerences [1 5] n paper. Paper copes o res. [1] and [4, 5] are avalable here!

7 Man ngredent the Momentum-Impulse Theorem Reormulate n terms o m m = F ( t dt + W cos θ ( t dt D ( m = F + max ( t t I F m W cos θ ( t dt Inlaton duraton Drag ntegral; gauges the shape o the drag vs. tme curve I F = F F max D ( t ( t dt t

8 Man ngredent the Momentum-Impulse Theorem Focus on ether vertcal trajectores (θ(t = 0 and on horzontal downwards trajectores (θ(t = 90 Assume ~ descent (.e. steady-state descent under ully nlated canopy Assume drag ntegral I F ~ 1/2 Extractng rom the MI-theorem under these condtons yelds the man results o ths paper Horzontal ertcal Obtaned rom vdeo coverage 2 = 1/I F F max 2m Fmax 1 ( t t ( t 2m t 1 Froude term descent descent g ( t + t

9 Whch parachute-payload system satsy the condton ~ descent? One can get ~ descent the drag orce s large enough and lasts long enough to generate the requred deceleraton In partcular ths constrant apples to hgh mass rato (R m systems! R m ρ hgh ( SC Why? Consder Netwon s 2 nd law agan (horzontal trajectory and reormulate n terms o the mass rato ma ( t = We get: δ 1 2 ρ hgh ( S ( t C ( SC D ( t 2 D 1/ 2 sd ( t m D ( t 2 ( t a( t = 3 / 2 sd 1 2 R m ( S ( t C ( SC D ( t D sd

10 δ ( SC D ( t 2 1/ 2 sd ( t a( t = 1 2 R m ( S ( t C ( SC D ( t D sd Ths means that the hgher the mass rato R m, the more deceleraton; hgh-r m typcally means R m > 0.1 Note that hgh-mass rato also means slow-descendng R m = 2 g ( SC D 1/ 2 sd ( hgh 2 descent So R m ~ 1.7 means descent ~ 25 t/sec or US. Army T-10, or R m ~ 6.0 means descent ~ 25 t/sec or US Army G-11 (one canopy In what ollows we consder descent < 30 t/sec as a necessary constrant or the estmate to work

11 Whch parachute-payload system satsy the condton I F ~ ½? One can get I F ~ ½ the mass rato s large enough, agan R m > 0.1. Why? The drag ntegral measures the area under the (normalzed drag vs. tme curve Drag ntegral ~ ½ Drag ntegral ~ 1

12 Ds-reeng case (long ater reeed nlaton Drag ntegral ~ ¼. Note: drag ntegral 0 as t ds t ree W/F ds << 1/2

13 When s I F ~ ½? Reerence [1] showed the rst expermental data suggestng ths value whenever R m > 0.1 (or so, on - Slder-reeed paraols - Permanently reeed or un-reeed hemsphercal canopes More expermental data analyzed here show the same trend to be workng also on -rngslottypes - slder-reeed rounds - deep cones - unreeed paraols (not always though; depends on lt Reerence [1] also shows that I F < 1/3 when R m < 0.1, at least or dsk-gap-band types and hemsphercal types Excepton: t seems that I F < 1/3 at both small- and large-r m wth chutes that ds-ree long ater reeed nlaton

14 aldaton Based on a large database (next slde Data must nclude load cell data (to calculate I F and Must also nclude vdeo coverage o each test, n order to obtan the nlaton tme t t (va rame-countng 2m Fmax 1 ( t t descent 2 = 1/I F va standard descent ormula vdeo Load cell F max ( t 2m t 1 descent + g ( t t, smulated or measured

15 Database: 14 canopy-reeng combos & 67 drops total Hemsphercal and sphercal types US Army T-10C (Table 4-1 USAF C-9, unreeed & permanently skrt-reeed (Table 4-2 ½-scale C-9, unreeed & permanently skrt-reeed (Table 4-3 Butler HX-600 (hemsphercal canopy wth slder reeng (Table 4-4 Crucorm, wth and wthout slder-reeng (Table 4-5 US Army 26t rngslot extracton parachute (Table 4-6 Deep-concal types Truncated Cone Decelerator (Table 4-7 Paraol types Unreeed paraols (Table 4-8 BLM Trlobe (Table 4-9 PD Sabre230 (Table 4-10 PDSabre120 (Table 4-11 PD Sabre150 (Table 4-12 PD Stletto150 (Table repeat jumps/drops

16 Results Hard to plot ths data on a sngle graph Data shown n tabular orm

17 US. Army T-10C Table 4-1. US Army T-10C (hemsphercal canopy Canopy specs: 35.0t nomnal dameter. Constructon detals can be ound n reerence [8]. Deployment method: statc lne. Good matches Act ID Drop# Act speed Deploy alttude (eet; MSL W R m Mass rato Estmated (true arspeed at lnestretch; t/sec descent (t/sec / descent I F (Drag ntegral; calculated rom data t -t (sec Traject. type durng nlaton horz Horzontal trajectory Measured vert ertcal trajectory UH-1 Helo Test KIAS ballstc UH-1 Helo Test KIAS ballstc UH-1 Helo Test KIAS ballstc

18 Table 4-4. Butler HX-600 slder-reeed hemsphercal canopy Canopy specs: 27.64t nomnal dameter (low porosty abrc. More constructon detals can be ound n [16]. Slder specs: span = 67n (Sombrero slder - rm dameter. Deployment method: statc lne. Good matches Act ID Drop# Act speed (KIAS Deploy alttude (eet; MSL W R m Mass rato Estmated (true arspeed at lnestretch; t/sec descent (t/sec (C D ~ 0.75 / descent I F (Drag ntegral; calculated rom data t -t (sec Traject. type durng nlaton horz Horzontal trajectory Measured vert ertcal trajectory Beech Kng Ar NW KTSI ballstc Beech Kng Ar NW KTSI ballstc Cessna Super Caravan YPG KTSI ballstc Cessna Super Caravan YPG KTSI ballstc

19 Slder-reeed paraol - note the drop-to-drop varatons n nlaton tme BUT not n I F Table 4-9. US Bureau o Land Management Trlobe slder-reeed, seven cell paraol Wng specs: span = 25.7t & chord = Slder specs: span = 2.08t by 1.83t. Deployment: ater reeall by parachutst (at least 10secs o reeall Reerence [13]. NA = not applcable Good matches Deploy alttude (eet; MSL W R m Mass rato Measured (true arspeed at lne-stretch; t/sec descent (t/sec / descent I F (Drag ntegral; calculated rom data t - t (sec Trajectory type durng nlaton horz Horzontal trajectory Measured vert ertcal trajectory vertcal NA vertcal NA vertcal NA vertcal NA vertcal NA vertcal NA vertcal NA vertcal NA

20 USAF C-9 unreeed (yelds hemsphercal shape Table 4-2. Full-scale USAF C-9 (unreeed and hemsphercally-shaped canopy; Canopy specs: 28.0t nomnal dameter. See reerence [8] or detals. Deployment method: statc lne, rom Cessna Caravan. Good matches Drop# Reeng type Act speed (KIAS Deploy alttude (eet; MSL W R m Mass rato Estmated (true arspeed at lnestretch; t/sec descent (t/sec / descent I F (Drag ntegral; calculated rom data t -t (sec Traj. type durng nl. horz Horzontal trajectory Measured vert ertcal trajectory YPG001 No reeng (80-20 Mea West ballst c YPG004 No reeng ballst c YPG005 No reeng ballst c YPG008 No reeng ballst c

21 USAF C-9 reeed (tght reeng - yelds sphercal shape Table 4-2. Full-scale USAF C-9 (unreeed and hemsphercally-shaped canopy; and permanently reeed and sphercally-shaped canopy Canopy specs: 28.0t nomnal dameter. See reerence [8] or detals. Deployment method: statc lne, rom Cessna Caravan. Good matches YPG011 24%reeng ballst c YPG014 24%reeng ballst c YPG020 24%reeng ballst c YPG024 24%reeng ballst c

22 Hal-scale C-9 unreeed (yelds hemsphercal shape Good to ar matches Table 4-3a. 1/2-scale C-9 canopy (hemsphercal canopy; unreeed Canopy specs: 14.0t nomnal dameter. Constructon detals can be ound n reerence [17] Deployment method: ery wde payload contaner; statc lne; ext rom sde door o Cessna 402 (NW12 and Cessna 411 (all others. Drop# Act speed (KIAS Deploy alttude (eet; MSL W R m Mass rato Estmated (true arspeed at lnestretch; t/sec descent (t/sec / descent I F (Drag ntegral; calculated rom data t -t (sec Traj. type durng nl. horz Horzontal trajectory Measured vert ertcal trajectory NW Mostly horz NW Mostly horz NW Mostly horz NW Mostly horz

23 Hal-scale C-9 reeed (tght reeng - yelds sphercal shape Table 4-3b. 1/2-scale C-9 canopy (permanently skrt-reeed; sphercally-shaped canopy Canopy specs: 14.0t nomnal dameter (unreeed [17]. Deployment method: statc lne, rom Cessna Caravan. NO match! Out o valdty range Drop# Reeng type YPG006 16%reeng YPG009 16%reeng Act speed (KIAS Deploy alttude (eet; MSL W (lbs R m Mass rato Estmated (true arspeed at lne-stretch; t/sec descent (t/sec / descent I F (Drag ntegral; calculated rom data t -t (sec Traj. type dur ng nl. Mos tly hor z. Mos tly hor z. horz Horzontal trajectory Measured Calculate d vert ertcal trajectory YPG012 24%reeng Mos tly hor z YPG015 24%reeng Mos tly hor z YPG018 24%reeng Mos tly hor z

24 Crucorm parachute (3:1 Aspect rato Table 4-5. Crucorm parachutes Full-scale specs: bult rom two 24.84t by- 9.25t rectangular panels (zero-porosty abrc; Hal-scale specs: bult rom two 12.24t-by-4.37t rectangular panels (zero-porosty abrc; Both versons were made o 200 dener nylon abrc (permeablty: 30-45cm. Deployment method: statc lne. Matches good only b/c o error cancellaton (next slde; out o valdty range! Chute ID Act ID Drop# Act speed Deploy alttude W R m Mass rato Estmated (true arspeed at lne-stretch; t/sec descent (t/sec / descent I F (Drag ntegral; calculated rom data t -t (sec Traject. Type durng nlaton Calculate d horz Horzontal trajectory Measur ed vert ertcal trajectory Full scale C-130 Test (no slder 130KIAS 18,000t MSL 1, Ballstc (mostly horz. 11,960 See sect ,416 14,910 Full scale C-130 Test (wth slder 130KIAS 10,000t MSL 1, Ballstc (mostly horz. 5,544 7, Hal scale UH-1 Helo Test (no slder 80 KIAS 1000t MSL ballstc

25 Error cancellaton n R m < 0.2 regme 2 = 1/I F here; 2 -actor should be replaced by a hgher value, snce n realty I F s smaller 2m Fmax 1 ( t t descent >> descent n ths regme; number nsde brackets should be smaller than 1 descent /

26 Concludng remarks Method works well or almost all parachute/reeng desgns Excepton: Parachutes that dsree long ater reeed nlaton has ended All valdaton cases came rom cargo drops or skydvng, where ~ t/sec What about the cases where >>200 t/sec? (ejecton seat, etc. Would the method work R m > 0.1? Yes, t t measures nlaton +post-nlaton deceleraton What about slow deployments? (BASE jumpng Here ~ descent. In prncple the method should work but must be measured very accurately

27 Smple Wndows-based program or manned parachutng Easy to use Free download at descent calculated wth C D0 = 0.7 (rounds or 1.0 (paraol F max ( t 2m t 1 descent + g ( t t

28 Questons?