Recovery System Design - Revision history

Parachute at 17:38, 13 June 2024

2024-06-13T17:38:44Z

Parachute: /* 7.1 REQUIREMENTS */

2024-06-13T14:59:53Z

7.1 REQUIREMENTS

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Parachute at 14:17, 13 June 2024

2024-06-13T14:17:41Z

← Older revision		Revision as of 14:17, 13 June 2024
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	= DESIGN OF A PARACHUTE RECOVERY AND LANDING SYSTEM =		= DESIGN OF A PARACHUTE RECOVERY AND LANDING SYSTEM =
	This chapter deals with the design of a parachute recovery and landing attenuation system for a military reconnaissance drone. The prime emphasis in the design of this system is on undamaged recovery of the drone from the total flight performance envelope during the development and test phase, on undamaged recovery after a completed mission during military operations, and on multiple use of the recovery system. An engineering team conducts performance and system analyses and chooses what recovery concept to use, what types of parachutes to select for high-speed deceleration and for final recovery, and what impact-attenuation system is best for the particular application. This chapter covers the selection process for concepts and components. Different engineers may make different selections based on experiences with particular types of parachutes or deployment concepts; experience is always a viable reason for selecting a particular approach. However, using the selection criteria shown in [[Figure 2-6]]. the designer must put reliability of operation, undamaged recovery, reusability of the landing system, and minimum weight and volume at the top of the list of requirements.		This chapter deals with the design of a parachute recovery and landing attenuation system for a military reconnaissance drone. The prime emphasis in the design of this system is on undamaged recovery of the drone from the total flight performance envelope during the development and test phase, on undamaged recovery after a completed mission during military operations, and on multiple use of the recovery system. An engineering team conducts performance and system analyses and chooses what recovery concept to use, what types of parachutes to select for high-speed deceleration and for final recovery, and what impact-attenuation system is best for the particular application. This chapter covers the selection process for concepts and components. Different engineers may make different selections based on experiences with particular types of parachutes or deployment concepts; experience is always a viable reason for selecting a particular approach. However, using the selection criteria shown in [[Figure 2-6]]. the designer must put reliability of operation, undamaged recovery, reusability of the landing system, and minimum weight and volume at the top of the list of requirements. There are several mistakes that have been noticed and corrected from the original Knake Guide they have been marked with this "*".

	== 7.1 REQUIREMENTS ==		== 7.1 REQUIREMENTS ==
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	=== 7.2.2 Impact Attenuator System ===		=== 7.2.2 Impact Attenuator System ===
	The design of impact attenuator systems is discussed in section 6.8 of this manual. [[Figure 7-1]] shows the reconnaissance drone and the air-bag attenuator systems that consist of two deflatable, two-compartment wing-bag bags (A); a single-compartment, deflatable nose bag (B); and a nondeflatable nose-buffer bag (C). The wing bags, the primary energy absorbers, need the already calculated 24-inch effective-deceleration stroke. For design reasons, 33 inches must be added to the bag height, 19 inches for the distance from the wing underside to the underside of the jet airducts, 10 inches for ground clearance, and 4 inches for bag bottom curvature. These additions result in a total bag height of 57 inches. To ensure landing stability, an air bag height-to-diameter ratio of 1.25 is selected for the two wing bags, resulting in a bag diameter of 48 inches. The cross-hatched lower part of the two wing bags (see [[Figure 7-1]]) deflates at impact, but the upper part stays inflated and keeps the drone off the ground. The nose bag, B, helps to absorb the impact and deflates, and the nose of the drone comes to rest on the nondeflatable buffer bag, C. All air bags are inflated from 3000 psi nitrogen containers using aspirators for a 50/50 nitrogen air mixture. The air bags are ~~prepressurized~~ to 2 psi for full bag inflation prior to landing. Multiple blowout valves consisting of staggered blowout rubber disks around the circumference of the air bags control the bag deflation to stay within the 9-g deceleration limit.		The design of impact attenuator systems is discussed in section 6.8 of this manual. [[Figure 7-1]] shows the reconnaissance drone and the air-bag attenuator systems that consist of two deflatable, two-compartment wing-bag bags (A); a single-compartment, deflatable nose bag (B); and a nondeflatable nose-buffer bag (C). The wing bags, the primary energy absorbers, need the already calculated 24-inch effective-deceleration stroke. For design reasons, 33 inches must be added to the bag height, 19 inches for the distance from the wing underside to the underside of the jet airducts, 10 inches for ground clearance, and 4 inches for bag bottom curvature. These additions result in a total bag height of 57 inches. To ensure landing stability, an air bag height-to-diameter ratio of 1.25 is selected for the two wing bags, resulting in a bag diameter of 48 inches. The cross-hatched lower part of the two wing bags (see [[Figure 7-1]]) deflates at impact, but the upper part stays inflated and keeps the drone off the ground. The nose bag, B, helps to absorb the impact and deflates, and the nose of the drone comes to rest on the nondeflatable buffer bag, C. All air bags are inflated from 3000 psi nitrogen containers using aspirators for a 50/50 nitrogen air mixture. The air bags are pre-pressurized to 2 psi for full bag inflation prior to landing. Multiple blowout valves consisting of staggered blowout rubber disks around the circumference of the air bags control the bag deflation to stay within the 9-g deceleration limit.

	The weight of the impact-attenuation system-air bags, nitrogen containers, plumbing, and A/C containers-is estimated from section 6.7 to be 2.2% of the total drone weight, or 105.6 pounds. The air bags should be stored in containers that can be easily removed from the drone for repacking. Air bags must be deployed after the main parachutes are fully open to prevent air-bag damage caused by high dynamic pressure. Air-bag deployment begins with simultaneous pyroejecting of the removable air-bag-container covers and opening of the nitrogen-container valves. The wing bags, the primary nose bag, and the nose-buffer bag inflate. At ground contact, the bags compress, increasing the pressure inside the bags. At a preselected pressure level, the blowout valves (rubber disks, metal disks, or rubber-type sleeves) open and limit the maximum drone deceleration to the preselected level.		The weight of the impact-attenuation system-air bags, nitrogen containers, plumbing, and A/C containers-is estimated from section 6.7 to be 2.2% of the total drone weight, or 105.6 pounds. The air bags should be stored in containers that can be easily removed from the drone for repacking. Air bags must be deployed after the main parachutes are fully open to prevent air-bag damage caused by high dynamic pressure. Air-bag deployment begins with simultaneous pyroejecting of the removable air-bag-container covers and opening of the nitrogen-container valves. The wing bags, the primary nose bag, and the nose-buffer bag inflate. At ground contact, the bags compress, increasing the pressure inside the bags. At a preselected pressure level, the blowout valves (rubber disks, metal disks, or rubber-type sleeves) open and limit the maximum drone deceleration to the preselected level.
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	True velocity at maximum deployment altitude in feet per second is		True velocity at maximum deployment altitude in feet per second is

	<math>v_o = v_{7000\ ft} = 200\ \cdot 1.69\frac{1}{\sqrt{\sigma}}= 200\cdot1.69\cdot1.~~1455~~ = ~~386~~.7 ft/s</math>		<math>v_o = v_{7000\ ft} = 200\ \cdot 1.69\frac{1}{\sqrt{\sigma}}= 200\cdot1.69\cdot1.11106 = 374.9 ft/s^*</math>

	==== 7.3.7.3 Force Calculation Methods ====		==== 7.3.7.3 Force Calculation Methods ====

Parachute at 12:47, 13 June 2024

2024-06-13T12:47:02Z

Parachute at 01:14, 13 June 2024

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 ==== 7.4.9.5 General Comments on Gore Design and Porosity Selection ====
-The canopy gore design-total canopy porosity, XT; spacing of vertical ribbon; size of
+The canopy gore design-total canopy porosity, XT; spacing of vertical ribbon; size of vent; and pocket-band arrangement-are the primary design features that determine the aerodynamic performance of the parachute. The most important characteristics of parachute performance are stability, smooth opening, drag, and opening-force coefficients.
-vent; and pocket-band arrangement-are the primary design features that determine the
+Determining porosity under a no-load condition is rather unrealistic, because most of the important aerodynamic characteristics occur under high-load conditions (opening shock) or medium-load conditions (descent). However, since the beginning of parachute development, aerodynamic parachute characteristics obtained in wind-tunnel and free-flight tests have been related to fixed design dimensions such as diameter and porosity.
-aerodynamic performance of the parachute. The most important characteristics of parachute
+Determining the effective porosity caused by the changing load during the opening process and by the venetian-blind effect of the ribbon grid design is practically impossible. Furthermore, the change in effective porosity is similar on all ribbon parachutes because of the similarities of the ribbon grid designs, load factors, and related changes in material elongation that cause deformation of the ribbon grids and the parachute canopies.
 ==== 7.4.9.6 Computer Programs for Determining Gore Design and Porosity Calculation ====
-Both gore design and porosity calculations can be determined by computer programs.
+Both gore design and porosity calculations can be determined by computer programs. Organizations involved in frequent design of ribbon parachutes should establish these programs.
 === 7.4.10 Ribbon Parachute Canopies with Continuous Horizontal Ribbons ===
-Ribbon parachute canopies are frequently designed and manufactured with continuous
+Ribbon parachute canopies are frequently designed and manufactured with continuous horizontal ribbons either in single or two-section canopies. The continuous ribbon design decreases weight and volume, increases the strength of the horizontal ribbon-radial connection, and simplifies manufacturing. Continuous horizontal ribbons change the porosity characteristics of the canopy.
-characteristics of the canopy.
+[[Figure 7-19]] shows how the individual horizontal ribbons orient themselves in a canopy manufactured from individual triangular gores. In the inflated canopy, the horizontal ribbons in the canopy crown area orient parallel to the canopy design. However, in the skirt area, the canopy design line is almost parallel to the airflow. This design, usually called the "venetian blind effect," causes the longer leading edge of each horizontal ribbon to bulge out and position the ribbon with a positive angle of attack to the airflow. The result is an increase in effective porosity under high dynamic pressure conditions. The venetian blind effect is discussed in section 6.2.4, and the influence of canopy loading on the change in effective porosity is shown in [[Figure 6-24]].
-Figure 7-19 shows how the individual horizontal ribbons orient themselves in a canopy
+Designing canopies with continuous horizontal ribbons changes the venetian blind effect. Returning to [[Figure 7.19]], it is obvious that continuous horizontal ribbons in the canopy skirt area do not bulge out since leading and trailing ribbon edges have the same length and do not position themselves with an angle of attack to the airflow. However, in the crown area of the canopy where each gore forms a triangle, the equal length of the leading and trailing ribbon edges now gives each ribbon a negative angle of attack thereby increasing the effective porosity in the canopy crown area. The effect is minimized by large number of gores arid by the use of a center vertical ribbon, or a miniradial, as Sandia engineers call it.
-manufactured from individual triangular gores. In the inflated canopy, the horizontal ribbons
+Discussion with Sandia and industry personnel indicates that no measurable difference has been found in the aerodynamic characteristics of ribbon parachute canopies designed with individual gores or with continuous horizontal ribbons so long as the canopies contain a large number of gores and a center vertical ribbon. However, a slight delay in initial inflation seems to occur on small parachutes with a small number of gores. Closer spacing of vertical ribbons in the canopy crown area should counteract this delay. Another method of counteracting the delay is by gathering the trailing edges of horizontal ribbons with several rows of stitching and using a lower porosity in the crown area.
 === 7.4.11 Use of Kevlar Fabrics ===
-Many modern ribbon parachutes use Kevlar suspension lines, risers, and canopy skirt,
+Many modern ribbon parachutes use Kevlar suspension lines, risers, and canopy skirt, lateral, and vent tapes, which results in a decrease in weight and volume. Section 6.5.5 discusses all aspects of working with Kevlar in the design of parachute assemblies. This includes physical characteristics of Kevlar fibers and fabrics, available Kevlar fabrics, and experience in designing in Kevlar. Section 6.6.5 should be studied before designing in Kevlar.

Parachute at 20:43, 12 June 2024

2024-06-12T20:43:37Z

← Older revision		Revision as of 20:43, 12 June 2024
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	==== 7.4.9.4 Gore-Porosity Recheck ====		==== 7.4.9.4 Gore-Porosity Recheck ====
	Geometric gore porosity, <math>\lambda_g =\lambda_{~~g{_a}~~}+[\frac{S_v^*}{S_o}[\frac{100-\lambda_{ga}}{100}]]-[\frac{S_{RR}}{S_o}\lambda_{ga}]</math>		Geometric gore porosity, <math>\lambda_g =\lambda_{ga}+[\frac{S_v^*}{S_o}[\frac{100-\lambda_{ga}}{100}]]-[\frac{S_{RR}}{S_o}\lambda_{ga}]</math>

	Grid porosity, Xg = 28.39% (See Table 7-9.)		Grid porosity, <math>\lambda_{ga} = 2.39% </math> (See [[Table 7-9]].)

	Open vent area, Sv = 1.272 - 0.59* _ 0.683 ~~ft2~~		Open vent area, <math>S_v=1.272-0.59^*=0.683\ ft^2</math>

	Canopy area, ~~So -~~ 155.50 ~~ft2~~		Canopy area, <math>S_o=155.50\ ft^2</math>

	Area of radial ribbons, ~~SRR~~ = (~~rgXBXNsL~~) = (83.7 in.X2.0 in.~~X24~~) = 4017.62 in.		Area of radial ribbons, <math>S_{RR}=(r_g)(B)(N_{SL})=(83.7\ in.)(2.0\ in.)(24) = 4017.6^2\ in.=27.90\ ft^2</math>

	~~27.90 ft2~~

	~~S2 F~~ 0.683 100 - 28.~~3911~~ =~~F27~~.~~9023~~		<math>\lambda_g=28.39+[\frac{0.683}{155.50}[\frac{100-28.39}{100}]]=[\frac{27.90}{155.50}28.39]</math>

	S- 28.39+ [~~155~~.50 [ ~~100~~ .50 28.~~3L5~~		<math>=28.39+[(0.0044)(0.7161)]-[(0.179)(28.39)]</math>

	- 28.39 + [(0.~~0044X0.7161)]~~ - ~~[(0~~.~~179X28~~.~~39)J~~		<math>=28.39+0.0032-5.08=23.31%</math>

	~~- 28.39 + 0.0032-5.08 - 23.31%~~

	Area covered by vent bands.		Area covered by vent bands.

	~~7-52~~

	~~NWC TP 6575~~

	Material porosity,		Material porosity,

	~~F• F~~[ ~~Xs1~~.0 . ~~- SRR~~+~~SVR~~+		<math>\lambda_m=\frac{\lambda_m^*}{27.4}[1.0-[\frac{\lambda_g}{100.0}+\frac{S_V+S_{RR}+S_{VR}+S_{ST}}{S_o}]]</math>

	~~Ribbon Specification Porosity, )Xm*:~~

	~~The upper half of the gore uses 500-pound ribbon; X = 0. The lower half, encompassing~~

	~~75% of the gore area, uses 300-pound ribbon; X. = 150 ft3/ft 2/min.~~

	~~The conversion from material porosity to geometric porosity at 1/2-inch H20 pressure is~~

	~~27.4 ft3~~

	/~~ft 2 min = 1% k. Therefore,~~

	~~= 150(0.75) = 4.1%~~

	~~27.4~~		Ribbon Specification Porosity, <math>\lambda m^*</math>:

	SV = 0.~~683 ft2~~		The upper half of the gore uses 500-pound ribbon; <math>\lambda</math> = 0. The lower half, encompassing 75% of the gore area, uses 300-pound ribbon; <math>\lambda = 150\ ft^3/ft^2/min. </math>

	~~SRR~~ = 27.~~90 ft2~~		The conversion from material porosity to geometric porosity at 1/2-inch <math>H_2O</math> pressure is <math>27.4\ ft^3/ft^2\ min=1%\ \lambda</math>. Therefore,

	~~Area of vertical ribbon covering horizontal ribbon, SVR:~~		<math>\lambda_{m_{grid}}=\frac{150(0.75)}{27.4}=4.1%</math>

	~~SVR~~= ~~NG-• A [hg - [(NHR - 1]]= (24)(5)(~~0.~~625)[82.6((27. 1)1.1)]~~		<math>S_V=0.683\ ft^2</math>

	= 38.~~7[82.60- ((26X1.1))] = (38.7)(54.0) = 2089.80 in2~~		<math>S_{RR}=27.90\ ft^2 </math>

	~~= 14.51 ft2~~		Area of vertical ribbon covering horizontal ribbon, <math>S_{VR}</math>:

	~~Area of skirt band, SSB:~~		<math>S_{VR}=N_G\frac{N_{VR}}{2}A[h_g-[(N_{HR}-1)6]]=(24)(\frac{5}{2})(0.625)[82.6((27-1)1.1)]</math>

	~~SSB - Nges~~ - (~~24X20~~.~~69 in~~.) ~~= 4%~~.~~56 in2~~ = 3.~~45 ft2~~		<math>=38.7[82.60-((26)(1.1))]=(38.7)(54.0)=2089.80\ in^2</math>

	km = ~~(15OX0.75) 1.- (23.31 + 0.683 +27.90 +~~ 14.51 ~~+ 3.45 f 27.4 1 100 155.50 J~~		<math>=14.51\ ft^2</math>

	~~= 4.106 1.0 - 0.2331 + 46543 4.106[l.0 - 0.5324]~~

	~~= (4.106X0.4676) = 1.92%~~		Area of skirt band, <math>S_{SB}</math>:

	~~Tbtal canopy porosity, XT~~ = ~~Xg + Xm~~ = 23.~~31 + 1~~.92 = 25.~~23%~~. ~~This porosity falls into the~~		<math>S_{SB}=N_ge_S=(24)(20.69\ in.)=496.56\ in^2=3.45\ ft^2</math>

	~~specified range of 25 to 26% as established in Table 7~~-6. ~~Porosity should be cross-checked with~~		<math>\lambda_m=\frac{(150)(0.75)}{27.4}[1.0-(\frac{23.31}{100}+\frac{0.683+27.90+14.51+3.45}{155.50})]</math>

	~~the method outlined in Reference 2~~.2.		<math>=4.106[1.0-(0.2331+\frac{46.543}{155.50})]=4.106[1.0-0.5324]</math>

	~~7-53~~		<math>=(4.106)(0.4676)=1.92%</math>

	~~NWC TP 6575~~		Total canopy porosity, <math>\lambda_T=\lambda_g+\lambda_m=23.31+1.92=25.23%</math>. This porosity falls into the specified range of 25 to 26% as established in [[Table 7-6]]. Porosity should be cross-checked with the method outlined in Reference 2.2.

	==== 7.4.9.5 General Comments on Gore Design and Porosity Selection ====		==== 7.4.9.5 General Comments on Gore Design and Porosity Selection ====

Parachute at 17:34, 12 June 2024

2024-06-12T17:34:36Z

← Older revision		Revision as of 17:34, 12 June 2024
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	==== 7.4.9.4 Gore-Porosity Recheck ====		==== 7.4.9.4 Gore-Porosity Recheck ====
	Geometric gore porosity, ~~Xk-- Xa~~ + [s [ 100 - J -~~-SRRX"~~		Geometric gore porosity, <math>\lambda_g =\lambda_{g{_a}}+[\frac{S_v^*}{S_o}[\frac{100-\lambda_{ga}}{100}]]-[\frac{S_{RR}}{S_o}\lambda_{ga}]</math>

	Grid porosity, Xg = 28.39% (See Table 7-9.)		Grid porosity, Xg = 28.39% (See Table 7-9.)

Parachute at 17:31, 12 June 2024

2024-06-12T17:31:22Z

← Older revision		Revision as of 17:31, 12 June 2024
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	<math>\Delta\lambda=2\ to\ 3%</math>		<math>\Delta\lambda=2\ to\ 3%</math>

	The porosity of a ribbon grid with variations in the distance of the horizontal ribbons is now calculated. The total porosity is estimated, and the most likable horizontal ribbon distance is selected for the first gore-porosity check (Table 7-9). The widths of the vertical ribbon, A, and the horizontal ribbon, B, are fixed values. The ratio of vertical ribbon spacing, to horizontal ribbon width, a/B, was previously selected to 1.25, which is equal to 2.5 inches. A horizontal ribbon distance, b, of 1.1 inches is selected as first approach based on data in [[Table 7-9]].		The porosity of a ribbon grid with variations in the distance of the horizontal ribbons is now calculated. The total porosity is estimated, and the most likable horizontal ribbon distance is selected for the first gore-porosity check ([[Table 7-9]]). The widths of the vertical ribbon, A, and the horizontal ribbon, B, are fixed values. The ratio of vertical ribbon spacing, to horizontal ribbon width, a/B, was previously selected to 1.25, which is equal to 2.5 inches. A horizontal ribbon distance, b, of 1.1 inches is selected as first approach based on data in [[Table 7-9]].
	[[File:TABLE 7-9. Gird Porosity as Function of Horizontal Ribbon Distance, b..jpg\|center\|thumb\|479x479px\|TABLE 7-9. Gird Porosity as Function of Horizontal Ribbon Distance, b.]]		[[File:TABLE 7-9. Gird Porosity as Function of Horizontal Ribbon Distance, b..jpg\|center\|thumb\|479x479px\|TABLE 7-9. Gird Porosity as Function of Horizontal Ribbon Distance, b.]]

	==== 7.4.9.3 Recheck of Gore Dimensions with Vertical Ribbon Spacing, b, Equal to 1.1 Inches ====		==== 7.4.9.3 Recheck of Gore Dimensions with Vertical Ribbon Spacing, b, Equal to 1.1 Inches ====
	With b equal to 1.1 inches, a gore recheck is required to determine the resultant number		With b equal to 1.1 inches, a gore recheck is required to determine the resultant number of horizontal ribbons and the gore height. The number of horizontal ribbons, <math>N_{HR}</math>, that can be spaced in the gore grid height, <math>h_c</math>, is

	~~of horizontal ribbons and the gore height~~. ~~The number of horizontal ribbons, NHR, that can be~~		<math>N_{HR}=\frac{h_g-B}{(B+b)}=\frac{80.28-2.0}{(2.0+1.1)}=25.25 </math> (see [[Figure 7-20]])

	~~spaced~~ in the gore ~~grid height, ti, is~~		To avoid a decrease in parachute diameter, 26 horizontal ribbons are selected, changing the gore dimensions from those shown in [[Figure 7-21]] to those shown in [[Figure 7-22]].
			[[File:FIGURE 7-22. Final Gore Dimensions..jpg\|center\|thumb\|516x516px\|FIGURE 7-22. Final Gore Dimensions.]]
			<math>h_g=26(2.0+1.1)+2.0=[(26)(3.1)]+2=80.6+2.0</math>

	~~NHR - h,-B 80~~.~~28-2~~.~~0 . 25.25 (see Figure 7-20) (B + b) (2.0 + 1.1)~~		<math>h_g=82.6\ in.</math>

	~~7-50~~		<math>e_S=20.11\frac{82.6}{80.28}=20.69\ in.</math>

	~~NWC TP 6575~~		<math>h_S=h_g+h_V=82.6+7.59=90.19</math>

	~~'lb avoid a decrease~~ in ~~parachute diameter, 26 horizontal ribbons are selected, changing the~~		<math>S_g=\frac{e_sh_s}{2}=\frac{20.69(90.19)}{2}=933.02\ in^2=6.48\ ft^2 </math>

	~~gore dimensions from those shown in Figure 7-21 to those shown in Figure 7-22~~.		<math>S_o=24\ S_g=24(6.48\ ft^2)=155.5\ ft^2 </math>

	~~Final Parachute Dimensions: 7~~.~~59"~~		<math>D_o=1.1284\sqrt{S_o}=1.1284\sqrt{155.5}=14.07\ ft </math>

	~~Diameter. D, 14.07 ft~~

	~~Canopy surface area~~, ~~S, 15S.5 ft2~~		Gore radius, <math>r_S=h_S\frac{1}{cos\ \beta/2} </math>

	~~Gore area~~. S. 6.~~48 ft 2~~		<math>r_S=90.19 \frac{1}{0.99361}=90.77\ in. </math>

	~~Vent area, S" 1.23 ft2~~

	~~rs-90~~.~~77"~~		Radius of ribbon grid height, <math>r_g=h_g\frac{1}{cos\ \beta/2}=\frac{82.60}{0.99361}=83.13\ in. </math> The number of vertical ribbons, <math>N_{VR} </math>, is five, based on free spacing of 2.5 inches and horizontal ribbon spacing, b, of 1.1 inches.

	~~rg=8 3 .l 3 " 82.6"~~		This change in diameter from 13.67 to 14.07 feet increases the parachute drag area by 6%, decreases the final rate of descent by about 3%, leaves the reefed opening force unchanged, and slightly increases the disreef opening force.

	~~90.19"~~

	~~FIGURE 7.22. Final Gore Dimensions.~~

	~~hs=26(2.0 + 1.1) +2.0 = I(26X3.1)J +2 = 80.6 + 2.0~~

	~~hg= 82.6 in.~~

	~~es = 20.11 826 - 20.69 in,~~

	~~80.625~~

	~~hs=hg + hv 82.6 + 7.59 = 90.19~~

	~~eshs -20.69(90.19)~~

	~~= _ .2i2= 64 t~~

	~~S 1= *-j- 2-93 . 2i 2 = 64 ft~~

	~~7.51~~

	~~i I~~

	I8

	~~NWC TP 6575~~

	~~So 24 S9 24(6.48 ft2) - 155.5 ft2~~

	~~Do 1.1284 f/ - 1.1284/rf55 -5 14.07 ft~~

	1

	~~Gore radius, rs - hs I~~

	~~cos P/2~~

	~~rs - 90.19 1 - 90.77 in. 0.99361~~

	~~Radius of ribbon grid height, rg - hg - 83.13 in. The number of~~

	~~cos #/2 0.99361~~

	~~vertical ribbons, NVR, is five, based on free spacing of 2.5 inches and horizontal ribbon~~

	~~spacing, b, of 1.1 inches.~~

	This change in diameter from 13.67 to 14.07 feet increases the parachute drag area by 6%,

	decreases the final rate of descent by about 3%, leaves the reefed opening ~~foce~~ unchanged,

	and slightly increases the disreef opening force.

	==== 7.4.9.4 Gore-Porosity Recheck ====		==== 7.4.9.4 Gore-Porosity Recheck ====

Parachute at 15:38, 12 June 2024

2024-06-12T15:38:31Z

← Older revision		Revision as of 15:38, 12 June 2024
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	<math>n</math> = allowable impact deceleration, ratio <math>n=\frac{a}{g}</math>		<math>n</math> = allowable impact deceleration, ratio <math>n=\frac{a}{g}</math>

	[[Figure 6-68]] of Chapter 6 shows the range of various impact attenuation systems as a function of rate of descent and allowable ground impact deceleration. The information indicates that air bags may be the most practical concept for this application. A cursory analysis indicates that a rate of descent of 25 ft/s at 5000 feet: altitude will result in a close to optimum weight ratio of the combined parachute air bag system (see [[Figure 6-83]]). Properly designed air bags will have an effectiveness of 65% as shown in the stroke-pressure diagram in Figure 6-78 and allow ground contact or final velocity of close to 0 ft/s.		[[Figure 6-68]] of Chapter 6 shows the range of various impact attenuation systems as a function of rate of descent and allowable ground impact deceleration. The information indicates that air bags may be the most practical concept for this application. A cursory analysis indicates that a rate of descent of 25 ft/s<math>\lambda_{ga}=\frac{porosity\ of\ grid\ area}{total\ grid\ area}=\frac{ab}{(a+A)(b+B)}</math> at 5000 feet: altitude will result in a close to optimum weight ratio of the combined parachute air bag system (see [[Figure 6-83]]). Properly designed air bags will have an effectiveness of 65% as shown in the stroke-pressure diagram in [[Figure 6-78]] and allow ground contact or final velocity of close to 0 ft/s.

	With these assumptions, the required effective air bag deceleration stroke is obtained.		With these assumptions, the required effective air bag deceleration stroke is obtained.
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	<math>\lambda_m=canopy\ fabric\ porosity,%</math>		<math>\lambda_m=canopy\ fabric\ porosity,%</math>

	Figure 7-20 shows that the porosity of a perfect ribbon grid, Xs., can be calculated '3:		[[Figure 7-20]] shows that the porosity of a perfect ribbon grid, <math>\lambda_g</math>., can be calculated <math>t_D</math>:

	~~X98 -~~ porosity of ~~slot~~ area = ab		<math>\lambda_{g_{a}}=\frac{porosity\ of\ grid\ area}{total\ grid\ area}=\frac{ab}{(a+A)(b+B)}</math>

	~~total grid area (a + AXb + B)~~		From the evaluation of numerous porosity calculations, the following estimate can be made:

	~~From the evaluation of numerous porosity calculations, the following estimate can be~~		<math>\lambda_T=\lambda_{ga}-\Delta\lambda</math>

	~~made:~~

	\T= KX- A

	where		where

	A = 2 to 3%		<math>\Delta\lambda=2\ to\ 3%</math>

	~~The porosity of a ribbon grid with variations in the distance of the horizontal ribbons is~~

	~~now calculated. The total porosity is estimated, and the most likable horizontal ribbon~~

	~~distance is selected for the first gore-porosity check (Thble 7-9). The widths of the vertical~~

	~~ribbon, A, and the horizontal ribbon, B, are fixed values. The ratio of vertical ribbon spacing,~~

	~~to horizontal ribbon width, a~~/~~B, was previously selected to 1.25, which is equal to 2.5 inches. A~~

	~~horizontal ribbon distance, b, of 1.1 inches is selected as first approach based on data in~~

	~~Thble 7-9.~~

	~~TABLE 7-9. Grid Porosity as Function of Horizontal Ribbon Distance, b.~~

	~~Desired total porosity, XT % 25 to 26% (see section 7.10.8.2)~~

	~~Selected horizontal ribbon spacing, b inches 1.0 1.05 1.1 1.15~~

	~~Calculated grid porosity, Xg1 % 26.67 27.54 28.39 29.21~~

	~~&X -g,.25.5% (XT) % 1.17 204 289 3.71~~

	~~====~~ 7.4.9.~~3 Recheck~~ of ~~Gore Dimensions with Vertical~~ Ribbon ~~Spacing~~, ~~====~~		The porosity of a ribbon grid with variations in the distance of the horizontal ribbons is now calculated. The total porosity is estimated, and the most likable horizontal ribbon distance is selected for the first gore-porosity check (Table 7-9). The widths of the vertical ribbon, A, and the horizontal ribbon, B, are fixed values. The ratio of vertical ribbon spacing, to horizontal ribbon width, a/B, was previously selected to 1.25, which is equal to 2.5 inches. A horizontal ribbon distance, b, of 1.1 inches is selected as first approach based on data in [[Table 7-9]].
	b, ~~Equal to 1~~.~~1 Inches~~		[[File:TABLE 7-9. Gird Porosity as Function of Horizontal Ribbon Distance, b..jpg\|center\|thumb\|479x479px\|TABLE 7-9. Gird Porosity as Function of Horizontal Ribbon Distance, b.]]

			==== 7.4.9.3 Recheck of Gore Dimensions with Vertical Ribbon Spacing, b, Equal to 1.1 Inches ====
	With b equal to 1.1 inches, a gore recheck is required to determine the resultant number		With b equal to 1.1 inches, a gore recheck is required to determine the resultant number

Parachute at 14:51, 12 June 2024

2024-06-12T14:51:51Z

← Older revision		Revision as of 14:51, 12 June 2024
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	==== 7.4.9.2 Preliminary Gore-Porosity Check ====		==== 7.4.9.2 Preliminary Gore-Porosity Check ====
	~~TWo~~ methods of calculating gore porosity are in use. The older method, described in		Two methods of calculating gore porosity are in use. The older method, described in Reference 5.39, has been updated in this chapter. This method allows calculation of the porosity for preliminary design purposes when no final gore drawings are available. Reference 2.2 shows how to calculate canopy porosity if a drawing is available based on the ratio of open spaces to total canopy area. Both methods include an estimation of the ribbon (material) porosity.

	~~Reference 5.39, has been updated in this chapter. This method allows calculation of the~~

	porosity ~~for preliminary design purposes when no final gore drawings are available.~~		The total canopy porosity, <math>\lambda_T=\lambda_g+\lambda_m</math> where

	~~Reference 2.2 shows how to calculate canopy~~ porosity ~~if a drawing is available based on the~~		<math>\lambda_g= gore\ porosity,%</math>

	~~ratio of open spaces to total canopy area. Both methods include an estimation of the ribbon~~		<math>\lambda_m=canopy\ fabric\ porosity,%</math>

	~~(material) porosity.~~

	~~7.49~~

	~~NWC TP 6575~~

	~~The total canopy porosity, XT~~ = ~~Xg + km where~~

	~~X - gore porosity, %~~

	-m canopy fabric porosity, %

	Figure 7-20 shows that the porosity of a perfect ribbon grid, Xs., can be calculated '3:		Figure 7-20 shows that the porosity of a perfect ribbon grid, Xs., can be calculated '3:

← Older revision		Revision as of 17:38, 13 June 2024
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	=== 7.2.2 Impact Attenuator System ===		=== 7.2.2 Impact Attenuator System ===
	The design of impact attenuator systems is discussed in section 6.8 of this manual. [[Figure 7-1]] shows the reconnaissance drone and the air-bag attenuator systems that consist of two deflatable, two-compartment wing-bag bags (A); a single-compartment, deflatable nose bag (B); and a nondeflatable nose-buffer bag (C). The wing bags, the primary energy absorbers, need the already calculated 24-inch effective-deceleration stroke. For design reasons, 33 inches must be added to the bag height, 19 inches for the distance from the wing underside to the underside of the jet airducts, 10 inches for ground clearance, and 4 inches for bag bottom curvature. These additions result in a total bag height of 57 inches. To ensure landing stability, an air bag height-to-diameter ratio of 1.25 is selected for the two wing bags, resulting in a bag diameter of 48 inches. The cross-hatched lower part of the two wing bags (see [[Figure 7-1]]) deflates at impact, but the upper part stays inflated and keeps the drone off the ground. The nose bag, B, helps to absorb the impact and deflates, and the nose of the drone comes to rest on the nondeflatable buffer bag, C. All air bags are inflated from 3000 psi nitrogen containers using aspirators for a 50/50 nitrogen air mixture. The air bags are ~~prepressurized~~ to 2 psi for full bag inflation prior to landing. Multiple blowout valves consisting of staggered blowout rubber disks around the circumference of the air bags control the bag deflation to stay within the 9-g deceleration limit.		The design of impact attenuator systems is discussed in section 6.8 of this manual. [[Figure 7-1]] shows the reconnaissance drone and the air-bag attenuator systems that consist of two deflatable, two-compartment wing-bag bags (A); a single-compartment, deflatable nose bag (B); and a nondeflatable nose-buffer bag (C). The wing bags, the primary energy absorbers, need the already calculated 24-inch effective-deceleration stroke. For design reasons, 33 inches must be added to the bag height, 19 inches for the distance from the wing underside to the underside of the jet airducts, 10 inches for ground clearance, and 4 inches for bag bottom curvature. These additions result in a total bag height of 57 inches. To ensure landing stability, an air bag height-to-diameter ratio of 1.25 is selected for the two wing bags, resulting in a bag diameter of 48 inches. The cross-hatched lower part of the two wing bags (see [[Figure 7-1]]) deflates at impact, but the upper part stays inflated and keeps the drone off the ground. The nose bag, B, helps to absorb the impact and deflates, and the nose of the drone comes to rest on the nondeflatable buffer bag, C. All air bags are inflated from 3000 psi nitrogen containers using aspirators for a 50/50 nitrogen air mixture. The air bags are pre-pressurized to 2 psi for full bag inflation prior to landing. Multiple blowout valves consisting of staggered blowout rubber disks around the circumference of the air bags control the bag deflation to stay within the 9-g deceleration limit.

	The weight of the impact-attenuation system-air bags, nitrogen containers, plumbing, and A/C containers-is estimated from section 6.7 to be 2.2% of the total drone weight, or 105.6 pounds. The air bags should be stored in containers that can be easily removed from the drone for repacking. Air bags must be deployed after the main parachutes are fully open to prevent air-bag damage caused by high dynamic pressure. Air-bag deployment begins with simultaneous pyroejecting of the removable air-bag-container covers and opening of the nitrogen-container valves. The wing bags, the primary nose bag, and the nose-buffer bag inflate. At ground contact, the bags compress, increasing the pressure inside the bags. At a preselected pressure level, the blowout valves (rubber disks, metal disks, or rubber-type sleeves) open and limit the maximum drone deceleration to the preselected level.		The weight of the impact-attenuation system-air bags, nitrogen containers, plumbing, and A/C containers-is estimated from section 6.7 to be 2.2% of the total drone weight, or 105.6 pounds. The air bags should be stored in containers that can be easily removed from the drone for repacking. Air bags must be deployed after the main parachutes are fully open to prevent air-bag damage caused by high dynamic pressure. Air-bag deployment begins with simultaneous pyroejecting of the removable air-bag-container covers and opening of the nitrogen-container valves. The wing bags, the primary nose bag, and the nose-buffer bag inflate. At ground contact, the bags compress, increasing the pressure inside the bags. At a preselected pressure level, the blowout valves (rubber disks, metal disks, or rubber-type sleeves) open and limit the maximum drone deceleration to the preselected level.
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	<math>\sqrt{\sigma}		<math>\sqrt{\sigma}
	</math> at 5000 ft is 0.9283 (see [[Table 3-3]]); therefore,		</math> at 5000 ft. is 0.9283 (see [[Table 3-3]]); therefore,

	<math>V_e{_o} = 25ft/s\ (0.9283) = 23.2ft/s</math>		<math>V_e{_o} = 25ft/s\ (0.9283) = 23.2ft/s</math>
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	Drone weight ............................................. <math>W_D</math> = 4800 lb		Drone weight ............................................. <math>W_D</math> = 4800 lb

	Maximum deployment speed ~~.......~~....................... <math>v_o</math> = 200 KEAS		Maximum deployment speed ....................... <math>v_o</math> = 200 KEAS

	Minimum deployment speed ........................ <math>v_o\ minimum</math> = 150 KEAS		Minimum deployment speed ........................ <math>v_o\ minimum</math> = 150 KEAS
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	Maximum allowable total parachute force		Maximum allowable total parachute force

	(two main parachutes) ................................~~...~~ <math>F_T</math> = 16,000 lb		(two main parachutes) ................................ <math>F_T</math> = 16,000 lb

	Deployment altitude .................................. H = 2000 to 7000 ft		Deployment altitude .................................. H = 2000 to 7000 ft.

	==== 7.3.7.2 Velocity-Altitude Profile ====		==== 7.3.7.2 Velocity-Altitude Profile ====
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	<math>q_2=1.1\frac{W}{(C_DS)_R}</math>([[Figure 7-8]])		<math>q_2=1.1\frac{W}{(C_DS)_R}</math>([[Figure 7-8]])

	<math>q_2 = 1.1\frac{4800\ lb}{2(82.37)+(C_DS)_{drone}}=\frac{1.1 \cdot 4800\ lb}{164.74+55}=\frac{1.1\cdot 4800}{219.74}=24.03lb/ft^2^*</math>, and		<math>q_2 = 1.1\frac{4800\ lb}{2(82.37)+(C_DS)_{drone}}=\frac{1.1 \cdot 4800\ lb}{164.74+55}=\frac{1.1\cdot 4800}{219.74}=24.03lb/ft^{2*}</math>, and

	<math>v_2=\sqrt{q \cdot y}\frac{1}{\sqrt{\sigma}}=\sqrt{24.03(840)}\cdot 1.1106= 157.8 ft/s^*</math> (see [[Figure 5-112]])		<math>v_2=\sqrt{q \cdot y}\frac{1}{\sqrt{\sigma}}=\sqrt{24.03(840)}\cdot 1.1106= 157.8 ft/s^*</math> (see [[Figure 5-112]])

← Older revision		Revision as of 12:47, 13 June 2024
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	<math>C_D{_o}=0.9\ to\ 0.92</math>		<math>C_D{_o}=0.9\ to\ 0.92</math>

	In a cluster of two parachutes, a drag loss of 2% is experienced (see Figure 5-110). Longer suspension lines can somewhat compensate for the loss. Choosing a suspension line/canopy ratio of Le/Do = 1.15 (see Figure 5-20) results in a drag gain of 1.5%. A drag coefficient <math>C_D{_o}</math> = 0.9 is selected for this application.If the drag coefficient is 0.9, the parachute surface area, <math>S_o</math>, is		In a cluster of two parachutes, a drag loss of 2% is experienced (see Figure 5-110). Longer suspension lines can somewhat compensate for the loss. Choosing a suspension line/canopy ratio of Le/Do = 1.15 (see [[Figure 5-20]]) results in a drag gain of 1.5%. A drag coefficient <math>C_D{_o}</math> = 0.9 is selected for this application. If the drag coefficient is 0.9, the parachute surface area, <math>S_o</math>, is

	<math>S_o=\frac{(C_DS)_p}{C_D{_o}}=\frac{3744\ ft}{0.9}=4160\ ft^2</math>		<math>S_o=\frac{(C_DS)_p}{C_D{_o}}=\frac{3744\ ft}{0.9}=4160\ ft^2</math>
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	2. The Pflanz method is quite accurate for all conditions including high altitude but neglects the effect of gravity. Parachutes opened in vertical descent will have a 1-g (one weight unit) higher force than calculated. It is necessary to calculate the canopy filling times for the various reefed stages (see section 5.4.3) and to determine the drag-area-versus-time profile for the specific parachute (see section 5.4.4). This method permits the investigation of variations in filling times and drag-area-versus-time profiles.		2. The Pflanz method is quite accurate for all conditions including high altitude but neglects the effect of gravity. Parachutes opened in vertical descent will have a 1-g (one weight unit) higher force than calculated. It is necessary to calculate the canopy filling times for the various reefed stages (see section 5.4.3) and to determine the drag-area-versus-time profile for the specific parachute (see section 5.4.4). This method permits the investigation of variations in filling times and drag-area-versus-time profiles.

	3. The force-trajectory-time computer method includes the effects of altitude, gravity, and changing trajectory angle. This method requires determination of a drag-area-versus-time profile for the entire parachute opening sequence (see Figure 5-52). Computers permit multiple runs with changes in times, drag-area-versus-time profiles, starting velocities, and altitudes.		3. The force-trajectory-time computer method includes the effects of altitude, gravity, and changing trajectory angle. This method requires determination of a drag-area-versus-time profile for the entire parachute opening sequence (see [[Figure 5-52]]). Computers permit multiple runs with changes in times, drag-area-versus-time profiles, starting velocities, and altitudes.

	==== 7.3.7.4 Reefed Opening Forces ====		==== 7.3.7.4 Reefed Opening Forces ====
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	<math> q_0 = dynamic\ pressure\ at\ line\ stretch\ = 135.14\ lb/ft^2\ </math>(see section 7.3.7.2)		<math> q_0 = dynamic\ pressure\ at\ line\ stretch\ = 135.14\ lb/ft^2\ </math>(see section 7.3.7.2)

	<math> C_x= opening-force\ coefficient\ at\ infinite\ mass\ </math>(see Table 5-2)		<math> C_x= opening-force\ coefficient\ at\ infinite\ mass\ </math>(see [[Table 5-2]])

	<math> X_1 = opening-force\ reduction\ factor</math> (see Figure 5-48)		<math> X_1 = opening-force\ reduction\ factor</math> (see [[Figure 5-48]])

	The allowable drag area of a single, reefed main parachute is		The allowable drag area of a single, reefed main parachute is
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	<math>X_1=0.77		<math>X_1=0.77
	</math> (See Figure 5-51)		</math> (See [[Figure 5-51]])

	<math>F_R=(82.37 ft^2)(135.14lb/ft^2)(1.1)(0.77) = 9428 lb		<math>F_R=(82.37 ft^2)(135.14lb/ft^2)(1.1)(0.77) = 9428 lb
	</math>		</math>

	It is interesting to investigate the effects of changing the canopy filling time ± 25% and changing the slope of the drag area profile on the parachute opening force. For the change of the drag area slope, a profile factor of n = 1.0 instead of n = ½ (see Figure 5-5-1) is selected. The resultant change in opening force is shown in Table 7.1.		It is interesting to investigate the effects of changing the canopy filling time ± 25% and changing the slope of the drag area profile on the parachute opening force. For the change of the drag area slope, a profile factor of n = 1.0 instead of n = ½ (see [[Figure 5-1]]) is selected. The resultant change in opening force is shown in [[Table 7.1]].
	[[File:TABLE 7-1. Reefed Opening Force as a Function of Filling Time and Drag-Area Profile..jpg\|center\|thumb\|439x439px\|TABLE 7-1. Reefed Opening Force as a Function of Filling Time and Drag-Area Profile.]]		[[File:TABLE 7-1. Reefed Opening Force as a Function of Filling Time and Drag-Area Profile..jpg\|center\|thumb\|439x439px\|TABLE 7-1. Reefed Opening Force as a Function of Filling Time and Drag-Area Profile.]]

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	==== 7.3.8.1 Parachute Design Data ====		==== 7.3.8.1 Parachute Design Data ====
	A total parachute assembly is shown in Figure 7-10.		A total parachute assembly is shown in [[Figure 7-10]].
	[[File:FIGURE 7-10. Main-Parachute Assembly..jpg\|center\|thumb\|602x602px\|FIGURE 7-10. Main-Parachute Assembly.]]		[[File:FIGURE 7-10. Main-Parachute Assembly..jpg\|center\|thumb\|602x602px\|FIGURE 7-10. Main-Parachute Assembly.]]
	Parachute type: Conical full extended skirt		Parachute type: Conical full extended skirt
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	==== 7.3.8.3 Main-Parachute Safety and Design Factors ====		==== 7.3.8.3 Main-Parachute Safety and Design Factors ====
	Section 6.4 is used as a guide for selecting the safety, load, loss, and design factors in [[Table 7.4]].		Section 6.4 is used as a guide for selecting the safety, load, loss, and design factors in [[Table 7-4]].
	[[File:TABLE 7-4. Determination of Design Factors for the Main Parachute Assembly (Section 6.4.2)..jpg\|center\|thumb\|577x577px\|TABLE 7-4. Determination of Design Factors for the Main Parachute Assembly (Section 6.4.2).]]		[[File:TABLE 7-4. Determination of Design Factors for the Main Parachute Assembly (Section 6.4.2)..jpg\|center\|thumb\|577x577px\|TABLE 7-4. Determination of Design Factors for the Main Parachute Assembly (Section 6.4.2).]]

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	<math>F_o</math> = maximum parachute force = 9255 pounds		<math>F_o</math> = maximum parachute force = 9255 pounds

	<math>D_p</math> = inflated parachute diameter - DOC (see Figure 5-78)		<math>D_p</math> = inflated parachute diameter - DOC (see [[Figure 5-78]])

	<math>DS</math> = design factor, 1.85 (see Table 7.4)		<math>DS</math> = design factor, 1.85 (see [[Table 7-4]])

	<math>t_c = \frac{9255}{(\pi)(72.7)(0.7)(12)}1.85=\frac{9255}{1918}1.85=8.9\ lb/in.</math>		<math>t_c = \frac{9255}{(\pi)(72.7)(0.7)(12)}1.85=\frac{9255}{1918}1.85=8.9\ lb/in.</math>
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	The nylon tape selected is 1-inch-wide MIL-T-5038, Type IV, with 1000-pound strength. Proper connection of the skirt tape to the radial seam (tape) and the suspension line must be ensured.		The nylon tape selected is 1-inch-wide MIL-T-5038, Type IV, with 1000-pound strength. Proper connection of the skirt tape to the radial seam (tape) and the suspension line must be ensured.

	2. '''Vent Tape'''. From the geometric design of the parachute vent (Figure 7-11). the force in the vent tape, <math>F_VT</math>, is calculated		2. '''Vent Tape'''. From the geometric design of the parachute vent ([[Figure 7-11]]). the force in the vent tape, <math>F_VT</math>, is calculated

	<math>F_{VT} = \frac{F_{RT}}{N_ {SL}\ 2\ sin[\frac{360}{N_{SL}}]}DF</math>		<math>F_{VT} = \frac{F_{RT}}{N_ {SL}\ 2\ sin[\frac{360}{N_{SL}}]}DF</math>
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	A 25-degree conical ribbon parachute is selected for this application. The conical ribbon parachute meets all requirements and has a higher subsonic drag coefficient than the equally suited hemisflo parachute. The subsonic drag coefficient determined the parachute size and its associated weight and volume. Numerous conical ribbon parachutes have been used successfully at this speed and diameter range.		A 25-degree conical ribbon parachute is selected for this application. The conical ribbon parachute meets all requirements and has a higher subsonic drag coefficient than the equally suited hemisflo parachute. The subsonic drag coefficient determined the parachute size and its associated weight and volume. Numerous conical ribbon parachutes have been used successfully at this speed and diameter range.

	Based on section 5.8, Figure 5-93, we obtain the following drag coefficients versus Mach number data:		Based on section 5.8, [[Figure 5-93]], we obtain the following drag coefficients versus Mach number data:
	{\| class="wikitable"		{\| class="wikitable"
	\|+		\|+