with regard to deployment. Determining compatibility is  more than simply determining the volume compatibility of  a canopy to a container size. Other factors, that need to be  considered are the deployment type, technical standard order  (TSO) certification, and placard limitations. When we ask the question, “How do you determine  compatibility between approved parachute components,”  the answer is, “Rig functionality must not be compromised.”  Some say if a reserve canopy is too bulky, the reserve  deployment bag is not easily extracted. If you can get the  bagged canopy in the container, it should take no more than  18 pounds of pull force to extract it.  This area is one where many riggers have some confusion.  According to AC 105-2, Sport Parachute Jumping, “the  strength of the harness must always be equal to or greater  than the maximum force generated by the canopy during  certification tests.” In the case where the harness is  certificated under TSO-C23b and the canopy under TSO- C23c, the maximum generated force of the canopy must  not exceed the certificated category force of the harness  and container (i.e., Low Speed Category (3,000 pounds)  and Standard Category (5,000 pounds)). In this instance, no  additional marking on the container is necessary.  In the case where the canopy is certificated under TSO-C23b  and the harness under TSO-C23c, the strength of the harness  must be equal to or greater than the certificated category  force of the canopy.  For the current TSO-C23d, the peak force measured during  the strength drops must be placarded on the outside of the  harness. In this case, the strength of the canopy must not  exceed that of the harness.  The rigger, when making the determination as to whether a  particular canopy and rig combination is compatible, must  consider all of the above areas. If there is any doubt, the rigger  should contact the rig manufacturer for guidance. TSO-C23b was originally written back in the 1940s before  the advent of square parachutes. It had two categories under  which a parachute system could be certified. The “Low  Speed” category was limited to use in aircraft under 150 miles  per hour (MPH) and certified to 3,000 pounds. This category  required large block letters decrying “limited to use in aircraft  under 150 MPH.” It also had a “Standard Category.” This  category required no warning labels and had neither weight  nor speed limitations and was tested and certified to 5,000  The X$_{1}$  factor is the key because it is based on pounds per  square foot loading multiplied by 1. If you try different  weight values and reiterate the formula, you can see it only  C$_{d}$ = .8 S$_{o}$ = 200 square feet Q = 33 PSF @ 117MPH  together = .8 × 200 × 33 = 5,280 pounds. This number is  then ameliorated by the X$_{1 }$ decreasing load factor and the C$_{x}$  shock load factor. If the C$_{x}$ is 1 (and we will assume this for  this example), then it has no effect on the outcome.  If we group the C$_{d}$  × S$_{o}$  × Q and calculate them, at first we  get a big number ie:  • C$_{x}$ = shock load coefficient which is derived from  testing and includes such things as slider size, brake  setting, angle of nose cut, etc. For this exercise we  will use a value of 1 as this number ranges from .5 to  1.5 or so. Without a slider it can go as high as 10.  •  X$_{1}$—decreasing load factor •  Q—dynamic pressure in pounds per/square foot  (½  ρʋ $^{2}$)  • S$_{o}$ —square footage of canopy  • C$_{d}$ —drag coefficient of canopy  •  Force—total opening forces  NOTE: There are 2 methods for deriving this factor.  The Pflanze method and a lookup of the chart included  in the reference manual. The chart is the simplest for  personnel parachutes and effectively results in being  one tenth of the pound per square foot loading.  Therefore: Force = C$_{d }$ × S$_{o}$  × Q × X$_{1}$  × C$_{x}$ The math model for opening forces is described in the  “Recovery Systems Design Guide” by Theodore Knacke.  The definitions and formula is as follows:  This seems counter intuitive until you think about it. Speed  is the critical factor that hurts us and our equipment when we  have the occasional hard opening. But because speed is often  derived from mass or weight, we associate the hard opening  with primarily weight. Let us look at the calculations.  Weight has only a minimum effect on parachute opening  forces. To be exact, if you were to increase a given weight  by 50 percent, you would only see a 5 percent increase in  opening force; likewise if you double that given weight, you  would only see a 10 percent increase in opening force.  pounds. It is important to note that neither category had a  weight limitation.  Reserve Bag Extraction Force TSO Certification and Placard Limitations Harness Strength 4-14