AboutDan Liddy Expertise Nearly anything pertaining to safety , and technique. 1100 jumps experience and some extreme altitude jumps.
Experience I was an active skydiver for over 24 years, participated in competitive meets, and in relative work meets quite a lot. Also I could be found at a drop zone nearly any weekend. I have made numerous intentional water landings, several night freefalls, and have participated in numerous large formation attempts.
Question QUESTION: hi. i am a mathematics student and hoping to join the raf on completing my course. i have been given 3 weeks to construct a model using mathematics for a military style jump in which an expert skydiver must reach the ground as quickly as possible so that he is less vunerable during decent. to do this i need to know what is considered the maximum vertical velocity considered safe to land at to an expert?
ANSWER: I would think a maximum SAFE rate of decent under a parachute would be less than 20 feet per second vertical speed. 12-13 is comfortable under one of the old ParaCommander canopies.
However , vulnerability is hampered dramatically by the manouverability of the ram air type 'square" parachutes in modern day use. It would be quite difficult to hit such a jumper with a rifle at any distance.
I sense that your question might involve other factors as well , such as jump altitude and freefall speeds, if so , feel free to write again.
Incidentally, even though I'm a Yank, I AM a member of POPS UK or "Parachutists Over Phorty Society" and have met many friends from the "Mother Country" at meets over here.
Good luck with your project.
Dan Liddy
Sarasota Florida USA
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QUESTION: thanks... you have made my life a little easier. however your answer has also caused me a little difficulty... for the project i must know the terminal velocity of an open chute, and i assumed this to be 20 fps. what would you say the terminal velocity of an open chute was?
Answer That depends entirely on the design of the parachute. The obsolete military "round" parachutes came in several sizes, the 35' (diameter) parabolic used by US Army Paratroopers was probably the largest , and was used during the Normandy Invasion.
The US Army STILL uses the bloody things today to train Paratroopers. Partially because they are quite reliable, partially because they give the average jumper (of about 170 Lbs.) a vertical decent of about 15 FPS. And partially because it doesn't take a lot of training to send a trooper out the door. They're safe in the hands of nearly anyone. In my career, I made one jump on that canopy, and one was enough ! They're not very manouverable, and slow to react to steering commands.
Most of us here in the US started on a 28 foot survival chute, which was worn by Air Force and Army pilots. They produced a rate of decent of about 17 -18 FPS which was particularly UN-comfortable on landing, hence the switch as soon as one could afford it, to the Pioneer Paracommander so popular in the 70's. The PC gave comfortable landings at about 13 FPS, and a lot of manouverability that had been un-available in the past.
Now days, nearly everyone begins (with considerable instruction) on the ram air type of rectangular parachute you see on TV. They are very manouverable , even in high wind, and have a built in forward flying speed of up to 30 MMPH, this allows the jumper wide latitude in selecting a landing site and allows him to avoid nearly any ground hazard, (such as a lion tameing area or alligator farm !!) The rates of decent again vary from canopy to canopy, and also depend on the weight of the jumper , but landings are similar in force to stepping off a street kerbing (how am I doing with the Limey-esque spelling ??)
Finally, the term "terminal velocity" relates to free falling objects, and is the maximum speed to which a body accelerates after beginning to fall from a fixed altitude. The stable free falling skydiver usually gets up to about 120 to 125 MPH (190 to 200 KPH) Wheras the rate of decent of a parachute depends up on a number of factors including the jumper's weight, and what manouvers he's performing at the time. Take it from one who knows, if he's turning the parachute while landing , it's going to HURT! Been there too many times !
