lasse
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Posts posted by lasse
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QuoteBrakes does not affect the angle of attack, risers do.
Brakes do affect the angle of attack one way or another. If you fly at full brakes you will get a lower glide ratio yet you havn't changed the pitch of the wing (at least not matching the decrease of the glide ratio). You've got an higher angle of attack.
Pilotdave - as far as I have understood lift and drag (as described at http://www.av8n.com/how/htm/4forces.html) the lift at steady state certainly are different since the drag has a different vertical component (the sum of the vertical components of the forces must be zero). -
Doesn't sound safe, not safe at all. Pull, pull at right altitude, pull at right altitude with stability... Pulling your reserve two seconds after impact is not going to save you. A two out is not so bad seen from that perspective.
Heres my idea: grab your handles - changes the airflow around your body - if that doesn't help (nothing happens) I'd cut and pull. Yes the main could start deploying and it could entangle with the reserve, but the result most likely is going to be better than before (and nothing will get much worse anyway even in case of a total on your reserve) -
Quotepretty sure, well not that i know of anyway but pretty certain that they did not throw up their breakfast thinking it could act as a reserve parachute. so this makes me wonder what is safer?
a/ a regular 6 month repack/inspection or..
b/ eating your breakfast in the morning.
Since most fatalities are caused by other problems than reserve problems the fatality frequency is not a good measure. Furthermore not all double malfunctions are related to the reserve packjob and those who are need not be related to the repack period.
Actually eating breakfast could increase safety. Most accidents happens because the jumper does something wrong rather than there is something wrong with the equipment. -
QuoteI tried some stuff with the equations and the results are working out pretty interesting. My computation went as follows. First, I assume that air density and area do not change on a low altitude BASE jump, which is fairly reasonable. Then, I define my Cd' = A*r*Cd / 2 to be my new coefficient of drag, so that I don't have to worry about things that we depend linearly on that I assumed to be constant, to give a very simple equation for drag:
D = Cd' * v^2
Note that I will use V for terminal velocity and v for arbitrary velocity. At terminal we have
W = D => mg = Cd' * V^2 => Cd' = mg / V^2
Now, from Newton's Second Law:
ma = mg - Cd' * v^2 = mg - (mg / V^2) * v^2, so
dv/dt = g - (g v^2) / V^2 = g (1- v^2/V^2)
Integrating both sides with respect to t gives:
v = g (t - v^3/ (3*V^2))
Finally, solving for t gives:
t = v/g + v^3 / (3*V^2)
This equation gives me 23 seconds to reach 53.33 m/s with terminal velocity 53.33 m/s. This is not particularly surprising, since actually reaching the complete terminal velocity should take a long time. For v = 40 m/s with V = 53.33 m/s I get 11.6 seconds. Consider the protrack graph in this thread: http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=390101;search_string=protrack%20graph;#390101.
The equation I derived predicts this graph with more than reasonable accuracy. Yes, I know that the poster is asking about inaccuracies in the graph
Edited to add: 53.33 m/s = 120 mph. If you want to plug numbers into the above equation, you HAVE to do it in m/s because of the units of g. Here is a units converter.
Your solving of the differential equation is quite wrong which should be obvious if you consider the behaviour after reaching terminal velocity.
The correct solution to the equation is a hyperbolic tangent function. Fitting the constants to the assumtion that initial acceleration is 32 feet per second squared and terminal velocity is 176 feet per second we get v=176*tanh(t/5.5). By this formula you should never reach terminal velocity (and cosequently never exceed it), 90% should be reached after about 8 seconds, 95% after about 10 seconds, 97.5% after about 12 seconds. -
Quotethe traditional distinction between the two is that accident implies no one was at fault, whereas an incident does not, and most events are more like the second. For people in that frame of mind, there are very few traffic accidents. People should say "I hit a car," not "I got into an accident."
IMO it's semantics that have add little value to the conversation.
So you really intended to hit a car or what??? Accident hasn't have to mean that someone wasn't at fault it only mean that noone intended the outcome.
Regarding FAA's definition as applied to skydiving: would a cutaway be considered an incident? I think it's a bad idea that USPA doesn't require reporting accidents. -
QuoteIf you're going to do that it would have to be:
1. Slow down to the correct speed
2. Pull
etc.
Slowing down has to come before the rest if damage is to be avoided. But that seems like a bad thing to put second; I would amend it to "do not exceed the rated limits of your gear" and then keep the pull stuff in its original order.
Pulling has to be done if death is to be avoided. A head down pull has better survival chances than a nopull so pull has to be top priority. -
I don't think the difference is very significant. Most of the time the main function properly. And the few times it doesn't the reserve function properly and the student lands safely anyway.
About education. You will need to have special education whatever choice of reserve you have done. If you use square reserves you will have to know how to handle two-out. For round reserve you have to know how to maneuver it. In both cases you will have to know your PLF anyway - you can have a hard landing with squares too you know. As for obstacles you should probably how to land with a square too, the use of radio is no excuse to not teach the students how to avoid and land in obstacles - radio as all other equipment can fail and the use of radio may in fact make the student neglect the nessecity to learn to land safely on his own from first jump.
And no round reserves does not guarantee that the student lands in the right place given that he is dropped at the right place. A student may fly a long way under a low speed "malfunction" before he decides to cutaway. Again education is the key. -
QuoteThe way I understand it is that AFF instructors are not obliged to teach the use of an RSL...it makes sense to me.
Sure the student should know the purpose of all the equipment the're using, but if you concentrate on the importance of an RSL too much I think you could run the risk of letting the student rely on it rather than ignoring the fact it is there and completing any cutaway and reserve pull as if you're not wearing an RSL.
However there has been fatalities like jumper has total malfunction, jumper pulls cutaway, jumper lands at 120mph... It may be that the jumper believed the RSL would pull the reserve (as explained in a sloppy manner), consequently it may not be a bad idea to tell the student exactly how the RSL works (and especially how it doesn't). -
QuoteI'm just completing my AFF. Here's my under canopy stategy for anyone interested. Maybe comments will help me adjust and others who are thinking about the plane ride up.
1. Ok its open and looks ok.
2. Do my canopy check: Left turn, right turn, flare x2.
3. Turn to find DZ.
You should probably check for other traffic too. -
QuoteWe often see warnings when we purchase skydiving gear.
For example, SSK sends a WARNNG that “one out of every 20,000-75,000 jumps results in death” “according to USPA…studies” That’s quite a broad estimation.
It seem to be in the one per 100,000 jumps range.Quote
Further, they expect parachutes to malfunction “once in each 333 activations”.
Makes me start wondering if this isn't based on very old information. I'd expect about one per 1,000 range (actually about one reserve ride per 1,000 jumps).Quote
I wonder if there has been any work done to make some estimation about the failure rate of mains vs. the failure rate of reserves? It seems to me that reserves would have a greater mean time between failures as a result of more positive openings with a spring-loaded pilot chute.
If mains and reserves have an equal failure rate of .003, then the parallel failure rate would be:
(.003)(.003)= .000009. In other words we could expect a double malfunction 9 times every million jumps, or once every 111,111 jumps.
I imagine that the “one out of every 20,000-75,000 jumps results in death” statistic is skewed by suicides and fatalities under functional parachutes (low turns, among others).
Most fatalities is of other causes than double malfunctions. About one out of ten fatalities (that is 1 out of 1,000,000 jumps) is due to double malfunction. In addition there might be double malfunctions that doesn't result in fatalities. -
QuoteQuoteDoes the sim contain info on basic turns / rolls / loops etc that was being asked about? I haven't seen it in there or am i missing something??..
Yes, but if you want illustrations and more details, get the book mentioned above (The Skydiver's handbook by Dan Poynter).
Where exactly? I read the SIM and couldn't find that information. -
QuoteI've never been sky diving before, but i plan to do it when i backpack through europe next summer. What is a good country to do it in? How much will it cost altogether? (equipment rental included) Thanx
In sweden normal rates seem to be about 950euros for AFF (incl 10 jumps). Jump tickets are about 12euros per jump. -
QuoteYou can find that info in the SIM.
Really? Where? -
QuoteAre argument is that you ought not jump a reserve that is a very different size to you main.
But then that leads to the question what "very" different size is. The PD website doesn't give any information on that.QuoteIf you are in the position of having two canopies out (then firstly you should consider leaving the sport cos your a dumbass) having two very different sized canopies will make you life drastically more difficult. Check out the PD website for their two canopy out evaluations.
Therefore if your on a small main, the disadvantages of a small reserve may be outweighed by the disadvantages of a reserve thats much bigger than your main.
Then again, I would just say, get a big reserve damnit, its your last fucking chance, why dick with it. If your worried about 2 out dont fucking pull low.
Assuming that people never make mistakes is a mistake when it comes to reserve considerations. If you've got your reserve out it means that you (or perhaps someone else have made a mistake). If you get your cypress to fire you either forgot to pull at right altitude (a mistake) or got knocked unconsious (you're not supposed to collide in free fall - a mistake). -
That depend on what you mean by "hell of a lot safer". Most injuries and incidents are NOT related to the static line system.
Do you worry about how you'd react to a malfunction?
in Safety and Training
You can also deploy your reserve with your right arm and of course cut away your main with the left. I think there are examples of people that have done one armed emergency procedures for different reasons.
If you're able to you could try to loose your right shoe and pull with your foot. Also you could try pulling with your hands anyway (if you broke lower arm pulling the RSL might be an idea). I don't say you're in an easily solved situation, but I don't think that there are other options for you to deploy something.
Besides that is a situation where an AAD comes handy (I think that those who argue against the use of it will tell that if you break both your arms you sholdn't go skydiving...)