Weight vs. Airspeed

[J-Rock 0]

I guess this question would be geared towards people that have experience drop testing canopy's or have done alot of testing/manufacturing in their days. My question is: which will more than likely cause a canopy to fail (structural failure) weight or airspeed? Or is it an even trade-off? Could you make a canopy fail if you toss it out with 4 times its designed working load at 80kts or maybe the same could be said by underloading a canopy and chucking it out at 280kts? Or am I totally looking at this the wrong way or need a Phd in mathmatics to really know the answer? Im not worried about flight performance or soft landings after deployment of course just mearly interested in whether weight or airspeed decide the final judgement. Thanks in advance if anyone can comment or give a confirmed answer.

Im gonna need a bigger hammer....

[VTmotoMike08 0]

Just my thoughts, but we know that

Force = (Mass) x (Acceleration)

So it seems to me that they both play an equal part because there is no coefficients on either mass or acceleration.

But then again, acceleration on earth is a constant 32 ft/ sec^2 so I guess we need another equation... ya forget that I said anything.

[SethInMI 145]

I remember this threadhttp://www.dropzone.com/cgi-bin/forum/gforum.cgi?do=post_view_flat;post=2326601;page=1;sb=post_latest_reply;so=ASC;mh=50;

That thread started with a jumper overloading a reserve and got into a big technical discussion about weight and deployment speeds and forces involved.

One poster (Sparky or Jerry B) posted a chart of some test data, some of which is:
NAB Data
5000lb test
Weight(lb) Speed(mph)
660 150
500 175
400 200
325 225
275 250
225 275
200 300
175 325
160 350
150 375
3000lb test
750 100
525 125
375 150
300 175
235 200
200 225

The tests say that deploying 660lbs at 150mph produces the same peak force as deploying 150 lbs at 350mph (5000lbs). So I would say velocity is a bigger factor.

I created and posted in that thread several spreadsheets that modeled a parachute deployment that agreed pretty well with test data, so if you are curious beyond just a yes or no answer track it down.

It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

[VTmotoMike08 0]

O ya, that reminds me of the other equation!

F= (M*V^2)/2

Force = (0.5)*Mass*Velocity^2

Which basically says that force is proportional to the mass of the object and the square of its velocity. If you care about calculus, that equations is derived by differentiating the first equation (F= M*A) that I posted. Good to dust off the memory from some old physics!

Therefore velocity is more (twice as) important as mass in determining opening forces on a parachute (I think).

[SethInMI 145]

Ke = 0.5 m v^2 is what you are thinking of. That is the kinetic energy equation, not the force equation.

Another important equation for this is the drag equation, Fd = Cv^2, which means that the drag force is proportional to the the square of the velocity * C, where C is determined from drag coefficent and area.

Peak force calculation is complicated because the parachute deploys over a period of time with slowly increasing area. The kinetic energy of motion is dissipated over this interval.

It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

[J-Rock 0]

Thanks Seth, thats exactly what I was looking for I just couldnt find anything in the forums that listed this type of information. To me it looks almost like a trade off in some ways, at least its that way to get the same amount of shock load on the canopy. Thanks for the help

Im gonna need a bigger hammer....

[VTmotoMike08 0]

Thanks for the correction, I knew I was a little rusty.

[riggerrob 558]

Since energy increases with the SQUARE of the velocity, velocity is the greater factor in determining opening shock.

For scary pictures of openings, go visit Bulter Parachutes' website.

CAUTION if you are using this discussion to justify operating outside of placarded limits ... make sure your medical insurance is paid up.

[J-Rock 0]

CAUTION if you are using this discussion to justify operating outside of placarded limits ... make sure your medical insurance is paid up.

[riggerrob 558]

Didnt know if manufacturers really ever pushed their products to the point of catastrophic failure like Manley Blutler did while testing his HX Rounds and weather or not airspeed had more to do with the failure then the suspended weight.

......................................................................

Whether you test parachute canopies to destruction depends upon whether you are
A: French or
B: have a large budget.

The old French EQ system required drop tests similar to American TSO, then test samples were pulled to destruction.

B: Have a large budget. In North America, only the military have large budgets.
In Manley Butler's case, he was trying to discredit some of the "warmed over, wimpy skydiver shit" made some of his competitors.
For example: most skydivers discarded their Featherlite, K20, Phantom, SAC, Tri-Conical, etc. round reserves during the acid mesh scare of the late 1980s, but thousands of pilots still wrare Phantoms.
Most sizes of Phantoms are only TSOed in the low speed category of TSO C23B .... making them silly to wear in fast warbirds.

[erdnarob 1]

It is a tricky question. For sure mass and speed are important factors but there are many other factors like the type of parachute, fabric used, the way it was packed, the type of pilot chute...etc.
One could design a parachute that even with a lot of suspended weight and speed at the opening could have a soft deployment force. Why? Because all depends on the deceleration. The deceleration depends on the "stopping" distance. If the deceleration is low which means a long vertical distance opening the force can be kept at the total weight + a force from say 5% to 200% of the weight (therefore between 1.05 and 3 G).

The people who could really give you a scientific answer are Jean Potvin and Gary Peek who did research on low speed aerodynamics at the university of St Louis MO. Both are very experienced skydivers. John LeBlanc from PD is certainly another fellow able to give you the proper explanation.

Learn from others mistakes, you will never live long enough to make them all.