How many Gs are you pulling?

[Royd 0]

I know that there are innumerable factors, but on a canopy loaded 1-1 how many Gs are you pulling on a hard toggle spiral. I'm guessing about 3 gs.

Any mathematicians out there want to verify this?

[Sockpuppet 0]

at the moment about 1, maybe 1.1 when I polish the snake later.

------
Two of the three voices in my head agree with you. It might actually be unanimous but voice three only speaks Welsh.

[cocheese 0]

I'm guessing about 3 Gs also. A 200lb. guy on a 150 sq.ft. canopy, one toggle burried. 3.5 Gs

4 Gs if you just ate a big lunch.

[Martini 0]

Depends a lot on canopy size, planform (shape), wingloading, line length, number of cells, and probably a bunch of other stuff. Me on a Manta 288, not much force. Fat Albert on a Xaos 49, enough to black out, enough in a spinning mal so Fat Al won't be able to lift his hands over his head. How many G's is that? I have no idea. Maybe Eugene can help with an answer, guesses don't mean anything.

Sometimes you eat the bear..............

[Chris-Ottawa 0]

Hey,

I've heard of ways to measure G force if you're interested. The device can be made very simply, but does require a few things. (plastic tube, fish scale, ball beaing, elastic etc)

This device would not be terribly accurate but it would give you a good idea.

See picture for details but essentially, hang the ball bearing in the tube from the elastic. Mark the point that it sits while not in motion, that is 1 G. now use the fish scale to pull the ball bearing the amount of double it's weight and mark that, keep doing that and you can make a a scale on the tube. Now to save the "highest" G you did, all you would need to do is make some sort of cardboard plate that fit the diameter of the tube and put some cotton balls behind it to hold it there. Then when you pull G's the ball bearing will push the plate and cotton down and it will stay there until you can check it.

You would need to attach this to your body and would probably have t reset it after opening shock. But if you're curious and can't afford anything that accurately measures G force, try it.


I'm sure you can find better pans on the net, I looked quick but didn't come up with much. I'd be curious to see, as I feel 3g's is a bit high. (Mind you a 200lb guy on a 150 could probably get spun up pretty good.

Chris

Let me know if anyone tries this and how it worked.

"When once you have tasted flight..."

[darkwing 5]

Easy to calculate if you know the following:

1. Time to complete one revolution
2. Radius of your spiral
3. And if you want to be really tricky you can measure the pendulum angle, because you need to add the acceleration vectors of the circular motion and earth's gravity as vectors, but that can be estimated easily.

In fact you could get good numbers fairly easily, especially with the help of a ground observer. The details of canopy, etc, are meaningless, although they can affect the result, they aren't part of the calculation.

Like almost everything else, it is just physics.

-- Jeff
My Skydiving History

[Martini 0]

It would be fun to build and test a G-meter even if it's sorta crude. BTW a 200 lb. guy with 25 lbs gear on a 150 is a wingload of 1.5, not high for an experienced flyer. There are folk on the forums who have jumped regularly at 3.0. That's your 200 lb. guy on a 75 square foot canopy. Oughta spin right quick.

Sometimes you eat the bear..............

[peek 21]

Quote

I know that there are innumerable factors, but on a canopy loaded 1-1 how many Gs are you pulling on a hard toggle spiral. I'm guessing about 3 gs. Any mathematicians out there want to verify this?

Pretty good guess.
http://www.pcprg.com/mnvr.htm
See graph of riser forces.

[JohnRich 4]

Quote

It would be fun to build and test a G-meter even if it's sorta crude.

I once bought an old aircraft G-force meter and mounted it on one of those triangular chest cushion altimeter mounts. Wear it out of the plane, crank yourself into a turn, and watch the meter. It had an arrow to show current force, positive or negative, as well as maximum readings reached in both directions. It was fun to play with for a while, and then I sold it. That would be easier and more accuraute then trying to build your own Rube Goldberg design from scratch.

[Martini 0]

Smoothing out the curves I approximate at max toggle turn 2.6 G's:
(suspended wt.=250)
LF=175
RF=200
LR=125
RR=150
total=650
650/250=2.6

I dont know what "hard right turn pulled down to toggle stow" means. Also I noticed that the RF riser force starts very high then diminishes wnile the other riser forces start up slowly then spike. A Stiletto at 1.7 seems like a useful model (although not representative of the high-end stuff available) but how hard was the turn? Turn duration seems short and was backed off due to turbulence. It is interesting that the guesses seem close to the measurements though. Thanks Gary.

Sometimes you eat the bear..............

[Martini 0]

I like that approach because it's simple and gives an indication of total G-force. Do you recall how high you were able to get the G's in a spin?

Sometimes you eat the bear..............

[kallend 2,146]

Quote

I know that there are innumerable factors, but on a canopy loaded 1-1 how many Gs are you pulling on a hard toggle spiral. I'm guessing about 3 gs.

Any mathematicians out there want to verify this?

I don't think you make 3G on a 1:1 canopy (basing this on having flown in planes with G meters)

...

The only sure way to survive a canopy collision is not to have one.

[peek 21]

Quote

I dont know what "hard right turn pulled down to toggle stow" means.

To the point where the brakes are set, about 10 inches or so for this canopy.

Quote

Also I noticed that the RF riser force starts very high then diminishes while the other riser forces start up slowly then spike.

I never analyzed that in particular, but there is a certain amount of variation from opening to opening or turn to turn.

Quote

A Stiletto at 1.7 seems like a useful model (although not representative of the high-end stuff available)

Well, a lot of people think that now that there are other designs, but the Stiletto turns very quickly. Mainly I just test what I have available. It's quite a bit of work, and no one has volunteered any money for test jumps to compare canopies.

Quote

... but how hard was the turn?

Not very hard, but for me, starting a turn causes the toggle pressure to become great enough that I can't hold it down anyway.

• Quote

[precision 0]

http://tinyurl.com/oqxmj

[Martini 0]

Thanks George, I'm watching that one and checking on others that may come up. I'll test my Xaos-21 98 but it doesn't turn nearly as fast as the 27. If I get measurements I'll post 'em for sure.

Sometimes you eat the bear..............

[Martini 0]

I thought that's what you meant about the hard right turn pulled down to toggle stow but wasn't sure.

Agreed that the Stiletto turns fast but Stilettos aren't generally jumped at high (over 2.0) wingloadings.

In talking with Eugene G. today we speculated on the comparison between fast turn rate on short lines vs. slower turn rate on long lines as it relates to G-force. My bet is on the short lines but measurements will tell. Naturally long lines are found on bigger canopies so it will be difficult to make a fair comparison.

Sometimes you eat the bear..............

[Chris-Ottawa 0]

Here's some other things I've found, may or may not be useful:

http://www.sportys.com/acb/showdetl.cfm?&did=19&product_id=6321

http://www.trossenrobotics.com/store/p/3231-PhidgetSensor-Accelerometer.aspx?feed=Froogle

This one is very simple and similar to what I suggested building earlier.
http://www.aircraftspruce.com/catalog/inpages/accelerometers2.php

Here's where I searched, there's tonnes to go through
http://froogle.google.com/froogle?q=accelerometer&btnG=Search&lmode=online&sa=N&start=0

Even better heres a cheap aircraft digital one, would just need to power it
http://www.aircraftspruce.com/catalog/inpages/gt50.php

I'm so curious about this because I fly alot and have pulled multiple g's in planes and once you get over 2 or 3 g's, it is incredibly difficult to lift your hands and feet. I did it once where we put the plane 90 degrees to the ground and yanked on the yoke, I put my hands on my legs and feet on the floor. I couldn't help but grunt as we were pulling, it was completely involuntary, and I couldn't lift my hands or feet from their positions. I moved my head from dead centre and it got pulled down so I couldn't lift it. Now this was in acessna and these planes are not rated very high for G forces. The pilot estimated 2-2.5 g's.

"When once you have tasted flight..."

[Eule 0]

Quote

http://www.sportys.com/acb/showdetl.cfm?&did=19&product_id=6321

This is probably the best one (out of the ones you posted) if you just want to buy a box and go jump. It might work a little better if you're jumping later in the afternoon or on a cloudy day; LED displays tend to wash out in bright sunlight.

Quote

http://www.trossenrobotics.com/store/p/3231-PhidgetSensor-Accelerometer.aspx?feed=Froogle

This one is tiny, but it's just the sensor - no display or memory. It appears to have a USB cable. Is that a laptop under your jumpsuit or are you just happy to see me? :)

Quote

Even better heres a cheap aircraft digital one, would just need to power it http://www.aircraftspruce.com/catalog/inpages/gt50.php

You might be able to get away with powering this one with a 9 V battery. The battery life might be kind of crap (they don't specify how much current it takes), but it should last for at least a jump or two. If 9 V isn't enough, then a 9 V in series with two AA or AAA batteries should make it happy.

I just got done working on a data acquisition system that used Crossbow accelerometers like this, connected to a PC with an A/D card for data logging. You could wire one of these to a $20 digital multimeter, but you'd have to interpret the numbers - it wouldn't read directly in G. These sensors run about $150-$200 each though.

Standard disclaimer: If you are going to add extra "stuff" to your rig, you need to make sure you are not adding snag points, making it hard to reach your handles, etc.

Eule

PLF does not stand for Please Land on Face.