Close Rocksim Values for ARR 15' Surplus Chute?

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Scott Evil

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Anybody have some close values I can plug into RS9 to get semi-realistic decent rates?

It's a "15 foot" silk surplus chute with 16 shroud lines.

I have it punched in as 12 feet in diameter with 18 foot lines with the lightest nylon as a material and a 4" spill hole but I seriously doubt if I'm all that close realistically.

I could chase it around the yard with a leaf blower and a tape measure or throw it off one of the stacks at work but neither would help my reputation much with the locals.

Thanks in advance for any info.

BTW, while I'm at it. There's a small wooden disk that separately captures all 16 of the paracords. Is this there just for line organization or is it meant for reefing purposes?
 
Measure the canopy and the lines, and enter those numbers. Then, toss the parachute on a scale and override the weight.

That will get you Close Enough.

Regarding that wooden disk, I wouldn't use it for reefing the parachute -- it's likely meant to work as a slider, slowing the parachute's opening, and in the process, reducing opening shock. But wood has this nasty habit of getting nicked, which can make it rough, and abrade the lines.

It's possible the parachute is designed as a single-use device, in which case the concern about damage from multiple uses wouldn't be an issue in its original application.

-Kevin
 
Thanks Kevin, yah it must be a slider. It has a thin (meant to be cut) thread attached to the end (bridal? help me here, I forget the terminology, tear drop/loopy shaped metal framis?)

I'll try the leaf blower + tape measure and do my own R&D if it's not too wet out tonight. If not, I do have access in the wee hours of the night to some pretty psychotic CFM while no one's lookin'.:dark:

I think the chute itself is reliable (the military thinks so), I just need to find some type of base line numerical RS9 values to predict various (.rkt+Spent Motor) desent rates.

Desent weight could vary with a spent 5 grain 75mm to a spent 98mm 6GXL.

LZ safety is a primary concern. Drifting an importantant secondary concern.
 
Get a load cell with a display calibrated in pounds and a video camera, and build a mast on the roof of your car or truck, high enough so the chute won't drag on the road when deployed. Attach the load cell to your mast and to the chute.

Find a straight stretch of road in an industrial park on a weekend, put the load cell readout next to the speedometer, and start the camera.

Accelerate to 20 mph and deploy the chute. Vary your speed from 10 mph to 40 mph while recording the speed and load from the load cell. Stop quickly from 15 mph so the chute won't drag. Repack the chute. Reverse direction and repeat to eliminate any wind based bias.

Go home. Review the tape and put the speed and load values in a spread sheet and perform a velocity squared fit to the data. If you measured the barometeric pressure and air temperature when you did the measurements, you can readily calculate the true CD of chute versus velocity.

Bob
 
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