safe decent rate

Jan 16, 2005 3 Replies
T

Hi again,



I recently used an online decent rate calculator on

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My rocket weighs around 11 lbs fully loaded, after the propellant has been burned, and I will be using two 36" chutes to bring it down. However the chutes are reefed and so they are supposed to have the same amount of drag as a



44" chute. These two parachutes together I asume would have around the same drag as an 88" chute. The calculator said that under these conditions, my decent rate would be about 17 fps. The note on the bottom of the page says that a safe decent rate is 15 fps or slower, however I have seen that the average decent rate is 20 fps.

Is this correct, or is 17fps still a safe landing? I know this is more of an opinion than fact, but I would still like to here what others have learned from exsperience.



Thanks a lot,



Tom Sak



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G

My heavyest(sp) rocket is only 6 lbs, but I think the problem is the same, and very relative. How hard is the recovery area? And how prone to damage is your rocket? 17fps is a nice, slow, descent but I wouldn't want my Amraam4 landing on my van any faster than 1 foot/sec! LOL

da rmr plumber Gary R Goldenbaum NAR #73669 L1 Northwest Florida remove 'nichspam' to reply

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D
17 fps is plenty slow enough for anything but a very hard landing area.

But, I think your math is wrong. two 44" chutes is not equivalent to an 88" chute. An 88" chute would have 4 times the surface area of a single 44" chute, not twice, so I believe your estimate is off by a factor of two.

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T

The lauch feild is a sod/ onion/corn field so the dirt is usually very soft and very loose...except for the road which has a lot of gravel. The rocket hasnt been flown yet but it is build very strong. My only concern was the off chance that a motor tube could get cracked, or whats more likely that the .062 G-10 fins could snap if the landing was too hard. I think it should be fine after hearing what you guys had to say.

Thanks for your opinion,

Tom Sak

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