Parachute question

[jj94]

Ok, let's say I choose two possible setups for a rocket's recovery system. Setup 1 has two small parachutes while setup 2 has one large parachute. If the surface area of setup 1's parachutes were combined and equalled the surface area of setup 2's single parachute, would the decent rates be the same?

 

[irishwebber01]

It would be different but for this application, the physics of it wouldn't account for much...the difference would only be marginal. Another advantage to this would be if one chute failed to deploy at least you have a partial backup....go for it.


Drew

 

[KDRaven]

This might be inmaterial but I did an experment once using D dual egg loft once. I launched the rocket using 1 34" chute and recorded that time and then launched it again using two chutes equal or larger than the first in total size and the time recorded was less than with the one chute. The others, that were there there when I launched it, and I discussed this aspect some and we came up with the conculison that when using 2 chutes they sit side to side with each other and are not able to capture the air in the chute as effective and allows it to spill out or the chutes slide through the air instead of capturing it and holding it in.
I also figured out that it was better to use one large chute for the recovery instead of two unless the nose and body tube are not connected together. I also found out that the one large chute can not be too large or it will not work properly because it does need the weight of the rocket to fully open it up and if not enought down force on it will not caues it to expand properly either.

 

[iowadan]

It's well documented, in the enginering liturature, that there is a loss of drag for parachutes used in clusters. Two flat solid parachutes used in a cluster will have a Cd .9 of a single parachute of equal area; for three parachutes the Cd will drop to.85. This effect can partially be over come by lengthening the shroud lines and risers.

 

[ga1ba2]

On the duel chute subject. If you use two small instead of one larger chutes do yo attach both parachutes to the screw eye or make some type of harness?

 

[Handeman]

That's a good question.

If I were using Estes chutes, I would make a harness that extended the chutes further from the attechment point.
If were using my homemade or modified chutes where the shroud lines are at least 1.5 times the chute diameter, then I might attach both to the screw eye.

Does anyone have a minimum length for shroud line + harness length when using 2 or more chutes that are attached to a common point?

 

[iowadan]

I've seen two recomendations for shroud line length and riser (harness) length. The first is Le = Do*square root (n) where Le is the length from the canopy to the conflunce point of the parachute harness, Do is the nominal diameter of the parachute (I think the measured diameter should work ok) and n is the number of parachutes in the cluster. The lengh Le is a combination of the shroud line and riser as you see fit; the shroud line length should, at a minimum, be equal to Do.

The other suggestion I've seen is that shroud line length of each parachute should be equal to Do. Then there should be a riser from each parachute to a central point of confluance. This riser should be 1.8*Do. Finally there should be a single riser from the point of confluance to the point of attachment. This second riser's length should be equal to should be equal to Do.

 

[troj]

The other thing to keep in mind is that one parachute is less prone to failure than a dual parachute system -- when you add a second canopy, set of lines, etc, you have that much more that can get entangled, resulting in a malfunction.

-Kevin

 

[jj94]

The other thing to keep in mind is that one parachute is less prone to failure than a dual parachute system -- when you add a second canopy, set of lines, etc, you have that much more that can get entangled, resulting in a malfunction.

-Kevin

That's a good point.