Parachute plans

I use a simple octagon.

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

Good site, but something doesn't rub me right about this statement:

"Air flowing around the parachute at a certain velocity (V) generates both lift and drag forces -- the drag (D) acting opposite to its line of motion, and the lift (L)acting perpendicular to this, tending to reduce the descent rate..."

Stop me if I'm wrong, but a symmetric parachute (ie not a parafoil or parawing) will approach an equilibrium velocity in the horizontal direction with respect to the wind (in other words, it will approach a horizontal velocity of 0 with respect to the wind). Lift really shouldn't be a factor a few seconds after popping the chute, right?

Dave

Darren J L> >

I think the airflow he is referring to is the vertical airflow as the chute descends through stationary air. The increased speed of the air flowing around the canopy is going to tend to create low pressure above the chute, causing lift.

Hmmm...if the lift force is perpendicular to the drag, then it will be acting horizontally, and will not reduce the descent rate.

Unless he means that the drag force reduces the descent rate, but is 'noting' that the lift force is there also.

Will the parachute necessarily travel *at* wind speed. I'm not sure myself, but I feel that it would not be inconceivable that the parachute would travel more slowly than the wind. I guess if all the air is assumed to be moving in the same direction at constant speed, if the rocket it moving at wind speed there will be no resultant force.

Hm, seems like I'd consider that drag more than lift. I would really only consider it lift if it's a force created via Bernoulli's principle.

Dave

David wrote:

generates

approach a

There was a thread here last year discussing this. If the parachute is moving at the same speed as the air and the air is moving at a constant speed there would be no lift, but I found it difficult to believe that that would be the case. If the wind is gusty or variable in direction, it seemed to me that there would be lift. You might find the thread of you googled for "parachute lift".

There was a big write-up in Extreme Rocketry in (July 2002, I think) that outlined the whole process of figuring out how to design and cut both hemispherical and semi-hemispherical parachutes. An excellent how-to that I still refer to. Six and eight panels 'chutes come out beautifully.

I'll figure out what I want and cut the patterns out of newspaper, then my wife will sew me one. She even uses Kevlar(tm) shroud lines. They work too well!

Parachutes, and parachute-like things:

Sadly, some of the better pattern sites are now 404.

I've written a program to calculate the gores for an arbitrary ellipsoidal parachute with any number of gores. I've even made a few, pictures of which can be seen here:

However, I haven't yet figured out how to print the gore patterns directly; instead, I print the numbers, lay them out on paper, and draw the gore by hand. Some day I plan on doing more with the program, including allowing arbitrary (read balloon) curves to be provided, and computing the gores to make them.

Mark E. Hamilton NAR #48641-SR

That is a good site, I tried to make one of those chutes but couldnt sew if my life depended on it. I just looked on ebay and got a bunch of 36" nylon chutes for dirt cheap.