### Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

#### jraice

##### Well-Known Member
I am trying to prove the point that if you have a drogue, even a small one, your fincan will not necesseraly lift up from the drag of the rockets speed. The only thing that can lift the fincan is horizantal wind. Any parachute should have more drag then a rocket body tube and fins. Here is some proof, ex) take your drogue and pull it in a downward motion with "X" force. Now take your rocket fincan and pull it down with "X" force. Sound logical???

What are you trying to prove exactly? That with a drogue there is no way that the fincan can be vertically higher than the drogue? So your saying that you will have an upside down V shape with the drogue at the apex and the two rocket pieces at either end? How about if your payload section is much heavier than everything else and is pulling everything down and your fincan is at the top?

Edward

I have seen some cases where the booster will spin rapidly during decent and sort of float . is that what your envisioning?

Originally posted by jraice
I am trying to prove the point that if you have a drogue, even a small one, your fincan will not necesseraly lift up from the drag of the rockets speed. The only thing that can lift the fincan is horizantal wind. Any parachute should have more drag then a rocket body tube and fins. Here is some proof, ex) take your drogue and pull it in a downward motion with "X" force. Now take your rocket fincan and pull it down with "X" force. Sound logical???

No. I can't understand your point. Especially considering "not necessarily". If doing what you say shows the thing you say it does, and it's "not necessarily" it doesn't prove anything except that "not necessarily" holds in this particular instance.

Trying to make a point about an interaction of bodies with relative drag by demonstrating drag, or lack of it, on them independently doesn't seem to make much sense. Maybe it would if you explained the point better.

basiclly all I am saying is a drogue has makes more drag then a fincan so the fincan cant lift above the drogue unless the horizantal wind causes it to but a lot of peole say the fincan can go above the drogue just from the speed of the rockets descent.

you will be fine as long as no noseweight is used. I have seen plenty of rockets fall fine drogueless as long as they didnt have noseweight. If you have a good long length of shockcord (I used 30 feet on my rocket, worked fine) and the peices fell at the same speed but they were far apart.

The only time you will have issues with the parts bumping is if one part is much heavier, and might fall straight down, (not tumble unstably) and then pull the other section, which stops the first, and pulls the second into it.

Originally posted by jraice
basiclly all I am saying is a drogue has makes more drag then a fincan so the fincan cant lift above the drogue unless the horizantal wind causes it to but a lot of peole say the fincan can go above the drogue just from the speed of the rockets descent.

I'm sure they're right for some cases. A big flat bottom bird coming down tail first would be easy to flip sideways due to high drag on the base (acting like a flat nose). If the fincan does turn sideways it'll definitely have more drag than a streamer unless it's huge.

When thinking about drogues, think about terminal velocity. If you separate the rocket into various pieces (fin can, nose section) each will reach their own, particular terminal velocity when the drag force equals the weight of that section. You don't even have to compute the actual terminal velocity, just a relative terminal velocity.

Measure the cross sectional area of each part of the rocket, as if it were falling sideways. Take that number, divide by the weight of that piece. Bigger numbers will have a lower terminal velocity.

When you tether them together, the part with the larger terminal velocity will make the slower piece speed up, which means it will fall seem to 'hang' below the slower part. If the difference is significant, then you don't need a drogue to keep the pieces seperate.

When you atttach a droge to either piece, it's like adding lots of area, and very little weight. You can simply add in the area of the chute and the weight of the chute and re-figure the relative terminal velocities.

This will give you a good idea of the configuration in which the rocket will fall. it woun't give you a descent rate for the whole disassmbled rocket.

urbanek

Replies
13
Views
2K
Replies
3
Views
819
Replies
7
Views
496