Does the ejection charge push out the parachute, or does the nose cone pull it out?

[cdondanville]

I would love to run your flight tests, are you going to replace any damaged rockets, cars, etc if the chute doesn't deploy? I'd be using a 4" dia. 10lb rocket.

I'm not sure testing for failure modes is a good idea in actual flights

Stop thinking rockets and start thinking science.

 

[Rocket86]

On my Rubicon it definitely pushes the nose cone off, which then pulls the parachute(s) out. I built a parachute compartment into one side of the upper body tube. It's a wall that is about 3 inches high that takes up about 1/3 of the width of the tube. I just put the chute and shock cord in it and the nose cone pulls them out.

 

[Handeman]

Stop thinking rockets and start thinking science.

In this case you can't separate the two. The idea brought forward was that ground testing does not accurately simulate flight tests. It was suggested that the test be done during flight. Using experiments with flying rockets to test failure modes will result in crashed rockets and little or no useful results. Not good science.

That's why my tongue in cheek comment about offering to fly the rockets. At least I get to have some fun even when the "science" doesn't work.

 

[donperry]

If i may add my 2 cents ...

the nosecone and the body tube has two different cross section area, thus two different Drag coefficient. Thus, in a free fall with air affecting both objects it will pull on one object more than the other.

So i'm thinking that its not the nose alone that pulls the chute out, but rather both the body tube and the nose that pulls away from each other and thus pulls the loosely packed chute out.

But i'm only speculating the concept

 

[Handeman]

If i may add my 2 cents ...

the nosecone and the body tube has two different cross section area, thus two different Drag coefficient. Thus, in a free fall with air affecting both objects it will pull on one object more than the other.

So i'm thinking that its not the nose alone that pulls the chute out, but rather both the body tube and the nose that pulls away from each other and thus pulls the loosely packed chute out.

But i'm only speculating the concept

That is right, only if the ejection charge transfered enough energy to the two halves to keep them moving apart and overcome the friction of a chute in the BT that wasn't pushed out by the charge.

Just falling, there is seldom enough difference between the two to cause either to get a chute to pull out. I had a rocket fall flat after the nose cone came off. After it landed, I picked the body up by the fin and the parachute fell out. It was only in the tube a couple of inches and very loose, but it didn't come out while the rocket and nosecone were falling. It can happen, but you certainly can't count on it.

 

[fleafrier1]

Okay, first post from a newbie old guy. Since a friend and I have gotten re-involved in sport rocketry (low power so far) we have discussed this very subject at length. At the LUNAR launch at Moffett the other weekend we heard the LCO mention that you should have a fairly tight fitting nose cone to let pressure build in the tube so that when the nose cone pops you will get a good positive ejection. Obviously nose cone tightess can reach a point of diminishing returns, but that little bit of advice has improved my recovery success rate considerably.

I think part of the reason is one force that may have been overlooked in this thread. When rapidly expanding gasses leave a sealed tube at high velocity those very same gasses have enough inertia to briefly create a lower than ambient pressure in the tube. Pulse jets or 2-stroke engines rely on this effect to function.

I think, but don't know, that a good, positive ejection charge should, in addition to pushing the cone and parachute out, actually create some "suction", thereby scavenging the body tube of it's contents, including any parachute that the charge happened to push past on it's way out.

I'm curious as to what some people with a lot more launch & recovery experience might think.