Ejection baffle question

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Some good baffle info can be found here:

www.apogeerockets.com/education/downloads/newsletter129.pdf

hcmbanjo has provide very useful informatiom on easily constructing your own baffle.

The picture you've provided shows the particles moving away from the center of the blast in a straight line.

In the baffles shown in the earlier posts and the drawing below, it's easy to see the particles have to navigate two 180 degree turns. The particles loose all their inertia while being forced to make those turns and banging into every surface within the baffle. After all that, the particles fall out of the gas flow. The particles are stopped by the baffle while the gas moves right on thru.

In the time it takes for all this to happen, the parachute has already been ejected and is long gone.

AMS rocket 113.jpg
 
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In the baffles shown in the earlier posts and the drawing below, it's easy to see the particles have to navigate two 180 degree turns. The particles loose all their inertia while being forced to make those turns and banging into every surface within the baffle. After all that, the particles fall out of the gas flow. The particles are stopped by the baffle while the gas moves right on thru.

One small technical point: inertia is a property of mass. If it has mass, it has inertia. The particles do lose their kinetic energy and momentum bouncing around inside the baffle assembly (imparting it to the walls of the baffle/body tube). But they keep their inertia.
 
Some good baffle info can be found here:

www.apogeerockets.com/education/downloads/newsletter129.pdf

hcmbanjo has provide very useful informatiom on easily constructing your own baffle.

The picture you've provided shows the particles moving away from the center of the blast in a straight line.

In the baffles shown in the earlier posts and the drawing below, it's easy to see the particles have to navigate two 180 degree turns. The particles loose all their inertia while being forced to make those turns and banging into every surface within the baffle. After all that, the particles fall out of the gas flow. The particles are stopped by the baffle while the gas moves right on thru.

In the time it takes for all this to happen, the parachute has already been ejected and is long gone.

So, now that we've agreed that the hot/burning particles travel ahead of the gas AND that these particles ARE members of the system AND you made no mention of them in your "Here's how a baffle works" post... :confused2:

I realize that most baffle designs account for the particles too, however, since the thread is about custom designs, I thought it prudent to elaborate on your post so that considerations for an important part of the system were not overlooked.
 
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So, now that we've agreed that the hot/burning particles travel ahead of the gas AND that these particles ARE members of the system AND you made no mention of them in your "Here's how a baffle works" post... :confused2:

I realize that most baffle designs account for the particles too, however, since the thread is about custom designs, I thought it prudent to elaborate on your post so that considerations for an important part of the system were not overlooked.

I was not trying to write a technical report. Reread the post. I have not agreed with you. How can the clay cap move faster then the expanding gasses that put the clay cap debris into motion.

Next you'll be telling us a bullets velocity increases after it leaves the muzzle of a gun in the same magical manner.
 
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Next you'll be telling us a bullets velocity increases after it leaves the muzzle of a gun in the same magical manner.

Again, momentum. You're saying that if you fire a gun at a target, no matter what the distance, that the gasses from the propellant reach the target at the same time as the bullet?
 
You're saying that if you fire a gun at a target, no matter what the distance, that the gasses from the propellant reach the target at the same time as the bullet?

That's not even close to what I said.

Your caught up on a detail that doesn't effect how a properly designed baffle performs its primary function.
 
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In the above analogy, I think the appropriate question is if the rocket motor is analogous to a bullet and the rocket body is analogous to the barrel of a gun, does the cool air in the barrel of the gun prior to the gun being fired exit the barrel prior to the bullet?

I don't know jack about guns and I don't think that this is a perfect analogy because the bullet fits the entire barrel of the gun and would consequently push the air in front of it. However, I don't believe that the bullet can be pushed by the propellant any faster than the rate of the expanding gasses behind the bullet.

Again, I don't know jack about guns.

However, in the case of our ejection baffle, hopefully I don't have to worry too much about the hot particles as I hope that they are being trapped by the baffle. Now, do I believe that the expanding hot gasses push the cool air in the body tube in front? Well, if they push a bullet out of a gun, I am inclined to believe that they will push the cool air and nose cone out before melting too much of my recovery system, hopefully.

I guess I should just get it built and launch the darn thing and report my results.

Cheers!
 
I like your baffle design and I'd bet that it will work just fine.
 
In the above analogy, I think the appropriate question is if the rocket motor is analogous to a bullet and the rocket body is analogous to the barrel of a gun, does the cool air in the barrel of the gun prior to the gun being fired exit the barrel prior to the bullet?

I don't know jack about guns and I don't think that this is a perfect analogy because the bullet fits the entire barrel of the gun and would consequently push the air in front of it. However, I don't believe that the bullet can be pushed by the propellant any faster than the rate of the expanding gasses behind the bullet.

Again, I don't know jack about guns.

I don't know jack about guns either. But I do know jack about physics :) I don't think a bullet is an appropriate analogy either, I was simply responding to bradycros' comment from the previous post:
Next you'll be telling us a bullets velocity increases after it leaves the muzzle of a gun in the same magical manner.

It's important to now the difference between acceleration and velocity.

Of course a bullet doesn't travel faster than any gas behind it INITIALLY. They exit the barrel at the same time and have roughly the same velocity. The difference is that the gas doesn't have as much mass as the bullet, therefore doesn't have as much momentum, therefore it decelerates more quickly (more technically, it has a higher negative acceleration). So if you examine three points in time/space:

The barrel exit: The bullet and gas leave the barrel at roughly the same time, at the same velocity. (The gas a bit faster, actually)​

6 feet from the barrel: The bullet passes this point before the gas. The bullet is traveling much faster than the gas because the gas has already started to slow down much more quickly than the bullet. They both have to push against the air but the bullet, having so much more momentum, MAINTAINS more of its initial velocity. (This 6 foot mark is not scientific since I don't know jack about guns, but you get the idea. It is at some point beyond the barrel of the gun.)​

The target. Finally, the bullet hits the target, but the gas never gets there. Why? Because it has slowed down to a stop before it got there. The bullet is traveling much slower than it did when it left the barrel, but still much faster than the gas at that point.​

It is of course NOT a good analogy to the ejection system of a rocket, but you could make that analogy to top end of the rocket motor itself- not the body tube. The gas pushes the clay (and other particles) out much like the propellant in a bullet pushes the round out of the shell. The difference is the particles "cut through" the existing air while the gas has to slow down. This difference in velocity is probably negligible right at the end of the motor tube, but is more pronounced the further you get from the end of the motor. That is one reason why it makes a difference how far the baffle is from the end of the motor.

There is the effect of the "air piston" as bradycros originally mentioned. But the hot and burning particles are important to consider, even though he doesn't think they are. If it was only a system of gas, and no particles, you wouldn't need any protection at all! The "piston of cool air" would simply pop off the nose cone and push the parachute out (with a long enough body tube anyway). But it doesn't work like that, because AS THE COOL AIR SLOWS THE PROGRESS OF THE HOT GAS, IT DOESN'T IMPEDE THE PROGRESS OF THE HOT PARTICLES AS MUCH. So the hot particles have a chance to destroy the parachute before the pressure wave or actual hot gas has a chance to burn the chute or pop the nose cone.

However, in the case of our ejection baffle, hopefully I don't have to worry too much about the hot particles as I hope that they are being trapped by the baffle.

Yes, it looks like they should be. It is a fine design. My intent was not to influence your design, you've obviously already made it! I just had to chime in when an important piece of the puzzle was missing from an explanation of "how baffles work." As long as we're posting information for people to learn from, I thought they should have the whole story.

Now, do I believe that the expanding hot gasses push the cool air in the body tube in front? Well, if they push a bullet out of a gun, I am inclined to believe that they will push the cool air and nose cone out before melting too much of my recovery system, hopefully.

I guess I should just get it built and launch the darn thing and report my results.

Sounds good!

PS: Watch this video: https://www.youtube.com/watch?v=J9o3N2Of_64&NR=1

Attached is a frame from that video showing the projectiles ahead of the gas.
 
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That's a gnarly ejection charge. It's a wonder that more rockets don't end up as balls of fire falling from the sky.
 
Bro, your baffle forces the gases and particles to make a couple of u-turns. That's pretty much what a baffles do (and most have less of a u-turn than your design). I say...fly the rocket, and give us a report. I think it will work. Let us know how you do, and I may have a new baffle design.

Rock on!!!
 
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