Ejection Buffer Placement

I am about to install my first ejection buffer and I am wondering how far down in the tube I need to place it? It's a 1.64 body tube and a 12" chute.

Tia,
-Bob

Do you mean baffle? I have never heard of an ejection "buffer." Maybe I am about to learn something new here.

Bruiser said:

I am about to install my first ejection buffer and I am wondering how far down in the tube I need to place it? It's a 1.64 body tube and a 12" chute.

Tia,
-Bob

Click to expand...

I don't know that there is a general guidance on locating a baffle.

Leave enough room above the baffle to pack the chute and shock cord?

Make sure that that mass of the baffle doesn't move the COM (COG) too far aft?

I did mean baffle.

Thanks,
-Bob

Coupler is usually easiest...

Do you have a restraint (lanyard) to keep it from sliding all the way down to the recovery wadding when the rocket is under acceleration?

It effects the center of gravity, have you modeled the rocket using simulation software such as Open Rocket? It's free.. and fun! https://openrocket.info/

The picture in this post is the baffle you are talking about, yes?

https://www.rocketryforum.com/threads/iqsy-tomahawk-sport-scale-bash.146392/#post-1792465

It looks like you've built it in a coupler.

From what you've posted in that thread, you've got OpenRocket. From your questions here, I am guessing you DID NOT model the rocket with the baffle in place.

Since it is an internal component, you don't have to model all of the parts of the baffle. You can just create a "mass component" with the same weight as the baffle and move it back and forth in your simulation, see how it affects the stability of the rocket (the rule of thumb is a stability greater than 1 caliber -- that is a COG more than one body diameter forward of the COP). Put it far enough back that you easily can pack your chute and shock cord, but not so far back that it makes the rocket unstable with the heaviest motor you intend to fly. For the rocket you are building, I'd guess that there will be a lot of distance between those two limits.

One other consideration, since it looks like you are going to attach the shock cord to a screw-eye in the dowel you put in the baffle: You might want to keep the baffle close enough to the forward end of the rocket that you can thread a new shock cord if (when) the first one gets toasted.

Oh, and you asked about changing to imperial units in Open Rocket. Go to "preferences". There should be a tab marked "units" where you can change from cm/grams to inches/ounces.

lakeroadster, the baffle will be glued in. That's why I need to get it right the first try. I did download OpenRocket and have played around building the rocket in there. I am in no way anything but a rookie but the balance seems good...

jlabrasca, So you've seen my build thread. I did "build" the rocket in OpenRocket and I'm sure you saw the different measurements with the three engines. I placed the baffle so I have a 8 inch compartment for the chute and cords. Even with the heaviest engine I seem to remember the difference was about 3.75 inches. It's a 1.64 body tube so that should be good. I'm just wondering if I need 8 inches. The chute doesn't take hardly any space and I can't imagine the shock cord and Kevlar line will take much room. The closer it is to the top of the tube, the better the CG and the easier it'll be to change the Kevlar when I need to. Maybe I should go 6 inches... Don't know.

Thanks,
-Bob

keep in mind that the shoulder of the nose cone takes up space that could otherwise be used for recovery gear. 8" is not a lot of tube when you need to stuff shock cord, chute, and nose cone in that 8".
Rex

Hey Rex,

Thanks for that. I just measured the nose cone and it will take up 1.5 inches of the space so I think I'll stick with the eight inches and not go any shorter.

-Bob