L2 decisions

P = Pluged
L = Long Delay
M = Medium delay

You can always use an altimeter and fire the charge at apogee and use the motor ejection as backup 1 or 2 seconds later, with an altimeter, you risk way less to have a zipper or broke the chute. All the motors not mark -P have a charge.

M is medium delay.

J500, 4" rocket, about 8 pounds to 3300' deployed at apogee.

Area66 said:

You can always use an altimeter and fire the charge at apogee and use the motor ejection as backup 1 or 2 seconds later, with an altimeter, you risk way less to have a zipper or broke the chute.

Click to expand...

Having motor backup has saved me twice when my primary failed...highly recommend this approach for your L2 or any launch for that matter. Better to make the delay long. Do a sim to calculate.

mpitfield said:

Having motor backup has saved me twice when my primary failed...highly recommend this approach for your L2 or any launch for that matter. Better to make the delay long. Do a sim to calculate.

Click to expand...

Can you change the delay with the delay drill tool for the 38's? I do understand using the altimeter for the Apogee and having the motor ejection for back up

Yes you can drill a 38mm.

Area66 said:

Yes you can drill a 38mm.

Click to expand...

ok that's what I thought... thanks for clearing everything up

AfterBurners said:

So at what size motor do you have to use an altimeter to fire the ejection charge? Looking on WM's site I noticed the SKU @ on a motor K1499N-P does the "P" stand for plug? Whereas the J500G-M does the "M" represent "Motor Ejection"

Click to expand...

Other than the AT Warp 9 loads, I don't know of any 38mm motors that don't have motor ejection available. There are a few large 54mm motors that are also plugged, but most are motor ejection. Most 75mm L motors have motor ejection available. When you get to M and above motors, the single use motors from AT are the only ones I know of with motor ejection.

As for what size to use an altimeter with, I think that depend more on the altitude the rocket will get than the motor size. If you are going to get over 4000 ft with a 29mm motor I would seriously consider DD.

"P" does stand for plugged, however "M" means a medium delay (10 seconds). "S" means a short delay (6 seconds) and "L" means a long delay (14 seconds). The newer Aerotech reloads come with a 14 sec delay and you drill them to get shorter times.

Handeman said:

Most 75mm L motors have motor ejection available. When you get to M and above motors, the single use motors from AT are the only ones I know of with motor ejection.

Click to expand...

Not really. 75s and higher are all plugged. I couldn't find any with a motor ejection.

cbrarick said:

Not really. 75s and higher are all plugged. I couldn't find any with a motor ejection.

Click to expand...

You're right, I must have been thinking 54mm.

dixontj93060 said:

Wow, glad I'm not the only crazy one. I have this innate need to do things differently nearly every time. It applies to rockets, yes, but anything remotely repetitive.

Click to expand...

You must make really interesting meatballs.

Area66 said:

you need motor between 640.01 and 5120.00 n/sec total impulse, your choice depend on the weight of the rocket.

Click to expand...

In other words, any J, K, or L; baby J's are fine.

I haven't done my L2 yet, though the rocket is 85% build and 10% painted. I compromised between kit and scratch by modifying a kit. I took a LOC kit and added 1) dual deployment, 2) a tail cone, 3) an av bay* for the second deployment, 4) an Aeropak retainer, 5) a custom centering ring forward of the motor mount that can laterally stabilize long motors without extending the mount tube, and 6) a pointy dowel sticking out the top of the nose cone, just for the heck of it. I moved the fins about 1/8" so that the motor mount, tail cone, and retainer could all butt up directly against each other. For me, that's enough modifying to feel like I haven't just slapped a kit together, even though I'm not doing it altogether from scratch.

* The kit as designed includes a payload bay that could take the electronics, but I became confused by the myriad ways of installing it all and I finally decided to just buy an av bay kit. The kit is part of the 15% that's not built yet. The rest is the extra centering ring; I discovered that my arms are too fat to reach in and install it where I want, so I'm going to have to cut the main tube, install the ring, and patch it up with an extra coupler. Or leave it out.

jqavins said:

* The kit as designed includes a payload bay that could take the electronics, but I became confused by the myriad ways of installing it all and I finally decided to just buy an av bay kit. The kit is part of the 15% that's not built yet. The rest is the extra centering ring; I discovered that my arms are too fat to reach in and install it where I want, so I'm going to have to cut the main tube, install the ring, and patch it up with an extra coupler. Or leave it out.

Click to expand...

I'd leave the ring out. Really no need to stabilize the ends of longer motors. being locked up in the tailcone and the length of motor mount tube on the base should be sufficient.

I keep going back and forth on it. The motor isn't locked in the tail cone, and I'm looking at maybe one day using engines that are three or four times longer than the motor mount, so I'm sure their forward ends will shake. I'm just only half convinced that it matters. Also, that forward ring makes a convenient place to anchor a parachute harness.

The tail cone is a PML 4" to 75 mm cone, and my Aeropak 54 mm retainer fits up inside it. That way the retainer does not impinge on either the airflow or the sight lines. It's a little hard to get my finger tips between the edge of the retainer and the inside surface of the tail cone, but it's doable. And I can make a tool for it if necessary.