L1 Build Question

I'm building a Madcow Super DX3 for my L1 cert flight. My intention is to go low & slow SD for L1, then add a DD bay for bigger engines & higher flights. I tend to overbuild, so this may also be used for L2 cert. To make it SD/DD capable I intend to use the DD ebay without the bulkheads for the SD flights (removable rivets, shear pins used for holding the lower airframe and payload bay together). In the standard (non-DD) config, the kit has a bulkhead on the coupler, so the ejection charge on the motor only has to pressurize the lower airframe. With an open coupler, it needs to pressurize both the lower airframe and the payload bay.

Here's the first question. Will the standard ejection charge on an Aerotech or CTI 38mm motor be sufficient for the SD deploy? The available calculators for sizing BP ejection charges say it can be sufficient or insufficient depending on the amount of desired force (pressure) you want on the nose cone. I would prefer to not have to do ground testing for a SD event, since I'm not really setup for it at this point and doubt if I'll have time to do it before I run out of launch window this fall. So, from anyone's experience with this kit and the config I specified, will the standard ejection charge suffice? I suppose I could always stuff a lot of dogbarf in the tube, but that's just another variable I would prefer to avoid.

Second question, if not, is it kosher to pop the red cap off of a single use (Aerotech) engine and add BP? Since this is a cert flight at a (likely) NAR shoot, it needs to be clean.

Final question, I have one other option I can consider, that being to use the extra coupler I have (I bought the ebay kit), cut it shorter and make a piston ejection system that sits on top of the DD coupler. That would keep the pressurization requirements the same. It adds a little complexity to the config, but I've done pistons before (PML Bullpuppy). All thoughts appreciated.

I would suggest just securing the bulkheads onto your avionics Bay with the all thread that you will use for future flights. Even if you fly it with no electronics.

I believe the stock ejection charge would be big enough to pressurize the full length of the 3 inch rocket. Just make sure you have the right amount of friction set on the nose cone. But pressurizing the whole length will leave a lot of black powder residue everywhere, instead of just in the lower section.

Aerotech HP loads all require you to install the ejection charge yourself. And then install the Red Cap. So you could add the amount of powder you felt necessary for your rocket. CTI says if you need to add powder just put it on top of the paper cap and tape it down.

There are many ways to do this, and many are just as right as the others. That said, what I would do is fly the L1 motor eject flight with the airframe just like it was your DD L2 flight. Put the solid bulkheads on the AV bay, shear pin on the nose cone, rivet the AV bay to the upper airframe. Then just put your main where the drogue would normally be and you have a motor eject flight ready to go. I would probably also leave out the shear pins from the lower airframe for both L1 and L2--friction fit and a good shake test are all you need here.

Of course, check stability with less weight up high in the rocket, but with an L1 motor you should probably be fine.

boatgeek said:

There are many ways to do this, and many are just as right as the others. That said, what I would do is fly the L1 motor eject flight with the airframe just like it was your DD L2 flight. Put the solid bulkheads on the AV bay, shear pin on the nose cone, rivet the AV bay to the upper airframe. Then just put your main where the drogue would normally be and you have a motor eject flight ready to go. I would probably also leave out the shear pins from the lower airframe for both L1 and L2--friction fit and a good shake test are all you need here.

Of course, check stability with less weight up high in the rocket, but with an L1 motor you should probably be fine.

Click to expand...

This is what I recommend also.

But I also strongly recommend building separate rockets for L1 and L2 in order to get more variety of experience.

I used the same rocket for L1 and L2, a LOC 4" Phoenix. It is motor eject, not DD. L1 flight normal, nothing fancy. L2 flight, bigger motor and a Jolly Logic chute release to open at 500'. Were able to see both entire flights. You do not have to have DD for an L2 cert flight. Your 3" rocket will have more than enough room to put a JLCR in her. I also fly many of my DD rockets as single deploy, motor eject. I have them all set up so that they will fly with no payload section and only the NC on the booster. Or, I will use steel 2-56 for the AV bay and then just blow the NC off. This makes one rocket do many different flights depending on weather, ceiling, and field size. Good luck.