Hey Rich, this sounds like a good plan to me. I know I am nowhere nearly as experienced as our esteemed experts, but it is similar to what I have been told. I am an L2 and I have asked John Wilke and James Russell to be my TAPs for my level 3. They have agreed. They both told me to get a number of dual-deploys under my belt. At Oktoberfest, James asked me what I intended to fly for the L3. I told him I was going to use a Performance Intimidator 4 all glass kit. James strongly suggested that I get it built and fly it a number of times as dual-deploy and work up from lower power motors like a J through L, before I go with an "M" for my level 3. That way I have the bird in the exact configuration as I practice that I will use for my Level 3. I mentioned this to John and he concurred, also mentioning that James knows what he is talking about and is very good and any thing he recommends, should be taken as a strong suggestion because he knows what he is doing. As you know, the Intimidator 4 is a 4" kit, like yours is. If you were to build this with the thought in mind that this is your L3 bird, you could do your L2 with it also and use your plan in your run up to L3. I think your plan is good.

The main reason for the main in the top and the drogue in the lower airframe (booster) is the mass of the objects at the ends of the harness:

With it set up how you're planning, when the drogue pops, the shock of the booster airframe pulling on the harness will likely pop out your main as well. Shear pins might alleviate this somewhat, but swapping them works much better.

I'd recommend the following:
1) don't glue your ebay to the upper airframe. Use rivets or screws. It helps greatly in preparation friendliness.

2) Use shear pins at the nosecone to upper airframe 3x 2-56 nylon screws work well for me on my 4".

3) Drogue in booster airframe, main in upper airframe

4) And finally... Groundtest to find your optimum ejection charge BP amount. This is a MUST! Waste a few grams of BP and some ematches, but save $100's in potentially destroyed rocket.

Just my $0.02.
-Ken

also I need the weight of the main up high. it helps with the CG and CP

Id agree with not gluing in your ebay, its just not necessary and rivets are quick and easy. For your apogee deployment I would deploy out your nose cones. Reason being if you deploy out the bottom your trying to move more weight. Its a lot easier to push out your laundry and nose cone, then it is to push your entire booster section.

Shredder, just about every dual deploy L2 and L3 bird I've ever seen deploys apogee out of the middle of the airframe and main out the nose. There are a variety of reasons for this:

1- When you break in the middle, you make far more of a change in the aerodynamics of the bird and ensure much greater body drag during the period when it is descending on a small chute.

2 - When the main deploys from the nose, the weight distribution ensures a better landing

3 - forward weight of the main chute ensures a better CG and CP position.

I could go on, but hopefully you get the picture.

Thanks everyone for the advice! I understand now why it's best to put the main up top and the drogue down below. And, I will definitely ground test my charges.

About using rivets/screws on the ebay instead of gluing it to the payload section: I originally planned on this, but considering the general advice I've heard/read to use only U-bolts or closed eye bolts because open eye bolts pull open, I assumed that screws/rivets wouldn't be strong enough. The airframe is PML's "QT polymer".

Would plastic rivets such as Giant Leap's "Large Removable Rivet" work? They're about 0.2" in diameter. (go to http://www.giantleaprocketry.com, then select "Products", "Components", and scroll to the bottom). How many would you recommend?

Or, should I use screws, with wood backing blocks installed in the ebay so they have something substantial to screw into?

And, one more question I've thought of: what size drogue would be reasonable? My guess was: given a 54" main, then use a 24" drogue, which gives (roughly) 1/5th the area.

Rich, I've built birds that weigh over 20# and have NO drogue. They just break apart at the ebay joint and deploy a long shock cord and fall from apogee without any drogue whatsoever. You'll find guys like John Wilke NEVER use a drogue. The main is all. When the airframe separates, the degradation in aerodynamics reduces the rate of fall substantially. My L3 bird - 30# or so at burnout - deploys an 18" chute or a 4' streamer. I could just as well deploy nothing as the break in the airframe prevents it from coming in aerodynamically intact - it tumbles and therefore slows substantially. Something on the order of 100fps as I recall. The small chute or streamer is solely for the purposes of of orienting things so that when the main deploys, the nose doesn't strike the lower airframe or allow the main to tangle with the lower shock cord.

Most of the altitude junkies use NO chute for apogee deployment.

Agreeing and adding to Warren's comments. Most of the altitude junkie birds have relatively small fin areas, so the booster section with motor casing will become unstable once detached from the upper section. This makes going "drogueless" perfectly acceptable.

In a different case, such as a giant Flis-kits Deuce (Chris L.), where you've got tons of fin area, the booster section may likely still be stable without the upper section. Adding a drogue forces it to fall in more of a flat spin attitude rather than ballistic.

Do some sims or calculations on just the lower part of the rocket with the spent motor weight and see where your stability lies.

-Ken