Can a parachute bag help on smaller rockets, or is relegated to the realm of big L3 rockets?
Anything smaller than about 4", and you'll have one heck of a time packing the parachute into the bag.
Also, is there a way to do this using an ejection charge that is under the main? Or also, separate at the tube coupler and pull it out of the back of the upper airframe?
There are those who would tell you that's fine. Personally, I'd never do it that way -- you need a small drogue to pull the bag up and off of the main.
Look to skydiving, NASA, and similar setups -- they use drogues to pull the bag up and off. You can do it two ways -- a free bag, where the main isn't attached to the bag at all, or a regular bag, where the bag is attached to the parachute.
The advantage of the former is that the weight of what the drogue is attached to doesn't matter. With the latter, if you have a heavy noscone attached to that bag, it will tend to collapse your canopy.
What some folks will do (using the Gates Brothers' Jayhawk as an example), the drogue is sized for the nosecone. The drogue comes out when the nose comes off. It then pulls the bagged mains up and out of the rocket, then pulls the bag off of the mains, and entirely clear.
Bag and nosecone come down on the drogue, the main body of the rocket comes down on the mains.
I would
never rely on inertia to extract a main from a bag. It's just a recipe for disaster.
Also, never shove and wad your parachute into a deployment bag -- a lot of friction is generated when the layers of nylon slip past each other, and the bag, when they're just shoved in. This leads to ruined parachutes. In the worst case, things can get jammed and not deploy properly.
It takes practice, but learn to fold your parachute into the bag. It should
not be difficult to pull the parachute out. When we have our big (28 foot) parachutes in their bags, a 3 year old can easily put enough tension on the lines to extract the parachute.
-Kevin
