I am not sure what your point is.
<g> That doesn't come as any surprise -- as I went back and re-read what I wrote and I left out too much and assumed even more. I apologize for that. (and, upon re-reading the below, may not be as much an improvement as I initially thought - give it a try...)
First off, understand that (once I got onto it), I always used a bag deployment system on every canopy 3 feet and above (which covered probably in excess of 95% of my flights). Altimeters and dual deployment were very much in its infancy at the time I was doing this - but I already had 'hit on' the approach I was going to use - in concert with the bag deployment that I was already familiar with. People weren't breaking their rockets in multiple pieces like you see today back in the '90s (they also weren't using bag deployment, either.)
Never used burritos, etc -- it was bag exclusively. This is what informed my thinking on how to solve the dual deployment approach.
The fundamental thing with the bag is that it (with the main canopy) and the pilot chute are ejected by the ejection charge at apogee (the outer container bag is tied to the nose cone with a 12"+- bridle to prevent loss - connected with the same quick link that ties the shock cord to the nose cone - but it rides pretty close under the base of the nose cone). The pilot inflates, pulls the rip-cord pin - allowing the outer container to open (itself a bag - imagine a (fabric) box with 4 flaps, overlapping, held closed by a loop of elastic threaded thru grommets at the 'common point' where the flaps overlap and the pin threaded thru that loop where it exits the top flap - thus holding the bag closed) and, once open, then extracts the actual (interior) canopy bag, stripping the lines (stowed zig-zag in elastic loops on the back side), pulling free the 'bights' of suspension line holding the inner bag closed (the bights into elastic loops thru three grommets on the flap) - whereupon it opens and the canopy proper is extracted and begins inflation. All this happens at apogee... under *normal* circumstances. There's nothing out of the ordinary here - this is just normal bag deployment.
The point in bringing up the reefing line cutter is that I would rig the above approach to *prevent* the pilot chute from pulling the rip-cord pin (holding the outer container bag closed) via a tie-down (just a little 30# dacron line as a 'belt' around the outer bag and through the reefing cutter and the rip-cord pin. There could be two cutters (one each side of the rip-cord pin) for redundancy). When the whole system (rocket and recovery system - aligned and descending as: pilot > main canopy bag at > nose cone > main body --- top to bottom) - when all this reached the terminal descent altitude (TDA), the reefing cutter(s) would fire - releasing the tie-down and allowing the pilot to then free the rip-cord pin and continue with the deployment -- same as would have happened at apogee - just in this case, inserting a several thousand foot 'interval' between ejection of the recovery system (and pilot inflation) at apogee and final inflation of the main canopy (at TDA). The pilot chute then becomes the drogue in this case (and could be increased in size to keep descent rates in check). Reefing the main canopy to further reduce opening forces would be an optional (additional) step, depending on necessity - and only confuses our discussion here. The main point is using the reefing line cutter (that I already had and had proved workable) in a different application from initially intended. The added benefit is that this aligns the entire vehicle in the exact orientation (pilot top - main body bottom) that is needed for main deployment BEFORE main deployment - lessening greatly any chance of fouling (or damage) of the components.
I don't know how much you are familiar with bag deployment (meant honestly - I just don't know), and my bag system is buried and lost somewhere around here (that I will be looking for) or I could take a few pix and upload, which would help clarify this a little more. I did spend a little time this afternoon searching online and found enough (generic) photos that I could upload with commentary a bit - if you think it would help further clarify things. (I *do* plan to cover some aspects of this down the road on the 'Ringsail' thread - even if I have to build another bag (something I've been wanting to do anyway, with a few design improvements, for years)). But, if those pictures would help, I'll get them up here.
But, the most important point to keep in mind is that I have never 'broken a rocket it two' (for dual deployment) and (generally) don't intend to -- as I feel my 'delayed bag' approach is simpler and more reliable. All my thinking comes from that foundation and philosophy. This will fly in the face of 'conventional wisdom' (based on present practice) - but only because I've been 'out of the loop' for awhile (and have, therefore, not grown accustomed to the (contemporary) 'standard approach'). Since you are more currently active, you will look at it differently, for sure.
CarVac said:
I do plan to use a bag. I don't have that yet, so if there is an elegant way to keep it closed under the weight of the rocket with the drogue/pilot pulling on it, I would like a description (or diagram).
First, we need to quantify with some reasonable degree of accuracy just what kinds of force that pilot/drogue exerts at various decent rates (it's not going to matter what the rocket weighs - outside of the fact that equilibrium descent rates will be higher with a heavier mass under the pilot). A small pilot chute will not exert such a massive force that it can't be countered with whatever method of securing the rip-cord pin in place is found (per my approach above). If 30# line isn't enough, then we'll try 60# line (testing, of course, that the reefing cutter can handle it) - or just use a zip tie like Archetype does. In my earlier reefing line work, I found that some classic 30# dacron deep sea fishing line could take a heck of a lot (as to reefing line forces) - even on 6 or 7 foot canopies - so I don't feel any major changes are going to be necessary in this application. But, regardless, there's still some design effort yet to be expended on making this 'elegant' (all of this depends on the exact design of the bag, too).
CarVac said:
I have a commercial parachute, so I can't easily/don't feel comfortable adding reefing to it.
I was planning on multiple parachute tubes within the airframe in order to protect against
black powder damage.
Putting in reefing rings isn't all that hard and we've had a discussion or two in the past on alternative approaches to 'hesitating' main canopy inflation (that may not involve an actual reefing cutter). The best approach is to have those cutters in the skirt (most nearly mimics the 'big boys' approach), but trying to fire that electrically is where things get challenging - since the control electronics are located elsewhere (thus, these alternative approaches).
We'll just have to continue down this road and solve the problems as we go.
(If I still didn't clarify things sufficiently, 'holler' back and we'll try again)
-- john.
