Ye Olde Rocket Forum - Break-apart recovery (a more detailed look)

Hello All,

In the 1990 Edition of his book titled "The Model Rocketry Handbook," Stuart Lodge criticized the break-apart recovery method as being "more trouble than it's worth." Until recently I thought exactly the same way. The old 'noseblow recovery' system always seemed like a lash-up at best.

However, some old Estes model rocket plans that I've come across, in combination with odd (pleasantly surprising) flight experiences that I had with a mid-body ejection streamer-recovery model that consistently malfunctioned, have prompted me to re-think my position on break-apart recovery systems. Examining the Estes plans more closely (links to these plans and to the plans of nine Estes break-apart recovery model rocket kits are provided below), it turns out that the mid-body ejection break-apart recovery system is actually a well thought-out design and method that has several advantages, which I will cover below.

After finding the Estes Sky Bird II, Mitosis, and Lil' Tinker break-apart recovery rocket plans online, I was reminded of the odd yet positive descent behavior of my Estes Mark II (see: http://www.spacemodeling.org/JimZ/k_02.htm and http://www.spacemodeling.org/JimZ/estes/k_02.pdf ), a mid-body ejection streamer-recovery rocket that was a modified version of Estes' original Astron Mark kit (see: http://www.spacemodeling.org/JimZ/k-02.htm and http://www.spacemodeling.org/JimZ/estes/k-02.pdf ), which used the standard nose cone ejection method to deploy its streamer. When I flew my Mark II, the streamer frequently remained stuck inside the upper portion of the rocket, but the lower section of the rocket always pulled away at ejection and remained attached by most of the length of the shock cord (a few inches of it would be jammed inside the upper section along with the streamer).

Despite the fact that I flew it from a hard-packed red Georgia clay cornfield that was "infested" with hard corn stubble, the Mark II never suffered as much as a scratch in all of its many "streamerless" landings. The two connected pieces of the rocket descended in a horizontal attitude, rolling about their longitudinal axes while simultaneously rotating in a flat spin. The Mark II never landed far from the launch pad when its streamer jammed, even when I used it as a second stage atop my Estes Apogee II's booster stage! That booster stage with its oversized fins (and the Mark II, which also had large fins) got me thinking about the Sky Bird II, Mitosis, and Lil' Tinker break-apart rocket designs:

These three rocket designs used mid-body ejection, as did the Estes Super Flea break-apart rocket kit. In each model, the lower section was approximately the same length as a typical "butt-joined" booster stage of a two-stage model, and fit into the upper section using a stage coupler (which also served as the thrust ring in the BT-20 size Lil' Tinker and the BT-5 size Super Flea). The lower and upper portions of the model were connected together with a length of shock cord, and the launch lug was usually glued onto the upper portion, flush with (even with) the separation joint. The lower section had rather large fins, like what one would expect to see on a booster stage. Large fins don't appear to make sense on a break-apart rocket, since it would seem that its higher velocity at landing would tend to break the fins. This feature, however, is part of the secret of how these models work.

While it is certainly advisable to glue on the fins of break-apart rockets with extra reinforcement (using larger glue fillets, paper "gussets" on the fin joints, and, if possible, through-the-wall [TTW] fin joints), their larger-than-average fins create more drag during descent, and these big fins' greater aerodynamic moments help cause the rapid two-axis motions (rolling and spinning) that generate sufficent drag for safe touchdowns.

Break-apart recovery rockets (the mid-body ejection types) were originally developed for spot-landing competitions because their very slight wind drift makes them easier to "aim" to reach a desired landing point. Their relative immunity to drifting also makes them excellent models for flying on windy days as well as in calm conditions. Since they land close to the launch pad, they are ideal models to fly on small fields. Their simplicity also makes them less prone to recovery system failure (there's no streamer or parachute to jam!) and makes them very easy and quick to prepare for launch. Just fold the shock cord into the rocket's upper section, slide both sections together, pop in a motor and go! (Due to these models' light weight, no elastic is necessary in the shock cord, and a length of Kevlar cord three to five times as long as the rocket will usually suffice. To make things easier for the Kevlar from a heat and erosion point of view, I use a small amount of wadding even though, strictly speaking, it isn't necessary.)

Another application for break-apart recovery rockets is to serve as boosters for parasite boost-gliders. With no streamer or parachute for the glider to snag on at separation, the glider deployment reliability should be higher for these rockets. Also, since the break-apart recovery booster usually lands within plain sight from the launch pad, one need not divide one's attention between taking note of the booster's touchdown point and watching the glider.

Front-motor boost-gliders that use jettisonable pop pods can also employ break-apart recovery. For these models' short pop pods, the "nose-blow" type of break-apart recovery would be the easiest to implement, simply by removing (or omitting) the streamer or parachute. As with parasite boost-gliders, the lack of a streamer or parachute with the pop pod should decrease the odds of the glider becoming tangled up with the pop pod's recovery system at pop pod/glider separation.

Below are links to online scans of break-apart recovery model rocket plans. Three of them are Estes Free Plans (bonus items shipped with mail orders) and plans from the Estes Rocket Design Book, and the other fourteen are plans of Estes kits. The parts for these models are available from Semroc Astronautics www.semroc.com . The rocket plans are:

Sky Bird II (Plan No. 02 and No. 43) http://www.spacemodeling.org/JimZ/eirp_02.htm and
http://www.spacemodeling.org/JimZ/eirp_43.htm

Mitosis (Plan No. 40) http://www.spacemodeling.org/JimZ/eirp_40.htm and http://plans.rocketshoppe.com/mrn/m...1/mrn_v6_n1.htm (Thank You for this link, BEC!)

Lil' Tinker (Plan No. 42 http://www.spacemodeling.org/JimZ/eirp_01.htm

Estes Javelin/Super Flea (#0815) http://www.spacemodeling.org/JimZ/est0815.htm and http://www.spacemodeling.org/JimZ/estes/est0815.pdf

Estes Star Dart #0860 http://plans.rocketshoppe.com/estes/est0860/est0860.htm

Estes Mini Tri-Pak #0866 http://www.spacemodeling.org/JimZ/est0866.htm

Estes Pulsar #0870 http://www.oldrocketplans.com/estes/est0870/est0870.htm

Estes Vector #0871 http://www.oldrocketplans.com/estes/est0871/est0871.htm

Estes Sparrow #0872 http://www.spacemodeling.org/JimZ/est0872.htm

Estes Hawkeye #0873 http://www.spacemodeling.org/JimZ/est0873.htm

Estes Mini-Scale Combo #0874 (Exocet and I.Q.S.Y. Tomahawk) http://www.spacemodeling.org/JimZ/est0874.htm

Estes Scout III (#0878) http://www.oldrocketplans.com/estes/est0878/est0878.htm (Thank You for reminding me about this kit, John Brohm!)

Estes Jammin' #0890 http://plans.rocketshoppe.com/estes/est0890/est0890.htm

Estes Lumina #0897 http://www.spacemodeling.org/JimZ/est0897.htm and
http://www.spacemodeling.org/JimZ/estes/est0897.pdf

I hope this information will be useful.