Other than the components must be unstable, once the rocket disassembles?
View attachment 535029View attachment 535030
I think
@lakeroadster is on to something, but one other factor, I think the fins in the pieces must be uni-planar or near so. Such is not the case for typical low power booster tumble recovery, which seems to tumble pretty much randomly. The tumbling creates drag, sure, but the drag surface area is constantly changing, so while it is certainly greater than ballistic recovery (ballistic recovery is sort of the “anti-ideal”, aka “worst possible case”), it is different from the “optimal” no chute or streamer horizontal recoveries of
@Dotini ‘s Horizontal Spin Recovery (with posssssssssible assistance of Magnus Force, although latter proven to be present but not proven to be beneficial in slowing descent rate) or the Alway Bros (Back Slide). A stiff* unstable uni-planar object with an eccentric CG** i theorize would spontaneously spin either in a flat orientation or maybe slightly cone shaped presenting maximum or near maximum surface area to the relative vertical airflow generated by gravity/fall trajectory. Aside from
@Flyfalcons spectacularly successful and ingenious guitar rocket
https://www.rocketryforum.com/threads/summer-buildoff-roc-n-roll-flying-v-guitar.134436/
I think there are few if any rockets with two planar fin attached orthogonally to the body tube.
hence both the maple seed rocket and FlutterBye separate into two part (I think one part of the Maple Seed has two fins no exactly uniplanar, but enough “off” to create a spin. You might consider these rockets “stablely unstable”, they don’t go ballistic but they DO Go into a controlled flat or cone shaped spin.
*stiff: I am thinking that you need to exclude a piece of paper, as it is constantly changing shape.
**eccentric CG: a flat circle or square of cardboard might not spin because there is no weight on one edge to pull it slightly down, i think you need a bit of eccentricity to get the airflow a bit off axis to get a spin.
doubting Thomas that I am, I am not convinced that EITHER the Maple Seed nor the FlutterBye are true helicopters, in the sense that I don’t think their spin creates significant LIFT. perhaps
@prfesser ,
@georgegassaway ,
@Rktman , or others “in the know” can correct me, but I think both the above and likely many if no most of my flat bladed “helicopter” designs (which are all flat blades, I.e. no true airfoil) produce most of not all of their recovery effect (slowing the descent to a safe velocity) predominantly by creating a high drag configuration rather than by generating true lift. From my personally and very unscientific documentation of my own rockets, my Air Brake recovery rockets which are designed intentionally to PREVENT spin with no blade angling (they often lazily spin anyway, certainly not enough to generate lift) and my nearly identical helicopter rockets which had around a 5 degree blade angle TO generate spin seem to descend at about the same rate, so I think it’s mainly drag that slows both. Four blades, each 18 inches long and 1 to 1.5 inches wide, plus four fins each about 2x2 inches, make up about 88-123 square inches of surface area, about the same as a 16-25 inch parachute if my math is right. My scientific knowledge is insufficient to compare the efficiencies of a fixed surface area of flat blades vs the same fixed area of a parachute or more commonly parasheet.
Turning almost any rocket sideways creates a good bit of drag, which for long lightweight low power rockets can significantly retard the descent velocity. Remember, the length of the body tube is largely ignored in terms of Drag/CP calculations by Barrowman and most Sim calculations due to assumption that rocket is at near zero angle of attack in boost phase. in
combination with fins and nose cone oriented sideways (a big drag element, especially fins) it is challenging to get a rocket to go very fast SIDEWAYS.