When I create an Open Rocket Simulation this rocket has a stability of 9.36 cal. Do these rockets weathercock an extreme amount?
One of the debates here is the need for a very high length to diameter ratio.
long skinny rockets do have a tendency to weathercock.
Horizontal Spin Recovery (HSR) rockets have (at least) 2 characteristics.
1. The horizontal spin orientation induces high drag, predominantly from fins and body tube. With the exception of saucers, just about ANY rocket will come down slower horizontally than vertically (aka ballistically.) I am NOT sure that the High Length to Diameter is REQUIRED for successful HSR (although it is I think absolutely required for Back Slide Recovery [BSR.]) Longer tube diameter WILL (assuming relatively light weight standard tubing) give you a SLOWER descent, since in the horizontal plane the longer the tube, the more surface area facing perpendicular to the air flow, the more drag, the slower the descent. (As an aside, I believe that some competition streamer recovery models used a āharnessā to intentionally have the rocket hang horozontally from the streamer to take advantage of this extra drag.). I have successfully HAD short rockets that did indeed recovery horizontally by HSR (I.e., they did successfully transition to horizontal and fall in a steady horizontal orientation) that were probably in the range of 12:1, example
https://www.rocketryforum.com/threads/bail-out-bill-and-the-horizontal-spin-recovery-rocket.147210/
as well as a booster that was just under 22:1
although not āpureā HSR as Bail Out Bill ejected the nose cone, and the booster HAD no nose cone, I donāt think the extreme length is required. A caveat is that you absolutely DO need a lightweight nose cone if you are going to do PURE HSR (no structural change at ejection). A heavy weighted cone will likely overcome the spin tendendency and come in ballistic. Fortunately most rockets of medium length or more donāt need added nose weight, Also I will add that the my shorter ones DID come down horizontal, but they come down a bit fast, so descent rate is in part inversely proportional to length. So I think I can extrapolate from
@Dotini ās reports that longer rockets (with lightweight tubing) that longer rockets are going to have a better hang time.
2. HSR rockets will also demonstrate Magnus effect, a LATERAL force imposed by the COMBINATION of the rapid spin AND the airflow over the rocket FROM the fall itself. this LATERAL force will cause the rocket to either translate directly lateral to the fall (vertical vector) or if unbalanced cause the rocket to spiral, although the rocket Axis will still be perpendicular to the fall vector. This is where
@Dotini and I may not be on the same page. As much as I WISH the Magnus effect would SLOW the rocketās descent rate, I theeeeeeenk since the physics dictates the force is LATERAL to the direction of fall, the Magnus Force which his rockets magnificently demonstrate is a cool byproduct of the recovery technique but neither a beneficial nor detrimental one in regards to descent rate. I would be delighted to be proven wrong on this.
a thus far unexplored rabbit hole in HSR is fin size. Larger fins would definitely induce more drag on descent, and also if appropriately shaped contribute transition to spinning faster than smaller fins. Downsize is the longer fins have longer lever or moment arm. HSR rockets spin induces a problem on landing, whereas standard rockets only need to dissipate the kinetic energy based on their descent rate and mass, HSR rockets have a substantial amount of ROTATIONAL kinetic energy that must be ādumpedā when they land. My solution as a partial ring fin that allowed the rocket to keep spinning when it landed until friction (relatively) gradually bled off the rotational momentum.
@Dotini ās solution started with heavy braces and has metamorphosed into a combination of curved fins and plastic fins. The curve allows the rocket to keep spinning a bit (the curve doesnāt abruptly stop like the 1/2 box fins would) and the plastic allows it to either bend or bounce or both. In all cases, any technique to extend the TIME taken to bleed off the rotational kinetic energy compared to the abrupt jarring of the 1/2 box fins reduces the stress (and thus potential for breakage) on the fins.
@jhill9693 i love the design, and I think the pinwheel maaaaaaay allow the rocket to spin a little bit on impact as the fins will be angled slightly away from the direction of rotation on impact. I also Theeeeeenk that the degree of pinwheel shooooouuuuuld be enough to get the rocket spinning. Will be interesting to see the results. As I am sure you are aware, it needs to be a heads up flight with EVERYONE in the potential landing zone having eyes on the rocket. And I believe weathercocking will be somewhat exaggerated with this design, so the potential landing zone may be larger than for a standard shorter rocket. So just two rules
1. Be safe
2. Have fun!
good luck!
).
Such a simple, yet elegant design.
it got three flights tonight, on 1/2A-2T, A10-3T, and A3-4T, respectively. Dead air, ramrod-straight boosts, and spectacular sideways orientation upon ejection, followed by horizontal free fall for just a second or so, followed by very rapid spinning and a slow rear-first spiral pattern down. Pasture landings, no damage whatsoever. Will follow up with closeups, video, and build instructions.
