Thoughts on Booster backslide recovery on two stage.

BABAR

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One of my Holy Grail engineering challenges has been to get a booster that recovers by gliding. Since I am strictly a black powder low power staging guy (okay, maaaaaybeee I might stray to mid power, but I am definitely and proudly L-0!), and I enjoy long gap staging, recovery of the booster is challenging, as typical long boosters with no streamer or chute tend to convert to “Core Samplers” soon after staging, as the longer boosters tend to remain stable.

I have tried Estes Tiger Shark (which I think is the same as the Centuri Black Widow) and was somewhat underwhelmed with the booster glide performance, both with ground and flight testing.

typical Back Slider single stage rockets require extremely long length to diameter ratios, like 40 or 50 to 1 (to my knowledge, trying it on boosters hasn’t been attempted, please correct me if someone knows otherwise). I am thinking part of that may be because the weight of the nose cone, however light, tends to drag the nose down. Wondering if, since post staging the booster is Nose-Less, maaaaaybeeee can get away with shorter length.

also, normal Back Sliders (perhaps an oxymoron) have a forward puff port that throws the angle attach hopefully way off zero, like Horizontal Spin Rockets (in fact, I HAVE used horizontal spin for booster recovery and it works.) I am thinking that at staging the booster is likely “blown out of whack” with black powder staging, as it doesn’t have that much mass and the open forward tube probably has a lot of initial drag, since staging occurs at max V for the STACK (max V for sustainer may be lower or more likely higher, since it is starting at a decent velocity and has a fresh motor.)

maybe @Rktman , @Dotini @lakeroadster , or @PeterAlway might have some ideas.
 
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Wondering if increasing the size of the boooster "wings" (fins) would improve performance? Retrimming the booster, if needed so that it glides, wouldn't be a difficult endeavor.
 

BigMacDaddy

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Can you explain backslide? Not sure I understand what you mean.

I am going to guess and say he means when the rocket semi-glides backwards and drifts down to the ground more or less horizontally (although drifting down horizontally is not exactly the same as gliding [backwards or forwards]).

My Mini Mean Machine does that with the tiny chute ejected (even if it is tangled). Bit hard to see but here is a video to see if this is what we are talking about.



I (maybe naively) was thinking that the surface area of the body would need to be equal to or more than the fins to get that horizontal drift. I guess that a small chute or streamer pushes the CP forward so could offset larger fins to create that backsliding. My Bomarc also came down pretty much horizontally after the chute got tangled (those big wings I guess).

I guess the difficulty in creating this with a booster is that there is no ejection so cannot eject motor to help balance weight (often an option for gliding). I have tried to hide a small chute or streamer in the coupler portion that connects booster to sustainer with the goal that it would split open when disconnected from sustainer (assumes a buffer tube) but do not have evidence this will work (no flights yet).
 

BABAR

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Can you explain backslide? Not sure I understand what you mean.
Okay, my take on Back Slide Recovery [BSR]

Barrowman equation stability [BES] (upon which most of the simulator rocket design programs are based) is valid for rockets flying with low angles of attack, and to a large extent these programs largely ignore the cross sectional area of the body tube. But if you go back to the old cardboard cut out stability test [CBCOS] , you can imagine that for a very long rocket, that cross sectional area may be sufficient to put CP ahead of CG. So long as the rocket is at or near zero angle of attach, the surface area of the body tube doesn’t come into play much, BES rules. But if we can, at or near apogee when rocket is slowed down, abruptly change angle of attack (ideally stop it, flip it horizontal), CBCOS dominates, and if the rocket is tail heavy it will start to fall BACKWARDS, tail first. As it picks up speed however, the fin drag picks up and lifts the tail until it is horizontal.

Successful BSR requires at least two things.

1. Rocket design. From a side view, the surface area of the rocket is such that the CBCOS center of pressure is AHEAD of center of gravity. I suspect many kits actually fall into this category, like the Estes Mean Machine.

2. An effective deflection of angle of attack such that the rocket is pointed just about anywhere but nearly down. The models i have seen and flown use a forward port on one side so the ejection gases “knock” the rocket off zero angle of attack flight path. Unfortunately, while this works, the ultimate position of the perturbation is unpredictable. From the standpoint of the CG, can be straight up, straight down, or a where North, South, East, or West in between. So long as it far enough off straight DOWN, CBCOS dominates. And the longer the rocket (the greater the CBCOS instability) the closer to vertical without being PERFECTLY vertical BSR will still work. However, just like the roulette ball sometimes ends up in the green slot, I think PURE BSR even when perfectly executed has a certain failure rate. Then again, stuff happens with streamers and chutes, too.

Note that without this sideways kick, most low power rockets rather than go straight up, stop, and fall straight back are more likely to arch over, maintaining a continuous air stream and NEVER get sufficiently off near zero angle of attack. So without some physical change of configuration (most commonly a chute or streamer) they go ballistic. @burkefj has a video of I think it is an Interceptor, did NOT deploy the chute but somehow got off zero angle of attack and accidentally (and in this case fortunately) executed an unintended BSR.

I DO think that many rocketeers have observed partial BSR, where a small chute or streamer is sufficient to slow the nose cone more than the rocket body, and the rocket descends nearly horizontal, tail first. I am not sure if there is a formal term for this, maybe Modified Back Spin Recovery [MBSR.] or Partial Back Spin Recovery [PBSR.]. I think that sounds better than Impure, Pagan, or Infidel Back Spin Recovery.


Here’s the patent which explains it in detail

 

BABAR

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I am going to guess and say he means when the rocket semi-glides backwards and drifts down to the ground more or less horizontally (although drifting down horizontally is not exactly the same as gliding [backwards or forwards]).

My Mini Mean Machine does that with the tiny chute ejected (even if it is tangled). Bit hard to see but here is a video to see if this is what we are talking about.



I (maybe naively) was thinking that the surface area of the body would need to be equal to or more than the fins to get that horizontal drift. I guess that a small chute or streamer pushes the CP forward so could offset larger fins to create that backsliding. My Bomarc also came down pretty much horizontally after the chute got tangled (those big wings I guess).

I guess the difficulty in creating this with a booster is that there is no ejection so cannot eject motor to help balance weight (often an option for gliding). I have tried to hide a small chute or streamer in the coupler portion that connects booster to sustainer with the goal that it would split open when disconnected from sustainer (assumes a buffer tube) but do not have evidence this will work (no flights yet).

Nice video, yup, that’s a picture perfect BSR!
 

burkefj

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Okay, my take on Back Slide Recovery [BSR]


Note that without this sideways kick, most low power rockets rather than go straight up, stop, and fall straight back are more likely to arch over, maintaining a continuous air stream and NEVER get sufficiently off near zero angle of attack. So without some physical change of configuration (most commonly a chute or streamer) they go ballistic. @burkefj has a video of I think it is an Interceptor, did NOT deploy the chute but somehow got off zero angle of attack and accidentally (and in this case fortunately) executed an unintended BSR.
In my case it was my Tri-Ceptor, a 2" psII based Trident with Interceptor cones/fins, so the middle is open like a Trident rocket, there was no kick, the ejection never happened, it got to the top but did not arch over, it started to fall flat and the shape caused it to spin sideways the entire way down, so not really backslide but maybe it started that way and turned into a spinning on the long axis recovery.
 

PeterAlway

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The original tube-fin design, the Infinite Loop, reprtedly back-slid if it lost its nosecone. The report and the plans are in old issues of Model Rocketry Magazine (I don't know which issues). The model used 9" of BT-30 (essentially heavy-wall BT-20) with six 1.5" long BT-30 tube fins. That's not crazy long for gap-staging with vent ports. It seems not crazy that this might be a useful booster for your scheme.

Peter Alway
 
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