BackSpin— An experiment in mixing BackSlide and Horizontal Spin recoveries

[Rktman]

...I am wondering if a second similar or smaller hole bored in the body tube on opposite lateral side wall of the body tube would counter the stress, you are kicking the nose to the right, the tail to the left, theoretically no net stress on the rocket tube.

If you punch a hole opposite the existing one on the forward end of your rocket, the force of the ejection charge exiting vent holes directly opposite each other would cancel each other out and the model would not be kicked sideways as required, no?

If you instead meant punching a smaller hole near the AFT end of the rocket above the motor and on the opposite side from the nose hole, I could see how that would work to kick the nose and tail in opposite directions and get the rocket oriented horizontally.

 

[Dotini]

I vote for “falling with style.”
Without any airfoiled surfaces, I can't see how a backslider would generate any lift at all.

In conjecture, the Holy Grail of lift arises with the forbidden science of the Magnus Effect.

 

[BABAR]

If you punch a hole opposite the existing one on the forward end of your rocket, the force of the ejection charge exiting vent holes directly opposite each other would cancel each other out and the model would not be kicked sideways as required, no?

If you instead meant punching a smaller hole near the AFT end of the rocket above the motor and on the opposite side from the nose hole, I could see how that would work to kick the nose and tail in opposite directions and get the rocket oriented horizontally.

Thanks for picking up my miss, I meant to specify the second hole just forward of the mount, kicking the tail in the opposite direction as the nose.

as for the orientation post ejection, it is not necessarily known. Partly it is dependent on the orientation of the rocket AT the time of ejection.

if early, it will go off with the rocket oriented nose up, toward horizontal.

if in the midst of arcing over, it is also dependent oN WHERE the hole or holes are, so could move it anywhere,

if late, nose is down, will move toward horizontal.

thing is, IT DOESN’T matter what orientation the rocket gets from the puff, it will in ANY case at least transiently pull the rocket OFF a zero angle of attack (only exception is a perfectly straight boost with ejection at apogee with rocket pointed up, seems like this happens sometimes with HPR rockets that have relatively low altitudes, I think it is because they have so much mass the inertia keeps them vertical. The 2018 Atlas model rocket (which I think is currently the reigning champion) is an example.

the other thing is that while the puff or puffs rotate the rocket, there is no way of predicting HOW MUCH it will rotate. Agains, doesn’t really matter, basically the goal is to screw up stable forward flight long enough to get the rocket to START to fall and tumble. For Horizontal Spin alone, if fin unit is designed right, spinning force takes precedence over tail drag and the positive feedback loop and preservation of momentum bring the rocket horizontal (aka Maximum Drag Orientation [theres humor in there somewhere , but let’s not go there today] or “Falling With Style.”

if it doesn’t spin you still have a chance of BackSlide, because when the rocket is tumbling, cardboard cutout CP wins over Barrowman (for large angles of attack) so it falls backward, except that once it starts falling it gains speed and is again unstable, so it compromises and settles into a roughly horizontal glide (not really sure I get why it doesn’t just tumble, still working on it.)

 

[BABAR]

In conjecture, the Holy Grail of lift arises with the forbidden science of the Magnus Effect.

Sorry @Dotini , I keep peeing in your cornflakes . Magnus effect will be transverse to the direction airflow if rocket is falling horizontally DOWN, so it will take the rocket sideways. If the rocket is also traveling ON AXIS laterally (a true tail first trajectory combo of two vectors, one down and one horizontal but along the rocket axis), the horizontal component is NOT perpendicular to the spin, so the HORIZONTAL component of vector will NOT generate ANY Magnus force, but the vertical or FALLING vector WILL generate Magnus Force, but it is still Lateral rather than UPWARD (so not really helpful.)

I think @Dotini that what you have built is a Horizontal Spin Rocket which achieves that goal extremely successfully WITHOUT a change in rocket parts contribution (I,e. No shift of CG or CP, your ejection puff AND fin configuration switches the rocket from Barrowman Stability CP to Cardboard CutOut CP, mainly by transiently throwing the rocket off axis.)

I still thing it is Magical and really darn cool (I wish I’d tried it first!). But while Magical, it’s not Magnus-ical, even though it does generate a potentially significant but unfortunately unHELPFUL Magnus Force PERPENDICULAR to the fall vector.

lol, but if you still want to call it Magnus, my friend, go for it. It’s Aces in my book either way!

 

[Dotini]

According to this presenter, the Magnus Force is perpendicular to the flight path and to the axis of rotation. Please see the graphic and table top example of BT-70 (?) tube on table top experiment at about 2:09 into the video. Watch the tube jump up!



That said, I realize the Force is controversial and said to be impossible to demonstrate in the realm of model rocketry. The Mars Society made a much ballyhooed contest prize for advanced students to demonstrate it in one of your attachments. I've tried contacting them, and....nothing. They appear to have failed.

Even so, the Grail beckons, the forbidden seduces, and on I go. Whether it is a bunny path, a rabbit hole, or just an excuse to do my own thing, well then, okay, Aces it is!

 

[Rktman]

I think you both might be saying the same thing? Magnus Force will be present in a spinning rocket...but will only provide lift if the rocket is moving sideways through the airstream, like the tubular "wings" in this example:



The spinning "wings" would be equivalent to a body tube moving sideways. (Falling vertically doesn't count; it only provides lift in a direction perpendicular to the direction the body tube is moving, i.e. "lift" that would be applied to the side of the rocket's body only).

 

[burkefj]

This was un intentional due to a faulty CTI plugged ejection, but worked perfectly with no damage....

 

[BABAR]

Whoa there, Seattle Slew! I think there is visible Magnus Effect with models. It’s not in a useful DIRECTION, but it’s there.

Here is the MARS challenge.

Web site at end of this post

“Magnus Recovery (Horizontal Spin)

The Magnus Effect is a force acting on a spinning cylinder in a moving airstream that produces a force perpendicular to the direction of the airstream and the axis of the cylinder. The Magnus effect can be used to recover a rocket because the implied force can generate lift on the body in rotation. To do this the rocket must spin on the axis of symmetry (long axis). As the rocket spins in a horizontal angle of attack lift is generated along the length of the body slowing the rocket down. Long slender rockets seem to work well for this type of rocket. The participants of this challenge will have to design mechanism that puts the rocket into a horizontal spin after apogee. Designing and developing a successful Horizontal Magnus Recovery rocket is sure to challenge even the most experienced builder.”


I think these guy have the physics wrong. And there’s also a reason why, even thought the Magnus Force is lateral, you don’t see it much. Think about the diagram video you posted above. Now think about the DIAMETER of the body. You wanna see a lot of Magnus Force, go find some gangs in Norway or Sweden (see reference at end), oops, wrong forum. You wanna see Magnus Force on a rocket, you want a @Scotty Dog fat bottom rocket with a big outside diameter. I think we do see some lateral force, as @Rktman says, but it is minimal BECAUSE we are using long thin rockets.

As for backsliding, @burkefj ‘s video is a great example of a backside. But it violated the extremely long 30-1 ratio normally used? The reason it worked MAY have been the rocket was clearly spinning. Not sure WHY, but it was. And I think the SPIN kept it horizontal. And it was definitely NOT a narrow rocket. It’s a great video, I believe his wife does his glider videos. I don’t know if she used a monopod mount or just has a really steady hand. I am guessing she uses something better than a cell phone, she gets amazing zooms on moving targets, so I expect there is a viewfinder.

Anyway, I think your rocket definitely meets the Spirit of the MARS challenge, and on my analysis (which may not be worth much, I did great in physics in high school and college but I am far from an engineer or expert) I am with Eric, you cannot generate effective VERTICAL SKYWARD lift from Magnus Force on a falling rocket without some sort of lateral propulsion.

The Magnus Force that IS generated is lateral, and will be more evident on a wide bodied rocket than a skinny one.


https://marsclub.org/mars-challenge/
https://nameberry.com/babyname/Magnus

 

[BABAR]

SUCCESS!

Call me Buzz Aldrin to @Dotini ‘s Neil Armstrong, the second to build an intentionally spinning successful horizontal spin recovery rocket (at least in recent years.). The blue model (Nerf Dart flat nose cone thanks to @jqavins and tube fin design courtesy of @Mugs914 ) left the pad like a bat out of hell on an A10-3, I really thought the long model with a flat nose and three loopy fins would be draggy but I’d estimate it made 300-400 feet in a flash, ejection likely early.

I will post video when I get a chance, but it effectively went horizontal almost immediately, and did a tight spiral on the way down. Landed on the asphalt (about 5 feet from the grass), no damage at all. Would have flow again but the motor (friction fit) is really stuck and I will need tools to get it out.

anyway, the fin can works great, and the nice thing is I can play with putting shorter and shorter lengths of forward body tube on to see how much the “spin” assists the “SuperRoc” length in achieving safe recovery. My gut tells me I can probably succeed with a 12 inch rocket (not including nose cone)+with six 1 inch long tube fins, meaning you could build the whole thing with nothing but an 18” length of BT-5 tube, a nose cone, and a launch lug.

 

[Dotini]

SUCCESS!

Call me Buzz Aldrin to @Dotini ‘s Neil Armstrong, the second to build an intentionally spinning successful horizontal spin recovery rocket (at least in recent years.). The blue model (Nerf Dart flat nose cone thanks to @jqavins and tube fin design courtesy of @Mugs914 ) left the pad like a bat out of hell on an A10-3, I really thought the long model with a flat nose and three loopy fins would be draggy but I’d estimate it made 300-400 feet in a flash, ejection likely early.

I will post video when I get a chance, but it effectively went horizontal almost immediately, and did a tight spiral on the way down. Landed on the asphalt (about 5 feet from the grass), no damage at all. Would have flow again but the motor (friction fit) is really stuck and I will need tools to get it out.

anyway, the fin can works great, and the nice thing is I can play with putting shorter and shorter lengths of forward body tube on to see how much the “spin” assists the “SuperRoc” length in achieving safe recovery. My gut tells me I can probably succeed with a 12 inch rocket (not including nose cone)+with six 1 inch long tube fins, meaning you could build the whole thing with nothing but an 18” length of BT-5 tube, a nose cone, and a launch lug.

Congratulations on your successful flight! I'm paying close attention to your fin configuration.

Question: Were you able to see what was going on at apogee and at the ejection charge event?

 

[BABAR]

Congratulations on your successful flight! I'm paying close attention to your fin configuration.

Question: Were you able to see what was going on at apogee and at the ejection charge event?

Thanks! It was very satisfying.

weird day videoing. Everything was a sun seeker, no matter where I aimed the rod everything flew right into the sun. Also tried videoing in landscape mode with my phone camera, most of the flight I missed on video.

not sure if I was just before, at, or after apogee, but seemed like as soon as the ejection charge fired, the rocket jerked, started falling, and almost immediately went horizontal. Your rocket kind of made a very broad spiral descent, mine was a bit tighter in the spiral. It really didn’t have much “on axis” forward motion, certainly nothing I would call a glide. I think the spiral itself might be because of ASYMMETRIC Magnus Effect, but I’m not sure. It would make sense that the Magnus Effect would be stronger at the fin end of the rocket due to a greater curvature. Certainly didn’t have anything like @Rktman described, a rocket hanging horizontal and heading longitudinally for the horizon. However, @Dotini and I may be victims of our own success, I don’t think Eric’s rocket was MEANT to spin, while spinning is just about the WHOLE point of our rockets, aside from their long length. I should finish SQUIRT! pretty soon, it is a relatively short rocket set up for horizontal spin.

I think stealing @Mugs914 idea for the tube fin can with the cutout has really provided a near optimal “spin catcher”.

offhand, aside from saucers and monocopters , which are inherently low performance birds (cool, but somewhere I read a review where the RSO watching a saucer go up on a high power motor described it as “a beautiful waste of propellant.” I think that was in RocketReviews, maybe @jadebox remembers it.). Anyhoo, aside from saucers I can’t think of any other rocket that recovers safely WITHOUT some major change in geometry, from the classic deploying chutes air streamer or helicopter blade or AirBrakes, through gliders and tumblers that have either a CG shift or a CP shift or both, through featherweights which eject the motors. We may really have a decent flier (not gonna get any altitude records, but the alternatives, saucers and monocopters set the bar pretty low) that really is about a simple as a model rocket can get, IF we can make it in breakable.

 

[BABAR]

For some reason this is the only thing in my fleet I've never snapped a pic of. So here you go, fresh off my camera's SDHC card.
View attachment 457926
View attachment 457927

Okay, build it sort of along the directions

http://www.gorgerocketclub.com/wp-content/uploads/2017/03/Backslider.pdf
I used the classic 1.5” square fins, although I moved them to the rear end margin of the tube.

I made my own 3” coupler out of two roles up pieces of BT-20.

I added a motor hook.

vaccuformed nose cone weighs 1.8 grams. 2.5 “ long.

plans say CG should be 7-9” from rear end with motor in place. Is that an EXPENDED motor casing (I would guess yes) or a full motor?

it’s taking me 3.5 grams of clay stuck on the protruding MOTOR CASING to bring the CG back to 9” with an EXPENDED motor casing!

 

[Rktman]

Okay, build it sort of along the directions

http://www.gorgerocketclub.com/wp-content/uploads/2017/03/Backslider.pdf
I used the classic 1.5” square fins, although I moved them to the rear end margin of the tube.

I made my own 3” coupler out of two roles up pieces of BT-20.

I added a motor hook.

vaccuformed nose cone weighs 1.8 grams. 2.5 “ long.

plans say CG should be 7-9” from rear end with motor in place. Is that an EXPENDED motor casing (I would guess yes) or a full motor?

it’s taking me 3.5 grams of clay stuck on the protruding MOTOR CASING to bring the CG back to 9” with an EXPENDED motor casing!

Um, I think the plans specify 7" - 9" from the rear of the MAIN tube (so above the line where the lower and upper tubes meet. That would probably then require slightly less weight. I balanced mine with an empty motor casing as well.

 

[BABAR]

Um, I think the plans specify 7" - 9" from the rear of the MAIN tube (so above the line where the lower and upper tubes meet. That would probably then require slightly less weight. I balanced mine with an empty motor casing as well.

Hmmm....
First option is "28 - 30 in from the nose tip" With a 3in nose cone and a 34 in main body tube and a 2.75 in long body tube that makes the total rocket length 39.75 in so subtract 28-30" from that and you have about 11.75 to 9.75" from tail, subtract the 2.75 and you nail it. 7_9" from base of main tube..

Thanks Eric, turns out I am right at 7 inches from the BACK end of the main tube, interestingly exactly 28 " from the tip of my nose cone which is only 2.75" rather than 3", with no clay at all. I did put the launch lug at the tube-fin joint as is my habit, keeps it on the rod longer than if I put it at CG.

Weighs in at 42 grams with a loaded A8-3. Really surprised how light it came out. No paint. I did paper the fins.

Here with SQUIRT! for comparison.

 

[Rktman]

Really like the paint job on SQUIRT! Looking forward to your flight report.

 

[BABAR]

Really like the paint job on SQUIRT! Looking forward to your flight report.

fingers crossed on the flight!

I just borrowed some of that Aqua paint from @rklapp that @neil_w was so impressed with......

 

[neil_w]

I just borrowed some of that Aqua paint from @rklapp that @neil_w was so impressed with......

Thoughtful of you to help him use up that can...

 

[Ronz Rocketz]

Thoughtful of you to help him use up that can...

I have more...