Pirouette- nose up version of Texas Twister/Gyroc

[BABAR]

While building Texas Twister, I thought, "Wow, there is so much more fin area to exploit with flaps", and came up with Twinkle Toes, a work in progress.

Twinkle Toes had a partial failure on maiden flight as the piston didn't completely deploy and only 2 rotors opened. Still a safe but ungainly recovery.

Both designs still bothered me in that the recovered nose first, thus landing on both a pointy and painted finished surface, things I don't like.

For a redesign of Twinkle Toes, I thought, "heck, just make the piston longer and make SURE the retention tabs are clear." Then thought, "heck, if I can move the piston an extra inch, why not 16 inches?" If i can do that, especially with a spent motor casing in the tail end, i can swap the CG around the rotors and come in tail first.

Not a very macho name, but i am hoping "Pirouette " describes both the appearance and if it works elegance of the design.

The fins and hinges are here, I will paper them. The forward triangle is the attachment point. The surface area of the rotor is absolutely humongous relative to the Twister, and even a bit more than Twinkle Toes. The forward position of the hinge will also assist in inverting the CG post deployment compared to Twister, the CG should be well BEHIND the fins post deployment, so this rocket should maintain nose up orientation for the whole flight, unless Horizontal Spin effect kicks in, in which case it will come down sideways.

 

[BABAR]

Nose cone will be glued in, so dump base.

 

[neil_w]

That's a really interesting idea, look forward to seeing how it works.

 

[BABAR]

Custom centering rings, on this bird really function as piston gaskets.

 

[mbeels]

Ah, so the fins turn into the blades for a heli recovery, and it comes down bottom first. Interesting idea.

 

[BABAR]

Sanding off attachment points for rotor retainers

 

[BABAR]

I white glue papered the fins and stuck them in wax paper and in a book. Left them overnight. They are rock hard. I paper directly over the hinge. I will cut the paper on the open or Inside Edge of the hinge to allow it to open

Here are both sides, with the third showing the cut

 

[BABAR]

Two mistakes.

The waxed paper book drying worked great, keeping the paper pressed, the fine from warping, and the fins including hinges straight.

Mistake 1

I leave the root edge unpapered, as this will be an attachment point and fillet margin. All well and good. But the ROTOR segment is NOT an attachment point, I should have done a wrap AROUND that edge rather than leave it bare. Maybe I will put some mylar tape around it for cosmetic reasons. "Oh yeah, I meant to do that!"

2.
I should have delayed the "cut" until AFTER the fins are attached AND the rotor retainers are attached to the pistons, since right now the two "uncut" fins are perfectly straight (hinge is "fixed" flat until I cut and release it.)

I will tape the cut hinge with blue painter tape to keep it flat.

Rationale will become clearer as build progresses.

 

[BABAR]

Piston

Close up shows where the brown outer gasket (a "real" BT-20 to BT-50 centering ring) serving as outer gasket WILL be relative to my "poor man" inner gasket tape rings when deployed . Specifically the outer gasket WILL be attached to the outer body tube and the inner gaskets will BE (and in fact already ARE) attached to the inner tube.



Close up with the Piston inserted all the way.

Full-length shot with the Piston deployed also shows where the fin attachment will be between the two pieces of masking tape. You can see that the distal tip of the Piston will be well below where the fin - rotors are attached, therefore this should descend with the motor and down and the nose cone up. I think I will put the vents up fairly High probably between the fin attachment points both for strength and to make sure that the pressure is released well before the Piston reaches its full Traverse or travel. I tried something like this a while ago with a horizontal spin recovery rocket designed to recover his one piece. This was with a d motor and the result was that the rocket fully ejected and separated from the Piston. Obviously a bummer.

 

[BABAR]

I thought about decorating the Piston before attachment. However, two things dissuaded me. While certainly some color on the ballerina's "bloomers" might be kind of cool, it would add weight that is not needed, and currently the Piston slides really really well in and out, if I decorated it I would need to sand down the gasket outer gasket. Once in awhile I do follow the saying, "if it ain't broke don't fix it. "Therefore this ballerina is going to have white stockings with spiral marks.

On the other hand after she lands the Piston may actually retract back into the body. In fact, this will have a partially pneumatic Landing as when it hits the Piston will be pushed back into the body, first easily as the air will go out through the windows, but once it gets past the Windows there will actually be a Pneumatic spring effect.

Really my biggest concern is that if the rocket continues rapidly spinning as it hits the ground and tips over that the rapidly spinning rotors will break when they hit the ground. The pneumatic spring effect may relieve this somewhat.

 

[mbeels]

I appreciate your creative ideas and unique builds. This will be an interesting one for sure.

 

[DrewW]

I have lots to learn

 

[Rktman]

Very cool concept. Can't wait to see how it turns out.

 

[BABAR]

Cheaters

For aerodynamics I have tapered forward and trail edges and rounded the edge lateral to the fins

Actually the first 3 are cheaters, they will be placed BEFORE fin is attached, to

1. assist alignment
2. Speed attachment
3. Strengthen attachment by providing more surface area

The second three are essentially balsa fillets. The will be attached AFTER the fins have been attached and dried, to provide additional strength on the side opposite the cheater. Since the attachment surface for the large rotor fins is relatively small for the size of the fins, and because these are supporting rapidly spinning (fingers crossed) rotors that may be affected by impact, I figure a little extra support may be worth a little extra aerodynamic drag

 

[BABAR]

Rotor stops on left

Mid is large rotor retainers, right is small rotor retainers (reason for difference in size to be explained later)

All of these are 2 ply 1/16" balsa, with orthogonal grain directions.

The rotor stops set up a 90 degree swing of the hinge. The "tilt" (? Pitch?) Of the rotor is built into the angle of the hinge, 5 degrees.

 

[BABAR]

Cutting out attachment site for rotor stops.

Glued paper is really well attached, had to use rotary tool to get it off!

Maybe next time will premark with duct tape, should peel out easily

The brown spot on the Top Fin is some Carpenter wood filler in a boo boo.

 

[BABAR]

Tricky. Holes for toothpicks band holders

 

[BABAR]

Pegs

 

[BABAR]

Band notch

 

[BABAR]

Improving aerodynamic efficiency of cheaters aka balsa fillets

Raw

Sanded with protective tape

Sanded without tape

 

[BABAR]

Rotor retainer

Not many times I wish I had a 3d printer, but this is difficult to create with cardboard and balsa

45 degree bevel on big pieces

Attached, glue drying, fingers crossed

 

[BABAR]

Vents

Another tricky decision.

The piston stop (impact between the inner piston ring and the outer body tube ring) will have to withstand pneumatic and kinetic forces. I can VENT the pneumatic force, but the kinetic for will be from both the velocity imparted by pneumatic force prior to the vents (I don't want piston to stop too soon) plus the reaction from the ejection gas). On a model many years ago it blew the piston right out the back!

The piston needs to be deployed enough to release the rotors AND invert the CG. Since it only needs to move one cm to release rotors, and the tube is 18" (about 47 cm) long, the first part is easy.

When stowed in launch config, the piston sticks out 1.5" from the base


At full extension the piston sticks out 17" from the base

Length of outer body tube is 18"

The BT-50 nose cone with base cut off is 10 g, 4" LONG without shoulder

An expanded 18mm motor casing I have at 11 g, it will however insert about 1cm into the tube

( oops that reminds me I need to stick a motor block 6 cm into the tube. I will do that now). Cut piece of BT-20, TRIMMED to roll up inside the BT-20 piston/motor mount. Weighs just about nothing on my scale, maybe 0.1 gram with the glue. I use white glue which sets slower so less chance of gluing motor casing pusher in. I avoid epoxy when possible, just don't want to mess with fumes and gloves. Okay, ring in. Whew!

The hinge is 14" back from the forward edge of the body tube (18" from nose cone tip.)

When piston is deployed, the tail end of the piston is 20" back from the hinge point.

Deployed, UNPAINTED, with an EXPENDED motor casing, the CG is tail ward of the rotor hinges, but not much.

 

[BABAR]

I put the vent ports relatively high. A couple inches ABOVE their lowest possible location (which would be just ABOVE or NOSEWARD of the forward piston centering ring with the piston fully deployed.


Why?

1. Even though the piston can still travel another two inches (and I hope it does) the extra travel time it takes to go those last two inches HOPEFULLY will fully decompress the tube. So HOPEFULLY the only residual energy driving the piston when it hits the stop will be KINETIC. I am expecting the ejection mass will have already been converted to kinetic energy by this point.

I theeeeenk that the kinetic energy will be enough to drive the piston the last two inches (note it was NOT sufficient on Twinkle Toes, but that had a much shorter piston and vented early, so little time or travel to develop kinetic energy.)

The CG deployed without paint is tail ward of the rotors, but not much. If I need more to get this to descend motor casing first, I can add mass with some couplers in the mid portion of the piston. When piston is stowed for launch, these couplers will be at or even forward of the launch config with propellant filled motor casing in place, so they will be either neutral or positive relative to launch config stability.

When piston deploys, they will BEHIND the rotor hinge point and will hopefully pull the rocket's heinie DOWNWARD.

2. Putting the vents forward placed them between the fin attachments with the cheaters. This is by far structurally the most solid part of the tube, so if you are going to weaken the tube by cutting holes in it, this is safest place.
had an interesting flight on Texas Tornado today (not filmed)

It spun like crazy, but couldn't seem to be able to figure out which end was up! I am wondering if it is borderline Horizontal Spin and Helicopter, maybe speed of rotation changes between phases, causing it to shift back and forth.

 

[BABAR]

These designs DO reopen doors to a one piece dedicated Horizontal Spin recovery rocket. To my knowledge and personal experience, true horizontal spin recovery has only thus far been achieved by ejecting forward mass usually nose cone with or without additional weight, so rocket comes down in two pieces, the nose on a chute or streamer, the body tube/tail is unstable, spins because of the clockwise or counterclockwise position of ring fin windows, and comes down horizontally due to Horizontal Spin Effect.

If I can balance the rocket with piston deployed CG near the ring (preferably WITHOUT the ejection charge either bursting the tube or shooting the piston completely out of the outer tube) this might be a nice, unique, easily priuiepped (put motor in piston, push piston into body, put in ignitor, attach the leads, clear the launch area for safety, count down and press the button.) No wadding, chutes, streamers runner bands, no nothing. Will come in a bit fast, a little slower maybe than Tumble, definitely faster than chute and probably than streamer. Assuming it doesn't break that's a plus for a small field (or a big one.) I am not convinced spinning rocket creates much Magnus effect.

 

[BABAR]

I should adjust that Magnus comment. I think there may be SIGNIFICANT Magnus force effect, BUT the force is perpendicular to the direction of fall. So while it does technically generate "lift", the direction is LATERAL to the vertical fall vector, so it doesn't help slow the rocket directly. It DOES hold the rocket horizontally relative to the descent vector, so from a descent perspective it creates optimal maximun DRAG, so for a lightweight rocket pretty decent.

 

[Dotini]

These designs DO reopen doors to a one piece dedicated Horizontal Spin recovery rocket. To my knowledge and personal experience, true horizontal spin recovery has only thus far been achieved by ejecting forward mass usually nose cone with or without additional weight, so rocket comes down in two pieces, the nose on a chute or streamer...

Why not put the motor in the front and use its ejection for the shift in CG?

 

[BABAR]

Why not put the motor in the front and use its ejection for the shift in CG?

Interest idea. A drawing would help.

If motor recessed in main outer tube greater than one diameter (caliber) you get significantly decreased thrust due to Krushnic effect
https://www.rocketryforum.com/threads/krushnic-effect.30772/
Pdf attached below

Without recessing motor, I am not envisioning how to work piston. Maybe you can draw a pic and upload it?

Forward motors, sometimes called "tractors ", are @Daddyisabar 's specialty!

 

[BABAR]

Well maiden flight complicated by blowing out the piston.

My solution is cord attachments.

These will stop the piston 2 cm before it completely ejects. The cords tuck into the vents during launch.

I am hoping the piston will also decompress the landing shock.

Glad I didn't glue the nose cone in. I will put some graphite in to help sliding.

When I drop this vertically, nose up, it lands nicely on the casing and piston slides back up into body.

Looking forward to next launch!

 

[mooffle]

I recently rebuilt my Texas Twister and instead of a retainer ring for the piston I left it out entirely and just ran some kevlar from the nose with a screw eye to the front of the sliding motor mount. Externally the rocket functions the same but no ring to bear the force on the airframe. As of now it's a totally untested idea, hopefully that changes soon (launch in the next week or two).
I'd have commented a weeks ago but got buried in other hobbies. Super cool design, good luck on your next launch.

 

[BABAR]

"Don't know my own strength", as Bulwinkle said

well, last time the ejection charge blew out the whole piston.

this time i reinforced the piston with three kevlar threads. Tex160, whatever that means. Ejection charge blew out the motor, snapped two of three kevlar threads. The third held, the piston was retained, but without the motor the mass even with the piston extended was juuuuuuuuuuuuust shy of what was needed to bring this in nose up,

so it came down nose first, unfortunately on pavement. I don’t know how much the theoretical ”piston decompression” would have helped. The nose cone is barely dinged. Broke off a fin, more likely due to the rapid rotation which meets an abrupt halt when the rocket tips over. It’s a conceptual defect of the model which I haven’t found a way to fix yet (solved it on horizontal spin rockets with either a ring fin on the outside, or split tube fins on the SQUIRT! And other rockets, these impact on the cover side rather than the concave ”edge” side, have much narrower outer diameter of curvature AND much less mass so less angular momentum.)

anyway, next version of Pirouette gets a motor hook (usually friction fit and external tape burnished down works, but not for pistons) and bigger vents. Not sure how much the bigger vents will help, I think most of the force is kinetic energy from the motor mass.

no good video on this, it was a perfect rocket day, no clouds, no wind, unfortunately nearly ever launch was a “sun seeker” and the video view was almost straight into the sun no matter where I aimed the launch rod! @georgegassaway would have been impressed, and I did it without electronics (also without intention....)

anyway, hang time was good, it looked purty coming down slowly but unfortunately nose first.

okay, corrections required.

1. Engine hook. at first I thought that was gonna cost me effective piston length, but the outer body tube rear centering ring does NOT require a pneumatic seal, so I can cut a big notch in it that will let the piston even with the hook slide in and out.

2. Either use stronger kevlar thread or go from 3 to 6 cords. The stuff has to be “soft” as it needs to easily tuck into the vents and easily slide out at deployment.

3. Put a curved edge on the external margin of the blades, so they are more likely to slide when they hit the ground rotating (when the rocket tips over sideways after it initially hits, tail first if I get the motor weight right.

4. Since I don’t have 3D printing, it will still be easier if I mount the fin retainers on a BT-50 section ATTACHED to the BT-20 piston rather than the BT-20 itself. Gonna cost me a little bit of weight, but will be a bit more aerodynamic PLUS the fin retainers themselves will be shorter and less breakable,

5. Bigger vents. Even though I theeeeeeenk the piston and motor blow outs have been from kinetic force, I can’t ex there may still be too much unvented pressure. Still have to make sure the vents are placed so the piston travels AT LEAST as far as required to get the CG below the rotor hinges to get this puppy to fall nose cone UP.