Upscale Modified Texas Twister

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BABAR

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I built but haven’t flown the apogee Texas twister. Neat idea. I think it can definitely be improved on. The surface area for the movable sections of the fence is certainly much less than it is possible. Also would like to upscale it to use standard 18 mm motors. This is the last of my Custom Rockets Fiesta
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custom r pack. I bought I think a 12 pack 10 years ago for around $10. Really like the nosecone. Salvage an extra body tube and the engine mount will work perfectly. We’ll see how it goes.
 
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BABAR

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I really like the fiesta nosecone especially for this Rocket. Given the Rocket descends pointy side first I am kind of glad the pointy side isn’t quite as pointy. It is also seamless and it fits extremely well into the body tube. Here it is compared with a standard Estes BT 50 nosecone and the Apogee Cone.
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BABAR

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Major mod from Apogee version is single rotor stop.
These are going to be a two ply 1/16” , with grains opposed.

1” quarter circle. I will clean up the edges after gluing
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the actual fins are 1/8”
 

BABAR

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The piston release mechansim on the Twister uses three centering rings, two on the piston, one o the end of the outer body tube. I think it can be done with just two

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BABAR

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vents, which will release any excess gas after piston deploys
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BABAR

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Since I don’t have a three D printer, I will need to create my own “plastic flap guide ring” equiavelent.

first, the 1/8” spacers, sanded so the are even with the lateral margin of the main tube.
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neil_w

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How big do folks think those vents really need to be for a 13mm ejection charge? Asking for a friend.
 

DrewW

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@BABAR is the idea with the TT that the ejection charge gasses blow out the exhaust ports and change the flap position?
 

BABAR

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How big do folks think those vents really need to be for a 13mm ejection charge? Asking for a friend.
Not a clue. This is upped for 18mm motors. On this case (which is NOT similar to staging), I think bigger is better except when it gets so big it compromises the structural integrity of the outer tube. So this is basically eyeballed and mind-simmed.
 

BABAR

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@BABAR is the idea with the TT that the ejection charge gasses blow out the exhaust ports and change the flap position?
The ejection charge initially is released (exploded? Expanded?) into a closed space, equally pressurizing the entire space forward of the piston. The piston however is (hopefully!) the only part that can move, so both the force of the pressure (and actually the action-reaction bit, since the net has output is forward out the wide open front of the casing versus the small bore nozzle) drive the piston (with the flap holder) BACKWARD.

the VENTS, as I understand it, are to prevent OVER-PRESSURIZING the rocket, I.e., bursting the tube. They are only exposed AFTER after the piston has slid Back to the “Release Flaps” position.
 

BABAR

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Two concerns I DO have.

I kind of wish I had used a longer motor mount and lined it with an aluminum can inside, as if you have ever seen a test motor fire (just in free air, not in a tube) there’s regular old candle like flame that comes out the forward end of the casing for a few seconds. Normally this doesn’t burn anything, I think because there is little air flow (the event in NORMAL rockets occurs inside a body tube open only at the far end.

the second concern I have is for the flaps. I am putting a 5 degree incidence angle on the flaps (when deployed, they should be straight on boost, unless I go to Hawaii and launch with @rklapp ), I suspect this puppy is gonna
Spin like crazy. It’s gonna land nose first, but then tip over. The inertia of the spin may break a flap when it tips over.
 

BABAR

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Put the side pieces on over the spacers, ADDED waxed paper coated spacer
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mooffle

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How big do folks think those vents really need to be for a 13mm ejection charge? Asking for a friend.
I've asked this before myself and after making a couple rockets like this (not enough to have great fact based evidence, just anecdotal opinion) I go with holes marginally bigger than the engine ID but smaller than the OD. For a 13 mm engine with a 10mm ID, two or three holes with surface area equal to 11-12mm.

@BABAR your mindsim vents look about the same as what I would've done and scaled in line similar to the original Twister.
 

BABAR

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I've asked this before myself and after making a couple rockets like this (not enough to have great fact based evidence, just anecdotal opinion) I go with holes marginally bigger than the engine ID but smaller than the OD. For a 13 mm engine with a 10mm ID, two or three holes with surface area equal to 11-12mm.

@BABAR your mindsim vents look about the same as what I would've done and scaled in line similar to the original Twister.
I am trying to think of the alternative reasons (aside from a piston) for venting.

first I think of is for gap staging. I believe there was an actual sounding rocket that had the booster coupled by struts of girders to the sustainer. The actual bird presumably had electronic staging of the booster (I have no inside knowledge of how two stage sounding rockets actually worked.). More pertinent, there WAS I believe a two stage model rocket built on this design, and it was gap staged, and the gap (which I think was only an inch or two) was COMPLETELY open, with just 4 or 5 struts holding the two together. The key was that the struts held the sustainer and its motor directly in front of the booster motor. For practical purposes it was an infinite size vent.

My point here is that for staging vent placement rules are like Real Estate, Location, Location, Location. They can’t be too big. Obviously they CAN be too small. For 18 mm I usually use two standard notebook paper size hole punch holes, I put them on opposite sides on the theoretical chance that I put it on one side, it might, during staging, produce an asymmetric fore throwing the rocket off vertical. Probably just a rabbit’s foot. The LOCATION must be either just AT the tubing below the sustainer motor (for minimum diameter staging where the sustainer motor “nests” in the booster), or for non minimum diameter with a chimney or stuff “guide” tube, leave a 1/4” (or so) gap between the end of the extended motor mount and the sustainer motor nozzle, you can literally put the vents just about anywhere except the motor mount itself, you can even use “open” booster centering rings (holes or gaps in ALL the centering rings) and vent the gas BACKWARD put through the tail. This is both an aerodynamic as well as cosmetic solution, as there are no unsightly holes in your streamlined outer surface and @neil_w. Doesn’t have to come up with a decal that says “Caution: Plasma Vent.”

second one I think of is cluster motors where you afraid if all the clusters ejections fire at once, you will overpressurize the tube and rupture the tube. I am curious if anyone has ever HAD this happen, I don’t fly m any clusters of this type, all except one have been staging clusters and this is not an issue. Here again, I don’t think you can make the hole TOO big, with exception for structural soundness and cosmetic and possibly aerodynamic compromise. Again I think an element solution is big gap (say 1/2” or larger) forward of the tube, some sort of flame resistant substance on the bulkhead directly in front (maybe JB Weld?), and vent the gases out the back between motor mounts.

third I can think of is outboard motors that are not ejected. These are likely best dealt with by plugged motors. (Ideally PURCHASED as plugged motors, I don’t want to start going down the “user plugged” motors rabbit hole, except to note that user plugged motors are at best strongly frowned upon if not outright refused at sanctioned NAR launches. I failed the Tripoli I.Q. Test, so I can’t speak for them ;) YMMV). If I WAS using retained outboard black powder motors, I’d definitely go with zero delay motors, no dedicated ejection charge (but still potentially significant force.). If not minimum diameter I would try to duct out the rear as for the clusters above. If minimum diameter, not sure, probably at least a total surface area of holes the size of the internal bore of the forward end of the motor, and LOTS of internal surface coating (again, maybe JB Weld?) as the inside would get repeated fried, assuming you have more than one successful flight!

the fourth and last case I can think of (there are likely more) is motor eject gliders, like I think the Hawk and Falcon. These out a hole up front presumably for PARTIAL venting, as the motor is intended to eject. For these, for 18 mm I always put at least two holes (standard hole punch size) one on each side, so there is no lateral force to break the boom. My suspicion however is that most broken booms on these are due to the motor ejection, which especially with Estes “Shotgun Blast” is a really big force. Because of the pylon, THIS force is off axis to the boom, and I suspect it forces the nose forward and downward, snapping the boom between the base of the pylon and the tail assembly. Just a guess.

interestingly I think @Rktman quoted Rob Edwards as saying that the nose cone on his models INTENTIONALLY partially covered the hole in his motor eject gliders. Given his incredible series of easy to build and successful gliders, Mr. Edwards certainly should know.
 
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Rktman

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I've asked this before myself and after making a couple rockets like this (not enough to have great fact based evidence, just anecdotal opinion) I go with holes marginally bigger than the engine ID but smaller than the OD. For a 13 mm engine with a 10mm ID, two or three holes with surface area equal to 11-12mm.

@BABAR your mindsim vents look about the same as what I would've done and scaled in line similar to the original Twister.
I've also heard this from Tim Van Milligan (Apogee Components), that the total vent area should at least equal the ID of the motor you're using.
 

BABAR

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I've also heard this from Tim Van Milligan (Apogee Components), that the total vent area should at least equal the ID of the motor you're using.
Hmm. I doubt three notebook paper punch holes equals the forward area of an 24 mm casing, and I have yet to have a staging fail from premature separation. Then again i think he actually worked for and got paid by NASA, I just built a few model rockets for them ;) . I also do much longer gaps, he says you can gap "up to 11 inches," it has been years since I have gapped anything UNDER 15 inches. So my rockets are less susceptible to rapid overpressure.

Anyway, for up to 24 mm motors I haven't needed more than three standard punch holes.
 

BABAR

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Ye old duct tape double tape hinge, and paper to cover.

I now only sew the dental floss into the edges of the hinge.
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BABAR

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The "divot " out of the medial base of the fin helps it fit better into the retainer section
 

BABAR

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Cheaters to help line up and support the fins
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BABAR

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BABAR

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Coming along.

Will cut back and round toothpicks
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BABAR

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BABAR

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Homemade coupler. Two pieces of bt-50 tubing rolled inside each other roll to fit inside a bt-50.
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BABAR

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Was a little loose. Added a layer of tube and some tape
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Rktman

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That extreme flap angle should really ramp up the spin rate on the way down! 👍
 

BABAR

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That extreme flap angle should really ramp up the spin rate on the way down! 👍
Actually your input would be interesting (I’d say helpful, but at least for this rendition, I think I’m already too far committed to change anything!)

other than rounding the fin edges (and the base of the flap edge is left flat, since it is against the tube on boost, even though it isn’t glued, I didn’t see any point in rounding it), so no real air foiling.

I think I built my Apogee Tornado wrong, as when deployed the flaps are at about 90 degrees. Which actually Is optimal for Air Brakes
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above pics, the rotating one from the Apogee site, the second from Amazon, show what looks like 45 degrees.

while I can definitely see the flap movement greatly increasing DRAG, it doesn’t seem like it would generate much LIFT.

PLUS, the flap is relatively small.

I guess I will see how it flies, more importantly how it recovers. I am thinking my kit model may not spin much if at all, given the stops as I placed then are resulting in a 90 Degree angle rather than 45 (I think I got the angles backward.). But if, as I suspect, the flaps when deployed aren’t generating any lift (no matter HOW FAST it spins), but really are only there for drag, my model should slow down more.

in any case, I don’t understand why the original model was designed with such relatively small flaps? mine are huge in comparison, I could have gone for more but I figured I needed a certain amount of surface area for actual attachment, and I didn’t want to make the tape hinge too narrow.

on my version, the flap rotation is actually ALSO (and intentionally) 90 degrees relative to the HINGE, the hinge line (plane?) is however 5 degrees off true lateral (also intentional, as I wanted to make sure this DID spin.)

so I am curious (okay, let’s be honest and say “ignorant”) on your comment that my angle is “Extreme”. Emphasize this is not a defensive reply, I really don’t have a clue what optimum would be. I just figured 5 degrees oughta be enough to at least get it started.

also not sure if my flat non-airfoiled flaps will generate much lift. IIRC flat blades spinning DO generate some lift, but it is minimal compared with airfoiled rotor blades. If not, then essentially all my helicopters since the Gyskelion and Whopper Flopper Chopper have really been AirBrakers from day 1, they just happen to spin as well. And I’m okay with that.

appreciate your interest and would like your thoughts, as always.


 
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Rktman

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While not packing the airfoiled surface area of a heliroc's rotors, your flaps are relatively large in relation to the rest of the rocket and even if the rotation doesn't provide the same amount of lift, they should provide quite a bit of drag resistance.

Suggestion: lighten the load by kicking the motor and engine tube out on a streamer. That would help to lighten it quite a bit. The prototype drag brake rocket I built a couple of years ago used this method to drop enough weight so that the rocket came down much slower then the motor and streamer did, and there was never any damage sustained. (Of course that would mean having to remove the rear CR, something you might not want to tackle until after you've flown and evaluated it the way it is). Just a thought, hopefully it works well the way you have it set up.
 

BABAR

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Suggestion: lighten the load by kicking the motor and engine tube out on a streamer. That would help to lighten it quite a bit. The prototype drag brake rocket I built a couple of years ago used this method to drop enough weight so that the rocket came down much slower then the motor and streamer did, and there was never any damage sustained. (Of course that would mean having to remove the rear CR, something you might not want to tackle until after you've flown and evaluated it the way it is). Just a thought, hopefully it works well the way you have it set up.
Definitely do-able, but I get nervous when I try to get an ejection charge to do more than one thing, in this case you are asking it to deploy the piston AND eject the motor, and obviously must be done IN that order. That's a little risky.

Another question about lift, these "rotors" are so big and so close to each other that I suspect that the "prop wash" or whatever you call it might spoil any possible lift as well.

My suspicion is that the original Gyroc, the Rebranded Tazz, and the Apogee Texas Twister are really more Air Brake than helicopter recovery. Doesn't take anything away from them, it is a relatively uncommon and apparently effective and safe recovery technique. If NAR ever gets back open to competition flying, if all the days were windy days one of these birds might win the duration copter competition, as they would be the only birds likely to be actually RECOVERED!

Anyway, I should finish this bird, and I've already started painting the Apogee Texas Twister, so a "fly off" will likely take place the next good rocket flying day I get.
 
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