Frangible assisted recovery

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BABAR

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Definition of frangible

: readily or easily broken

Okay, so the first question is why would you want to make part of your rocket breakable?

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The answer is that it may be a good idea to put something that's easily breakable on the rocket in order to salvage something that you don't want broken. In the case of my upscale Texas twister, the problem is this thing comes down spinning so fast that while it takes the impact on the nose cone, when this puppy tips over the fins are spinning so fast that they tend to break. So I'm going to try something different. I'm going to tape straws on the ends of them and hopefully the straws will impact, saving the Finns from breaking off which has been my experience when this thing lands on anything other than grass.

test flight Monday.
 

GlenP

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Very good concept, kind of like the landing gear struts on the Lunar Lander with a crushable core to absorb the shock, good for just one landing, and hopefully, you stick it.

Maybe add one more straw, form the mid-span trailing edge to the middle of the exposed straw? And cut a small notch in it at the middle...
 

teepot

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Maybe put one straw inside another straw so that the landing force pushes the one straw into the other one like a shock absorber.
 

mooffle

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Try some bendy straws, they may never need replacing and you can bend them to any landing position.
 

rklapp

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Another reason not to paint the rocket...:D

I just ordered one so looking forward to your results. What about longer rubber bands?
 

BABAR

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Another reason not to paint the rocket...:D

I just ordered one so looking forward to your results. What about longer rubber bands?
Be careful with the rotor stops, I got them backwards and the rotor deploys too far and the beads fall off.

longer rubber bands won’t work,, and the issue isn’t that the bands put out too much pressure, it is that with my larger surface area it spins at least as fast with far more angular momentum.
 

GlenP

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Be careful with the rotor stops, I got them backwards and the rotor deploys too far and the beads fall off.

longer rubber bands won’t work,, and the issue isn’t that the bands put out too much pressure, it is that with my larger surface area it spins at least as fast with far more angular momentum.
could you add another slice of the pie to extend the rotor stops a bit, so that they don't deploy at such a large angle? The wood grain in the rubber band slot is prone to that portion of the stop that is retaining the band to split off, you might reinforce that part of the slot with some paper.
 

BABAR

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could you add another slice of the pie to extend the rotor stops a bit, so that they don't deploy at such a large angle? The wood grain in the rubber band slot is prone to that portion of the stop that is retaining the band to split off, you might reinforce that part of the slot with some paper.
The rotor stops are intentionally orthogonal (90 degree) 2ply balsa and papered.

the stops are set for a 90 degree angle when deployed. The HINGE joints are angled 5 degrees off pure horizontal, so this is where the spin comes from.

it’s one of the things I DON’T understand about the stock Texas Twister, there is SO MUCH MORE surface available to rotate/utilize. My versions (this and Piroutte) descend much more slowly than the stock Twister, my main problem is dissipating all that angular momentum. There is also the question of how much of this or the original Texas Twister is “Helicopter” vs “Air Brake” recovery.

the question is more than just semantic.

true helicopter recovery (to me) means that as the blades turn, either the pitch or the airfoil generates lift. Now, as opposed to powered helicopters, I theeeeeenk (calling @Rktman and @georgegassaway) that helicopter rockets, being unpowered during descent, REQUIRE a certain negative pitch angle (otherwise they would never start spinning in the first place.). But on Contest versions (or simply to maximize flight duration, which depending on the size of your field, the winds, and your personal ability and/or desire to chase that puppy down) they usually are airfoiled and/or have a mixed pitch angle so the blades do generate SOME actual LIFT.

Air Brake recovery is simply reconfiguring the rocket surfaces to maximize surface area relative to vertical descent. It doesn’t really matter whether the surfaces are rotating or not. The rotor surfaces on the Apogee Texas Twister as well as my knock-offs......er, modified clones, are NOT airfoiled, and in the case of the Apogee original definitely negatively pitched (mine are minimally negatively pitched by the hinge angle.). So a good question would be, do I really buy anything by making the model spin, especially since it makes it more likely to break on landing? Would I be better off with both a 90 degree deployed rotor position AND a 90 degree HINGE angle? The rocket would have little “incentive” to spin, MAXIMUM surface area perpendicular to descent vector (although I only lose 4% from my 5 degree angle). Due to all the fins pointing in the same radial direction, it will likely spin some (ALL of my AirBrake rockets are set at 0 degree angle of attach, but those with the integrate rotor fins, where the fins radially all point in the same direction, counterclockwise or clockwise, do spin even when I don’t WANT them do!). But likely much less than the current models, which spin like crazy.

key is, Air Brake blades, even if rotating, generate little or zero lift, but they generate a heck of a lot of drag

that does it, next version has zero degree angle of attack.
 
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BABAR

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I don’t see any practical way to put a positive airfoil on the blades, since they act as fins on boost, they would cause significant spin on ascent. Would look like something launched by @rklapp ;) !
 

BABAR

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Maybe put one straw inside another straw so that the landing force pushes the one straw into the other one like a shock absorber.
I like this. I may experiment with the different size soda straws to see if I can get some telescoping. Bonus points for recycling!
 

Rktman

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The rotor stops are intentionally orthogonal (90 degree) 2ply balsa and papered.

the stops are set for a 90 degree angle when deployed. The HINGE joints are angled 5 degrees off pure horizontal, so this is where the spin comes from.

it’s one of the things I DON’T understand about the stock Texas Twister, there is SO MUCH MORE surface available to rotate/utilize. My versions (this and Piroutte) descend much more slowly than the stock Twister, my main problem is dissipating all that angular momentum. There is also the question of how much of this or the original Texas Twister is “Helicopter” vs “Air Brake” recovery.

the question is more than just semantic.

true helicopter recovery (to me) means that as the blades turn, either the pitch or the airfoil generates lift. Now, as opposed to powered helicopters, I theeeeeenk (calling @Rktman and @georgegassaway) that helicopter rockets, being unpowered during descent, REQUIRE a certain negative pitch angle (otherwise they would never start spinning in the first place.). But on Contest versions (or simply to maximize flight duration, which depending on the size of your field, the winds, and your personal ability and/or desire to chase that puppy down) they usually are airfoiled and/or have a mixed pitch angle so the blades do generate SOME actual LIFT.

Air Brake recovery is simply reconfiguring the rocket surfaces to maximize surface area relative to vertical descent. It doesn’t really matter whether the surfaces are rotating or not. The rotor surfaces on the Apogee Texas Twister as well as my knock-offs......er, modified clones, are NOT airfoiled, and in the case of the Apogee original definitely negatively pitched (mine are minimally negatively pitched by the hinge angle.). So a good question would be, do I really buy anything by making the model spin, especially since it makes it more likely to break on landing? Would I be better off with both a 90 degree deployed rotor position AND a 90 degree HINGE angle? The rocket would have little “incentive” to spin, MAXIMUM surface area perpendicular to descent vector (although I only lose 4% from my 5 degree angle). Due to all the fins pointing in the same radial direction, it will likely spin some (ALL of my AirBrake rockets are set at 0 degree angle of attach, but those with the integrate rotor fins, where the fins radially all point in the same direction, counterclockwise or clockwise, do spin even when I don’t WANT them do!). But likely much less than the current models, which spin like crazy.

key is, Air Brake blades, even if rotating, generate little or zero lift, but they generate a heck of a lot of drag

that does it, next version has zero degree angle of attack.
Affirmative. Lift achieved by 1) airfoiling or 2) by changing the angle of attack along the length of the rotor, achieved either by rotor twist/curvature (see attached Apogee Components newsletter issue 342) or by making a diagonal cut in the rotor and bending it, the technique used in eRocket's Heli-Roctor, among others, which achieves the same thing:

Heli_Roctor.png
and as described by the late great Gary Byrum: http://www.rocketryforum.com/showthread.php?139554-Helicopter-recovery (see post #2).
 

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Aeronerd

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Did you get to fly it yet? Curious to know if the straws worked an protected your flaps?
 
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