bluetube speed limit

What sort of velocity could I expect to hit with a bluetube airframe, not reinforced, before structural failure?

Hello watermelonman,
According to always ready rocketry's website, blue tube can handle mach with ease without any modifications. Heres more info https://www.alwaysreadyrocketry.com/about-us/blue-tube-2-0/

20 in a school zone

M power works well.

littlemisterbig said:

Hello watermelonman,
According to always ready rocketry's website, blue tube can handle mach with ease without any modifications. Heres more info https://www.alwaysreadyrocketry.com/about-us/blue-tube-2-0/

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Thanks, saw that but wanted to know if mach two or more was possible before reinforcement.

Yes, it is people have made minimum diamter rockets with blue tube with no problems.

Speed is not the problem, bending loads are the problem. I shattered a BT rocket (54mm MD on a CTI K1440) at around 1600 mph but I think the rocket was at highish angle of attack.

mikec said:

Speed is not the problem, bending loads are the problem. I shattered a BT rocket (54mm MD on a CTI K1440) at around 1600 mph but I think the rocket was at highish angle of attack.

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Exactly what I was hoping to see for numbers, and interesting note about the bending load. I am sure there is a correlation there and should look more into the physics.

Thanks!

watermelonman said:

Exactly what I was hoping to see for numbers, and interesting note about the bending load. I am sure there is a correlation there and should look more into the physics.

Thanks!

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And ask how an airframe got to a "highish angle of attack" at 1600mph. Bending loads on a non-maneuvering rocket are very low relatively speaking.

I had problems above mach 2 with it delaminating. I only used a short section for a fin can though.

enderw88 said:

And ask how an airframe got to a "highish angle of attack" at 1600mph.

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Either because of instability, coning, misalignments, or possibly vectored thrust from the motor. You might also be interested to read www.rsandt.com/media/Sounding Rocket Structural Loads.ppt

mikec said:

Either because of instability, coning, misalignments, or possibly vectored thrust from the motor. You might also be interested to read www.rsandt.com/media/Sounding Rocket Structural Loads.ppt

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Don't forget wind shear. That has destroyed many a rocket at BALLS. When this happens it looks like they hit an invisible wall basically.

Binder Design said:

Don't forget wind shear. That has destroyed many a rocket at BALLS.

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I had a rocket shred at BALLS 2014 myself at max-q (fins stayed on but the airframe broke at the coupler, much like my 54mm MD above), and I would love to believe in wind shear, but I'm having a hard time believing that you could have a strong enough wind shear over the length of an amateur rocket that would cause a problem. Maybe I'm just not understanding the physics. I know wind shear played a big role in the Challenger disaster but that is a different regime of scale.

I've heard that blue tube, not reinforced, starts failing at around mach 2. I've heard however that a fiberglass veil can keep it together upwards of mach two. I hope to put it to the test soon with a 38mm MD rocket.

mikec said:

I would love to believe in wind shear, but I'm having a hard time believing that you could have a strong enough wind shear over the length of an amateur rocket that would cause a problem.

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There were reports of a high number of Balls flights a few years back torn apart by wind shear IIRC.

I would think that bending load has to depend on tube length... I seen those super roc competitions, where the rocket is way too long (think Estes Mean Machine) and many of them would fold in half for no reason.

If you want high mach number you'll need fiberglass or something.

Chris Flanigan has done a lot of interesting analysis on Super-Rocs. That's an extreme case of body length and bending, but I suspect there are analogies to HPR rockets. From https://www.nar.org/wp-content/uploads/2014/08/Avoiding_the_Bends.pdf

Super-Roc models have two primary failure modes. The most common failure mode is where the vehicle crimps or buckles during ascent. This is often attributed to “my model must have hit a wind shear at high altitude.” However, as this article will describe, the problem is caused by a combination of aerodynamics and vehicle flexibility, not wind shear.

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