Mach 2 with blue tube

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Mach 2 with blue tube

  • yes

  • no

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It's not the speed that's an issue, it's how much acceleration and any side forces from non-zero AOA.

I flew an unreinforced Blue Tube rocket on a K300 to Mach 1.6; the same rocket on a K1440 folded up at max Q around Mach 2.4, but I'm not sure why -- the fin can was recovered intact but the rest of the tube was shattered into little pieces.
 
its been proven up to Mach 3 so I have to say yes to Mach 2. Also I agree with mikec.
 
I used it for a fin can that approached mach 2 once. It delaminated. I was not brave enough to use it for the upper airframe. Longer rockets will bend under high thrust.
 
ok thanks everyone. im going to go with it and see what happens:):)
 
Most airframes fail by column buckling. The overloading may either inertial and/or aerodynamic in nature, and long skinny rockets are more susceptible to it than short stubby ones so you can't always blame the failure on g-loading or velocity as it is almost always a combination of the two, and it can be enhance by coning (roll-pitch coupling) which can be a problem in high performance rockets with marginal stability.

A column is normally very strong however a defect in the airframe such as a dent or crease can act as a stress concentrator to initiate folding, or it can be initiated by resonant vibration modes of the airframe. Longer tube resonate at lower frequencies with larger amplitude displacement excursions than shorter tubes which have higher frequencies but lower amplitude displacement excursions which again is why long skinny rockets will tend to fold up whereas short rockets on the same motor will not.

The vibrations can be induced by aerodynamic asymmetry in the vehicle, or from combustion instabilities in the motor, and high thrust fast burn motors tend to have more combustion instabilities than long burn low thrust motors. A common airframe failure point on minimum diameter rockets is located at the top of the motor where the airframe is no longer backed by the motor casing. This intersection acts as a stress concentrator and pivot point for airframe rotation.

Making the airframe stiffer increases the resonant frequency and therefore make the airframe more resistant to column bucking. This is why using a thicker airframe tube or using a full length coupler glued inside the airframe can often eliminate column buckling. Cutting all airframe joint perpendicular to the flight axis to provide uniform column loading and using screws or rocket rivets to prevent joint movement will also help prevent column bucking.

Bob
 
Last edited:
bobkrech said:
Most airframes fail by column buckling. The overloading may either inertial and/or aerodynamic in nature, and long skinny rockets are more susceptible to it than short stubby ones so you can always blame the failure on g-loading or velocity as it is almost always a combination of the two, and it can be enhance by coning (roll-pitch coupling) which can be a problem in high performance rockets with marginal stability.

A column is normally very strong however a defect in the airframe such as a dent or crease can act as a stress concentrator to initiate folding, or it can be initiated by resonant vibration modes of the airframe. Longer tube resonate at lower frequencies with larger amplitude displacement excursions than shorter tubes which have higher frequencies but lower amplitude displacement excursions which again is why long skinny rockets will tend to fold up whereas short rockets on the same motor will not.

The vibrations can be induced by aerodynamic asymmetry in the vehicle, or from combustion instabilities in the motor, and high thrust fast burn motors tend to have more combustion instabilities than long burn low thrust motors. A common airframe failure point on minimum diameter rockets is located at the top of the motor where the airframe is no longer backed by the motor casing. This intersection acts as a stress concentrator and pivot point for airframe rotation.

Making the airframe stiffer increases the resonant frequency and therefore make the airframe more resistant to column bucking. This is why using a thicker airframe tube or using a full length coupler glued inside the airframe can often eliminate column buckling. Cutting all airframe joint perpendicular to the flight axis and using screws or rocket rivets to prevent joint movement will also help prevent column bucking.

Bob
Click to expand...

Thanks. The stiffness should be no problem. The motor case runs up the whole tube minus 6" at the top for a streamer and shock cord. I'm going to fly it on a J510 which is an aerotech 38mm 1320 case.


Sent from my iPod touch using Rocketry Forum
 
2007-06-mach-busted-series2.jpg

For a point of reference, a similar rocket on an I540 folds up real nice at ~1050 mph....

On a J??? Good Luck! :wink:

Bob
 
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Yep thanks will fly it on some smaller impulse motors first to see how it flys/holds up.


Sent from my iPod touch using Rocketry Forum
 
I say go right for the J510. I love that motor, and the best way to see if it'll survive a J510, is to use a J510
 
I'll avoid responding with a typical "it depends," but here goes:

1. Almost any material can be designed to go to that speed, with the operative word being "designed." Bluetube is a fairly robust material that is capable of withstanding high performance flights. The 38mm has a pretty good wall thickness for its diameter.

2. I recommend that you keep unreinforced spans to a minimum, especially around your center of gravity. This includes where your parachute resides. It may be beneficial and of relatively low weight penalty to double-wall that section with a length of coupler, just for safety.

3. As Mike Fisher pointed out, as a laminated material it is prone to delamination under duress. I'd suggest a fin profile with a long root (4-5x the diameter of the rocket) and a well formed, large-radius fillet. For this size rocket, a 5/8" or 3/4" dowel using a filleting epoxy is probably more than appropriate. I would expect that 1/16" G10 is more than adequate, no need to go thicker. As long as the root chord is as straight as you can get it the fins should be just fine with proper bonding and filleting, no additional lamination necessary.
 
SinfulDarkLord said:
its been proven up to Mach 3 so I have to say yes to Mach 2. Also I agree with mikec.
Click to expand...

Can you link me to that? I did a search and found nothing… maybe I didn't look hard enough. I am just interested in the flight profile and the design of rocket. Thanks!
 
ok thanks Dan. the root cord is 6.444'' long which is just over 4X the diameter of the body tube. I was thinking of using fiberglassed 1/8'' plywood for the fins so I can air foil them. I think that glassed plywood should be fine. I will take your advice and make larger fillets on the fins. also will have some left over coupler I can use to stiffen up the the unenforced parts of the tube.
 
A5tr0 An0n said:
Can you link me to that? I did a search and found nothing… maybe I didn't look hard enough. I am just interested in the flight profile and the design of rocket. Thanks!
Click to expand...

It used to be on the website of ARR, but it looks like they removed it. Basically it was a 38mm rocket on an EX motor. The rocket was very long. It lost a fin in flight and they claim that their tube did not shred. Reached a speed over Mach 3. The tube on the pictures looked like it was on the brink of falling apart.


Alexander Solis

Level 1 - Mariah 54 - CTI-I100 Red Lightning Longburn - 6,345 Feet
 
bobkrech said:
Most airframes fail by column buckling. The overloading may either inertial and/or aerodynamic in nature, and long skinny rockets are more susceptible to it than short stubby ones so you can't always blame the failure on g-loading or velocity as it is almost always a combination of the two, and it can be enhance by coning (roll-pitch coupling) which can be a problem in high performance rockets with marginal stability.

A column is normally very strong however a defect in the airframe such as a dent or crease can act as a stress concentrator to initiate folding, or it can be initiated by resonant vibration modes of the airframe. Longer tube resonate at lower frequencies with larger amplitude displacement excursions than shorter tubes which have higher frequencies but lower amplitude displacement excursions which again is why long skinny rockets will tend to fold up whereas short rockets on the same motor will not.

The vibrations can be induced by aerodynamic asymmetry in the vehicle, or from combustion instabilities in the motor, and high thrust fast burn motors tend to have more combustion instabilities than long burn low thrust motors. A common airframe failure point on minimum diameter rockets is located at the top of the motor where the airframe is no longer backed by the motor casing. This intersection acts as a stress concentrator and pivot point for airframe rotation.

Making the airframe stiffer increases the resonant frequency and therefore make the airframe more resistant to column bucking. This is why using a thicker airframe tube or using a full length coupler glued inside the airframe can often eliminate column buckling. Cutting all airframe joint perpendicular to the flight axis to provide uniform column loading and using screws or rocket rivets to prevent joint movement will also help prevent column bucking.

Bob
Click to expand...
Great stuff! Thanks.
 
haha ya I was thinking about that too but it also comes out to mach 2.3.
 
conman13 said:
maybe but when I do the center of pressure shift it only has 1.14 calibers of stability at mach 2.28
Click to expand...

I can't remember...does OR automatically calculate stability at supersonic levels? I know that the CG shifts during supersonic flights but I don't know how much. I suppose that's not a very good margin in either case.
 

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