homemade casings for rockets

[FredA]

beeblebrox - chill!
Yes, you can wind whatever angle you want....and perhaps 55 is the best...but there's NOTHING in the RULES regarding wound cases or liners, which is what your language implied.
That was my point.

 

[grouch]

Toy rockets guys....just toy rockets.

 

[cbrarick]

Seriously. This is getting to glue thread level of emotions!

Back to the OP. If you're buying the grains why would you go thru the bother of making a case? they're pretty available and at a fairly cheap price considering that someone had to make it. if you have access to a machine shop and have lots of time to kill, and are able to machine (experience & knowledge) then look at the CAR rules or come on down to your local TRA USA club.....just seems like a lot of effort for a little gain (unless you're a machinist, machinist want-to-be.
Now, full on EX is a different story, but you seem to be a little young for that.

 

[Ez2cDave]

Seriously. This is getting to glue thread level of emotions!

Back to the OP. If you're buying the grains why would you go thru the bother of making a case? they're pretty available and at a fairly cheap price considering that someone had to make it.

My best guess is that the OP wants to be able to "stack" Bates grains in configurations that are not commercially-available . . . Most likely, extending the motor length to increase Total Impulse, without increasing motor length. Depending on the "configuration", I see burn-through's and /or over-pressure's looming on the horizon.

Be careful !

Dave F.

 

[mholmes]

@beeblebrox the link to the journal article is broken, could you provide a title so I can hunt it down? (If this 8 year-old thread can be revived)

 

[SolarYellow]

^^^That follow-up request is likely to work better with a quote or tag.

Wind angle is important. 55 degrees is optimal for rocket motors constructed of straight cylinders of filament wound material. That does not mean that other wind angles wont work. they just wont be as strong. BUT if the case can withstand 2000psi with optimum wind and 1000psi with non optimum wind for example, running the motor at 500psi wont be a problem. not trying to do a full class on motor design, but why not use what other engineers have determined to be the best? look at this for some information...
https://www.polymerjournals.com/pdfdownload/994244.pdf

 

[CoyoteNumber2]

@beeblebrox the link to the journal article is broken, could you provide a title so I can hunt it down? (If this 8 year-old thread can be revived)

The Wayback Machine is your friend.

 

[MarsLander]

https://web.archive.org/web/20180619132902/https://www.polymerjournals.com/pdfdownload/994244.pdf

 

[kramer714]

Wind angle for the case is VERY important, it affects the overall pressure rating, but, as important it affects the mode of failure and the case deformation under pressure. Also important to the wind angle is the method used to hold the ends on.

At the day job (ok actually previous day job designing filament wound pressure vessels) we ALMOST never used a single wind angle. For pressure vessels there was ALMOST always a hoop wrap in addition to an axial wind. The hoop wrap is important during consolidation and cure too!

Mike K

P.S. Vitrify low, postcure, and understand thermal stresses and strains under loading.

 

[rocket_troy]

Wind angle for the case is VERY important, it affects the overall pressure rating, but, as important it affects the mode of failure and the case deformation under pressure. Also important to the wind angle is the method used to hold the ends on.

It might be worth adding that an equal pressure rating can be attained with non optimum winding angles, it's just the casing wall will need to be thicker and the vessel heavier than for optimal winding.

TP

 

[tfish]

The wind angle for a motor case might not be good for a body tube.

A refurbished AT O525O with 22 pounds Swamp Gas. Fins glassed to the motor case. Another section of FG motor case used for recovery bay.
Rocket folded between motor FC and nose cone shoulder.

Tony

 

[rocket_troy]

The wind angle for a motor case might not be good for a body tube.

A refurbished AT O525O with 22 pounds Swamp Gas. Fins glassed to the motor case. Another section of FG motor case used for recovery bay.
Rocket folded between motor FC and nose cone shoulder.

Tony

The optimal wind angle for a body tube would be completely different to a motor case. A motor case is a pressure vessel pure and simple. A body tube has no internal pressure. Most of the load will be from longitudinal buckling (from compressive forces) and bending moments and whatnot and it would rely on the rigidity of the resin much more than a pressure vessel.
Saying that, I'd be surprised if a composite motor casing being repurposed as a piece of body tubing would fail as a body tube because the stresses a motor casing experiences (both radial and longitudinal) generally far surpass those experienced by body tubing - unless it was an unusually low pressure motor. However, again, because a body tube has a greater reliance on the resin rigidity and is exposed to compressive stresses that a motor casing isn't, it's more susceptible to buckling from thermal softening of the resin within the composite. Also, composite pressure vessels are often manufactured with the minimal amount of resin required for the application ie, just enough for the fibres to hold their places to the accompanying structure they're bonded to as it's basically relying completely on their (the fibres) tensile strength to support the stresses. Not ideal for body tubing.

TP

 

[SolarYellow]

The wind angle for a motor case might not be good for a body tube.

A refurbished AT O525O with 22 pounds Swamp Gas. Fins glassed to the motor case. Another section of FG motor case used for recovery bay.
Rocket folded between motor FC and nose cone shoulder.

Tony

I would agree with that. It appears that the case had no longitudinal fibers. With the wrap angle being so far off the longitudinal axis, it was basically relying on the tensile strength of the adhesive to resist bending on the tension side. With the comments above about potentially sub-optimal resin content, plus the fact that the fibers constitute a massive number of very small-radius potential crack initiation sites when loaded in the transverse direction, the failure is not totally surprising.

 

[kramer714]

I would agree with that. It appears that the case had no longitudinal fibers. With the wrap angle being so far off the longitudinal axis, it was basically relying on the tensile strength of the adhesive to resist bending on the tension side. With the comments above about potentially sub-optimal resin content, plus the fact that the fibers constitute a massive number of very small-radius potential crack initiation sites when loaded in the transverse direction, the failure is not totally surprising.

Yeah, a few things to unpack here,

• Motor Case - Under Pressure BETTER body tube, so the motor case stress go DOWN axially if it is also the body tube. Easy to think about, the pressure creates axial stress in tension, during launch on a 'body tube less design' the tube is in compression, canceling out some of the axial forces.
  • Having pressure will increase Brazier buckling loads (high load to failure)
  • Centaur was (is) actually stabilized by the pressure in the tank.
  • Another way to look at this is to understand there is no axial forces on a tie rod cylinder just hoop
• For a body tube if you just had axial fibers (bamboo fishing pole) the tube would be VERY susceptible to Brazier buckling, and have a VERY low impact and damage resistance,
  • Low angle winds are very poor for voids and fiber volume. (wet wound without vacuum bagging)
  • adding 10-20% hoop wrap significantly improves the laminate quality, and significantly increases the buckling resistance / impact resistance
• For a pressure vessel wind (without integral domes) having a combination of hoop and axial fibers increases the damage tolerance, reduces the hoop strain, and produces a better laminate than a single angle.
  • For a pressure vessel (without integral ends) you want something like +/-20 degree and 90 degree fibers (hoops)
  • About 40 percent by thickness +/-20 degree fibers, and 60 percent by thickness hoop wrap
• During heat cure, Carbon hoop fibers have a lower CTE than the mandrel, compressing the laminate

Lots of the failures I see are due to buckling and or poor consolidation of the laminate. Another thing is using the wrong resin. Just because you can wind a resin doesn't mean you should. Laminating resins are usually poor filament winding resins. Plus using surfactants / de foaming agents and keeping the fibers and resin DRY and warm during winding all add to the overall strength.

Keeping with a theme of providing unsolicited advice, try Atomic brand horseradish, a condiment that will change your life. They cut it with a little parsnip still hot but a really good flavor. Try adding some to coleslaw with a little celery seed. or mixed with good mustard.

Mike K

 

[SolarYellow]

Another section of FG motor case used for recovery bay.
Rocket folded between motor FC and nose cone shoulder.

Yeah, a few things to unpack here,

• Motor Case - Under Pressure BETTER body tube, so the motor case stress go DOWN axially if it is also the body tube. Easy to think about, the pressure creates axial stress in tension, during launch on a 'body tube less design' the tube is in compression, canceling out some of the axial forces.
  • Having pressure will increase Brazier buckling loads (high load to failure)
  • Centaur was (is) actually stabilized by the pressure in the tank.
  • Another way to look at this is to understand there is no axial forces on a tie rod cylinder just hoop

I understood tfish's post and photos to mean the part that failed was not the pressurized part. It was the recovery bay part, which appears to have no axial fibers, just 45 degree-ish angled wraps.

 

[rocket_troy]

I understood tfish's post and photos to mean the part that failed was not the pressurized part. It was the recovery bay part, which appears to have no axial fibers, just 45 degree-ish angled wraps.

What's more, what happens at burnout in the case of utilising internal pressure for tensile rigidity. Works well for tanks, but not so well for motor/combustion chambers.

TP