There is no way that this rocket is successful, but darn it I am going to try! (Mach 5+ Composite Case 38mm rocket)

[Brainstormz123]

I'm curious to see how the fins hold up / hold on. The motor case diameter is gonna grow quite a bit with thin fiberglass and a sock under pressure, preloads the joint - ignoring temperature. From a flutter standpoint the rigidity of the joint is part of the factor.

At the day job using 55% fiber by weight (careful about by weight and by volume) 1" long 'chopped' fibers we were getting around 5MSI as the tensile modulus, and around 4 MSI for the flex modulus (D790). Molded at about 1,000 PSI and 350F. I'm guessing you are around 2-3 MSI tensile and 2MSI flex.

Look into wetting agents and vacuum impregnation if you are trying to get higher fiber volumes.

Launching at FAR this weekend?

I didnt think about deflection of the tube from chamber pressure, am calculating approximately a 3% increase in diameter.

Ive been assuming 2MSI in every direction for sims on the fins and cross checked with naca tn 4197 regarding flutter. The entire rocket also probably falls apart before then, but we can dream.

As for making the fins, ive been meaning to do a tensile and flex sample, but my fiber fraction is around 60% by mass (exactly 62.5% for the 4 fins on the rocket). Ive tried going to higher fractions, but chopped compressively molded parts make that annoying. If I am going to go through that work, ill just lay up flat plate and cut it myself. The chopped fins are just so easy.

 

[kramer714]

I didnt think about deflection of the tube from chamber pressure, am calculating approximately a 3% increase in diameter.

Ive been assuming 2MSI in every direction for sims on the fins and cross checked with naca tn 4197 regarding flutter. The entire rocket also probably falls apart before then, but we can dream.

As for making the fins, ive been meaning to do a tensile and flex sample, but my fiber fraction is around 60% (exactly 62.5% for the 4 fins on the rocket). Ive tried going to higher fractions, but chopped compressively molded parts make that annoying. If I am going to go through that work, ill just lay up flat plate and cut it myself. The chopped fins are just so easy.

What is your chamber pressure, and how thick is the sock?

 

[Brainstormz123]

What is your chamber pressure, and how thick is the sock?

Chamber pressure should be a max of around 1300psi and the sock is 2 layers of 10 thou glass (20 thou glass) and 1 layer of 40 thou carbon (12k fibers). Total thickness = 61 thou. Resulting “wind angle” of 58 degrees. Following tsai hill, with 50% fiber fraction by volume, im computing a burst of 22ksi but theres knockdowns and stuff.

Also dont trust my math, im a bioengineer by training.

Oh yeah, and launching at far this weekend.

 

[kramer714]

Chamber pressure should be a max of around 1300psi and the sock is 2 layers of 10 thou glass (20 thou glass) and 1 layer of 40 thou carbon (12k fibers). Total thickness = 61 thou. Resulting “wind angle” of 58 degrees. Following tsai hill, with 50% fiber fraction, im computing a burst of 22ksi but theres knockdowns and stuff.

Also dont trust my math, im a bioengineer by training.

Oh yeah, and launching at far this weekend.

ok, so....

50% fiber by volume is an aspirational goal with a braid like that, plus 12 tow is pretty thick for that diameter.

Assuming 50% filament wound with an angle of 58 degrees (hoop is 90) gives you a hoop modulus of about 5msi and an an axial modulus of 1.2MSI
Ignoring the glass (the modulus is so much lower than the carbon - doesnt load up until the carbon has failed).

Stress hoop - 18.7 ksi
Stress Axial - 9.3 ksi
Shear Stress, +/- 4.7 ksi

Strain Hoop .37%
Strain Axial .7%

This ignores any local loads due to the end attachment. Typically for filament wound pressure vessels it is combination of an axial angle and a hoop wrap, something like +/- 20 degree and 90 degree (hoop). I would be equally concerned about pinholes cutting the wall. I would have done a pressure test with water to check for this.

Or, bunker up and light it off....

Mike (25 years of composites as the day job) K

 

[Brainstormz123]

ok, so....

50% fiber by volume is an aspirational goal with a braid like that, plus 12 tow is pretty thick for that diameter.

Assuming 50% filament wound with an angle of 58 degrees (hoop is 90) gives you a hoop modulus of about 5msi and an an axial modulus of 1.2MSI
Ignoring the glass (the modulus i so much lower than the carbon).

Stress hoop - 18.7 ksi
Stress Axial - 9.3 ksi
Shear Stress, +/- 4.7 ksi

Strain Hoop .37%
Strain Axial .7%

This ignores any local loads due to the end attachment. Typically for filament wound pressure vessels it is combination of an axial angle and a hoop wrap, something like +/- 20 degree and 90 degree (hoop). I would be equally concerned about pinholes cutting the wall. I would have done a pressure test with water to check for this.

Or, bunker up and light it off....

Mike (25 years of composites as the day job) K

Yeah, I've considered adding other layers, but having launched a very similar motor before (linked in first post and the video there) it does hold up. The 50% fiber by volume is a measured value of this specific tube (Notebook says 51%, but math is easier at 50). 54.7 would be the idea angle from trigonometry to optimize for both axial and hoop loads (sin²(54.7°) ≈ 2*cos²(54.7°). Ideally I would do some filament wound case like GEM, but thats just not doable in my tiny apartment bedroom.

The point of the 1k fiberglass is to act as a sort of liner, but mostly to prevent the pinhole leaks. It appears to have made a lot of difference between the one that burned through everywhere and the one that "worked"

I do want to hydrotest a casing like this eventually, but the same exact process held up for a similar motor a month ago, so bunker up and light it off we go!

Some pics of the last rocket that didn't immediately burnthrough:

 

[r1dermon]

Please get wide angle video of the launch. Lol

 

[b.wieting]

I checked the flutter on these fins and it claims to be good to mach 10 (I think that has to do with the really short height and them being randomly oriented carbon, but we shall find out).

T- 45 hours to launch

You'll be at FAR tomorrow? Too bad I'm already booked for the day....

 

[b.wieting]

Not a chance. Again, you cannot use M/s/s on a 3 tenths if a second burn. 6000 M/s/s is over 13,000 mph.......
Mach 5 is 3700 mph.......
Once you realize that your burn time of the motor is only burning for 30 percent of the time the sims are estimating it to go, then you will get better numbers.
3700×.3 =1100 mph or just under mach 2.
Look up Dissappearing Act on this forum. Its a virtually identical project.

I didn’t follow this…

If motor produces acceleration A for t=0.3 sec, then crudely (i.e. neglecting other forces like drag[!] and gravity), at burnout, velocity V = A*t [of course, mass and thrust aren't constant either, but this is a first order estimate].
When A = 500G, then A = 500*10m/s2 = 5E3 m/s2
V = 1.5E3 m/s, or ~ 3000+ mph

 

[b.wieting]

In any case, an extraordinary project!
With I1299 thrust ~ 1300N & launch mass ~ 0.5kg ==> a = F/m ~ 1300N/0.5kg ~ 2600m/s2 ~ 260G

If it weren't for that pesky [~ V^2] drag force...

 

[Brainstormz123]

In any case, an extraordinary project!
With I1299 thrust ~ 1300N & launch mass ~ 0.5kg ==> a = F/m ~ 1300N/0.5kg ~ 2600m/s2 ~ 260G

If it weren't for that pesky [~ V^2] drag force...

Thank you! The thrust curve is progressive so it should get faster as the burn goes on, peaking at 500gs or so, but I expect the starting thrust to not align with simulations and instead be a bit higher. Guess we will find out tomorrow what really happens

 

[86mustang408w]

Awesome build, as I read down I agree as well. OP, pull the trigger and find out.

 

[b.wieting]

One thing I missed (pardon if I overlooked it) is how you did nozzle and forward motor closure.
Maybe you could describe when you get a chance.
Hope you have a good [no wind] drive out to FAR--looking forward to the news!

 

[Brainstormz123]

One thing I missed (pardon if I overlooked it) is how you did nozzle and forward motor closure.
Maybe you could describe when you get a chance.
Hope you have a good [no wind] drive out to FAR--looking forward to the news!

The nozzle is bonded like the aerotech single use emks, in a “carrier” and then bonded. The forward end is just a flat disk of epoxy. Here are some pictures of the first launch motor (burned through everywhere)

View attachment IMG_4967.jpeg

 

[kjhambrick]

oh by 500 Gs I do mean 500Gs (or apparently more?), open rocket says 6000 m/s/s deceleration post burnout and rasaero says 500Gs which is why I have decided that simulation software is not up to the task of this rocket. As for max speed, if the motor burns faster than simulations, the rocket will have a higher top speed because similar impulse but much much less drag
View attachment 619832

@Brainstormz123 --

What sensors do you fly in your AV-Bay ?

Will you be able to measure 500 Gs ?

Thanks and good luck today !

-- kjh

 

[Brainstormz123]

Sorry for not updating this yesterday, but launch went surprisingly well for being as stupid as it was. Ill attach video, but if you zoom in like a bigfoot sighting video, you can see the rocket in one piece post burnout. There are 3 frames of the rocket in one piece I can see post burnout, which is epic.

As for locating the rocket, I was so excited during the flight because my tracker was still beeping. Went walking towards it, and it tracked me to a random patch of sand. I spent a couple minutes looking, but that area was closeby and I would have seen the rocket come in if it were there (about 50ft from the launch tower). I think the tracker must somehow have fallen off? Maybe at apogee or if it drag separated somewhere else. As for data, I got one packet during the flight and it doesnt help much. Gonna work on getting that going faster.

Overall, im pleasantly surprised with how well this worked out and will be trying again. The rocket probably didnt land far away and someone will probably find it eventually. Will update if it gets found. The motor also appears to have burned twice as fast and max acceleration extrapolated from the video is 800 gs (thats crazy)

View attachment IMG_6801.mov

 

[b.wieting]

You're up pretty early after a long day!
Super that you captured an image in flight with that acceleration.
A thought (tho it adds some weight): paint different sections in contrasting colors, maybe that could help photographic analysis.

 

[Brainstormz123]

In addition, @zyrtyme caught some stills of my flight with his epic 60fps camera. The end of his photos (when the rocket leaves frame) should be approximately burnout if the video is to be believed. 0.1 second burn I-6000 is so unreasonable.

Forgot to mention I painted the rocket white at far to see if there would be any fun mach rash post flight.

 

[Zbench]

That does appear to be coming out of the gates like a scalded dog.

Did you in fact find the loose tracker on the ground?

 

[Brainstormz123]

Did not find the lose tracker, but also didnt look too hard (they are so tiny and was dumped in epoxy which is the same color as the sand, poor choice I know)

 

[kjhambrick]

Awesome, @Brainstormz123 !

I counted frames in your .MOV and burnout was around the 11th frame after ignition ...

frame zero ( ignition )

frame 10 ( last with any visible flame ).

frame 11 ( no visible flame )


Wow !

Sorry about the rotation but that's the way VLC captured them.

-- kjh

 

[3stoogesrocketry]

She went boom. Most likely either the nozzle let go or it just blew the bottom out . Valiant try I will give you that. You gotta do this again.

 

[Brainstormz123]

She went boom. Most likely either the nozzle let go or it just blew the bottom out . Valiant try I will give you that. You gotta do this again.

I saw that frame and was a tad confused because when the nozzle blows it, it still is at over 600psi. Should have kept flames after, but did not have any. Im not sure if it snuffed itself so i do plan on an instrumented static fire of an equivalent motor next. If the next one burns out at 0.1 seconds, then I think this flight a success (or if the rocket is found ill show it off here).

The static test will tell a lot I think

 

[Brainstormz123]

Yeah thinking more about it, no way the motor puts itself out after losing a nozzle. The motor geometry has an aggresive taper off, and it could just be shutdown. An I500 flown earlier that day has a frame that looks the same, but it definitely recovered and did not shred

 

[3stoogesrocketry]

Yeah thinking more about it, no way the motor puts itself out after losing a nozzle......

Best of luck moving forward and pushing the edge. You should think of adding a recovery device and a data logger before mastering motor dynamics.

 

[Brainstormz123]

Best of luck moving forward and pushing the edge. You should think of adding a recovery device and a data logger before mastering motor dynamics.

There is a recovery device onboard and a data logger. Its just a bajillion gs makes life hard. I dont see it as unreasonable that the beacon got ejected at apogee with the recovery.

(Either that or it shredded into a bajillion pieces, which doesnt seem likely from video. The beacon was epoxied directly to the motor casing but the shock cord could have dislodged it if it became taught very quickly which is likely from my absolutely enormous ejection charge)

 

[3stoogesrocketry]

There is a recovery device onboard and a data logger. Its just a bajillion gs makes life hard. I dont see it as unreasonable that the beacon got ejected at apogee with the recovery.

(Either that or it shredded into a bajillion pieces, which doesnt seem likely from video. The beacon was epoxied directly to the motor casing but the shock cord could have dislodged it if it became taught very quickly which is likely from my absolutely enormous ejection charge)

That would be my mistake. I thought you just had a nose cone on top of the motor. Would you do a build thread (without propellant modification or anything research) on some of your stuff. I'm curious on your construction now.

 

[kjhambrick]

That would be my mistake. I thought you just had a nose cone on top of the motor. Would you do a build thread (without propellant modification or anything research) on some of your stuff. I'm curious on your construction now.

As a @Brainstormz123 follower, there is a sufficient built thread here in this thread, starting with the first post.

But I've got some background with his builds ...

This is one of my favorite of @Brainstormz123's build threads: I500 Submin (iHop)

It is where I learned about forged composites and a kit that even I could pull off with my primitive tools

-- kjh

p.s. then there is this classic: ENTER AT YOUR OWN RISK 38mm submin w/ forged hair fins (experimental full I motor) - One Giant Leap for Mankind but you really have to read the iHop thread first

 

[Brainstormz123]

Guess I missed out on a couple pictures of the rest of the rocket. The nosecone was laid up in glass and had a bonded coupler. This was sanded to be a nice fit in the motor and airframe tube. The av bay contained the flight computer along with a beacon and was bonded to the forward closure and basically dunked in epoxy. In the nose was around 5ft of kevlar and a square of nomex. I figured that if it miraculously made it to separation, I just needed it to flat spin because this has a lower ballistic coefficient than an average estes rocket (like even the Estes alpha).

 

[3stoogesrocketry]

As a @Brainstormz123 follower, there is a sufficient built thread here in this thread, starting with the first post.

But I've got some background with his builds ...

This is one of my favorite of @Brainstormz123's build threads: I500 Submin (iHop)

It is where I learned about forged composites and a kit that even I could pull off with my primitive tools

-- kjh

p.s. then there is this classic: ENTER AT YOUR OWN RISK 38mm submin w/ forged hair fins (experimental full I motor) - One Giant Leap for Mankind but you really have to read the iHop thread first

I don't know how I missed these. Thank you for the links

 

[StreuB1]

As someone who has worked on a few (literally 3 so is that a few? lol) hypersonic projects, I can tell you this little bit.

The closer you think you are to getting there, the further away you actually are.

Those who know, know.

One thing else, the more you blow your load at the pad, the slower you are going to go. It is extremely counter-intuitive.

Cool project nonetheless!