Don't Debate This, Too

Discussions on mid/high powered model rockets using F powered motors and above.

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Passaretti
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
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Re: Don't Debate This, Too

Postby Passaretti » Wed May 30, 2018 4:23 am

air.command wrote:Thanks for sharing all the great details of your build Mike! Looks a like a fascinating project. Would it help to cool the mandrel with ice when extracting it from the tube?



air.command wrote:I am looking very closely with what you do with carbon fiber casing, as we too are in the process of making some high-pressure chambers at the moment. We are using the carbon fiber biaxial braids to make them, but size them so that when we stretch them on the mandrel the fibers are oriented close to 55 degrees - the ideal winding angle for pressure chambers. We've had a smaller one (60mm diameter) hold up 1500psi in a recent test and an 80mm one blowing out a glued-in cylindrical plug at 1250psi, but the chamber itself still held fine.


I'm all ears! Do you have a reference for the 55-degree number? I heard something similar before but could never find a source. I would also be very interested to understand how you are estimating your case strength and how this is stacking up against test results. One of my big questions right now is - what is the actual strength (vs calculated) of the material/tubes I am building? I am planning on a hoop strength tests on samples and hydrostatic pressure tests of sealed tubes. I should be in a position to start stressing the CF tube sections soon - but I'm a sponge for information from anyone that has made composite pressure vessels...

Any info would be helpful. Thanks!
Mike Passaretti, TRA 5369

Passaretti
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
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Re: Don't Debate This, Too

Postby Passaretti » Wed May 30, 2018 4:32 am

SpaceManMat wrote:Hold the nut still (weld it to an end plate) turn the rod instead (either a lock nut on the end of the rod weld a nut on). By turning the rod you can also use a drill or air gun to speed things up.


Good idea!
Mike Passaretti, TRA 5369

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Re: Don't Debate This, Too

Postby air.command » Wed May 30, 2018 11:30 pm

Passaretti wrote:I'm all ears! Do you have a reference for the 55-degree number? I heard something similar before but could never find a source. I would also be very interested to understand how you are estimating your case strength and how this is stacking up against test results. One of my big questions right now is - what is the actual strength (vs calculated) of the material/tubes I am building? I am planning on a hoop strength tests on samples and hydrostatic pressure tests of sealed tubes. I should be in a position to start stressing the CF tube sections soon - but I'm a sponge for information from anyone that has made composite pressure vessels...

Any info would be helpful. Thanks!


Here are a couple of references on winding angles:

http://iopscience.iop.org/article/10.1088/1757-899X/50/1/012061/pdf
http://www.polymerjournals.com/pdfdownload/994244.pdf

We are really not doing any calculations in terms of trying to work out the strength before hand. Since we are limited to the available CF sleeves, we just make a number of test pressure chambers and test them. There are too many factors in terms of materials and construction techniques to consider that ultimately doing an actual test gives us the most accurate results. We are trying several different sleeves to get the strength to weight ratio that will work for our application. Though we do hydro tests on these pressure chambers it is only a part of the whole picture because it doesn't take into account the temperature increase during air compression heating which can weaken the composite, and also the longitudinal compression forces during acceleration. (we're looking at around 70G for these ones)

We build our pressure chambers in two stages. The first one involves making the inner pressure chamber out of several sections that are glued together. A tube and two end closures can be easily made on mandrels and molds (plugs). These sections are thin walled (~0.6mm) and essentially form the internal liner and also give the pressure chamber its shape. Each piece is made from Carbon Fiber biaxial sleeve. When all the glue is cured we pressurise this inner liner to around 50 psi and check it for leaks. If there is a leak then its easy to fix with a small patch or a dab of epoxy. When leak free we pull one heavy Carbon sleeve over the entire thing again making sure the fiber angle is close to the optimal (at least on the widest part of the pressure chamber). The good thing about the sleeve is that it nicely conforms to the shape over which you pull it. We normally put it on dry and then work the epoxy into it using a roller. Putting it wet on a 2.5m long inner liner would be very difficult.

Here are the end closures before gluing into the inner tube.
Image2.jpg
Image2.jpg (100.29 KiB) Viewed 276 times


Here it is after gluing, and prepping to put the outer sleeve on.
Image43.jpg
Image43.jpg (141.84 KiB) Viewed 276 times


Here is the outer sleeve being put onto the inner liner
Image1.jpg
Image1.jpg (114.42 KiB) Viewed 276 times


We also put 1 layer of 85gsm fiberglass over the top of that to make the surface much smoother. We've used peel ply before and it works quite well too. The extra thin layer of glass is mostly going to be sanded through though in order to get a nice smooth finish without cutting through the outer carbon fiber layers.

To increase pressure containment you just pull on more sleeves as needed. We get the sleeves from Soller Composites. http://www.sollercomposites.com/NewSoller/index.html They have a good selection and reasonable prices.

We have used this techinque a few times in the past and seems to be working well. Last time we made the inner liner with just 85gsm fiberglass, but this time we are using CF for that as well.

We then stick the whole thing on a rotiserrie and let it rotate in front of heat lamps for a couple of hours to make sure that the epoxy doesn't pool on one side. Ideally you would probably want to stick it in a vacuum bag but we don't have the set up. You would probably also want to pressurise the inside while its in the vacuum bag so it doesn't crush it.

Although your end closures are going to be very different to what we use, this is how we make ours:
We used to machine the end closure molds/plugs by hand out of wood, but now we just 3D print them as it is much more accurate and faster to get the shape we want. We just give them a sand to make them smooth but that's all the prep they need. We then pull a balloon over the top of it to give a nice smooth finish, coat it with silicone grease and then pull another balloon over the top of that. Then we give it a very light coat of silicone and you can then directly put the sleeve and epoxy on that. To get it off the mold is very easy because the two baloons just slide over one another and the end closure comes right off. I do like how you used the heat shrink though, I may give that a go especially on concave shapes. For larger end closures we used silicone swimming caps instead of balloons. :)

I am putting together a video of this technique so will post it when complete.



Here are the final test chambers with threaded inserts for hose connection for hydro test:
image4.jpg
image4.jpg (72.12 KiB) Viewed 276 times
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Re: Don't Debate This, Too

Postby RGClark » Sat Jun 30, 2018 7:56 am

Passaretti wrote:The goal is to fly and safely recover a minimum diameter CTI N5800 rocket in a single-use composite motor case.
The target launch is BALLS 27, 21-23 September (147 days left). This project has been in the works since returning from BALLS in 2014. I've been working on it on and off since then. Unfortunately, due to work, I haven't been able to commit to a BALLS launch, but that's FINALLY not the case this year. Work on the project has increased steadily this past year, thanks to a more manageable work schedule and having a home workshop. I feel I am on a good pace for September. The stars are aligning!
Why am I doing this?
A) It's cool (Does there need to be more of a reason?)
B) It's not going to be easy,
C) I think there's quite a bit more altitude that we can squeeze out of this motor.
A big question has always been - How high or fast can the N5800 go? Well, the answer is, relatively speaking - Really high and really fast ... Exactly how much? Well, at least 63,818 ft AGL, that much we know. But the consensus seems to agree there's at least a little more left :) After my flight in 2012, Nic's in 2013 and Matt Orsak's (big props to this guy!) just this past year it's clear that what once seemed impossible, is totally possible, repeatable and there's still room for improvement. Matt's most recent flight, a more optimized version of Nic and my project squeezed out another 9,000 feet or so. Is that the limit? Of course not. So let's take what we've all learned and push that limit.
The question I asked myself following my 2012 flight was - What could be gained by eliminating my fin can? Most cans have at least 0.125" or better wall thickness. The total cross-sectional area of the rocket is increased significantly by a can or a body tube. In this case for a 98mm motor, you're talking about 10-12% reduction in area by eliminating this part which will have a significant effect on total drag. But to get rid of the can or body completely, you are committing to attaching your fins directly to the motor case. More on this in a later post ...
The second question I asked myself was, where could I shed weight - lots of weight. It's no secret that I was conservative with my 2012 design. I knew I was heavy, and I didn't care. It was never about speed or altitude for me. I wanted the damn thing to work and knew that I could make improvements later. So here I am. Where could I lose significant weight, bearing in mind the ever important rule of M2+ flights - If you don't respect and manage your CP shift - You go sideways. And nothing survives. And it's sure fun to watch. Oh, is it fun to watch. More on this in later posts ...
To answer both of these questions, I started looking hard at the aluminum motor case. If I switched to a composite case, I could drop significant weight. CF composite is about 40% less dense than Al6061. A composite case also opens up a number of possibilities for directly attaching much higher performance fins. But ... if you'd don't know what you're doing. You're asking for a world of hurt. So, I've been doing a lot of reading, and a lot of material and construction tests ... a lot!
...


I'm investigating high strength, lightweight metal alloys for aerospace use. I was pointed to a high strength steel alloy, the 17-7 PH stainless steel CH900 alloy:

Re: SpaceX second stage secret sauce?
https://forum.nasaspaceflight.com/index ... msg1626634

Based on the strength-to-weight ratio given there it is better on that measure than even carbon composites. Because it is steel it also has better heat resistance for use as a solid motor casing.

I believe it is only available in sheets or rods, not tubes. For a tube you would have to mill out nearly all the metal to get a thin walled tube. Because it is a specialty steel it is expensive so this is probably not the best cost effective solution. Most likely you would want to bend a sheet into a tube and weld the edges together.


Bob Clark
Towards an amateur cubesat launcher:

Orbital rockets are now easy, page 2: solid-rockets for cube-sats.
https://exoscientist.blogspot.com/2017/ ... age-2.html

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Re: Don't Debate This, Too

Postby RGClark » Sat Jun 30, 2018 8:19 am

BTW, this blog on high power rocketry has discussions on using the N5800 to form a two-stage rocket to suborbital space:

Friday, October 28, 2011
Are two N motors enough for space?
http://highpowerrocketry.blogspot.com/2 ... space.html

Tuesday, September 4, 2012
Bare Necessities: N5800 competition entry.
http://highpowerrocketry.blogspot.com/2 ... entry.html

Bob Clark
Towards an amateur cubesat launcher:

Orbital rockets are now easy, page 2: solid-rockets for cube-sats.
https://exoscientist.blogspot.com/2017/ ... age-2.html

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Re: Don't Debate This, Too

Postby RainierWolfcastle » Sun Jul 01, 2018 12:05 pm

Bob, I get your enthusiasm for out there design ideas. In fact I can't escape it no matter what mailing list or forum I go to, but it would probably be for the best to make a new thread and leave existing build threads for realistic material and design ideas.
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Re: Don't Debate This, Too

Postby drew » Mon Jul 02, 2018 10:30 am

RGClark wrote:Tuesday, September 4, 2012
Bare Necessities: N5800 competition entry.
http://highpowerrocketry.blogspot.com/2 ... entry.html


That's a pretty poor example Bob. That project looked good but flew terribly.
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Re: Don't Debate This, Too

Postby RGClark » Tue Jul 03, 2018 12:50 am

drew wrote:
RGClark wrote:Tuesday, September 4, 2012
Bare Necessities: N5800 competition entry.
http://highpowerrocketry.blogspot.com/2 ... entry.html


That's a pretty poor example Bob. That project looked good but flew terribly.


OK, but perhaps someone would want to do a sim of the two stage case, to see of it could reach the 100 km altitude for suborbital space.

Bob Clark
Towards an amateur cubesat launcher:

Orbital rockets are now easy, page 2: solid-rockets for cube-sats.
https://exoscientist.blogspot.com/2017/ ... age-2.html

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Re: Don't Debate This, Too

Postby drew » Tue Jul 03, 2018 11:53 am

RGClark wrote: OK, but perhaps someone would want to do a sim of the two stage case, to see of it could reach the 100 km altitude for suborbital space.


From that other link you shared (not the Bare Necessities one) I read it as the N5800 to N5800 didn't have the guts to reach space so he bolted a N10,000 to the bottom of it to make a three stage rocket.

So we would need to add a booster stage to augment the first N5800. If I use an N10,000, and use the 2 upper stage liftoff weight + 6 lbs as the empty weight for the 3-stage rocket


Given that I believe the answer to the question of "Are two N motors enough for space?" is a fairly solid NO, at least with COTS motor hardware.
Andrew Hamilton
AMRS 28 L3
AMRS Records Committee Chairman
Max Alt AGL - 23,908ft - K300 - Balls 22
Max V - 2,488 ft/s, ~Mach 2.2 - M2250 - THUNDA 2015

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Re: Don't Debate This, Too

Postby Oldboy » Wed Jul 11, 2018 8:37 pm

Into it quicker than I thought !
Now hopefully back into some hard core "wires and pliers" rocket porn .
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Re: Don't Debate This, Too

Postby RGClark » Wed Jul 18, 2018 10:14 pm

drew wrote:
RGClark wrote: OK, but perhaps someone would want to do a sim of the two stage case, to see of it could reach the 100 km altitude for suborbital space.

From that other link you shared (not the Bare Necessities one) I read it as the N5800 to N5800 didn't have the guts to reach space so he bolted a N10,000 to the bottom of it to make a three stage rocket.
So we would need to add a booster stage to augment the first N5800. If I use an N10,000, and use the 2 upper stage liftoff weight + 6 lbs as the empty weight for the 3-stage rocket

Given that I believe the answer to the question of "Are two N motors enough for space?" is a fairly solid NO, at least with COTS motor hardware.


Thanks for that. I'll continue this discussion under a separate thread subject on suborbital rockets.

Bob Clark
Towards an amateur cubesat launcher:

Orbital rockets are now easy, page 2: solid-rockets for cube-sats.
https://exoscientist.blogspot.com/2017/ ... age-2.html


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