Rocksim file design 98mm (N5800) What you think?

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I went ahead and took a look and I like it. I just have some advice about the fins. You should consider down-scaling them for more stability and less drag. Overall awesome design. I have begun making plans for myself.
 
So, this particular motor has consumed 16 or 17 all-composite minimum-diameter airframes.

What are you doing that's so radically different that you think yours will work?

The two that have worked (Mike Paseratti and Gerald Meux) both used significant aluminum components.

-Kevin
 
So, this particular motor has consumed 16 or 17 all-composite minimum-diameter airframes.

What are you doing that's so radically different that you think yours will work?

The two that have worked (Mike Paseratti and Gerald Meux) both used significant aluminum components.

-Kevin
+1 on Kevin's question.

DISCLAMER: These are just observations from previous attempts and my opinions on the logical way of handling this motor. I'm not smart, but I like to pretend like I am.

I honestly don't think this can be done with hobby grade composites. Most epoxy's TG is wayyy to low to withstand those temperatures. With very expensive, high grade composites it might be possible, but anything in the hobby realm wont stand a chance unless it's EXTREMELY overbuilt.
If you are looking for a cheaper rocket (and "cheap" is very relative) to handle the N5800, I'd go with aluminum or other lightweight metals.

Also, for a more accurate Altitude prediction use RasAero. Rocksim will not be accurate at those speeds.

Alex
 
Reality check!! I know that its gonna take more than just hobby epoxy for this build. I am in the process of trying to find a certain kind of epoxy that could possibly take the heat. I am willing to entertain ideas.
My ideas are to make the booster section a short as possible to still allow clearance for the coupler, motor, motor retainer, and shock cord. As for the payload section I am making it as short as possible to have enough room for coupler, shock cord, parachute. The shorter the rocket I predict that there is less a chance of it folding over onto itself. In the areas where there is shock cord and or parachutes I will be adding another coupler. So on top of the aeropack retainer I will glue in a coupler then the ebay and switch band will sit nice up to. As for the payload a coupler will be glued in on top of the ebay and then when the nose cone is in place it will sit on top of that coupler. I also plan to use the shortest shock cord possible and the smallest skyangle possible. With altitudes I am gonna see I want it to come done faster. My thinking in recovery is that the least amount of weight I have in the rocket the better. When it is pulling the amount of G's its gonna pull extra weight of recovery is going to be like a lead weight, its gonna slamm down on the internal parts of the rocket.
There will be a double wall throughout the airframe and least amount of recovery. My thinking is this will also help to eliminate folding over.

Andrew
 
Could you please elaborate on you statement?


It would not make 2000ft before shredding. Fin root is 2ft long, you are just inviting harmonics & fin flutter.

What ever you build, if you can put it in a fixture with the fins supported on tips, place 700-800lbs on the airframe,have the fins still be there................................ you may have a shot.

This is just one of the design matters that must be overcome.

I am not being mean, you asked for what some of us think & I am answering based on 2yrs of design work I have been doing also. Plus discussions I have had with engineers, machinists, welders and many others in aerospace industry. One does not have to re-invent the wheel to do this, one just needs to do some research into sounding rockets of the 50's............. it's all there.

I firmly do not believe this can be done with composites UNLESS one is at the level of Boeing or Lockheed & has access to such materials & techniques.
For now I see metal in the immediate future for this type of flight, why argue with success?


Now that I have turned the hounds loose on the composite issue, I'll just wait for someone to prove my theory incorrect.


PS. Have you read Mike P's summary of design and flight? There is much proven info there.
 
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Dam CJ, you ole heart breaker you!

Hoooowwwwwllllllllllllll!!!!

imagesThis-is-the-guy-who-let-the-dogs-out.jpg
 
Rocksim won't run on my machine, but just to confirm - all the fins are lightweight honeycomb covered in carbon fibre, the way monocoque race car bodies are done?
 
This idea could be completely off the wall. Remember when on Mythbusters a long time ago. The guys were trying to break a glass with someone singing. The sound had to get to the correct frequency to match the glass in order to break it correct? Is there in some way to reverse that? A rocket traveling as fast as it does with a N5800 is going to shred it at a certian speed/frequency. As far as we know it seems to be that when you take just composites at those speeds/frequency it taking its tole on the rocket, enough to vibrate everything apart. From previous people who have failed at this project with just the use of composites its not working. But those who have succeeded are those who use aluminum/metalic construction. The speeds/frequency at this rate using aluminum/metalic does no cause as much damage, the rocket is flyable again/survivable.
Now the million dollar question. Is there a way to change the frequency at which simple composites vibrate/rip apart? Something that can be put on or done to the rocket in which it raises or lowers its frequency that its not going to rip apart.
Similar to putting high temp paint on an engine block to lessan the amount of heat transfer. Another thought is how they put sound deading insulation around music studios so that it does not let exterior noise in and does not allow interior sound to escape.

Just something that I thought up, may be crazy but IDK
Andrew
 
Mass distribution, stiffness distribution (and orientation with composites), choice of materials for dampening properties (Kevlar for instance has high dampening whereas carbon fiber has low), physical geometry, aero effects...

CP migrates as a function of speed and alpha. That is part of what makes the job more difficult. Otherwise one could pretty much make a fin with mass centered at the CP for the fin and then make it stiff enough to handle bending loads at a maximum design alpha at max Q. Bending could be designed to be perpendicular to the airframe (or pretty close) so one wouldn't get flutter. Think mass distribution on airplane wings, for instance. But it gets uglier here due to the wide speed range and the movement of CP. One needs dynamic stability over the expected speed range and alpha range.

Honeycomb core structures require careful attention to bonding between the core and the skins. The bond surface area is small. Therefore the loading per unit surface area of contact between the core and the skins is much higher. There may not be a margin for loss of structural properties due to heating the bond, for instance.

Sorry for rambling a bit.

I'd suggest perhaps mass balancing the fins to match the expected CP range around max Q. And then including some materials in the structure which are good for vibration absorption - as well as paying careful attention to torsional stiffness. It seems when I've seen pictures of tip-to-tip work the fibers are often oriented 0-90 for all layers. That provides the greatest bending stiffness (for a fabric layup) but the least torsional stiffness. Also note that only half the fibers cross the tube to fin boundary, and the axial fibers on the body tube likely accomplish nothing structurally. A better structure may be IM unicarbon tip-to-tip, in a shell of carbon spread tow fabric at a bias. IF the bonding properties are not compromised, then having Kevlar on a bias in the structure would be a good plan as well to greatly increase dampening of any oscillation which arises in the twist direction.

From a simple physics perspective, if your dampening exceeds the rate energy is added to the system, then oscillations decay. All carbon structures are lousy at dampening. All Kevlar structures are very good at dampening, but suffer from other structural issues. Glass is not that great at dampening (not compared to Kevlar at least). I have no idea where Basalt properties lie, or boron. But it is likely that if one wants to persue composites there are better ways to do them then the typical examples one sees.

Gerald
 
Short of CFD, is there a fast or convenient way for individuals to calculate the Cp(Mach) curves for just the fin?
 
https://tripolimn.org/files/Nose Cone & Fin Optimization January 2011.pdf - I ran across this again when searching for a quick and dirty answer for you. You might find it interesting.

Anyway, I don't have a quick cheap answer offhand. The software I usually use for analysis is optimized (and tested) for subsonic and I generally do most of my engineering for wings in the lower Reynolds number range and far below sonic speeds. Perhaps someone can recommend something easy and cheap with proven accuracy for the mach 1-5 range. I use RasAero for full rocket sim but I'm not sure what to trust for reliable answers for just the fins. I have not researched the problem sufficiently.

Gerald
 
Cool!! What I thought about tip to tip is 1st layer of 5oz 2x2 twill Kevlar, 2nd layer 5.7oz 2x2 CF Twill, 3rd layer 5oz 2x2 twill Kevlar, and 4th layer 5.7oz 2x2 twill. Both have their strengths and weakness. I figure them both together makes it best of both worlds.
 
Turns out the inter-laminar bond between Kevlar and carbon is a bit weaker. You can do a test sample to prove it to yourself. One doesn't want to interleave the layers that way as it will be a little more prone to delamination. Anyway a couple posts back I suggested a layup pattern to consider.

You want to determine the direction of loads and the nature of those loads, and then orient sufficient fibers of appropriate types to handle those loads plus an adequate safety margin.

Then you want to consider the environment the fins need to endure (temperature, dynamic pressure, if fast enough then chemical activity, anything else that comes to mind) and choose the matrix, the fibers, and the outer layer(s) to withstand this environment for long enough to get the job done. That may be through insulation, through ablation, or through simply using materials that would still be within their normal acceptible operating range within that environment.

Gerald
 
If you'll notice, that paint requires a post drying heat cure cycle to achieve the rated performance.

Gerald
 
Lets say I do all that. Let say I use the best epoxy I can find, https://www.cotronics.com/catalog/ Even if when I do tip to tip and lay the fibers the correct way it is only as strong as the epoxy can withstand. What about doing coats of this.

https://www.tcpglobal.com/spraypaintdepot/VHT-curing/curing_VHT-FP.html#curing


The paint probably won't help. This is what happens to that paint on a mach 3 flight even with a post cure.
IMG_0583.jpg
I used the 550 degree rated paint because the post cure (200 degrees for 20 minutes) wouldn't melt the rocket. The post cure on the 2000 degree paint would not be too healthy for a composite rocket.

I feel like maybe you should reconsider doing this rocket in composites. From what I saw last weekend, aluminum is definitely the way to go for a rocket like this. It's not that a composite rocket CAN'T be done, it's just that it would be way more expensive. To get a composite rocket to hold together on that motor, I think it needs to be vacuum bagged, autoclave cured, and post-cured in an oven that is EXTREMELY accurate. Like CJ said, you need to would need to have access to the tools and materials that professional aerospace companies have.

If you really want this rocket to work, I would make it out of aluminum. If you really want to do a composite 98mm MD, then I would say use a long burn motor like the N2540 or N1100. I'm not trying to be mean, just brutally honest. I learned the hard way last weekend by shredding my rocket on an N3301, while still pretty extreme is no N5800.

Manny
 
I'm with CJ on this.

For a hobby rocket, you are looking at metal. There are few rocket legends that may be able to pull it off, but for most of us I think we should look at metal. And I say that as a pro-composite guy.

Remember that Mach 3+ speeds, the rocket is basically in the slipstream of an explosion, so there is not much room for error. There were valid engineering reasons why the YF-12's and SR-71's were built from exotic metals. I'm not saying that an MD N5800 rocket has to made of titanium, but I think it at least need to be made from aluminum, with some critical parts being made of steel.

The one who takes an MD, all-composite rocket on a successful N5800 ride, will have done his homework first. And likely have spent a fair bit of cash in the process before getting there.

Anyway, I wish you success in cracking the N5800 Composite Barrier.

Greg
 
So basically in you guys opinons and some are backed bay experience that all composites will fail becuase of the resources that we in this field have are not good enough to handle those specified speeds? Except for the big high powered aerospace companies. So what you are saying is the material itself (carbon fiber, kevlar, fiber glass tubes) that fail or is it the glues are not heat resitant enough and so in return it falls apart? What comes first the chicken or the egg? The glues get soft and everything falls apart or the composite materials give way, while the glue is still in tacked?
 
Now I've not done projects moving anywhere near the speed of one of these MD 98mm rockets. Not fast enough for thermal issues to be a real concern. I have worked a fair bit with composites and am used to achieving very good results. That said, I'm also used to working with metal. In terms of time, effort, and relative ease of success (sort of), I'd be going metal for the project. Do I think I could do it in composites... yes, but not without a lot more time, effort, and cost than I'd want to put into it. And this is a person who already has a stash of suitable materials and tools from which to start (spread tow carbon fabric, HM carbon, Kevlar twill, S-glass, vacuum system, pressure system, etc) and is at least somewhat used to doing that sort of thing. But were I doing it right now I'd be tempted to look at something like copper leading edge on aluminum fins (taking suitable precautions against possible galvanic corrosion) that bolt onto an aluminum tube, painted with an ablative (possibly commercially through a high temp coating service). Alloy chosen for best properties when heated (aluminum loses a lot of strength and stiffness when heated). Or some other metal or metal combination. I could simply mill the fins out on my Bridgeport once a few fixtures were made. Materials cost would be relatively low, effort would be relatively low, and odds of success a little bit better. Cost of making extra test samples would be relatively low. Cost of changing tooling would be relatively low. Like I said, I THINK I could do it either way, but I could be thinking wrong! Anyway I could manually mill a metal test sample probably in a weekend were I sufficiently inclined. For composites? Likely a month of work before the first test part is pulled, the way I think it should be done.

Gerald
 
So basically in you guys opinons and some are backed bay experience that all composites will fail becuase of the resources that we in this field have are not good enough to handle those specified speeds? Except for the big high powered aerospace companies. So what you are saying is the material itself (carbon fiber, kevlar, fiber glass tubes) that fail or is it the glues are not heat resitant enough and so in return it falls apart? What comes first the chicken or the egg? The glues get soft and everything falls apart or the composite materials give way, while the glue is still in tacked?

You are missing the point of many.

Composite rocket + N5800 = low probability of successful flight
Metal rocket + N5800 = higher probability of successful flight

If you are confident you can pull it off, do it! Order parts, motors cases, reloads, parachutes, etc... it's good for the vendors.:cheers:



Justin
 
Take a look at some composite structures that have been up to this sort of speed range. I've only had the chance to directly examine the second stage of a 2 stage so it hit the speeds at a higher altitude so dynamic pressure and heat transfer should be a bit lower. As it was, leading edge fabric failure leading to delamination peeling layers... The structure survived sufficiently for a successful flight but the Cd had to have gone up more than just a bit! There was clear evidence of deformation (likely swelling) of the matrix as well. Clearly it had exceeded Tg and was very close to total failure.

Interlayer bond with composites is an issue because the fabric or uni structure is typically planar or linear and there is no 3D interlocking (or very minimal). This can be improved with some state-of-the-art additives to the matrix that improve the mechanical properties of the resulting matrix itself while maintaining relative ease of working with the epoxy. Whether these can be obtained yet through commercial channels in small quantities is unknown to me. Last I checked, this winter, only one manufacturer was making the powder additives available. All others were keeping it proprietary and using it only for internally produced products.

Epoxy may well not be the best matrix material anyway. Epoxy and similar materials are simply easiest to use for us.

Gerald
 
Appropriately chosen and used composite materials can take it. That's just a structural and thermal issue and not likely all that hard to solve. Particularly not if one disregards any weight budget. Carbon fiber can take the heat. S-glass can take the heat. Basalt fabric can take the heat. Various ceramic fabrics can take the heat. Some are better thermal conductors; some are better insulators. The matrix and the surface protective layer are the biggest issues IMHO with composites (and perhaps keeping it nicely attached to an appropriate tube). Metals won't typically peel apart from direct exposure to the slipstream. Composites on the other hand... One could try bonding a metal skin over a composite fin for protection. As long as the bond works well enough and the fin core can take the heat soak for long enough it should work. Then one could use a thin insulating layer as an adhesive - perhaps polyurethane based.

Anyway, there are many options. It is your rocket; do what you think best!

Gerald
 
I think composites can do it. Most of the rockets that have attempted have used lower TG resins <250F. Some BMIs go over 550F. If you change the layup of the fins so that you don't have an exposed edge on the leading edge maybe use an ablative you better your chances. But this isn't something you can just throw together you really have to plan your flight loads and temps and build accordingly close enough probably wont work. [/peanutgallery]
 
The type of rocket you are talking about can only be launched at black rock correct?

A composite N5800 minimum diameter will have to be flown at Black Rock as well. Realistically, any Pro98 6GXL minimum diameter should be flown at Black Rock.
 
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