Mad Max II - more of the same

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cryoscum
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Mad Max II - more of the same

Postby cryoscum » Thu Oct 02, 2014 9:28 am

Hi All

Before leaving for Balls earlier in the year I had time to start work on Mad Max II, yet another 4" sub-minimum diameter rocket intended for an O3400. Apart from the fact that I actually have one of these, they are also less aggressive than the N5800 and should make for a smoother ride & less confetti near burnout. I hope.

Now that we have significant airspace available to us in Australia, we don't have to go to Black Rock just once a year to do these kind of flights! Every Westmar launch can be an attempt at ridiculousness :twisted:

Started by doing the sim in the usual weight-conservative way and checked the stability margin, once again likely to be the most important aspect of the design.
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Seems OK, so I moved on to the airframe construction, essentially the exact same design as was used on No Big Deal, i.e. pushing anything with significant weight as far forward as possible. Accordingly the alu tip can be significant as you want some weight there and the longer alu section means less aeroheating occurs on the actual composite airframe. The airframe is a 7.5:1 VK with an extended shoulder of 150mm. The wall thickness is approx 2.5mm and OD is 98.5mm.
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The coupler was the next issue and, given that an alu coupler would weigh close to 1kg I decided to just do it in carbon. This is the design:
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The whole thing is made up of 200GSM 2x2 twill.
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The initial tube was made on an 83mm mandrell and machined down to the correct OD
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A lasercut jig helped with the assembly
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Lots of Epiglue
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8 hours at 90 deg C
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Final product ready to go. MUCH faster than machining it from alu and only weighs 287g

More to follow...
AMRS L3 | NAR L3 | QRS 089 | MDRA 224
AMRS Technical Advisory Group

Total impulse for 2016: 32,458 Ns (thus far)
Total impulse for 2015: 84,231 Ns
Total impulse for 2014: 40,757 Ns
Total impulse for 2013: 62,927 Ns

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Re: Mad Max II - more of the same

Postby jase » Thu Oct 02, 2014 11:38 am

Baking carbon cupcakes - how sweet! :P
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Re: Mad Max II - more of the same

Postby drew » Thu Oct 02, 2014 11:54 am

As per usual amazing work Nic. Quick question though. It appears that your fin design has evolved to what looks roughly equivalent to the Don't Debate This fin design. Is this fin design more desirable from a speed/stability perspective to your previous designs?
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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: Mad Max II - more of the same

Postby ROCKet STAR » Thu Oct 02, 2014 12:10 pm

You mean you are going to put some fins and a nosecone on a motor case? You must be some kind of mad man. :wink:

I am looking forward to the flight!
Chris Barnes

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Re: Mad Max II - more of the same

Postby A5tr0 An0n » Thu Oct 02, 2014 1:25 pm

From your OR screenshot it appears that the fins extend fore of the can, how does this work with your taper? Seems like this might be a concern, unless the fore portion of your fins taper with the fin can transition. Or I suppose it could be a bolt on fin can with the fins in-between "plates." I am mostly just curious. Maybe a more important question is, is this fin can composite or metal? :)

Anyways nice work as always and look forward to your results.

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Re: Mad Max II - more of the same

Postby cryoscum » Thu Oct 02, 2014 2:04 pm

Mat, that fincan is still based on the No Big Deal design and I'll be changing that soon. I'm not yet sure what material the fincan will be, but carbon is the quick and easy way. It'll be either that or a brazed alu fincan.

Drew, the fin design is identical to No Big Deal, in fact, the exact same size too, just 4 of them not 3. I've been toying with a 4 fin design for a long time now, but after a long discussion with Jerry McKinlay one night at Bruno's, I am convinced that it's a better option for this flight than 3 fins. The main reasons are:
- using 4 fins allows them to be smaller for the same stability margin, this makes good structural sense
- I am told that 4 finned boosters tend to spin less during drogue descent, reducing tangling, important if you're spending a lot of time under drogue
- the intense CP shift experienced above M2.7 is less pronounced with 4 fin designs, i.e. you can start with a lower static stability margin on the pad and still retain enough margin at max V. This is seemingly confirmed by the sims and possibly also why so many military designs are 4 finned. I don't recall ever seeing 3 fins on anything used for war, weather or space??
As for the shape, it seems to be the compromise sweet spot between stability and flutter risk, i.e. the more swept back it is the more stability it gives, but it gets more 'fluttery' too.
AMRS L3 | NAR L3 | QRS 089 | MDRA 224
AMRS Technical Advisory Group

Total impulse for 2016: 32,458 Ns (thus far)
Total impulse for 2015: 84,231 Ns
Total impulse for 2014: 40,757 Ns
Total impulse for 2013: 62,927 Ns

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Re: Mad Max II - more of the same

Postby drew » Thu Oct 02, 2014 2:24 pm

Cheers mate. I can't wait to see it fly!
Andrew Hamilton
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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: Mad Max II - more of the same

Postby CATO » Thu Oct 02, 2014 6:41 pm

Very nice Nic...
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Impulse:
2017: 00,000 Ns (00.00% A)
Ns 16: 34,558; 15: 35,955; 14: 6,016; 13: 10,208
PB - Gorilla N2717WC, H: 10,260', S: 1.14M

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Re: Mad Max II - more of the same

Postby cryoscum » Sun Dec 07, 2014 2:02 pm

Time to make the AvBay. It's again based on the No Big Deal design, but modified for a 98mm airframe.
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The parts were extracted from the 3D model.
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With all the t-nuts in place the parts were glued and press-fitted together
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It needed just a small amount of tweaking to get it to fit correctly, i.e. crucially the ply makes contact with the airframe along its full length.
8.JPG
AMRS L3 | NAR L3 | QRS 089 | MDRA 224
AMRS Technical Advisory Group

Total impulse for 2016: 32,458 Ns (thus far)
Total impulse for 2015: 84,231 Ns
Total impulse for 2014: 40,757 Ns
Total impulse for 2013: 62,927 Ns

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Re: Mad Max II - more of the same

Postby kopius » Sun Dec 07, 2014 2:49 pm

Very nice as always! Guessing there is some new airspace in Australia that you are going to spank with MMII?
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Re: Mad Max II - more of the same

Postby CATO » Sun Dec 07, 2014 7:03 pm

Just awesome Nic.
"In thrust we trust"

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AMRS Technical Advisory Group - CO

Impulse:
2017: 00,000 Ns (00.00% A)
Ns 16: 34,558; 15: 35,955; 14: 6,016; 13: 10,208
PB - Gorilla N2717WC, H: 10,260', S: 1.14M

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cryoscum
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Re: Mad Max II - more of the same

Postby cryoscum » Sat Jan 03, 2015 11:43 am

Had some time in the last few days to make the fin can. As mentioned earlier it is a 4 fin carbon arrangement with SS leading edge caps. The fin can tube wall thickness is 3mm and the fins are 5mm thick. The fins are made up of 19 layers 200 GSM plain weave 3k carbon, the outer 3 layers of each face was tip-to-tip vac-bagged onto the bevelled core layers. Resin was the usual Araldite K3600, heat treated with a ramped regime to a max of 90 deg C, where it spent approx 8 hours. This should have the Araldite at its peak tensile strength of around 90MPa. The SS caps are 0.5mm thick grade 304 SS with 'half-hard' temper glued onto the leading edges with JB weld and tapped into place with a hammer (they press-fit onto the leading edges). Total weight is just over 1100g.
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2.JPG

Still need to make the alu leading edge for the fin can tube (to protect it from the mildly energetic breeze of 2400 mph)
AMRS L3 | NAR L3 | QRS 089 | MDRA 224
AMRS Technical Advisory Group

Total impulse for 2016: 32,458 Ns (thus far)
Total impulse for 2015: 84,231 Ns
Total impulse for 2014: 40,757 Ns
Total impulse for 2013: 62,927 Ns

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Re: Mad Max II - more of the same

Postby kopius » Sat Jan 03, 2015 12:25 pm

cryoscum wrote:(to protect it from the mildly energetic breeze of 2400 mph)

you mean like a fart?

looks fantastic! can't wait to see that tear apart the Darling Down skies ;-)
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Re: Mad Max II - more of the same

Postby SinfulDarkLord » Sat Jan 03, 2015 12:30 pm

Thats a beauty,

Question: since carbon heats up quickly, what are you going to do to prevent it from getting too hot?


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cryoscum
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Re: Mad Max II - more of the same

Postby cryoscum » Sun Jan 04, 2015 4:43 pm

Alexander, the SS caps are thermally isolated from the underlying carbon and besides, SS is generally a bad conductor of heat.

Made and installed the fin can tube leading edge from 5083 alloy. Must say that I hate the stuff! It anneals badly, machines badly and is generally hard to work with. Will be staying with 6000 series in future. The SS caps are folded in under the alu leading edge to help avoid the caps coming off...
3.JPG
3.JPG (123.73 KiB) Viewed 2952 times
AMRS L3 | NAR L3 | QRS 089 | MDRA 224
AMRS Technical Advisory Group

Total impulse for 2016: 32,458 Ns (thus far)
Total impulse for 2015: 84,231 Ns
Total impulse for 2014: 40,757 Ns
Total impulse for 2013: 62,927 Ns


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