75er mk. II

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drew
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75er mk. II

Postby drew » Fri Mar 20, 2015 4:18 pm

For Thunda I decided my primary project should be a single break 75mm minimum diameter rocket utilising a CTI 4 grain case loaded with a M2250. My original L3 project utilised the same fin design, airframe(PR FWFG), and motor but was really overbuilt and dual break in design. This second iteration would be more finely tuned with the primary goal of breaking Mach 2. I came close with my L3 flight but just fell short. I figured this might do the trick.

For the fins I decided to do a single layer of 2x2 twill over the fiberglass fins to provide added stiffness and to utilise Araldite 3600 epoxy. Nic put me on to this stuff, it's extremely low viscosity so it wets out fabric really well. It also becomes significantly harder when post cured in an oven.

Getting ready to cut the carbon fiber.
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Fins and fillets sanded and cleaned.
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Peel Ply and waiting for the Araldite to kick.
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Not too bad.
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All of the electronics in this rocket are located in the nose cone. Strud had some kit he wanted to test incuding his most recent revision of his flight computer with a 9DOF sensor as well as a 1W 70cm transmitter. I decided on a Raven 3 for deployment duties and used a BRB high power 70cm GPS for tracking. Here are the intial sled layouts. I ended up moving the Raven 3 more to the center line of the sled as to protect the terminal block.

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Here's the final "flight ready" layout of the avionics compartment.

Strud FC + BRB GPS.
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Raven 3 + Strud 1W 70cm transmitter.
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"Ground Control" the receiver for Strud's transmitter.
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Once I had finished with the booster I gave it a post cure in the oven, along with my 38s booster.
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After finishing the nose I did a dry assembly of the unfinished components to get an accurate OpenRocket sim for the High Altitude Review Committee. The sim put my max velocity at Mach 2.33. My builds always come in a bit heavier so I expected my actual max v to be in the Mach 2.1-2.2 range.
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Paint was applied, and here's the end result ready to be boxed up and flown to Thunda!
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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

drew
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Re: 75er mk. II

Postby drew » Fri Mar 20, 2015 4:19 pm

Flight

I didn't fly until Sunday afternoon. The airframe had fin slots and I believe the post cure actually contracted the airframe slightly on the tail end. On Saturday I spend a fair amount of time sanding on the flight line. A tip of the hat goes to Scoop who provided me with tools to more efficiently accomplish the task. Next time I'll ensure the motor casing fits before leaving home!

Here's the rocket in the tower.
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And we have liftoff! Holy smokes!
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I was also able to catch the flight on video from the flight line.


The rocket came down ~4km from the flight line and a few hundred meters on the other side of the lake. Phew!
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Last edited by drew on Fri Mar 20, 2015 4:34 pm, edited 1 time in total.
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

drew
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Re: 75er mk. II

Postby drew » Fri Mar 20, 2015 4:21 pm

Post Flight Analysis

HOLY COW, that was fast! I wasn't able to get logging from the BRB as I didn't have data wrap enabled and it sat powered in the tower for over 1 1/2 hours before liftoff but as you can hear in the video the highest packet I received from the GPS ws 25,492 ft ASL. That places the GPS max altitude at ~24,600 ft. The Raven 3 reported Baro max Alt at 23,356ft AGL. I suspect that is a little short given the GPS output. As for max velocity, the Raven recorded that as 2488 ft/s which is roughly Mach 2.2. EXCELLENT. The Raven's axial accelerometer reading maxed out at 47Gs.

Here's the Raven 3 graph displaying velocity and altitude.
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And here are a couple pictures of the Mach rash the rocket sustained. Safe to say I need to start using two pack paint for these sorts of builds, rattle cans just can't cope with the heat.
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Once Strud returns from the states we'll dump the data from his flight computer and I'll update y'all with the results.
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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jase
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Re: 75er mk. II

Postby jase » Fri Mar 20, 2015 5:16 pm

Nice thread Drew, great build, images and flight.

Congratulations on a top notch result. That water obstacle nearly claimed me too :shock:

Consider your current top coat now a baked on undercoat :wink:

...should sand up nice!
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cryoscum
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Re: 75er mk. II

Postby cryoscum » Fri Mar 20, 2015 5:32 pm

Well done, Drew! Perseverance and focus! That's all it took and you beat the crap out of that Mach 2 threshold! Not many have done that and I suspect you're not done with this rodeo yet? :twisted:
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october sky
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Re: 75er mk. II

Postby october sky » Fri Mar 20, 2015 8:10 pm

Awesome Drew...great build and launch ! Congrats !! 8)
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drew
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Re: 75er mk. II

Postby drew » Fri Mar 20, 2015 8:35 pm

Thank you gentlemen, I really appreciate the comments. And Nic, you're quite right, there's still a long way to go. :twisted: I've already got two flights rolling around in my mind for Williams this year! Onwards and upwards!
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

Lamp
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Re: 75er mk. II

Postby Lamp » Sat Mar 21, 2015 6:56 am

Yep, great flights Drew, what's next? The N5800 perhaps?

Personally I think the 75er looks great with the Mach Rash, kind of like a badge of honour!
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Re: 75er mk. II

Postby air.command » Sat Mar 21, 2015 8:18 am

Definitely great flights Drew, they looked very fast off the pad! Amazing what air can do to the paint job. You wouldn't get that much rash kicking it around the car park.
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drew
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Re: 75er mk. II

Postby drew » Sat Mar 21, 2015 11:08 am

Yep, great flights Drew, what's next? The N5800 perhaps?


Not quite Lamp, I don't suspect I'll get into the N game for a while. I'm thinking more along the lines of the M840/M2245 path.

Amazing what air can do to the paint job.


I agree air.command. I've been looking into the 2 pack stuff to attempt to remedy this issue. Painting rockets is what I'm arguably worst at when it comes to vehicle construction. The nose on this rocket had a huge paint run on the side of it. I just shrugged my shoulders as I knew I'd be melting it off anyway! :lol:
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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