Building MD 98mm rocket for competition, looking for some advice on design

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morros266

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Hello,

I'm apart of a team building a rocket for a competition where we carry 8.8 pounds of payload to a specified altitude. Our goal is 30,000 feet. The competition is the Spaceport America Cup IREC 2017. All the rules can be found on their website. (https://www.soundingrocket.org/sa-cup-documents--forms.html )

We are currently designing a 98mm MD and planning on launching on a motor around the N3301 from Cesaroni. From talking to other people and my research, I know this isn't going to be easy. I was hoping someone with experience building something this size can help. The team is worried about aerodynamic heating, fin flutter, whether the fins would stay attach, the heat and strength required for the epoxy, and anything else that might cause an issue. I've attached a copy of our current rocksim design so anyone can look over it.

General Design

  • 98mm MD
  • Standard dual deploy using Stratologger CF as primary and secondary deployment system (We have talked about the lack of oxygen for black powder charges at 30,000 feet but unsure what to do exactly)
  • Filament wound fiberglass tubes for everything including couplers
  • G10 or carbon fiber fins (haven't decided)
  • Main about 91 inch diameter and drogue about 24 inch diameter (planning on using spherachutes for main and drogue with Kevlar harnesses)
  • Aluminum tip nose cone (plan on having an all thread run down the length of it attaching to the bulk plate with some other electronics on board like a transmitter)
  • Payload is required to fit inside 5x5x5 cm cube form factor (can have multiply cubes and can be anything, we plan on using metal cubes like brass and 3D print to fin tune the amount)
  • Haven't decided using a tip to tip brace on the fins using composites or something else like Max Q Aerospace fin can yet.
  • We are using a MD retention device off the shelf

Performance
(rocksim flight simulation data on N3301)
  • Max speed: Mach 1.94
  • Max Gee force: 18.04
  • Velocity at deployment: 46.52 ft/sec
  • Apogee: 30907.68
  • Launch Static Margin: 2.55
  • Velocity at launch guide departure: 134.37 (using an 18 ft rail guide also require by competition rules to leave guide at 100 ft/sec or faster

Other design parameters and simulation results can be found in the rocksim file.

Currently plan on using Adtech 820 epoxy and some high temp epoxy (not sure what kind yet could use suggestions)

If possibly, having technical documents can be useful when presenting and verifying safety margins.

If someone can help, the team and I would appreciate it.
 

rharshberger

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Welcome to TRF!

Jim Jarvis is your man on TRF for using Black Powder at High Altitude (he even has a paper on the design of the system he uses), there are also CO2 based systems like the Tinder Peregrine/Raptor and the RouseTech CD3 systems.

MaxQ is the purview of Mike Fisher of Binder Design also a member of TRF.

AeroPack makes a MD motor retainer system.

OneBadHawk Recovery is a premier source of recovery harnesses, both tubular nylon and tubular kevlar, when it comes to harnesses (shock cords if you will) Ted Chernok of OBH is the man!

Listen carefully to whenever Bob Krech chimes in he has a huge amount of useful knowledge if you can decipher techno/science speak.

We also have a number of other very knowledgeable people in exactly the right areas for your project.

They will want to know some answers like who you are representing, do you have a mentor, and other questions.

Black Powder doesn't need oxygen it has its own oxidizer (KNO3) however there are considerations for high altitudes (again Jim Jarvis has a wealth of information on BP use at high altitudes, among others).

All-thread in close relation to antennas do funny things to transmission, so its just something to be aware of, any of the manufacturers of the tracking/telemetry systems can key you in on how their systems can be affected.

What kind of tracking system are you going to be using to get the pieces/parts back? Some examples BigRedBee, Altus Metrum, Missleworks Rtx, Eggfinder and Eggfinder TRS (both Eggtimer products are kits), and others that I have missed (all the ones mention iirc are GPS units).

Other very capable altimeters are available from Marsa, Missleworks, Eggtimer Rocketry (kits only), Featherweight Ravens, Altus Metrum. IMO Marsa is probably the most configurable altimeter via its Marsa Net addons, its also one of the more expensive.
 
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Zebedee

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For Mach 2 and 30K feet you should be fine with standard G10 fins and some tip to tip reinforcement using either glass or carbon fiber cloth. Rocketpoxy for attaching the fins and fillets plus Aeropoxy laminating epoxy for the tip to tip is good.

At 30K feet you can use a few inches of PVC tube with a PVC cap as a charge canister packed with wadding and sealed with several layers of masking tape on the "open" end. Drill the cap and feed the igniter through it then seal it in with epoxy.
 
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Nytrunner

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Woo! another IREC year has come!

Have they relaxed the "Do not exceed 2 caliber static margin" overstability rule?

Forum members have used a program called FinSim to work on flutter effects.
My team's entry was in the 10k category and didn't need to exceed Mach, so we didn't end up using it, but it could be really helpful for y'all
 

FredA

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Have they relaxed the "Do not exceed 2 caliber static margin" overstability rule?

That seems like a pretty foolish rule for rockets that approach Mach 2.....
 

morros266

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Thank you for all the information. We are students at the University of Arizona. Our mentors/advisors are Mark Langhenry and James Villereal. For tracking, we plan on using BigRedBee and/or Eggfinder.
 

morros266

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I'm not sure how relaxed they are but we had a static margin of like 3 last year so I think they are somewhat flexible
 

Nytrunner

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The competition was 2.5 months ago. Maybe they'll pick up for next year's build.
 

Zebedee

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Can you share the design and some details on the flight?
 

morros266

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Much of what I originally posted ended up being the final design. We did use Max Q aerospace for our fins. The motor was a custom designed one that we built and tested. For our final flight we ended up getting 23000ft. We were expecting 31000ft. The loss of altitude in our opinion is because the nozzle wasn't manufactured right and because of that we lost about a third of our thrust.
 

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