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Blackhawk 38 build plan, critique please

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spowers42

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Last night I ordered a blackhawk 38 kit from wild man for my big winter build. As such I want to go pretty all out with it and try a bunch of stuff. Before buying parts though I wanted to lay out my plan and get advice on anything that might be a bad idea or not work.

Goal:
* experience building a HP minimum diameter rocket
* optimized av bay setup, possibly redundant
* build with minimal use of metallic hardware, eliminate all-thread
* tip to tip practice (maybe)
* try out another avionics package (i have used an rrc3 in the past)

For the altimeter I want to use the Eggtimer TRS. I have some concerns about it working inside the airframe since the kit uses some graphite in the tube layup instead of just straight fiberglass. Does anyone have any experience with either an egg finder in this airframe or the egg timer wifi switch? To protect the whip antenna I will likely use a small bit of bt2 with a layer of kevlar on it. this would be affixed to the avbay bulk plate.

The biggest design challenge I think will be removing the all thread from the construction of the avbay. I don't think it is particularly complicated, however it is non standard setup. I have two ideas on how to accomplish this. The first would be to 3d print a custom sled using a high strength plastic like nylon or polycarb and gluing in some nuts in the structure. Then I could use machine screws to close everything up, kind of similar to a normal avbay. In this case the forces would all be carried through the 3d printed sled. That is my major concern with this design, though it would probably result in the best packaging of the electronics. Obviously tensile testing would be needed to confirm the part design. What would a reasonably safe tensile strength be to carry the forces at deployment (using either stock parachute or large streamer)?

The other idea I had was to do something similar to the apogee components e-bay kits except using fiberglass or kevlar. This would allow me to put a couple layers of uni fiber in the layup schedule which should help with the tensile strength. This is likely the more straightforward option, though it doesn't lead to as clean of a setup.

For motor retention I will use a slimline retainer. I fly at MMMSC which requires active retention. I know this will diminish performance some, but I might make some of it up by eliminating rail buttons and using fly away guides.

I also plan on using some carbon to reenforce the shock cord anchor.
 

timbucktoo

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Fun rocket to fly! You'd be surprised how high that thing will go even on a 3 grain! I am also using the slimline retainer. Just didn't want to mess with friction fit. I am flying with a Stratologger SLCF & a 9 volt. According the Cris Erving, the TRS will fit in a 38mm frame but it'll be tight!
As far as tracking, I stuffed a BRB900 into the NC and had no issues with telemetry.
I did not do tip to tip but it can't hurt! Good luck!
 

warnerr

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I have flown wifi switches in carbon fiber 28 and 32 and the range was unexpectedly great- over a hundred feet- so i dont expect any major issues with the graphite. Once you sync up near the rocket signal stays locked well. You can do a rough test just setting transmitter inside tube and verify that your results will be as good as mine.
 

markkoelsch

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I think you will have problems with GPS due to the airframe.

The AV bay- consider using aluminum all thread. Lighter than steel and should be strong enough.

Friction fit the motor, and then use aluminum tape to retain it. Works well.
 

BDB

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* optimized av bay setup, possibly redundant
* build with minimal use of metallic hardware, eliminate all-thread
* tip to tip practice (maybe)
Subscribed! These are some of my goals for my winter builds too. I fly with RIMRA and occasionally with CMASS, but I'm hoping to make several trips up to MMMSC this fall and next spring. Hopefully I can see this baby fly. Good luck!
 

spowers42

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Unfortunately friction fit is a no go for me. One club I fly at requires all motors to have active retention. I am also specifically trying to not use any all thread, regardless of material. Though Al all thread is a reasonable backup if other ideas don't work out.
 

crossfire

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Isn't tape active retention?
 

spowers42

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Isn't tape active retention?
I do not know if it counts for MMMSC. They are very strict because of land owner requirements. Kenn could probably comment on this, but my guess is no. For any other field yes.
 

crossfire

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Always got to do what the land owner wants.
 

Titan II

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From their website....

All Rockets launched at M³SC will have positive motor retention on the motor mount of the rocket. NO “Friction Fit Retention” will pass RSO.
 

spowers42

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From their website....

All Rockets launched at M³SC will have positive motor retention on the motor mount of the rocket. NO “Friction Fit Retention” will pass RSO.
right. And it is the RSOs judgement on the exact meaning to that. For simplicity I am going with a fairly "standard" retention. Will not be as optimized, but we have a 10k waiver anyway, so no need to make it perfect this go around. (read as going to build a fully scratch built carbon MD sometime soon :) )

The part I am actually worried about is the non standard av bay design I am planning.
 

markkoelsch

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I would argue that aluminum tape is active retention attached to the motor mount. I might lose the argument, but it has been a very successful and time tested method of retention. It is in addition to the friction fit.
 
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