Mini-Old School Cool - 38mm MD Rocket with ACME Fin Can

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patelldp
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Mini-Old School Cool - 38mm MD Rocket with ACME Fin Can

Postby patelldp » Wed Nov 25, 2015 3:48 pm

It's 2015, soon to be 2016...what's the last thing you expect to see in a rocket build thread?

*Jeopardy Music*

If you answered an ACME fin can, you answered right! These things have been around for a long long time and used to be incorporated in "extreme" rocket designs. They're robust, but weigh a ton and are excessively draggy when compared to a nice set of CF fins adhered to the body tube. Their saving grace is being simple to use...just glue it on! You can build a rocket that can fly on a J570W or comparable commercial motor in less than a half-hour.

The purpose of this rocket is very simple: flyable on 38mm and smaller motors with minimal prep time while being robust in nature. There's a few design choices that were made in order to fulfill this purpose:

  1. ACME fincan for ease of use, ruggedness, and nostalgia
  2. AeroPack motor retainer ease of use
  3. Hawk Mountain FWFG tubing for ruggedness and sexiness
  4. AIM Xtra 2.0 Altimeter for GPS Telemetry and ability to "Fly all day" on a 1000mAh LiPo battery
  5. Giant Leap Rocketry Hardpoint Anchor that will be made removable

And so begins my build thread...first off is the basic parts required to build this thing!

IMG_3148.JPG

  • Hawk Mountain 1.53" x 36" FWFG Tube
  • ACME 38mm Fin Can
  • AeroPack 38mm Retainer
  • Rocketry Warehouse 38mm x 3" Coupler
  • Pinnacle 1.5" Nosecone
  • ACME 38mm Conformal Railguides (Fincan model)
  • Giant Leap 38mm Hardpoint Anchor and eyebolt
Dan Patell
TRA 10904 L3

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patelldp
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Re: Mini-Old School Cool - 38mm MD Rocket with ACME Fin Can

Postby patelldp » Wed Nov 25, 2015 4:04 pm

So, focusing again on that ancient ACME fin can...why would anyone use one? Well, I have a strong desire to use an AeroPack external motor retainer on this project for a couple of reasons. The first reason is their ease of use, the second reason is that the external model is a lot easier to use than the internal model, and the third is that Slimline retainers don't play nicely with snap ring EX hardware. On an MD rocket, this poses an issue...it's quite non-sensical to make a streamlined rocket and stick a retainer on the back end. Now that I am settled on using the external AeroPack...enter the ACME fin can!
OSC38 - 1 (1).jpg

As you can see, the fin can "hides" the retainer. For the original 54mm "Old School Cool," I left the arrangement this way. While it's certainly adequate, I took a look at my lathe and it whispered "I want to bore that out."
IMG_3145.JPG

IMG_3146.JPG

Once I pulled the boring bar out, it was the AeroPack's turn to get in there.
IMG_3150.JPG

I cut the ID far enough that the collar bottoms out before the retainer cap hits the aft of the fin can. There's about a 1/64" to 1/32" gap between the two.
Dan Patell
TRA 10904 L3

dixontj
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Re: Mini-Old School Cool - 38mm MD Rocket with ACME Fin Can

Postby dixontj » Wed Nov 25, 2015 4:06 pm

That's nice.

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patelldp
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Re: Mini-Old School Cool - 38mm MD Rocket with ACME Fin Can

Postby patelldp » Wed Nov 25, 2015 4:09 pm

Last post pre-turkey day is likely to be a picture of the full "stack":
OSC38 - 2.jpg

Here's how the little guy compares to its bigger brother, the original Old School Cool:
OSC38 - 1.jpg


This is an itty bitty rocket. I see this thing flying on a very wide range of motors next year, specifically a few of the Syner-jet 22mm G117, Ellis 24mm G37, Aerotech 29/40-120, and CTI 38/1G motors I have laying around. I will also fly several 29mm experimental motors in this rocket and intend to test out some unique geometries including D-grain and monolithic core burning. These things are PERFECT test bed rockets.
Dan Patell
TRA 10904 L3

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patelldp
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Re: Mini-Old School Cool - 38mm MD Rocket with ACME Fin Can

Postby patelldp » Wed Nov 25, 2015 4:15 pm

dixontj wrote:That's nice.


Thanks, Tim! It's a motor-eater, plain and simple. I am going to use this as a way to test motors and collect .kml files. The real fun begins with the altimeter bay design...hold on for that installment! Now, where do they carry 1.5" diameter dowels...Lowes does but it's a few towns over...
Dan Patell
TRA 10904 L3

dixontj
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Re: Mini-Old School Cool - 38mm MD Rocket with ACME Fin Can

Postby dixontj » Wed Nov 25, 2015 4:18 pm

You're going to make a wooden av-bay?!!?

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patelldp
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Re: Mini-Old School Cool - 38mm MD Rocket with ACME Fin Can

Postby patelldp » Wed Nov 25, 2015 4:20 pm

dixontj wrote:You're going to make a wooden av-bay?!!?


The av-bay is going to resemble something like what Andrew at Additive Aerospace has in his altitube line. I don't have access to a printer, nor do I want to overload Andrew with the burden of designing/printing me something similar, so i get to use my lathe and chiseling ability to make an integrated av bay design. We'll see how it goes, and it should be a fun endeavor.

Dual deployment will be via a cable cutter.
Dan Patell
TRA 10904 L3

DBMcCann
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Re: Mini-Old School Cool - 38mm MD Rocket with ACME Fin Can

Postby DBMcCann » Wed Nov 25, 2015 8:26 pm

Should be a sweet little grain gobbler.

This av bay should be interesting....

Alexander
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Re: Mini-Old School Cool - 38mm MD Rocket with ACME Fin Can

Postby Alexander » Wed Nov 25, 2015 11:32 pm

Dont tell me you lost that glass tube I sold you lol, just kidding. That rocket looks awesome, keep up the good work Dan.
Alexander Solis

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patelldp
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Re: Mini-Old School Cool - 38mm MD Rocket with ACME Fin Can

Postby patelldp » Mon Dec 07, 2015 12:51 pm

Gahh, where has time gone? I went on a short work trip to Salt Lake City, so nothing got done on rocketry projects for a bit!

I finally got back to this project, and that means it's essentially done! These fin can and fiberglass rockets essentially assemble themselves with very little attention required by the monkey typing these posts.

Step one is to mark where the fincan and AeroPack retainers will fall on the tube. This allows you to know where to scuff, apply epoxy, and also where to mask off to prevent errant epoxy.

IMG_3195.JPG


Once marked, I scuffed all surfaces that will be epoxied to the tube with 40 grit sand paper. This includes the tube, the inside of the fin can, and the Aeropack retainer (not necessary as they rib the ID of the glued area, but smart none-the-less).

IMG_3196.JPG


One issue with the ACME fin can assembly is that the ID is slightly larger than the OD of the Hawk tube. The thought here is that the ACME design is "one-size-fits-all" and therefore was made large to accommodate many different tubes. As a result, a few rings of masking tape were added to the tube to make the fin can fit snugly. 15 minute epoxy was then generously applied to the tube to fill the small gap between the tube and the fincan and securely adhere the can to the tube.

IMG_3197.JPG


A picture wasn't taken of the following step, but it's pretty self explanatory...the installation of the Giant Leap Hardpoint anchor. The anchor has a 1/4" eyebolt installed with a nylock nut to keep it in there permanently. I spaced it such that my largest 38mm case still fits, permitting a possible K motor flight at some point! A 1/8" Kevlar leader was tied to the eyebolt and heat shrink tube placed over the loose end of the knot to keep things neat. You can see the Kevlar leader hanging out and the anchor epoxied in.

IMG_3199.JPG


Here's a full-stack picture of the rocket with a simple Pinnacle nosecone. If you're flying this rocket with motor deployment, you're effectively done at this point. I'll be using a 24" x-form parachute from Top Flight for single deployment flights with the main at apogee. I'll be using a Spherachute 36" parachute and cable cutter for dual deployment flights. You can see through the translucent tubing in this shot and see the 24" chute and cord...it all fits nicely! (You can also see my other project, my 3.72" Proteus)

IMG_3200.JPG
Dan Patell
TRA 10904 L3


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