54mm Minimum Diameter Little Dog

[BlazingAngel665]

I'm starting a new project, mostly because I picked up a Little Dog in the Yard Sale. My university's shipping department lost it for a little bit because of a mix up, but they recently found it. BUILD TIME!

Motor Mount?

Nah! It's minimum diameter time! This is my first minimum diameter, so if I do a stupid, please say something.

Fiberglass PPE keeps the splinters out of me.

Cutting switchband piece from forward fuselage.

Stepped bulkheads, these make my day when they fit perfectly.

Avionics hardware. I'm using a TeleMetrum 2.0 for recovery and telemetry. I'm looking for over 24,000 ft on this bird so the GPS is essential for recovery. I have a seven element yagi for the ground station. All aluminium hardware to maximize the altitude per motor.

Nose cone is polished up.

All the bits are layed out. The next project is the fin attachment and tip to tip layup. I'm hoping for my first flight to be on Saturday the 30th. I have a J280 which should send this 6,600ft above Berwick, ME. This vehicle's name is "Laika" which is the name of the first living creature to orbit the Earth. I'm thinking a Soviet Army Green with a red and yellow star to show good comradeship. [EDIT: pretend I spelled that right]

 

[dhbarr]

How are you handling the pre-slotted / surface mount arrangement? Those slots represent a substantial weakening on MD birds AFAIK.

Edit: NM, looks like maybe you chopped that section?

 

[claytonbirchenough]

Hmmm regarding the slots, couldn't you just mount the fins between the slots and just fill/cover over the slots with the tip-to-tip?

Following!

 

[BlazingAngel665]

How are you handling the pre-slotted / surface mount arrangement? Those slots represent a substantial weakening on MD birds AFAIK.

Edit: NM, looks like maybe you chopped that section?

Nope, that section is still there. I wasn't aware that those slots would be a serious issue. Care to elaborate? My plan was to put the fins in the slots to ensure they were clocked correctly and then do a layup over that.

Hmmm regarding the slots, couldn't you just mount the fins between the slots and just fill/cover over the slots with the tip-to-tip?

Following!

Is there a particular reason why mounting in the slots is bad?

 

[dhbarr]

Think of a coke can's strength before & after it has a tear in the skin. With TTW you're mounted to the MMT & again to the BT.

In the MD case your fins are fairly effective levers, with the fulcrum at the rear. Since the tube is slotted, it is significantly weakened in this same area.

 

[tfish]

I'll disagree that it makes for a weaker rocket. I think it actually will make the fin attachment stronger. Maybe the body tube in that area is weaker, but in an area where it does not matter. There was a company called 3 Dogs Rocketry that made a 54mm min dia rocket called KestreL. The Kestrel was a very clean design! It came with a slotted body tube. The AeroPac 100K team has used a modified "slot" for fin attachment. I do a few min dia rockets and would slot my tubes if I had a jig or other set-up to do it quickly.

https://www.rocketryforum.com/showthread.php?17131-KestreL-Ex-build-thread
https://groveraerospace.com/?page_id=217

Tony

 

[dhbarr]

Certainly I'll defer to those with more experience, it just seemed a stronger attachment to a weaker tube.

I've wondered for a while why nobody does a post-in-hole type fin attach for at least the leading edge.

 

[BlazingAngel665]

Think of a coke can's strength before & after it has a tear in the skin. With TTW you're mounted to the MMT & again to the BT.

In the MD case your fins are fairly effective levers, with the fulcrum at the rear. Since the tube is slotted, it is significantly weakened in this same area.

I see how this makes sense, but the fins are then pressing against my motor case, which is significantly stronger than my body tube, so this doesn't worry me too much, as long as the tube interior is flush and the surface prep is adequate.

I'll disagree that it makes for a weaker rocket. I think it actually will make the fin attachment stronger. Maybe the body tube in that area is weaker, but in an area where it does not matter. There was a company called 3 Dogs Rocketry that made a 54mm min dia rocket called KestreL. The Kestrel was a very clean design! It came with a slotted body tube. The AeroPac 100K team has used a modified "slot" for fin attachment. I do a few min dia rockets and would slot my tubes if I had a jig or other set-up to do it quickly.

https://www.rocketryforum.com/showthread.php?17131-KestreL-Ex-build-thread
https://groveraerospace.com/?page_id=217

Tony

Examples are great, thank you.

Certainly I'll defer to those with more experience, it just seemed a stronger attachment to a weaker tube.

I've wondered for a while why nobody does a post-in-hole type fin attach for at least the leading edge.

Post in hole sounds interesting, but I'm past that point for this vehicle.

I'll try this and make a report. At the very least I may be an example for future rocketeers of what not to do.

 

[llickteig1]

Don't sweat about the fin slots. If you lay-up across the fins, i.e. tip-to-tip, any failure will be higher-up on the BT, IMO. I agree completly with Tony's assessment of strength gained in the fin attachment.

The Little Dog is a great flier as an MD build. I have one with many, many flights on it that we had Tim extend the main airframe to accommodate a long 2800Ns motor. Best one to date is in the 14,000' range on a Loki K350. Mine isn't built to be light, it is build to survive and it has many miles of altitude on it.

Good luck - it is a great kit.

--Lance.

 

[blackjack2564]

I'll disagree that it makes for a weaker rocket. I think it actually will make the fin attachment stronger. Maybe the body tube in that area is weaker, but in an area where it does not matter. There was a company called 3 Dogs Rocketry that made a 54mm min dia rocket called KestreL. The Kestrel was a very clean design! It came with a slotted body tube. The AeroPac 100K team has used a modified "slot" for fin attachment. I do a few min dia rockets and would slot my tubes if I had a jig or other set-up to do it quickly.

https://www.rocketryforum.com/showthread.php?17131-KestreL-Ex-build-thread
https://groveraerospace.com/?page_id=217

Tony

+1

I have built several using slots.

Tip: put a motor in the airframe while tacking fins on. I use packing tape to cover area exposed to slots. It's thin & no glue sticks to it. Helps keep the fins root flush with tube.

 

[FredA]

Wrap the motor in one wrap of saran wrap and glue the fins into the slot so they sit flush with the motor.
Bonus that the fins will be square.

You can't put a big enough motor in this kit to worry - no tip-to-tip needed with good epoxy.

 

[Binder Design]

I'll disagree that it makes for a weaker rocket. I think it actually will make the fin attachment stronger.

I concur. That's the way I used to do all of mine before I started making aluminum fin cans.

 

[dhbarr]

TIL something new, glad to know it.

 

[BlazingAngel665]

So Laika didn't make it out for the Berwick launch this week, but I did get 8 hours of sleep the night before the launch. Sunday I had some excellent motivation to continue the project. The fin overwrap is done as of this morning. The quality of this overwrap is in the top 10% of overwraps I have done, so I'm quite proud of it. The pictures here don't show it, but the telemetrum is now mounted to the sled properly. I also re-worked the sled so it can fly in both of my 2.1in rockets with no modifications. Two connectors to the bulkheads and I'm ready to fly. I'm also irrationally excited by the possibility of turning this rocket into an upper stage for a can-o-boom booster. I'd like to stick a K2440 in a 98mm min diameter 1st stage. That's a project for another day though.

The bulkheads have been sanded and epoxied. Switchband has been epoxied as well. I've done a bit of sanding on the nosecone as well. Surface prep took a while. It's always hard to start desecrating the pristine surface of these parts, but the results are nice.

Only fin overwrap image I got, wet epoxy is bad for cellphones.

Apogee order is in, including this delightful minimum diameter retainer from Aero Pack. In the background is my nosecone's new bulkhead retaining ring.

My nosecone is the only payload bay I'll get on this rocket, so I'm loathe to seal it up. This is my solution. 8 4-40 bolts on the bulkhead retaining ring will keep everything together during flight. In between these can be unscrewed to access the nosecone payload bay. Payloads are still unknown. This was my machining jig. Unfortunately my machine shop is only accessible Tues-Thurs so This weekend project got shorted the CNC mill it deserved.

Completed bolt circle looks really nice.

Picked up my first motor for this girl. A J280 keeps me under 7.5k ft. I'm limited to the ceiling at Berwick, ME most of the time, so I bought an extension for my motor retainer and two 54mm spacers for my 4 grain case. A sparky or smoky will further limit my altitude.

 

[DavidMcCann]

Every time I open this thread Time Warner sheds tears

Reminds me of the 28.8K days

 

[BlazingAngel665]

Every time I open this thread Time Warner sheds tears

Reminds me of the 28.8K days

For the young'uns in the room, care to explain?

 

[dhbarr]

Lots of big photos inline, in times past a mortal offense which would make the whole thread unreadable for dialup users.

 

[DavidMcCann]

Yea. I'm on broadband and they're loading row by row over the span of two minutes or so, lol. Not a huge worry or anything, but I haven't seen it happen in ages.

 

[DavidMcCann]

it goes like this-

then five minutes waiting for this to load, listening for floorboards in the house to creak-

 

[blackbrandt]

I'm on an AT&T DSL connection... currently getting somewhere around 80-100Kbps. -_-

 

[watermelonman]

I was concerned about slots impacting strength so I built a smaller version first. It holds well and feels quite strong, so I gave it a go on a 3 inch rocket. Again it feels strong, much better than I expected.

I used JB Weld for the slot bond. My theory is that the filler material is about right for the slot gaps and imperfections, while heat resistance is good right next to the motor.

 

[blackjack2564]

Thank you "someone" for re-sizing the photos, the thread now opens instantly.

Good luck with this project, very well done.

 

[crossfire]

Not resized here

 

[BlazingAngel665]

Thank you "someone" for re-sizing the photos, the thread now opens instantly.

Good luck with this project, very well done.

Not resized here

I've resized the photos down twice. Linking the raw images is what gets the ugly hugeness. I'm linking the "thumbnails" now. Hypothetically I can internet.

Somewhat less hypothetically, I can rocket. Today I started sanding. Using my remarkable powers of foresight I see many layers of bondo and high build in my near future. I'm always open to paint tips though, so hit me with your best sanding, priming, and painting know how. I'm also looking for recovery harnesses and aluminum eyenuts for everything. I'm considering doing my own harness. I wonder how short I can make my webbing and still get away with it? Finally, I'm looking for camera mounting suggestions. I don't want the camera hanging outside, but I'm considering putting an 808 or mobius in the nosecone facing down or out. Alternatively I could attach the camera to the recovery webbing? Thoughts? I want the camera to be easy to change out for when I decide to let this gal off the chain, but video is always nice to have.

 

[BlazingAngel665]

Only one new picture from hours of sanding.

The fin can has two tip to tip layups, and now two coats of bondo. The joints aren't quite as nice as I'd like them yet, so I think I'll do one more layer just in the fillets.

In other news however a couple of orders showed up. I now have a Mobius camera to fly on this vehicle. Even better, I have live video equipment to go with it. I'm using a 2.4 Ghz transmitter to live stream the video to my laptop. I also got an extender for my motor retention hardware. It will be nice to be able to fly to altitudes less than 15,000ft. It'll really help with finding a field to fly at.

 

[Scoops]

I'm also looking for recovery harnesses and aluminum eyenuts for everything. I'm considering doing my own harness. I wonder how short I can make my webbing and still get away with it? Finally, I'm looking for camera mounting suggestions. I don't want the camera hanging outside, but I'm considering putting an 808 or mobius in the nosecone facing down or out. Alternatively I could attach the camera to the recovery webbing? Thoughts? I want the camera to be easy to change out for when I decide to let this gal off the chain, but video is always nice to have.

Great build so far! I am working on my first 54mm MD rocket too. Isn't all the filling and sanding for the tip-to-tip fun? :cry:

I decided to go with OneBadHawk kevlar recovery harnesses because I've used them in other projects and they work great. Fireproof, incredibly strong, and light weight. I wanted to do a camera too (have a Mobius) but can't figure out where to mount it, except on the outside facing down during more mild flights. It won't fit in my nosecone (have gps tracker in there) or altimeter bay. Hopefully someone else has done this and can comment.

What switch did you decide to use for your altimeter? How are you planning to fasten the nosecone bulkhead to your nosecone? I'm saw your pictures but am not following.

Steve
L2