Feedback wanted on 3X5: an L2 scratch build design for Freedom Launch

[jhill9693]

Freedom Launch is 2 weeks out. Having just confirmed as of today that the qualified personnel will be present, and a vendor has a Cesaroni J270 motor in stock, I'm ready to design and build my L2 qualification vehicle.

Design requirements:

• 38mm motor mount
• Dual deploy
• Assemble quickly
• Use stuff I have on hand

The airframe is 3" mailing tube from Office Depot, the nose cone is 3D printed by KN Aeronautics (eBay), and the rings and fins will all be 1/4" lite plywood. Engine mount is a piece of PML phenolic that I have laying around, and I think I have an Aeropack retainer that I can use. 18" drogue and 36-45" main nylon parachutes will be employed, all on hand. Electronics will be the Eggtimer Quantum altimeter and Eggfinder Mini GPS tracker.

I'm calling it the 3X5 (3" diameter, 5ft long).

This design sims at about 4800ft, and should stay below mach 1.

Before my build starts tomorrow, I'm putting the design out for comment and feedback. If you have any advice, I'd love to hear it!

 

[tsmith1315]

Freedom Launch is 2 weeks out. ...
I'm ready to design and build my L2 qualification vehicle

Use stuff I have on hand

I love it! Fun constraints!

I see nothing I'd change. You'd likely be okay with motor ejection and eyeball tracking if time gets tight, but 3"/4800' is borderline visibility. It'd do it in a second in low wind, if it came to that. Actual weight may end up a bit higher, nothing wrong with that. Please post some pics when you, so we can see your progress.

Be sure they're bringing the L2 test materials to the launch! Like, check again a couple days before the club packs everything.

@Sandy H. , are you watching?

 

[jhill9693]

Cut and beveled fins. Went with aircraft grade 1/8” plywood I had from a hobby shop. It’s noticeably stiffer than 1/4” lite ply.

 

[jhill9693]

Chop saws are wonderful for cutting these heavy tubes. Go slowly, and use a sacrificial straight edge if your table angles inward or you won’t get a straight cut.

 

[jhill9693]

By far the hardest part was slotting the lower airframe. The cuts need to be very precise or the fin can will jam when it slides in.

I folded a piece of paper two ways and then marked 1/2 of the OD from the center to ensure the tube was centered on the fold. Marked the tube on the outside then transferred the marks around the edge to the inside, and cut on a table saw being VERY careful and taking my time.

I marked the table at the point where the cuts need to stop so that they would all be uniform in length.

 

[jhill9693]

The second hardest part was cutting centering rings and bulkheads from 1/4” lite ply. It should be very easy but my circle cutter is hard to set accurately.

I made sure to not cut all the way through the center so as to leave an alignment hole for the center bit. This ensures that the centering rings actually… center.

 

[jhill9693]

This is my build buddy, Bob

 

[jhill9693]

Now for the fun part! Commencing the build, over Lost.

 

[jhill9693]

Dry fit and first look!

 

[Hobie1dog]

I'm looking forward to meeting you down there. I'll be in the blue powerchair.

 

[tsmith1315]

Dry fit and first look!

Always fun to see it for the first time!

 

[jhill9693]

Gluing the fins to the motor mount, using the slotted tube and some paint stirrers to ensure alignment.

 

[jhill9693]

Tonight was all about epoxy. Attached a 25ft flat nylon shock cord, and added internal fillets to the fins and rings.

 

[jhill9693]

Cut parts for the av bay tonight. No pix yet, but it's super lightweight, has no metal hardware, and has minimal wood. Interest piqued? I hope so! It's probably gonna get its own thread. More to come on this tomorrow.

 

[Rocketjunkie]

Freedom Launch is 2 weeks out. Having just confirmed as of today that the qualified personnel will be present, and a vendor has a Cesaroni J270 motor in stock, I'm ready to design and build my L2 qualification vehicle.

This design sims at about 4800ft, and should stay below mach 1.

Before my build starts tomorrow, I'm putting the design out for comment and feedback. If you have any advice, I'd love to hear it!

Need a tracker? The club has a receiver and Walston trackers you can rent (IIRC $5 or $10). I also have some that you can borrow and the club receiver will get their signal. I also have plenty of batteries if the club tracker needs them.
I'll be experimenting with the TeleMini in my sub minimum 18 mm rockets with F23 experimental motors. These are without the altimeter/trackers. Add another 6-7" for the payload bay. Fins are glued to the motor, couplers fit inside the motor and body tube. Body tube ID is same as motor ID.
Once you get your L2, you can make experimental motors like these

 

[Hobie1dog]

Need a tracker? The club has a receiver and Walston trackers you can rent (IIRC $5 or $10). I also have some that you can borrow and the club receiver will get their signal. I also have plenty of batteries if the club tracker needs them.
I'll be experimenting with the TeleMini in my sub minimum 18 mm rockets with F23 experimental motors. These are without the altimeter/trackers. Add another 6-7" for the payload bay. Fins are glued to the motor, couplers fit inside the motor and body tube. Body tube ID is same as motor ID.
Once you get your L2, you can make experimental motors like these
View attachment 534062

I'm interested in tracking my Level 1 rocket this time since I lost my coveted PML MR-1 rocket last time. You need to make sure you introduce yourself to me, I'll be in the power chair

 

[samb]

Nice job jhill9693. Build pics look good, I’m jealous of all your shop tools. Not your first rodeo with electronic deployment, right? Good luck with the cert flight and more Build Buddy Bob!

 

[jhill9693]

Need a tracker? The club has a receiver and Walston trackers you can rent (IIRC $5 or $10). I also have some that you can borrow and the club receiver will get their signal. I also have plenty of batteries if the club tracker needs them.
I'll be experimenting with the TeleMini in my sub minimum 18 mm rockets with F23 experimental motors. These are without the altimeter/trackers. Add another 6-7" for the payload bay. Fins are glued to the motor, couplers fit inside the motor and body tube. Body tube ID is same as motor ID.
Once you get your L2, you can make experimental motors like these
View attachment 534062

Those look fun!

Thanks for letting me know about the tracker. This will be my third launch with the club and it’s good to know what’s available. I’m planning to fly one of my two Eggfinder Mini GPS trackers.

 

[jhill9693]

38mm av bay going together! If it looks suspiciously like an engine mount, that’s pretty much exactly what it is, with end caps at both ends and a pressure vent.

In this design, the tube doesn’t take the shock, the 3/8” tubular kevlar does.

By the way, did you know that the tube that a 29mm Aerotech reload comes in is the exact size used for 38mm motor mounts? And furthermore, the same tube is the exact inside diameter of an Estes BT-60 tube (meaning you can use it as a heavy coupler?

This will be more than enough room to house an Eggtimer Quark and an Eggtimer Mini GPS tracker. Maybe an altimeter too!

 

[jhill9693]

T+3 days to Freedom Launch!

Last night was all about electronics. I recently came into a bunch of Eggtimer equipment, and was able to test most of it. I decided on the Eggtimer TRS which is a dual deploy altimeter with GPS tracking and telemetry built in. It will allow me to run a single battery and fits nicely in the 38mm avionics bay.

Then all the batteries got charged… which was a job unto itself.

 

[jhill9693]

Trimmed and sanded the business end up and prepped the motor tube for the engine retainer. Time to finish this puppy tonight!

 

[jhill9693]

Filled the fin can entry slots with Elmer’s CWF, and JB Welded an Aeropac retainer on. Next up: fillets.

 

[jhill9693]

Altimeter sled assembled, snug fit in the bay with no play whatsoever.

 

[jhill9693]

Weighs in at exactly 3.3lbs without the motor!

 

[tsmith1315]

What, no paint? :ducking:

Nice job, well done!

And good luck with the cert flight.
You might want to call or email whoever is bringing the test to remind them one last time. Been there, didn't do that.

 

[jhill9693]

What, no paint? :ducking:

Nice job, well done!

And good luck with the cert flight.
You might want to call or email whoever is bringing the test to remind them one last time. Been there, didn't do that.

No paint, just TYVEK!!!

 

[jhill9693]

T-36 hours… and we are DONE. Had a successful ejection test (sorry too dark for photos).

 

[tsmith1315]

No paint, just TYVEK!!!

I love it!

 

[Hobie1dog]

highly impressed, There's no substitute for experience and you definitely have that. Hopefully you will shoot it off on Saturday. And I'll be able to watch it.

 

[jhill9693]

highly impressed, There's no substitute for experience and you definitely have that. Hopefully you will shoot it off on Saturday. And I'll be able to watch it.

It was sure great meeting you!