I have no idea what I'm doing- 54mm MD CF rocket for LDRS

[djs]

So- I'm looking to build a rocket to do one thing:
1. Break Mach 2
2. On a MD CF scratch built rocket
3. With an EX motor

Ideally it would be a reusable airframe, but recovery would be enough.

The main design is 54mm with carbon fiber body tube and fins (from SinfulDarkLord on this forum). AV bay + nose cone is from Wildman. Rocket will be head end dual deploy. Electronics will be an eggtimer proton. Maybe an RRC3 backup?

Motor will be an EX L motor using the 54mm case in the picture below.

Rough design in OR. I'm thinking of making the fins a little smaller.



Obligatory pile of parts:



Open design issues:
1. Epoxy- probably will use proline
2. Onboard camera? I think it would be ridiculous to fly this without something to watch later on
3. Motor retention?
4. Tracking- Have to figure out how to get a signal out of the rocket

FYI- the title is mostly because some of this stuff is new to me- not that I'm completely ignorant- just mostly ignorant.

 

[DaveW6DPS]

4. Tracking- Have to figure out how to get a signal out of the rocket

What kind of tracker are you thinking about? If you are looking as something in the 70cm ham band (I am partial to Big Red Bee) you could look at a horizontal dipole or even a whip running at right angles to the axis. There would be some drag, but with one or two 6.25 inch antenna elements it shouldn't be much. Maybe .3mm piano wire would stiff enough.
On the 900 MHz band stuff they would be even smaller.

If the nose cone is fiberglass, you could just put a tracker or beacon transmitter inside it.

I agree a camera would be cool, but at Mach 2+ a keychain on the outside is not a great idea. Do you have room to put one inside with a window in the switch band? 54mm MD is small to be able to put much inside.

 

[blackjack2564]

Use a large fiberglass 3-4 in. vent band and 9in. coupler in NC
This gives you plenty room for camera and tracker that Wildman NC is black fiberglass ..so good to go radio transparency there.
Just copy any good fin design for a 54...Punisher...Falcon... kestrel etc.
Get a good OR design of those and use fin measurements...voila one and done.
Tracker antenna...can hang out of bulk plate or be inside av-bay coupler depending on size .
Motor retention friction fit with wrap of aluminum duct tape on outside motor/airframe.
Been doing it for years it works. Keep it simple.

 

[Glasspack]

Use a large fiberglass 3-4 in. vent band and 9in. coupler in NC
This gives you plenty room for camera and tracker that Wildman NC is black fiberglass ..so good to go radio transparency there.
Just copy any good fin design for a 54...Punisher...Falcon... kestrel etc.
Get a good OR design of those and use fin measurements...voila one and done.
Tracker antenna...can hang out of bulk plate or be inside av-bay coupler depending on size .
Motor retention friction fit with wrap of aluminum duct tape on outside motor/airframe.
Been doing it for years it works. Keep it simple.

Jim, Am I correct in thinking your saying "large fiberglass 3-4"
That you mean 3-4" Dia,

Paul

 

[blackjack2564]

No...normal vent band 1 to 2 inches, I'm saying increase the length to get more interior room of coupler.
Doing this keeps av-bay from going into fincan deeper, allowing for shorter fincan= higher/faster flight.

 

[manixFan]

I’ve built 2 CF MD 54mm rockets - a Mongoose and a scratch built. Just Proline fillets on the fins. Used a couple of different motor retention methods but the simplest is a internal plate with a 1/4” hole to run a piece of all-thread through that’s threaded into the forward closure. A/V bay is built into the coupler which is glued in place. I’ve never used a switch band. All magnetic switches so only hole or protrusion is for baro vent. Tracker in nose cone. Hit Mach 2.4 on a CTI L935 out of a tower at BALLS.

I would look at the Mongoose fin shape, it works well. Most folks say a high Mach flight should have a stability margin of around 2. It sounds like you won’t have room for nose weight so you’ll need to watch out for that if you make the fins smaller.

Good luck,


Tony

 

[OverTheTop]

Have fun with this. I have a 38mm and a 54mm on the slow-burner currently. Have a look here for motor mounting which is quite low mass. Feel free to steal any of the ideas or thoughts. They might not even be mine anyway
https://forum.ausrocketry.com/viewtopic.php?f=6&t=6030

 

[djs]

Use a large fiberglass 3-4 in. vent band and 9in. coupler in NC

This was my plan- to have a long vent band, and put the tracker inside the coupler. My concern here is the interference from all thread for the tracker signal. The trackers I normally use are ComSpec.

As for the camera, I was thinking of building a "platform" in the av bay to put a camera on, looking out a hole on the vent band. I have some ideas here, but have not built anything yet.

 

[djs]

I
would look at the Mongoose fin shape, it works well. Most folks say a high Mach flight should have a stability margin of around 2. It sounds like you won’t have room for nose weight so you’ll need to watch out for that if you make the fins smaller.

Yes- this is why the fins are a little oversized right now. I''m hoping to mess around with finsim a little bit to make sure I have something that won't flutter at high speeds.

Fortunately it being HED, will give it more weight on the top end to help with stability.

 

[tfish]

The 808 cameras don't like high G's even when laying flat inside a 54mm rocket. Lots of corrupted files. We were able to piece bits and pieces together for STEM project. Still lots of frozen visual with out of sequence audio. That flight was only 1.6 mach.

Tony

 

[djs]

The 808 cameras don't like high G's even when laying flat inside a 54mm rocket. Lots of corrupted files.

Maybe a mini mobius? Alhough is this a camera problem, or an sd card problem?

 

[Glasspack]

No...normal vent band 1 to 2 inches, I'm saying increase the length to get more interior room of coupler.
Doing this keeps av-bay from going into fincan deeper, allowing for shorter fincan= higher/faster flight.

Thank You

 

[Luke]

Watching with anticipation

 

[plugger]

So- I'm looking to build a rocket to do one thing:
1. Break Mach 2
2. On a MD CF scratch built rocket
3. With an EX motor

Ideally it would be a reusable airframe, but recovery would be enough.

As long as you stay in the mid Mach 2 range or below you should be fine for reusability.

Open design issues:
1. Epoxy- probably will use proline

Proline should work fine in this use case.

2. Onboard camera? I think it would be ridiculous to fly this without something to watch later on

I've not flown it yet but I've built a 54mm AV Bay that can take a GoPro Hero Session camera. I'd recommend looking at those cameras for use in a 54mm rocket.

3. Motor retention?

Use a cable cutter as well as HED and you can put everything in the NC and use the aft bulkhead of the AV Bay for a threaded rod internal retention mount point. See below.

4. Tracking- Have to figure out how to get a signal out of the rocket

Use a TeleGPS and have the antenna in the nose. Given your NC is FG you should be able to get telemetry for the entire flight.

 

[djs]

Thanks for the info Plugger. Not sure I want to do the cable cutter idea yet, but it does solve few problems. Go pro hero session is a nice idea, but not sure I can afford it

 

[plugger]

Thanks for the info Plugger. Not sure I want to do the cable cutter idea yet, but it does solve few problems. Go pro hero session is a nice idea, but not sure I can afford it

My pleasure. FYI the Hero Session 4's can be found on Amazon refurbished for ~$100.

 

[manixFan]

Plugger - your images have given me an idea of how to setup my next MD rocket. The nosecone coupler will act as motor retainer and A/V bay and will be glued into the airframe. The nosecone sans coupler will eject and I'll either use a wire cutter or a Jolly Logic chute release. I am on a kick to not have any external protrusions on my MD rockets and am now working on going as short as possible. The only hole I'll have will be for the altimeter vent - I use magnetic switches so no holes needed there.

Thanks for the info.


Tony

 

[plugger]

Plugger - your images have given me an idea of how to setup my next MD rocket. The nosecone coupler will act as motor retainer and A/V bay and will be glued into the airframe. The nosecone sans coupler will eject and I'll either use a wire cutter or a Jolly Logic chute release. I am on a kick to not have any external protrusions on my MD rockets and am now working on going as short as possible. The only hole I'll have will be for the altimeter vent - I use magnetic switches so no holes needed there.

Thanks for the info.


Tony

No worries Tony. That's the exact design I used in my flight a couple weeks ago. More info can be found here.

https://forum.ausrocketry.com/viewtopic.php?f=10&t=6216

I used a FingerTech screw switch to power up my Raven 3 and a TeleGPS for tracking. I turn on my tracker on the flight line before closing up the AV Bay so I also only need one vent hole which also doubles a switch activation port.