Carbon fiber, radio opaque?

Discussion in 'Rocketry Electronics and Software' started by Kosmo, Jun 25, 2019.

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  1. Jun 25, 2019 #1

    Kosmo

    Kosmo

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    So I'm recently L2 certified. I got my first carbon fiber kit which I'm very excited about, my intention was to build my first mach-buster and I figured carbon fiber was a good way to go.

    I have a telemetrum altimeter/tracker and their instructions suggest that carbon fiber is radio-opaque, it is a radio and GPS device. I'm sure there are people here that have experience with this. Is there any way I can still use this device without any external antennae? I've never used the telemetrum before in a carbon fiber rocket, but I worry that if I need external wires/antennae it may be difficult to achieve a mach-busting flight.
    Is there any way around this? Is carbon fiber really radio opaque?
    My club doesn't allow launches over 3000' without a tracker, am I doomed to have an external wire on my rocket?

    Thanks.
     
  2. Jun 25, 2019 #2

    dhbarr

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    You have the kit and the tracker, yes? Put it on your porch and walk the neighborhood. Get a solid feel for if the attenuation is enough to slow you down closed or open.
     
  3. Jun 25, 2019 #3

    manixFan

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    Carbon fiber is generally radio opaque, but how much depends on thickness. I use RDF trackers and could get a decent signal though the old thin-wall carbon fiber Mongoose 54. But the signal through heaver CF (like the 98mm Mongoose) is much more strongly attenuated. However since the tracker is attached to the shock cord once the drogue is out I can easily pick up the signal.

    However for a GPS tracker I would be very surprised if you can get a good lock through the CF. As dhbarr says you'll need to test it. My solution is to put the tracker in the nosecone which is just regular fiberglass. I did that at BALLS last year with the Featherweight tracker and had no issues. Both rockets used CF body tubes. But if you are using a combo unit that does present some issues. Maybe you can just use the Telemetrum as a tracker and a regular altimeter in the body of the rocket.

    Good luck,


    Tony
     
  4. Jun 25, 2019 #4

    GrouchoDuke

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    I haven't had good luck with any RF through carbon fiber. Carbon conducts, so it does a great job of whisking the signals away. If you have a fiberglass nosecone, you can put it in there or in the body above the body tube seated in a fiberglass coupler attached to the carbon body.

    It's way easier to just use a fiberglass body tube though unless you need every gram of weight reduction. I sent a way-modified Go Devil 38 (with carbon fins) to about Mach 1.8 on an I216 last month and just did my first supersonic 24mm MD flight (to about Mach 1.4). You can definitely go supersonic on most min-diameter rockets.

    It looks like Madcow has Go Devil 38s in stock. It looks like a stock GD38 should hit somewhere in the 1.4 to 1.5 range and about 10,000'+ with an AT J270W. The TeleMetrum will fit fine in there. Doooooo iiiittt!
     
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  5. Jun 25, 2019 #5

    Kosmo

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    Thanks for the responses. The entire body, including the e-bay and nose cone is carbon fiber in this kit. Our club does offer the radio trackers that you can attach to the shock cords. I was just hoping I could use some of the additional GPS/RF functionality of the telemetrum in this rocket that will likely go very high.

    I will try testing it out. If it doesn't work I'll probably swap out the telemetrum for my other altimeter which is an Easymini (no tracking) and just use the club tracker on the shock cord.
     
  6. Jun 25, 2019 #6

    cerving

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    Many CF kits use fiberglass nose cones, I would imagine just for this reason. The Mongoose 29 has a polycarbonate nose cone, and the Mongoose 38 has a fiberglass nose cone... they work fine with trackers (like Eggfinders). If you're using an altimeter with a wireless interface (such as the Eggtimer Quantum or Proton), it may be challenging to get a signal outside the AV bay. One way to make it work is to cut a thin vertical slot of the right length (1/4 wave, or about 1 1/4" for 2.4 GHz WiFi) through the AV bay. This acts as a waveguide and will allow you to pick up the signal, as long as you're even with the slot.
     
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  7. Jun 25, 2019 #7

    Kosmo

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    Ha. So I was mistaken. The nosecone in this kit is fiberglass after all. (It certainly looked like CF.)

    I'm not sure if that changes things much as I'm not sure how I'd wire the telemetrum for dual deploy in the nosecone. It may however allow me to mount a tracker in the NC rather than the shock cord.

    Thanks for the responses.
     
  8. Jun 26, 2019 #8

    JimJarvis50

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    I have several rockets that have the altimeter in the nose cone. I use a bulkhead in the normal ebay position with a charge below it for the drogue and a charge above it for the main. The wires just pass through the main bay with a breakwire or fitting for the drogue wire. This is not difficult. If you would like to pursue this approach, I can post some pics.

    Jim
     
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  9. Jun 26, 2019 #9

    Kosmo

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    Jim,
    Yes, please! It may be a little late for my current project because the bulkhead is already attached to the nosecone. But I'd love to see your design(s) for future reference.
    Did you build them that way for the carbon fiber issue?
     
  10. Jul 3, 2019 #10

    ksaves2

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    Get a new nosecone and start over. It's not that pricey. If you are going to be sending the rocket up real high, you need a reliable tracking solution.
    Alternative is make a tracker bay you can where you mount the tracker securely and entirely in a radiolucent bay and attach it to the apogee harness
    so it gets ejected out into the open at apogee. If using GPS, let it get a lock first before packing inside the rocket. Though this remedy might not
    be an option for minimum diameter. Kurt
     

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