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Thread: Techpod HD: a heavy duty upgrade build thread

  1. #1
    Techpod designer Hobby UAV's Avatar
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    Techpod HD: a heavy duty upgrade build thread

    I originally designed the techpod with the intention of flying it around 4.5 lbs and a cruise speed of around 30 mph. However everyone wants to fly faster and longer, myself included. Along with the fact that control loss is quite frequent when performing long range FPV flights. This has led to weights in excess of 7 lbs and speeds in excess of 65 mph being achieved in an uncontrolled dive. This has led to catastrophic wing failure.

    In an effort to modify the techpod to handle the higher loads and higher speeds, I have began this thread and will be posting pictures of my progress and testing. The goal is to come up with a upgrade kit for anyone who needs something a little tougher then the stock techpod.

    first I installed some plastic tubes so servo wires can be installed after the wing is complete. I used goop on the spar and CA on the foam to foam areas.



    I attached the two basswood pieces using some gorilla glue.


    next I removed the control surfaces. I cut the wing so a couple of 1/2 x 1/4 x 24 inch pieces of basswood a can form a new flap hing line.


    I drilled out the spar to accept a 7 inch piece of brass tube.


    the Brass tube slides in and will form a sleeve for a steel connecting rod.



    after some trials and tribulations, I came up with molded corbon fiber wing skins.
    Last edited by Hobby UAV; 1st February 2014 at 03:36 PM. Reason: updates

  2. #2
    I see you... Derrick's Avatar
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    Due to the high aspect ratio wings and relatively thin airfoil section, your best "bang for the buck" upgrade is going to be to the "skin" of the wing. The ideal solution is to vacuum bag a fiberglass skin with unidirectional carbon reinforcement (though this is something that an average modeler can't do). The next best option is to add ribbon spars top and bottom in addition to laminating the entire wing (this will add bending stiffness from the ribbons and torsional rigidity from the laminate). The second alternative is something that any modeler should be able to do. It is also effective cost wise too.

    Check out the build instructions for a windrider bee to see how to effectively ribbon spar a wing.
    When nothing else out there will suit your needs... design and build it yourself.

  3. #3
    Techpod designer Hobby UAV's Avatar
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    hey Derrick, I am going to try something like what airtruck has going on.

    plus I want to expand on his idea with laminate top and bottom on the root.

  4. #4
    Techpod designer Hobby UAV's Avatar
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    so I spent the day making a box so I can heat up the wings while they cure. an electric blanket gets it up to 110F. I am aiming for 125 so i will try adding some insulation tomorrow.



    The plan is to laminate some 5 OZ CF cloth to the to and bottom of the inboard half of the wing. this is a paper pattern I made to help cutting out the CF.

    and here is the CF cloth

  5. #5
    Test pilot addict airtruksrus's Avatar
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    I took a good look around different curing techniques and different brands of resin and the variety of curing temps landed to the same conclusion, as long as it's not too hot of a batch and if setting a curing temp that it doesn't compromise the integrity of the foam, you should end up with a good layup. Are you making a shell or using an epoxy based adhesive to attach it to the wings?

    All the wrap of the wings should maintain a really stiff wing as I found another defect after many landings on the older Techpod. I finally gave up the reigns and let a friend of mine launch it for me, unfortunately he launched it at a climbing angle and lost too much airspeed then stalled with a rough landing. Had one good flight before this. Where the weak spots came up was the forward inner corner of the flaps on both wings, developing cracks at that same location. The lamination stopped it from spreading further forward but a question of more flex in the wings. Probably time to move into the new one as the motor mount also suffered from continuous flexing and didn't take much for it to snap at the bottom where the holes are drilled for the lower motor mounts. might need to use a sturdier material to reduce the operational stress. I have some 1/8" fiberglass plates that I can cut out using the original piece as a template, they should be light and resilient to withstand the rigors of continuous flights. I looked at it further and looked like it weakens up from repeated twisting and eventually gets looser. Hope it helps and looking forward to seeing the new updates on the kit.
    KF7TSE

    youtube.com/channel/UCzoOpmJK8_WOlBl65sZAfGw
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    Airtruksrus Cockpit Ground Station Systems.
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    Always under revision to make it better.

  6. #6
    Techpod designer Hobby UAV's Avatar
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    Ok thanks Scott. I have some 1 - 8th fiberglass as well. I will see if my home made cnc machine will handle it. The flimsy 3 ply plywood they sent with the kit really start to fall apart over time. If my machine can't handle the FG, I may try laminating CF cloth over some 5 ply aircraft grade plywood.

    Here is the heat box all insulated.


    If you could post some pictures of the flap area cracks and engine mount I would appreciate it. Ty!

  7. #7
    Techpod designer Hobby UAV's Avatar
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    I think the way I am putting the second spar just in front of the flap, should prevent cracking in that corner.

  8. #8
    Techpod designer Hobby UAV's Avatar
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    So here are the CF darts and kevlar leading edge.

  9. #9
    Test pilot addict airtruksrus's Avatar
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    Wayne, the laminate did the job of holding the foam together but the stress from the hard landing is what cracked it and stretched the laminate enough on both sides.


    The strengthened up motor mount should fix any stress problems from occurring again. Was kind of strange that the motor was oscillating back and forth during regular flying but didn't break until the motor was running full throttle when it landed, not any more stress than it usually goes through.


    Hope it helps. I could probably continue to try to repair it further but after looking at the rest of the structure, probably best to move it to the improved airframe. It should hold up much better, just surprised that this one survived as much as it did, one amazing and tough airplane. Was also considering adding a single wheel down the centerline and pull pull control for the rudder.
    KF7TSE

    youtube.com/channel/UCzoOpmJK8_WOlBl65sZAfGw
    vimeo.com/airtruksrus/videos

    Airtruksrus Cockpit Ground Station Systems.
    Open for business
    Always under revision to make it better.

  10. #10
    Techpod designer Hobby UAV's Avatar
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    Cool thanks. I was considering whether to vacuum bag the CF directly to the wings or to make the CF into plates to be wrapped after they are cured.

    Vacuum bagging the CF to the wing would probably give the best bond, but if I make some plates cut to size, people who have the kit already can apply it and it would be less expensive and time consuming.

    I'm going to try the pre cured plates first I think.

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