Heavy Lift RC Plane

A foam airplane made to lift a payload to 1,000'+ AGL for parachute testing in a rocketry project

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The development of an RC plane for payload lofting.


  • Currently a FT Guinea Pig airframe
  • Eventually capable of lifting several pounds of avionics to an elevation of several thousand feet AGL.
  • Live on-board video feed
  • Long range (70cm UHF link) control and 5.8GHz live video / telemetry (OSD)

  • Putting LiPo Batteries in Parallel

    J. M. Hopkins10/27/2016 at 06:09 0 comments


    In the RC forums you'll find mostly incorrect information about mixing batteries in parallel. You'll here that you shouldn't run battery packs in parallel, shouldn't mix capacities, and shouldn't mix C ratings.

    I'll go over the basics of how to determine safe operation of mixed capacity/C rating batteries.


    LiPi batteries will usually have a published cell count, capacity, constant C rating and burst C rating.

    Cell count tells you how many individual LiPo cells there are, and hence the voltage. Fully charged each cell is 4.2V, and the battery pack follows the convention of "3S" or "4S". A 3S battery at full charge will be 12.6V.

    Capacity is listed in mAh, or Ah. Pretty self explanatory.

    C rating is a number that tells you at what rate the battery can be discharged at without damage (or fire hazard). A 5,200mAh 10C battery can discharge constantly at 52A without damage.

    The Situation

    My plane has two 30A ESCs, and I have a 5.2Ah 10C 3S battery pack and a 2,250mAh 75C battery pack I want to fly in parallel. Is it safe?

    The Math

    Once both packs are fully charged to 12.6V, they are connected in parallel. Total capacity is now 7.45Ah, but what about the C rating?

    Current will drain from both batteries at a ratio defined by their capacity. So for every 74.5mA drained, 52mA will come from the 5.2Ah battery and 22.5mA will come from from 2.25Ah battery.

    So even though the 2,250mAh battery has a 75C rating, it is limited to the 10C rating of the 5.2Ah battery, and if we pull more than this from our parallel pack we run the risk of damaging the lower C rating battery.

    But just because we are limited to 10C, doesn't mean we can only pull 52A. The 10C rating now applies to the whole parallel pack.

    So 10C of 7.45Ah is 74.5A constant current without hurting the lower rated battery.

    74.5A is plenty of current for my system, so all is good.


    When combining multiple LiPo battery packs in parallel:

    • Use the same cell count (3S, 4S, etc.)
    • Must be charged to the same voltage
    • Total capacity is equal to the sum of the two battery capacities
    • C rating is equal to the lowest C rating of the packs, but relative to the total capacity of the two battery packs

    For example using two equal batteries, let's say two 1Ah 10C batteries, the parallel battery capacity is now 2Ah, and the C rating is still 10C, but now the highest discharge rate has doubled to 20A because the discharge rate is determined by C rating AND total capacity.

  • Testing RSSI Values

    J. M. Hopkins10/15/2016 at 02:39 0 comments

    Alright, so in this post I'll be going over some of my incremental testing of my new UHF transmitter.

    RSSI is the Receive Signal Strength Indicator value, and it comes from the onboard UHF receiver on the aircraft. This data is brought back to my ground station over the on screen display. The lower the RSSI value, the worse the control signal quality is to the aircraft, so it is important that we understand how it works with incremental testing of the system.

    For the first couple minutes of this flight, I have taken the OSD data and graphed it. You can see I took the aircraft to 500m, and then out to 700m. The Orange line at the top is the RSSI value, and you can see when the aircraft gets close to the transmitter.

    I believe I may need to alter the calibration on the RSSI curve a little bit to get a more consistent linear response. I also need to see where control dropout starts to occur.

    Here are the videos! The first in HD with no OSD, the second is what I saw while flying (minus the skipping, which I believed is caused by a lower quality SD card in my DVR).

  • Testing Range + Video

    J. M. Hopkins09/06/2016 at 02:39 0 comments


    I'm going to be flying a UAS system capable of lifting several pounds to over a couple thousand feet, so I did some testing of range of both the on-board telemetry/video feed and my transmitter itself.

    Overall the test was successful, but I will be needing to do a few things now to maintain legality and to further the design.

    1. With the increase in range required to get my aircraft to this elevation and with a larger payload, I will be changing to a 1.5 watt 70cm control link (dialed down to 1 watt to fulfill FCC requirements on transmitter power to arial platforms) requiring a amateur radio certification. This is not an issue as I already have this from other projects in the past. (Callsign KC3EFJ), I'm just putting it here for others interested in the project.
    2. Directional antennas for both 70cm (control) and 5.8GHz (video/OSD). I have experience again in making my own directional antennas. The control link might be doable with an omnidirectional dipole.
    3. FAA Certification/Waivers
      1. Option #1. Fly in accordance with the Special Rule for Model Aircraft (Public Law 112-95 Section 336). Under this rule, operators must:
        • Fly for hobby or recreational purposes only
        • Follow a community-based set of safety guidelines
        • Fly the UAS within visual line-of-sight
        • Give way to manned aircraft
        • Provide prior notification to the airport and air traffic control tower, if one is present, when flying within 5 miles of an airport
        • Fly UAS that weigh no more than 55 lbs. unless certified by a community-based organization
        • Register the aircraft (UAS over 0.55 lbs. and less than 55 lbs. can be registered online at; UAS 55 lbs. or greater must be registered through the FAA's paper-based process)
        Option #2. Fly in accordance with the FAA's Small UAS Rule (Part 107). This requires operators to:
        • Obtain a remote pilot certificate or be under the direct supervision of someone who holds such a certificate.
        • Register the aircraft as a non-modeler at
        • Follow all the operating rules in accordance with the regulation


    Here's a video of my recent test, which validates data paths to and from the aircraft at medium range. The next round of testing will use the long range electronics, capable of the distances necessary.

    Since I live near the coast, there is almost always significant wind. In this case 15-17 knots from the west (the ocean). It certainly makes landing a bit more interesting.

  • Mid Size Cargo Plane

    J. M. Hopkins08/17/2016 at 03:24 0 comments

    My mid size cargo plane was built to teach me advanced flight with flaperons and differential thrust. My full size plane will be about 150% of this 58" wingspan with a more utilitarian body style.

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Jasper parker wrote 01/05/2017 at 05:46 point

Fantastic footage and build. Iv always wanted to get into FPV flying, I used to fly stunt helicopters before Drones became all the rage.

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Christine Banek wrote 08/18/2016 at 23:43 point

Super impressive!

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