9 Planes Combine To Make One Giant Flexible Flier

[Ran D. St. Clair] has created a unique flying machine in the Flex 9. It’s not every day that you see a completely new and unusual aircraft, but the Flex 9 definitely fits the bill. [Ran] took 9 radio controlled planes, connected them together, and made one giant plane — and with an 18-foot wingspan, giant isn’t a misnomer.

The planes that make up the Flex 9 are simple aircraft – foamboard wings, a boom, and a basic tail. The individual planes only have elevator control – no rudder, no ailerons. Power comes from a standard LiPo battery, ESC and brushless outrunner motor. The control system is interesting – every plane has a KK board flight controller running OpenAeroVTOL firmware. The center plane has a radio receiver and communicates to the other KK boards over standard servo wires. Rudder (yaw) and aileron (bank) control are achieved through mixing handled by flight controllers.

Even the couplings between the planes were carefully designed. [Ran] used an EPP foam core as a rubbery dampener, with plywood to strengthen the joint. Each joint is mounted at a 20-degree angle. As the planes bank relative to each other, the angle forces the airframe to twist, which should help the whole system stay level.

Check out the videos below for an explanation and a flight test. The Flex 9 launch isn’t exactly stable – there’s some crazy sinusoidal wobbling going on. But the mechanical and electronic dampeners quickly spring into action smoothing the flight out.

If you’d like to know more about the KK board, you can read about right here.

18 thoughts on “9 Planes Combine To Make One Giant Flexible Flier

  1. I would love to see what would happen if one of the units failed. would the others compensate.
    would also be way cool if each had a separate radio so that if they detached they could be controlled independently.

    1. I saw another flying ring on RCGroups several years ago (before these fancy controllers were cheap and available), where the ring had an airfoil profile. It was not VTOL. It had to be hand launched overhead (off of the top of a hill if I remember correctly), but it flew very well. It was smaller, lighter, and lower powered. If I remember correctly it would glide when power was cut. It was very cool. I’m having trouble finding it now though.

  2. Yes the ring runs rings around other things in the air. Did I hear someone say UFO in the vid. Just waiting to be skinned in some kinda lights. The wing could hold one line of text.

    Years ago I watched dome buildings go up spun in a spiral with styrofoam square logs. The were melted on a flat surface and quickly stuck together, good as welded. Might work better than all of the tape and whatever stiffener is under it to make the ring.

  3. I am the designer, builder, and pilot, so I can answer your questions.

    How long can it fly? About as long as this video. There was 27% of battery capacity left at landing, so a good safety margin.
    Why does it want to turn left? It only does that when Auto Level is turned off. Slight trim issues with the various elevator settings.
    What is the point? To see if it is possible. To learn how to do it. Because it’s fun.
    What is the application? High altitude solar powered aircraft are very large and delicate. This technique would reduce structural stresses when flying in turbulence.
    What is not the application? Man carrying aircraft. This is suitable for use with autonomous aircraft.
    How does it work? 3 receivers, all bound to the same transmitter, send identical signals to all 9 planes. 9 flight controllers interpret those signals to tell each plane what to do. Each plane has only throttle and elevator. Differential throttle gives yaw control (steering). Differential elevator gives roll control (like ailerons). All elevators together control pitch (up-down).
    What does the flight controller do? It provides rate gyro stabilization as well as AutoLevel stabilization. It also mixes the input signals differently depending on the planes location in the array.
    Is P factor making it turn? No, P factor relates to differential thrust across the propeller disk due to the air coming through the disk at an angle. It’s not an issue here, in part because the propellers on opposite sides of the plane turn in opposite directions so any P factor would cancel out.
    Can you wrap it in a circle and fly it? Circle or Ring planes can fly, but not this one. There is no structure that would allow it to hold its circular shape.
    Is it more efficient? In theory yes. Induced drag, that is drag due to lift, is reduced by the square of the span, so a very large span has very low drag. This specific plane is not very efficient because it is not very streamlined.
    How much does it cost? Not much. All the gear is simple low cost hobby grade stuff.
    How does it get power? Each plane has a small 2 cell lithium polymer batter, 1A hour capacity. It uses small brushless motors and electronic speed controllers (ESC) to drive them It’s all inexpensive hobby grade stuff, and readily available.
    Why does it flap and wiggle so much? Mostly because it isn’t properly tuned yet. This was the very first flight. It will always wiggle and bend in turbulence though, that is kind of the point. If it was rigid then the structural stresses would be higher.
    What’s it made of? It looks like cardboard, but it is really foamboard. It’s the same stuff you can buy at your local store that kids use to make presentations. It is brown because the paper on the outside is brown and water resistant. It’s held together, mostly with hot melt glue. The fuselage is a fiberglass tube like an arrow shaft. It’s a very simple, cheap, and not very elegant building technique, but it works fine for a quick experiment.
    Was it hard to build? No, it’s about as easy as a plane can be, except that you have to build 9 of them.
    Who launches on 4? I guess I do. 3 would have worked just as well.
    Why launch it from the wing tips? Because there is no other good way to grab it. You could have 4.5 people hold 2 planes each, but it would be hard to get them all coordinated.
    Why not add landing gear? Because it’s simpler to live without it, and the flying site we use is covered with grass, so wheels would not work easily. On a flat smooth surface, wheels would work just fine.
    Can you make one with 100 planes? In theory yes, but it would be a lot of work, hard to launch, and a logistical pain in the neck. Besides, for the intended full scale purpose, 9 each 40 ft. modules would be 360 ft. span, which is already way bigger than a 747 at about 200 ft.
    Would it fly better if the modules were swept back like a flock of geese? Not really. Geese fly that way because they are not attached. Ideally the multiple modules would be one smooth continuous wing, but this is just a science experiment. Geese do fly in a V for the same basic reason though, to increase their combined span for better efficiency.
    What kind of drone was used for filming? It was a more or less stock “race quad” with 5” props and a Go-Pro on the font. The pilot, however, is exceptionally skilled.
    Why was it so grey? The smoke from the “Camp Fire” in Southern California settled in the San Francisco bay area for several days, plus it was cloudy.
    Will it fly again? Yes, it has already flown and crashed since then. Flights will continue each weekend, weather permitting, until we get it tuned as best we can. There will be more video, but without all the flapping it will probably be boring.
    Is it hard to land? Yes, it is. If all 9 planes don’t touch down at the exact same time it tears the foam couplers between the planes. It’s an easy thing to fix, but even a good landing is a slight crash. I never said it was a practical model aircraft.
    How would you launch the full scale version? You get 2 really tall ladders… Just kidding. The Odysseus uses a really wide cart called a “strong back”. They mount the plane on it, and tow it up to speed with a truck. The plane flies really slow so it lifts off easily.
    How would you land such a big aircraft? The Odysseus needs a really wide runway. For full scale it is possible to have the modules break apart and land separately. That would offer huge advantages when operating in areas where a big runway is not available. It would also make the modules much easier to manage in less than ideal weather conditions. The model is not designed to break apart in flight, but it is theoretically possible.

    1. > Yes, it is. If all 9 planes don’t touch down at the exact same time it tears the foam couplers between the planes.
      Could maybe deliberately break the coupling about a second before landing?

  4. I am the designer, builder, and pilot of the Flex Plane x9. If you like this video you may also like:
    Flex Plane Explainer: https://www.youtube.com/watch?v=GWGqs3zqttA&t=66s
    33 ft. Flying Wing: https://www.youtube.com/watch?v=HUUqy4XLHjU
    33 ft. flying wing explainer: https://www.youtube.com/watch?v=gCjHWOUMZFo&t=2s
    Flying barn door: https://www.youtube.com/watch?v=MKJNE2slGPs
    Two Planes, One Pilot: https://youtu.be/2SMqG4pNMFE
    Two Planes, One Pilot explainer: https://youtu.be/WDIEJIrgROc
    Xtreme VTOL: https://www.youtube.com/watch?v=rzIXe8OeAzI&t=192s
    Xtreme VTOL explainer: https://youtu.be/L7Ie9sTB3qk
    Plus Size VTOL: https://www.youtube.com/watch?v=DS3VyABT068
    Ring Wing Air Gate: https://www.youtube.com/watch?v=OAHz_gt6Cig&t=167s
    Whirligig: https://www.youtube.com/watch?v=Hl-g4zlLnLk
    Flying Runway: https://www.youtube.com/watch?v=mJBK9lqvSDM
    Flying Runway w Quads: https://youtu.be/u3fr2v2hOk0
    XC-142 Scale VTOL: https://www.youtube.com/watch?v=VQRr-hHbA7c
    VTOL Explorer: https://www.youtube.com/watch?v=72vj69Hluwk
    VTOL Bixler at NASA: https://www.youtube.com/watch?v=fOJ8TWYUedA
    Winged Utility Vehicle VTOL: https://www.youtube.com/watch?v=DL2HrNPq0LI&t=2s

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