My Homebuilt RC Micro Paper Se5a

Discussion in 'RC Aircraft & Watercraft' started by liftline, Jun 18, 2011.

  1. liftline

    liftline Member

    I've been designing my own scale, flyable paper airplane models for many years, for my own amusement. Mostly gliders, but a few electric free flight as well. In September of last year I started a quest to upgrade my odd little hobby to radio control. What followed was a rather long (16 page) thread which documented the design and building of a 1/24 scale Se5a. You can still find this thread under Radio Control/ Need Advice About RC options......

    This gripping account told more than anybody needs to know about the process of going from a hare brained concept to an actual working prototype and indoor short hop testing & first crash. It is chock full of photos that are frankly awful - taken with a low res photo cam as things were a-building. Tiny and/or blurry.

    This new thread is devoted to showing off my model with high resolution photos taken during the rebuild of the Se5a, in anticipation of an outdoor test flight whenever it actually stops raining in south east Ohio, USA.

    The pix focus on how the electronics fit into the airframe. Nothing about how the wings and tail surfaces are built up from flat patterns, which is quite interesting to me, but probably much less so to anybody else. Maybe later.

    Here is my beauty, in pre-production white. Color printing is expensive, so my prototypes are traditionally "white wings." Hope this grabs your attention, the electronically painted color version is much prettier!

    My thanks to fellow Zealot Poster, quadcopter guru and 3d printer Schorhr, who gave the technical help to get started and the encouragement to keep going.:thumb:

    Attached Files:

  2. liftline

    liftline Member

    Model specs

    Model Specifications

    Scale: 1/24
    Span: 30.5 cm (12”)
    Length 24.1 cm (9.5”)
    Airframe Wt. 17.5 g (mostly 75 g/m^3 paper)
    Take off Wt. 42.5 g
    Max thrust equiv. 20.g (measured)
    Cubic wing loading <8 (advanced trainer?)

    Motor: Hextronik 2g brushless outrunner with matched prop
    Battery Turnigy 1s Lipo 138 mAh
    Servos 2X HobbyKing ultra micro 1.7g (rudder & elevator)
    ESC HobbyKing 3A 0.7 g
    TX/RX Fly Sky CT6 (six channel proportional)

    The airframe printed in full color:

    Attached Files:

  3. liftline

    liftline Member

    Electronics Bay

    All things electrical are crammed into the forward fuselage, AKA the electronics bay. The dimensions are roughly 14 X 4 X 3 cm (5.5 X 1.6 X 1").

    You can make out the outlines of an access hatch (hood) at the extreme nose (left) that allows access to the engine. The blob just above the lower line of the hatch is a faux valve cover. I like to add a little 3D realism where practical. The cockpit opening remains uncut at the right. The small ovals are markers for lugs used to attach inner wing struts to the fuselage.

    The whole model with TX & charger can be built for about 100 of the green scale marker below the fuselage.

    Attached Files:

  4. liftline

    liftline Member

    RX jacket

    The model is basically built around the little 6 channel receiver. Getting the center of gravity right requires putting the relatively heavy RX in the extreme nose. In fact, the model cannot be properly balanced with less than 7.5 g of weight well forward of the wings. I could lose about 3 g by removing the plastic case from the RX, but since it's likely the first component to make contact in a crash, I went for the sturdy stock "brain case." The receiver is held in place by means of a paper "jacket" matching the contours of the plastic case. The sturdy plastic case provides a lot of additional structural strength to the nose one of those head butting dinosaurs:rolleyes:.

    Attached Files:

  5. liftline

    liftline Member

    Box girder = lower forward fuselage

    The forward fuselage has two halves, the lower is basically a pierced box girder. The RX (in its jacket) is white glued to the upper side of the girder, with the RX connection pins protruding through the piercing. I had absolutely no choice in this matter! Space dictates all. The center section of the lower wing ultimately completes the bottom of the box.

    The box is folded from a single paper pattern. Two other patterns form corrugated stiffeners that prevent lateral movement of the RX.

    Moving diagonally on the photo, upper left to lower right: cockpit cutout, wiring port, RX pin port & corrugations. Little arrows & left right notations clarify the mind while gluing tiny pieces.:twisted:

    Attached Files:

  6. liftline

    liftline Member

    RX in place

    The receiver is nestled in place between the corrugations to either side. The antennae protrudes forward and is bend down and around to the back. No choice in that matter, space dictates all.:curse:

    A small lipo battery box is glued to the bottom of the receiver jacket. It's a simple piece, so I don't bother to show it in detail. You can see the slot cut through the nose to allow the battery to be inserted. I don't charge the lipos in situ.

    Attached Files:

  7. liftline

    liftline Member

    Attaching the motor and servos

    The motor and servos are mounted to the upper side of the box girder. So, lets flip the girder over and have a look :eek:

    There are little folded paper mounts for the servos, I've included a closeup to give you a bit of a closer look at them. Those little push pull servos are amazing.

    The servos are rotated 180 deg. to each other and slightly offset left forward and right aft, to accommodate the push rods for the rudder and elevators, respectively. Note the RX pins protruding through the deck. Channels and polarities are labeled to avoid embarrassment later. The stock servo wire connectors don't actually hang out the back like that.

    Note the slot and tabs for the lower wing.

    Attached Files:

  8. liftline

    liftline Member

    Motor, mounts and plugs

    Somebody may sell a mount for my motor, but I just make a lug from a piece of popsicle stick and epoxy it onto the housing behind the can.

    The lug is mounted to the fuselage using a a two piece spring clip and mount.

    I solder home made plugs to my motor, using male and female sub D connector pins available at Radio Shack. This makes it much easier to assemble the model, and if the motor runs the wrong way it's easy to reverse the polarity. The plugs and clips make an engine change a theoretical possibility.

    Attached Files:

  9. liftline

    liftline Member

    tail surfaces

    I salvaged the old tail surfaces from the crash of build one.

    Each tail surface requires multiple patterns to form skins, internal structure, hinges and pivots. Not that hard to build, really.

    The rudder and elevator horns are build from paper reinforced with music wire.

    Attached Files:

  10. liftline

    liftline Member

    wings, struts and wheels

    Wings struts and wheels were also salvaged. I'm a lazy, lazy man.:cool:

    The wings are of semicircular cross section on the top side, flat on the bottom. Two internal spars. They are fitted with ailerons, but I've fixed them in place for this early prototype.

    The wheels are of paper, with bead bearings and music wire axles.

    Struts are paper, elliptical in cross section, paper and glue. The front struts of the undercarriage are reinforced with a bit of music wire. No need on the other struts.

    Attached Files:

  11. liftline

    liftline Member

    Attach lower wing, under carriage, tail

    I had to build a new rear fuselage, but it's just two patterns and ultra simple.

    Glue it all together and voila, a monoplane.

    Attached Files:

  12. liftline

    liftline Member

    Thread the pushrods thru guides and attach

    Push rods are thin gauge music wire, Z bent with a needle nose pliers. Actual Z bend pliers have been on back order since the Tang dynasty. You can just make out the ESC visible thru the cockpit cutout.

    Attached Files:

  13. liftline

    liftline Member

    Attach plugs, bundle the wires, system check

    In the first model I used recycled wire from a phone cord, which was too stiff to manipulate easily. Flexible spaghetti wire is much easier to pack. Quick system check, verify motor polarity, bundle the wires with electrical tape and check again. Note the paper wire restraint loop just above the RX pins. This makes attachment of the upper forward fuselage much, much easier.

    It's a tight squeeze, but trust me, everything will fit :thumb:.

    Attached Files:

  14. liftline

    liftline Member

    Seal up the electronic bay with upper cover

    The top of the forward fuselage is glued on. This is where the hatch and latch are attached too. Another system check.

    Views with closed and open hatch. Note the battery plug in the nose beneath the Rx The hatches main function is to make it easy to install or change the prop. Motor replacement is theoretically possible, but demanding of great manual dexterity and a good set of medical forceps.


    Attached Files:

  15. liftline

    liftline Member

    Details on the forward fuselage

    Valve covers, machine gun, cockpit fairing, gun sight and headrest. These details add little weight and make the model much more pleasing to the eye.

    Note the lugs for attaching struts on the fuselage and the lower wing.

    Attached Files:

  16. liftline

    liftline Member

    Top wing goes on

    The lugs are basically glue traps and position aids to get a strong, true wing/spar attachment without the use of jigs.

    Exhaust pipes go on at this stage. Note the Lewis gun on the top wing. People always ask if it fires. No, it does not :cry:

    Check to see the open hood clears the wing.

    Attached Files:

  17. liftline

    liftline Member

    battery hatch

    An important detail, keeps the battery out of the prop. Simple latch mechanism, can be backed up by removable tape if you want a bit more assurance. Works on the engine hatch too.

    Note to self: the hatch would close more easily if the flange cut-out wasn't blocked by the wire retaining strap. Cut the strap back!

    Note to readers: This is an example of designing in the cloud.

    Attached Files:

  18. liftline

    liftline Member

    A few more views

    Nice poses of the beauty.

    Attached Files:

    Uyraell likes this.
  19. Zathros

    Zathros Guest

    That is really sweet. I want to make one of these, but want to make something that flies as slow as possible. Very nice looking plane there.
  20. schorhr

    schorhr Member

    Great job!
    The fruits of long planning and building :)
    Real clever design (and much tidier then my projects :D )

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