My Homebuilt RC Micro Paper Se5a

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

  1. liftline

    liftline Member

    My trike weighs in at around 30 lbs, a little less. It is a lot, but not that bad for a recumbent trike.

    Not bad at all!

    Plus, with a trike you always have a spare wheel handy!
  2. liftline

    liftline Member

    Still raining here :-( and windy too. Next week's forecast is looking much better.

    Until then, I'm figuring out where to put that 3ed servo for the ailerons. Just enough room over the lower wing (CG neutral weight), but I'll have to move some wires. If the plane can land safely on the undercarriage I'll consider removing the RX case to save 3g, but that may actually cause some CG issues.
  3. Zathros

    Zathros Guest

    It's nice to land in very tall grass too. I used to make really intensive rubber band planes. They would have suited the new micro controllers well. We had a field with 3 foot high grass in it and I would always launch the planes into the wind, so that they would land in that grass, it really cushioned the fall.
  4. liftline

    liftline Member

    I have a couple of candidate launch sites.

    One is a 20 foot plus hill surrounded by many acres of flat, mowed grass. The hill gives me a launch comfort factor, and the site will work over a wide range of wind headings. This is a standard test spot for my gliders. The main problem is that there tends to be a lot of people about - it's a recreational center. One of the gyms at this center was my indoor taxi and hop venue, so management knows me.

    Site two is a smaller hill overlooking a golf course. The golfers don't seem to mind, I'm well away from the greens & fairways. There is high grass under the hill, so if you get a bad launch, the cushion can help. More restrictive with respect to wind headings. Another standard site for me.

    Site three is a meadow at a county park. Nice tall grass as far as the eye can see - which isn't that far 'cause the grass is very high. I haven't used this site myself, but if I can find a good launch position it might be the safest place to try the first flight. The meadow is surrounded by forest, so if I lose control of the ship I'm in trouble.

    Site 4 is another small local park, very flat mowed grass and ball diamonds. Good wind shadowing. I've flown several radio control toys here, the main risk is landing hazards and trees are fairly close to the boundary on the short axis.

    Weather is predicted to be good in the next week, so I guess I'll have to do some decision making. Nothing is risk free.
  5. liftline

    liftline Member

    start up stutter-

    Weather clearing, ground drying. Some tweaking and general prep for first hand launch evening. Better battery hatch. Batteries charged and on standby.

    I just remembered to reprogram my .7 g Hobbyking ESC to High timing setting. This gives roughly 25% more power, but the motor often stutters at start up if I goose the throttle. Is this normal? :confused: Once the prop is spinning fast it seems pretty responsive to quick throttle shifts.

    I first noticed this with the Strarting mode set to default fast, since this default for low inductance motors, which I think the 2 g Hextronik is This didn't seem to help much if at all. Shoot, could be worse.:confused:


    I have glued the motor into the airframe - that motor really pulls and I don't entirely trust my "spring" clip.
  6. Zathros

    Zathros Guest

    I can only speak for myself, but I am learning from you! Maybe the Capacitors don't fill up as much, causing the motor to stutter, not sure though.
  7. liftline

    liftline Member

    :p OK, this is kind of embarrassing. When you program the ESC by means of the transmitter (which is what we cheap newbies do-we don't need no stinkin' card) you need to look at the data flimsy sheet very carefully. The process involves a lot of beeping from the ESC, which you must count carefully, and you must throw the throttle up or down within the time window to make your selection. You cannot consult the flimsy while you do this, or at least I can't. You need to make a plan and stick to it. The plan should be right.

    So, my Timing option should be set to HARD option 3. OK. On o Start mode, which I want to be FAST, option 1, not 3, which is very soft. I pick 3, cause fast should be a big number, right. Nope. Trying to do this at 2:00 am is not a good idea - no matter how much a night person you think you are.

    Motor works great now that timing and start are where they belong. To get a smooth start you just need to move the throttle up very slowly until it catches. Once it catches you can move it aggressively without trouble. I actually made a note of this back in Jan, but forgot I had made the note until today.

    Back on track :steamtrain: mostly

    I have borrowed a digital video cam, but my brother needs to find the charger before it will do me any good.

    Did Kelly Johnson have to put up with all this minutia at his Skunk Works? Bet his weather was better, it rained again this evening.
  8. Zathros

    Zathros Guest

    Might be worth making a mount for it and then "flying it" firmly mounted to make your adjustments before free flight.
  9. liftline

    liftline Member

    What sort of mount do you have in mind? Last minute suggestions are welcome!

    I'd like to make a wind tunnel with a stress gauge calibrated sting for models of up to 2 foot span. That would really take a lot of worry out of first flight, but it's a major project in its own right. A big outrunner motor and prop would be a good air mover.

    For the moment I have glide tests on a ballasted boiler plate airframe and from this I'm pretty confident where the CG should be.
  10. liftline

    liftline Member

    Looks like today may be the first outdoor flight. High front, clear skies and very little wind. I'll wait until evening to get the lowest possible breeze.

    I've had an inspiration about relocating the servos to increase push rod efficiency, so I won't be horribly upset if this results in a rebuild.... just so long as my Rx survives! My video guy is iffy for tonight, but the weather looks so good I can't put off a flight.
  11. Zathros

    Zathros Guest

    I used to run electric planes with a small hook at the C.G. (monoplanes) and attach the wing in a manner that made the wing parallel but able to move a little (loop of string attached at the inward wing with around a half inch of loop) around the string that leads to the the end of the string. This kept the loading off of the wing and transferred it to the fuselage. When taking off, the plane, attached at the end of 8 feet of strong string, would then flies in circles ( the other end of the string mounted to a post in the center ) and by having a little rudder applied, this would kick the plane outwards and the centrifugal force would take over shortly. You can actually fly the plane tethered like this, to a certain degree. It will give you a good indication of what could happen in free flight, and you won't lose the plane.

    My son was 5 at that time and would invariably run into the string, but that was fun in itself. You can actually take the plane off and land with this arrangement.
  12. liftline

    liftline Member

    First flight test of the rebuild today.

    Decided the weather was too good not to try taking the model up. :mrgreen:Barely perceptible winds, gusting to maybe 1-2 mph. I taped down the hood for the first flight and charged the battery. Did a quick check, put the plane in a box and drove off to my local park about 5 min from my house. :car1:Flat, grassy, with a good wind shadow. Useful flying area of about 150 X 150 m, give or take. I'm on a soccer pitch, houses to my left, trees ahead, parking lot to the right.

    Immediately ran into a problem when I got there - the ESC wasn't recognizing the motor. :v8:Turned out a motor lead had come loose - I think the prop may have banged into the box on the trip over. I had to travel back home to figure this out and fix it.

    So, it's about 6:00 PM when I get back to the field. The wind had actually picked up a bit, but is still very gentle. I'm doing the hand launch solo, Tx in my left hand, plane in my right. I make 3 attempts, and the plane stalls out each time before I can get my hands firmly on the joysticks. I can' dial in enough trim with the slider switch to compensate. The model tends to roll off to the right, :rolleyes: I think this is direct engine torque, which seems to dominate the prop wash that bedeviled me when I tried indoor runway takeoffs.

    The crashes are surprisingly gentle, the first two hit tail first, the third noses in hard enough to slip the prop up the shaft. I think I almost got this one under control. The engine still runs perfectly when I pull the prop back into position. The motor mount holds and the only damage is a small tear in the fuselage aft of the lower wing.
    Repairs will be trivial.

    So, I consider this exercise a useful failure. Lesson 1, the motor pulls hard but the model is tail heavy. Looks like I'm going to have to ballast the nose a bit. Not sure how much, maybe a gram full forward? Lesson 2, the model is really very sturdy. It can't handle plowing into a gymnasium wall, but grass is a lot more forgiving. Lesson 3, have somebody else toss the model until I get balance issues better resolved. I'm going to reconfigure the elevator horns to get more elevator deflection. Rudder authority is good.

    I met an RC enthusiast who ran out of his house to watch the show. He, was very interested in the whole concept, and ran back into his house to get his digital camera. Nice fellow, ex-Navy, served on the submarine Nautilus! So I'll get some post crash stills to post.
  13. Zathros

    Zathros Guest

    Do you have a "Trim" tab on the Rudder. Some of the older planes I have worked one (real full size planes) had a piece of aluminum you would bend by hand, really scary eh! It works though, the same thing can be done with the ailerons. If you think the problem is from the torque, it could also be the P-Factor. "Quote:

    Single engine propeller aircraft
    (As viewed by the pilot), the aircraft has a tendency to yaw to the left if using a clockwise turning propeller (right hand), and to the right with a counter-clockwise turning propeller (left hand). The right-hand propeller is by far the most common. The effect is noticeable during take off[2] and in straight and level flight with high power and high angle of attack."

    Vans RV8's use a trim tabs on the rudder much in the same way I have described. When I flew rubber band powered gliders, I would design them looking much like a "Blohm and Voss" asymmetrical observation plane to try and get a straight ascent and had a trim tab mounted on the aileron which would make it glide back in gentle wide circles, did not lose the plane that way. A steep ascent in a Piper Warrior (180 H.P.) requires substantial right rudder to keep it over the runway. I hoped this helped out. You also must make certain the wings are completely on the same plane, relative to each other, especially in a Bi-Plane. :)
  14. liftline

    liftline Member

    Didn't see this until late tonight. My brother advocates something along these lines, but in my experience the centripetal force on the string makes it difficult to analyze what's really going on. Force on the string can be large and their is no real analog to this vector in free flight.

    It turns out the paper plane is a lot more durable than I expected - I didn't stove in the nose or tear off the undercarriage. Ah, the blessings of light weight and slow speed. Oh, and 4" of grass as a cushion. And luck.:thumb: I'll be flying as soon as I glue on a repair patch. Learned quite a bit
  15. liftline

    liftline Member

    Taxi tests revealed my plane (with its anticlockwise turning prop) tends to yaw strong to the right on takeoff - could be the P factor and also the helical flow of the prop wash hitting the riight side of the rudder more. I actually didn't have enough rudder to avoid yawing on the initial roll at full throttle. This problem became manageable as the plane rolled faster. I didn't notice much right hand yaw in free flight, perhaps because the plane had a fair amount of speed when it left my hand, or maybe just because yaw is much harder to perceive in the air. The plane did seem to roll strongly to the right, that could be engine torque or now that I've had more time to reflect, it could result from dihedral coupling the roll to the theoretical yaw I might not see. Tricky.

    It's now clear I didn't have nearly enough elevator travel. Checking everything post flight I find I had rudder set at full travel (+/- 120) but elevator at only +/- 100. Pre-flight pilot error, not sure how that happened or why I didn't notice. The last time I programmed the Tx was in January -I wonder if this reflects some now long forgotten thinking having to do with indoor flight from a taxi takeoff. Nothing in my notes about this - but my note organization is far from perfect and a yellow post it may show up or such like. I mean to put them in the computer log, but often forget. (This is one reason I'm blogging on Zealot).

    I have the equivalent of bendable trim tabs on my models. I just bend the edge of the paper control surface down a bit, and it stays put. That little trick covers up a lot my building errors and I use it a lot. If things are really off I've been known to add a physical tab. The fixed elevators on the current model serve as way too complex bendable trim tabs.
  16. Zathros

    Zathros Guest

    The first "Flying Fleas" had too little range of movement and could not get out of a dive.n I think the only way you can perceive this in flight is by the amount of input you make. If you have the radio set with the trim mostly in one direction or another, that could be a good indication. As these things become more pronounced at steep angles of attack, as far as in relation to forward movement, it could just be that you have a very powerful motor and "Less is More' in this case. If it is it flying as a normal balanced plane, except for take off, then it just may mean that you need to ascend less steeply, or make a bigger rudder to give it more authority. Sounds like you're real close though. I would love to see a video clip of it flying. It is such a cool looking plane!
  17. liftline

    liftline Member

    Lots of good ideas.

    I reprogrammed the elevators last night. I hope the increase travel will just allow me to just trim things out without having to add ballast. I need to find a forceps to load the battery before I can try things out on the bench and verify the elevator travel is significantly improved. Seems I dropped the old one in the grass.

    The rudder is a bit too small for scale - it's an error I've been meaning to fix (along with the slant and how it fairs into the slid), but it's nothing huge, maybe 10% Rudder authority seemed good, but things were always "Mayday, Mayday" before I so much as got my fingers firmly on the sticks and my mind focused. I think you need a very well trimmed airplane to get away with a solo hand my old free flights which were smaller, lighter and utterly crash tolerant. You could just bend the elevators and rudder until you learned what worked. The simplicity of a pager motor and capacitor battery! An alternative is just loads of experience, which I do not have.

    The motor seems pretty powerful - the thing was really clawing through the air right into a stall. You do not like to see an airplane climbing at such a low airspeed!

    This really is basement R&D, you have to expect to take some early disappointments. I'm just astonished the plane is so intact - if you didn't know where to look you'd swear it was still unflown! Three crashes!
  18. liftline

    liftline Member

    Here is a pic of me and the airplane after the 3rd crash. Taken by the fellow who lives adjacent to my flying field. Hope it's small enough to load, if not I'll edit it later today. Getting a bit behind schedule today!

    Attached Files:

  19. liftline

    liftline Member

    Ship in the grass, you can just make out the rip in the fuselage, its the vertical line from just behind the lower wing cut-out notch traveling to the exhaust pipe. That's it as far as damage goes. Which is why I quit while still ahead.

    Enough, I've gotta make some $$$$$$$$

    Attached Files:

  20. Zathros

    Zathros Guest

    Great looking plane you got there! Looking at the pictures I can't help thinking that the plane is too close to the real one's dimensions. Things don't scale up or down well in aviation. The fixed part of the Rudder looks too small and too short. I only say this when looking, in reference to the height of the turtle deck, that it does not seem to stick up high enough, some guys I used to fly with would use clear plastic and trim it till they got it where it flew right.. The rudder seems too small from the side view, this could be a problem as far as "auto" recovery. Planes theoretically should always want to recover, unless you are making an acrobatic aircraft and want high initial instability..

    Try removing weight from the tail section, this will help in reducing wing loading. Set up a jig and find the center of gravity on the wings. The center of gravity should be forward of the center of lift. The attached pictures show the center of pressure (Lift) changes and how they relate to the angle of attack (which is different from the angle of incidence). The other picture shows the relationship of the forces involved. It is important that you establish the center of gravity on the bench first, otherwise you will go in circles trying to figure out what is wrong. You will have to interpret the center of lift from the shape of your airfoil.

    The pictures explain it better. The moving center of lift can only be dealt with when the center of gravity is established. The the amount of authority needed on the moving surfaces, and the fixed surfaces, can then be balanced.:)

    Attached Files:

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