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  1. #31

    Join Date
    Jun 2013
    Location
    Sunnyvale, CA
    Posts
    72

    Fair Point

    RX – Receiver
    TX – Transmitter
    ESC – Electronic Speed Controller (Motor Control Module) Different types are used for brushed or brushless motors.
    BEC – Battery Eliminator Circuit – Converts Power battery voltage to approximately 5V to 6V to drive the RX and other radio gear. Also known as a DC to DC converter
    SBEC – Switching BEC – A more efficient BEC that uses a slightly more sophisticated and expensive technology that wastes less power as heat.
    Ah as in 3.3 Ah – Amps times Hours – A measure of the total energy stored in the battery.
    S as in 3S – S stands for “Series”. 3S means 3 cells in series. Series means “in a row”, like cars in a train.
    P as in 2P – P stands for “Parallel”. 2P means 2 cells in parallel. Parallel means side by side, like lanes on the freeway.
    Y Harness – A special cable that allows 1 RX output to drive 2 (or occasionally more than 2) servos or ESCs
    AWG – American Wire Gauge – Larger numbers are for smaller diameter wire.
    JST – Japan Solderless Terminal as in J.S.T. Mfg. Co, a company that makes many types of connectors, some of which are used in the RC (Radio Controlled) industry. Within the RC industry the small red 2 pin male and female connectors that are used for currents up to about 12A are called JST connectors.
    XT-60 – A popular polarized battery connector, or the mating connector, most commonly yellow in color, that is rated for up to 60A.

  2. #32

    Join Date
    Jun 2013
    Location
    Sunnyvale, CA
    Posts
    72
    The B-17 has flown and landed safely. It is underpowered but otherwise OK. Video soon.

    It took about an hour to set up. Some of that may have been due to answering questions and taking video.

    The rigging techniques all worked as planned. One cable tie head broke during cable tensioning so I doubled up on the cable tie heads for the main Kevlar flying wires. It is fairly amazing that a plane of this size can be held together with tape, Velcro, and cable ties, but it works. There is very little glue involved, mostly 3M Super 77 spray contact adhesive to laminate the fuselage, and just a little foam safe CA.

    The CG turned out to be on the edge of tail heavy. It’s not a problem. Big light weight models such as this have a lot of aero-damping and they tend to go where you point them. They also tolerate being tail heavy much better than heavy models.

    The B-17 is not difficult to fly for an experienced pilot. We passed the transmitter to several pilots and flew for about 20 minutes. After the flight the batteries were at about 33%. The controls are sluggish but effective. The biggest issue is that it barely has enough power to climb slowly at full throttle. It is necessary to fly efficiently in order to do so. The angle of attack needs to be managed within a narrow range. If the angle of attack is too high or too low it won’t climb. Sloppy turns that lose altitude are not acceptable. It’s a bit like flying a large sailplane. Rudder via differential thrust is quite effective. Ailerons are more slowly effective. I saw no evidence of any bad characteristics like tip stalls. For such a large airplane it makes fairly sharp turns with low bank angles, mostly because it flies so slow. It has lots of drag, so the glide angle is poor. Basically you either fly it at full throttle to climb, or Ύ throttle to maintain altitude. It descends nicely at ½ throttle and is easy to land. Below ½ throttle is pretty useless.

    It looks great in the air, very stately. The way it flies so slowly makes it look like it is really big and far away. In other words it flies at something close to “visual scale speed”. The fact that it is a flat plate profile model mostly disappears at a distance.

    There were no structural issues, but we did not stress it either. The winds were light, about 3 MPH, and there were some mild thermals and sink, but it handled the resulting turbulence without difficulty. I would not want to fly it in heavy winds.

    I think it would be a better model at 10 ft. span instead of 12 ft. More power would make a big difference. I am looking into upgrading the motors but at 12 ft. span and 13 pounds it will always be a very gentle flyer. At 8 ft. span it would probably be mildly aerobatic. It remains to be seen if the structure would be strong enough but I suspect that it would be if built with the same techniques at a smaller size.

    Full disclosure, I did managed to hit a tree…. I made my final approach well above the tree, or so I thought. Being so big, it was farther away than I thought, and I managed to nick a branch with a wing tip. The tree bounced around, but the plane didn’t wiggle. The landing was otherwise uneventful.
    Last edited by Ran D. St. Clair; 06-05-2017 at 06:08 PM.

  3. #33

    Join Date
    Jun 2013
    Location
    Sunnyvale, CA
    Posts
    72

    We have video


  4. #34

    Join Date
    Jun 2013
    Location
    Sunnyvale, CA
    Posts
    72
    The B-17 flew again, this time in a bit more wind and turbulence and with a bit more power to handle it. I upgraded from the Emax MT2213-920KV to the Emax GT2215/09 1100kv motor and used the stock Emax 10x4.5 props. The motors draw about 20A and get fairly warm when run on the ground but I think they unload adequately in the air. The motors did not seem overly warm after landing. The APC 10x5.5 multi rotor props draw about the same current on the ground, but I have not tested them in the air yet.

    I am making good progress on the build instructions. They should be done in a week or so.

  5. #35

    Join Date
    Jun 2013
    Location
    Sunnyvale, CA
    Posts
    72


    Detailed build instructions for the 12 ft. Flat Plate Foamie B-17 are now available here:

    https://www.dropbox.com/sh/p032ofk04...XDpxXlkYa?dl=0

    I will upload an article shortly.

  6. #36

    Join Date
    Jun 2013
    Location
    Sunnyvale, CA
    Posts
    72

    + Size VTOL

    The 2nd build in the "Go Big At Flite Fest" series has begun. This time it is the "+ Size VTOL", which is a simple cruciform tail sitter with an 8 ft. span, 22” chord, and 4 ft. “span” on the verticals, so it’s a + Quad. I plan to give it 4 control surfaces for yaw control in hover, and more importantly solid control in forward flight. It will be externally braced with no spars and break down easily for transport. An entire sheet of 4’ x 8’ x 1” insulation foam is just slightly over 3 lbs. and it will use less than Ύ of a sheet. I figure I will need 2 each 3.3A 3S batteries in parallel since each motor can draw up to 20A and produce about 2.5 lbs. of thrust with a 10” x 4.5 prop. Hopefully it will be between 5 and 6 lbs. complete. I am also hoping that it will be able to do an auto-rotation tumble among other tricks.

    This is definitely a build that could be done at Flite Fest in a day, especially as a group build. There is a catch though. You have to build it at home first, then strip it down to a small pile of parts, less the Styrofoam. The theory is that you can buy the Styrofoam insulation at a local home improvement store after you get to Flite Fest. The one sheet of 4' x 8' x 1" Styrofoam is only $11. Of course, if you have more room to transport parts, I will also design it to break down into 2 pieces roughly 2' x 4' and 2 pieces that are 2' x 2'. My personal version will have 2 each 2' x 2' pieces and one piece that is 2' x 8', since I have the ability to transport it like that.

    Since this is a VTOL it will have a flight controller. I will be using the KK2 with OpenAero VTOL firmware of course. It supports tail sitters like no other flight controller that I know of. Given that it has a flight controller it will be tunable for anything from a totally tame beginner plane to a wild 3D machine. It will not be fast, and it will not handle much wind though. You could probably fly it in higher winds, but it wouldn't be much fun. At some point you spend all your time just plowing into the wind to stay in one place. Tail sitter landings that are dead easy when it is calm become challenging in the wind. You can still hand launch it and fly it like a regular plane though. If it tips over on landing, so what? It is not likely to hurt it much.Click image for larger version. 

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    Last edited by Ran D. St. Clair; 06-19-2017 at 03:08 PM.

  7. #37

    Join Date
    Jun 2013
    Location
    Sunnyvale, CA
    Posts
    72
    The airframe is complete at 2.77 lbs. Now it is just a matter of adding the radio gear, batteries, wiring etc. The batteries weigh 1.164 lbs. so it might make it in at under 5 lbs. Each motor has roughly 2.5 lbs. max thrust so performance should be quite good. Forward flight duration was never a goal, but it would not surprise me if it makes 15 minutes when flown gently.

    Click image for larger version. 

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  8. #38
    Maneuvering With Purpose SlingShot's Avatar
    Join Date
    Sep 2016
    Location
    Campeche, Mexico
    Posts
    472
    Big is beautiful! It's nice that it lends itself to passing the transmitter too.
    Hanger: Calypso, FT Flyer, FT Delta, FT Tiny Trainer, Tiny Trainer (Sport), FT Mini Arrow, FT Mini F-22, FT Mini Mustang, FT Mustang, Tiny Racer Trainer,

    Retired: B-25 Super Sport.

  9. #39

    Join Date
    Jun 2013
    Location
    Sunnyvale, CA
    Posts
    72

    The + Size VTOL has flown

    The + Size VTOL has flown, hover mode only, indoors (Yes, I fly 8 ft. span VTOL's in my spare bedroom).

    All control functions check out, so it is ready for an outdoor maiden, which will hopefully be early tomorrow morning. The power is good, it hovers at a little over half throttle. It weighs 5.85 lbs and the CG is 5.5" behind the leading edge which places it at 25%. 25% is a little tail heavy for a plank wing, but I am guessing it will be fine thanks to the combination of lots of aerodamping and a flight controller.

    Tail sitters are nothing new for me so that is not where the risk lies. I am using a new technique for external bracing and it might shift under load. The front and rear bracing lines are each one long line that goes all the way around the aircraft. It makes a loop around the plywood plates attached to each wing tip. Hopefully the "cinching" effect of the loops will keep it from shifting. At the end of the line there is a small hook made from a paperclip. It hooks into the tip plate to complete the circuit. So long as the lines stay reasonably tight they should hold.

    I am using 40 lb. test monofilament fishing line so it has a bit of stretch. I just attach the top and bottom center plates with Velcro and wrap the bracing lines around the aircraft. The setup should take about 5 to 10 minutes as compared to about an hour for the B-17.

    As with every new aircraft, there are tuning risks. I know it hovers reasonably, but I may have too much or too little feedback gain in forward flight so it might try to oscillate. Eventually as I fly it and gain confidence I will shift the tuning parameters to allow for more extreme maneuvers. Eventually it should be fully aerobatic.

    This is the biggest VTOL I have ever built by span. It will be interesting to see how it handles. I do not expect it to handle much wind but I am hoping it will surprise me.

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    Last edited by Ran D. St. Clair; 06-24-2017 at 04:17 AM.

  10. #40

    Join Date
    Jun 2013
    Location
    Sunnyvale, CA
    Posts
    72

    The + Size VTOL has flown (outdoors)

    She flew this morning with little drama. I have some tuning to do, but it was nice in beginner mode, with AL (Auto Level) in both hover mode and FFF (Fast Forward Flight).

    For the 2nd flight I turned off the AL in FFF and did some minor aerobatics, loops, rolls, etc. The structure held fine with no slipping of my "quick turn" bracing wire system. She didn't feel tail heavy at all, nose heavy at 25% if anything. I need more aileron throw, it is sloooow in rolls. So much so that it is hard to do a roll and keep it flying in a straight line. Rudder and elevator are quite effective so you have to fly it through the roll and my 3D piloting skills aren't that great. I have already increased the throws and made some other changes that I hope to test tomorrow morning.

    Oh, I did manage to crash it once. I was having too much fun and ran the battery too low. It tipped out of a hover from about 20 feet but she fell so slowly that there was no damage, not even a broken prop.

    I usually provide 3 tuning options for VTOLs:

    Very Easy Mode - AL in both hover and FFF. This is the VTOL version of the most gentle beginner plane you ever flew.

    Easy Mode - AL in hover but more or less regular airplane mode in FFF. This is actually my favorite mode because you can still safely hover even when the aircraft is too far away to be seen well and you lose visual orientation.

    Expert Mode - Rate mode, meaning no AL in hover, and the same regular airplane mode in FFF. In this case hover mode isn't really just for hovering anymore. Since it can fly in any attitude it can hover or fly in FFF just as easily. The use of integral feedback in all 3 axes makes it quite precise. It probably can't do any real flips because it is just too big and slow, but it can do all the normal airplane stuff and more.

    This mornings flights were in wind up to about 5 MPH and it handled it just fine. The only real issue is takeoff and landing. It has a wide enough ground base so it doesn't tip over easily. The other problem is that it could quickly get blown downwind in the instant after takeoff. This is best handled by jumping it off the ground quickly, and then immediately pushing the nose forward. Even flipping into FFF mode immediately after takeoff would be fine. It is also possible to flip into a half-way mode between hover and FFF. In this mode It naturally wants to fly at 45 degrees nose up, but the actual nose angle depends on the throttle. At lower throttle settings it will drop the nose and fly almost level, or at full idle it will glide, though poorly. All of these characteristics are easy to handle and fun to explore. I still would not recommend it in over a 10 MPH wind though. You might get away with it but it would not be much fun.

    I will get some video after it is fully tuned. I will also write up the build. It's pretty easy and should make a good Flite Fest build.

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