My Homebuilt RC Micro Paper Se5a

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

  1. liftline

    liftline Member

    Scaling up or down is always challenging. I have a paper Fokker Dr1 that flew well at 1:24, it was actually the first paper AC scale model I tried to motorize - way back at the turn of the century (love saying that). It would not fly at all scaled down to 1:32 - too much drag. However, I have a half dozen WWI biplane fighters that work just great at 1:32. All are biplanes, I think it's the small space between successive wings that doomed my 1:32 DR1. (See the following link for some of my 1:32 WWI and 1:48 paper gliders :mrgreen:

    The Se5a is 1:24 and I have a lot of experience gliding it at this scale and also at 1:32. It performs very well in both sizes, giving a glide ratio of about 8:1. It is very docile, flairs nicely when it enters ground effect. Admittedly, the wing loading of the RC version is about 21% greater than my gliders. I tested an up ballasted glider version this winter and it performed about as I expected, faster, but still about 8:1. I didn't get many flights because bad landings on hard wood floors were murder.

    Wing sections that would never do in real airplanes work just fine for me at my small scales. As is so for many of my models, I use a semicircular cross section for the top of the wing and a flat section for the bottom. It's easy to build and is reasonably efficient - Clark-Ys don't seem to work any better for me at this size range. About the only time I don't use it is when aesthetics take over.

    I don't know as much as I'd like about where the center of lift is in my semicircular section wings. I believe it's well back from the quarter cord, possibly quite near the mid cord. The limits of permissible CG in your drawing are about the size of my uncertainty! In practice I ballast my glider so the cg is about midway between mid and quarter cord and just play with my bendable elevators until the things glides nicely. The little gliders are so light they are practically indestructible if flown over a mowed lawn. Trial and error suffices, I start with a bucketful of up and work my way down.

    Frankly, I'm pleasantly astonished at how durable my 42.5 g RC version is over grass. Three crashes, just little rip. Once I get the elevator deflection limits right, I'll probably just try putting in successively greater down trim until the model takes off without climbing into a stall. I really need to find somebody to do the hand launch - it takes too long for me to "climb into the cockpit" when I have to do it all myself.
  2. Zathros

    Zathros Guest

    I think flat bottomed wings work really well in flying model aircraft ( or no bottom, just the curve!). I could not give a technical answer as to way, but this has also been my experience. I have a Park Flyer that has a V-Tail. My son is learning to fly with it. It has foam wings (easily replaceable) , no ailerons. The Ruddervators are quite effective. It definitely looks like something that was engineered to fly at that scale though, with no consideration to anything real, well, there's a kit plane somewhat similar but that's stretching the use of the word "somewhat".

    Making planes to fly at scale like your doing is indeed difficult and the line is fine. Probably taboo to say in a papermodel forum, but I would probably try foam wings made out of the sheets you can get at craft stores. They are so light and strong compared to paper. That being said, it is just a matter of time before we see a video of this posted I'm sure.

    I used to fly really big RC planes but Urban sprawl just made it too difficult, (then I went to real planes, another story), here in Connecticut, they want insurance policies on planes that can go through roofs. I find the electric planes more enjoyable for some reason. Maybe it's the size and the ability to fly slow and actually see the plane fly up close, better pricing and I don't cry as much if I total one! Almost as good as flying the real thing, well, not really, but fun anyways!
  3. liftline

    liftline Member

    I've appreciated the discussion about what to do next.

    It was supposed to be sunny today, but we got rain instead, and the ground is soaked. Weather prediction is unreliable in the Mid West USA.

    Here is my plan. I going make sure I know where the CG is on the current RC prototype. Then, I going to build an non-electrified airframe and ballast it to 42.g at the same CG point, which I believe is still very near the quarter cord of the lower wing. I can do this in one evening.

    When the weather clears I'm going to fly the glider on my favorite grassy hill and see if I can adjust the elevators to achieve stable flight. The moment arm on the horizontal stabilizer is generous, so it may not take a lot of deflection. If a lot of down deflection is needed, than I will consider tilting the entire stabilizer so that the airplane flies well with the elevators set at the near neutral position. If I can achieve this, then I will modify the RC airframe to the new standard. That should result in a model that is more stable during the launch phase. Of course, a nice plan doesn't always work out in practice, but this seems like a quick method to get some data without risking existing, harder to build RC airplane.

    If things are seriously out of whack, I may tweak the model a bit "off scale" by either stretching the nose a bit or moving the wings a tad. I depart from scale as little as possible, but sometimes it's the only reasonable approach. Like reversing the dihedral of my 1905 Wright Flyer design.
  4. Zathros

    Zathros Guest

    This is all kind of serendipitous. I was reading this article (studying) as I was thinking of making a flying version of the A90 Ekranoplan model that I'm currently working out in paper. This article has some really good info. I haven't checked out the links yet, but I thought I would post it, maybe you could glean some useful info off of it? Aircraft/centre.html

    If you get a plane gliding fine with weight in place of all the electronics, controls rods, etc., and it flies right, then it really will be just the relationship of torque of the motor, P-Factor, and trimming it all up. I sure would like to see a model of your "Mule" aircraft.
  5. liftline

    liftline Member

    Updated, deleted
  6. Zathros

    Zathros Guest

    Yes, we are definitely from the same era!! I am happy to be from that era, as happy as I see you are.:thumb:
  7. liftline

    liftline Member

    Thanks Zathros, that is one very informative article. Actually, a whole bunch of 'em.

    Right up in the introduction I see:

    "In the good old free flight days, test glides were the norm, trimming out a model into long grass until the model flew straight and level just off the stall."

    I have never left the good old days!:killer:

    Those CG spreadsheets are extremely familiar looking - I still use Excel a lot in my own design process and have dozens of home brewed ones on file. I'll have to try them out and see how close they come to reality. It would be interesting to do a sensitivity analysis of the programs, but alas, who has the time?

    The "mule" will look just like the horse, save for the prop and the push rods. It won't take me too long to build, and I'll leave out the internal stuff related to mounting the Rx, servos, etc to save time. I could do it in an evening but I'll probably spread it out over a few days. It's good practice really. Building in thin paper is very technique dependent, use it or lose it.

    I still have an early "mule" from last summer, when I was mulling whether or not the whole idea of a paper RC was a practical proposition (still unanswered a year later, but I think it will turn out a "yes"). I tested it at 35 g, which was simply twice the weight of the empty airframe. It glided rather well when trimmed right, I once got a beautiful slope soaring experience where the model actually flew parallel to the crest and ended up a few feet higher than I launched it. The model is actually a bit too light for outdoors at 35 g. The lowest possible weight to balance the model is 25g, with 8 g full forward in the nose. Too light even for indoors! I flew it indoors weighted to the full 42.5 g in the gym and crunched it quickly while trying to trim it out. That was sometime around December, it's a museum piece now, along with a color printed model that is still pretty nifty looking.

    I have a web site on file that might interest you that has the math required to accurately predict the thrust from a given prop at a given rpm. Quite accurate in my experience, about 10% optimistic. I don't have the URL handy (not at my own computer just now) but I'll forward it. If I forget (highly likely, see smiley above) just yell at me. announce1

    I still need to fire up the model and see how much deflection I get with the full deflection settings. Lost my lipo extraction/insertion tool in the grass during flight test, had to buy another today. AKA tweezers.
  8. Zathros

    Zathros Guest

    Sounds good. I attached a link to the forever it seems, model I am working on. I have been toying with the idea of actually having a ducted fan for the front lift engines. That info would come be handy, if it isn't too heady for me! I wonder if there are any contra-rotating prop set ups?
  9. liftline

    liftline Member

    Here is the link:

    There are implementations of this available. I wrote my own in mathematica, but when I upgraded to Windows 7 I couldn't download my very old Mathmatica to my new computer. I may have an Excel implementation somewhere.

    I just tested out the range of motions with the new settings and the elevator travel is much greater. Don't know how I could have missed it during preflght.
  10. Zathros

    Zathros Guest

    Wow, I started reading that and my head blew a fuse. I tried it again and my left eye started twitching. Makes you see the genius of the Wright brothers and their incredibly efficient propeller!
  11. liftline

    liftline Member

    It's a very cool model. The Wrights got it half right, but they picked the right half (Blade element theory).
  12. liftline

    liftline Member

    Having not much to do early this AM, I put my latest build on the scales to get a weight. :eek: It had gained 4 g compared to the original!

    Now I had made a few modifications to the fuselage, but 4g is nearly one whole sheet of extra paper. Had I forgotten to weigh the battery in the earlier build? ...that would be embarrassing, but my notes clearly state I did. What else had I changed? Same servos, same model ESC, same prop. Then it hits me. The new spaghetti wires. I had used recycled phone cord wires on the first build. Could the new flexy wire be that much heavier? Yep. .0493 g cm-1 vs 0.0183.

    Almost accounts for the entire weight gain. How embarrassing. :oops:. Just because it looks trivial doesn't mean it is! Now I'm on a weight reduction mission. That Flysky Rx case is going to be next - that's 2-3 g right there.
  13. Zathros

    Zathros Guest

    I would think with that small current, you could just run bare wires glued along the opposites sides to avoid contact, and get the weight down to as little as possible. If it is a solid core, single strand wire, I would try taking some lamp wire, stripping off the insulation and twist up 6 strands or so, till you get the right gauge. Insulation, either clear coat it, or tun it like I said, you should be fine. Solid core isn't good because the inside of the wire is not conducting electricity, it is the outside, small bundled strands can carry more current because of the surface area..
  14. liftline

    liftline Member

    Schorhr suggested roughly the same thing way back when I first started. I could actually run the wire strands along the insides of the fuselage and solder in some short connection leads to mate up with plugs etc. It's an attractive idea and I'm going to pursue it. It would neaten up the interior considerably. Phone cord wire is six stranded and I know it can carry the load. I'll have to see how much weight I can save stripping off the insulation.

    My Rx is the 500 lb gorilla in the room - well 12 g gorilla in the 17.5 g fuselage. It's a great little unit, works like a charm and so flexible, but it's mini, not micro. Maybe Flysky has a genuine micro in the pipeline at an affordable price? I imagine these things show up a few months before the Christmas season. Or, I can pare down the Flysky as Schorhr has suggested. Better buy a few spares to play with.

    I'm going to try flying the heavy second build again, its still better than 40% thrust to weight ratio and ought to be flyable if I get it adjusted right.
    On rainy days I'll start a fresh 3rd build and wire it up with the phone strands. Should be enough time to tinker with building my own specialty wire. Attack the problem from multiple directions.
  15. Zathros

    Zathros Guest

    An electric screw driver can make some pretty tight strands if you make a long piece and keep tension and turn very slowly. While you have it pulled out, a quick light coating over the wires of some clear coat could ward off any corrosion. I'd sure like to see some pics when (if) you rewire it. :)
  16. liftline

    liftline Member

    Ramping up again after the 4th. Hot as hell at home, I like to build early in the morning so I don't sweat on the paper. AC is used sparingly!

    I've been looking into wire alternatives, and it's going to be hard to beat the 6 strand phone cable wire for price and weight. I may be able to obtain some incredibly light strain gauge wire from a friend, but I'm not counting on it and really, the weight difference would be little, it would just be easier to bend. Unless I can figure out a practical way to strip the insulator off the phone cable, possibly using an citrus based paint remover.

    I'm moving the esc forward to above the lower wing to cut the amount of cable roughly in half.

    Now that I think I know why the 2nd rc model was so tail heavy, I'm just going forward with a new 3 rd build rather than building a mule from scratch. I'll save the wings and tail surfaces from build 2 (recycled from build one) to make a mule if need should arise.

    A few other minor alterations will be made to build 3.

    The rudder area will be increased by 20% by extending it vertically to below the fuselage. This is actually accurate scale. The non moving vertical stabilizer remains unchanged.

    The tail skid will be simplified and lightened, it was overbuilt since I added a small piece of music wire for the heavier RC model. Partial compensation for the larger rudder, but frankly the changes probably won't be noticed in terms of weight or cg, both pieces are very small.

    The opening in the nose providing access to the battery will get a flange to make it stiffer, this will make it easier to close the hatch without accidentally bending it.

    The latch on the motor hood will be landed, tape seems to work fine for now, it may come back in future.

    The motor lug (popsicle stick wood) will be drilled out, not much weight to save, but it will look cool and I can say I did it.

    I put the revised vertical stab and rudder together tonight, tested the hinge and dry fitted it to an old rear fuselage. Ah, it just looked right!
  17. Zathros

    Zathros Guest

    Measure the diameter of the wire. Get a small block of aliminum and drill a hole into it ever so slightly oversize to the wire. Mount an x-acto blade perpendicular to the hole so that it just goes into the wire enough as you pull it through the block. You can use a good 2 part epoxy, the Grey stuff that comes in the tubes, to mount the exacto blade. When you pull it through, the wire will split along the seam and it will peel right off. When you finish this, attach the longest possible piece of wire to a firmly fixed position. Pull on the wire and it will stretch. This stretching will in effect harden the wire, making it able to hold it's shape much better (1 strand at a time). The other benefit is, the wire will weight less as you have stretched it and the same wire covers more length. You could also just make the whole thing out of a expose "steel" tube and before it dries, mount the x-acto blade. You can then drill the hole right where you need it relative to the blade tip. Just an idea. You can also use 1 thicker strand copper wire and obtain similar results.:)
  18. liftline

    liftline Member

    Genius! ME LIKEY
  19. liftline

    liftline Member

    I save 0.048 g for every square inch I can remove from my patterns. .0075 g cm2. Easy enough to do, might save a fraction of a gram with due diligence. I have been a bit lazy with some of my patterns to save scissor work.

    I just went to my plans and made 8 cutouts in my wing spar/spacer patterns (I call 'em sparsers). That knocks out 24.37 cm2 per left or right wing saving 0.183 g per wing and 0.731 g from all four. That's 4% of the current airframe wt! I would not have thought that! By applying the same approach to the short center sections of the upper and lower wings I can shave almost another 0.1 g. All told, these simple expedients can trim nearly a gram from all up weight. This is very low hanging fruit and worth going after! Would it be worth going after the control surfaces as well?
    I'll check that out too. Generally pays to reduce the weight of the tail, most paper models build tail heavy in my experience.
  20. Zathros

    Zathros Guest

    This will be interesting. When I first moved into my house, there was this kid who would burn barrels of wire that he got from who knows where, probably 5 finger discount, and would stink up the whole neighborhood., so he could get the copper. When I found out where the smell was coming from, I showed him how to do it correctly. Then told him if I ever smelled that again I'd call the fire department. The fumes are very noxious! He told me he was able to do what took him hours, only a few minutes, and thanked me.

    This economy has people doing all kinds of things to make a buck. What are you going to do? I try to help people. I don't have any money, just Brains.

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