How many of you guys fly RC Planes too?

Discussion in 'Hangar Flying' started by Pietenpolflyer, Jan 23, 2004.

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  1. Jan 23, 2004 #1

    Pietenpolflyer

    Pietenpolflyer

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    Hey guys, title says it all. I'm not a homebuilder yet... mostly just doing research, but I"m an avid RC Airplane and Heli pilot.

    I've been flying planes for about 9 years now. I started flying glow planes, then switched to electric before they really started getting popular, now I'm switching back to glow for some planes.

    Here's a picture of my latest project. A Sceadu Evo .50 (a .50 is half a cubic inch displacement)

    --Paul
     

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  2. Jan 23, 2004 #2

    StRaNgEdAyS

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    Yep :D
    I started out when I was 9 flying control liners, and graduated to planes, gliders, helicopters, cars and boats.
    The planes were always my favorite, and I was always looking for something bigger and faster, so I started building my own models.
    I guess that's what brought me here, I just had to Build myself a really big one. :gig:
     
  3. Jan 23, 2004 #3

    orion

    orion

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    Me too. I got into flying RC in my late teens and kept with it for quite a few years. I did a bit of pylon racing and eventually I got into instructing new pilots. However most of the stuff I flew was for fun.

    I used the RC models to test several ideas I had at the time and so, pretty much had stopped building kits and for the most part built my own. I think that's about the time I started to discover how inadequate RC models are at predicting full scale airplane behavior.

    Being into full scale planes now, I just don't seem to have the time any more to get back to RC. A couple of years ago my wife gave me a beautiful large scale P-51 kit for Christmas. Having had a couple in the past, I know that the P-51 is one of the squirreliest airplanes out there so I decided to get a trainer first to get my thumbs back in shape.

    I built the trainer, and a year later it is still sitting in my office, never flown. Oh well, maybe eventually I'll get back into it.
     
  4. Jan 26, 2004 #4

    Jorear

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    Hi Paul:

    I am a long time RC builder/pilot. Started building rubber band models when I was 9. Then moved into control line models. Got interested in girls in junior high and the modeling was put on hold.

    My future wife found out I was interested in RC airplanes when I was in dental school, so she bought me a Sig Kadet Jr. and a Fox .19 engine for it. Gawd I love that girl!

    Built and flew RC for over 16 years until they started getting so big (quarter scale) that I decided the time was right for me to get my pilots license and build one I could get into. Seemed to be the normal next step.

    I have found that my RC building/flying experience has really helped me both in learning to fly full size and building a homebuilt. Just another really big model when you get right down to it.

    Regards,

    Jeff Orear
     
  5. Jan 26, 2004 #5

    Pietenpolflyer

    Pietenpolflyer

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    Jeff, I'd totally agree that model building would help. I took Pietenpol Aircamper plans and built a 1/3rd scale model of it. It was accurate to the last nut and bolt. So essentially I did build a full scale Piet, it just fit in my work shop a little easier. ;)

    --Paul
     
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  6. Jul 2, 2009 #6

    fly_kc

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    im modeler too
     
  7. Jul 2, 2009 #7

    Topaz

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    Used to fly control-line quite a bit, and some free-flight planes from kits. Did a little RC, but I didn't get into it as much as I could have. Spent more time playing with smaller scratch-built free-flight gliders, testing ideas: anything from multiple flying surfaces, to flying wings, to lifting bodies. Lots of fun. :gig:
     
  8. Jul 2, 2009 #8

    bmcj

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    Count me in the ranks too. Not lately, but in my youth (my first youth, that is... still in my second youth).

    Bruce :)
     
  9. Jul 2, 2009 #9

    PTAirco

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    I was building models from a very early age and always hankered after some R/C stuff, but it was unaffordable. My thing was always accurate scale modelling. By the time I could afford it, I thought I might as well spend the money on the real thing. I still have an early 1980's Futaba 6 channel set sitting in a box somewhere, unused. The low cost and sophistication of today's stuff is mindboggling as I found out when I picked up an RC magazine somewhere, twenty years after I read the last one.
     
  10. Jul 2, 2009 #10

    MadRocketScientist

    MadRocketScientist

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    I still fly RC models, have been since I designed and built my own 2 channel glider at 12yrs old. At the local airstrip they have me on about still building RC aircraft (the CriCri isn't much bigger:gig:)

    I have also designed my own 450 size heli frame sets.

    Here's a couple of pics of my park flyer triplane

    Shannon
     

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  11. Jul 2, 2009 #11

    Topaz

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    Beautiful!
     
  12. Jul 2, 2009 #12

    Mac790

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    I've read about similar opinions, but is it really so inadequate even for such a big RC models, probably weight diference is the key factor
    [video=youtube;kYrL-eGEOUY]http://www.youtube.com/watch?v=kYrL-eGEOUY&feature=related[/video]

    Seb
     
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  13. Jul 2, 2009 #13

    orion

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    Depends on what the scale really is. But in general, the model will reasonably reproduce things like reaction to stall, spin entry and recovery, and the overall look and feel of the airplane in flight - in other words, qualitative information. However, the specifics of some of those and anything that has factors that depend on Reynold's Number will be dramatically skewed. Things like airfoils don't scale well so anything performance related, flow based or even the simple stall progression might not be well represented in the scale plane. But I will say one thing for it - getting your design to fly, even in scale, is simply a great ego boost.
     
  14. Jul 3, 2009 #14

    ultralajt

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  15. Jul 3, 2009 #15

    addaon

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    Having finally read Tailless Aircraft, Nickel is huge on using (very small, often cardboard) models for finding CG for stability, finding control deflection for trim, and finding pitch moment of flaps. The third is particularly interesting to me... he claims that on an unpowered cardboard model with the correct planform, when trimmed for flight by deflecting the elevons, deflecting partial-span flaps accurately reflects whether the flaps will cause a nose-up or nose-down moment.

    This seems a bit odd to me at first glance, because a cardboard model is inherently using near-zero-moment airfoils, no washout, and has other obvious approximations to the actual design. On the other hand, I suppose that if the CG is placed in the correct position, and the elevons are deflected to trim (which, due to the approximations, will be a different elevon deflection than for the same angle of attack on the actual design), it might work.

    (Also, I want this to work, since my AVL-designed 50%-span pitch-neutral flaps seem to work by this standard.)
     
  16. Jul 3, 2009 #16

    Topaz

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    Ah, you got through Nickel! How did you find it. Maddening and enlightening? :)

    I think a small model would be able to show gross characteristics, even for something as esoteric as zero-net-moment flaps. Fine-detail characteristics, though, probably would go missing at that level of scale. Still, I've played with a lot of small free-flight gliders of the sort Nickel is discussing, myself, and yeah, you can learn a lot that way that you'd struggle to understand, just reading in a textbook. Makes the concepts in the book much more concrete and easy to comprehend.

    My dad had piles of flat foam sheeting (only about 1/16" thick) that came between the floor tiles when he built his house. The stuff was easily cut with scissors, but rigid enough to hold a firm shape in-flight, and was closed-cell on the flat surfaces, for a nice smooth skin. Perfect for this sort of use. Some tape and soda straws, and a couple of paper-clips to position the CG, and you had airplanes. Or just the foam and some tape for a flying-wing.

    I went through all of it, making gliders of various configurations and trying them out. Boy, did that ever clear up some things I'd been reading! And it was a lot of fun.
     
  17. Jul 3, 2009 #17

    addaon

    addaon

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    I found getting Nickel maddening. Took more than four months (and two changes of address) for the print-on-demand house to actually get it to me... but it was still cheaper and easier than finding it used.

    I found it... limited but interesting. The math (thanks for the errata!) is nice and all, but AVL was already sufficient for that (and for things like winglets, likely more accurate than the rule-of-thumb equations). The focus on "optimal" flying wings makes a whole lot of sense, and the SB-13 is pretty close to what I'm doing (although I had already incorporated both of his recommended changes, more sweep and smaller winglets, to the basic SB-13 design); but it's a bit light on consideration of deliberately sub-optimal flying wings, for those of us with power who care more about handling.

    The chapter on hang gliders is somewhat out of place, especially without a companion chapter on paragliders (although I'm of course biased here). Many times throughout the book he mentions that he's ignoring vertical CG position / pendulum stability, yet I'm discovering in my own research that this is really not at all a negligible effect for even an SB-13 style glider; and, having flown hang gliders and paragliders, I know from experience it's not at all negligible there.

    The vertical CG discussion only real omission that I feel he could have addressed (since paragliders grew up after the book was written), and it's not as if he could have had more case studies. It would have been nice to have a Raymer-style walk-through of, say, designing a flying wing RC glider as an appendix, to pull together the math and establish a process (and there's really quite a bit of process implied in the book). It would also be nice, and probably quite possibly, to put together an appendix with critical stats (span, power loading, planform, etc) for all "successful" flying wings (including the military ones), just to get that complete and get it in one place; there's an awful lot of hopping back and forth between diagrams.

    After reading Riblett and similar recently, though, I'd definitely give Nickel two relative thumbs up.
     
  18. Jul 3, 2009 #18

    Topaz

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    Your impressions largely match my own. The hang-glider stuff was a sop to Mr. Wohlfart, who is an avid hang-glider enthusiast.

    The vertical CG material is lacking, yes. The larger omission for me was really anything at all about dynamic stability issues - other than a brief discussion of short-period motions (his "pecking" treatise) that is not developed numerically, he avoids the subject altogether.

    A Raymer-style walk-through would be a huge improvement on the book, as would the table of aircraft data you mention. It's neat to see all that data for the Horten gliders, but seeing similar data for, say, the Northrop 'wings and such would provide better basis for comparison.

    The gold in the book is the basic approach to flying-wing design: Lift distribution is king. That's what really turned me around and allowed me to get beyond 'eyeball engineering' with tailless designs.

    I disagree about the induced-drag emphasis. Everyone should be flying sailplanes. ;)
     
  19. Jul 3, 2009 #19

    addaon

    addaon

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    At some pretty deep level, the purpose of a fast cross-country machine for me is to get my sailplane (paraglider) to the good launches. Hence the paraglider baggage compartment specced into all my designs (and yes, it fits in the 701).

    Yeah, the pecking thing is interesting. It sort of seems that, between the lines, the summary on the SB-13 is "great plane, great performance, but no fun to fly because of pecking." Solution to pecking? We don't know, but we haven't seen it on anything with sweep > 20°, so recommend that. It's an annoying way to handle it, but I don't really blame Nickel for it; I'm not convinced the material is out there, and the book is a synthesis, not original work.

    With "lift distribution is king", I had sort of already arrived there... but Nickel probably could have done a bit more treatment of constrained lift distributions. Two examples come to mind...

    1) Hang-gliders, as he mentions, have a washout induced by air flow, and influenced almost entirely by trailing edge pressure. As such, the designer can choose maximum washout, and washout at the tips (which, on a hang-glider, is always less than maximum washout)... but the curve between them is basically a catenary, no option of doing an arbitrary distribution shape.

    2) Metal designs, if flat-wrapped, have (piecewise, if multiply flat-wrapped) linear washout distribution.

    In these cases, his guidance is still usable (calculate the full lift distribution and work from there), but his fancy "optimals" are not obtainable. Here you have tradeoffs of buildability for induced drag. A more practical approach might have come in handy here.
     
  20. Jul 3, 2009 #20

    Topaz

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    You're right. Nickel is of an older generation, with a different mindset. More math-theory, more simplification of the models, because they simply didn't have the computational capacity then to handle more detailed, intricate modeling.

    I think there is a quite adequate solution to the 'pecking' problem, but it's simply beyond the reach of homebuilders and amateurs. It's no different than any other airplane - you 'simply' perform a full six-DOF dynamic stability analysis, in great depth. The 'pecking' is a very lightly-damped, short-period phugoid, as far as I can tell - or at least a similar motion. It would require accurate inertial and aeroelastic modeling as well as the aerodynamic modeling, but I see no fundamental reason that "pecking" should be different than any other dynamic motion of the airframe. That kind of analysis was cutting-edge, I believe, even for the aerospace majors in the 1980's when the SB-13 was designed, and really wasn't done for that aircraft. They did some aeroelastic work, but not a full CFD dynamic stability analysis in the sense I'm talking about here.

    And yes, my understanding of the SB-13 is that you're right: Highly competitive with 'conventional' sailplanes of the time, but very tiring and annoying to fly in rough air. Which, of course, is what sailplanes are looking for...

    Mmmmmm... Yes and no. Their focus upon induced drag can be annoying when you're working upon a powered aircraft - being sailplane designers, they'll throw just about anything on the fire in sacrifice to that. Nickel caught a bit of that bug from the Hortens, although they took it to greater extremes. You can get into Nickel's 'optimal' parameters, as he describes them in the book, but it places severe constraints upon wing geometry, twist, and other factors. As for methods, I agree with you. I don't like his. They're fine if you want to do theoretical studies of the math of flying wings, but not well suited for finding a practical geometry that satisfies a given set of goal parameters. You end up iterating over and over to get where you want to go, which is annoying. Or you use his graphical solutions and constrain your design to the parameters he used for those. It's not really practical at all.
     

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