[NSRCA-discussion] How I became an expert Snap Judge (TIC)

Sun Oct 18 12:15:17 AKDT 2009

Jim:
Interesting definition.  Back when I started flying "Radio Control Aerobatics"  (the name then, as I recall) one definition of a snap roll was a "horizontal spin."  Inasmuch as the (then) inputs were the same, it wasn't totally incorrect to define it that way.
Bill Glaze
  ----- Original Message ----- 
  From: James Oddino 
  To: General pattern discussion 
  Sent: Saturday, October 17, 2009 12:14 PM
  Subject: Re: [NSRCA-discussion] How I became an expert Snap Judge (TIC)

  Hi Ron,

  I found a definition that I think we can live with.

        Snap Roll; Flick roll; Flick A family of rapid autorotational or "horizontal spins," not unlike spins. Rotation is induced by a rapid pitch input followed by rapid yaw input, thus stalling one wing further than the other. This imbalance in lift causes the high speed roll.  

  Notice that it says rotation is induced by one wing stalling further than the other.  It doesn't say the roll can't be maintained (prolonged) by using ailerons.  I also believe "stalled further than the other" simply means producing less lift than the other not stalled beyond the critical angle of attack.  

  So I guess it is up to the judge to determine if he sees a break in pitch and a break in yaw that starts the rotation before ailerons are applied.  Just kidding.

  Jim

  On Oct 16, 2009, at 8:11 AM, Ron Van Putte wrote:

    Yes, I agree with the elimination of the autorotation/stall requirement and describe the desired flight path, not how to achieve it.

    Ron VP

    On Oct 16, 2009, at 9:41 AM, James Oddino wrote:

      Ron, I agree completely with you and Jerry.  My point is we can get a similar airframe response at similar asymmetrical lift on the left side by using ailerons along with rudder and elevator.  Autorotation refers to rolling induced by an unstable CL/alpha that occurs only on the right side.  There, as alpha increases lift decreases so the wing descends resulting in alpha increasing and so on.  On the rising wing, alpha is decreasing so lift is increasing so the wing keeps rising.  The result is a spontaneous, continuous  roll.

      This is untrue on the left side but we can and do induce rotation with ailerons.  If we want to fix the rules we should probably get rid of the autorotation/stall requirement and describe the desired flight path, not how to achieve it.  Agree?

      Make sense?

      Jim

      On Oct 16, 2009, at 6:58 AM, Ron Van Putte wrote:

        Jerry's point is that the airplane can't get to the portion of the CL/alpha curve to the right, above the critical alpha.  Too many Gs on the airplane at normal flying speed.

        Ron VP

        On Oct 16, 2009, at 12:36 AM, James Oddino wrote:

          The way I see it, most of the folks think that the wing is stalled or it isn't.  This is not the case.  Stalled typically refers to the portion of the CL/alpha curve to the right, above the critical alpha.  The CL does not go to zero when alpha exceeds the critical 15 or so degrees but drops with a relatively low slope.  That means it is still providing lift.  It can also be at different values on each panel.  This is what Jerry was talking about when he referred to stalling the wing asymmetrically.  (See excerpt below).

          I submit we can create a similar asymmetrical Lift on the left side of the curve, below the critical angle and produce a SNAP ROLL with the application of ailerons.  This is probably not a true autorotation that would occur with rudder and elevator only if we were on the "stalled" side of the curve, but the resulting airframe response looks the same.

          I rest my case, Jim

          I am not an aeronautical engineer.  Where is Jim Alberico when we need him?

          On Oct 15, 2009, at 6:23 PM, Ron Van Putte wrote:

            I was busy when this came in and didn't sit down to read it until tonight.  I'm an aeronautical engineer and EVERYTHING Jerry wrote made sense to me and I'm a picky engineer.  I hope everyone was able to wade their way through it and understood what Jerry wrote.  He used some technical stuff that may have slowed some down, but it was presented in such a way that most R/C aerobatic pilots should understand the logic.

            Well done Jerry.

            Ron Van Putte

            On Oct 14, 2009, at 5:12 AM, Budd Engineering wrote:

              So what are we doing to make the plane present what appears to be a snap roll when we can't actually be stalling the wing asymmetrically to induce autorotation like many claim?

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