Rudder offset on Ringmaster

[Mark Seibert]

Hi all. I am an RC flyer and just getting back into control line. Really missed control line. Am building Ringmaster and see that there is no longer offset in the rudder. I built many Ringmasters when I flew control line and all had rudder offset. Why the change? Thanks for any help.

[Dan McEntee]

   It's not needed. It causes excessive yaw that hinders proper flight.  You can over do the offset stuff. An airplane flies better when it's not going sideways! A subtle airfoil in the rudder help, flat side outboard, but make sure the flat side is parallel to the center line of the airplane, with a little Philips entry at the flat side of the leading edge. A little engine offset helps to eliminate any torque or P-factor problems but don't overdo that either.
  Type at you later,
   Dan McEntee
 

[Mark Seibert]

Thanks for the reply. Understand.

[Howard Rush]

I was impressed as a kid when my Ringmaster flew better after the vertical tail broke off.

[Motorman]

I put a tiny bit in just to make sure it's not going the other way. Hope you get it going before the flyathon.

Motorman

[Brett Buck]

I was impressed as a kid when my Ringmaster flew better after the vertical tail broke off.

  Nobler, too.

    Brett

[Wayne Collier]

I put a tiny bit in just to make sure it's not going the other way. Hope you get it going before the flyathon.

Motorman

I tend to do this ever so slightly. Just don’t want to accidentally induce a turn toward the center of the circle.

[Phil Spillman]

I sand a bit of radius on the inside of my rudders and I think that that helps me do better with my Ringmasters, Yaks, and Mustangs, all formerly Sterling Kits! Try it out for the Annual Ringmaster Fly-A-Thon come October's first weekend! Just ;leave the entire outside of the rudder(s) flat!

Phil Spillman

[Brett Buck]

I sand a bit of radius on the inside of my rudders and I think that that helps me do better with my Ringmasters, Yaks, and Mustangs, all formerly Sterling Kits! Try it out for the Annual Ringmaster Fly-A-Thon come October's first weekend! Just ;leave the entire outside of the rudder(s) flat!

   Just make it straight and symmetrical. Sanding in an airfoil is no different from offsetting it slightly.

     Brett

[wwwarbird]

 A Ringmaster will be plenty happy with everything simply mounted straight and true.

 Always remember that we fly in a tethered circle. With that in mind I've always figured that even with the fin/rudder mounted straight inline there is still what equates to an amount of built in "offset". The "offset" amount would vary microscopically with different line lengths. I wouldn't doubt Brett and Howard possibly having wizardly formulas for it. My suggested Ringmaster formula would be 0+0=0. 

[kevin king]

Kinda glad i came after the golden era of 45 degree rudder offsets.

[Brett Buck]

A Ringmaster will be plenty happy with everything simply mounted straight and true.

 Always remember that we fly in a tethered circle. With that in mind I've always figured that even with the fin/rudder mounted straight inline there is still what equates to an amount of built in "offset". The "offset" amount would vary microscopically with different line lengths. I wouldn't doubt Brett and Howard possibly having wizardly formulas for it. My suggested Ringmaster formula would be 0+0=0. 

Actually, I would just look a Lou Crane’s paper from about 40 years ago, but… it’s atan(tail to cg/radius of circle). It’s a tiny number that is probably within normal building tolerances.

I think you don’t want anything aerodynamic trying to torque the airplane in yaw, no matter what the source, and if you trim using normal methods you will end up adjusting the rudder offset to null out this torque, no matter what the source. Other people do it differently, but usually with great difficulty.

Brett

  p.s. as an example, CG to fin CP is about 1 foot, radius is about 67 feet (60 foot lines+2 feet leadouts, 5 feet from center of rotation to handle), 1/67= 0.85 degrees.

[wwwarbird]

Brett

  p.s. as an example, CG to fin CP is about 1 foot, radius is about 67 feet (60 foot lines+2 feet leadouts, 5 feet from center of rotation to handle), 1/67= 0.85 degrees.

 I knew it! 

[Brett Buck]

I knew it! 

   Not exactly wizardly - it's dividing one number by another!  I did it with a slide rule and a small angle approximation (that tan(alpha) ~= alpha in radians for small angles, 1/67 - angle in radians, multiply by 2pi to get degrees, so, 57.3/67 = ~.85 degrees).

    Brett

   

[Gary Dowler]

   Not exactly wizardly - it's dividing one number by another!  I did it with a slide rule and a small angle approximation (that tan(alpha) ~= alpha in radians for small angles, 1/67 - angle in radians, multiply by 2pi to get degrees, so, 57.3/67 = ~.85 degrees).

    Brett

   

Uh yeah.........what he said........

[Dan McEntee]

   Not exactly wizardly - it's dividing one number by another!  I did it with a slide rule and a small angle approximation (that tan(alpha) ~= alpha in radians for small angles, 1/67 - angle in radians, multiply by 2pi to get degrees, so, 57.3/67 = ~.85 degrees).

    Brett

   

    One of these days you should post a picture of a good beginner's slide rule, and the title of a good book or video on how to use one. I know they are considered antiques but I have always been intrigued by them but never had the need to learn to use one, and I'm old enough to remember engineers walking around with them at some of the earlier places I have worked at . Math just isn't my thing, and maybe this might help. I have lots of drafting equipment and such, but never acquired a slide rule. They show up on eBay all the time pretty cheap but I don't know which is the best to buy. Just learning the basics would satisfy me.  I could let it sit out on my drawing table and let people wonder if I know how to use it!
  Type at you later,
    Dan McEntee

[Tim Wescott]

    One of these days you should post a picture of a good beginner's slide rule, and the title of a good book or video on how to use one. I know they are considered antiques but I have always been intrigued by them but never had the need to learn to use one, and I'm old enough to remember engineers walking around with them at some of the earlier places I have worked at . Math just isn't my thing, and maybe this might help. I have lots of drafting equipment and such, but never acquired a slide rule. They show up on eBay all the time pretty cheap but I don't know which is the best to buy. Just learning the basics would satisfy me.  I could let it sit out on my drawing table and let people wonder if I know how to use it!
  Type at you later,
    Dan McEntee

Any is better than nothing.  A cheap-ass one that's in good condition is better than a super-good one that spent ten years in salt water.  You want one that has all the bits (the frame, the sliding rule, and the cursor), that moves freely, and that isn't worn.  So, basically free of corrosion, rot, strawberry jam, hasn't been bent, etc.

Figure that a foot-long slide rule will be accurate to about three decimal places (it'll show two, you estimate the last one).  When I went to Worcester Polytechnic University the mechanical engineering department had a spiral one on display that was 2 feet tall and about six inches in diameter.  If I recall correctly, that stretched it out enough that it was good to about 5 decimal places (and it was probably an absolute triumph of mechanical engineering, in and of itself).

I suspect that if you budget for four bad YouTube videos before you find the good one, you'll find joy well within budget.

Or -- print one out.  No cursor, but what do you want for the cost of some stiff paper?  http://leewm.freeshell.org/origami/sliderule2.pdf

[Brett Buck]

Uh yeah.........what he said........

  No offense intended, but what part of that is not clear?  Converting radians to degrees is a matter of recognizing that there are 2pi (6.28...) radians in a full circle, or 360 degrees. 360/6.28 = 57.3.

     1foot/67 feet forms a triangle that is 1 foot high and 67 feet wide. The tangent of the angle it makes is the rise/run, or 1/67. 1/67 = 0.01492..., the inverse tangent of that is .8548 degrees.

    The small angle approximation is done to simplify the problem to a single operation. For small angles, the sine or tangent of an angle is almost no different numerically from the angle itself in radians, so, the inverse tangent of that angle is approximately equal to the angle. For example, 1 degree is about 0.0174533 radians and the tangent of 1 degree is 0.0174551 - almost identical. So, I don't have to care about computing the arctangent of .01492, I can just treat 1/67 as the arctangent and convert it to degrees. So the computation simplifies to 2pi/67 or 57.3/67, which is a single slide rule operation.

    I also note that slide rules typically will not give you the tangent or sine of numbers <about 5.7 degrees because they assume you can use the small angle approximation below that and not lose any accuracy. 5.7 degrees = 1/10 of a radian.

  I actually am interested in the answer, which part of this is tripping people up? I am not trying to browbeat anyone or show them up, I really don't see where it might trip someone up.

    Brett

[Brett Buck]

    One of these days you should post a picture of a good beginner's slide rule, and the title of a good book or video on how to use one. I know they are considered antiques but I have always been intrigued by them but never had the need to learn to use one, and I'm old enough to remember engineers walking around with them at some of the earlier places I have worked at . Math just isn't my thing, and maybe this might help. I have lots of drafting equipment and such, but never acquired a slide rule. They show up on eBay all the time pretty cheap but I don't know which is the best to buy. Just learning the basics would satisfy me.  I could let it sit out on my drawing table and let people wonder if I know how to use it!

Here is one, sufficient for this particular problem:



   Note that it is highly remiss in that it doesn't also show the Ci scale, which keeps your multiplications from going off-scale, but it does show you can just shift it to the other index. Divides always stay on-scale, so you can use Ci (C scale inverse) to change a multiplication to a division, always stays on scale.

    For our particular case, that doesn't matter,  line the cursor/hairline over 5.73 on the D scale, slide the slide to line 6.7 up with the cursor/hairline, then move the cursor to the index. Read off value at the hairline on D, it's 8.55xxx. You know the value is about .6 over .7, that's .8-.9, so you know it is really .855 degrees.

    Brett

[Wayne Collier]

Great video. I was introduced to slide rules in a ninth grade physical science class. Pocket calculators were becoming readily available by the time I got to higher math and science but we were still drilled on significant figures. I think in some ways the lectures on precision, accuracy, and significant figures were almost as helpful as the math itself, at least in helping me learn how to think.

[wwwarbird]

  I actually am interested in the answer, which part of this is tripping people up? I am not trying to browbeat anyone or show them up, I really don't see where it might trip someone up.

    Brett

 Just poking a bit of fun with the "wizard" reference but the formulas are way above my head, that's the the difference between you guys and us mere mortals.

[RC Storick]

this was my slide rule   

[Don Jenkins]

Hey Sparky, how do you use this method while flying???  Take your shoes off???  LOL!

Don

[Dave_Trible]

Hi all. I am an RC flyer and just getting back into control line. Really missed control line. Am building Ringmaster and see that there is no longer offset in the rudder. I built many Ringmasters when I flew control line and all had rudder offset. Why the change? Thanks for any help.

Mark I wouldn’t over think such a simple thing.  The Ringmaster is a fine airplane but certainly not high tech or high performance.  Either way you wouldn’t tell much difference unless it got really slowed down or you got in the wind wrong.  Some rudder offset may keep the nose turned out and keep you out of the ground.  I wouldn’t worry about running a Yugo at Indy.  I’d likely build it as originally designed.

Dave

[Brett Buck]

Hi all. I am an RC flyer and just getting back into control line. Really missed control line. Am building Ringmaster and see that there is no longer offset in the rudder. I built many Ringmasters when I flew control line and all had rudder offset. Why the change? Thanks for any help.

    You don't want the airplane to be yawed with the nose out, *as long as you get the wing straight, have enough tipweight, and the leadouts in the right position*. Flying it sideways makes it much more difficult to fly, since any time you put in any significant control effort, it will want to roll and yaw, too.

    It is my opinion that this is shown on most plans primarily to cover building tolerances, like getting the wing skewed with respect to the fuselage.

    While we are at it, the single most important thing you can do for any Ringmaster is to make sure that the *controls are slow*, that is, you have a very small elevator movement with full handle deflection. This doesn't mean to "block" it to limit the travel, it means set the control ratios up slowly enough (small handle spacing, short arm on the bellcrank, and long arm on the elevator) that even when you give it full wrist motion, it only goes about +-3/4" at the trailing edge, or less.   Make it so you can adjust it ,either at the horn or at the handle, to reduce the travel to the only as much as will induce a stall with nearly full hand motion.

     This is far more critical than the weight, the power, or just about anything else. The airplane has a reputation as a complete dog at least partially because of the stock control horn being so short and leading to the +-60 degree "flipper" that it is nearly impossible to fly it without stalling the wing with even gentle control. Fix it, and while it is not a killer stunt machine, it is at least reasonable and enjoyable to fly.

   Brett

[fred cesquim]

i just sand a bit of an airfoil on the inside in all of my planes tail
never had an issue with plane going after me
as long as fuse/wing are properly aligned and engine power is sufficient, you don´t need extra rudder to drag and yaw the plane ( no physics here, simply result of doing it over and over)

[Dave_Trible]

Let’s be sure to disconnect all those Rabe rudders out there!

Dave

[Brett Buck]

Let’s be sure to disconnect all those Rabe rudders out there!

   

   Most people would be far better off if they did exactly that, even those who you would think would know what they are doing.

     I also note that Al intended it to remove the residual yaw motion you couldn't otherwise remove with trim adjustments - not intentionally induce more yaw.  Unfortunately, his methodology for adjusting it certainly didn't do that, and, it required far better observational skills that almost everyone has. My recommendation for those who want to experiment is to put it in a fixed position, spend a long time trimming it to get the yaw motion as small as possible, and then and only then hook it up so it move, then put in just enough movement to get rid of the rest of the yaw motion you couldn't trim out.

  What you will find is that the necessary rudder motion might be +-1/16" or less, and completely symmetrical (since precession effects are also symmetrical). Als and most people's wound up assymetrical because they were fighting the leadouts, and the yaw restoring force from the leadouts goes up as you yaw nose-out/positive and down (and to zero) as you yaw nose-in/negative. To have the same effect in either direction, it will have to apply much more effort to yaw the nose out than in. But it also means that you have the rudder fighting the leadouts all the time, not just in corners.

     The movement necessary to remove residual yaw motion from precession is generally *tiny*, and almost everyone's mechanism has more slop that the total motion required. Only Keith Trostle's linear cam system could have reliably created the necessary movement.

  I think Igor is using it for a fundamentally different purpose, trying to hold yaw into it while rotating around a skewed axis.

    Brett

[Trostle]

   
Only Keith Trostle's linear cam system could have reliably created the necessary movement.

      Brett

In all due respect, I think it would be best described as a programmable cam system.

Keith

[Brett Buck]

In all due respect, I think it would be best described as a programmable cam system.

Keith

OK. I was attempting to distinguish it from a rotary cam, which what most people think of when you talk about cams.

No slight intended, no matter what it is called, it is the only way I have seen to accomplish the intended purpose!


Brett

[Trostle]

OK. I was attempting to distinguish it from a rotary cam, which what most people think of when you talk about cams.

No slight intended, no matter what it is called, it is the only way I have seen to accomplish the intended purpose!

Brett

OK, so it really should be called a slider with a slot that can be made to program the rudder movement with elevator. 

Anyway, thanks for the compliment.

You are correct, it does not take much rudder movement to get desirable results.  On the Rabe Bearcat I flew for several years, the rudder was off-set to the right about 1/8" at neutral elevator, the rudder moved about another 1/8" to the right with the elevators probably less than 30^o down, and then the rudder moved about another 1/16" to the right with the elevators probably less than 30^o up.

The semi-scale Bearcat presented an unusual configuration because the rudder was tall and was well above the thrust line.  Too much right rudder wanted to yaw the airplane to the right while wanting to roll the airplane to the left.  (Not a comfortable feel at the handle.)  Rudder movement had to be kept small.  Once the solution was found, it was a pleasure to fly, particularly the high outside turns of the vertical eights, the hour glass and the four leaf clover.

Igor's rudder, by comparison, is relatively small when compared to most semi-scale stunt models, has a relatively low aspect ratio and is essentially on the thrust line.

I think most of those who tried the Rabe rudder used way too much rudder travel for any control movement at the handle and discarded the idea without fully exploring what his idea could do for how well a model could fly.

There are many models that have won the National Stunt Championship (Walker Cup) without the use of the Rabe rudder idea.  Only two models have won the National Stunt Championship using the idea.  Plus another won the Open Nationals, but not the Walker Cup with the Rabe Rudder.

Keith

[Ken Culbertson]

OK. I was attempting to distinguish it from a rotary cam, which what most people think of when you talk about cams.

No slight intended, no matter what it is called, it is the only way I have seen to accomplish the intended purpose!


Brett

And it works.

ken