Not one word was changed

[RC Storick]

Control-Line Aerodynamics Made Painless

By BILL NETZEBAND


Control-Line Aerodynamics Made Painless, Roger Wildman with his Invader, Jul/Aug 1966 AM
 Roger Wildman with his Invader, one of several aerobatic aircraft used to check out calculations. Weighs 60 ozs., McCoy .40, 600 squares, 48 mph.


  
 Crewcut Bill goes long-hair! And he has conspirators, many of the nation's leading designers. Line rake angle is an all-important factor, they agree.


Since the beginning of control-line models, back in the 40's, the design phase, viewed from published information, has been a "black art" relying on phases of the moon, superstition, etc. "Designers" appeared to ignore, or misunderstand, the unique effects of flying in circles tied to a pilot in the center.

We were told to balance the model on front lead-out; or balance it on the bellcrank pivot; or to balance one thumbprint forward of the main spar, or any other such nonsense that pop­ped into a designer's head. All we really knew was that his model balanced there and he liked it! Always they were half right-and half wrong. Actually, we lived by the "Flea Fright" practice of adjusting each ship to tailor out the kinks, if it survived the first flight! Ultimately, we were subjected to a lot of marginal designs (mine, too) flown by talented pilots who took it upon themselves to explain phenomena they didn't understand. Luckily, we do not wipe out pilots during crashes.

Back in 1951 I started serious investigation into miniature aerodynamics. It is simply a matter of applying classic aerodynamics to our size whenever we could. The principles, happily enough, apply directly; the problems are in the constants. Guess and test methods were used to backup mathematical correction of lift, drag and inertia factors, finally coming up with "numbers" useful to our size airplanes. One slight point irks me. Only a scale model of a man-carrying airplane qualifies for the name "model." If we design an airplane for a specific performance criterion, then it's an airplane, no matter how small!

In future issue we'll present a generous portion of concentrated CL aerodynamics; concentrated meaning, any mathematical procedure will be explained in English and useful equations will be reduced to simple nomographs. We will be shooting for those of you interested in knowing Why and How, but who have not elected to follow a career in engineering or science. We assume that Math and Aero majors will be reading very critically looking for mistakes!

Basic Physical Facts: This installment covers a phenomenon not recognized in any other branch of science, at least not in books I've been able to read. So we had to develop our solution. We tie our airplane to a handle, pick up that handle and stand there while the airplane zooms around us. The physical reactions caused by moving a body (object) in a hemispherical plane, supported by thin flexible lines, with motive power applied at the object, are unique to CL airplanes.

Flying above the handle introduces forces not covered in classic aerodynamic work, and the effects of the lines themselves are interesting. Our phenomenon is the curve that appears in the lines: How do we measure it accurately, its effect on the airplane, and what do we do in the design of the airplane to achieve the best performance? Where should the line-guide be located?
 
Since Isaac Newton discovered that an object pulled by a force tends to move in a straight line, we must apply another force to make that object move in a circle. This is called Centripetal Force, which you apply at the handle. There then exists an equal and opposite force to balance it called Centrifugal Force. (EQ 1) These two keep the circle round because, if unbalanced, like a broken line, the object heads back toward its straight line. The amount of centripetal force is determined by the weight of the airplane, the angular rate at which it moves around the circle, and the length of the lines. For our purposes we convert angular velocity to tangential velocity and call this the airplane speed (V) generally in miles per hour (mph).
 
By convention, we make lines to a length which will give standard distance from handle to airplane centerline. The center of gravity (CG) of the airplane is very close to center­line, so we now state that airplane speed (V) is that of CG. To simplify matters let's assume the Thrust of the prop passes through the CG. This done we could throwaway the airplane and use a dimensionless lump, same weight, at the CG. If it were possible to mount the bellcrank pivot exactly on the CG and the load of each line didn't change (it does) we could fly without a line guide.
 
Since precise location is not practical, we add some form of line support between the bellcrank and the handle. After adding the line-guide one problem is solved, another created. For years we were fooled into believ­ing that the position of the bellcrank in the airplane controlled its attitude. Not so. The bellcrank can be almost anywhere in the airplane.

A simple cardboard outline of an airplane will show this relation (photograph in continued portion). Place an eye (U-shaped bent pin) in one wing tip and tie a pin on the end of a thread. Run the thread through the eye and stick a pin anywhere in the cardboard.

Observe how the thing hangs and then move the pin (string end) to some other location. Right! Anywhere you' stick that pin the airplane hangs the same. Now move the eye (line-guide). The airplane assumes some new posi­tion. The CG of the airplane will line up with the line-guide. (Note: It would be nice to mount the bell crank on a line between the CG and the line­guide, because the control lines could lead straight through the line-guide, therefore operating with the least stiff­ness.)
 
 We must qualify the above facts by stating that the line must be very flexible compared to the weight of the airplane. A perfectly flexible wire can carry no side load without bending. Misplaced bell crank side load is re­acted inside the airplane, not appear as an aerodynamic force. Notice that this effect is factual for the fore-and­aft and also the vertical position of the CG. Were you to use say 1/16-in. diameter lead-outs on a V2 A ship, running them beyond the line guide 4 or 5% of the total line length, and then placing the bell crank at a kooky position, you have established an exception. All practical cases so far.

The next problem is line shape. Closest parallel in engineering mechanics is the Catenary, a curved line between two points similar to a slack flexible cord hanging between two poles. This cord is assumed to be carrying only its own weight (uniformly distributed load) and its hangs in a mathematically predictable shape.

The point of maximum deflection from a straight line between the support points is in the exact center of the wire. The deflection is inversely proportional to the tension in the line (more tension, smaller deflection), and directly proportional to the weight of the lines. You can demonstrate this one with a piece of control line, so we'll not describe the experiment. It will prove that in horizontal flight your lines will droop from gravity causing a slight vertical angle leading into the airplane CG. For most airplanes "going around flat and fast" this angle is too small to measure.

To determine line shape in the horizontal plane (top view), we resort to forces shown in Fig. 1. Here the load on the line is not uniformly distributed. Load is caused by aerodynamic drag which is proportional to a constant times velocity squared. The velocity of the wire is assumed to be zero at the handle end (as in a pylon) and increases directly proportional to the distance away from the handle finally reaching airplane speed (V). Therefore, each little piece of line travels at a different velocity. This dictates the process of mathematical summation to find line drag. (More later.) To move this force system we apply thrust (T) to the CG, T being just enough to carry the effective line drag (DL). To establish equilibrium in the system we need a thrust at the handle (TH). Surprised? Fact is, without a pylon, whipping is a way of life. (Say it isn't so!-Ed.) At a later time we'll show how to whip best. But back to the lines.

It is conventional in vector analysis to resolve a vector (a force with a definite magnitude and direction) into two vectors 90° apart, or vice versa. Thus, vector force FA (line tension) is the combined result of T and CF. It has an angular relationship to both, but we're interested in its angular relation to the line of action for CF. This is (∞) Eq. 2. Likewise angle (f3) Eq. 3 is related to FH, TH and Centripetal Force (not shown). Once we know (∞) we know where to place the line guide! The development of an exact equation for (∞) was a laborious chore. We'll not cover every detail, but a brief history should be enlightening.

Math Solution Development: Progress started in response to my published force diagram inside the airplane during the March/April 1963 CLC column in this magazine. Basically, it referred a portion of the line drag (DL) equal to (T) applied to the line-guide. This may not be 100% valid, since the lines slide through holes, but wear on the back of such holes proves some force exists. Right or wrong, we then searched out a coupling force to keep the airplane from turning into the circle. The reacting couple turned out to be CF and Cen­tripetal force if the CG were moved forward in space to develop an arm between them. The resultant angle turned out to be exactly the amount as (∞) from the last paragraph.

When the bellcrank center is exactly on the CG, and if thrust is exactly through the CG the force at the line guide will disappear, if (∞) is correct. It should be reemphasized that bell crank pivot should be close to the CG, to reduce the bending at the line-guide which can cause stiff controls. At the time we didn't have a reliable drag coefficient for the lines, so progress ceased.

Receipt of math from Rex Powell and Charles Klabunde provided an equation for line shape and angles (∞) and (β) Eq. 4. They had some trouble agreeing on drag coefficient (Cd), otherwise complete agreement existed. Their work disclosed that with proper manipulation and substitution (∞) was indeed proportional to the ratio of DL to CF. Also they proved the centroid of line drag was at a point three-quarters of the distance out from the handle. Thus airplane thrust is three times handle thrust. It was further shown that since both DL and CF are proportional to V2, the system angles should be independent of velocity. This turns up frequently in our aerodynamics and, when estimating, we take advantage of it. However, Mom Nature wasn't so kind as all that there. (Figures-Ed.) Enter the villain in this piece, Mr. Reynold's marvelous number.

Osborne Reynolds was first to discover, understand and define the effects of object size, shape, speed of flow and viscosity of medium. Crudely put, he found that if two objects have the same shape but different size they will not have the same drag coefficient (or lift coefficient), unless speeds of flow and viscosity are varied to make their Reynolds numbers equal. (Eq. 5) is a simplified version of this with the viscosity held constant for air under NACA standard conditions of pressure and temperature.

When this is done, R becomes proportional to V and "some dimension defining length in the direction of flow." This dimension in our case is (d) the dia. of our lines in inches. Our lines are the same diameter from handle to airplane, the same shape, and air viscosity is constant, but (V) varies. So we can't completely ignore velocity because Cd does not remain constant from handle to airplane.

Reverting to experimental data, by old timers, it was found that, over our range of interest in R, Cd wandered from 2.4 or higher to around 0.98. Three different people ran experiments that appeared to agree well enough to believe. Unfortunately, the variation wouldn't nicely convert to an equation so we could plug it in. We were held for the moment to saying "Let's use CD = I." This gave a fairly reasonable number considering we were looking at thin, dirty, vibrating lines. But there was more to come.

Ed Fort sent along a complete line­drag equation using an approximate equation for Cd as estimated by F. Eisner (Eq. 6). By substituting for R in terms of V and d, and solving a definite integral he allowed as how total line drag was per Eq. 7. One glitch in this Cd, it continued decreasing where experimental data proved an increase occurred. This would cause error in large lines and high-speed airplanes like C-Speed ships. But it was the best yet.

We made a nomograph of this one, congratulating ourselves and all concerned. Meanwhile Pete Soule confirmed Rex's and Charles' work tying in nicely with my stuff and picking Cd = 1. (We were going to publish the results but job changes, fires etc. short-stopped that.) We tried it out on several models with reasonable experimental results. (It was close! )
Pete Soule showed up one evening with a solution giving "effective line drag" based on thrust horsepower used to pull a portion of the lines (Eq, . He had also resolved the Cd problem by finding an "effective drag coefficient" based upon the Reynolds number of a line traveling at airplane speed. This bit involved complex curve fitting by Gaussian Quadrature (Who he?-Ed.), and I'll leave it lying right there. The validity is unques­tionable so we constructed the final nomographs which appear here. You think that part was tough? Those are the answers. You should have been around for the questions!

Two other gentlemen got in hot licks. Piper Mason went at the problem with a jet model and careful observations, outlining a good test method. Bob Ormiston's observations pretty well concurred with what we finally got. What did we get, you ask?
 
 We Got Results:

1. An angle between the CG and the line-guide which if built into an airplane will fly that airplane squarely tangent to the circle; theoretically providing least drag, most thrust and good line tension.
2. If you don't want to fly squarely tangent to the circle, you can correctly bias the angle to suit your whim. No Guesswork when yawing in or out.
3. An exact method of determining the line drag the engine has to move. This will lead down the musty corridors to finding airplane drag coefficients, measur­ing the effect of streamlining, engine hop-up, prop thrust etc. We still need 1% accurate engine Bhp characteristics and any kind of propeller thrust data.
4. A basis for evaluating the best techniques for "whipping."

And we finally opened a door that was closed.

Practical Considerations:

For about two years we subjected the calculated results to flight testing. Speed work by Roger Theobald, TR by Pete Soule, Rat and TR by John Barr. Stunt by Roger Wildman and "li'l ole line-maker me" dashing around with Combat, Carrier and 1/2­bugging all concerned. Each time we carefully adjusted speed and CG-to-line­guide relation to airplane weight we con­firmed the accuracy of the calculations.

 Just to keep it from being too simple we got "wind." Real briefly; wind, when headed directly into, causes an additional line-drag load, this one uniform (like the catenary) so TH and T to balance it are equal. It can be troublesome since V is not increased and is sometimes decreased which means ∞ will get larger. Upwind the nose pulls in. Downwind the effect is opposite. Jolly old experience (the results of poor judgment) shows us the ½A through .15 sport airplanes and all stunt types need increased line rake for breezy flying. Reasoning process, backed by flight work, says for large Cd, like with slow velocities and small lines, the build up of drag is more drastic. Also, slow basic speeds (around 50 mph) mean a 30-mph wind is over 50% of the base speed. So we simply provide these air­planes with extra holes in the line guide to increase rake in 1½° intervals.

If your ½A is stuck with one leadout location add 15 mph when calculating DL. This about covers a 30-mph wind condition. A stunt ship should be flown with rake as close to ideal as possible to
hold down lateral glitching on tight(?) corners. Half-A's generally are marginal on basic line tension, so we must guaran­tee that they'll stay under control. Speed jobs are still subject to more testing, but don't bother correcting for wind. Combat, Rat and TR ships have worked out best with ideal calculated angles. Carrier ships are calculated at 40 mph speed to cover the speed range accurately.

Look over Table 1 for some extreme values in any category. Lines used are either required by rules or "most used" size. Weights are a little "outside" both directions. Final numbers pretty well box in each category. Numbers are "straight", no adjustment for wind.

How about engine offset and rudder? The facts vary widely so that each case is a new game. The CF-DL force is much larger than the combined forces of any normal engine offset or normal rudder area. Again Stunt and ½A sport must be evaluated each to its own. IF you build-in the right ∞, bad judgment on engine offset and rudder area won't hurt much. Incidentally, the side force from engine offset isn't what we look for, unless you put in 100 or more. We examine the thrust line's distance in­board of the CG (it had better be inboard) to evaluate its turning moment to keep the nose headed properly under all weird conditions.

If you want to tell me about that extreme case that shoots all this down, be very certain you send all of the facts! There are no mysteries; only a lack of complete knowledge.

We have not deliberately ignored the Scale buffs. Your problems are always very special and we recommend that you play the game straight. It was convenient to end the weight scale on Nomograph 4 at 100 ounces, but if you have something heavier, divide the weight by 2, perform the calculation and double the CF. Nomographs and Procedures: The nomograph is a handy tool, similar in operation to a slide rule, in that logarithms of numbers are added or subtracted geometrically to perform multiplication or division. The two dimensional layout essentially operates on the principle of similar triangles allowing answer or pivot line's location to automatically include constant factors. Each nomograph is designed to solve a specific equation; making it ideal for often-used calculations. The only other tools necessary are a straight edge, preferably clear plastic (and very straight) and a thin sharp pointed instrument (like a pencil). Throughout the projected series we will provide nomographs for all significant mathematics.

Finally, the nomograph generally allows sliderule accuracy, always precise enough to match our building capabili­ties. Our nomographs will be designed to start on outside scales (Left and Right), working through pivot lines 1 and/or 2 and the inside scales toward the answer. After you gain experience you'll find that they can be solved in different order to work backwards toward some independent variable. [Example-Find weight of airplane on 60'x.015 dia. lines to generate 50# of CF @ 100 mph. (Ans. 4½ lb.)]

For practice you might solve the examples in Table I to see how estimates of points are handled. Let's take the "Sport 35" at 18 ounces for a trial run. Step by step: (Note-Examples shown on Nomographs are to demonstrate procedure only).

A. Reynolds Number from Nomograph I
1. Place pointer on V scale (LH) at 60 mph.
2. Slide straight edge firmly against pointer and move right end until it lines up with .015 line diameter on RH scale.
3. Read answer of 700 from center scale.

Now you have the whole basis. Hit the first point with pointer, slide straight edge to it, swing edge to other point and read.

B. (Cd). This one is simply read from Graph I.
Note that the R scale is logarithmic, the Cd scale is linear and use your noodle when estimating. Cd in our case is 1.12. C. Drag for One Line-Nomograph 2
1. Pointer on 60 mph (LH outside) (V)
2. Straight edge from pointer to 60' line length (r) (RH outside)
3. This time instead of reading, lift pointer and move over to where the straight edge crosses Pivot Line 1. Place pointer there.
4. Holding edge against point on PL 1 swing edge down to 1.12 on the Cd scale (inside R H) .
5. Pick up and hold point at Pivot Line 2.
6. Holding point at PL 2, swing left edge down to .015 line dia. (d).
7. Now read the answer from Drag scale (DL) (.20 lb/line ).

D.  Centrifugal Force-Nomograph 3
1. Pick up model weight (18 oz.) on LH scale using inside divisions.                  .
2. Set straight edge to cross line length scale at 60'.
3. Pick up and hold crossing of Pivot Line.
4. Swing edge up to 60 mph on RH Speed scale.
5. Read answer from CF scale as 4.4 lbs.

E.  Rake angle-Nomograph 4
 1. Determine line drag (DL) by multiplying DL from step (C) by the num­ber of lines. (2 x .20 = .40#)
2. Pick up line drag on DL (LH scale) at .40 lb.
3. Set up straight edge to cross CF (RH scale) at 4.4 lbs.
 4. Finally! Rear rake either in degrees (5.5°) or in inches back in 10" of span (.98" in 10"). The latter method is a bit more accurate for layout purposes, particularly if you don't have a good big protractor.
The whole operation should take less than 5 minutes and both speed and ac­curacy improve with practice.

Wrap Up: One last item. The angle we calculate is partially phantom, in that it falls exactly half way between the line guide holes for a two-line system, when the lines are equally loaded. That "equally loaded" is important. As the elevator is moved from neutral the point shifts to the line under greater tension. If you operate a limited bell crank movement, as in combat, the load will be carried completely by either wire during maneu­vers and the point of action will coincide with that lead out. These facts dictate that line-guide holes should be very close together or through the same hole. One' hole is practical only if you connect the clips inside the wing, or if you stagger the leadout ends. Otherwise the holes should never be farther apart than one inch, preferably closer than a half inch.

With a three-line Robert's system it is conventional that pull on the middle line closes the throttle. It is desirable to bring this line out closer to the aft line, also arranging controls so that the aft line is "UP". This trick will allow slow flight at maximum yaw angle. The over-and­under lead-out system in Stunt is somewhat shaky, since the airplane responds in the lateral direction (roll), generally unfavorably, if you're looking for maximum smoothness in sharp comers.

If, perchance, your use of these data shows apparent errors, please try to consider every variable involved before you condemn us. Many carefully observed experiments have been performed to establish our high degree of confidence. If you still have trouble ship us every bit of information and we'll check it out.

All trademarks, copyrights, patents, and other rights of ownership to images and text used on Stunt Hangar website are hereby acknowledged. If you own material used here and want it to be removed, please send an email

If you are going to reply to this just to argue I don't need you and neither does anyone else.

[john e. holliday]

Thanks Sparky, I now have my bed time reading material and it is 8 pages.

[Brett Buck]

Ed Fort sent along a complete line­drag equation using an approximate equation for Cd as estimated by F. Eisner (Eq. 6). By substituting for R in terms of V and d, and solving a definite integral he allowed as how total line drag was per Eq. 7. One glitch in this Cd, it continued decreasing where experimental data proved an increase occurred. This would cause error in large lines and high-speed airplanes like C-Speed ships. But it was the best yet.

We made a nomograph of this one, congratulating ourselves and all concerned. Meanwhile Pete Soule confirmed Rex's and Charles' work tying in nicely with my stuff and picking Cd = 1. (We were going to publish the results but job changes, fires etc. short-stopped that.) We tried it out on several models with reasonable experimental results. (It was close! )
Pete Soule showed up one evening with a solution giving "effective line drag" based on thrust horsepower used to pull a portion of the lines (Eq, . He had also resolved the Cd problem by finding an "effective drag coefficient" based upon the Reynolds number of a line traveling at airplane speed. This bit involved complex curve fitting by Gaussian Quadrature (Who he?-Ed.), and I'll leave it lying right there. The validity is unques­tionable so we constructed the final nomographs which appear here. You think that part was tough? Those are the answers. You should have been around for the questions!

If you are going to reply to this just to argue I don't need you and neither does anyone else.

    LINEII does the same calculation used to generate the nomograph, and note that it refers to the position of the leadout guide with respect to the CG, not the bellcrank pivot. Note also that it tells you that the reason to consider the bellcrank position is only to reduce the drag on the leadouts causing by running through the guide at an angle, exactly as was stated in this thread from 2005:

http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=183427&mesg_id=183427&listing_type=search#183430

    where you said Bill was wrong.

    Brett

[RC Storick]

Ok Brett please on your next plane mount the bellcrank ahead of the CG. Let us know how that works out. I am done arguing with you . No mater what you believe YOU DON'T KNOW and HAVE NOT DONE EVERYTHING.

[Bill Morell]

Why not just be more respectful of each other and simply agree to disagree?

[RC Storick]

The bold lines I added are just things I have always stated and then the bill Netzeban magic bullet is whipped out and I am shot down. I have always said what we do is complex. I was told and I quote it was basic. Well the magic bullet was put up for proof.


I was told centrifugal force need not be considered because of the hanging trick.

Since Isaac Newton discovered that an object pulled by a force tends to move in a straight line, we must apply another force to make that object move in a circle. This is called Centripetal Force, which you apply at the handle. There then exists an equal and opposite force to balance it called Centrifugal Force. (EQ 1) These two keep the circle round because, if unbalanced, like a broken line, the object heads back toward its straight line. The amount of centripetal force is determined by the weight of the airplane, the angular rate at which it moves around the circle, and the length of the lines. For our purposes we convert angular velocity to tangential velocity and call this the airplane speed (V) generally in miles per hour (mph).
 
By convention, we make lines to a length which will give standard distance from handle to airplane centerline. The center of gravity (CG) of the airplane is very close to center­line, so we now state that airplane speed (V) is that of CG. To simplify matters let's assume the Thrust of the prop passes through the CG. This done we could throwaway the airplane and use a dimensionless lump, same weight, at the CG. If it were possible to mount the bellcrank pivot exactly on the CG and the load of each line didn't change (it does) we could fly without a line guide
My thoughts
Remember this all changes as we go from up to down in a hemispherical line

"Basic Physical Facts: This installment covers a phenomenon not recognized in any other branch of science, at least not in books I've been able to read. So we had to develop our solution. We tie our airplane to a handle, pick up that handle and stand there while the airplane zooms around us. The physical reactions caused by moving a body (object) in a hemispherical plane, supported by thin flexible lines, with motive power applied at the object, are unique to CL airplanes."


Then I was told you can mount it anywhere. but in the next sentence he states  It should be reemphasized that bell crank pivot should be close to the CG

Now he feels the load he feels in the handle is the steep angle and friction. "I believe its the force by the centrifugal force that I was told does not exist. Thus the faster you fly the more nose heavy it feels.

But heck after being told I know nothing Maybe I don't but I will continue to think the way I do and build the airplanes with as close to inline  CG.LO.BC and tip weight as possible.

For the JCT
Here is how it goes
The Bellcrank woes

Place the bell crank where you like
there is no need to fight
you will find out if its wrong or right.
the first snap turn of the square
you will know you are there.

One blip of down
it will chase you around.
If its ahead of the CG
makes no difference to me.

[BillLee]

....

Then I was told you can mount it anywhere. but in the next sentence he states  It should be reemphasized that bell crank pivot should be close to the CG
...

Robert, you can cherry-pick words all you want, take them out of context, and delete my posts that point that out. But the bottom line is Netzeband said:

"The bellcrank can be almost anywhere in the airplane."

 and then later said

"It should be reemphasized that bell crank pivot should be close to the CG, to reduce the bending at the line-guide which can cause stiff controls."

You can't take the "close the the CG" part without the "to reduce the bending at the line-guide which can cause stiff controls" part, which has been the point that many, many have made before.

O.k.: this is not in any way argumentative. Neither was the first response I made, which you apparently deleted.

Oh, well......

[BillLee]

Robert, you can cherry-pick words all you want, take them out of context, and delete my posts that point that out. But the bottom line is Netzeband said:

"The bellcrank can be almost anywhere in the airplane."

 and then later said

"It should be reemphasized that bell crank pivot should be close to the CG, to reduce the bending at the line-guide which can cause stiff controls."

You can't take the "close the the CG" part without the "to reduce the bending at the line-guide which can cause stiff controls" part, which has been the point that many, many have made before.

O.k.: this is not in any way argumentative. Neither was the first response I made, which you apparently deleted.

Oh, well......

[RC Storick]

Why instead of trying to be little me contribute something anything. Show me what you have designed and built that works. All I get from a select few is grief. I didn't pick anything out. He wrote it exactly as posted. Read and understand what he has written.

A private message sent to me re posted with permission.

Start with, By the way, Windy has probably built 50 times more airplanes
than any of the people on this side of the fence and has no doubt learned 10 times what most of this clan has learned, especially when some of us build  an airplane perhaps every 5 years and more.  As noted, even the great Bill Nutzoband had to( make) and fly airplanes to analyze and verify the answers to questions he and others had about this subject.  Even though he is not a rocket scientist, Windy knows what he seen and felt many times over with the many changes in aircraft ( HE )
built.   P.S. Get the CLUE.

And to verify the clue look at Yatsinko's airplanes he's got it.

[Howard Rush]

Why not just be more respectful of each other and simply agree to disagree?

Because both Robert and Brett know that each other is dead wrong.

I have a background similar to Brett's, so I know how he would approach this kind of problem.  One starts with basic physical concepts proven experimentally hundreds of years ago and reproven continually in high school physics labs ever since.  He then models these concepts mathematically using models developed by Isaac Newton and subsequently used successfully to industrialize the world, travel into space, and stuff like that.  If Brett and a colleague don't both have the same understanding of a technical problem, they will sit down with a pencil and paper and figure it out from these basic principles.  One of them will then say, "Oh, I see." and they'll go on to the next problem.  Each problem is approached from scratch: "X said so" is not an adequate explanation.  In the case of the bellcrank location problem, they would draw a "free body diagram", which would give them the lowdown.  

I think that Sparky's way of looking at it is based on his being convinced by his own hands-on experimenting.  He is not convinced that we have correctly modeled reality.  In particular, I don't think he accepts: 1) that the center of gravity of a rigid body is determined by all the pieces of mass in the body and their distances from a point, 2) that for static cases, all the mass of a rigid body can be considered to be at the CG, and 3) that gravity can be used as a surrogate for acceleration due to control line tension.  I don't know how to justify those things, and I haven't seen anybody else here justify them, but they need to be accepted before any theoretical argument about how bellcranks hang is to be convincing.  

There's another misunderstanding involved, and that's that people who aren't trained in a technical discipline don't really know what it is that those who are know.  Two examples from aero engineering are how bellcranks hang and how wings make lift.  How bellcranks hang is freshman-level stuff, plus or minus a year.  On the other hand, probably most BSAE graduates don't understand how wings make lift.    

[RC Storick]

Howard re read and understand the magic bullet. There is more there than meets the eye. Read slowly.

[Howard Rush]

I do read slowly, but what's the bullet?

[RC Storick]

I do read slowly, but what's the bullet?

If you read the article. Bill had to build many airplanes to answer these questions that he had and many others had. Not hypothesize with some math equations that was not in any book he obviously read or knew of. So if the guy who wrote the magic bullet article thought he was close but didn't have the exact answers ( according to him) where do you get your exact answers?

[wwwarbird]

Please, children, GET OVER THIS CRAP!!!

 This whole ongoing finger pointing, flame throwing, personal wannabe fame claiming, "I know more than you", "I've built a bazillion airplanes", Windy or Netzeband or anyone else is absolute "CLPA GOD", the bellcrank has to be here, the plane has to be built this way or that way, or lighter or heavier, or it needs this or has to have that, or electric is the ONLY way anymore, or my OPINION is right because it's not your OPINION, Whaaah-Whaaah-Waaah, Blaaah-Fricking-Blaaah-Blaaah-Blaaah, has gotten to be TOTAL CRAP!!!

 FACE IT, GROW UP, AND ADMIT IT, everyone has their own personal preferences in how they want, or have the ability to make, their model perform. When it comes to chosen applications in our models 99.999999% of everything being argued about here is based on ones own PERSONAL PREFERENCE. If a guy wants to mount the effin' bellcrank one the nose or on the stab WHO CARES???!!! If you don't care for it that way, hey, Rocket Scientist, THEN DON'T DO IT THAT WAY!!!
 There is no ONE answer for anything or everything in this hobby that everyone will always agree with. If anyone here can't figure that out and deal with it, then it's a direct symptom of their own skull thickness. I have applied no science in that finding.

 Build what you like, the way you like, for yourself, and STOP the cry baby whining back and forth. And knock off the d--n "I didn't start it" or "I don't care how you do it" garbage too. A couple here would find out otherwise if they go back and honestly read their old posts and/or responses.

 Merry ------- Christmas.

[wwwarbird]

Because both Robert and Brett know that each other is dead wrong.

I have a background similar to Brett's, so I know how he would approach this kind of problem.  One starts with basic physical concepts proven experimentally hundreds of years ago and reproven continually in high school physics labs ever since.  He then models these concepts mathematically using models developed by Isaac Newton and subsequently used successfully to industrialize the world, travel into space, and stuff like that.  If Brett and a colleague don't both have the same understanding of a technical problem, they will sit down with a pencil and paper and figure it out from these basic principles.  One of them will then say, "Oh, I see." and they'll go on to the next problem.  Each problem is approached from scratch: "X said so" is not an adequate explanation.  In the case of the bellcrank location problem, they would draw a "free body diagram", which would give them the lowdown.  

I think that Sparky's way of looking at it is based on his being convinced by his own hands-on experimenting.  He is not convinced that we have correctly modeled reality.  In particular, I don't think he accepts: 1) that the center of gravity of a rigid body is determined by all the pieces of mass in the body and their distances from a point, 2) that for static cases, all the mass of a rigid body can be considered to be at the CG, and 3) that gravity can be used as a surrogate for acceleration due to control line tension.  I don't know how to justify those things, and I haven't seen anybody else here justify them, but they need to be accepted before any theoretical argument about how bellcranks hang is to be convincing.  

There's another misunderstanding involved, and that's that people who aren't trained in a technical discipline don't really know what it is that those who are know.  Two examples from aero engineering are how bellcranks hang and how wings make lift.  How bellcranks hang is freshman-level stuff, plus or minus a year.  On the other hand, probably most BSAE graduates don't understand how wings make lift.    

 Very well put Howard.

[RC Storick]

What do you know Wayne? and who put you in charge? I just reposted what the GREAT WILD BILL wrote and there are a few who just like to argue with me. Well guess what it ain't my article its the magic Bullet that everyone refers to. If you think I am wrong don't read it there are over 100000 threads to read.

You will also notice I NEVER go to someone else's thread and say they are wrong but there are a few who follow me and tell me I am wrong.

If the bellcrank could be put anywhere it would be stated like that. Almost is NOT anywhere its almost.

al·most

/ôlˈmōst,ˈôlˌmōst/

adverb: almost

not quite; very nearly.
"he almost knocked Georgina over"


synonyms: nearly, (just) about, more or less, practically, virtually, all but, as good as, close to, near, not quite, roughly, not far from, for all intents and purposes; approaching, bordering on, verging on; informalpretty near, pretty nearly, pretty much, pretty well; literarywell-nigh, nigh on
"we're almost done with the attic"



Mount it anywhere you like.

[Bill Morell]

You did when you started this ridiculous argument again. I thought that this was why you had a debate zone? At least Wayne has a mature conclusion to this.

[RC Storick]

Read the first page close. Its a repost of the original topic nothing more. Nothing added nothing subtracted. NOTHING!

Mount it anywhere you like.

[RC Storick]

I guess from now on I will have to lock all threads I start and refer all questions to the engineers that like to tell me how to do things.

[wwwarbird]

What do you know Wayne? and who put you in charge?

 I don't know everything. I'll also admit it, anytime.

 I do know enough though to realize that this ongoing battle about what should or should not be applied in our model designs is primarily opinion based and will never, ever, be completely agreed to by everyone. It's the people that can't figure that simplicity out, and continue to beat their heads and flat-out argue about it, that I can't figure out.

[RC Storick]

Its a reposting of his article but some want to come on here and bash me for posting it. Its not my words. No one can leave it alone because I posted it.

[wwwarbird]

 I'm gonna go back downstairs and do some more sanding. 

[Serge_Krauss]

More ridiculous meandering!

First and most important is that several us - and that includes ME - have time after time mentioned EVERY darned thing highlighted by Robert in stating the other considerations that make certain bellcrank positions slightly better than others, and NOT ONE of these considerations compromises the basic fact that the position of the bell crank in NO WAY affects the aerodynamic response of an airplane, nor does it in any way affect how the basic weight, radial, aerodynamic drag and lift forces affect it. We have all  mentioned the friction, wear, and structural considerations- ad infinitem, it seems.

Second is that IF this fact is untrue, then the natural laws that have governed all engineering progress are fractured, and many things that work would not do so. That is not because inverses are logically equivalent (they are not), but because contrary laws would have to be true and would mess up a lot of things we've found to work.

Third is that the laws that forbid the bell crank position to make a dynamic difference are extremely common-sense laws. Many things would cease to make sense, were these laws not to hold. There is no hocus pocus involved. This simple fact is determined by straight application of Newton's three basic laws of motion, with no embelishment.

SO let's stop bickering about whether the Earth is flat. This is neither rocket science, nor the product of any appeal to authority. It's simple common sense and logical thinking based on common sense and proven laws of nature, as well as something demonstrated too many times by simple experiment.  It is neither fair, logical, nor productive to claim that because there are other considerations like structure and friction, that a basic principle is wrong, nor is it right in any way to state or imply that well-meaning people who generously give of their time to try to help others understand what is really happening have said things that they manifestly have not said.

Some things are NOT rightly matters of opinion, and it is indeed harmful to encourage people to believe in false principles simply because good rules of thumb have been developed for very standard configurations. Howard has told the truth, but one should be careful not to see it as rhetoric or compromise. If you want to know how a plane really works, go to Howard, Igor, or Brett. They may disagree on some things, but not the basics, and like any true engineers and scientists, humility in the face of nature is their first principle. Don't confuse arrogance with assuredness based on assiduous study, itself based on the discoveries the all-time giants in research and learning.

SO...I'll have to disagree with one other post here. When knowledge is distorted, it is neither petty nor argumentative to try to rectify that. Truth is important and profitable to know. Somewhere along the line, even the most innocent looking falsehood can have dire consequences. I repeat: this stuff is not based on "formulas"; "formulas" are based on this stuff. It is worth knowing and understanding.

[RC Storick]

Mount them anywhere you like but I can surely feel it ,if its in the wrong spot and that's all that counts. Its all about the feel.

[Tim Wescott]

Its a reposting of his article but some want to come on here and bash me for posting it. Its not my words. No one can leave it alone because I posted it.

No one is bashing you for reposting it, Robert.  People are pointing out that the conclusions that you're drawing from it are opposite of what it, itself, says.

If you're feeling bashed and put-upon by engineers, I suggest that you go work for a real engineering organization for a while and see how we treat each other.  "Nice" isn't keeping your mouth shut when someone is in error.  "Nice" is pointing out the error as early and comprehensively as possible.  Pointing out such errors, early and comprehensively, is not "bashing".  It is helping, and helping in a huge way.  If it isn't keeping your name from being attached to some error that cost the company huge bucks, it's keeping your name from being attached to some error that killed someone.  In Brett's case, it may be keeping your name from being attached to the technical glitch that started world war III (I'm glad I don't have Brett's job).

So you can take it for the bashing that it isn't, or the favor that it is -- your choice.

[Tim Wescott]

but I can surely feel it and that's all that counts.

Howard gave you a perfectly good, scientifically sound explanation for why you can feel it.  His explanation in no way contradicted your reported physical evidence, nor questioned your experimental technique. 

All it did was contradict your explanation of why what you felt happened.

You rejected it.

Why?

[Howard Rush]

If you read the article. Bill had to build many airplanes to answer these questions that he had and many others had. Not hypothesize with some math equations that was not in any book he obviously read or knew of. So if the guy who wrote the magic bullet article thought he was close but didn't have the exact answers ( according to him) where do you get your exact answers?

I don't particularly like Netzeband's article, but it looks like the experimenting was to validate the basic leadout position calculation, maybe to check the drag coefficients or to see if he'd missed anything big.  The nomographs aren't there, but my guess is that they show no experimental correction to the simple calculation.   The article suffers from excessive hype: no, it is nothing new to Science, nor did it require all the purported work to do.  The main work was probably in making the nomographs.  They were pretty cool at the time, but we have computers now that make the calculation trivial.

The "exact answers" question is a good one.  We tend to make simplifying assumptions, for which a calculation gives exact answers.  Whether a set of simplifying assumptions is valid is subject to scrutiny.  The assumptions for the leadout position calculation that Netzeband mentioned, as I recall, that would lead to inexact answers were that the leadouts were perfectly flexible and that airplane aerodynamic forces and moments were negligible.  Although the nomographs are missing, I'll bet that bellcrank position doesn't appear as an input, because he assumed that it doesn't matter.  Equivalently, he could have assumed that the bellcrank was on the CG and that airplane aerodynamic forces and moments are negligible.  I don't know which he did.  

As far as I can tell without the nomographs or equations, what this Netzeband article does is to calculate leadout position at zero wind and with the above assumptions.  I think Bob Reeves's program, http://www.tulsacl.com/Linelll.html , does this better and without the hype.  The program is great for those who just want to calculate leadout position.  For those who want to see proof of the method, he includes Pete Soule's great paper.

[RC Storick]

Well in my limited knowledge of model aircraft I NEVER plotted CG by lead out or bell crank location. I always used a percentage of the root cord. But like you said I know nothing.

One question? How can you accurately calculate anything when everything changes from line to line and attitude to AOA while flying in a hemisphere? (edit: I forgot to add the changing wind) Someone has some x-ray vision and a super computer for a brain.

Face it its just a SWAG.

[Howard Rush]

Well in my limited knowledge of model aircraft I NEVER plotted CG by lead out or bell crank location. I always used a percentage of the root cord.

That's what I'd do, too.   I'd decide where to put the CG relative to the wing chord, then pick a leadout guide range and bellcrank location.  To be more precise, I'd put the CG where Paul Walker said to put it, then pick a leadout range, then pick a bellcrank size, throw, and location that gives the right control geometry and minimizes the swath the leadouts make in the wing without putting the bellcrank too far from the CG.  My bellcrank is pretty far behind the CG on my current and next dogs, hence my interest in getting some really smooth leadout wire. 

[RC Storick]

After reading and thinking on this thread I have decided to build a test bed that will allow the movement of the bellcrank not to hang but to fly. So we can put this to bed. I hope to have it ready by next contest for anyone to fly. Being able to move the bellcrank from in front of the cg to way aft should be a eye opener.

It will be a basic airplane with a solid wing (I have a solid foam Geo wing) and bellcrank located on the top. Anyone can fly it and report what you feel. FEEL FEEL FEEL

I can tell you this it will be UN trimable in the extremes. I guess I should make it electric to illustrate the Brick effect as well. I am sure it will be interesting with the brick trying to line up with everything else.

[Howard Rush]

One question? How can you accurately calculate anything when everything changes from line to line and attitude to AOA while flying in a hemisphere? (edit: I forgot to add the changing wind) Someone has some x-ray vision and a super computer for a brain.

Face it its just a SWAG.

That is a good question, too.  I've calculated leadout position for flying level in a wind, but doing it for the upper left corner of a square eight in the wind is too hard for me.  Even calculating the optimal tip weight for different places on the hemisphere is complicated.  Throw in a bunch of engine offset and it's just a SWAG.

[RC Storick]

Throw in a bunch of engine offset and it's just a   SWAG.

[Howard Rush]

After reading and thinking on this thread I have decided to build a test bed that will allow the movement of the bellcrank not to hang but to fly. So we can put this to bed. I hope to have it ready by next contest for anyone to fly. Being able to move the bellcrank from in front of the cg to way aft should be a eye opener.

It will be a basic airplane with a solid wing and bellcrank located on the top. Anyone can fly it and report what you feel. FEEL FEEL FEEL

Good idea.  I was wondering how to deal with the pushrod length problem.  Maybe use one of those electrical connectors at the elevator control horn like the Ukrainian F2Ds have.  To keep the CG put, you could move a chunk of ballast the weight of the bellcrank, pushrod, and half the leadouts forward whenever you moved the bellcrank the same distance aft.  

[Serge_Krauss]

While it may work for a pretty standard configuration and standard adjustments, we shouldn't oversimplify without understanding something of the limits. The cg is positioned relative to where the lift of the entire aircraft is centered (and our personal control-sensitivity preferences). That aero center includes the tail, but rules of thumb allow a pretty good estimate of its position relative to the wing's aerodynamic center. This is necessary for longitudinal stability to be set. IOW, the cg position is placed relative to lift and not leadouts or rudder angles; they are instead placed relative to the longitudinal cg position.

My problem with what has been said is that using the root chord as an estimate increases error to a point where it can be potentially damaging. With wing sweep, usually inherent in wings with straight hinge lines and swept leading edges, the a.c. is behind where you'd get it by using the root chord as a basis. The tail makes it even further back. George Aldrich's plans for his highly-tapered "Magnum," with a more extremely swept leading edge, indicate that he missed by a mile. He had found his plane to fly badly and later had drawn in leadouts actually passing through the wing's leading edge to compensate. Drawn-in additions dated a year later showed a longer tail and shorter nose, equivalent to moving the wing forward about an inch. I don't know what route later builders used, but it's obvious that their cg's were further aft, and their planes flew satisfactorily.

We make a lot of estimates, but I think you should take the time to make a better one, just on general principles. If you know what works well on your own general design, that's fine, but if you try something with more sweep (either direction), then you shouldn't use the root choord with your normal adjustments for it.

SK

[Howard Rush]

Serge is right.  Actually, I use distance forward of the flap hinge.  I always use an Impact wing, so there's no reason to translate to %MAC each time. 

[Steve Thomas]

Back in the days before we thought this was all settled, Paul Turner (a many-times Australian Nats winner) built a model with the bellcrank back near the tailplane, but the leadouts in the usual place. I gather it flew quite normally, and proved the point he was trying to make.

[Tim Wescott]

Good idea.  I was wondering how to deal with the pushrod length problem.  Maybe use one of those electrical connectors at the elevator control horn like the Ukrainian F2Ds have.  To keep the CG put, you could move a chunk of ballast the weight of the bellcrank, pushrod, and half the leadouts forward whenever you moved the bellcrank the same distance aft.  

If you're not trying to have working flaps, then just make up a bunch of different elevator pushrods of different lengths, to match whatever stations you can install the bellcrank at.

For that matter, if you do have working flaps, then instead of doing the usual bellcrank -> flap -> elevator linkage, go bellcrank -> elevator -> flap.

To really be conclusive you probably want to correct for the geometry change that Howard cited -- this could probably be safely neglected in a no-flap plane until the bellcrank was quite close to the elevator.  Ditto for a bellcrank -> elevator -> flap setup.  But the usual bellcrank -> flap -> elevator already has some pretty severe side-effects from the control geometry (as, no doubt, Howard's spreadsheet calculates) that would only get more severe as the bellcrank approaches the flap.

[Igor Burger]

Ballancing line drag by CG position front of LO guide is perfect idea, but I affraid perfect only for speed and team racers ... what will happen if I fly overhead, gravity will lower the CG pull, line drag will be realtively stronger and model nose will look to me standing down on ground  ... something goes wrong here 

[Trostle]

After reading and thinking on this thread I have decided to build a test bed that will allow the movement of the bellcrank not to hang but to fly. So we can put this to bed.

It has already been done and I have reported it several times on these endless threads regarding the bellcrank position.

American Modeler, July 1966.  Walter Williamson wrote an article titled "Case of the Wandering Bellcrank" where he constructed a sport plane, no flaps, looks like about a .35 for power, straight non-tapered wing with something over 48" span.  Controls were mounted externally so that he could put the bellcrank in nine different places from six inches in front of the CG to ten inches in back.  On the wing tip, he moved the lead outs to 11 positions, five in front of the CG and six in back.  The range of these leadouts were from in front of the wing LE to behind the wing TE.

Different leadout positions affected the amount of line pull felt at the handle and the speed of the model (duh!!).

With any given leadout position, he found it makes no difference where the bellcrank is located.  "What matters is where the leadouts exit through the guide plate."

It will certainly be interesting to see if a test plane with different bellcrank positions in 2014 will show the same results as the article fromn 1966.

I hope this post is not deleted like my previous post evidently was.

[James_Mynes]

I don't have time for this hurt feelings fest. I'm going flying. Now, where's my U-reely...

[Bob Reeves]

After reading and thinking on this thread I have decided to build a test bed that will allow the movement of the bellcrank not to hang but to fly. So we can put this to bed. I hope to have it ready by next contest for anyone to fly. Being able to move the bellcrank from in front of the cg to way aft should be a eye opener.

Been done more than a few times, our own Joe Gilbert put together a UKEY that he could place the bellcrank on the CG, way aft and way forward, think he made 3 pushrods. He brought it out to field and flew it with the bellcrank in all 3 positions. Don't think I need to repeat what his conclusions were.

Love this thread, it's entertaining.

[john e. holliday]

I hope this don't turn into the boy with the bat story.  He couldn't play the position he wanted, so he took the bat and went home.  No more baseball according to him.  But, how many remember stick ball?   I had fewer tell me a canard will not do the pattern, but it  does.   May not be a NATS style pattern, but it does it, I have witnesses.

[RC Storick]

Ballancing line drag by CG position front of LO guide is perfect idea, but I affraid perfect only for speed and team racers ... what will happen if I fly overhead, gravity will lower the CG pull, line drag will be realtively stronger and model nose will look to me standing down on ground  ... something goes wrong here 

Igor gets it.

[Scott Hartford]

If you like your bellrank position, you can keep your bellcrank position. Period.

[Bob Hunt]

If you like your bellrank position, you can keep your bellcrank position. Period.

That's great! 

Bob Hunt

[RC Storick]

Let me say this while putting it anywhere will work. My SWAG is putting it in one spot will work in one state of trim. Moving it the airplane will have to be re trimmed for optimal flight. So my question is if you have to re trim it does is make a difference? Maybe this will get the point across, maybe not.

Because the airplanes wing has only one optimal spot. As has been stated there is no formulas for flying in a hemisphere at changing speeds, wind directions and AOA.

[Don Curry AMA 267060]

now let us move on to the BOM debate

[Dave_Trible]

Next one with the Walker Cup wins!

Dave

[RC Storick]

Nonsense.

I guess I wont have to re trim it judging from your experience

[SteveMoon]

Sparky: Why do you give a s**t what others think about where you mount your
bellcrank? Do whatever you want. If it makes you happy and you are satisfied
with the results then that's all that really matters.

Later, Steve