STUNT NEWS MAY/JUNE 2004

[t michael jennings]

Gentlemen,

Recently studying the old issues of Stunt News.  The cover of the STUNT NEWS  MAY/JUNE 2004 issue is one of the best covers that I have ever seen on a magazine.  STUNT NEWS editor did not indicate who took the photo.

The cover is a photo of Ted Fancher and his "Tucker Special."  If you can get past Ted's hairy legs, one can see the control lines. 

Because this is a front view, one could develop the mathematical formula for the catenary shape of the control lines.  Very few parameters are not available.  For instance, distance from Ted's hand to the wing leadouts is approximate 65-68 feet.  The wing span of the Tucker special is known, therefore the leadout location is about 5/8 to 3/4 inch behind the Center of Gravity.  One could make a good estimation of the horizontal distance between Ted's hand and the leadouts position, due to the vertical telephone pole in the background.

Mathematician's go to work.

t michael jennings     
Knoxville, TN

[rustler]

I think you'd have to know wind direction and speed and coefficient of drag of the model in the same direction as the wind. Yes, it is/was a good pic. I seem to remember he had a good engine in it as well!

[Shultzie]

Gentlemen,

Recently studying the old issues of Stunt News.  The cover of the STUNT NEWS  MAY/JUNE 2004 issue is one of the best covers that I have ever seen on a magazine.  STUNT NEWS editor did not indicate who took the photo.

The cover is a photo of Ted Fancher and his "Tucker Special."  If you can get past Ted's hairy legs, one can see the control lines. 

Because this is a front view, one could develop the mathematical formula for the catenary shape of the control lines.  Very few parameters are not available.  For instance, distance from Ted's hand to the wing leadouts is approximate 65-68 feet.  The wing span of the Tucker special is known, therefore the leadout location is about 5/8 to 3/4 inch behind the Center of Gravity.  One could make a good estimation of the horizontal distance between Ted's hand and the leadouts position, due to the vertical telephone pole in the background.

Mathematician's go to work.

t michael jennings     
Knoxville, TN

OK! Why not stick the cover of the photo under your scanner and show the rest of us what you are talking about?

[t michael jennings]

Gentlemen,

Attached is the cover of the STUNT NEWS MAY/JUNE 2004 issue.

t michael jennings
Knoxville, TN

[Jim Thomerson]

It has been done.  There is an account of the study in one of the early Frank Zaic yearbooks.

[Brett Buck]

It has been done.  There is an account of the study in one of the early Frank Zaic yearbooks.

   A more advanced version of the same analysis is the basis for LINEII from Pete Soule's now-extinct Geocities site. The paper behind it was on there, too. I think the original from the Zaic yearbook didn't account properly for the Reynolds number.

    Note that when this same airplane was loaded up with 8 oz of lead on the CG, shortly after this picture appeared in print,  the lines were a lot straighter, and it flew A LOT better.

     Brett

[phil c]

If the picture was taken on the upwind side in a stiff wind, the line sweep looks about right.  If that is on the downwind side the plane is seriously underweight/too slow for the length and diameter of the lines.

[Howard Rush]

How far the lines bow back is pretty much independent of speed.  Both forces on the lines are approximately proportional to the square of speed.

[Jim Thomerson]

What I referred to is on pages 196-197 of the 1951-52 Model Aeronautic Yearbook.  The study was done in wind tunnel by the Tech Model Aircrafters at M.I.T.  They were talking about speed models in the 50 - 150 MPH range, and corrections for Reynolds Number are mentioned several times.  Their figures shows that .024 monoline will be faster than two .016 lines.   At around 150MPH  lines account for 5/6 of drag. Takes about 1.5 HP with 80% prop efficiency to go 160MPH, monoline would be 10-15MPH faster.  If one could get two faired lines to work, maybe 10-15 MPH over non faired twin lines.

[Larry Fulwider]

   A more advanced version of the same analysis is the basis for LINEII from Pete Soule's now-extinct Geocities site. The paper behind it was on there, too.  . . .

     Brett

Hmm, does anybody have that? That would be fun to take a look at. I had assumed it was mostly a gravity cat, with just a little fluid cat to distort it. If I did the math right, a 48 oz airplane at 3 Gs only has about a 1/32 catenary droop! So, it's pretty much all fluid if that number is right. I wonder now if they used any G cat calcs at all.

       Larry Fulwider

[Jim Pollock]

Hmmm,

With the extra 8 ounces on the CG, I presume that the Netzband Wall effect was eliminated?

Jim Pollock,  Just Curious.......

[Clint Ormosen]

   Note that when this same airplane was loaded up with 8 oz of lead on the CG, shortly after this picture appeared in print,  the lines were a lot straighter, and it flew A LOT better.

     Brett

This might be thread drift, but.....

 How do you add 8 oz to the wing loading and get it to fly better? If I added 8 oz to anything I fly, it would just fall out of the sky. (assuming it got off the ground in the first place.)

No argument here, just wanted to know.

[Brett Buck]

This might be thread drift, but.....

 How do you add 8 oz to the wing loading and get it to fly better? If I added 8 oz to anything I fly, it would just fall out of the sky. (assuming it got off the ground in the first place.)

No argument here, just wanted to know.

     Because with the added weight it had a better ratio of line tension to speed. It could fly more slowly and still have enough tension to move the controls, and because it was slower, it was easier to move the controls in the first place. Its a classic illustration of the Netzeband Wall. Adding weight moved the wall in a good direction. Also, the added line tension and reduced airspeed covered the residual trim issues by allowing the line tension to keep the airplane straighter in roll and yaw. As a result, it had good tension everywhere, cornered much more tightly, had minimal tendency to get "upset" in roll and yaw. And it's not like it was running out of lift because the wing loading was too high, nowhere close, in fact.

    Bear in mind that this only works if the weight is reasonable to begin with, and you have sufficient power to provide adequate vertical performance. As I recall the weight went from 39 oz (very very light for a Nobler-based airplane) to ~47 (right in the ballpark of the design weight) and the power was a Rustler-Merco 40 which puts out ponies the guys in the Fox days could only dream of.

    Note that even stuffing a giant engine into a tiny airplane (without also increasing the weight) doesn't solve the problem. In fact it can cause MORE problems because the line tension still isn't much if any higher, but you have more trim-disturbing engine effects to deal with. There was a sterling example of this at the 2009 NATs that could have been mostly corrected, in my opinion, by greatly unloading the engine, straightening out the rudder/fin offset (added to "manufacture" line tension on the otherwise feather-light plane, but the cause of remarkable yaw oscillations) and adding a large amount of weight on the CG. Uncle Jimby's Vector 40/PA65 had a similar issue, and the Systrema has a bit of it, but not nearly as bad - because it is straight, and importantly, weighs 10 oz more.

      Brett

[Steve Fitton]

         ...... There was a sterling example of this at the 2009 NATs that could have been mostly corrected, in my opinion, by greatly unloading the engine, straightening out the rudder/fin offset (added to "manufacture" line tension on the otherwise feather-light plane, but the cause of remarkable yaw oscillations) and adding a large amount of weight on the CG. Uncle Jimby's Vector 40/PA65 had a similar issue, and the Systrema has a bit of it, but not nearly as bad - because it is straight, and importantly, weighs 10 oz more.

      Brett

Oh, you mean, oh wait I know whose plane that was....
What is meant here by "greatly unloading the engine"?

[L0U CRANE]

Pete Soule' also printed an article, in the 1971-72 Aeromodeller Annual, titled," Flight Mechanics of Control Line Wires" pp 100-107.

He describes the sag aft, and the resulting " accelerated catenary" form they take from air (or fluid, Larry    )drag. He was mostly interested in CL Speed applications in this article, and provided some formulae - in metric, drat! - that helped CL Speed fliers understand leadout rake at the model.

He worked at the accelerated air drag (drag calculates from square of velocity; velocity rises as you move out from the center to the model) as the aft consideration, and centrifugal as the outward radial consideration*. *(Just trying to find generic words, that don't suggest a specific mathematical or mechanical definition...) As Howard posted, both calculate from the square of velocity. Unlike the MIT study in the 51-52 Zaic Yearbook, Pete estimated that an FAI Speed model going 145 MPH would need about 0.544 HP for line drag alone, and at 70% prop efficiency, it would need about 0.78 HP from the engine to provide that.

A speed model with line guides that cause excess yaw in flight - whether inward our outward - is presenting more of the model's surface to the airflow, and slightly aiming-off the engine thrust. Optimum leadout location should yield minimum fuselage drag...

Pete presumed a drag coefficient for the wire, and an approach to estimating Reynolds Number. This article seems to me to be a first step on the path that led to the Line II and Line III apps. Long before the Line XX programs appeared, I'd converted Pete's info from this article for my own line 'rake' estimates. Worked well enough to keep me happy... but, then I'm easy...

[Clint Ormosen]

     Because with the added weight it had a better ratio of line tension to speed. It could fly more slowly and still have enough tension to move the controls, and because it was slower, it was easier to move the controls in the first place. Its a classic illustration of the Netzeband Wall. Adding weight moved the wall in a good direction. Also, the added line tension and reduced airspeed covered the residual trim issues by allowing the line tension to keep the airplane straighter in roll and yaw. As a result, it had good tension everywhere, cornered much more tightly, had minimal tendency to get "upset" in roll and yaw. And it's not like it was running out of lift because the line tension was too high, nowhere close, in fact.

    Bear in mind that this only works if the weight is reasonable to begin with, and you have sufficient power to provide adequate vertical performance. As I recall the weight went from 39 oz (very very light for a Nobler-based airplane) to ~47 (right in the ballpark of the design weight) and the power was a Rustler-Merco 40 which puts out ponies the guys in the Fox days could only dream of.

Brett

Umm.... ok. Sounds reasonable. So all this time I spend working to make a super light model is really just a waste of time? Needing a little weight out there to manipulate the controls is understandable, but isn't a lighter model going to perform better better with the available power on it (especially in the vertical)? If you add weight, arn't you giving up some power? Then you have to add more engine to make up the difference.

Not being disagreeable. Just trying to get my head around it.

[Howard Rush]

PJ can tell you how to fix the problem without adding weight.

Hinge moment, the amount of torque you gotta put into the flaps and elevators to deflect them, also increases with the square of airspeed.  If there's not much line tension, you can't get much differential line tension to react the hinge moment. 

Lou, when I did the line angle calculation, the thing that impressed me most was how the zero-yaw line angle variation in wind varied with line tension.  I don't know if Line XX has wind in it, but the wind effect was interesting.

Two more reasons to give my dog another toot of clearcoat. 

[Brett Buck]

Oh, you mean, oh wait I know whose plane that was....
What is meant here by "greatly unloading the engine"?

     I am not sure how you know that...

     In this case, unloading the engine means running less-than-maximum prop diameter. The airplane had a very powerful engine but only weighed 53-54 oz. It certainly didn't need full output to get to the top of the circle, or to keep the speed up in the maneuvers, and reducing the prop diameter would greatly reduce the destabilizing effects. So the lack of tension-induced roll and yaw stability would have less effect. The light airframe greatly reduces the need for thrust in the corners (since the induced drag is less) so you don't need a great deal of prop to keep it going in the corners. I will say the *engine* ran reasonably soft in the corners and didn't cause a problem with explosion corners, like it easily might have.

     Brett

[Brett Buck]

Umm.... ok. Sounds reasonable. So all this time I spend working to make a super light model is really just a waste of time? Needing a little weight out there to manipulate the controls is understandable, but isn't a lighter model going to perform better better with the available power on it (especially in the vertical)? If you add weight, arn't you giving up some power? Then you have to add more engine to make up the difference.

   If the engine power was limited, you would possibly be right. That was pretty much the situation before the mid-late 80s, and people built the airplanes as light as they could to maximize performance. Now, you aren't using the full power of the engine anyway, it's grotesque overkill with almost any modern engine. The Tucker was designed around engines like Fox 35 and Ted's had a Rustler-Merco 40.  So, hypothetically you might think you need more power to get it to the top of the circle. And in any case, the design weight of a Nobler (very close, conceptually and dimensionally,  to the Tucker) is around 45-46 oz even with a Fox. So its not way over the design weight even with the lead

    As it turns out, it actually took *less* power. Ted had been trying to overcome the line tension/control feel issues by flying it faster. That was sort of a self-defeating plan since while it had more line tension, it also took more effort to move the controls. So it was flying around at 4.5-4.6 but still wasn't much better. With the added weight, it was possible to *reduce* the power considerably and fly the airplane much more slowly. maybe 5.25 or 5.3. Slowing it down, it still had the same or more tension as it had when it was light, but the effort required was greatly reduced. To slow it down that much, the *needle had to be opened significantly* - i.e. LESS power, about 65% of what it had been, in level flight.

   Of course, if you did a calculation of the minimum possible turn radius, it opened up by about a factor of 20% because the wing loading went up.  In practice, the corners tightened up dramatically because now you could use more deflection, and it was nowhere close to running out of lift in either case. Even a Masters-level pilot like Ted can't consistently make "maximum effort"/"minimum radius" corners without messing up something else, to the hypothetical minimum radius doesn't matter at all.

  So, adding the weight fixed the issues it was having, and didn't hurt to anything else to noticeable degree. The 47 ounce airplane flew, overall, *much, much better*. It wasn't a matter of opinion, it wasn't subtle, arguable,  it was DRASTICALLY superior.

   Brett

[Clint Ormosen]

Thanks Brett. Certainly gives me something to think about when deciding a plane/engine combo.

[Dean Pappas]

Hi Clint,
Hi All,
What it should actually do is make us think about control system geometry.
best regards,

Dean Pappas

[Brett Buck]

Hi Clint,
Hi All,
What it should actually do is make us think about control system geometry.
best regards,

   Certainly. And this airplane did indeed use a 3" bellcrank. But there's a practical limit to everything. In any case, the control geometry is not going to affect the ratio of roll/yaw disturbing forces to line-induced rigidity.

   I certainly don't mean to suggest that adding dead weight is a universal solution to anything. If nothing else the weight would have been better spent beefing up the structure.

    But it definitely proves that making any particular airplane/engine combo as light as possible does not necessarily make it fly better - as long as you have sufficient effective "power".  In this case it flew dramatically better in all respects *half-a-pound* (20%) heavier. It wasn't close, it subtle, it was a blowout.  I think it would hard to say that Ted Fancher and myself didn't know the right trim tricks needed to make it work as it was.

   I know where this conversation ends, and I wasn't trying to kick the hornet's nest, but it was a very valuable experiment that I thought was on the  original topic.

     Brett

[Jim Pollock]

Gee,

I had a Nobler back about '58 that had been built from the Kit - same kit wood and all; it weighed a whole total of 36 ounces fueled and ready to fly.  Of course, it could fly, but little old 8th grader me could not fly so well and it ended up getting a big mouth full of grass after I tried a wing over with my engine (Fox .29) eight stroking......
Proof positive I didn't know how to fly yet!

Jim Pollock        

[Howard Rush]

"What it should actually do is make us think about control system geometry."

"And this airplane did indeed use a 3" bellcrank."

Ha ha.  Got a 4" in mine.

[Jim Pollock]

I use 4" Bellcranks in all of my airplanes now.  I even have a 4"er in a slightly modified twister...

Jim Pollock   

[john e. holliday]

What I referred to is on pages 196-197 of the 1951-52 Model Aeronautic Yearbook.  The study was done in wind tunnel by the Tech Model Aircrafters at M.I.T.  They were talking about speed models in the 50 - 150 MPH range, and corrections for Reynolds Number are mentioned several times.  Their figures shows that .024 monoline will be faster than two .016 lines.   At around 150MPH  lines account for 5/6 of drag. Takes about 1.5 HP with 80% prop efficiency to go 160MPH, monoline would be 10-15MPH faster.  If one could get two faired lines to work, maybe 10-15 MPH over non faired twin lines.

Jim, we did that back in the 70's.  One line had little tape tabs holding cut up syringe needles.  The other line went thru the cut up syringe needles.  They were spaced about every six inches.  Bob Hunt caught us making up a set at a Lake Charles NATS.  That was the only year we used them as they did allow the planes to go faster by about 10-15 mph.  But, if you got a twist in the line, the pilot had his hands full.  All of us at the time started a campaign to get them out lawed.   

[Larry Cunningham]

At least Ted has the fashion sense to wear socks that coordinate nicely with the trim on his Tucker Special..

L.

Q. "It is considered in bad taste to discuss two subjects at nudist camps. One is politics, what is the other?"
A. Paul Lynde: "Tape measures."

[phil c]

How far the lines bow back is pretty much independent of speed.  Both forces on the lines are approximately proportional to the square of speed.

Make that ground speed Howard.  Obviously, when the plane is flying into the wind the ground speed goes down, the centrifugal force goes down, and the lines bow significantly further back. The airspeed really wouldn't change much, so the line drag goes up relative to the line pull.

[Howard Rush]

That's right.  The shape of the curve varies with wind direction, too.  I'm fixing to write a short monograph on this stuff.  I hope to use Ted's plane as a data point.