Amazing

[frank williams]

Amazing.  Just amazing.
 
I ran across this photo and was amazed at how far back the leadouts are located.  This flyer should know that this rearward placement will result in hunting and loss of line tension overhead…. at least by gasser standards.  Its probably an electric due to the unusal shape of the nose and we have heard that electrics do need the lines back more than for gassers, though we don’t know why.

When I fly electric I run pusher props, although some have told me that they just don’t do right at the top of the hourglass.   
I have noticed one thing that is interesting between tractors and pushers .. in the hourglass; the gyro yaw and the swirl yaw are complementary.  That is to say that with a tractor prop, the yaw at the top of the hourglass is inboard for both gyro and swirl.   For pusher props the gyro and swirl effects both yaw the nose outboard.  nice

I thought, that with outboard yaw at this delicate part of the pattern, that I was in great shape.  Recently though I have had problems with the top of the hourglass with a particular electric plane.  Very bad stall, with a plane that wasn’t too heavy and with a good known airfoil. 
My suspicion was that I was just getting too much yaw out.  The gyro yaw would be difficult to change.  To reduce the swirl effects I took the rudder off.  Drastic? Yeah but ..Bingo.  Now perfect turn at the top of the hourglass.

I’m gonna rename the plane Genesis …. Ok maybe Revelations.

Come on guys … we’re smart … why the excessive leadout position for electrics.  Is swirl a factor?, vibration?   A gasser with the leadouts at 40% of the tip chord , like the plane in the picture, wouldn’t work at all.

[Ken Culbertson]

Frank I am as baffled as you are.  Maybe my designs just don't have the problem or I am just to dumb to know that I do.  I first flew pusher because I was told that is what you did with electrics.  Better takeoff but that was where it ended so I switched back to tractor.  I have no clue why you need such an aft leadout position.  I usually end up with them pretty far forward yet some fairly good fliers sure do have them way back.  One of life's mysteries.   It is possible that the CAM rudders I use on all of my planes tighten the lines in maneuvers which keeps the line tension more even....or not.

Ken   

[Paul Walker]

It's all about flying qualities.

With the LO back, there is a very noticable improvement in damping exiting hard corners. That's mostly why they were there.

What IS real important is the 16g props. They really reduce the yaw due to the gyroscopic effects. There is no way I could fly now with a heavy prop.

[Perry Rose]

I tried the leadouts aft thing and the plane was unflyable. Never again. I set the electrics up, battery installed, the same as my normal planes. It may work on Pauls plane but it don't work on any of mine.

[Tom McClain]

From the American modeler magazine of the 60s and late 50s, Bill Netzeband, did a very definitive study on lead out position.  His nomograms show that the leadout position that seems to be the best for just about any Control Line aerobatics model is 2 1/2 to 3° of line rake.  I static line set up my models so that the nose hangs 2 to 3° nose low before the first flight. It works every time. Too much line rake causes the model to crab and lose energy during heavy maneuvering.

[Dennis Toth]

I think a lot depends on the line diameter used. Some fliers use heavier lines then needed. They claim it cuts down on stretch so they will use 0.018" when 0.015" will do. With Spectra lines the diameters can be even thinner. I think the 2 - 3 deg starting point (~5/8" back of the CG) seems to work then adjust from there for the lines you are using.

Best,    DennisT
 

[Doug Moon]

I have often though the LO position moving back more and more has to do with the main weight of the model, the battery, being closer to the CG. I have also noticed some electric models fly with the CG further forward than the glo models as well. There again the weight is close to the CG with less weight, light motor and even lighter props, on the end having alot less effect on the trim. CG and LO position on the bench are only a starting point. The plane will dictate where it wants them based on the flight characteristics and what is asked of it.

I have a couple of the Igor props. They are so light I wonder how they don't just flex all over the place. 

[Jim Hoffman]

There are many, many variables in play,  including aircraft alignment, pilot skill and his ability to evaluate the effects, power, and the myriad of trim settings possible. 

I frequently make and log trim changes to evaluate the result.

I am having good success w/ an E-power model, including at top of the hourglass w/ a 16-gram Igor 3 blade prop, forward. CG, aft LO placement.

[Paul Walker]

My most forward LO position has about 4 degrees sweep back from the  CG.  The most rearward, 6.5 degrees.
Before (and after in this case) many state that this simply doesn't work,  I applaud your shortsightedness. Open up your minds and consider that different aircraft configurations, trim settings, weights, line lengths, tip weight balance, CG position etc can influence this.  How many trim conditions have you tried to evaluate this?  I think Frank is open minded, and that is why he asked the question.

My GUESS is there is a perverted inverse relationship between CG location relative to the MAC and LO position.  Old gassers have generally more aft CG's relative to MAC than  my electric planes. The farther back the CG in relation to MAC the less the LO sweep, and the farther forward the CG relative to the MAC, the more sweep they seem to need.

My P-47 balanced at 8% of MAC and the LO sweep was clearly at the large end. It would not work at 4 degrees sweep. At the aft end it still scored a 596 in the Nat's finals, so maybe the extreem aft sweep works....
The plane I have used for the last 4 years used to have the LO way back, and that was with a more forward LO location. Moved the CG back to 18% MAC, and the LO's moved forward. Even at 5.5 degrees sweep, it flew through the 25 mph winds in the finals. There goes the loss of energy statement.

I am not saying I can explain, but there appears to be some emperical data that leads me to this conclusion.

Let the hating start....

[Doug Moon]

My most forward LO position has about 4 degrees sweep back from the  CG.  The most rearward, 6.5 degrees.
Before (and after in this case) many state that this simply doesn't work,  I applaud your shortsightedness. Open up your minds and consider that different aircraft configurations, trim settings, weights, line lengths, tip weight balance, CG position etc can influence this.  How many trim conditions have you tried to evaluate this?  I think Frank is open minded, and that is why he asked the question.

My GUESS is there is a perverted inverse relationship between CG location relative to the MAC and LO position.  Old gassers have generally more aft CG's relative to MAC than  my electric planes. The farther back the CG in relation to MAC the less the LO sweep, and the farther forward the CG relative to the MAC, the more sweep they seem to need.

My P-47 balanced at 8% of MAC and the LO sweep was clearly at the large end. It would not work at 4 degrees sweep. At the aft end it still scored a 596 in the Nat's finals, so maybe the extreem aft sweep works....
The plane I have used for the last 4 years used to have the LO way back, and that was with a more forward LO location. Moved the CG back to 18% MAC, and the LO's moved forward. Even at 5.5 degrees sweep, it flew through the 25 mph winds in the finals. There goes the loss of energy statement.

I am not saying I can explain, but there appears to be some emperical data that leads me to this conclusion.

Let the hating start....

Why on earth would anyone hate on this? Exchange of information and discussion is always a good thing.

What you find is interesting for sure. I fly with Mike Scott and he has a foreign take apart for electric and the LO would not go as far back as the pic of your model above. The slider is not built that long....  Interesting..... I wonder if that is leading to some of the trim issues he is running into.

[Paul Walker]

Why on earth would anyone hate on this? Exchange of information and discussion is always a good thing.

What you find is interesting for sure. I fly with Mike Scott and he has a foreign take apart for electric and the LO would not go as far back as the pic of your model above. The slider is not built that long....  Interesting..... I wonder if that is leading to some of the trim issues he is running into.

I assume you are referencing Mike.  If that is the case, I have some insights.

[Tom McClain]

My question is “Was Wild Bill Netzeband wrong?”  I use his nomograms for my ships and find they work and my understanding of energy maneuverability leads me to trim a ship so it maintains the best corner speed and G available.

[wwwarbird]

Amazing.  Just amazing.
 
I ran across this photo and was amazed at how far back the leadouts are located.  This flyer should know that this rearward placement will result in hunting and loss of line tension overhead…. at least by gasser standards.  Its probably an electric due to the unusal shape of the nose and we have heard that electrics do need the lines back more than for gassers, though we don’t know why.

 Might want to check yourself Frank, the record books show that "this flyer" has a pretty good idea what he's doing. 

[Air Ministry .]

"
I ran across this photo and was amazed at how far back the leadouts are located. "

AND there 3/4 aft of the C.G. . 

[pmackenzie]

It is all an optical illusion, the checkerboard on the flaps makes them look skinny......

[Paul Walker]

Why on earth would anyone hate on this? Exchange of information and discussion is always a good thing.

What you find is interesting for sure. I fly with Mike Scott and he has a foreign take apart for electric and the LO would not go as far back as the pic of your model above. The slider is not built that long....  Interesting..... I wonder if that is leading to some of the trim issues he is running into.

Doug, what issues is Mike having?  What specific plane is it?

[Paul Walker]

My question is “Was Wild Bill Netzeband wrong?”  I use his nomograms for my ships and find they work and my understanding of energy maneuverability leads me to trim a ship so it maintains the best corner speed and G available.

It is perfectly clear in my mind, but maybe I didn't specify enough. One of those old age problems. 😩 The aft LO issue is unique to electric power only. When I flew IC, the LO's were right on Wild Bills nomograph location.  Started electric that way, and was quite surprised. The first few electric planes were heavier than they could have been, and thus had the LO more forward.  As the power systems got lighter, things changed. The current crop of planes have "sufficient" line tension even though they are lighter.

With electric, there is far less concern about energy management, and that gives more options for trim adjustmants.  I assume you are still using IC power, and your comment is more appropriate if that is the case.

Sorry if I was not clear enough about this being an electric phenomon.

[Mark Schluter]

Interesting comparison; pic from the 2019 NW regionals....(I hope it attaches)

[Brett Buck]

My question is “Was Wild Bill Netzeband wrong?”

   Well, sort of. The original nomographs were wrong because the underlying analysis did not consider the Reynolds number. This was later corrected and the LINE II program accurately reflected the arc the lines make due to drag. I note that Bill was not the prime experimenter. I will dig out the original and update papers that included wind tunnel testing, at MIT, I think.

     But- define "right". What Bill did was report on some analysis about the shape of the lines due to tension and drag. If your goal is to have the airplane track tangent to the circle and also have the lines enter the wing at exactly the spot at which they would naturally arc, then it is "right".

   If someone made a "mistake", it was me, because I strongly suggested (and still suggest) that most people would be pretty well off if they put the leadouts there, left them alone, and adjusted the rudder for minimum yaw transients at corner entrance. That doesn't preclude people from trying other strategies that might be better.

   So, none of it is actually wrong. I still think it an excellent starting point and also, that most people will never do a lot better, because it takes a lot of careful san sensible experimentation to now how to change it and optimize everything else around that change.

    Paul is obviously far beyond the average when it comes to trimming airplanes and is far more than qualified to find other approaches. I have to admit that I don't understand the underlying mechanism here, Pauls airplanes do not appear to fly yawed out all the time, looking from the outside, and obviously show none of the ill effects you would expect from a large yaw angle.

    I do at least have a guess on why the CG can be so far forward - superior speed stability in the corners because of the governor. That seems to be a common characteristic with lots of electric airplanes, you have have the CG far forward (compared to an IC engine) without having anything like the ill effects on control pressure. But not everybody (or at least, other qualified experimenters) wind up with the leadouts so far aft.

   I also note that Pauls airplane has a very long nose and relatively little aft area. That means it seems to have less built-in "arrow stability" in yaw than other airplanes (mine in particular) which would permit it to yaw without lots of ill effects.

     Brett

[Tom McClain]

Thanks Paul Walker and Brett Buck.  Yes, I am still a dinosaur and using OS 35 Max S's and OS 40 Fps.  Something about the sight, sound, smell, taste, and feel.  I am an old McDonell Douglas Phantom Driver and flying trimmed and using energy conservation for the best corner speed and minimizing energy loss is my objective.  Control Line Aerobatics is the closest to flying the Phantom I can come without being in one.

Thanks again for the lesson. We all can learn if we listen.  I had no idea that there is such a difference between IC and Electric.

[Doug Moon]

Doug, what issues is Mike having?  What specific plane is it?

I am note sure if it would matter but the first plane he had always hunted. Tried many different things but it would not go away. That plane was crashed. Yours truly is rebuilding the nose and we will get it back in the air asap and see what we can do.

[Paul Walker]

I am note sure if it would matter but the first plane he had always hunted. Tried many different things but it would not go away. That plane was crashed. Yours truly is rebuilding the nose and we will get it back in the air asap and see what we can do.

So it's not a MaxBee clone.