Wait a minute. We didn't consider how the change of incidence in the control surfaces may differ in effect as it is moved through the angle shifts in control. For instance will 17 degrees of flap incidence exert half the lift augmentation of 34 degrees incidence. But I guess the aim is to deflect the flap/elevator up/down in equal proportion to handle movement in order to equalize feel at the handle as it relates to the airplane's turn inside and out. Is there an algorithm programed into fly by wire systems that make a non one to one relationship between stick moves and control deflection? What about grand prix cars. How have the racers worked out the ratio of steering wheel to the front wheels. Is it a constant ratio or does it change in relationship to the angle of input. Slop in the elevator. Haven't some folks advocated a dead zone near neutral.
I spent an hour typing out a great reply Dennis, but it disappeared into the great maw of the internet.
I'll try to remember what I said, and re type it.
Dennis, I don't believe we've met in person, so though I'm inclined to consider your post as legitimate, a small part of me feels like you may be jabbing a few of us with a stick though. For the sake of this discussion, I'll try to answer your questions as I understand the answer to be.
"Wait a minute. We didn't consider how the change of incidence in the control surfaces may differ in effect as it is moved through the angle shifts in control. For instance will 17 degrees of flap incidence exert half the lift augmentation of 34 degrees incidence. But I guess the aim is to deflect the flap/elevator up/down in equal proportion to handle movement in order to equalize feel at the handle as it relates to the airplane's turn inside and out."What follows is a lot of verbage to say yes, that is the aim.
I'm going to assume that you mean angular rotation, rather than incidence in your question. It's easy to get the two mixed up, but they really are two different things.
Though the change of rotation with the control surfaces, and it's affect on the planes turn quality is important, it's not really the total issue we are trying to correct with our "Corrected Geometry'.What is more important, is the ratios between the bellcrank,flaps, and elevators. These ratios work best when they remain as nearly constant as we can get them throughout the rotation. a moving variable within the constraints of one of these points in our control system will cause asymmetry with in the system. Eliminating such variables will result in an easier, and more repeatable turn regardless of the amount of input needed.
Over the years, after being involved in literally hundreds of drawings, or redraws, of OT, Classic, and Modern stunt designs, I've seen tremendous differences in asymmetry, if you please, in control systems. One of the worse, involved a well known Classic Stunt design, a Nat's winner for the designer pilot, but not always so well behaved for the average pilot/builder in todays time. After checking the controls, I found that if built as shown on the plans, the controls had asymmetry problems, as well as ratio problems, with a difference of about 7 degrees between up and down, as well as 3-4 degrees difference between the flap and elevator, up and down.
In the classic era, we simply learned how to fly them this way, but today we'd find it difficult to switch to different planes, like flying Classic, and PAMPA classes on the same day at a meet.
"Is there an algorithm programed into fly by wire systems that make a non one to one relationship between stick moves and control deflection? What about grand prix cars. How have the racers worked out the ratio of steering wheel to the front wheels. Is it a constant ratio or does it change in relationship to the angle of input." The simple answer is yes. The problem, and the solution, is related to your question about Grand Prix cars and the steering arrangements. I'm sure you and others are aware of the fact that when turning, the inside wheel of a 4 wheel vehicle must turn and trace a smaller diameter, than the outside wheel. It also has to do this regardless of the radii of the circle, or whether or not the radii remains constant through out the turn.
The same thing happens in our bellcrank to flap link, and like the solution for a turning car, we attach our push rod at the 90 degree point, relative to the pushrod.This is "Corrected Geometry" in it's simplest form. As shown by Lou, and others, there are other items we can factor in to reduce additional small errors, but, the 90 degree attachment of the bellcrank to flap horn pushrod is the major contributor to getting rid of asymmetry in the control system. The smaller errors are basically lost in the noise of most systems.
Further more, with modern control systems that use a elevator mounted above the flap chord line, leads to simpler layouts for the flap/elevator link.
It's possible to layout this link to dispose of nearly all errors produced, but I believe it's more of an exercise for those of us who enjoy figuring this type of solution. Larry Cunningham published an article in Stunt News some years ago, describing "Magic Geometry" He discovered an angular relationship between the flap elevator pushrod, at neutral, and the extremes. When this relationship fell with in certain variables, the ratio between the flaps and elevator would even out, "magically", corrected.
Since the greatest amount of asymmetry comes from the bellcrank/flap link, I've come to believe that once that is corrected, there's little to be gained, realistically, by finding the solution to possible flap/elevator asymmetries. Modern designs, when checked, usually fall with in a 1 to 1.5 degree error, and is usually within the noise. The solution in my case, often has the elevator pushrod attaching to the flap horn 90 degrees relative to the wing chord, and the same 90 degrees relative to the stab chord at the other end.
Modern practise advocates the use of Ball Links through out the control system. This gives us a very tight, not sloppy, and accurate control system. It will react linearly, and instantly to control inputs. It's now much more important to use the right incidences, and get alignments correct to make a plane into a 'point and shoot" competition machine.
So, your last question takes on new meaning when it comes to modern stunt designs and thinking.
"Slop in the elevator. Haven't some folks advocated a dead zone near neutral."My own personal experiences, from back in the day, through even today, is that some people suggest slop in the elevator as a solution for hunting in level flight, upright, and inverted. Back in the day we noticed that our planes seemed to fly better as they aged. Maybe we also were getting used to them, but our older planes did not seem to hunt as much as brand new fresh ones.
When one of these older planes went in, we usually found, post mortem, that the hole for the elevator end of the pushrod, had worn and had slop. when we purposely made the holes sloppy, those modified planes also hunted less. Not wondering why, we were only kids anyway, we simply knew that it worked.
Fast forward to today. Modern stunter design has progressed, along with our collective education. We've learned why things happen, and how to design in the corrections needed to help prevent problems in the first place. Because of this, many of us relegate building slop into the elevator to sport planes, or perhaps to planes that we wouldn't consider placing high in competition with. It works, but it also adds just a slight sluggishness around neutral, a hesitation at intersections, that can present a lack of crispness, or authority, a pilot needs to compete at the higher levels.
Now, the design solutions have been discussed on these various forums for years. I will mention them, basically in order of importance as I perceive it to be.
First three elements to consider are design, power, and practise. Design and power could be interchangeable.
Power must be appropriate for the job. If you're serious, you need to save up and get a serious power plant. If you're fighting the engine, or motor, you cannot make the best of your practise.
Speaking of practise, if you're serious, use a coach, if at all possible . I know many who have practised their mistakes and now perform them perfectly.
I saved design for last, even though it should be either first, or second.
If you're serious, the design you select to fly should have the capability to perform with the best out there. It should have the right "numbers". further more, If you use modern, tight, not sloppy controls, then you need to use the proper geometry with in that control system. When you do so, other aspects of the planes design will come into play. How do you keep the plane from hunting? You should search out the threads and discussions on using downthrust, out thrust, positive incidence in the stab. flap elevator ratios become important and vary with weight and flight speed.
Learn to build light, straight, and only strong enough. Over building only adds weight.
There's more, but your a smart person, you'll find it. Last but not least, don't be afraid to ask questions. Listen carefully to the answers you get. Some may not apply to your goals.
Topic: 4" Bellcranks. (Read 15785 times)