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Jay Kempf

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No, because control forces (and g-force for a given amount of deflection) vary with airspeed.

-Dana

I do not feel obliged to believe that the same God who endowed us with sense, reason and intellect has intended us to forgo their use. -- Galileo Galilei
Springs can keep the stick centered to give a sense of center and force increasing with distance from center only. But Gs building with stick deflection load the seat of your pants proportionally so I wouldn't say that there is no feedback. There is just no feedback in the stick. I do not think that one couldn't learn to fly a system like that Many small airplanes with side sticks have very little actual feel or force feedback. They have tiny control surface widths and so little force. Full flying tails have virtually no feedback so people add servo tabs to them to give designer feedback.

Anyway, my point is that you can fly sims, models, games with no force feedback. It can be learned. Pull back on the stick the Gs build up quickly. Pull back softly and the gs build slowly. One thing about digital controls is that you can put in reduced control volumes and limits that are triggered by G limits or speed limits. That isn't what I wanted to start with but it could be done. Accelerometers are fairly straight forward now.

One could add modes to the system in phases. Mode switch between an established mode and a proposed or mode that is being tested until the debugging is done.
 

Jay Kempf

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Pretty much all the cars now will have the sensor at the throttle pedal. No cables or other mechanical linkage. My 2006 Hyundai has it, and Toyota is trying to settle a mess of lawsuits arising out of rogue throttles accelerating and causing accidents. The Hyundai uses a Hall-Effect sensor, which has many benefits over the potentiometer. Pots cause all kinds of trouble as they wear and carbon dust gets under the runner, and they're subject to contamination by dust and liquids. To experience this, you only have to fly an older flight simulator and watch the stupid thing make uncommanded maneuvers when those old pots start to introduce spectacular resistance changes. Cars that had the throttle position sensor at the throttle body used to have failures too, like my old Ford F-150. A pain, due to potentiometer wear.

Many RC servos use potentiometers for postional feedback. I wouldn't want those in any airplane I ride in. Pot failure means that the servo will continue to move while the computer looks in vain for indication of movement. A crash is pretty much certain.

To me (and maybe it's just because I'm getting older and have been around long enough to see lots of stuff fail) the idea of FBW in small airplanes is a solution looking for a problem. By the time one adds up the input machinery (using Hall-Effect stuff, I hope, or inductive sensors), the wiring, the force-feedback stuff, and servos big enough to cope with controls surface loads at speeds up to or 10% beyond Vne plus some safety margin, it will all weigh considerably more than a few feet of cable and a few pulleys. It would in my Jodel, for sure. The control surfaces just aren't very far away or too big to handle manually. In large airplanes that cruise near Mach 1 and have things like swept wings it makes more sense, as it can permit cruising closer to the coffin-corner on the performance graph and still prevent mach tuck and maintain stability as CG is very close to the center of lift in such machines, to reduce drag. And weight in a large airplane is much less critical than in a small homebuilt.

The throttle in my Hyundai has a tiny lag that is annoying. I sure wouldn't want any lag in an FBW system.

Dan
I wouldn't use a wiper pot servo either. I would use a redundant position and drive circuit actuator. Still, off the shelf stuff. Hall sensors are all the rage now. In microelectronics optical position sensors are cheap and easy as well. Not a lot of resolution is needed. Speed and holding position are important.
 

Pops

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I built a homemade autopilot a few years ago and installed it in my single seat Cub. I used giant scale model airplane servos to operate trim tabs large enough to control the airplane but weak enough that I could override the autopilot with the controls. I have plugged the RC receiver into the servos and operated the servo tabs on the ground with the transmitter while setting in the seat, but never controlled it in flight with the transmitter. The autopilot had roll (wing leveler), with electric trim, Pitch( lock on a pressure alt.) with electric trim. Also could set a ROC or decent and fly a standard rate turn rt and Lt. Never did hook it up to the GPS. After a few months getting tired of watching the autopilot fly the airplane,and not having the fun of flying it, I took it out. :)
So I guess it could be a fly by wire.
 
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Hot Wings

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I wouldn't use a wiper pot servo either.
Just to be fair to the FBW throttle that left me stranded - when I used the word "pot" I was not meaning that it used a typical wiper/resistance potentiometer for position sensing, only that it has the position sensor in the pedal assembly.
 

autoreply

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Springs can keep the stick centered to give a sense of center and force increasing with distance from center only. But Gs building with stick deflection load the seat of your pants proportionally so I wouldn't say that there is no feedback. There is just no feedback in the stick. I do not think that one couldn't learn to fly a system like that Many small airplanes with side sticks have very little actual feel or force feedback. They have tiny control surface widths and so little force. Full flying tails have virtually no feedback so people add servo tabs to them to give designer feedback.
Virtually all sailplanes except for the really old ones have centering by springs, nothing else. Control feel (pitch) between 40 and 120 kts barely differs, roll is mostly internal friction, not aero forces.
Most folks adapt without even realizing it. The only problem they run into is the lack of noise at high speeds, which can make you fail to notice you're already going really fast.
 

Jay Kempf

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Virtually all sailplanes except for the really old ones have centering by springs, nothing else. Control feel (pitch) between 40 and 120 kts barely differs, roll is mostly internal friction, not aero forces.
Most folks adapt without even realizing it. The only problem they run into is the lack of noise at high speeds, which can make you fail to notice you're already going really fast.
That's kinda the impression I have. Most really modern side stick aircraft have very little stick force and take some getting used to in terms of force of the stick vs. speed and Gs.
 

Toobuilder

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Though I have yet to fly it, a buddy tells me the Extra 300 with aileron spades has zero force or feedback. If you throw the stick hard over, it stays there until you return to center by hand. Just like in the hangar.
 

Jay Kempf

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Though I have yet to fly it, a buddy tells me the Extra 300 with aileron spades has zero force or feedback. If you throw the stick hard over, it stays there until you return to center by hand. Just like in the hangar.
Yup,

So here's another possibility: if you have a computer interface system you could have a safe mode or sport mode, and you could have an aerobatic mode. Safe or sport mode would go like this: if the pilot let go of the stick and it returned to center and there was no input for say 2 seconds the aircraft would return to straight and level. If you switched to aerobatic mode it would just continue in the direction that it was last heading. If you wanted to tie throttle into that there are more combinations. That gets more into intertial navigation sorts of complexity but there are probably simple ways to do it safely with less than Airforce level of accuracy in the sensors and a relatively low sample rate between decision events in the control system to keep it simple.
 

Himat

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Fly By Wire, light airplane style.

So what would it take?
It would take determination and faith in the technology. Some good engineers and maybe more important, a pilot that trusted an electric powered and electronic controlled system as much as a mechanical system in a light plane.

It have been done, actually on a higher level: http://www.homebuiltairplanes.com/forums/rotorcraft/11340-very-exciting-first-manned-flight-electric-multicopter.html

This is not just electric actuators on the control surface instead of mechanical ones, it’s fly by wire with a control computer doing all mixing and dynamic stabilization of the vehicle.

It would be quite possible and even easy to build a simple FBW system today with currently available components... look at the autopilots they have right now for R/C models, or the controls for R/C quadcopters. The issue now is reliability...
The military drones don’t fall out of the sky in droves. Not even the small simple ones. R/C planes mostly crash because of pilot interference. I do think that reliability is ok if operated by a competent engineer.

For R&D, maybe, but an airplane without any control feel is not a good thing. There's a good reason why FAR 23 requires minimum stick force per g, etc. R/Cers get away with it because the planes are absurdly strong compared to a full size aircraft, so you can't overstress it... and the lack of feedback is one of the reasons that R/C is actually more difficult to learn to fly than the real thing.
R/C model airplanes are absurdly strong. Maybe, but I have folded more than one set of wings.:) Actually I do think that pilot induced oscillations might be more problematic. In the 1950 when fighter planes first got boosted controls a lot where crashed due to this. SAAB got the same problem, pilot malfunction, which had to be rectified within the FBW software.

... To me (and maybe it's just because I'm getting older and have been around long enough to see lots of stuff fail) the idea of FBW in small airplanes is a solution looking for a problem. By the time one adds up the input machinery (using Hall-Effect stuff, I hope, or inductive sensors), the wiring, the force-feedback stuff, and servos big enough to cope with controls surface loads at speeds up to or 10% beyond Vne plus some safety margin, it will all weigh considerably more than a few feet of cable and a few pulleys...
Maybe the weight question here is similar to weight of composite design vs. metal design. Design a composite airframe with “metal” thinking and it’s at least as heavy. Design as composite with “composite” thinking from the start it is lighter. This might apply in this case too.
 

rtfm

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I'd cut up the system in many actuators and sensors. 1 ft span flaperon sections (with a single actuator each) and both your elevator and rudder also split in at least 3 surfaces or so.
Hi Autoreply,
OK, I'm intrigued. What would be the value of splitting your control surfaces like this? How would this be more effective?

Do I assume that in a roll, for example, one would deflect the outside flaperon panels more than the inside panels? Or vice versa? This is non-intuitive to me. Likewise with multiple rudder panels. How would you design/plan their differential deflection, and how would deflecting the panels to greater or lesser relative degree improve the rudder effectiveness? And the same question for multiple elevator panels. I just don't see how this would be beneficial.

Sexy, yes. But more effective?

I can quite see the value of being able to deflect all panels simultaneously for TO and landing. Huge effective flap area. But how does one use aileron control with everything deflected like this?

Differential inner and outer panel deflection to act as air brakes on landing: get this...

Regards,
Duncan
 

autoreply

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Hi Autoreply,
OK, I'm intrigued. What would be the value of splitting your control surfaces like this? How would this be more effective?

Do I assume that in a roll, for example, one would deflect the outside flaperon panels more than the inside panels? Or vice versa? This is non-intuitive to me. Likewise with multiple rudder panels. How would you design/plan their differential deflection, and how would deflecting the panels to greater or lesser relative degree improve the rudder effectiveness? And the same question for multiple elevator panels. I just don't see how this would be beneficial.

Sexy, yes. But more effective?

I can quite see the value of being able to deflect all panels simultaneously for TO and landing. Huge effective flap area. But how does one use aileron control with everything deflected like this?

Differential inner and outer panel deflection to act as air brakes on landing: get this...
That's not something I can explain in a few words. Nevertheless a try.

Theory (pure academics) say a fully morphing wing is optimal. Local deflection is roughly proportional to the spanwise station to the power 1.5 or so. Open-class sailplanes come pretty close. A modern open-class sailplane has 4 spanwise surfaces. Flap action is roughly mixed in (inboard to out) 100%, 75%, 50%, 0%, while aileron deflection is 0%, 50%, 100%, 100%. The outboard panels only move upwards (to avoid tip stall).

In reality, breaking it up in 2 or 3 sections (drooping ailerons basically) approaches the ideal pretty well. Above everything else it allows you to design a wing where the wing stalls at every spanwise station at the same time (bad, dropping tip=>spin). That's great for max performance, except when you're likely to stall, namely with flaps. Dropping flaps (reduces local stall aoa) is a healthy barrier against tip stall, so then drooping ailerons half as much as your flaps gives you both maximum lift and a healthy protection against tip stall.



But my preference for many small stations has another reason. Redundancy and simplicity. The individual "flaperon" sections are small enough to easily cope with a mechanical/electrical failure of one of them. Sure, you'll need a lot of actuators and trailing edge surfaces. But you can move away from the mechanical complexity. It also relieves you from some other nasty issues like flap/aileron bending, torsional stiffness etc.

Add the increased lift and it's a pretty interesting idea. Just a reality-check; compared to a classic wing with 50% straight flaps and 50% straight ailerons you might be able to have a wing that needs 25-30% less area and thus weight. Himat's last remark is an excellent one, you really need a different (fundamentally different) mind-set to fully appreciate the possibilities. Everything changes.
 

sachaknoop

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And this one, sorry I did not read this thread, but as stated in the beginning, all the stuff is there!

 
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Dan Thomas

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I wouldn't use a wiper pot servo either. I would use a redundant position and drive circuit actuator. Still, off the shelf stuff. Hall sensors are all the rage now. In microelectronics optical position sensors are cheap and easy as well. Not a lot of resolution is needed. Speed and holding position are important.
Optical stuff relies on a light source (failure point) and must be sealed against dust. I would much prefer variable inductors: a moving core in a coil. They don't need a light source, they have no dust issues. They just need a small AC input and a current-measuring circuit.

Dan
 

Dan Thomas

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Maybe the weight question here is similar to weight of composite design vs. metal design. Design a composite airframe with “metal” thinking and it’s at least as heavy. Design as composite with “composite” thinking from the start it is lighter. This might apply in this case too.
Not in my experience. We had a Cirrus SR20 whose empty weight was nearly as much as the gross of the Cessna 172, and it had only 20 more Hp and carried the same four folks a few knots faster. Not a good example of the "lightness" of composite construction.

Dan
 

autoreply

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Not in my experience. We had a Cirrus SR20 whose empty weight was nearly as much as the gross of the Cessna 172, and it had only 20 more Hp and carried the same four folks a few knots faster. Not a good example of the "lightness" of composite construction.
Exactly. The Cirrus is an excellent example of metal thinking in composites. Apply "conventional design" to a FBW airplane and you'll also end up with an overweight contraption. 3 redundant connected servo's to one aileron for example are what you would come up with.
 

cluttonfred

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Aren't the structural design loads required for certification of composite structures higher than for metal structures? I know that used to be true and was part of the reason than the few certified production composite planes were sleeker but not generally lighter than their metal contemporaries.

Exactly. The Cirrus is an excellent example of metal thinking in composites. Apply "conventional design" to a FBW airplane and you'll also end up with an overweight contraption. 3 redundant connected servo's to one aileron for example are what you would come up with.
 

Jay Kempf

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Exactly. The Cirrus is an excellent example of metal thinking in composites. Apply "conventional design" to a FBW airplane and you'll also end up with an overweight contraption. 3 redundant connected servo's to one aileron for example are what you would come up with.
Yup, but apply non-conventional thinking to the combination of both and I believe one could design an overall simplification of structures/parts counts and a weight reduction. Boeing did a lot of that in their new offering. They are going through growing pains but they'll sort it out. 30% reduction in weight is the number I have heard quoted. It is a lot simpler to just put a servo at a moving surface than to build a mechanical control system that spans the entire airframe.
 

cavelamb

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Yup, but apply non-conventional thinking to the combination of both and I believe one could design an overall simplification of structures/parts counts and a weight reduction. Boeing did a lot of that in their new offering. They are going through growing pains but they'll sort it out. 30% reduction in weight is the number I have heard quoted. It is a lot simpler to just put a servo at a moving surface than to build a mechanical control system that spans the entire airframe.
I take strong exception with your reasoning, Jeff.

Are you thinking of something like RC model airplane servos? That won't do at all.
Scaled up to have enough force and speed to handle control surfaces on a full sized airplane they would be huge - and heavy.

Voice coils? Have you ever seen the power supply in an old CDC disk drive?
And that's just to move a few light weight heads.
NOTHING like moving an aileron or elevator.
Dude!

I think you need to rethink your thinking...
 

cavelamb

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I was just reading Karlolina's excellent blog: http://designaplane.blogspot.com

And this question of large leaps of innovation in aviation starting with available fly by wire is a great thought. So I thought I would like to have a discussion based on what ifs.

What I know is that the rest of the aviation world from Drones to RC to Airbus and all the others are working on FBW solutions for everything. What I also know is that things like Arduino are making high speed progress along the lines of progression in the personal computing hardware and software sort of speeds. So all the building blocks are there.

It seems that digital proportional computer driven controls are not just possible right now but actually everything needed to do it is off the shelf and cheap right now. So instead of talking about why it can't be done why not talk about how it can be done. What would someone have to do to design and test and open source type of system in order for it to become commonplace?

Some examples in the automotive world that are already intervening between operator and vehicle are traction control and throttle and brakes by wire. Steering by wire is coming very soon to the US. So it is happening. Again, Airbus especially and many others are already there but those systems and the development are astronomically priced.

Take a look at a project like the Megasquirt fuel injection system. It is not harder technically to take that same development environment and scale it to a control system with redundancy.

So what would it take?
Aircraft Cable Galvanized & Stainless Steel, Nylon & Vinyl Coated Cable, Cablelaid, & Strand | WorldWide Enterprises, Inc.

1/8" steel cable weighs .029 pounds per foot.
Double that for pull-pull arrangement and it comes to a whopping .06 pounds per foot.
20 feet means about 1.2 pounds from wing tip to wing tip.


Cost runs about a buck a foot - give or take.


Now, you want to replace this with WHAT?
 
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