Control surfaces actuators design/preferences

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Dan Thomas

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the idea is to keep the wire rope from jumping out of the groove and getting caught between the side of the pulley and the mounting or guard and jamming up and stopping the rope from moving.....not a good idea to have your control completely immobilized. a drilled hole for a cotter pin might be easier that two bends and a hole for the pulley in just the correct places so the rope can not rise up out of the groove.
It also keeps the cable in place when they are loosened or disconnected during maintenance.
 

maya.ayoub.32

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Oh I see! We'll modify the Affordaplane's design to create two sides attached by a bolt then. Thank you for the suggestions!
 

Stefan P

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Hi everyone, I’m new to the site, I haven’t built a plane, yet but I hope to in the near future.
FBW (fly by wire) means to me; no mechanical connection only wires. Like when they first removed the throttle cable/linkage from gas pedal to carb/throttle body on cars. I don’t think redundancy has any bearing on the definition. Just my 2 cents.
 

dog

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Hi everyone, I’m new to the site, I haven’t built a plane, yet but I hope to in the near future.
FBW (fly by wire) means to me; no mechanical connection only wires. Like when they first removed the throttle cable/linkage from gas pedal to carb/throttle body on cars. I don’t think redundancy has any bearing on the definition. Just my 2 cents.
Hi
FBW is synonymous with redundancy.
Horribly complex,multi system,computerised,
just the descriptions of the blueprints is
enough to give pause.
And each component must be extremely reliable,which is its own world of testing and
verification.
And in Canada,we got rid of the penny,and when the price of something ends in 3¢ or 4¢
we round up but for 1¢ or 2¢ we round down.
what do you want to build?
 

Dan Thomas

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Sep 17, 2008
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6,208
Hi everyone, I’m new to the site, I haven’t built a plane, yet but I hope to in the near future.
FBW (fly by wire) means to me; no mechanical connection only wires. Like when they first removed the throttle cable/linkage from gas pedal to carb/throttle body on cars. I don’t think redundancy has any bearing on the definition. Just my 2 cents.
Like Dog says, it's way too complex and presents many more failure points. And more weight. And more cost. It makes sense in big airplanes because they can handle the weight and justify the costs and they can have at least three systems for redundancy. Carmakers use it to get better efficiency out of the engine and because cruise control is there anyway. No homebuilder does it, for all the reasons listed.

My Hyundai has an electronic throttle. It works fine, except when the pedal-operated potentimeters got worn and carbon dust caused resistance errors. The thing has two pots that operate together but feed separate computer circuits that compare the two readings, and if they differ by something like 4% the computer puts the car into "limp" mode so you can limp home on vastly-reduced power. They do that so that the computer doesn't suddenly open the throttle wide due to a bad reading from a potentiometer. It cost me nearly $300 for a new throttle pedal assembly, and I installed it myself. A new throttle cable for my Ranger would be a fraction of that, and I'd only have to replace it if it broke. Which they seldom do.

Now, suppose that happened in an airplane? Full down-elevator or something. Instant death. So you need multiple inputs and multiple feedbacks from the controls, and some means of ignoring stuff that doesn't make sense. Complexity, cost, weight, risks. All to replace a few feet of 1/8" cable and a handful of pulleys? Nope.

Edit: We also need to remember (which I didn't last night when I posted this) that airliners have to have boosted controls. The forces required to move those controls on a heavy airplane at high speeds are very high, so they use hydraulics. The pilot either moves cables to tell the hydraulics what to do (old airliners) or a computer, which tells the electrically-controlled hydraulics what to do. The addition of the computer to make full FBW enabled the makers to take out all the many feet of cables and all those pulleys and stuff. Then they had to add computers for redundancy, redundant power sources, and control surface position sensors to tell the computer whether the surface has moved the commanded amount, and so on. It really adds up. Then they get fancy and program the computers to refuse to do certain things that might cause the airplane some harm, and we get some stupid accidents.
 
Last edited:

Stefan P

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Jul 6, 2021
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Hi
FBW is synonymous with redundancy.
Horribly complex,multi system,computerised,
just the descriptions of the blueprints is
enough to give pause.
And each component must be extremely reliable,which is its own world of testing and
verification.
And in Canada,we got rid of the penny,and when the price of something ends in 3¢ or 4¢
we round up but for 1¢ or 2¢ we round down.
what do you want to build?
I should have done some research, I am wrong. i guess the car industry hijacked “fbw” and misused it.
I too am from Canada On a small lake.
I’m just starting to learn about aviation. I was always under the impression you have to be rich to fly, which I’m not. But in the last year or so I’m learning about ultralight planes and ultralight pilot licence. Maybe I could fly one day.
From my research so far and money was no object, I would like a Zenair/Zeneth ch701 on amphibious floats. But I think I will be lucky to start off with a quicksilver mx2 or similar.
 

Stefan P

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Jul 6, 2021
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Like Dog says, it's way too complex and presents many more failure points. And more weight. And more cost. It makes sense in big airplanes because they can handle the weight and justify the costs and they can have at least three systems for redundancy. Carmakers use it to get better efficiency out of the engine and because cruise control is there anyway. No homebuilder does it, for all the reasons listed.

My Hyundai has an electronic throttle. It works fine, except when the pedal-operated potentimeters got worn and carbon dust caused resistance errors. The thing has two pots that operate together but feed separate computer circuits that compare the two readings, and if they differ by something like 4% the computer puts the car into "limp" mode so you can limp home on vastly-reduced power. They do that so that the computer doesn't suddenly open the throttle wide due to a bad reading from a potentiometer. It cost me nearly $300 for a new throttle pedal assembly, and I installed it myself. A new throttle cable for my Ranger would be a fraction of that, and I'd only have to replace it if it broke. Which they seldom do.

Now, suppose that happened in an airplane? Full down-elevator or something. Instant death. So you need multiple inputs and multiple feedbacks from the controls, and some means of ignoring stuff that doesn't make sense. Complexity, cost, weight, risks. All to replace a few feet of 1/8" cable and a handful of pulleys? Nope.
I wasn’t condoning fbw on an ultralight, I’m one of the KISS (Keep It Simple Stupid) rule guys. I don’t think I would feel comfortable with that technology off the ground.
 

dog

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Dec 29, 2019
Messages
578
I should have done some research, I am wrong. i guess the car industry hijacked “fbw” and misused it.
I too am from Canada On a small lake.
I’m just starting to learn about aviation. I was always under the impression you have to be rich to fly, which I’m not. But in the last year or so I’m learning about ultralight planes and ultralight pilot licence. Maybe I could fly one day.
From my research so far and money was no object, I would like a Zenair/Zeneth ch701 on amphibious floats. But I think I will be lucky to start off with a quicksilver mx2 or similar.
You are wrong about bieng wrong.Fail fast,fail often.Build soon to be scrap.Fail forward.
You have a lake.Lots and lots of project planes
for very reasonable prices.Bucket of quarters and loonies in your truck,and stop at any yard sale showing rust,tools,tools,hardware.
Kijiji has airplanes.
Some smaller online aircraft dealers in Canada also have projects and parts.(not going to show up at the top of a search,you gona have to dig)
Awsome deals out there.
 

Eric W

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Mar 7, 2021
Messages
2
Back to Geo's original question, nobody mentioned steel tube. Low cost, stiff, and would require lower diameter than Aluminum for a given force. Might not be as lightweight as cables for a given run, but close enough to win the trade in my Sonex, and probably many other small aircraft. Sonex is a push-pull system, not torque. If I followed, part of Geo's issue was getting control up to a high wing. Could do that with push-pull tubes, but there would be some linkage to work out to get to the ailerons.
 

wsimpso1

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Saline Michigan
Hi everyone, I’m new to the site, I haven’t built a plane, yet but I hope to in the near future.
FBW (fly by wire) means to me; no mechanical connection only wires. Like when they first removed the throttle cable/linkage from gas pedal to carb/throttle body on cars. I don’t think redundancy has any bearing on the definition. Just my 2 cents.
Oh, fly by wire without redundancy can be done, but is only acceptable where severity times likelihood is low. RC's do it.

Automotive single thread drive-by-wire is unacceptable to most of us in airplanes - failure results in immediate forced landing. Change it to default on failure to open throttle, and its set of failure modes might become acceptable...

You might get to single thread operation of trailing edge devices on each wing acceptable with six or eight separately controlled surfaces per side.

Another way you might get low enough sum of severity × likelihood is by adding a ballistic parachute capable of a safe landing, but you still have that window at very low altitude.

Billski
 

Topaz

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Moderator Note: Broke the discussion on flight safety, flight training, etc. off to its own thread, here.

This thread is about flight controls. Let's stay on-topic, gentlemen.
 

Heliano

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Dec 24, 2015
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Location
Campinas, SP, Brazil
One more comment: fly-by-wire aircraft have electrical system redundancy. Multiple generators, and in some cases RAT (Ram Air Turbines) on top of that. And a certified FBW system is extensively HIRF (High Energy Radiated Fields) tested (perhaps the exception to that is the Sukhoi Superjet which had a mishap due to being hit by a lightning). The basic principle is: simpler systems have less failure modes, and less failure mode combinations. Simple is beautiful.
 

Bill-Higdon

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Feb 6, 2011
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Location
Salem, Oregon, USA
One more comment: fly-by-wire aircraft have electrical system redundancy. Multiple generators, and in some cases RAT (Ram Air Turbines) on top of that. And a certified FBW system is extensively HIRF (High Energy Radiated Fields) tested (perhaps the exception to that is the Sukhoi Superjet which had a mishap due to being hit by a lightning). The basic principle is: simpler systems have less failure modes, and less failure mode combinations. Simple is beautiful.
The early Blackhawk Helicopters were placarded against getting to close to Radio stations as they tended to become a "lawn dart". The Government eventually sorted out the issues but it was "interesting" for some pilots
 

TFF

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Apr 28, 2010
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Memphis, TN
Life long RC airplane builder and flyer. I never had many radio issues, but I witnessed plenty. I would say a my RC has been 95% reliable since the mid late 70s. Ok equipment, never the bottom stuff. A friend just got some low end servos for a robotics project, first 4 had issues. Servos are dime a dozen and it’s getting hard to know who is good or not. There is probably 100 brands now when 4-5 was the old normal. I have many friends with IFR planes. Every one has complained about their autopilot at some point. Doesn’t matter if it’s homebuilt or million dollar plane. Sometimes down right scary things they do. I have two Tundra trucks and my foot can
beat the throttle, sometimes it chooses wrong. Especially if it’s abrupt demand or too soft. Making electronics do it all the time including still working if it gets fried is a long way away, at least for this butt to sit in. There will be plenty of shortcuts with will demand new laws on the subject. Most of those are at wait and see right now.
 
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