Control surfaces actuators design/preferences

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proppastie

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And then there is Dyneema...... very slippery so perhaps no pulleys very light and strong ......sailboat stuff learn knots
Used on Goat
 

Bigshu

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And then there is Dyneema...... very slippery so perhaps no pulleys very light and strong ......sailboat stuff learn knots
Used on Goat
Or get out the fid and learn to splice!
 

rtfm

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In my opinion, it would be very difficult to make a DIY fly-by-wire primary flight control system sufficiently reliable.
Why is an electrically-operated flight control suddenly fly-by-wire? What's the difference between having a couple of servos, a linear actuator or a hydraulic system?

Duncan
 

rtfm

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Don't overlook Teleflex style cables. They DO have some disadvantages, but are simple to design and bend nicely where needed.
Saddler Vampire is one example.
View attachment 111436
Hi,
This is a possibility. The difficulty with mating bellcranks is that (unlike the gliders or the Onex which have space inside the fuselage) it is extremely difficult to activate the inboard bellcrank in my design. Check this out. How/where would you route the pushrods? At least Teleflex cables could be run up inside the masts, through the rib and across to the outer panel.
1623295882664.png
 

Marc Zeitlin

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Why is an electrically-operated flight control suddenly fly-by-wire?
Because that's basically the definition of "fly by wire"?

What's the difference between having a couple of servos, a linear actuator or a hydraulic system?
When hydraulic systems are used to run primary flight controls, or anything that could cause a catastrophic failure (in SSA terms) in a DAL-A system, there will generally be three redundant circuits to operate the system and after the DC-10 (L-1011? Don't remember) crash due to a zonal failure of all three hydraulic systems, they need to be spatially separated and have no cross-talk as well. If you use electrical "fly-by-wire" for primary flight controls, you will also need (to be TC'd in Part 25) three redundant circuits that do not have any cross-talk or exist in the same spatial area.

Now, none of these requirements exist for E-AB aircraft - you can do whatever you want. But there's a reason that the rules exist, and it's not so that companies that make actuators can sell three times as many. There is no world in which I'd get into a homebuilt airplane that had a single string electrically operated primary flight control rather than mechanical flight controls. Do the SSA/Fault Trees for the system and it will immediately become obvious why. To get to the DAL-A level of failure of 10e-9 for catastrophic failures, a triply redundant system has to have each circuit have a minimum failure rate of 10e-3. That's one failure every thousand hours. Are you OK with your primary flight controls failing catastrophically once every 1000 hours? Didn't think so...
 

dog

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Because that's basically the definition of "fly by wire"?

When hydraulic systems are used to run primary flight controls, or anything that could cause a catastrophic failure (in SSA terms) in a DAL-A system, there will generally be three redundant circuits to operate the system and after the DC-10 (L-1011? Don't remember) crash due to a zonal failure of all three hydraulic systems, they need to be spatially separated and have no cross-talk as well. If you use electrical "fly-by-wire" for primary flight controls, you will also need (to be TC'd in Part 25) three redundant circuits that do not have any cross-talk or exist in the same spatial area.

Now, none of these requirements exist for E-AB aircraft - you can do whatever you want. But there's a reason that the rules exist, and it's not so that companies that make actuators can sell three times as many. There is no world in which I'd get into a homebuilt airplane that had a single string electrically operated primary flight control rather than mechanical flight controls. Do the SSA/Fault Trees for the system and it will immediately become obvious why. To get to the DAL-A level of failure of 10e-9 for catastrophic failures, a triply redundant system has to have each circuit have a minimum failure rate of 10e-3. That's one failure every thousand hours. Are you OK with your primary flight controls failing catastrophically once every 1000 hours? Didn't think so...
Do you think that there has been any significant change in the reliability of electronics since the first adoption of FBW ?
It's just that 1000 hrs of run time seems ,hmmmm, very, very, likely, considering that many devices get thrown out or shelved not for failing, but just by being superseded.
Its a question as so many parts of an airplane are becoming electrically dependent that in order to achieve that 10e-3 minimum failure rate
by having triply redundant systems could drive weight and complexity up and start to become self defeating in a HBA.

SO how on earth does a failure rate for any single component get established in the world of HBA? Is it up to builders to make a test circuit ,put it on a wall and have an arduino cycle it for six months continiously?
Or to put my interest another way, anybody got a nicopress for sale real cheap?
 

Vigilant1

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Now, none of these requirements exist for E-AB aircraft - you can do whatever you want.
And yet...
I wonder if the "EXPERIMENTAL" placards on E-AB aircraft should increase in size, number, or prominence based on some sort of point system or FSDO subjective appraisal.
- Wing truss design never static tested?Increase sticker size 15%
- Indeterminate//untriangulated structure in primary load path? Increase sticker size another 20%
- "Novel" primary flight control actuation method? Increase sticker size 20%.
Etc.

An "EXPERIMENTAL" placard that is legible from 200 yards, or too big to fit on the aircraft structure, would serve as a quick heads up to everyone.
 

TFF

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I believe Marc Z has his friends put their butts on the line for the real equipment, and it’s not good enough for his butt yet.

As much as the stuff is cool to talk about, if your butt does not pucker when you think of sitting in something extremely different, you are not understanding the ramifications. Anyone have a runway trim or wonky autopilot will know the expensive stuff does not work everyday.

Arduino test running stuff is a good idea. Last weekend a good friend called me up to barrow a servo. I had just packed and shipped it all for a move and could not oblige. He and his “crew” had either wired the Arduino up wrong, bad programming, or had some major servo mortality. Running servos with a computer have been around since Apple II and Trash 80s were new; nothing new under the sun. From flying RC from then to now, stuff was made better then.

A side note. Although it is Experimental, you still have to convince your government that it’s safe. Not for your butt, but to keep you and your plane from raining down on the kingdom. Not saying they won’t sign it off, but the restrictions might be hefty enough that it would not be useful. It is their sandbox that we play in; they are in charge.
 

BJC

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While I
And yet...
I wonder if the "EXPERIMENTAL" placards on E-AB aircraft should increase in size, number, or prominence based on some sort of point system or FSDO subjective appraisal.
- Wing truss design never static tested?Increase sticker size 15%
- Indeterminate//untriangulated structure in primary load path? Increase sticker size another 20%
- "Novel" primary flight control actuation method? Increase sticker size 20%.
Etc.

An "EXPERIMENTAL" placard that is legible from 200 yards, or too big to fit on the aircraft structure, would serve as a quick heads up to everyone.
Although I appreciate your sentiment, I never would support giving the FAA / FSDO or any other imperial government bureaucracy any more subjective authority than they already have.


BJC
 

Vigilant1

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While I
Although I appreciate your sentiment, I never would support giving the FAA / FSDO or any other imperial government bureaucracy any more subjective authority than they already have.


BJC
Agreed. I guess my "compulsory klaxon to accompany engine start" idea isn't great, either. :)
 

Jay Kempf

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Is it true that electrically actuated and FBW are the same thing? If no computer is involved is it still fly by wire?

This definition from Wikipedia: "The movements of flight controls are converted to electronic signals transmitted by wires, and flight control computers determine how to move the actuators at each control surface to provide the ordered response" implies that controls are driven by output from some sort of flight control computer.

A straight analog input that feeds output system is a simplification of that definition. So is a simple electric trim system FBW? Been noodling on an entire secondary flight control system that is just servos and trim tabs. Basically designed for only a fraction of the pitch, yaw, roll rates that the primary controls can create. Only reason is to be able to drive an autopilot.
 

Marc Zeitlin

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Is it true that electrically actuated and FBW are the same thing? If no computer is involved is it still fly by wire?
You're correct - my definition was too expansive. Electrical actuation is a necessary but not sufficient component of FBW. But that doesn't change the rest of my commentary regarding primary flight control safety.

For secondary flight controls (trim, etc.) _IF_ there is no catastrophic or hazardous failure mode (per the SSA definitions) and only Major failure modes, then electrical actuation without redundancy may be fine, if the failure RATE is low enough.
 

Pops

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Is it true that electrically actuated and FBW are the same thing? If no computer is involved is it still fly by wire?

This definition from Wikipedia: "The movements of flight controls are converted to electronic signals transmitted by wires, and flight control computers determine how to move the actuators at each control surface to provide the ordered response" implies that controls are driven by output from some sort of flight control computer.

A straight analog input that feeds output system is a simplification of that definition. So is a simple electric trim system FBW? Been noodling on an entire secondary flight control system that is just servos and trim tabs. Basically designed for only a fraction of the pitch, yaw, roll rates that the primary controls can create. Only reason is to be able to drive an autopilot.
Installed my homemade autopilot in about 2012 and flew with it for 2 years in the SSSC. Autopilot controlled trim tabs on aileron and elevator with electric trim position for each and switch for standard rate turns. Held altitude within 25'. Just wing leveler, not coupled to any heading input.
 

Bigshu

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Or to put my intetest another way,anybody got
a nicopress for sale real cheap?

I don't know where you live, but if you're in/near an EAA chapter, there might be a builder or chapter nicopress tool to borrow. Not to mention, the cost of a used one might not be bad, and if you bought a new one, used it on your project, then sold it, you'd only have paid the difference between new and used. Maybe there's a tool rental place you could use? Lots of ways to skin the tool cat.
 

wsimpso1

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Why is an electrically-operated flight control suddenly fly-by-wire? What's the difference between having a couple of servos, a linear actuator or a hydraulic system?
  • The standard way is we have a rock simple very robust mechanical linkage;
  • Then airplanes got bigger and/or faster, so we started boosting these controls with hydraulics. The mechanical linkage was still there, so when a cylinder leaked or the valves stuck, or... the flight crew could still just apply muscle and get the surfaces to move enough to safely end the flight;
  • Eventually forces got big enough and the manual linkage was done away with, but now you need redundant circuits, valves, pumps, actuators within actuators, ways of automatically dealing with failed circuits, blah, blah, blah;
  • That set of hydraulics could be replaced with electric actuators, and again, redundant circuits, sensors, amplifiers, ways of automatically dealing with failed circuits, etc;
  • From there, it is a short trip to having an autopilot fly the airplane and the pilot just tells the autopilot what is wanted with voltages off the stick and rudder pedals, and the autopilot keeps the pilot out of trouble by limiting pitch and yaw angles, not allowing flight above Vne, avoiding stall, etc.
The first one you rely on robustness and sometimes multiple cable runs. The second one relied on the mechanical linkage as backup. After that everything needs ways of working fine even when stuff breaks - failure mode management becomes much more complicated. The simple way is the hydraulics or electrics just do what the stick and pedals do, but you need sensors and logic to check that you are getting what you command, notify you of faults, and compensate for any part of the system that is out... The full authority stuff needs all that stuff on the output end, but it also has all sorts of processing on the input end too - your inputs are from strain gages.

Let's imagine we do not have all that stuff, just a single servo attached to each surface like in many RC. Now imagine a servo goes hard over to one end of travel (for any number of reasons) - with no redundancy, well, it will be a bad day. If it is roll axis hard over, even a ballistic parachute might not save you. The system must have multiple ways of operating safely despite any failure occurring in the system.

How do we get away with single thread systems in RC's? Mostly because they are not rated for carrying humans...

Billski
 

Aesquire

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Re: Dyneema cables.

Recently rediscovered kites, hobby and bigger, after not paying attention. :)

The parafoil & other types used in kitesurfing, paragliders, etc. Often use Dyneema lines. SOP seems to be the line ends sewn to loops, and Lark's Head knots used to join. Nifty stuff.

Do some research for stretch & fatigue before buying, Line stretch is a maintenance/tuning factor that's critical to safety. Some manufacturers brag on their lines.

Also consider sheathed lines for UV resistance and safety.

Re: my preference for control actuation

I've been catching up on paragliders tech & technique. Impressive. Ditto Paramotors. I'm soooo tempted by a light trike paramotor, throw in hatchback, fly. Almost anywhere, with the flexibility of legs as landing gear, hence trike with my plastic knees.

But I keep remembering why I tried, then forgot, paragliders. I just didn't like the pendulum swings and canopy collapses. That's amazingly improved, today, but still an issue for me.

OTOH, I'm quite comfortable with weight shift control with a hang glider, and understand the limitations.

This internal struggle/revelation came to a head when I saw a video of a Brit flyer comparing his paramotor & sub70 trike. He said he prefers to fly the trike in calm morning air, and the paramotor when it got active.

The exact opposite of my preference. So it's really down to what you like.
 

Dan Thomas

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Every so often these electric or hydraulic system ideas comes up. For any homebuilt, they are solutions in search of a problem. In any homebuilt they will add nothing but weight, complexity, cost, and failure points. I just don't see any advantages over cables or pushrods at all. Just because the technology is available doesn't make it smart to incorporate it.

Systems like that are used in transport-category aircraft, where control loads are high. I worked for awhile on Lockheed Electra fire bombers, old airliners from the late 1950s. They had control cables that ran from the cockpit back to the wing and tail, and there were hydraulic boosters for the ailerons, rudder and elevator. The airplane had three hydraulic systems, and the control system ran off two of them. There were two-section hydraulic double-acting cylinders for each control, and if one hydraulic system failed the other would continue boosting. If both failed, the pilots pulled emergency handles that pulled cables that ran back to each actuator and changed the control ratios so that the pilots could manually move the controls but the travels were cut in half. There were drawbacks, not least the changing cable tensions with temperature and fuselage flexing. The system was necessary, though, for a large, fast airplane to be controllable without fatiguing the pilots.

But for a homebuilt??? Why would one incorporate a complicated system that costs money, takes up space and adds weight and chances of failure, in place of light, cheap cables that never fail if they've been properly assembled and are inspected occasionally? The only reason I can think of is snob value. Owning a fly-by-wire airplane.
 

gtae07

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Electrical actuation is a necessary but not sufficient component of FBW
Minor little nit... fly-by-wire as implemented today almost never uses electrical actuation. Almost every FBW aircraft still uses hydraulics to provide the "muscle" for actuation; FBW replaces mechanical linkages at the servovalves. So, you have a hydraulic cylinder pushing the surfaces around, supplied by a normal hydraulic system, with the valve being computer-controlled. Some aircraft have a setup where the actuator has its own little hydraulic system complete with a little electrically-driven pump; the A380 and the FBW Gulfstreams (and possibly more, I don't know for sure) use a setup like this as a backup to actuators powered off the main hydraulic system, and I think the F-35 may use it as a primary system for some/all surfaces.

I've seen electrically-driven actuators for slow-moving things like flaps and movable stabilizers (for trim), and apparently the 787 has a couple electrically-actuated spoilers. But I don't know of anyone (yet) who is using electric actuation for ailerons, rudder, or elevator.

I guess if you want to get picky, the insides of the servovalves are electrically-actuated... ;)
 
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