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Hans S

Fly by wire?

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Anyone tried it in one of the variety of homebuilts?

If they have, they won't be replying here, because they'd be dead.

 

Do you have any idea how much more reliable a mechanical linkage is over jury rigged (which is what you'd get in a homebuilt - witness the difficulty that BMA has in getting their equipment to be reliable, and all they're doing is MEASURING stuff - they're not CONTROLLING anything, least of all primary control surfaces) electro-mechanical or electro-hydraulic linkages? There's a reason that the only aircraft that use multiple redundant computer controlled fly-by-wire systems which are tested for hundreds of thousands if not millions of hours are the military ones and the big commercial jets. Unless you need a boosted control system, which you don't in small GA aircraft, there's no advantage to the FBW.

 

If the only thing controlling the pitch, roll, and yaw of my aircraft were the knobs on my autopilot, which is essentially what you're proposing, I wouldn't get anywhere near the thing.

 

Not to mention that you'd have an extremely hard time making a redundant, reliable, FBW system lighter than a couple of aluminum tubes and some SS cable.

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Thanks Marc, but, I didn't mention at all that I wanted to do it. I already know I have nowhere near the knowledge base for the electronics. I was just wondering about it and if there were tinkerers out there working on stuff like this, hence the Design & Modification Forum.

 

So what are the stats on the reliability between mech and wire? Any real hard numbers? Military and commercial jets are pretty reliable.

 

If they have, they won't be replying here, because they'd be dead.

That's quite a big assumption. More than likely they wouldn't post because of the backlash of not building to plans.

 

Just because old technology works, does not mean it is the best or only way.

 

Predators and other UAVs of that size are fly by wire!

 

 

And there is a lighter system that I'll be using, tho it isn't FBW. To me it is simpler, lighter, better routing, and more reliable. In a few years when I'm done building I'll post the results.

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So what are the stats on the reliability between mech and wire? Any real hard numbers? Military and commercial jets are pretty reliable.

Yep. That's what billions of $$ and many years of development will get you.

 

That's quite a big assumption. More than likely they wouldn't post because of the backlash of not building to plans.

Yes, they're hiding out with they guys with the 200 mph carburetors. No publicity at OSH or any other fly-in, no web postings, no nothing - just flying their safe aircraft privately, without telling anyone else what they're doing :-).

 

Just because old technology works, does not mean it is the best or only way.

True. But there's a reason "tried and true" is usually the best solution. Not always - of course - or else there'd be no progress, but sometimes, new stuff ISN'T better, depending upon the situation. As I said, for the heavy iron, FBW is great. For small GA, it's the wrong thing.

 

Predators and other UAVs of that size are fly by wire!

All remote control aircraft are FBW, by definition - the controls that the pilot moves are linked electromechanically with the flying surfaces. They also have no people in them, and have poor failure rates.

 

And there is a lighter system that I'll be using, tho it isn't FBW. To me it is simpler, lighter, better routing, and more reliable. In a few years when I'm done building I'll post the results.

Waiting with bated breath...

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The last numbers I saw say preds have a incident rate of 8.7 per 100,000hrs. That's really worse than any of the homebuilts? It's better than an F-16 at 10.2 per 100,000hrs. And the propulsion system was the biggest problem, turbo rotax 914.

 

I'll get you a mint after years of bated breath;)

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ya, what marc said...

 

 

I do seem to recall that a Berkut was turned into a UAV. So I guess it has been done. I think there's videro floating around of it landing or something.


Drew Chaplin (aka the Foam Whisperer)

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www.Cozy1200.com - I'm a builder now! :cool:

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Brace for impact...

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yI do seem to recall that a Berkut was turned into a UAV. So I guess it has been done.

You're talking about the "Mobius. Nope. That's not FBW - more like an autonomous and/or remote autopilot. That just had a computer running servos driving something akin to the the standard Berkut control system. The standard control system with mechanical linkages is still there, and is usable by the human pilot when the plane is flown manned (and the computers either turned off or disabled).

 

FBW means that there's no mechanical/hydraulic linkage between the human powered controls and the primary flight control surfaces - only electrical signals to a servo.

 

It makes no sense to talk about UAV's or autonomous vehicles as being FBW, as if there were another choice - since there's no human in the airplane, there can be only electrical signals (wires or wireless) between the human on the ground or the computer on the ground or in the plane to the servo mechanism.

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Stick this guy in the right seat. Might still need some ballast...

 

Posted Image

 

Can't think why somebody would try FBW in a homebuilt, and expect it would end in tears.

 

Read on another forum, what does an inexperienced Airbus pilot say?

 

"What the f&*^ is this aircraft doing!"

 

And what does an experienced Airbus pilot say?

 

"Its doing it again!!!"


Mark Spedding - Spodman
Darraweit Guim - Australia
Cozy IV #1331 -  Chapter 09
www.mykitlog.com/Spodman
www.sites.google.com/site/thespodplane/the-spodplane

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If you are thinking about FBW, you first have to think of what problem you are trying to solve. Is the EZ mech system too complex, too heavy, too hard to actuate, etc? I contend that there is nothing to be solved.

 

In your heavy commercial and military aircraft, the pilot does not even have the control power to move the surfaces himself. In the old days (and now) they needed hyd powered controls like on your car. One of the problems in going to hyd power was that now the pilot had no feedback in the stick. That problem was solved with some complex bob-weights (and on the F-4, they had some sort of bellows something or other on the tail which somehow fed into the flight control system to give some sort of speed feedback----kind of outside my expertise---I only have 10 or so hours in the Phantom's trunk).

 

Later on, they were able to greatly lighten up the hyd system by removing most of the lines and replace with wire. Still hyd actuators---but electrical power going to the actuator. And with electrical power, you could feed the control inputs through a computer---and hopefully remove some undesireable flight characteristics.

 

The point is that FBW came about to solve some real problematic issues----and in the process introduced new problems that had to be overcome.

 

So before you start----what problem are you trying to solve?

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If you are thinking about FBW, you first have to think of what problem you are trying to solve...So before you start----what problem are you trying to solve?

Bingo. And Bingo again, to get more than 10 characters so that the forum software will accept the posting.

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They are using FBW for the throttle bodies of some RV-10's and I saw Tracy had one of these on his three rotor engine on his RV-10.

This was a simple solution to hooking up the throttle but I do not like the idea of yet another wire(s) that could break making the throttle stick or go to one extreem or the other.

The reason we picked the Cozy was no cables in the control system, ok the rudders but this is not so much a stick and rudder plane as some and even then there's a 50/50 chance since we have two rudder cables. Otherwise the controls are something you can have complete confidence in; bearings, tubes and pushrods.


CG Products

www.CozyGirrrl.com

Cozy Mk-IV RG 13B Turbo

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I agree with the statements made here, FBW for the experimental crowd is probably a recipe for disaster and unwarranted.

 

However I can see some positives, so I'll play the devils advocate and speculate some things that would be brought to realization by a FBW system.

 

Stability Augmentation: You could add a FBW system to an aircraft designed to be INHERENTLY UNSTABLE. This type of design has benefits of lower drag and greater maneuverability.

 

My friend designed the autopilot system for the Rutan Voyager, he said that aircraft would go unstable in a few seconds without pilot input. So you can do the same with any autopilot with mechanical linkage. However, FBW is even faster in responding than mechanical linkage, with ability to respond to perturbances on the order of 1/1000's of a second, versus the ~1.6 second response time of a quick pilot. You don't have any delay caused by torsion, stretching or bending of the linkages, or the connection between the linkage components, or hingemoment effects.

 

The other possibility I can imagine is the ability to add intelligence to the FBW system, to not allow the pilot to perform certain attidues and rule out a pilot input. While this could prevent CFIT or malicious intentions from being carried out, it is not a quality I would want in my aircraft.

 

Lastly, with feedback, you could program in the feel of your aircraft. You could basically load the flying qualities you want for that flight and either go up in an F-16 or cruise around like a cessna 172.

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So what are the stats on the reliability between mech and wire? Any real hard numbers? Military and commercial jets are pretty reliable.

 

Google the Cooper Harper scale. This is what is used to measure flying qualities level on various aircraft systems, at least it was when I learned aerospace engineering. Actually this is not what I was looking for to address the question.

 

Along with the scale flowchart I found on wikipedia, there is also a log plot of the system failure probability vs probability of catastrophic failure due to system failure (or severity of system failure affecting ability to complete mission), which is used to determine redundancy levels of systems. If anyone could help me out with the name of this or a link online I'd appreciate it, or I'll look it up in my Roskam when I get home from work today.

 

I can't remeber the name of this plot or the design tolerance for catastrophic failure but I think the allowable probability of catastrophic failure is 1 in 10 million or 1 in a million. This is one of the "secrets" of aircraft design that maybe you don;t want to know as a commercial airline passenger. I believe most commercial and military jets have triple or quadrulpe redundancy of the electronic FBW controls.

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Google the Cooper Harper scale.

The CH scale says nothing about reliability - just flying qualities (and it's pretty subjective, although widely accepted and used, so there's certainly much commonality of judgement). See:

 

http://en.wikipedia.org/wiki/Cooper-Harper_rating_scale

 

IMO, the COZY would be a "3".

 

... but I think the allowable probability of catastrophic failure is 1 in 10 million or 1 in a million....

Commercial airliners are designed to catastrophic system failure rates of 1/10^9. This means that any particular system is allowed to fail catastrophically no more than 1 in 1 billion hours or operation. Catastrophic means an expectation of loss of life (1 or more) or loss of airframe.

 

Commuter airliners are allowed a higher failure rate, as are business jets and GA aircraft. See AC23.1309 for the definitions of Class I, II, III, and IV aircraft, as well as the allowable failure rates for each class of failure (Minor, Major, Hazardous, Catastrophic). Part 25 aircraft have the same allowable failure rates as Part 23, Class IV.

 

Interestingly enough, structures (and that includes any mechanical operating parts, such as mechanical landing gear parts and mechanical flight controls) are NOT included in the systems analysis - the assumption is that mechanical systems are protected by the design margins and safety factors used.

 

Having spent the time period from December through April of this year performing the FMEA/FTA (Failure Modes Effects Analysis/Fault Tree Analysis) on the WK2 aircraft and all of it's electrical, hydraulic, pneumatic, avionics, etc. systems, I'm intimately aware with the failure analysis methodology :-).

 

For those considering FBW, consider that the WK2 is a completely mechanical flight control systems aircraft - it's not even boosted.

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Thanks Marc, I figured that would be something you'd know. It's been 10 years since I dealt with this, my memory on the subject is rusty.

 

Now that you mention it, I remember 1x10^9, that was something we were repeatedy instructed to memorize. That's why I'm not an aerospace engineer.

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This just calls up a vision of a group of Crash Test Dummies brainstorming (?) about a new gizmo for their plane....

 

Hey Mikey, go test fly our new Fly By Wire controls and let us know if you survive, OK?


CG Products

www.CozyGirrrl.com

Cozy Mk-IV RG 13B Turbo

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I've been testing/troubleshooting FBW controllers in automotive engine control modules for about 10 years now.

 

I could probably design, build, and write the software to control one for the Cozy. But I'd never go up with it.

 

The risk is too high. The most likely outcome of a failure is death.

 

The benefits are not worth it. What were the benefits again?


Mike LaFLeur - Cozy MkIV #1155
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The benefits are not worth it. What were the benefits again?

Well, according to post #3, Hans is going to do it, so in a few years he will let us know.:cool2:


Self confessed Wingnut.

Now think about it...wouldn't you rather LIVE your life, rather than watch someone else's, on Reality T.V.?

Get up off that couch!!! =)

 

Progress; Fuselage on all three, with outside and inside nearly complete. 8 inch extended nose. FHC done. Canard finished. ERacer wings done with blended winglets. IO540 starting rebuild. Mounting Spar. Starting strake ribs.

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Well, according to post #3, Hans is going to do it, so in a few years he will let us know.

No I'm not. I am not going with the stock set up, that is true. But I'm not using a FBW. I was just wondering if anyone had done it.

 

Try reading the first two sentences of post #3

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No I'm not. I am not going with the stock set up, that is true. But I'm not using a FBW. I was just wondering if anyone had done it.

 

Try reading the first two sentences of post #3

Try not to bristle. According to your post, there is a problem with a part of the plane that needs attention...albeit a VERY robust part of the plane, that has not contributed to concerns over the years.Then you treat us to a mindset that "tinkerers" are capable of concocting a FBW system in their garages. YOU used the word tinker, not me. Then you finish off with a revelation that you are going to hybrid something together that..well, fill in the blank for us...inquiring minds want to know!!! Youve got some ace up your sleeve. Put it on the table and lets have a look at it!

Self confessed Wingnut.

Now think about it...wouldn't you rather LIVE your life, rather than watch someone else's, on Reality T.V.?

Get up off that couch!!! =)

 

Progress; Fuselage on all three, with outside and inside nearly complete. 8 inch extended nose. FHC done. Canard finished. ERacer wings done with blended winglets. IO540 starting rebuild. Mounting Spar. Starting strake ribs.

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Sorry, I wasn't trying to be bristly (sp). Didn't sound that way when I wrote it, but re-reading it does sound that way.

 

I don't think there is anything wrong with the stock set-up, as you said, it has worked for years, I just want to try something different, but I need to do a bench test first. Someone emailed me and told me all the control hardware up to the point where it attaches to the control surface weighs roughly twenty five pounds. tubes, bearings, cables, pulleys, etc.

 

There's lots of tinkerers, Long-ez strakes on a Cozy, forward hing canopy, air conditioning, retractable gear, not to mention the vast amount of unstock engine configurations.

 

There's a whole EFI group out there building fuel injections for everything, hit and miss til it works. I'm not one of those, but I find the idea interesting. I like to learn things even if I don't plan on using them.

 

FBW sounds neat and was wondering if some NASA escapee was in some back yard shed messing around with old UAV guidance systems, that is also why I didn't restrict it, but just said homebuilts. Not that I have the technical know how or ambition to blaze the trail in this area.

 

Some of the "thinking out of the box" makes me go Hmmm.

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I have sort of been following along the NASA Active Aeroelastic Wing project lateley. I think an aeroelastic wing with FBW FCS would be a really cool project. This discussion got me thinking about it and designing an inherently unstable aircraft. Or using FBL and designing around that concept. I was just pondering this when I realized the Wright brothers had this figured out.

 

I sort of remember something about Bodie Diaphrams and root locust plops. :cool:

 

but I guess Mr. Bode and the MEMS came along later.

 

But seriously that's not gonna happen until a long time ago in a galaxy far far away.

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My friend designed the autopilot system for the Rutan Voyager, he said that aircraft would go unstable in a few seconds without pilot input. So you can do the same with any autopilot with mechanical linkage.

The way I read the story of the flight Voyager was only unstable (as in dynamically unstable - I think I've got that right) for the record flight when it took off at the highest weight it ever flew at. Dick HAND FLEW it when this was the case, wouldn't let Jeanna have a go, let alone your mate's autopilot.

Mark Spedding - Spodman
Darraweit Guim - Australia
Cozy IV #1331 -  Chapter 09
www.mykitlog.com/Spodman
www.sites.google.com/site/thespodplane/the-spodplane

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