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Guest CRJ700FO

Control surface mechanic questoin.

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Small planes' control surface are usually controled via cables. At what stages in size/weight do they switch to electrical/hydrolic? What do aircrafts like the size of Baron 58 use? Thnx

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Thnx for the info. I actually interested to find out what aircrafts (in size) are using cable mechanic to control the surfaces and what arcrafts are using hydrolics.

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>What do aircrafts like the size of Baron>58 use? ThnxOh, no. Even much larger King Air still has purely mechanical connections to control surfaces. 27,500 lbs Hawker Horizon business jet is all-hydraulics however. I suspect that you must be approaching around 10 tons takeoff weight to have hydraulics control but I can't give you precise figure.Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

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Are you sure? This sounds scary. I though they are at least electrically controlled if not fly-by-wire.

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>Are you sure? This sounds scary. I though they are at least>electrically controlled if not fly-by-wire.I am sure, no nothing scary about it. Mechanical connections are probably more reliable so what's scary?. Forget about fly-by-wire - this you will only find on the most expensive jetliners.Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

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Or you could do it the right way like Mooney and have rods. No chafing involved there. You ought to see the elevator control rod coming out of the tail cone...thing is HUGE.Edit #1Also, remember that aircraft have trim tabs, which 99% of the time make a huge difference, especially in the rudder department. Take a twin engine airplane (your Baron for example) and fail one engine. You'll temporarily give your leg a workout, but once you get it trimmed out to the side of the operative engine, you still have enough umph left to kick it into a shallow turn toward the operative engine, without exceeding the limits specified by 23.143. That is the reason why there are 2 sections to that chart...temporary and prolonged application.Can't meet the limits for prolonged application simply using a bigger rudder? Stick a trim tab on there and you probably can.Edit #2BOPrey, you can take a stab at looking up Type Certificate Data Sheets (TCDS) for specific aircraft. It's just a guess, but you might be able to find the answers to whether the aircraft is designed with mechanical, hydraulic, or FBW control systems. Someone correct me if I'm leading him in the wrong direction. These TCDS are the way an aircraft has to be built in order to be airworthy in the eyes of the FAA.

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The simple answer is that there is no magic size/weight figure at which powered flight controls takes over from manual controls. At high speed, compressibility effects pretty much dictate that powered control surfaces must be used.

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Sure. I think rods are more reliable than cables, and requires no maintaince too.

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>Sure. I think rods are more reliable than cables, and>requires no maintaince too.Push/pull tubes with smooth acting rod end bearings on each end, are less maintenance, and usually tighter tolerences. My kitbuilt uses push/pull tubes connected to a stick for ailerons and elevator, and cables for the rudder. I'd rather have this setup than a yoke, chains wrapped around sprockets, and cables looped arounnd pully's, anyday!L.Adamson

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Why the fixation on size? - size is not the only criteria.costweightcomplexity/redundancyaerodynamic loadingcompressibility effectsreliabilityBoeing 707 big and manual. (forget rudder boost - it's optional anyway.)Boeing 737 small (relatively) and hydraulically powered.The beauty (??) of Fly-by-wire is that it facilitates integration of the flight controls with other computerised systems (AP,FMC,.. etc)

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Good to know about this. Another question. How are the trim wheels connected? Thnx.

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I thought the small the plane, the easier to control. As a lot of people here pointed out, that is indeed not a deciding factor. By this day and age, I also thought things like those would've be control digitally. Look how wrong I was.

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>factor. By this day and age, I also thought things like those>would've be control digitally. Look how wrong I was.Yes, indeed. The digital steering of control surfaces that could withstand all the rigor of FAA certification and had all the necessary backups would probably cost many times more than the whole plane. Certainly not something you would put in an aircraft with less than say $50 mln price tag. It can of course change in the future.Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

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Just to clarify, hydraulic boost is not the same as fly-by-wire. As I recall, not even 757/767 is truly fly-by-wire. In the 757/67, moving the yoke or rudder pedals a certain distance will move the corresponding control surface a proportional distance, whether you're parked at the gate or going Mach .8 at FL 350. With fly-by-wire, which first appeared in the 777 for Boeing, the flight control computer decides how much to move the control surface, based on the current flight regime.

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When we were researching the ATR 72, that we built for Flight One, we visited the factory in Toulouse, France, and toured an aircraft that was being assembled in the very same facility that the first Caravelle jet was built decades before.The cabin was still "bare bones", and I'll never forget seeing those control cables going back from the cockpit, turning around pulleys, and going out to the wings.Also happy to see mention of the 707. Rudder boost was all it had, everything else was manual.I flew a 707 sim at Lufthansa 4 years ago. It was a pleasure to hand fly, even on an ILS to minimums. :-)Regards,http://www.dreamfleet2000.com/gfx/images/F...R_FORUM_LOU.jpg

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Even when the controls are hydraulically powered there will still be mechanical (cable or rod) connections from the pilot's controls in the cockpit to to the hydraulic jacks which are generally located close to the control surfaces.

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Power assisted controls? That sounds much better. I can imagine that rod (cable) running the full length of the entire ATR72 body. BTW, I bought the F1 ATR72, excellent plane and every thing works.

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>Even when the controls are hydraulically powered there will>still be mechanical (cable or rod) connections from the>pilot's controls in the cockpit to to the hydraulic jacks>which are generally located close to the control surfaces.thats what it is in the canadair regional jet.the yokes are independently controlled (ie the right yoke controls the right elevator and right aileron and vice versa). two torque tubes interconnect the yokes so they move in tandem on both axis.cables run from the yoke to the elevators and airlerons (run through fancy systems of anti-jam mechanisms, etc). from there they connect to a hydraulic PCU (primary control unit if memory serves me correct). it is this PCU that moves the flight control surface.in addition the ailerons are assisted by flight spoilers (a set, x2, on each wing plus 2 ground spoilers for a total of 8 spoilers).each control surface is affected by 3 PCU's, each tied to its appropriate hydraulic system (1 routed through the #1 engine, 2 routed through the #2 engine, 3 is an independent system used primarily for the landing gear). this way each control surface has triple redundancy for any failures (engine loss, hydraulic leak, PCU runaway, etc).typically on a hydraulic flight control system there are no trim "tabs". trimming simply moves the entire control surface. usually the elevator is not moved, but rather the entire stabilator (hence the term stab trim) is moved. in the crj the aileron "trim" simply moves the yoke in the desired direction (ie it "resets" the yoke neutral position).hope this helps.

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