Ian Posted March 22, 2015 Report Share Posted March 22, 2015 Looks like this topic could run & run!! Link to comment Share on other sites More sharing options...
Anticept Posted March 22, 2015 Report Share Posted March 22, 2015 Thought experiment... Which needs more nose down trim: a CT flying into a 50kt headwind, or one flying with a 50kt tailwind? Which would be louder in the cockpit? Which would run cooler? If the answers to any of those are not obvious, I would again recommend a read - or reread - of Stick and Rudder. Assuming all other factors the same (specifically, power settings), the answer is neither! It helps to stop thinking of air movement as "wind" and instead just think of the earth spinning below you in the opposite direction of the wind. For most stuff in flight, this simplification works very very well, because, to the airplane, the air isn't moving. Link to comment Share on other sites More sharing options...
FastEddieB Posted March 22, 2015 Author Report Share Posted March 22, 2015 50kt headwind for the first and second questions. Need more information for the third but likely a 50kt tailwind. Obvious really. I always tend to fly a lower airspeed when i have a good tail wind for fuel economy. There's a Latin term: Ceteris Paribus. It means, roughly, "all things being equal". I did not think to mention that my thought experiment had "at the same power setting" as implied. But I did, and Coery, at least, picked up on that. If you were assuming you would use a higher power setting into the wind, and lower with the tailwind, then your answers have some validity. And can serve as a springboard for a discussion of why it makes sense to fly faster into a headwind and slower with a tailwind. But now, how about my thought experiment with the same power setting? Link to comment Share on other sites More sharing options...
Jim Meade Posted March 22, 2015 Report Share Posted March 22, 2015 Ed, I'm shocked, shocked! that you did not use the treadmill analogy. If one plane is on a treadmill going 50 mph forwards and another on one going 50 mph backward, which.........., oh, OK, excsue me, I'm going flying. I'll let you know if I find any wind up there. BTW, I did find myself flying at 167 kgs the other day. I suppose I should have slowed down, but in a frenzy, I slightly declined the nose and found myself at 175 kgs. Drat!, I always get it wrong. Toodle-oo. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted March 22, 2015 Report Share Posted March 22, 2015 I did find myself flying at 167 kgs the other day. I suppose I should have slowed down, but in a frenzy, I slightly declined the nose and found myself at 175 kgs. Drat!, I always get it wrong. Toodle-oo. 175 kilograms? now that's smokin Link to comment Share on other sites More sharing options...
Tom Baker Posted March 22, 2015 Report Share Posted March 22, 2015 The autopilot in the FD CTLSi centers the ball. The plane is not trimmed before it's activated. The rudder and aileron trim wheels are left in neutral at all times. The elevator trim is randomly set before setting the autopilot. The Dynon Skyview autopilot immediately begins to fly the plane in a coordinated fashion when it's activated regardless of where the elevator trim is at the time it's turned on. I report this from experience using the device almost daily. Maybe others who own a CTLSi with Dynon Skyview and the Dynon autopilot can offer what their experience is, anyone? I don't have a CFI. I am a license private pilot. Like I said try this little experiment and then report back on how well the autopilot centers the ball. Maybe you will learn something. "The autopilot does nothing to keep the ball centered. Having the airplane trimmed before you turn on the autopilot will help to keep the ball centered. If you want proof of this go flying and trim the rudder until the ball is not centered and turn on the autopilot and see what happens." Link to comment Share on other sites More sharing options...
Jim Meade Posted March 22, 2015 Report Share Posted March 22, 2015 175 kilograms? now that's smokin Ah, hoist on my own petard. I didn't know how to abbreviate knots ground speed. Link to comment Share on other sites More sharing options...
FastEddieB Posted March 22, 2015 Author Report Share Posted March 22, 2015 How about this... Headwinds and tailwinds effectively cancel each other out on a round trip with a constant wind. True or false? Link to comment Share on other sites More sharing options...
sandpiper Posted March 22, 2015 Report Share Posted March 22, 2015 False. But, then, I always have a headwind! Link to comment Share on other sites More sharing options...
FastEddieB Posted March 22, 2015 Author Report Share Posted March 22, 2015 Devil's Advocate: But if I have a TAS of 100k and a 10k wind... I'll fly over at 90k if its a headwind going out. But I'll fly back at 110k. Should cancel out and result in the same time as a no-wind flight, no? Link to comment Share on other sites More sharing options...
WmInce Posted March 22, 2015 Report Share Posted March 22, 2015 How about this... Headwinds and tailwinds effectively cancel each other out on a round trip with a constant wind. True or false? False. For those that doubt this, do an experiment with your E6-B to find out. Link to comment Share on other sites More sharing options...
sandpiper Posted March 22, 2015 Report Share Posted March 22, 2015 100 mph airplane. 50 mph wind constant in direction and force. Fly 1 hour directly downwind and go 150 miles. It would take you 3 hours to get back. So, no. Link to comment Share on other sites More sharing options...
sandpiper Posted March 22, 2015 Report Share Posted March 22, 2015 You should qualify your puzzles by limiting responses only to those who know it all. Link to comment Share on other sites More sharing options...
Ian Posted March 22, 2015 Report Share Posted March 22, 2015 A way to convince yourself of the truth of the answer is to consider the limiting condition where the wind is equal to the IAS of the aircraft. In that case, the tailwind means that you halve the time over nil wind conditions, but the headwind means you will never complete the journey! Of course in Bloggs Wonderplane with magic dust for fuel and an autopilot with a brain the size of a planet other realities may prevail Link to comment Share on other sites More sharing options...
FastEddieB Posted March 22, 2015 Author Report Share Posted March 22, 2015 Good responses, guys! At first it seems non-intuitive. The key I think is that while you spend equal distances at each speed, you spend more time at the slower speed*. I take sandpiper's reductio ad absurdum one step farther and step it up to 100k wind. Sure, if you have a tailwind you'll get there fast. But turn around and, alas, you'll never get back! edited to add: I just notice Ian scooped me. Darn! Oh, well, great minds and all that. *Anyone who's ridden a bike in hilly terrain sees this effect as well. Half your distance is uphill, half is downhill. But you spend excruciatingly more time slogging up the hills, only to come screaming down the other side for a depressingly short time. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted March 22, 2015 Report Share Posted March 22, 2015 A way to convince yourself of the truth of the answer is to consider the limiting condition where the wind is equal to the IAS of the aircraft. In that case, the tailwind means that you halve the time over nil wind conditions, but the headwind means you will never complete the journey! Of course in Bloggs Wonderplane with magic dust for fuel and an autopilot with a brain the size of a planet other realities may prevail Gotcha Ian, you mean to say where wind is equal to TAS of the aircraft Link to comment Share on other sites More sharing options...
Ian Posted March 22, 2015 Report Share Posted March 22, 2015 Ah CT you spotted my deliberate mistake I plead slight insobriety as I've just got back from a Sunday lunch in the pub where beer was imbibed! Link to comment Share on other sites More sharing options...
FastEddieB Posted March 22, 2015 Author Report Share Posted March 22, 2015 I plead slight insobriety as I've just got back from a Sunday lunch in the pub where beer was imbibed! So, how was the flight? Link to comment Share on other sites More sharing options...
Ian Posted March 22, 2015 Report Share Posted March 22, 2015 So, how was the flight? Pretty sure I must have been on autopilot as I reckon the ball was in the middle all the way!! Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted March 22, 2015 Report Share Posted March 22, 2015 I only read S&R once long ago but I remember learning about 'gates' and in my CT each gate change calls for rudder trim change. If you feel your rudder is always in the correct position you are not paying attention. Some things I trim rudder for: climb to pattern level in pattern approach from abeam numbers initial climb cruise climb cruise cruise descent 500 fpm descent throttle setting changes My CT is pretty happy skidding and slipping around but I'm only happy if I keep my ball mostly dead center and it results in even fuel usage. Link to comment Share on other sites More sharing options...
FastEddieB Posted March 22, 2015 Author Report Share Posted March 22, 2015 Apropos of not much... None of the planes I've owned, C150, two Grummans, two Citabrias, a Cirrus and now my Sky Arrow* had/have rudder trim. Nor was it missed. Bigger, more powerful planes can certainly benefit from it, but in a small plane I count it as "maybe nice to have but probably not worth the added complexity". Interestingly the Cirrus early on had rudder trim. They found it troublesome and unnecessary and removed it for most of the fleet going forward. Only relatively recently was it reinstituted as an option. *You CAN get it on a Sky Arrow - but as part of a handicapped option. For those who cannot use their feet! Link to comment Share on other sites More sharing options...
Karl Posted March 23, 2015 Report Share Posted March 23, 2015 trim.FFA077DD-B1B6-46B3-BFA6-B9F705186D0B.MOV I had my new CTLS with Dynon auto pilot tracking level and balanced with auto pilot engaged Then with both feed of the rudder pedals I changed track on the Skyview the result was the ball going out of center Karl Link to comment Share on other sites More sharing options...
Jim Meade Posted March 23, 2015 Report Share Posted March 23, 2015 None of the planes I've owned, C150, two Grummans, two Citabrias, a Cirrus and now my Sky Arrow* had/have rudder trim. Nor was it missed. Bigger, more powerful planes can certainly benefit from it, but in a small plane I count it as "maybe nice to have but probably not worth the added complexity". Interestingly the Cirrus early on had rudder trim. They found it troublesome and unnecessary and removed it for most of the fleet going forward. Only relatively recently was it reinstituted as an option. Why did Cirrus originally have it, then discard it, and now offer it again? Why ever offer it in the first place if it didn't seem like a good idea to some designer? One wouldn't offer it if not needed. All your planes are slow and low powered. My T210 had and really used rudder trim. I wonder if a CTSW is also short enough and powerful enough in relation to it's size to have a "big plane" feel to the rudder? Maybe it's a combination of things or the various characteristics in some combination that call for rudder trim? From the discussion here, it's possible that some don't feel a need for rudder trim because they don't care if the ball is in the middle. One can live with that in some circumstances. in the patter for an hour, I probably get lazy about trimming. On a climb to 9500 feet for a cross country, I probably trim. Link to comment Share on other sites More sharing options...
FastEddieB Posted March 23, 2015 Author Report Share Posted March 23, 2015 From the discussion here, it's possible that some don't feel a need for rudder trim because they don't care if the ball is in the middle. One can live with that in some circumstances. in the patter for an hour, I probably get lazy about trimming. On a climb to 9500 feet for a cross country, I probably trim.I think that maybe misses the point. A pilot does not need rudder trim to keep the ball in the center. That's what his feet are for. In the Cirrus it was mainly the convenience of not having to hold constant right rudder pressure in the climb. But in a normal cruise climb it was just not that much of an inconvenience. Just resting one's right foot on the right rudder pedal was really all it took. I'll have to check to see if rudder trim was ever added back onto the Cirrus. What I think it got was a full yaw damper (as an expensive option*) and that's different. By the way I have a fair amount of 210 time and in a plane like that on a long climb the rudder trim was certainly appreciated. Please don't think I'm arguing against rudder trim. I just wanted to point out that until recently its presence in small GA aircraft was fairly rare. And each extra system adds a little bit of weight, complexity and cost, and should be carefully analyzed as to real need. *$14,900 standalone, but included in one of the Perspective premium packages. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted March 23, 2015 Report Share Posted March 23, 2015 I think the best argument for rudder trim on the CT is for fuel management on long flights, given the design of the fuel system and often differential fuel tank flow rates. It's not really a necessary feature otherwise, more just a "nice to have". I would say my CT needs a lot of right rudder on takeoff and low speed climb. Link to comment Share on other sites More sharing options...
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