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FD Logic?


ryanbatc

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The FD on this thing is really bugging me. First off, the needles swing around when making turns and climbs/descents etc. Also the FD does not indicate where I really should be pointing the aircraft. See this for example... my HSI says I'm a little right of course. Yet the FD bars say I should be left of course. Is this FD different than most in that it's trying to tell me the vector of the aircraft in its current state? If so that's quite backwards from industry standard.

http://i141.photobucket.com/albums/r43/ryanbatc/twotterFDwtf.jpg~original

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The FD bars does not indicate direction to fly as such.

They indicate where You should point Your aircraft in order to achieve what You have set on the autopilot.

F.ex setting a heading to the left of Your present heading will make the lateral indicator move to the left. As You bank Your aircraft the bar will center as You reach the lateral attitude the AP would have used inorder to capture the heading.

Point is that as long as You keep the two bars form a uniform cross (With the lateral bar displaced downwards), then You are doing what the Autopilot would have done.

This one isn´t different from how other FD's are working, but peolle seem to misinterprete what they should indicate, though the FSX FD code isn´t perfect.

Finn

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I just flew a checkflight....

It worked flawless at my end. Following the FD bars put me right over the VOR station.

Question is if there where any winddrift of if the rudders wasn´t centered, maybe the rufdder trim was still set in T.O position and no Yaw damper active.

Finn

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  • Deputy Sheriffs

The FD bars does not indicate direction to fly as such.

They indicate where You should point Your aircraft in order to achieve what You have set on the autopilot.

F.ex setting a heading to the left of Your present heading will make the lateral indicator move to the left. As You bank Your aircraft the bar will center as You reach the lateral attitude the AP would have used inorder to capture the heading.

Point is that as long as You keep the two bars form a uniform cross (With the lateral bar displaced downwards), then You are doing what the Autopilot would have done.

This one isn´t different from how other FD's are working, but peolle seem to misinterprete what they should indicate, though the FSX FD code isn´t perfect.

Finn

To continue Finn's example with a cross-pointer or command bar system, say you're in heading mode and on heading in cruise flight. Now, you move the heading bug 90 degrees to the right of where it was. The vertical bar (which provides lateral steering commands (or bank commands for practical purposes) will displace to the right. As you roll into a 25 degree right bank (because a flight director will always command a 25 degree bank in this condition), the bar will begin to center, indicating you're starting to satisfy the bank command. At a 25 degree bank, it will be centered and remain so as long as you stay in that bank and until you approach the desired heading. If you increase the bank, the bar will displace slightly left telling you to shallow the bank. Even though your desired heading is to the right, because you're overbanking, it will displace to the left. As you approach the point where you should begin your rollout to exactly hit the new heading, the bar will displace to the left, telling you to decrease right bank. This is true, even though you're desired heading is still off to the the right a little. The bar is simply telling you what to do with bank to get where you're going, not where that place is, left or right.

So, vertical bar to the right means increase right bank or decrease left bank, depending on which one you're in. Left bar deflection means increase left bank or decrease right bank, again, depending on which one you're in.

The FAA Instrument Flying Handbook (here) starting on page 5-23 has a little more info on this.

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To continue Finn's example with a cross-pointer or command bar system, say you're in heading mode and on heading in cruise flight. Now, you move the heading bug 90 degrees to the right of where it was. The vertical bar (which provides lateral steering commands (or bank commands for practical purposes)) will displace to the right. As you roll into a 25 degree right bank, the bar will begin to center, indicating you're starting to satisfy the bank command. At a 25 degree bank, it will be centered and remain so as long as you stay in that bank and until you approach the desiered heading. If you increase the bank, the bar will displace slightly left telling you to shallow the bank. Even though your desired heading is to the right, because you're overbanking, it will displace to the left. As you approach the point where you should begin your rollout to exactly hit the new heading, the bar will displace to the left, telling you to decrease right bank. This is true, even though you're desired heading is still off to the the right a little. The bar is simply telling you what to do with bank to get where you're going, not where that place is, left or right.

So, vertical bar to the right means increase right bank or decrease left bank, depending on which one you're in. Left bar deflection means increase left bank or decrease right bank, again, depending on which one you're in.

The FAA Instrument Flying Handbook (here) starting on page 5-23 has a little more info on this.

Very good explained Herman :)

Finn

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