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TracyQ

Hate to admit my ignorance, but...trim when landing?

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Been so long since I took lessons, I have forgot everything I might have ever learned.

 

GA aircraft. I usually drop the flaps and gear (if applicable) when in the pattern, and then slowly feed in "up" trim. Is this the way it is done in real life?

 

Gads, I can't even believe I have asked such a basic question but there you go...be kind, please.

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You are describing the trim for a 'hands off' flight on a stabilized approach. That sounds correct to me. However, I'm only a sim pilot, so we may have to rely on some good sources on e.g. GA plane flying. Fortunately, there is such a thing, right from the FAA.

 

http://www.faa.gov/l...plane_handbook/ Pick the chapters 7-9 pdf (you are looking for 8) and find your assumption confirmed. As the general rule, you trim for no forces on the flight controls so that you can move the elevator in each direction and with the largest amount of travel available to either flare nicely or avoid a too high pitch when applying go-around power.

 

You mainly try to avoid running out of elevator travel in each direction if a problem arises. So approaching stabilized, with no large changes in speed, pitch or on the throttle, is the basis for the trim setup, allowing the 'hands off' flying.

 

Correct me if I'm wrong, but that book alone is a jewel and it also is completely free. :smile:

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You'll get a few opinions on it, and you have to be careful to note that on some aircraft, you would probably do things different to some others, since on some types it is possible to trim things to the point where you have minimal control authority left in the bag. So expect advice on it to vary depending on people's real world experiences on various types.

 

Generally you trim for speed, whatever the phase of flight, so that would be your approach speed you'd be trimming for on a landing; in most types I fly for real that would be for 70 knots when held in a descent, but it would be different for other people who fly other aircraft to the ones I fly.

 

I know some pilots who trim for the flare at the speed you would fly level and bleed the speed off and who then hold the stick manually for the short final, so that when they get to the flare the trim will be of some assistance in getting it right. Don't think I'd do that myself, but I concede that it is a novel idea.

 

Being that the trim in FS is fairly crap compared to real life, I'd say trim for a descent at your approach speed if you can. Of course in a real aeroplane it is a crapload easier, since you just hold the stick and then adjust the trim until you can let up your grasp on the stick a bit and not feel the stick moving very much if at all. Can't really do that with an FS computer joystick or yoke.

 

Al


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I've found the force feedback feature together with a good stick and some soft like FSForce to be very nice on the trim feel. I actually don't know how FSX feels with a static spring load force and without force feedback since I'm running that setup since years.

 

So if one flies with e.g. the Logitech G940 or the MS Sidewinder plus the mentioned soft, he will receive a lot of feedback bringing the old sim closer to the real thing. That's just from judging about the feel when sitting on the right seat though.

 

It sometimes comes in awkward when writing about force feedback because some folks seem to relate it to the simple rumble feature of some PS2 controllers. But that's not what it's about and e.g. feeling some stall buffet arising or the off-centre trim is a blast.

 

You can also adjust things like the resistance or some damping, to take care of the different feel when flying old, non powered or very responsive controls. This may take some time to set up, but it renders that rather dead channel of the 'feel' to become alive.

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If I am flying General Avation the last moment I would adjust trim is on Downwind when I am doing last minute landing checks and the trim would be the last item I would do. From there on I wouldn't touch it.

 

I throttle back just before base and lower flaps on Base Leg


Matthew Kane

 

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Trim is your friend. Everytime you adjust a flight characteristic (flaps, power setting, airspeed) you'll have to adjust the amount of pressure you need to apply to the elevator. Trim as you need to so you aren't constantly pushing or pulling at the controls. It will provide for a more stabilized approach.


Brian Thibodeaux | B747-400/8 First Officer, C-130 Flight Engineer, ATP, CFI

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GA aircraft. I usually drop the flaps and gear (if applicable) when in the pattern, and then slowly feed in "up" trim. Is this the way it is done in real life?

 

Short answer, yes, trim as your speed changes, once at final approach speed, leave it alone.


Jay

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Short answer, yes, trim as your speed changes, once at final approach speed, leave it alone.

 

.. and then use only your power to change the descent angle. i.e. fix the touchdown point on a particular spot on your windshield and then keep it there with small power adjustments.

Runway moves up - add some power: runway moves down - pull back the power - don't pump the elevator - actually - if she's trimmed right and no wind - hands off!

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I constantly make trim and power adjustments during the final approach phase both real life and simming. My instructor would advise me to not use too much trim and that I may lose responsiveness during final approaches. For me it takes a little work load off while concentrating on speed and wind corrections on final.


Brian Riggs

PPL 2001

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My instructor would advise me to not use too much trim

 

I imagine this comes down to potentially leaving yourself trimmed to the point where a emergency abort/go-around is difficult.


"It's too small, IT'S....TOO...SMALL"

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I imagine this comes down to potentially leaving yourself trimmed to the point where a emergency abort/go-around is difficult.

 

That's exactly why he recommended that I rely less on trim during final.


Brian Riggs

PPL 2001

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As stated prveviously, much depends on the plane. For my RV6A (nosegear).........I'll trim for speed at the descent rate I'm looking for. This will be a bit of down trim. Then I leave it, and don't even change it for the next takeoff. That's my preference, because I prefer the feel of actively rotating. My plane will become airborne earlier than I prefer, if I don't. But much of that, has to do with my preference of building up a little more speed, and more agressive climbouts. This plane will climb well on the takeoff, because of a fairly good power to weight ratio. Quite different than a Cessna 172. BTW--- that bit od downtrim I mentioned, takes little effort to push against. It's nothing like a Piper Warrior/Archer with too much down trim on a takeoff roll. For those, I'd always set trim at the "takeoff" indication.

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Trim in FSX is not exactly what it should be, a relief from constantly fighting against stick pressure. It does have this function but at trim extremes it actually INCREASES the amount of elevator authority. This can be demonstrated by pulling back fully with neutral trim and observing the positive G achieved (press Shift Z a few times for the red text display - and you need to be going fast so you don't stall when pulling back).

 

Now select a lot of up trim and temporarily hold the stick forward to counteract the trim, accelerate then pull the stick hard back. You'll see that will full aft stick you likely as not get a higher G reading. This isn't entirely accurate because trim is there in most aircraft to save constant pressure on the stick, not to create more elevator authority overall.

 

Thus many sim pilots don't trim too much on short finals because it means the flare tends to be too sensitive. I personally trim on approach so I still need a bit of back pressure. This stops the trim's tendency to create an artificially higher elevator authority than it should and helps you to flare with more control. It also discourages ballooning when doing a quick go around.

 

Another point is that it is much easier to apply a bit of back pressure with good control than forward pressure. So even if you want to trim all the way down to the runway, it is best to err on the side of a tad too little up trim. Pushing the stick forward to maintain level flight is very much harder than a little back pressure which is more natural.


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I imagine this comes down to potentially leaving yourself trimmed to the point where a emergency abort/go-around is difficult.

That's exactly why he recommended that I rely less on trim during final.

0

 

As a CFI myself I would actually encourage trimming whenever my student feels the need. A 172 for instance on final is 60 kias on a normal landing. If you trim it out for 60 and have to go around the aircraft will most definately pitch up on its own accord due to increased lift generated by propwash but it shouldn't be uncontrollable and part of your training should be on how to deal with it. But to simply dismiss trimming because of the rare occurrence of a balked landing is a bit much. Look at it from a play by play using an example listed up top. Mr. Ytzpilot said the last time he would touch his trim is on downwind (no offense intended using you as a example). In a 172 thats 90 kias or so. You start to configure and slow down the aircraft base then to final. All of a sudden your at 60kias you've added all sorts of drag also. The nose of the aircraft is trying to drop on you while your managing your aim point (touchdown spot) on the runway. Now lets throw a a 15 kt headwind into the mix and for funzies lets say its a bit gusty. You finally make it flying over the threshold and are gonna initiate your round out and start to flare. Bring the power to idle (requires more back pressure on the yoke in addition to whats required to flare), the nose slowly comes up and all of a sudden you lose say 5 kts of wind on the nose cause its gusty. Thats an additional 5 kts of back pressure you need to add. See where I'm going with all this? The last time you trimmed the aircraft was downwind at 90-100 kias. Now your trying to fly an aircraft probably around the 45 kias due to wind. And at that height above the runway (talkin maybe 10' or so) you might find yourself in a bad spot even if you try to initiate a go around. By the time you add power the nose might have dropped substantially and plant the nose into the ground.

Now all thats pretty extreme and most likely not going to happen but as a pilot probably somethin that should be going into the back of your mind on any approach honestly. With my two years of instructing before I went to the airlines the one time I actually found myself overly cautious with a student is those brief few seconds in the round out and flare.

When your in slow flight such as that the only direction the aircraft is exceptionally responsive is nose down movement. Rolling or pitching up a bit more sluggish. So I guess the point of the response is, trim the airplane and get rid of the pressure on the yoke, the only time you should really just stop trimming is when you've pulled all the power out and your bringing the nose up to land. And even that only goes so far as to what plane your flying (in the Beech 1900 we hold the electic trim up during our flare) cause the plane is so nose heavy.


Brian Thibodeaux | B747-400/8 First Officer, C-130 Flight Engineer, ATP, CFI

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thibodba57, is it possible that the availability of the electric trim (the 'rocker on the yoke or stick) and therefore the lets say convenience factor adds to the habits pilots develop on the (re-)trim needs? I mean, if I can leave the left hand on the yoke, the right one on the throttle and still am able to trim thanks to that rocker, this may be different to the guy having to grab that trim wheel.

 

While my understanding would always suggest to trim away elevator pressure, just because you may run out of travel in certain situations, the folks flying the non electric trim planes may pick the slight elevator pressure over the need to grab that trim wheel again, depending on the workload.

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