Trim question...

fiveoboy01

fiveoboy01

Pattern Altitude
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Dirty B
Yeah yeah I just passed my checkride last week but I still don't know everything, and there is always something to learn.

Today's question centers around using trim on final approach. I've seen it mentioned here many times. I realize the main purpose of trim is to relieve control pressures. I guess I am trying to determine why many talk about using it so much on final. Whether or not it was on purpose, my CFI didn't say much about trimming on final throughout the course of my training and certainly didn't stress it... I use it frequently throughout the various phases of flight, but I definitely don't find myself with a boatload of trim when crossing over the numbers. Normally I watch outside and check my airspeed every few seconds, messing with the yoke to keep pitched for the desired speed.

Perhaps the control pressure required to get to the runway/flare/hold it off doesn't bother me, or maybe I'm just doing it wrong. Or maybe utilizing the trim will help make my usually less-than-perfect landings easier...:dunno:

I'm not trying to reinvent the wheel and I feel like my approaches are just fine for the most part, but I like to know how stuff works...:D Any insight/explanation on this is appreciated. Thanks!
 
Trim is to control your speed, every speed change gets a trim change. I trim all the way down final.
 
I'm not sure what the question is because I couldn't find any question mark in your post.

That said, my understanding is that trim serves two distinct purposes:

* Reduces muscle fatigue.

* The muscles in the fingers and wrists allow for finer motor control than those in the arms, but if you have to exert a lot of force then most of it comes from the coarser controlled arm muscles, making finer control motions more difficult. So trim allows use of muscles better tuned for finer force adjustments.

Not sure how accurate the second paragraph is, but seems to match my perceptions.
 
Planes fly themselves, planes will land themselves with just a little back pressure on the yoke if you set power and trim properly.
 
On the one hand, "flying the trim" is considered to be a bad habit.

Instructors tend to be on the lookout for it. It manifests itself with "chasing" airspeed and/or altitude.

Without hijacking the thread into the hoary "what controls what" morass, if the plane was a tad high on the glideslope, I'd want to see the stick positively moved to correct, with trim to follow as necessary to relieve pressure. NOT simply trim the nose down and wait.

On the other hand, I believe many autopilots can fly very precisely using trim for correction, so in theory it can and does work.

The key is, if the needles stay where they belong throughout the approach, it matters little exactly how it's being accomplished, or what the pilot's thought processes are. It's when a student or a pilot is struggling that adjustments may need to be made in his or her sequence of control pressure vs. trim.
 
Henning said:
Trim is to control your speed, every speed change gets a trim change. I trim all the way down final.
Click to expand...
Exactly. If you want a good lesson on how trim relates to an airplane in flight, search for one of Al Haynes lectures on the Sioux City crash.
 
Change speed change trim. Also isn't landing a phase of flight?
 
I believe you may be over thinking this my friend. Trim to relieve control pressures as you see fit. I trim all the way down like others have said. Sometimes it can be hard for an instructor to know when you are not trimming well because they cannot feel the controls, but with that said, if you were out of whack much it would show in other ways.
 
What plane u fly I did 152 and my instructors said set it and forget it not like everyone on forum trimming all through pattern it bugged me hearing the two differences.
 
Trim is not only to relieve control pressure. Sometimes I want to increase control pressure, like when wheel landing a Cessna 185.

Right before touchdown I like to be holding a little back pressure so that just as the wheels touch, that pressure can be released and the airplane lands itself. This is important because pilots tend to sleep apnea during landings.
 
flyingmoose said:
I believe you may be over thinking this my friend. Trim to relieve control pressures as you see fit. I trim all the way down like others have said.
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Agree with Matt and others.

The only time I do not apply as much "nose up" trim as usual on final is when I am planning a solo or two up front/fwd CG go-around. Otherwise, just prior to full power application, one can of spinach should be eaten. Learn your plane, practice various methods and be consistent.
 
Why do you 'trim all the way down' final approach? Set a speed an fly it, no?
 
kgruber said:
Sometimes I want to increase control pressure, like when wheel landing a Cessna 185.

Right before touchdown I like to be holding a little back pressure so that just as the wheels touch, that pressure can be released and the airplane lands itself.
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That is pretty much what I do when wheel landing in the 170. I trim so that I need to increase pressure to flare and once the wheels touch, I simply relax pressure on the yoke to pin it.
 
The point of trim is NOT to relieve control pressures. That's HOW you trim, not why. The reason is precision. Fatigue isn't a factor in many aircraft, especially trainers. But you're much more precise using control pressure only to correct (small) deviations from the desired trajectory, rather than trying to incrementally adjust a large pressure for the same deviation.
 
Clark1961 said:
Ya'll are confusing trim with attitude, pitch for airspeed.
Click to expand...

Your post is confusing. I hope this thread doesn't degenerate into claiming experienced pilots don't understand how trim works.

To the OP - I don't know who all these people are who talk about using trim "so much" on final. Most trim for their final airspeed early, and then leave it, and fly final without changing trim. How you use trim is individual preference.
 
Are you familiar with the term "trim speed"? That is the speed that the airplane will maintain at a given power setting. To experiment, choose a power setting and trim "hands off." Then pull back on the yoke and release it; the plane will describe a phugoid (up and down) search for trim speed. It will take a few minutes, but when it settles down in level flight you will know the trim speed for the existing conditions (density altitude, weight) at that power setting. Now, without touching anything, apply forward pressure to the yoke and release it. Once again, you will experience phugoid excursions but the end result will be the same trim speed you found before.

To condense what others have said, establish the speed you want with elevator presssure and then trim that pressure off....the airplane will maintain its trim speed unless you change the power setting and have to establish a new trim speed.

Bob Gardner
 
Captain said:
Why do you 'trim all the way down' final approach? Set a speed an fly it, no?
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No. Only in a jet.

In a light aircraft I usually am at cruise across the FAF. Then it is a gradual deceleration to touchdown.

A "stabilized" approach in a light aircraft is where deceleration is constant.
 
Henning said:
No, I'm usually decelerating on final.
Click to expand...

It's probably worth pointing out that HP retracts are different from trainers in this regard, and instrument approaches are different from VFR patterns. I think the question is really about single trainers in a VFR pattern, in a student pilot context. I suspect multis are different still, but I have no experience in that at all.

It's possible (even easy) to decelerate in a 172 while descending at constant rate and partial power on final, but that's not what students are taught.
 
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every time you change power settings. you hand should then move to the trim wheel
 
MAKG1 said:
It's probably worth pointing out that HP retracts are different from trainers in this regard, and instrument approaches are different from VFR patterns. I think the question is really about single trainers in a VFR pattern, in a student pilot context.

It's possible (even easy) to decelerate in a 172 while descending at constant rate and partial power, but that's not what students are taught.
Click to expand...

Even in a 172 I will be 1.3Vso at the top of final and 1.1 Vso at the threshold.
 
Henning said:
I found that was the key to getting slick landing in the Comanche, I'd just hold the trim switch through the flare.
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Arrrrgggghhh! I rarely trim in the flare. Tried it a few times and just don't find it necessary in my glorified trainer with a big-assed stabilator.
 
kgruber said:
No. Only in a jet.

In a light aircraft I usually am at cruise across the FAF. Then it is a gradual deceleration to touchdown.

A "stabilized" approach in a light aircraft is where deceleration is constant.
Click to expand...

One technique, I guess.

For the Cirrus Standardized Instructor Program, you slow down and put in approach flaps within 2 minutes of the FAF, then a constant speed is maintained from the FAF. It's how I always did and taught approaches.

Never actually heard of constantly changing the airspeed on final approach - seems like a lot of extra work and complexity.
 
Clark1961 said:
Arrrrgggghhh! I rarely trim in the flare. Tried it a few times and just don't find it necessary in my glorified trainer with a big-assed stabilator.
Click to expand...

Yeah, Cherokee finesses landings considerably different from a Comanche.
 
Clark1961 said:
Ya'll are confusing trim with attitude, pitch for airspeed.
Click to expand...
Like I said in an earlier post, go watch one of the Al Haynes presentations on the Sioux City crash. It is very educational.

Bob Gardner summarized much of it above.
 
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Henning said:
Even in a 172 I will be 1.3Vso at the top of final and 1.1 Vso at the threshold.
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Not that I doubt you, but that seems really slow, except in the context of a short field landing where you're trying to touch the mains just past the threshold.
 
Fearless Tower said:
Like I said in an earlier post, go watch one of the Al Haynes presentations on the Sioux City crash. It is very educational.

Bob Gardner summarized much of it above.
Click to expand...

That's still not a reason to use the word trim as a substitute for pitch or attitude.
 
One other observation-- in some planes if you are trimmed out on downwind, when you add notches of flaps it will work out that your airspeed will drop to your next desired airspeed with each successive addition. When training in the Diamond DA 20, I trimmed for 75 on downwind after pulling back the power abeam the numbers, added a notch on turning base and it settled at 70, added another notch turning final and it settled at 65-- which was the desired approach speed.

Obviously, this isn't always true, and this is not to be relied on, but that may be why the OP isn't necessarily feeling the need to re-trim on final-- because it just happens to be pretty well trimed out without having to do anything.
 
MAKG1 said:
Not that I doubt you, but that seems really slow, except in the context of a short field landing where you're trying to touch the mains just past the threshold.
Click to expand...

I fly every landing that way. Why would I want more energy and more time floating down the runway than necessary? That is the 'danger zone'. If I want to land mid field, I just adjust my aim point.
 
PPC1052 said:
One other observation-- in some planes if you are trimmed out on downwind, when you add notches of flaps it will work out that your airspeed will drop to your next desired airspeed with each successive addition. When training in the Diamond DA 20, I trimmed for 75 on downwind after pulling back the power abeam the numbers, added a notch on turning base and it settled at 70, added another notch turning final and it settled at 65-- which was the desired approach speed.

Obviously, this isn't always true, and this is not to be relied on, but that may be why the OP isn't necessarily feeling the need to re-trim on final-- because it just happens to be pretty well trimed out without having to do anything.
Click to expand...

The 172 & taper wing PA-28s are the same way.
 
jordane93 said:
i guess so
Click to expand...

Good. What about just engaging alt hold and letting the auto-trim function do the work?

And everskyward has told me wonderous stories of just setting the attitude she wants and the airplane does the rest...
 
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