Trim question...

[MAKG1]

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.

To be honest, I couldn't tell you how fast I am over the threshold, as I'm NEVER looking at the ASI that close to the ground. But I generally don't try to round out and flare until closer to the ground. If I'm following a PAPI, it will aim me for 300 or 1000 feet past the threshold, so I'm too high for a round-out over the threshold. I'm presuming the speed is constant until the round out as the attitude and trim are constant and the control pressures very light, but maybe it isn't.

If I'm doing a soft field landing, I won't pull off the power completely until the mains touch. Short field, it will be all the way down over the fence.

 

[Henning]

To be honest, I couldn't tell you how fast I am over the threshold, as I'm NEVER looking at the ASI that close to the ground. But I generally don't try to round out and flare until closer to the ground. If I'm following a PAPI, it will aim me for 300 or 1000 feet past the threshold, so I'm too high for a round-out over the threshold. I'm presuming the speed is constant until the round out as the attitude and trim are constant and the control pressures very light, but maybe it isn't.

If I'm doing a soft field landing, I won't pull off the power completely until the mains touch. Short field, it will be all the way down over the fence.

I'm not looking at the ASI either, I go by yoke/stick feel, when it's mushy, I'm there. That's why accurate trim is important.

 

[fiveoboy01]

The point of trim is NOT to relieve control pressures. The reason is precision.

They go hand in hand. Little or no control pressure=precise control. Example, slow flight, I was able to maintain pitch control with that horn screaming much easier with the airplane trimmed out and me not having to haul back on the yoke.

That said, perhaps I am just overthinking this all as far as the landings go, I know I've read here "trim all the way down"(maybe it was Henning saying it somewhere else) like you're jockeying the trim through the entire final approach and frankly I don't think I've ever had a single final approach where I touched the trim once... So I was starting to think maybe my technique has been wrong.

 

[MAKG1]

They go hand in hand. Little or no control pressure=precise control.

It's a good point, but it's not correct.

You will get little or no control pressure with the elevator cables broken.

The reason you trim is for precision. The mechanism by which you trim is the control pressure.

There are analogs in other control systems (i.e., ones that don't involve humans); it's the essentials of how a servo works. And even numerical optimization algorithms have the same behaviors. Superpose constant offsets and the stability and/or convergence goes down.

 

[fiveoboy01]

I won't argue with someone who obviously knows more than me and I'm sure you're right. I do know it's really tough to keep precise control if the yoke is feeling heavy. It's like the "death-grip-on-the-yoke"... more tense=less ability to be smooth/precise.

If the cables are broken, I think I have bigger problems than wondering why the yoke is moving so easily

 

[Henning]

To be honest, I couldn't tell you how fast I am over the threshold, as I'm NEVER looking at the ASI that close to the ground. But I generally don't try to round out and flare until closer to the ground. If I'm following a PAPI, it will aim me for 300 or 1000 feet past the threshold, so I'm too high for a round-out over the threshold. I'm presuming the speed is constant until the round out as the attitude and trim are constant and the control pressures very light, but maybe it isn't.

If I'm doing a soft field landing, I won't pull off the power completely until the mains touch. Short field, it will be all the way down over the fence.

Also the aim point is irrelevant, what I want to minimize is my time floating down the runway waiting for the plane to quit flying, that is where things will go wrong badly, and I also don't want to put the plane down before it quits flying because I have more energy than necessary and a crosswind gust of wind has a greater chance of lightening me up enough to send me off the side of the runway. It doesn't matter where I'm aiming to set down, by the time I am getting ready to flare, I want to be 1.1Vso. Note, the flare is after the round out and is down in Ground Effect where the plane will actually quit flying around .93-.95 Vso.

 

[Clip4]

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...

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... Any insight/explanation on this is appreciated. Thanks!

When I first learned to fly, I never trimed from down wind to flare. Its a whole lot easier if you trim - even on short final.

 

[dell30rb]

No, I'm usually decelerating on final.

Same here. I tend not to fly a square pattern anymore either. A constant, gentle turn all the way from downwind to final with the airspeed steadily decreasing.

 

[Henning]

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.

IIRC 65 is No Flaps approach speed on a DA20, 60 is normal with flaps. Also Vso is 34kts at gross, less below gross, so 65 is at least 1.9 Vso, that is a far cry from 1.3 Vso. If you are coming into your round out in a DA-20 at 65, I bet you use a hell of a lot of runway. As clean as the DA20 is you should be crossing the fence at or below 50kts and slowing to cross the threshold at or below 40 kts.

 

[Everskyward]

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

Found out the airplane still remembers how to land...

 

[Sac Arrow]

Why do you 'trim all the way down' final approach? Set a speed an fly it, no?

Kinda what I was thinking....

 

[Clark1961]

Found out the airplane still remembers how to land...

Good to hear that you're back in the air.

 

[Graueradler]

I determined the trim and power setting that would give me 85 mph and 500 fpm sink with one notch of flaps. That gets set abeam the numbers. I add a notch of flaps turning base and pitch to slow to 75 after turning final. Adjust as necessary when I misjudged something.

 

[Henning]

I determined the trim and power setting that would give me 85 mph and 500 fpm sink with one notch of flaps. That gets set abeam the numbers. I add a notch of flaps turning base and pitch to slow to 75 after turning final. Adjust as necessary when I misjudged something.

What are you flying?

 

[kujo806]

I have had some questions in my mind about trimming during landing as well. Since my training, I set/adjust the trim to get to my approach speed of 90mph with full flaps (for the arrow), fly it to the runway, and pull back some yoke to gently level and flare until the plane kisses the runway. A while back I was thinking about buying a Mooney, and my instructor at the time (different than during PPL training) said that Mooneys are very pitch sensitive airplanes especially on landing. I really don't know what that means. How is it different than what I have done in Pipers and Cessnas? Do you have to continuously adjust the trim in Mooneys all the way to the ground or can you trim to approach speed and use the yoke to flare? Hopefully I will get to try landing a Mooney soon and get a feel for what he meant.

 

[flyingmoose]

Why do you 'trim all the way down' final approach? Set a speed an fly it, no?

I assume you were talking to me, but if not my apologies. Yes if you can set a pitch attitude and it holds that speed then awesome, but its a dynamic event and sometimes minor adjustments are made. My point was that if I need to make an adjustment at the marker or 50 above threshold or anywhere in between I will. I don't see that as too awful crazy, but heck maybe ive lost it...

 

[Bill]

said that Mooneys are very pitch sensitive airplanes especially on landing. I really don't know what that means. How is it different than what I have done in Pipers and Cessnas?

Pitch sensitive? I don't really know about that, but Mooneys are very speed sensitive on short final, and that is different than most Pipers and Cessnas.

Come in ten knots hot in a Mooney and you'll likely not be able to land unless the runway is LONG. I fly a 201 and on short final will have the trim almost fully nose up and the speed at 65kts. Short field light will be full up and 60kts. Above 70kts and you're going to float. Also, you cannot force a Mooney onto the ground before it's done flying.

Be on your speed numbers and the Mooney is easy to land.

 

[Henning]

I have had some questions in my mind about trimming during landing as well. Since my training, I set/adjust the trim to get to my approach speed of 90mph with full flaps (for the arrow), fly it to the runway, and pull back some yoke to gently level and flare until the plane kisses the runway. A while back I was thinking about buying a Mooney, and my instructor at the time (different than during PPL training) said that Mooneys are very pitch sensitive airplanes especially on landing. I really don't know what that means. How is it different than what I have done in Pipers and Cessnas? Do you have to continuously adjust the trim in Mooneys all the way to the ground or can you trim to approach speed and use the yoke to flare? Hopefully I will get to try landing a Mooney soon and get a feel for what he meant.

90mph over the threshold in an Arrow, I bet you use a lot of runway. Vso for an Arrow is like 64mph, so you're trying to land starting at 1.6 Vso. You should be flying final at 1.3 Vso which is 72mph, and that is at Gross Weight, so these numbers are fast when you are solo and light on fuel.

If you try to fly a Mooney like you fly an Arrow you will find out why Mooneys have the prop eating 'hard to land' reputation they have, the only Mooney I know the numbers on is the M-20F and Vso on it is 62mph so it's even a bit slower than the Arrow, I used to be over the fence in it at 70mph and no faster unless I had a big runway because that sucker would float forever, if I didn't have the speed where I needed it it would be a go around since I was flying it into 1800'. If you try to force a Mooney down you will set up a porpoising event that would end up with a destroyed prop.

 

[geneseib]

Normally I watch outside and check my airspeed every few seconds, messing with the yoke to keep pitched for the desired speed.

Get it trimmed up right and airspeed will take care of itself.

 

[Henning]

Pitch sensitive? I don't really know about that, but Mooneys are very speed sensitive on short final, and that is different than most Pipers and Cessnas.

Come in ten knots hot in a Mooney and you'll likely not be able to land unless the runway is LONG. I fly a 201 and on short final will have the trim almost fully nose up and the speed at 65kts. Short field light will be full up and 60kts. Above 70kts and you're going to float. Also, you cannot force a Mooney onto the ground before it's done flying.

Be on your speed numbers and the Mooney is easy to land.

I think the reference to 'pitch sensitive' on landing is about not allowing pitch to drop to drive it onto the ground. That's the sure way to eat a prop.

 

[Bill]

I think the reference to 'pitch sensitive' on landing is about not allowing pitch to drop to drive it onto the ground. That's the sure way to eat a prop.

Yup, like I said, you can't force it on the ground before it's done flying!

 

[kujo806]

90mph over the threshold in an Arrow, I bet you use a lot of runway. Vso for an Arrow is like 64mph, so you're trying to land starting at 1.6 Vso. You should be flying final at 1.3 Vso which is 72mph, and that is at Gross Weight, so these numbers are fast when you are solo and light on fuel.

If you try to fly a Mooney like you fly an Arrow you will find out why Mooneys have the prop eating 'hard to land' reputation they have, the only Mooney I know the numbers on is the M-20F and Vso on it is 62mph so it's even a bit slower than the Arrow, I used to be over the fence in it at 70mph and no faster unless I had a big runway because that sucker would float forever, if I didn't have the speed where I needed it it would be a go around since I was flying it into 1800'. If you try to force a Mooney down you will set up a porpoising event that would end up with a destroyed prop.

Checklist full flap approach speed in the arrow is 90mph. Over the numbers speed will be lower, and if light I will use something closer to 85mph on approach, but that thing sinks like a rock. For short field, I will use 80mph and it will sit down quickly and firmly.

 

[tmyers]

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.

Likewise, trim for over the fence and just land. To be honest it is something I do as needed without a lot of conscious thought.

 

[Dan Thomas]

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.

1.1 at the threshold is just fine. It isn't going to stall. Many, many airplanes are wrecked when pilots approach and try to land at higher speeds. The least damage is ruined tires from heavy braking to try to avoid running off the end. More damage involves busted nosegears from porpoising, groundlooping from wheelbarrowing, and so on.

If the stall warning isn't squawking in the flare, you're too fast. If you can't land and stop in book distance, you're too fast. If you are paying for new tires and brake linings too often, you're too fast.

Dan

 

[MAKG1]

1.1 at the threshold is just fine. It isn't going to stall. Many, many airplanes are wrecked when pilots approach and try to land at higher speeds. The least damage is ruined tires from heavy braking to try to avoid running off the end. More damage involves busted nosegears from porpoising, groundlooping from wheelbarrowing, and so on.

If the stall warning isn't squawking in the flare,you're too fast. If you can't land and stop in book distance, you're too fast. If you are paying for new tires and brake linings too often, you're too fast.

Dan

Fully agreed. But the threshold is too high for the flare in some cases. I'm not arguing for faster finals (quite the opposite -- as slow as is safe, for the reasons given), but one doesn't always begin a flare over the threshold.

1.1 Vs0 at the threshold won't stall in ground effect, but it might be a tad close at 50 feet, if you're flaring that high.

 

[ifconfig]

Like I said in an earlier post, go watch one of the Al Haynes presentations on the Sioux City crash. …

You have a link?

 

[Henning]

Fully agreed. But the threshold is too high for the flare in some cases. I'm not arguing for faster finals (quite the opposite -- as slow as is safe, for the reasons given), but one doesn't always begin a flare over the threshold.

1.1 Vs0 at the threshold won't stall in ground effect, but it might be a tad close at 50 feet, if you're flaring that high.

That depends where you aim. This ends up 1.1 at the threshold. Fast Forward to 5:45.
https://m.youtube.com/watch?v=lFR0BKqTs6U

The other day on my BFR I decided to do a short field landing, on short final my CFI commented, "We're below the white arc." "Yep, we're also below gross weight", "ahhhh..." "We're still flying aren't we? Do you hear a stall horn or feel a buffet?" "Yep, still flying with no stall horn."

 

[bobmrg]

I found that was the key to getting slick landing in the Comanche, I'd just hold the trim switch through the flare.

In my experience, that works just fine with Twin Comanches as well. They have an undeserved rep for being hard to land.

Bob Gardner

 

[poadeleted20]

Trim is to control your speed, every speed change gets a trim change. I trim all the way down final.

Amen. Each time I change speed, I retrim so the plane will hold that speed if I let go of the yoke, including all the way down final until I flare (I don't use trim to flare since that would trim the plane for way too low a speed if I have to abort the landing).

 

[ferrari-tech]

I was taught for every attitude there is a pitch/power setting.
So pretty much anytime one of these changes the required trim changes.

One of my instructors was much more into trim use on final than the other and between them I figure what works for me...every time I change pitch or power in any faze of the flight I adjust the trim to suit.

 

[Fearless Tower]

That's still not a reason to use the word trim as a substitute for pitch or attitude.

Um, yeah. Are you thinking that if you set your attitude for, say 10 degrees up on the AI and trim out any control pressure that your airplane is going to stay at 10 degrees up through the climb? Or am I misreading you?

Attitude at a given power setting will give you an initial speed, but unless you change power of make additional pitch changes, the airplane us going to revert to its trim speed not trim attitude.

 

[Clark1961]

Um, yeah. Are you thinking that if you set your attitude for, say 10 degrees up on the AI and trim out any control pressure that your airplane is going to stay at 10 degrees up through the climb? Or am I misreading you?

Attitude at a given power setting will give you an initial speed, but unless you change power of make additional pitch changes, the airplane us going to revert to its trim speed not trim attitude.

Please read what I originally typed: pitch for airspeed. Do I really need to type anything more? If you want to substitute one term for another that is your business. I would ask that you not try to obfuscate to seek the appearance of authority but that is your call entirely.

 

[Henning]

I was taught for every attitude there is a pitch/power setting.
So pretty much anytime one of these changes the required trim changes.

One of my instructors was much more into trim use on final than the other and between them I figure what works for me...every time I change pitch or power in any faze of the flight I adjust the trim to suit.

For every speed, there is a trim setting, for every rate of climb or descent there is a power setting.

 

[Fearless Tower]

Please read what I originally typed: pitch for airspeed. Do I really need to type anything more? If you want to substitute one term for another that is your business. I would ask that you not try to obfuscate to seek the appearance of authority but that is your call entirely.

Oh my, my aren't we a little testy.

You did not answer my question -did I misunderstand your point of view or not?

And I did read what you originally typed...that is why I asked the question,

 

[Jimmy cooper]

Let me say this......about that. ( dick Nixon) I flew mooneys quite a bit. When I was checked out in one, a super 21, I was taught to slow to 70 entering downwind, gear down, full flaps, hold 70 until final, then get off the throttle, holding just a bit. Fly it down and come back on the yoke until it stops flying. This was on a 2200 feet paved runway. It worked just fine. I landed it just like I would a taildragger, setting up for a three pointer. Naturally the longer the runway, more experience, a little different technique. Very easy airplane to fly, very stable and will land short if you pay close attention to speed, flap setting on final. Otherwise it acts like a taylorcraft and floats on and on down the runway. Later I flew a 201 quite a bit. Same o same o. Great airplane. ( trim setting back a half from neutral, then play with it as you get closer to the runway.) in a taildragger, like say a champ or a t craft I just left it trim neutral a lot of time and three pointed it or wheel landed it. With some time in each, you get a distinct feel of what it's doing.

 

[TMetzinger]

I use trim whenever I need it.

When I need it depends on the phase of flight and the airplane being flown.

I guess my point is that there's no right answer. In a 172 I'll probably make my last trim change shortly after turning final and setting flaps for the landing. In a PA32RT (Turbo Lance) I'll be trimming on short final as I decelerate from final approach speed of 95 KIAS to touchdown speed under 80 KIAS).

Oh, and as a proficiency exercise I will sometimes fly the airplane in cruise with nothing besides trim and rudder pressure. I find it reinforces the concept of what trim does, and the concept of yaw/roll coupling.

 

[kenjr]

...I fly a Cherokee 235 and I'm trimming all the way down to the flare. By the time I'm there I usually have the trim just about all the way nose up. The 235's are quite nose heavy and drop like a rock when you cut power so if you don't keep up with trimming it out you're probably in for a rough landing.

 

[Dan Thomas]

Fully agreed. But the threshold is too high for the flare in some cases. I'm not arguing for faster finals (quite the opposite -- as slow as is safe, for the reasons given), but one doesn't always begin a flare over the threshold.

1.1 Vs0 at the threshold won't stall in ground effect, but it might be a tad close at 50 feet, if you're flaring that high.

Another mistake I often see is flaring really late. That usually means 1.3 (or more) into ground effect, and a long float or the other problems mentioned before (ballooning, porpoising, wheelbarrowing, runway excursions, wrecked tires). The flare is actually a long affair, starting at 15 to 30 feet, with the early part called the round-out, to dissipate speed and arrive in ground effect with too little to cause floating or anything else.

Dan

 

[Clark1961]

...I fly a Cherokee 235 and I'm trimming all the way down to the flare. By the time I'm there I usually have the trim just about all the way nose up. The 235's are quite nose heavy and drop like a rock when you cut power so if you don't keep up with trimming it out you're probably in for a rough landing.

The early PA-28's have a little stabilator compared to the 236 and 201T. Dunno exactly when the change happened on the assembly line. The pitch authority and balance is more than sufficient to land without trimming in the round-out/flare in the later models.

 

[asechrest]

Another mistake I often see is flaring really late. That usually means 1.3 (or more) into ground effect, and a long float or the other problems mentioned before (ballooning, porpoising, wheelbarrowing, runwain excursions, wrecked tires). The flare is actually a long affair, starting at 15 to 30 feet, with the early part called the round-out, to dissipate speed and arrive in ground effect with too little to cause floating or anything else.

Dan

It took me a good chunk of my training to figure this out. My landing attempts were a dive toward the ground with a last minute arresting rather than a smooth round out. I actually don't much care for the term flare, because I think it gives the student and an inaccurate picture of what should I actually be happening.