I think I am using Pitch trim incorrectly

Find or share aviation knowledge
William Hughes
Senior Airman
Posts: 222
Joined: 13 Dec 2014, 11:38
Location: Saskatoon, SK
Contact:

Re: I think I am using Pitch trim incorrectly

Post by William Hughes »

Another way to think of pitch-trim is that it functions as a speed control feedback device. The pitch trim allows the pilot to set a speed where the elevator is stable. If the aircraft is too fast at that trim setting the elevator will pitch the aircraft up until it is at that speed, and vice versa. The aircraft will oscillate around the stable speed until it zooms in on it. That is why you want to set a speed with the elevator and then trim the pressure off. Less flopping around in the sky.

Once the speed is set using the pitch trim you then control your descent, level, or climb flight with how much power is applied. So if you have set a given speed for an approach and the aircraft is stable, you control your rate of descent by varying the power. You can get quite fine adjustments by small adjustments to the throttle.

User avatar
Styggron
Master Sergeant
Posts: 1031
Joined: 30 Oct 2015, 14:28

Re: I think I am using Pitch trim incorrectly

Post by Styggron »

William Hughes wrote:Another way to think of pitch-trim is that it functions as a speed control feedback device. The pitch trim allows the pilot to set a speed where the elevator is stable. If the aircraft is too fast at that trim setting the elevator will pitch the aircraft up until it is at that speed, and vice versa. The aircraft will oscillate around the stable speed until it zooms in on it. That is why you want to set a speed with the elevator and then trim the pressure off. Less flopping around in the sky.

Once the speed is set using the pitch trim you then control your descent, level, or climb flight with how much power is applied. So if you have set a given speed for an approach and the aircraft is stable, you control your rate of descent by varying the power. You can get quite fine adjustments by small adjustments to the throttle.
Thank you William. This helps me a great deal.

With take off there is a marker for where to put the trim, should I have it somewhere specific for landing ? so as I am descending should I have it on "TO" again ? Sometimes I make a boo boo and I have it pitching down..... ooops :shock:
Accufeel V2, C172 , B377+L049+COTS, B17G, Piper Cub,Commanche,Cherrokee,Spitfire,Bonanza, P47,P40,both Mustangs
Aircraft Factory Avro Anson, Albatros DIII,Heinkel He-219, F4U Corsair, P51H Mustang, Avro 504, BF109
Watch my incompetent flying Twitch

User avatar
AKar
A2A Master Mechanic
Posts: 5208
Joined: 26 May 2013, 05:03

Re: I think I am using Pitch trim incorrectly

Post by AKar »

Yes, exactly as William says: the easiest way of thinking the trim control is that it sets the speed where the airplane (with given loading, in given conditions) wants to be.

There is an addition one may (or may not!) want to make, even if it is not important for initial learning. To be more accurate, the trim sets the angle of attack at which the airplane wants to fly. Where this comes important is when noting that an airplane does not, in general, stabilize to an airspeed without pilot assistance, but oscillates around it in something called phugoid cycle, keeping more or less constant angle of attack but transferring in between airspeed and altitude in a 'roller coaster motion'. These oscillations typically don't dampen out on their own. But they are of such a long period that it is easy to correct them out without actually noticing. But if you let an airplane to fly hands-off indefinitely, you'd note the airplane going up and down around your trimmed airspeed.

But for all practical purposes, unless you want to get deeper into flight mechanics, you can think the trim as your primary long-term speed control.
Styggron wrote:With take off there is a marker for where to put the trim, should I have it somewhere specific for landing ? so as I am descending should I have it on "TO" again ? Sometimes I make a boo boo and I have it pitching down..... ooops :shock:
No, in general you don't put the trim into any specific position but trim for a stable approach. Because you can't trim by feel on the ground, the takeoff setting is provided as a rough reference of more or less neutral trim for takeoff conditions, so that control forces won't be excessive. After takeoff, you can basically forget any specific trim settings in these airplanes, and trim "as required" instead.

-Esa

User avatar
Styggron
Master Sergeant
Posts: 1031
Joined: 30 Oct 2015, 14:28

Re: I think I am using Pitch trim incorrectly

Post by Styggron »

AKar wrote:Yes, exactly as William says: the easiest way of thinking the trim control is that it sets the speed where the airplane (with given loading, in given conditions) wants to be.

There is an addition one may (or may not!) want to make, even if it is not important for initial learning. To be more accurate, the trim sets the angle of attack at which the airplane wants to fly. Where this comes important is when noting that an airplane does not, in general, stabilize to an airspeed without pilot assistance, but oscillates around it in something called phugoid cycle, keeping more or less constant angle of attack but transferring in between airspeed and altitude in a 'roller coaster motion'. These oscillations typically don't dampen out on their own. But they are of such a long period that it is easy to correct them out without actually noticing. But if you let an airplane to fly hands-off indefinitely, you'd note the airplane going up and down around your trimmed airspeed.

But for all practical purposes, unless you want to get deeper into flight mechanics, you can think the trim as your primary long-term speed control.
Styggron wrote:With take off there is a marker for where to put the trim, should I have it somewhere specific for landing ? so as I am descending should I have it on "TO" again ? Sometimes I make a boo boo and I have it pitching down..... ooops :shock:
No, in general you don't put the trim into any specific position but trim for a stable approach. Because you can't trim by feel on the ground, the takeoff setting is provided as a rough reference of more or less neutral trim for takeoff conditions, so that control forces won't be excessive. After takeoff, you can basically forget any specific trim settings in these airplanes, and trim "as required" instead.

-Esa
ok thank you.
I use it to pitch down sometimes though.
Accufeel V2, C172 , B377+L049+COTS, B17G, Piper Cub,Commanche,Cherrokee,Spitfire,Bonanza, P47,P40,both Mustangs
Aircraft Factory Avro Anson, Albatros DIII,Heinkel He-219, F4U Corsair, P51H Mustang, Avro 504, BF109
Watch my incompetent flying Twitch

User avatar
DHenriques_
A2A Chief Pilot
Posts: 5711
Joined: 27 Mar 2009, 08:31
Location: East Coast United States

Re: I think I am using Pitch trim incorrectly

Post by DHenriques_ »

After all the technical stuff has been read you can break trim down to a very simple understanding. Consider trim as your "helper". You FLY the airplane using the main controls, the yoke, the rudder, and the throttle. You TRIM the airplane AFTER using the main controls to put the airplane where you want it to be and doing what you want it to do......................THEN you use your trim to remove any pressure off the main controls so that the job of maintaining the airplane where you have it is easier for you. The basic rule for trim is that no matter where you are in the sky and no matter what you are doing, the airplane should always be in trim or very near to being in trim as it is during your flare when landing.
This explains in very basic terms what the trim does. How you use the trim is even easier. Remember this simple rule and you won't go wrong;
NOSE.......POWER.......TRIM. It's that simple really. Put the nose where you want it and hold it there. Adjust the power. Trim the airplane.
This basically covers pitch trim. If you have other trims available such as aileron and rudder trim, they are usually used to "maintain" a trimmed condition if necessary. Fuel burn for example might produce an imbalance in flight. Aileron trim will help with that. Rudder trim can be set and used to help trim after a power change if needed.
Just consider trim as a secondary control to make your job of using the main controls easier and you are pretty much in the ball park.
Dudley Henriques

User avatar
Styggron
Master Sergeant
Posts: 1031
Joined: 30 Oct 2015, 14:28

Re: I think I am using Pitch trim incorrectly

Post by Styggron »

DHenriquesA2A wrote:After all the technical stuff has been read you can break trim down to a very simple understanding. Consider trim as your "helper". You FLY the airplane using the main controls, the yoke, the rudder, and the throttle. You TRIM the airplane AFTER using the main controls to put the airplane where you want it to be and doing what you want it to do......................THEN you use your trim to remove any pressure off the main controls so that the job of maintaining the airplane where you have it is easier for you. The basic rule for trim is that no matter where you are in the sky and no matter what you are doing, the airplane should always be in trim or very near to being in trim as it is during your flare when landing.
This explains in very basic terms what the trim does. How you use the trim is even easier. Remember this simple rule and you won't go wrong;
NOSE.......POWER.......TRIM. It's that simple really. Put the nose where you want it and hold it there. Adjust the power. Trim the airplane.
This basically covers pitch trim. If you have other trims available such as aileron and rudder trim, they are usually used to "maintain" a trimmed condition if necessary. Fuel burn for example might produce an imbalance in flight. Aileron trim will help with that. Rudder trim can be set and used to help trim after a power change if needed.
Just consider trim as a secondary control to make your job of using the main controls easier and you are pretty much in the ball park.
Dudley Henriques
Hello Dudley, thank you so much. Every time after speaking with you, things always make far more sense.

Ok so when I am descending, and I use my controls, I set the trim to remove pressure of my touching the controls.

This is what I think might be my mistake
1. If I need to pitch down a little I don't touch the control, instead I use pitch trim to point me down a little

This is wrong from my understanding of what you wrote yes ?
Accufeel V2, C172 , B377+L049+COTS, B17G, Piper Cub,Commanche,Cherrokee,Spitfire,Bonanza, P47,P40,both Mustangs
Aircraft Factory Avro Anson, Albatros DIII,Heinkel He-219, F4U Corsair, P51H Mustang, Avro 504, BF109
Watch my incompetent flying Twitch

User avatar
DHenriques_
A2A Chief Pilot
Posts: 5711
Joined: 27 Mar 2009, 08:31
Location: East Coast United States

Re: I think I am using Pitch trim incorrectly

Post by DHenriques_ »

Styggron wrote:
DHenriquesA2A wrote:After all the technical stuff has been read you can break trim down to a very simple understanding. Consider trim as your "helper". You FLY the airplane using the main controls, the yoke, the rudder, and the throttle. You TRIM the airplane AFTER using the main controls to put the airplane where you want it to be and doing what you want it to do......................THEN you use your trim to remove any pressure off the main controls so that the job of maintaining the airplane where you have it is easier for you. The basic rule for trim is that no matter where you are in the sky and no matter what you are doing, the airplane should always be in trim or very near to being in trim as it is during your flare when landing.
This explains in very basic terms what the trim does. How you use the trim is even easier. Remember this simple rule and you won't go wrong;
NOSE.......POWER.......TRIM. It's that simple really. Put the nose where you want it and hold it there. Adjust the power. Trim the airplane.
This basically covers pitch trim. If you have other trims available such as aileron and rudder trim, they are usually used to "maintain" a trimmed condition if necessary. Fuel burn for example might produce an imbalance in flight. Aileron trim will help with that. Rudder trim can be set and used to help trim after a power change if needed.
Just consider trim as a secondary control to make your job of using the main controls easier and you are pretty much in the ball park.
Dudley Henriques
Hello Dudley, thank you so much. Every time after speaking with you, things always make far more sense.

Ok so when I am descending, and I use my controls, I set the trim to remove pressure of my touching the controls.

This is what I think might be my mistake
1. If I need to pitch down a little I don't touch the control, instead I use pitch trim to point me down a little

This is wrong from my understanding of what you wrote yes ?
Yes. You don't want to ever get in the habit of flying the airplane with the trim. This being said I will state one exception to this rule. On a long cross country, sometimes, especially in smooth air, some pilots including myself, will trim out for a specific power setting then use trim to make very minute corrections to maintain altitude Doing this is especially handy using electric trim as in some high performance airplanes................but I put in a strong caveat here. This is an exception and is considered to be a "lazy practice for lazy bored pilots
:-)
But basically speaking, for an average flight when any pitch change is made you first make the change with the yoke or stick, then you adjust the power, and then you re-trim the airplane to the new configuration.
Nose;power;trim!
Dudley Henriques

User avatar
Styggron
Master Sergeant
Posts: 1031
Joined: 30 Oct 2015, 14:28

Re: I think I am using Pitch trim incorrectly

Post by Styggron »

DHenriquesA2A wrote:
Styggron wrote:
DHenriquesA2A wrote:After all the technical stuff has been read you can break trim down to a very simple understanding. Consider trim as your "helper". You FLY the airplane using the main controls, the yoke, the rudder, and the throttle. You TRIM the airplane AFTER using the main controls to put the airplane where you want it to be and doing what you want it to do......................THEN you use your trim to remove any pressure off the main controls so that the job of maintaining the airplane where you have it is easier for you. The basic rule for trim is that no matter where you are in the sky and no matter what you are doing, the airplane should always be in trim or very near to being in trim as it is during your flare when landing.
This explains in very basic terms what the trim does. How you use the trim is even easier. Remember this simple rule and you won't go wrong;
NOSE.......POWER.......TRIM. It's that simple really. Put the nose where you want it and hold it there. Adjust the power. Trim the airplane.
This basically covers pitch trim. If you have other trims available such as aileron and rudder trim, they are usually used to "maintain" a trimmed condition if necessary. Fuel burn for example might produce an imbalance in flight. Aileron trim will help with that. Rudder trim can be set and used to help trim after a power change if needed.
Just consider trim as a secondary control to make your job of using the main controls easier and you are pretty much in the ball park.
Dudley Henriques
Hello Dudley, thank you so much. Every time after speaking with you, things always make far more sense.

Ok so when I am descending, and I use my controls, I set the trim to remove pressure of my touching the controls.

This is what I think might be my mistake
1. If I need to pitch down a little I don't touch the control, instead I use pitch trim to point me down a little

This is wrong from my understanding of what you wrote yes ?
Yes. You don't want to ever get in the habit of flying the airplane with the trim. This being said I will state one exception to this rule. On a long cross country, sometimes, especially in smooth air, some pilots including myself, will trim out for a specific power setting then use trim to make very minute corrections to maintain altitude Doing this is especially handy using electric trim as in some high performance airplanes................but I put in a strong caveat here. This is an exception and is considered to be a "lazy practice for lazy bored pilots
:-)
But basically speaking, for an average flight when any pitch change is made you first make the change with the yoke or stick, then you adjust the power, and then you re-trim the airplane to the new configuration.
Nose;power;trim!
Dudley Henriques
Understood.

So what is the problem is I make changes with the trim instead of the controls. The results seem to be the same. I want to pitch down a little, I just trim down and down she goes without touching the controls.
Accufeel V2, C172 , B377+L049+COTS, B17G, Piper Cub,Commanche,Cherrokee,Spitfire,Bonanza, P47,P40,both Mustangs
Aircraft Factory Avro Anson, Albatros DIII,Heinkel He-219, F4U Corsair, P51H Mustang, Avro 504, BF109
Watch my incompetent flying Twitch

User avatar
Oracle427
Chief Master Sergeant
Posts: 3916
Joined: 02 Sep 2013, 19:30
Location: 3N6
Contact:

Re: I think I am using Pitch trim incorrectly

Post by Oracle427 »

You can't set and hold an attitude with trim. You'll end up chasing it all over the place while you wait for oscillations to end. On the other hand if you set and hold a pitch with the yoke and then relieve pressure with the trim, the aircraft will remain the way you trimmed it without oscillations.

This also you to precisely set and fix attitude and performance with minimum delay.
Flight Simmer since 1983. PP ASEL IR Tailwheel
N28021 1979 Super Viking 17-30A

User avatar
Styggron
Master Sergeant
Posts: 1031
Joined: 30 Oct 2015, 14:28

Re: I think I am using Pitch trim incorrectly

Post by Styggron »

Oracle427 wrote:You can't set and hold an attitude with trim. You'll end up chasing it all over the place while you wait for oscillations to end. On the other hand if you set and hold a pitch with the yoke and then relieve pressure with the trim, the aircraft will remain the way you trimmed it without oscillations.

This also you to precisely set and fix attitude and performance with minimum delay.
Ummmm actually I can.
Say I am at 3000 ft and I want to go down a little. I just use the trim to point me down a little and down I go slowly. When I want to level off I just pitch trim up a little and I level off.

simple.
If I want to make a more drastic change I use the controls else I tend to just use the pitch trim to get me higher or lower which is clearly wrong but it seems to work.

This is why I asked what is the consequence of doing it this way. No idea what you mean by "oscillations" do you mean instability ? fluctuations ?
Accufeel V2, C172 , B377+L049+COTS, B17G, Piper Cub,Commanche,Cherrokee,Spitfire,Bonanza, P47,P40,both Mustangs
Aircraft Factory Avro Anson, Albatros DIII,Heinkel He-219, F4U Corsair, P51H Mustang, Avro 504, BF109
Watch my incompetent flying Twitch

User avatar
Oracle427
Chief Master Sergeant
Posts: 3916
Joined: 02 Sep 2013, 19:30
Location: 3N6
Contact:

Re: I think I am using Pitch trim incorrectly

Post by Oracle427 »

What airspeed, power and pitch attitude are you using for the descent? Is it what you wanted or you just took what you got? How would you make sure you started and ended your descent and made it at the desired spee performance so that you were at the desired point at the end of your descent?

The correct procedure requires one to use specific speeds, power settings and a stable attitude.

There's a lot more to it than just, "go down" when you are a pilot vs just flying a plane. Don't take this the wrong way, I'm not putting down what you are doing, but these are the reasons that you asked about. :)
Flight Simmer since 1983. PP ASEL IR Tailwheel
N28021 1979 Super Viking 17-30A

User avatar
Styggron
Master Sergeant
Posts: 1031
Joined: 30 Oct 2015, 14:28

Re: I think I am using Pitch trim incorrectly

Post by Styggron »

Oracle427 wrote:What airspeed, power and pitch attitude are you using for the descent? Is it what you wanted or you just took what you got? How would you make sure you started and ended your descent and made it at the desired spee performance so that you were at the desired point at the end of your descent?

The correct procedure requires one to use specific speeds, power settings and a stable attitude.

There's a lot more to it than just, "go down" when you are a pilot vs just flying a plane. Don't take this the wrong way, I'm not putting down what you are doing, but these are the reasons that you asked about. :)
Oh I know this is not the right procedure absolutely. I understand. I am just trying to understand the "Why". Saying it is not procedure is not an explanation. Understanding requires knowing the "whys".

You are 100% spot on, I am indeed asking what are the consequences because I am not doing this correctly. Everyone states use the controls to get what you want and then trim to put the pressure off etc.

But when I am at stable flight and I want to "go up a bit" I just trim up and increase throttle if I have to.
If I want to "go down a bit" I trim down and decrease throttle if I have to

All that depends where I am and what I'm doing at the time.
I control the descent with the throttle generally. How would I make sure I started and ended ? easy. If I want to go up a bit I trim up, if I want down I trim down, if I want to level off I make little trim adjustments, it is fairly stable.

How do I do speed ? flaps and throttle. :)
It always works.

I am sure these are VERY bad habits. It leads to a situation that during landing I pitch down with trim to get me down. This is VERY dangerous in reality I was told. This is an example of "bad habits".
Accufeel V2, C172 , B377+L049+COTS, B17G, Piper Cub,Commanche,Cherrokee,Spitfire,Bonanza, P47,P40,both Mustangs
Aircraft Factory Avro Anson, Albatros DIII,Heinkel He-219, F4U Corsair, P51H Mustang, Avro 504, BF109
Watch my incompetent flying Twitch

User avatar
Oracle427
Chief Master Sergeant
Posts: 3916
Joined: 02 Sep 2013, 19:30
Location: 3N6
Contact:

Re: I think I am using Pitch trim incorrectly

Post by Oracle427 »

Well the big picture is missing for starters.

Why are you going up or down? Do you want smoother air or is there a big mountain up ahead? You might want to climb at Vx for the latter and at cruise climb speed for the forner.
What is your target altitude? Are you VFR or IFR? The altitude you need to go to depends on many rules.
What is your groundspeed? For a descent using the 3/6 rule, this is the input you use to select to vertical speed (6 x GS)
What is the distance before you need to be at that altitude? Multiply the thousands of feet to descend to determine the distance you need.

These are some immediate questions that would pop ip in my mind.

Now on e you wish to execute the action it is just a matter of conducting the aircraft, letting it stabilize and then trimming out. These are significant enough changes that trying to trim them in would be challenging and requiring too much attention.
Flight Simmer since 1983. PP ASEL IR Tailwheel
N28021 1979 Super Viking 17-30A

User avatar
Styggron
Master Sergeant
Posts: 1031
Joined: 30 Oct 2015, 14:28

Re: I think I am using Pitch trim incorrectly

Post by Styggron »

Oracle427 wrote:Well the big picture is missing for starters.

Why are you going up or down? Do you want smoother air or is there a big mountain up ahead? You might want to climb at Vx for the latter and at cruise climb speed for the forner.
What is your target altitude? Are you VFR or IFR? The altitude you need to go to depends on many rules.
What is your groundspeed? For a descent using the 3/6 rule, this is the input you use to select to vertical speed (6 x GS)
What is the distance before you need to be at that altitude? Multiply the thousands of feet to descend to determine the distance you need.

These are some immediate questions that would pop ip in my mind.

Now on e you wish to execute the action it is just a matter of conducting the aircraft, letting it stabilize and then trimming out. These are significant enough changes that trying to trim them in would be challenging and requiring too much attention.
Hi Oracle
1. Up or down, depends what I want
2. If there is a mountain ahead I take the controls
3. Climb vx ? no idea what vx is sorry
4. target altitude ? depends what I want at the time I guess. I set alt capture and it's done
5. VFR IFR I am generally VFR
6. Ground speed ? no idea I don't look at that I check airspeed only
7. 3/6 rule ? sorry not heard of that
8. What is the distance I need to be before that altitude ? This is something I choose completely when just flying around.

Like I said. I just trim pitch up if I want to go up a bit and down if I want to go down a bit. It all works.

Despite that it all works the incorrect way I do things I will try Dudley's method. Use controls then use trim to take the pressure off. If you need to adjust, controls again, and then trim.
Accufeel V2, C172 , B377+L049+COTS, B17G, Piper Cub,Commanche,Cherrokee,Spitfire,Bonanza, P47,P40,both Mustangs
Aircraft Factory Avro Anson, Albatros DIII,Heinkel He-219, F4U Corsair, P51H Mustang, Avro 504, BF109
Watch my incompetent flying Twitch

User avatar
Oracle427
Chief Master Sergeant
Posts: 3916
Joined: 02 Sep 2013, 19:30
Location: 3N6
Contact:

Re: I think I am using Pitch trim incorrectly

Post by Oracle427 »

I'm just answering your question, I understand that you aren't flying using standard procedures.

Very generally speaking if you are talking to ATC and they tell you to climb or descend to an altitude, they expect a minimum of a 500FPM rate. If you can't maintain that rate which is possible due to a hot day in a heavy plane at high power setting, you need to advise them that you are unable.

2. If there is a mountain ahead I take the controls
So how do you plan to ensure that you climb at the fastest rate or angle to clear the mountain. I was actually wrong when I typed Vx on my bus ride home. I meant Vy. Vy is the airspeed that provide the best RATE of climb at a given altitude and loading. At this speed you'll get your best sustained vertical climb speed.

3. Climb vx ? no idea what vx is sorry
Vx is the best angle of climb. It allows you to cover the least lateral distance while climbing, but it trades climb rate to minimize distance.

4. target altitude ? depends what I want at the time I guess. I set alt capture and it's done
There are VFR altitudes to fly depending on your heading to help with separation from other aircraft. Could be risky to be at the wrong altitude going the wrong way in a busy airspace.

6. Ground speed ? no idea I don't look at that I check airspeed only
Ground speed is very important in flight planning. One needs to keep track of their progress over the ground to determine how much time they'll need to get to their distination. Fuel consumption is based on time at a given power setting. This is also important when determining where you will be or need to be when changing altitudes, turning, planning to avoid obstacles, etc.

7. 3/6 rule ? sorry not heard of that
3/6 rule helps in descent planning. 3xaltitude in thousands of feet to descend = distance to begin descending and 6xgroundspeed = rate of descent. Using this rule you should generally be able to arrive fairly close to a point over the ground at the desired altitude from a higher altitude.

8. What is the distance I need to be before that altitude ? This is something I choose completely when just flying around.
For VFR flying around without a plan outside of busy airspace, this is perfectly okay. When you get near busy areas or arrive at a busy airport, you need to be at the right altitude at the right place to ensure orderly entry into the traffic pattern.

There is a lot of constant evaluation decision making going on and a lot of structure to make the behavior measurable, predicatable and therefore safer. If everyone just goes and does anything it can get very confusing and dangerous. Anyway, in the sim world none of this applies, but just background.

The trim is a tool and like any tool it can be used incorrectly to the detriment of the user.
Flight Simmer since 1983. PP ASEL IR Tailwheel
N28021 1979 Super Viking 17-30A

new reply

Return to “Flight Academy”

Who is online

Users browsing this forum: No registered users and 7 guests