Is there a proper technique to trimming?

[guitarxe]

I take off, establish a level flight, and now try to trim. In this particular example I have to push the stick forward in order to keep a level flight, so I press on the trim down button several time (or rather, I hold it down), until the aircraft begins to pitch down. At this point I start to move the stick slowly back to neutral position while still applying trim, hoping that I can match the rate of pitch change from the trimmer with the rate of pitch change from the stick, until the point where the stick is in neutral and the pitch from the trimmer is now enough to keep me level.

 

However, that never seems to work out for me. I either end up overshooting and applying too much trim, or I end up moving the stick back to neutral before there is enough trim and the airplane pitches up.

 

What's even worse is that, if I make any changes to the aircraft, such as increase/decrease thrust or make a turn, I now have to again re-adjust my trim.

 

In other words, I'm a complete newbie to flying and would like to know if there are some kind of established techniques to proper use of trim, or maybe some tips on how to go about doing it. I've flown the A-10C and the KA-50 modules of DCS and they both have autopilot that can stabilise your flight for you, so I'm not used to manually trimming all the time and seem to be very bad at it.

[lleviatan]

Hello guiterxe

 

 

 

Trimming is an art in the SU-25, we would need to know what the reality on the actual SU-25. Any partner who can enlighten us on this topic

 

 

 

regards

[aaron886]

Doubt you'll find any SU-25 pilots to answer, but aircraft tend to work in predictable ways so I think I can help you.

 

In a real airplane, we trim to relieve control pressures. This means you will HOLD the aircraft in a desired attitude, then trim while releasing pressure until you do not have to hold the aircraft there anymore. DO NOT "fly with trim," which is to use the trim control to adjust attitude.

 

However, that never seems to work out for me. I either end up overshooting and applying too much trim, or I end up moving the stick back to neutral before there is enough trim and the airplane pitches up.

You're falling prey to the aircraft's natural stability tendency. (In this case, what is known as the phugoid mode, long-period stability, or dynamic stability.) If you displace an aircraft, over a relatively long period of time (30 seconds to multiple minutes,) it will undergo gradually decreasing oscillations of altitude. Aircraft equipped with a automatic trimming system may feature little to no phugoid mode, and simulator aircraft with simplified or poor flight models may not display this. The SU-25 in DCS does, and you will have to account for that. The good news is, knowing is half the battle, so you should be roughly half-way there! :smilewink:

 

To solve this problem I would recommend "testing" your trim applications with small, momentary releases of control pressure as you trim, but remember that you MUST control the aircraft's attitude to achieve the desired effect. If you want to trim for level flight, hold a pitch attitude that corresponds with level flight.

 

What's even worse is that, if I make any changes to the aircraft, such as increase/decrease thrust or make a turn, I now have to again re-adjust my trim.

 

That's the nature of the beast. We teach pilots to build a habit of correct and constant trimming because that's the way 99% of the world's aircraft must be flown. As your experience level increases, you will hopefully find that it becomes instinctive. Primarily, you should be re-trimming for airspeed and weight changes. (read: dropped stores)

 

 

Let me know if this helps, it's a potentially deep subject and I was forced to leave many gaps as I head for work.

[Britchot]

The fixed wing aircraft trim differently than the helos. What it sounds like is you're trimming how I do on the UH-1H.

 

Aaron886 hit the nail on the head, without the control pressure, it's somewhat difficult to estimate. I'm just going to post to emphasize to use small increments until you get the desired attitude. This goes for yaw and roll as well.

 

1. Push forward on the stick to keep the aircraft level.

2. Trim nose down 1-3 "clicks"

3. Release the stick to neutral and evaluate the aircraft's attitude.

4. Repeat 1-3 as necessary.

 

This goes the same for the A-10C, which you have to trim every time you release a bomb!

[guitarxe]

Thanks, guys, I really appreciate it! I've tried setting trim more gradually, and testing each time, like you suggested, and this has worked much better now! I am sure with more practice I can become even better at it :)

 

About the phugoid mode. I've read the article on it on wikipedia and have a basic understanding what it is, but the article doesn't mention how an aircraft enters this state, or what to do about it.

From what I understand, this is a state the aircraft will enter by itself depending the aircraft's aerodynamic properties, and not because the pilot did something wrong, correct?

 

I also understand that eventually the aircraft will leave this state and resume level flight, in which case the pilot should do nothing about it? Or is there something I should do? Because it seems to me if I try to correct pitch during this state it will only serve to make it worse? Like trying to rock a boat that's already rocking from the waves underneath it?