Sign in to follow this  
cagrikartal

747 v3 Trimming logic

Recommended Posts

hello everyone,

 

 

Do you think 747 has a trimming logic closer to the 777 or the 737 ? or Neither  ?

 

 

 

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

The trim in the 777 is very different from most other ac ive flown (sim). The trim there controls speed mostly, while in the 737 it controls pitch. I think the trim is closer related tonthe 737 than the 777. 

Share this post


Link to post
Share on other sites

hmm how about -8 ?I heard it has new fency stuf on it :Tounge:  like fbw etc....

 

It does not have elevator/stab FBW like the 777 or 787, the only FBW on the 748 is the roll channel. Pitch is 100% conventional just like the 400.

The trim in the 777 is very different from most other ac ive flown (sim). The trim there controls speed mostly, while in the 737 it controls pitch. I think the trim is closer related tonthe 737 than the 777. 

 

Trim in any airplane controls the speed the airplane tries to return to with your hands off the controls. If you trim out the control forces in a Cessna flying at 80 knots, then speed up or slow down, the plane will pitch and try to return to 80 (through a series of phugoid oscillations of course, but eventually it will dampen out at 80). The 777/787 trim system is essentially a software simulation of the way a normal airplane trims. The system is 100% FBW at all times, but to the pilots it behaves conventionally in that it'll return to whatever speed the airplane is trimmed for when displaced above or below it.

 

This was important to Boeing to retain physical cues that the airplane is in an out of trim situation - with the Airbus and similar systems that autotrim in their normal mode/law, you may not notice certain problems developing until they threaten the safety of the airplane. See the Perpignan A320 crash for instance - the airplane was getting progressively more and more out of trim in an unprotected FBW law and because there's no physical feedback, the pilots didn't realize it until it was too late and the system ran out of combined elevator/stab range. It would be really difficult for that to happen to a 777 or 787 because the control forces would become immense, letting them know to manually trim.

  • Upvote 1

Share this post


Link to post
Share on other sites

It would be really difficult for that to happen to a 777 or 787 because the control forces would become immense, letting them know to manually trim.

 

This is why in the sim we get the FBW in blue in the pfd to compansate the backforce of yoke as most of us dont have a motorised joystick or yoke.

 

Now, tell me i dont deserve a free 747v3 copy !!!   :dirol:

Share this post


Link to post
Share on other sites

 

 


This is why in the sim we get the FBW in blue in the pfd to compansate the backforce of yoke as most of us dont have a motorised joystick or yoke.

 

However, if you're having to maintain backpressure (or forward pressure) then you are out of trim... and you should be able to feel if you are holding pressure on the yoke/stick, regardless of whether you have force feedback or not ;)

 

As Ryan says, it's easy to overthink the 777 trim - it's a lot of complicated software to essentially make it behave almost exactly how an aeroplane with conventional controls does by itself. Just fly the aeroplane and trim to relieve the force on the controls, exactly like a C172.

  • Upvote 1

Share this post


Link to post
Share on other sites

However, if you're having to maintain backpressure (or forward pressure) then you are out of trim... and you should be able to feel if you are holding pressure on the yoke/stick, regardless of whether you have force feedback or not ;)

 

As Ryan says, it's easy to overthink the 777 trim - it's a lot of complicated software to essentially make it behave almost exactly how an aeroplane with conventional controls does by itself. Just fly the aeroplane and trim to relieve the force on the controls, exactly like a C172.

Yeah i still do over complicate it i guess :wink:

 

 

Ryan said 

"Trim in any airplane controls the speed the airplane tries to return to with your hands off the controls. If you trim out the control forces in a Cessna flying at 80 knots, then speed up or slow down, the plane will pitch and try to return to 80 (through a series of phugoid oscillations of course, but eventually it will dampen out at 80)"

 

I think why i complicate it is becuase i saw a video were the captain was using the trim on a 777 to change flight level i think

 

Michael Moe

Share this post


Link to post
Share on other sites

 

 

I think why i complicate it is becuase i saw a video were the captain was using the trim on a 777 to change flight level i think

 

You cont change flight level with trim only a decrease or increase in altitude window allows that or the pilot was flying manual.

Share this post


Link to post
Share on other sites

 

I think why i complicate it is becuase i saw a video were the captain was using the trim on a 777 to change flight level i think

 

You cont change flight level with trim only a decrease or increase in altitude window allows that or the pilot was flying manual.

he was flying manually - 

 

Michael Moe

Share this post


Link to post
Share on other sites

 

I think why i complicate it is becuase i saw a video were the captain was using the trim on a 777 to change flight level i think

He was demonstrating how trim works in 777.. Not using trim to change flight level....

 

You cont change flight level with trim only a decrease or increase in altitude window allows that or the pilot was flying manual.

Share this post


Link to post
Share on other sites

 

I think why i complicate it is becuase i saw a video were the captain was using the trim on a 777 to change flight level i think

 

You cont change flight level with trim only a decrease or increase in altitude window allows that or the pilot was flying manual.

I think all flight instructors teach their students to fly the trim...., this doesn't mean you use trim instead of elevator pressure but that you learn to fly attitude and trim the control forces.  Even with manual trim in a Cessna, one hand on the yoke and the other on the trim wheel. It's becomes second nature and occurs without thinking about it.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this