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Questions About The Horizontal Tail On A CRJ?  
User currently offlineMr spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Posted (9 years 4 months 3 days 19 hours ago) and read 6417 times:

Hi guys.

What are the 2 white boxes that can be seen in this photo inside the top of the tail of this CRJ-100 used for? (due aft of the leading edge's top). They look like small actuators that are connected to the larger round disc shaped objects below. Is that what they are... actuators?


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Photo © Stephan Kruse



It appears to me from looking at outside photos of CRJ's tails that the horizontal stabilizer's angle of incidence is variable. Are the white boxes/actuators in the photo above what moves this surface?


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Photo © Jerry Search



All of the CRJ aircraft versions appear to have a horizontal stabilizer that can move, and an elevator. How do they work regarding pitch changes & trim?

Does the elevator control pitch changes via the cockpit control columns, and the horizontal stab controls fine trim adjustments during cruise flight ....for example?

I'm a little confused about how some airliner's T-Tails work. Especially after reading posts about how the "flying tails" on MD-80 series jets work.  scratchchin 

Thanks,

Chris  Smile


"Just a minute while I re-invent myself"
17 replies: All unread, jump to last
 
User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4211 posts, RR: 37
Reply 1, posted (9 years 4 months 3 days 19 hours ago) and read 6402 times:

Those look like the stab trim actuators. Just a guess.  Smile We have two stab trim channels, which are electrically driven...so it would make sense.


Chicks dig winglets.
User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 2, posted (9 years 4 months 3 days 19 hours ago) and read 6392 times:

Hello XFSUgimpLB41X.

Thanks for your reply. Big grin

OK, so it sounds like it is the horizontal stabilizer that's used for trimming pitch (via those 2 actuators)....and not a trim tab on the elevator like in a little Cessna-150.

Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4211 posts, RR: 37
Reply 3, posted (9 years 4 months 3 days 19 hours ago) and read 6372 times:

Oh yeah..forgot to mention.. the entire plane of the stabilizer moves when we trim, unlike a cessna.


Chicks dig winglets.
User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 4, posted (9 years 4 months 3 days 19 hours ago) and read 6362 times:

Hello XFSUgimpLB41X.

"Oh yeah..forgot to mention.. the entire plane of the stabilizer moves when we trim, unlike a cessna."

Thanks for clearing that up for me. Big grin It was just one of those things I wasn't sure about.

Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineRadialman From Canada, joined Aug 2001, 33 posts, RR: 0
Reply 5, posted (9 years 4 months 3 days 16 hours ago) and read 6142 times:

There are actually 4 white boxes.2 for left hand side elevator and 2 for right hand side.The top little box is the pitch feel linear actuator and the bigger one below on the same side is the pitch feel simulator unit.
The pitch feel simulators supply the pilots with the necessary positive feel force to help control the aircraft. Its basically the feel the pilot gets when he/she moves the control column to move the elevators for a pitch up or pitch down movement.

The horizontal−stabilizer control−surface system contains the horizontal stabilizer. The horizontal stabilizer supplies longitudinal (pitch) trim to the aircraft, and is moved up or down by the operation of the horizontal stabilizer trim actuator (HSTA).
The range of horizontal stabilizer movement is from +2 degrees (leading edge up)to −13 degrees (leading edge down).
Operation
A. When the HSTA is operated, the driven nut of the HSTA moves the horizontal stabilizer up or down in relation to the horizontal−stabilizer pivot axis. The operation of the horizontal stabilizer causes a pitching movement of the aircraft to occur. When the leading edge of the horizontal stabilizer moves up, the nose of the aircraft moves down.
When the leading edge of the horizontal stabilizer moves down, the nose of the aircraft moves up.
B. Movement of the horizontal stabilizer is transmitted to the input linkage of the elevator power control units (PCU). These elevator PCU inputs occur because of the geometric relationship between the horizontal−stabilizer pivot axis and the input linkage of the elevator PCU. The movement of the elevators increases the performance of the horizontal stabilizer.


Hope this helps.
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User currently offlineDc8friendship From United States of America, joined Apr 2005, 243 posts, RR: 3
Reply 6, posted (9 years 4 months 3 days 1 hour ago) and read 5592 times:

Quoting Mr spaceman (Thread starter):
I'm a little confused about how some airliner's T-Tails work. Especially after reading posts about how the "flying tails" on MD-80 series jets work.

Most large jet aircraft today have the "flying tail" as a means for controlling the trim of the aircraft. this allows for greater flexibity in CG area, and allows the controls to stay streamlined to reduce drag.



Come fly the Friendly Skies of United
User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 7, posted (9 years 4 months 1 day 20 hours ago) and read 5505 times:

Hi guys.

>> Radialman, that's excellent information. Thank You, for explaining how the two sets of boxes up there in the tail work, etc.

Quoting Radialman (Reply 5):
The pitch feel simulators supply the pilots with the necessary positive feel force to help control the aircraft.

It's interesting to learn that the forces the pilots feel through the control column during pitch changes are not based on just natural aerodynamic forces on the elevator, but are aided by the pitch feel simulators. I guess other airliner types use this equipment too.

>> Dc8friendship .........

Quoting Dc8friendship (Reply 6):
Most large jet aircraft today have the "flying tail" as a means for controlling the trim of the aircraft. this allows for greater flexibity in CG area, and allows the controls to stay streamlined to reduce drag.

Thank You, for your explanation. You have me wondering though, by "large jet aircraft", do you also mean airliners with conventional type tails at the back of the fuselage .... not just large T-Tail aircraft?

Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineJeb94 From United States of America, joined Oct 2004, 603 posts, RR: 5
Reply 8, posted (9 years 4 months 3 hours ago) and read 5430 times:

If you take a close look at even conventionally tailed aircraft you may be able to see little rub marks where the horizontal gap seals are rubbing on the empennage. Normal and harmless but gives a great clue as to the normal movement range of the horizontal. Even on the old DC9 family the pilots don't feel the natural forces on the tail. Douglas used 'Load Feel' springs to allow the pilot to feel a load. The rudder, elevator, and aileron controls all have these. Again, the entire horizontal moves with the use of the infamous jackscrew driven by electrical motors coupled through a gearbox.

User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 9, posted (9 years 3 months 4 weeks 1 day 10 hours ago) and read 5393 times:

Hi guys,

After reading Dc8friendship's words .....

"Most large jet aircraft today have the "flying tail".

As well as Jeb94's words .........

Quoting Jeb94 (Reply 8):
If you take a close look at even conventionally tailed aircraft you may be able to see little rub marks where the horizontal gap seals are rubbing on the empennage.

...... I did a photo search and gave up on trying to find a modern airliner that doesn't have a "Flying tail", whether or not the aircraft's Horizontal Stab is in a conventional location or it has a T-tail.

>> Jeb94, Thank You, for your very good info. Big grin


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Radialman, explained the CRJ's Horizontal Stab's range of movement in degrees in this statement ....

Quoting Radialman (Reply 5):
The range of horizontal stabilizer movement is from +2 degrees (leading edge up)to −13 degrees (leading edge down).

It appears that all airliner's Horizontal Stab's leading edge can move down a lot more than up ...... which makes perfect sense to me based on how much Stab deflection is needed to either help an airliner oppose gravity or fall with it.

The ERJ-175's Horizontal Stab in the one photo above seems to have an almost equal range of movement up or down (according to the leading edge degrees markings), unlike the A319 in this photo ......


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Photo © Michael Carter




Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1610 posts, RR: 52
Reply 10, posted (9 years 3 months 3 weeks 5 days 22 hours ago) and read 5312 times:
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One tiny correction Mr Spaceman: In your last post you include a picture of a L-1011's horizontal tail. The L-1011 is an exception, in that it has no elevators. The entire horizontal tail moves for trim and to provide control. This is commonly called a stabilator. Most jet fighter aircraft have stabilators.


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Otherwise, on most transport aircraft, the forward part of the horizontal tail (the stabilizer) moves for trim and the aft part (the elevator) moves for control. Other exceptions, in the business jet category, are the Lockheed JetStar, where the entire tail (including the vertical tail) moves for trim, while the elevator provides control and the HS.125/Hawker 800 series, where the stabilizer is fixed and the elevator provides both trim and control.


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User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 11, posted (9 years 3 months 3 weeks 5 days 18 hours ago) and read 5293 times:

Hello AeroWeanie.

Thanks for your information. Big grin OK, I understand now that an L-1011 is an exception .... it has no elevators. The entire horizontal tail moves to provide both pitch control & trim. (My first ever airliner flight was to {& from} Atlantic City (KACY) on this Worldways Canada L-1011 - a GREAT aircraft!  spin  )


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Your comments .........

Quoting AeroWeanie (Reply 10):
This is commonly called a stabilator. Most jet fighter aircraft have stabilators.

Yeah, it's amazing to watch the stabilators on a fighter jet moving so quickly (with the left & right sides moving individually) from computer commands during short final .... especially during an aircraft carrier landing!

I guess an L-1011's stabilators don't move individually .... L-1011's don't get into to many "Dog Fights!"  Silly

Question .......

Does the MD-11 also have a stabilator like an L-1011? The one in this photo sure looks like it does.


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Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1610 posts, RR: 52
Reply 12, posted (9 years 3 months 3 weeks 5 days 16 hours ago) and read 5276 times:
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Quoting Mr Spaceman (Reply 11):
Does the MD-11 also have a stabilator like an L-1011? The one in this photo sure looks like it does.

The MD11 has a conventional stabilizer/elevator combination. In the picture you refer to, the elevator is in trail with the stabilizer, so its hard to see. Look closely at the tip and you can see evidence of the elevator.


User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 13, posted (9 years 3 months 3 weeks 4 days 19 hours ago) and read 5228 times:

Hello AeroWeanie.

OK, Thank You Sir, for letting me know that an MD-11 has a conventional stabilizer/elevator combination.

Here's a few photos that show the separate elevator a bit better.


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Photo © Justin Idle
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Photo © Benedikt Pressburger



After a photo search, it appears to me that the horizontal stabilizer (not the elevator) plays a more active roll in pitch control during landing than during takeoff. But then again, it may not actually be that way, it may just look like that because of when the photos were taken.

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Photo © Roy Loyson



Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1610 posts, RR: 52
Reply 14, posted (9 years 3 months 3 weeks 4 days 13 hours ago) and read 5198 times:
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A pilot uses trim to reduce the control forces required to maneuver the aircraft. In landing, large control deflections are required to flare the aircraft. The stabilizer is moved to trim the aircraft so as to minimize the amount of force the pilot needs to exert to move the elevator to perform the flare.

User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 15, posted (9 years 3 months 3 weeks 3 days 21 hours ago) and read 5165 times:

Hello AeroWeanie.

Thank You, for that explanation.

It feels good to have confusion about how an aircraft works "removed from my mind!!!"  spin 

Chris  Smile



"Just a minute while I re-invent myself"
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 16, posted (9 years 1 day 11 hours ago) and read 4909 times:

Quoting Mr Spaceman (Reply 11):
Thanks for your information. OK, I understand now that an L-1011 is an exception .... it has no elevators.

The L-1011 is the only airline with a flying stabilizer, the entire horizontal stabilizer moves to provide both pitch and pitch trim control. It also has two elevators in the trailing edge. The elevators are geared to stabilizer movement. When the stabilizer moves nose down, the elevators move up. This aids in low speed pitch control. When the stabilizer is moved full nose up the elevators are faired.


User currently offlineCrjmech From United States of America, joined Jun 2000, 260 posts, RR: 1
Reply 17, posted (9 years 1 day 10 hours ago) and read 4884 times:

Mr. Spaceman- just FYI, the horizontal stab trim actuator is barely visible in the first pic you posted. It's the black device just aft of the elevator pitch feel assy. It's partially obscured by the small bulkhead.

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