TravelAVNut From Netherlands, joined May 2010, 1409 posts, RR: 5 Posted (2 years 7 months 2 weeks 1 day 10 hours ago) and read 1895 times:
One for the Pilots!
So I was watching this random take-off video at Youtube containing a lot of turns just after take-off, presumably at climb thrust. And this got me wondering; do the handling characteristics of 2 or 4 engined airliners change with higher/low thrust settings?
I can imagine that having 1 or 2 fixed points per wing where the pulling force of the engine can increase/decrease dramaticly have some effect on the way the airplane flies? Maybe pitch moments or some force on the controls?
UAL747 From , joined Dec 1969, posts, RR: Reply 1, posted (2 years 7 months 2 weeks 1 day 10 hours ago) and read 1881 times:
I'm not a pilot, but I think there is a pitch forward and back movement with thrust changes. But I think that's during the change only, as the energy changes. When you stabelize the thrust, it should have no bearing. (At least that's what I would assume).
Of course we all know that speed is the major factor in handling characteristics, and at higher speeds, the controls will be more "tight" so to speak.
I think manufacturers probably try to eliminate any type of handling issues that would arise from changes in thrust.
Mir From United States of America, joined Jan 2004, 19815 posts, RR: 56 Reply 2, posted (2 years 7 months 2 weeks 1 day 9 hours ago) and read 1863 times:
Quoting UAL747 (Reply 1): I'm not a pilot, but I think there is a pitch forward and back movement with thrust changes
There is, depending on the location of the engines. And it's a pitch up or pitch down moment, not forward or back.
Quoting UAL747 (Reply 1): But I think that's during the change only, as the energy changes. When you stabelize the thrust, it should have no bearing.
It's always there, actually. The only way to get rid of it is to trim off the additional control pressure, which is easy enough. But when you change power settings, you may need to re-trim if the change was significant enough.
-Mir
7 billion, one nation, imagination...it's a beautiful day
Pihero From France, joined Jan 2005, 3598 posts, RR: 72 Reply 3, posted (2 years 7 months 2 weeks 1 day 8 hours ago) and read 1847 times:
Quoting TravelAVNut (Thread starter): do the handling characteristics of 2 or 4 engined airliners change with higher/low thrust settings?
By design, the engine thrust lines are below the airplane CoG. Starting from a stabilised state,this means that an increased thrust will cause a pitch-up moment. and a decreased thrust a nose-down effect.
That is until you fly an FBW 'Bus in which the flight control systems keeps the aircraft in treim at all times.
DiamondFlyer From United States of America, joined Oct 2008, 1299 posts, RR: 3 Reply 4, posted (2 years 7 months 2 weeks 1 day 7 hours ago) and read 1845 times:
Quoting Pihero (Reply 3): By design, the engine thrust lines are below the airplane CoG.
On some airplanes. Its not like there aren't airplanes out there that have the thrust line above the CG, which reverses the things you said about pitch changes caused by throttle adjustments.
Pihero From France, joined Jan 2005, 3598 posts, RR: 72 Reply 5, posted (2 years 7 months 2 weeks 1 day 7 hours ago) and read 1841 times:
Quoting DiamondFlyer (Reply 4): Its not like there aren't airplanes out there that have the thrust line above the CG, which reverses the things you said about pitch changes caused by throttle adjustments.
Never heard of any airliner builkt that way. Could you provide some examples ?
Regards
DiamondFlyer From United States of America, joined Oct 2008, 1299 posts, RR: 3 Reply 6, posted (2 years 7 months 2 weeks 1 day 7 hours ago) and read 1831 times:
Quoting Pihero (Reply 5): Never heard of any airliner builkt that way. Could you provide some examples ?
Regards
Wow, so I figured this was obvious, but I'll go ahead and point them out. Any of the Dash 8 series, or the ATR 42/72. Surely you've heard of them.
Mir From United States of America, joined Jan 2004, 19815 posts, RR: 56 Reply 7, posted (2 years 7 months 2 weeks 1 day 4 hours ago) and read 1789 times:
Quoting Pihero (Reply 5): Never heard of any airliner builkt that way. Could you provide some examples ?
CRJs. Many business jets.
-Mir
7 billion, one nation, imagination...it's a beautiful day
pilotpip From United States of America, joined Sep 2003, 3084 posts, RR: 12 Reply 8, posted (2 years 7 months 2 weeks 1 day 3 hours ago) and read 1778 times:
Handling is effected much more by airspeed than power changes. While it's true that thrust will effect depending on where the engines are placed on the aircraft some FBW aircraft have thrust compensation built into the software. The ERJ-170 has thrust compensation.
Mir From United States of America, joined Jan 2004, 19815 posts, RR: 56 Reply 10, posted (2 years 7 months 2 weeks 1 day 1 hour ago) and read 1751 times:
Quoting UAL747 (Reply 9): Wouldn't the L-1011, DC-10, and MD-11, MD-80, 717, or anything with tail mounted engines also have a pitch down moment when thrust is applied?
In the case of the L1011, DC-10 and MD-11, the two wing-mounted engines provide a counter to the tail engine, so you'd probably still get a nose-up pitch moment with increased thrust in normal operation. If you manipulated the thrust of the tail engine only, however, then you would see the nose-down moment with an increase in thrust.
-Mir
7 billion, one nation, imagination...it's a beautiful day
Pihero From France, joined Jan 2005, 3598 posts, RR: 72 Reply 11, posted (2 years 7 months 2 weeks 19 hours ago) and read 1704 times:
Quoting DiamondFlyer (Reply 6): Any of the Dash 8 series, or the ATR 42/72. Surely you've heard of them.
Don't know about the -8 but I do the ATRs : Funny enough, push the throttle and you have a pitch-up movement, mainly due, in this case to the augmented lift caused by the accelerated airflow. I would be very surprised to hear the -8 behaving differently.
Quoting UAL747 (Reply 9): Wouldn't the L-1011, DC-10....,
I have some 4,000 hours on the 10-11 and she behaves as I said. The -10, I only know through the simulator. Nothing out of the ordinary here.
Quoting UAL747 (Reply 9): ...MD-80, 717, or anything with tail mounted engines also have a pitch down moment when thrust is applied?
Tested the MD-80 for a previous airline...Here again, nothing unexpected.
Let's face it, an airliner has to demonstrate *stability* in all axes. I therefore expect that airplane to show - on a short term reaction- a pitching moment to tend to keep the acftual airspeed steady.
Otherwise, the Sioux City DC-10 and the Baghdad A310 wouldn't have been so easy (!!!) to pilot with engines' thrust only.
NW747-400 From United States of America, joined Jun 1999, 488 posts, RR: 0 Reply 13, posted (2 years 7 months 2 weeks 17 hours ago) and read 1678 times:
Quoting Pihero (Reply 5): Never heard of any airliner builkt that way. Could you provide some examples ?
All CRJ models will pitch down when a thrust increase is commanded, and pitch up when the thrust is decreased. Seems like most airplanes with only tail mounted engines would behave in this manner? Anyone have any experience with the DC9/MD80 series? I'm curious to know about that.
To the OP, as long as all engines are operating normally and with equal thrust settings, there is no affect on the aircraft's turning forces. Should an engine fail, the aircraft will yaw about the vertical axis in the direction of the inoperative engine, which will in turn cause the aircraft to bank in said direction should no corrective rudder inputs be made.
tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80 Reply 14, posted (2 years 7 months 2 weeks 6 hours ago) and read 1591 times:
Quoting Pihero (Reply 3): That is until you fly an FBW 'Bus in which the flight control systems keeps the aircraft in treim at all times.
Not limited to Airbus...anybody who uses a C*-esque pitch control law gets this benefit (F-16, A320 and onwards, 777, etc.). Good overview here: https://dspace.lib.cranfield.ac.uk/bitstream/1826/186/2/coareport9303.pdf
Quoting NW747-400 (Reply 13): Should an engine fail, the aircraft will yaw about the vertical axis in the direction of the inoperative engine, which will in turn cause the aircraft to bank in said direction should no corrective rudder inputs be made.
Several FBW aircraft don't do this, or only do it because it's programmed in to provide pilot annunciation of an engine failure. Good yaw control laws will reject the disturbance of an engine failure.
tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80 Reply 16, posted (2 years 7 months 1 week 5 days 3 hours ago) and read 1364 times:
Quoting Pihero (Reply 15): I'd wanted such a document for a very long time without spending 80 quid on a tech book.
I was very surprised to find that one online without a fee...not sure why I haven't stumbled across it in the past when doing similar searches, but I'm thankful that it's there!
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