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Comparing Landings  
User currently offlineIl75 From Argentina, joined May 2001, 263 posts, RR: 0
Posted (7 years 6 months 1 week 18 hours ago) and read 1937 times:

I travel often from Sweden to South America. It means I usually have a first leg to a major European destination with a narrow body plane where I change to a wide body aircraft for the transatlantic flight.

I notice that the small plane climbs faster than the heavy one. I do not know and I do not mean that they reach cruise altitude faster. They simple seem to climb in a steeper angle and you get the impression that you are up in the air quicker.

But I can not notice any difference on the other direction. So my question is: Given the same conditions (weather, traffic, approach line, load/wheig factor) does an A320, MD8X or 737 normally descend/ land faster than a wide body?

Best regards
Erico

8 replies: All unread, jump to last
 
User currently offlineArniePie From Belgium, joined Aug 2005, 1265 posts, RR: 1
Reply 1, posted (7 years 6 months 1 week 16 hours ago) and read 1912 times:

Quoting Il75 (Thread starter):
I notice that the small plane climbs faster than the heavy one.

I think (not sure) that is a subjective feeling , the bigger ones climb with a lower AOA because they usually climb at 250 knots once above 2500ft.
Many small commuters (F50, Dash8,...) may be climbing at similar Ft/min but because they fly slower they have to increase their AOA.
I always had the idea that the faster commuter jets (Embraer or CRJ's) where very similar with the bigger planes performance wise.
The only "slow" climbers are the ones that do the Longhaul and Ultra Longhaul routes (eg. the 744's from QF flying out of LAX )

just  twocents 

Quoting Il75 (Thread starter):
But I can not notice any difference on the other direction.

Flying regular flights the airplanes ,small or large, will fly a very similar pattern ,around 3° slope when using ILS and probably something similar when flying a visual app.
Because the airspeed is not all that different feeling wise you will probably get a similar feeling comparing between small and larger planes.

Again all speculation on my part



[edit post]
User currently offlineIl75 From Argentina, joined May 2001, 263 posts, RR: 0
Reply 2, posted (7 years 6 months 6 days 20 hours ago) and read 1776 times:

I never thought of that relationship between AOA and speed in climbing. I understand the logic but, having no idea of the physical laws of flying, I always thouth that the steeper the angle of climb the more speed you needed to keep the plane flying.
Thank you! Interesting reading.
Erico


User currently offlineSpeedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0
Reply 3, posted (7 years 6 months 6 days 19 hours ago) and read 1764 times:

Quoting Il75 (Thread starter):
I travel often from Sweden to South America. It means I usually have a first leg to a major European destination with a narrow body plane where I change to a wide body aircraft for the transatlantic flight.



Quoting ArniePie (Reply 1):
I think (not sure) that is a subjective feeling , the bigger ones climb with a lower AOA because they usually climb at 250 knots once above 2500ft.

I'm pretty sure that AOA on climbout has nothing to do with it, nor can any passenger "Feel" differences in AOA from one aircraft to the next. What you'd feel is the deck angle, and any plane climbing on a steep climb gradient will be climbing at a relatively steep deck angle. There's no correlation between AOA and percieved climb gradient that you could feel as a passenger.

The difference in percieved climbrate between shorthaul narrowbodies and longhaul widebodies on the routs that IL75 describes is simple:

A 737, for example, flying from Sweden to pretty must anywhere in western Europe will be relatively lightly loaded and can climb rather quickly.

A widebody taking of for a transatlantic trip, while not likely fully loaded, will be heavy enough to climb somewhat more slowly. However, since any plane you fly, big or small, will likely takeoff with reduced thrust settings, percieved climb performance is as much about the level of thrust reduction as it is about the takeoff weight of the aircraft.



Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
User currently offlineIl75 From Argentina, joined May 2001, 263 posts, RR: 0
Reply 4, posted (7 years 6 months 5 days 19 hours ago) and read 1623 times:

Of course! That is a factor I never thought of even if I am always impressed how this big planes can manage to lift with around 400 pax, a lot of baggage and fuel for 13 hours flight.
But I can not quite follow you about the difference between AOA (I suppose it is Angle OF Ascent/ Attack) and the deck angel. Should any increase in one lead to an increase of the other?

In any case, and I hadn't realized that, a steeper climb angle doesn't necessarily means a faster ascent rate. And the ascent rate is also related to the load factor of the plane.

Thank you for your answer!
Erico


User currently offlinePihero From France, joined Jan 2005, 4679 posts, RR: 77
Reply 5, posted (7 years 6 months 5 days 18 hours ago) and read 1614 times:
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AoA = Angle of attack . Used purely for aerodynamics purposes, it is the angle between the reference airfoil chord - a "line" between the leading edge and the trailing edge - and the flight path vector . That said, AoA has an effect on the body angle of the aircraft - which pilots visualise on the artificial horizon as "attitude" - as the wing is already attached to the fuselage at a designed angle.
Therefore, you must understand that " attitude", " body angle ", " decK angle " which is about the only erception the passengers would feel inside a cabin are the same thing. How fallacious the feeling can be demonstrated by saying that on most airplanes, the attitude during an intermediate approach (i.e before intercetion of the final path) is steeper than for normal climb, although the flight is level.
We talk more of " climb gradient " than AoA. For performance reasons, it is more useful as it is the ratio between ground speed and climb speed... The regulations are the same for all airliners regarding required performance. That means let's say a 737-800 should demonstrate the same climb capability as a 777-300ER, a 330-200 or a 318 . That sort of performance is demanded with an engine failure and is of course dependant on engine thrust and - very simplistically - wing loading, so it would seem that the bigger the engine - relatively to the size opf the airplane - the better the performance. Right, but the engine thrust must be somewhere restricted to the required performance, for reasons of economics - airlines do not want to pay for excessive thrust just to please A.netters. On this subject, for economical reasons, some airlines with a big fleet of a certain family would like engine communality and in this case you might well find the smallest of the family with an engine which is in theory too big but fits the maintenance bill. ( I refer in particular to the 320, 319, 321, 318 family )

Quoting Il75 (Thread starter):
Given the same conditions (weather, traffic, approach line, load/wheig factor) does an A320, MD8X or 737 normally descend/ land faster than a wide body?

No, the descent paths are the same for everybody, for ATC constraints. But if you're talking about landing speeds, as a ball park set of figures, a long range wide body would approach 10 to 15 kt faster than a 320.



Contrail designer
User currently offlineIAHFLYR From United States of America, joined Jun 2005, 4790 posts, RR: 22
Reply 6, posted (7 years 6 months 5 days 16 hours ago) and read 1600 times:

Quoting ArniePie (Reply 1):
I always had the idea that the faster commuter jets (Embraer or CRJ's) where very similar with the bigger planes performance wise.

A heavy E135/145/CRJ1/CRJ2 do not go well in the climb once above FL180 compared to a B73X....but when they finally get to cruise altitude, these will run along just fine around .77ish which is leaving the B732-B735's in most cases at would be considered to be econ cruise speeds....now the B737-B739's are slightly faster econ cruise and much better climb performance.

The E45XR/E170/E190's as well as the CRJ7/CRJ9, different animal in climb performance from their earlier models.



Any views shared are strictly my own and do not a represent those of any former employer.
User currently offlineIl75 From Argentina, joined May 2001, 263 posts, RR: 0
Reply 7, posted (7 years 6 months 4 days 17 hours ago) and read 1484 times:

Quoting Pihero (Reply 5):
How fallacious the feeling can be demonstrated by saying that on most airplanes, the attitude during an intermediate approach (i.e before intercetion of the final path) is steeper than for normal climb, although the flight is level.

Do you mean by this than a approaching plane loses at that stage more altitude -- still flying flat -- than a climbing plane wins altitude in spite of the evident deck angle? If so I understand your point.

Thank you all for your explanations.
Erico


User currently offlineSEPilot From United States of America, joined Dec 2006, 7199 posts, RR: 50
Reply 8, posted (7 years 6 months 4 days 17 hours ago) and read 1481 times:

One other factor is that if your long haul plane has four engines it will have a lower thrust to weight ratio because a twin must have enough thrust to take off with only one engine, while the quad only has to be able to take off with one out. Even with twins the thrust to weight ratio varies; I believe that the 757 has one of the highest, as it is one of the few planes that can take off from the highest airports in Tibet. It is also my experience that it climbs with the steepest deck angle of any plane that I have been in.


The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
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