Heavy aircraft landing performance
Thread Starter
Join Date: Jun 2006
Location: in a cave, grrrr!
Posts: 55
Likes: 0
Received 0 Likes
on
0 Posts
Heavy aircraft landing performance
With B777 200 we 're used to land on a 1680m LDA runway.772 can do it, even, at its MLW (208t) , with flight dispatch margin: average LD around 1000m in relation with atm cond, dry condition required!
descent turn around time, and good brake temp.Are B773, B744, A330/340 able to do so?
Please tell me, I'm willing to know
Join Date: Aug 2005
Location: fairly close to the colonial capitol
Age: 55
Posts: 1,693
Likes: 0
Received 0 Likes
on
0 Posts
Lightly loaded A342 or -300 can do your LDA. Mid weight still gets you on the ground safely with a 1680m runway. Go up to max and you will need a bit more tarmac - about 400m more than your proposed 1680. Small problem arises when its time to leave,though.
I think the 744 LD figures are a bit more than 1680m.
I think the 744 LD figures are a bit more than 1680m.
Join Date: Apr 2005
Location: uk
Posts: 260
Likes: 0
Received 0 Likes
on
0 Posts
B744 at max. ldg wt. (pax a/c) 285,000kgs, using flaps 30, all engines reverse and max. manual braking = 3950ft, for max. autobrakes = 4660ft. I don't have exact metric equivalent to hand.(assumes dry runway).
Join Date: May 2003
Posts: 409
Likes: 0
Received 0 Likes
on
0 Posts
Regardless of the type of aircraft (heavy 747 or light jet, for example), the published landing distance is typically dependent on the landing speed only, since their tires are generally made of the same material. Of course, use of thrust reverser and lift dump systems will mean a reduction.
Hawk
Hawk
Join Date: May 2003
Posts: 409
Likes: 0
Received 0 Likes
on
0 Posts
Just to clear things up....
Reading my last post now in the light of day, I thought perhaps I'd clarify what I was trying to say. Two different jets, even at different weights, will still typically have the same landing distance as long as their landing speeds are the same. As before, a few factors can affect this, ie effectiveness of lift dumpers, reverse thrust, etc.
Join Date: May 2000
Location: Seattle
Posts: 3,197
Likes: 0
Received 0 Likes
on
0 Posts
Not even close to that simple...
While the tire material may be the same, the number of tires, number of brakes, size of tires, tire pressure, energy capacity of the brakes, and likely many other factors come into play. I doubt even the 747 Classic and 747-400 have the same landing distances at the same weight...
While the tire material may be the same, the number of tires, number of brakes, size of tires, tire pressure, energy capacity of the brakes, and likely many other factors come into play. I doubt even the 747 Classic and 747-400 have the same landing distances at the same weight...
Join Date: May 2003
Posts: 409
Likes: 0
Received 0 Likes
on
0 Posts
…and I’d doubt it too. Were there not changes to the wing between the classic and the 400? Does this affect landing (or approach) speed?
That landing distance for different jets is typically similar if they are landing at the same SPEED (not weight) is no coincidence.
And is in fact quite a simple concept.
With the PRIMARY retarding force being brakes (in this case), the decelerating force from them F = mu * Weight, where mu is the coefficient of friction between the landing surface and the tires, say .6 or so for a dry hard surface runway. A heavier aircraft means more weight to slow down, but also the decelerating force (mu * Weight) is proportionally higher. Ergo, an aircraft with twice the weight will have twice the decelerating force, resulting in approximately the same landing distance as long as the landing speed is the same.
As indicated earlier, other factors can come into play when a landing distance is determined. Lift dump systems not only destroy lift to allow the aircrafts weight on wheels to increase, but also can provide an additional down force, increasing the apparent weight of the aircraft, without affecting the mass, and so increased deceleration is possible. Profile drag. Thrust reversers. Energy capacity of the brakes. Degraded hydraulics. Antiskid issues. Etc. But the OP wasn’t addressing these considerations in his post question.
The manufacturer has already decided how best to equip his aircraft. Thus any issue of number of wheels, number of brakes, size of tires, tire pressure, etc has already been analyzed, along with the many trade offs involved in aircraft production. If Boeing or Airbus simply got it wrong, the competition would eat them up. In any case, what is doubling the number of wheels/tires on a 747 from 18 to 36 going to accomplish? Now each wheel has half as much apparent weight on it, with those that do brake producing half as much decelerating force.
Comparing the landing distances of the 747 400 and classic “at the same weight”, as you suggested, would only add support if they are landing at the same speeds. Not being informed on the 747 series, I’ll not comment on any different wing aerodynamics that may or may not affect landing speeds.
It would be interesting to hear from ppruners based on their aircraft type what the landing speed (or Vref, or Vsr, or appropriate term) is, and the published landing distance. One could appreciate then just how accurate this relationship is.
That landing distance for different jets is typically similar if they are landing at the same SPEED (not weight) is no coincidence.
And is in fact quite a simple concept.
With the PRIMARY retarding force being brakes (in this case), the decelerating force from them F = mu * Weight, where mu is the coefficient of friction between the landing surface and the tires, say .6 or so for a dry hard surface runway. A heavier aircraft means more weight to slow down, but also the decelerating force (mu * Weight) is proportionally higher. Ergo, an aircraft with twice the weight will have twice the decelerating force, resulting in approximately the same landing distance as long as the landing speed is the same.
As indicated earlier, other factors can come into play when a landing distance is determined. Lift dump systems not only destroy lift to allow the aircrafts weight on wheels to increase, but also can provide an additional down force, increasing the apparent weight of the aircraft, without affecting the mass, and so increased deceleration is possible. Profile drag. Thrust reversers. Energy capacity of the brakes. Degraded hydraulics. Antiskid issues. Etc. But the OP wasn’t addressing these considerations in his post question.
The manufacturer has already decided how best to equip his aircraft. Thus any issue of number of wheels, number of brakes, size of tires, tire pressure, etc has already been analyzed, along with the many trade offs involved in aircraft production. If Boeing or Airbus simply got it wrong, the competition would eat them up. In any case, what is doubling the number of wheels/tires on a 747 from 18 to 36 going to accomplish? Now each wheel has half as much apparent weight on it, with those that do brake producing half as much decelerating force.
Comparing the landing distances of the 747 400 and classic “at the same weight”, as you suggested, would only add support if they are landing at the same speeds. Not being informed on the 747 series, I’ll not comment on any different wing aerodynamics that may or may not affect landing speeds.
It would be interesting to hear from ppruners based on their aircraft type what the landing speed (or Vref, or Vsr, or appropriate term) is, and the published landing distance. One could appreciate then just how accurate this relationship is.
Join Date: Sep 2002
Location: La Belle Province
Posts: 2,179
Likes: 0
Received 0 Likes
on
0 Posts
I'd suggest that the biggest factor which breaks (brakes? 
) the relationship between approach speed and landing distance is going to be altitude, unless you express approach speed in terms of TAS, not IAS.
That aside, here are some numbers for sea level, ISA, calm conditions:
80,000lb aircraft : Vref=132kts, ALD 2680ft
38,000lb aircraft : Vref=132kts, ALD=2830ft
38,000lb aircraft : Vref=132kts, ALD=2800ft (not the same aircraft as #2, not even common wings, brakes or engines)
) the relationship between approach speed and landing distance is going to be altitude, unless you express approach speed in terms of TAS, not IAS.That aside, here are some numbers for sea level, ISA, calm conditions:
80,000lb aircraft : Vref=132kts, ALD 2680ft
38,000lb aircraft : Vref=132kts, ALD=2830ft
38,000lb aircraft : Vref=132kts, ALD=2800ft (not the same aircraft as #2, not even common wings, brakes or engines)
Last edited by Mad (Flt) Scientist; 19th Sep 2006 at 17:33. Reason: typo: lbs for kgs
Join Date: May 2003
Posts: 409
Likes: 0
Received 0 Likes
on
0 Posts
Christiaan, wet runway landing distance is the only time I know of when credit for reversers can be applied.
MFS, as expected I guess. Interesting while at the same Vref the heavier aircraft can indeed acutally stop shorter than the lighter.
MFS, as expected I guess. Interesting while at the same Vref the heavier aircraft can indeed acutally stop shorter than the lighter.
Join Date: May 2000
Location: Seattle
Posts: 3,197
Likes: 0
Received 0 Likes
on
0 Posts
Comparing the landing distances of the 747 400 and classic “at the same weight”, as you suggested, would only add support if they are landing at the same speeds. Not being informed on the 747 series, I’ll not comment on any different wing aerodynamics that may or may not affect landing speeds.
747-400 Vref = 140 KIAS at 250,000 Kg
747-200 Vref = 140 KIAS at 240,000 Kg
So, the difference in "wing aerodynamics" => 10 tonnes for 140 KIAS approach.
At 140 KIAS approach, 747-400 landing distances (including 1200' air distance):
Autobrakes 1 = 8100'
Autobrakes 2 = 6800'
Autobrakes 3 = 6000'
Autobrakes 4 = 5000'
Autobrakes Max = 4200' (close to max manual braking)
I cannot readily find a similar chart for the 747-200.
Please provide similar info for other aircraft at 140 KIAS approach.
Join Date: Sep 2002
Location: La Belle Province
Posts: 2,179
Likes: 0
Received 0 Likes
on
0 Posts
140 KIAS, SL, ISA, Calm:
91,500lbs, ALD=2950ft, LFL 4900ft manual max braking
The same aircraft gives "HI" autobrakes (extrapolated to 91,500lbs) as 2600ft + 1500ft (air distance) = 4100ft landing distance, so I'm a bit wary of comparing autobrake numbers between aircraft, because it's very sensitive to system design. The manual 'max braking' is the best number to compare, I think.
91,500lbs, ALD=2950ft, LFL 4900ft manual max braking
The same aircraft gives "HI" autobrakes (extrapolated to 91,500lbs) as 2600ft + 1500ft (air distance) = 4100ft landing distance, so I'm a bit wary of comparing autobrake numbers between aircraft, because it's very sensitive to system design. The manual 'max braking' is the best number to compare, I think.
Join Date: Jan 2005
Location: France
Posts: 2,315
Likes: 0
Received 0 Likes
on
0 Posts
But I thought that, if anything, you got more drag from a high-angle stalled wing (i.e., keeping the nose up a bit) than from dropping the nose too early.
Of course, spoilers/airbrakes and getting the full weight on the wheels sooner probably cancels that equation....
Join Date: May 2003
Posts: 409
Likes: 0
Received 0 Likes
on
0 Posts
You may get more drag from holding the landing attitude than by lowering the nose to the runway and coasting. However, I can't say I've heard of airliners using the technique of increasing pitch angle after landing, in order to increase drag. Fighters often do it, but tail strikes need to be considered.
Join Date: May 2000
Location: Seattle
Posts: 3,197
Likes: 0
Received 0 Likes
on
0 Posts
That landing distance for different jets is typically similar if they are landing at the same SPEED (not weight) is no coincidence.
And is in fact quite a simple concept.
With the PRIMARY retarding force being brakes (in this case), the decelerating force from them F = mu * Weight...
And is in fact quite a simple concept.
With the PRIMARY retarding force being brakes (in this case), the decelerating force from them F = mu * Weight...
The equation you cite may be valid, but it does NOT explain the similarity in landing distances as you represent it.
I did just a bit more ciphering in the 747-400 tables and came up with the following:
Base airplane is 250,000 Kg gross weight, Vref = 143 KIAS, max manual braking, antiskid on.
At Vref, landing distance is 4250'
At Vref + 20 KIAS (163 KIAS), landing distance is 5200'
For a 320,000 Kg gross weight, Vref = 163 KIAS and landing distance is 5770' for the SAME CONDITIONS -- a difference of 10%.
So, your assertion that landing speed is the only variable is incorrect in reality. If such a significant difference is apparent for the SAME drag/brake/wheel/tire configuration, there is likely to be a significant difference among airplanes with different parameters.
Join Date: May 2000
Location: Seattle
Posts: 3,197
Likes: 0
Received 0 Likes
on
0 Posts
Comparing the landing distances of the 747 400 and classic “at the same weight”, as you suggested, would only add support if they are landing at the same speeds. Not being informed on the 747 series, I’ll not comment on any different wing aerodynamics that may or may not affect landing speeds.
For the 747-400, Vref = 140 KIAS at 240,000 Kg
or 143 KIAS at 250,000 Kg.
That represents a 4% difference in "wing aerodynamics" at 140 KIAS and the -400 is actually landing FASTER at the same weight...
Join Date: Sep 2002
Location: La Belle Province
Posts: 2,179
Likes: 0
Received 0 Likes
on
0 Posts
Two questions:
Does the Vref+20 data assume any kind of failure scenario which may invalidate the comparison?
Does either case take you to some kind of brake energy limit condition? Or to some kind of brake torque limit? Either would pull you off the simple mu relationship.
Does the Vref+20 data assume any kind of failure scenario which may invalidate the comparison?
Does either case take you to some kind of brake energy limit condition? Or to some kind of brake torque limit? Either would pull you off the simple mu relationship.
Join Date: May 2000
Location: Seattle
Posts: 3,197
Likes: 0
Received 0 Likes
on
0 Posts
The Vref+20 scenario is at flaps 25 vs flaps 30 ("stuck stab" scenario). However, there is no adjustment in the tables for flap position, except for resulting approach speed.
If anything, flaps 30 would shorten the landing roll slightly (due to higher aerodynamic drag), making an even larger difference betwen that and the 320 Ton scenario.
I don't know about brake energy or torque limit effects. But the "pull you off the simple mu relationship" factor is EXACTLY what I am trying to bring out here. The simple equation cited by hawk37 may look good on paper as a basic equation with simplifying assumptions, but does not reflect the reality of stopping different size/weight airplanes with different brakes, tires, footprints, tire pressures, etc. The fact that such a substantial difference can be readily illustrated using 2 IDENTICAL airplanes is a clear contradiction of hawk37's premise.
If anything, flaps 30 would shorten the landing roll slightly (due to higher aerodynamic drag), making an even larger difference betwen that and the 320 Ton scenario.
I don't know about brake energy or torque limit effects. But the "pull you off the simple mu relationship" factor is EXACTLY what I am trying to bring out here. The simple equation cited by hawk37 may look good on paper as a basic equation with simplifying assumptions, but does not reflect the reality of stopping different size/weight airplanes with different brakes, tires, footprints, tire pressures, etc. The fact that such a substantial difference can be readily illustrated using 2 IDENTICAL airplanes is a clear contradiction of hawk37's premise.