Using aerodynamic braking
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Using aerodynamic braking
It seems to me that the manufacturers manuals for civilian airliners that I have flown recommend against using aft control input in order to use aerodynamic braking the way some military aircraft do.
I did find some interesting information though, published by the FAA in an accident report I have been reading about a certain rare situation where it is recommended to use such a technique, as a last resort. It is the first time I have seen such a recommendation but it does have some logic to it. I just wonder how much effective aerodynamic braking one could achieve...
"The FAA Airplane Flying Handbook offers the following advice to reduce the risk of hydroplaning if this appears to be a danger: When confronted with the possibility of hydroplaning, it is best to land on grooved runway (if available). Touchdown speed should be as slow as possible consistent with safety. After the nose-wheel is lowered to the runway, moderate braking should be applied. If deceleration is not detected and hydroplaning is suspected, the nose should be raised and aerodynamic drag utilized to decelerate to a point where the brakes so become effective."
Avoiding Hydroplaning/Aquaplaning
• Land on a grooved runway if available.
• Touch down as slow as is safely possible.
• Apply moderate braking after the nose-wheel is lowered to the runway.
• If hydroplaning is suspected, raise the aircraft’s nose and use aerodynamic drag to decelerate to a point where the brakes become effective.
• Apply the brakes firmly until reaching a point just short of a skid. At the first sign of skid, release brake pressure and allow the wheels to spin up.
• Maintain directional control as far as possible with the rudder.
https://reports.aviation-safety.net/...135_ZS-SJW.pdf
I did find some interesting information though, published by the FAA in an accident report I have been reading about a certain rare situation where it is recommended to use such a technique, as a last resort. It is the first time I have seen such a recommendation but it does have some logic to it. I just wonder how much effective aerodynamic braking one could achieve...
"The FAA Airplane Flying Handbook offers the following advice to reduce the risk of hydroplaning if this appears to be a danger: When confronted with the possibility of hydroplaning, it is best to land on grooved runway (if available). Touchdown speed should be as slow as possible consistent with safety. After the nose-wheel is lowered to the runway, moderate braking should be applied. If deceleration is not detected and hydroplaning is suspected, the nose should be raised and aerodynamic drag utilized to decelerate to a point where the brakes so become effective."
Avoiding Hydroplaning/Aquaplaning
• Land on a grooved runway if available.
• Touch down as slow as is safely possible.
• Apply moderate braking after the nose-wheel is lowered to the runway.
• If hydroplaning is suspected, raise the aircraft’s nose and use aerodynamic drag to decelerate to a point where the brakes become effective.
• Apply the brakes firmly until reaching a point just short of a skid. At the first sign of skid, release brake pressure and allow the wheels to spin up.
• Maintain directional control as far as possible with the rudder.
https://reports.aviation-safety.net/...135_ZS-SJW.pdf
The landing performance of commercial aircraft is based on wheel braking, etc; the effect or contribution of aero braking is not quantified and would be difficult to asses - attitude, duration, … , risk of tail strike.
Many aircraft systems use weight on wheels switching - lift dump, reverse, brakes, antiskid.
Aero braking will have a residual lift component which may delay or even prevent wow switching, thus reducing the overall retarding force.
The FAA advice is poorly considered.
Given "the risk of hydroplaning if this appears to be a danger: When confronted with the possibility of hydroplaning,"
If the risk has been identified then avoid the hazard. Commercial operations should have an alternative course of action - diversion, wait for runway to drain.
The risk of hydroplaning after touch down should be low providing there was an adequate prelanding assessment of the conditions. The use of landing performance calculated for a flooded / contaminated runway will provide some alleviation, but never provide assured stopping capability. Check if the performance on a flooded runway takes credit for reverse thrust, also check any assumptions in factored distance, the safety margins might be reduced according to likely exposure, i.e. not the same as everyday operations.
Many aircraft systems use weight on wheels switching - lift dump, reverse, brakes, antiskid.
Aero braking will have a residual lift component which may delay or even prevent wow switching, thus reducing the overall retarding force.
The FAA advice is poorly considered.
Given "the risk of hydroplaning if this appears to be a danger: When confronted with the possibility of hydroplaning,"
If the risk has been identified then avoid the hazard. Commercial operations should have an alternative course of action - diversion, wait for runway to drain.
The risk of hydroplaning after touch down should be low providing there was an adequate prelanding assessment of the conditions. The use of landing performance calculated for a flooded / contaminated runway will provide some alleviation, but never provide assured stopping capability. Check if the performance on a flooded runway takes credit for reverse thrust, also check any assumptions in factored distance, the safety margins might be reduced according to likely exposure, i.e. not the same as everyday operations.
Given that the FAA handbook is aimed mostly at newbie-fliers getting into the seat of a C-172 for the first time, I'm not sure all its recommendations can be extended to large transport-class aircraft.
What I notice is that most aircraft in which holding the nose off for aerodynamic braking is common (Shuttle Orbiter, military fighters) have a bob-tail construction - less fuselage behind the main gear. Thus they can achieve higher pitch angles on the ground than the general run of airliners, without risking a tailstrike, especially as airliners have been stretched for more capacity. Same may be true to one extent of another for Concorde or other tail-engine aircraft, due to the weight distribution and main gear being further aft, and/or having taller main-gear relative to tail length.
I would imagine that AB drag/effectiveness goes up exponentially (as with many things in flight physics) with the pitch angle that can be achieved.
(One could argue that dragging some aluminum along the ground will add its own braking effect - but it's not very economical: Accident: ACT B744 at Dammam and Jeddah on Feb 1st 2020, tail strike on departure
. But as a last resort....maybe better than the alternative)
As a last resort AB has another weakness - the drag will decrease exponentially as airspeed drops. It won't help as much if delayed to the last second.
All that being said, AB is a real effect. It may or may not be a significant effect (deceleration of x-many m/s^2) in any particular combination of situation and aircraft type.
What I notice is that most aircraft in which holding the nose off for aerodynamic braking is common (Shuttle Orbiter, military fighters) have a bob-tail construction - less fuselage behind the main gear. Thus they can achieve higher pitch angles on the ground than the general run of airliners, without risking a tailstrike, especially as airliners have been stretched for more capacity. Same may be true to one extent of another for Concorde or other tail-engine aircraft, due to the weight distribution and main gear being further aft, and/or having taller main-gear relative to tail length.
I would imagine that AB drag/effectiveness goes up exponentially (as with many things in flight physics) with the pitch angle that can be achieved.
(One could argue that dragging some aluminum along the ground will add its own braking effect - but it's not very economical: Accident: ACT B744 at Dammam and Jeddah on Feb 1st 2020, tail strike on departure
. But as a last resort....maybe better than the alternative)As a last resort AB has another weakness - the drag will decrease exponentially as airspeed drops. It won't help as much if delayed to the last second.
All that being said, AB is a real effect. It may or may not be a significant effect (deceleration of x-many m/s^2) in any particular combination of situation and aircraft type.
Flew with a Captain that had flown HP Victors in the RAF.
One day our A300 had both thrust reversers locked out, so he thought using aerodynamic braking would be a good idea until I pointed out that the engines stayed at flight idle until the nose wheels spun up.
>8000 lbs fwd thrust rather than <4000 lbs.
One day our A300 had both thrust reversers locked out, so he thought using aerodynamic braking would be a good idea until I pointed out that the engines stayed at flight idle until the nose wheels spun up.
>8000 lbs fwd thrust rather than <4000 lbs.
p i f, re - "… the drag will decrease exponentially as airspeed drops. It won't help as much if delayed to the last second."
You may have inferred that this effect also applies to lift, which also involves pitch control. Thus, depending on aircraft type, it is possible to maintain a nose-high attitude longer than there is capability to control a nose-lowering manoeuvre. If so then the nose wheel will hit the runway very, very hard.
You may have inferred that this effect also applies to lift, which also involves pitch control. Thus, depending on aircraft type, it is possible to maintain a nose-high attitude longer than there is capability to control a nose-lowering manoeuvre. If so then the nose wheel will hit the runway very, very hard.
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tcasblue
Even A320 FCTM advises against aerodynamic braking as it is inefficient and in all airplanes increases tail strike possibility. Aerodynamic braking comes in the picture if normal braking has a problem like hydroplaning. That too to get some deceleration till wheel brakes get a grip. A point to consider is the purpose of spoilers on touchdown which is to kill the lift so weight of aircraft is on wheels which increases the braking. But if we increase the AoA on wings it will negate the effect of spoilers. So it not recommended in normal circumstances.
Even A320 FCTM advises against aerodynamic braking as it is inefficient and in all airplanes increases tail strike possibility. Aerodynamic braking comes in the picture if normal braking has a problem like hydroplaning. That too to get some deceleration till wheel brakes get a grip. A point to consider is the purpose of spoilers on touchdown which is to kill the lift so weight of aircraft is on wheels which increases the braking. But if we increase the AoA on wings it will negate the effect of spoilers. So it not recommended in normal circumstances.
It is not recommended to keep the nose high in order to increase aircraft drag during the initial part of the roll-out, as this technique is inefficient and increases the risk of tail strike. Furthermore, if auto brake MED is used, it may lead to a hard nose gear touch down.
Last edited by vilas; 4th Feb 2020 at 09:54.
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aerodynamic braking
Flew with a Captain that had flown HP Victors in the RAF.
One day our A300 had both thrust reversers locked out, so he thought using aerodynamic braking would be a good idea until I pointed out that the engines stayed at flight idle until the nose wheels spun up.
>8000 lbs fwd thrust rather than <4000 lbs.
One day our A300 had both thrust reversers locked out, so he thought using aerodynamic braking would be a good idea until I pointed out that the engines stayed at flight idle until the nose wheels spun up.
>8000 lbs fwd thrust rather than <4000 lbs.
Given that many large aircraft use main gear compression (aka "Weight On Wheels" or WOW) to enable various braking devices such as thrust reversers and spoiler/speed brakes, "aero-braking" could easily lengthen stopping distances by preventing timely use of the devices that are intended to slow and stop the aircraft.
On the 757/ 67 autobrakes will not engage after touch down until pitch attitude is beneath a preset value (forget what it is)
An excellent reason to get the nose down (gently)
An excellent reason to get the nose down (gently)
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The idea of a pull on the controls on the Victor, was Not to raise the nose but to brake hard and Tend to raise it. In this way more braking torque was achieved against an aerodynamic input. Only used if the braking chute didn’t stream on a short RW.
Same technique was mentioned for hydraulic failure landings (with limited or no flap etc.) in an airline I know. The point is that the control deflection should be countered by braking. Nose stays down.
Knocks hell out of the brakes of course and was not meant for daily use.
Same technique was mentioned for hydraulic failure landings (with limited or no flap etc.) in an airline I know. The point is that the control deflection should be countered by braking. Nose stays down.
Knocks hell out of the brakes of course and was not meant for daily use.
Given that many large aircraft use main gear compression (aka "Weight On Wheels" or WOW) to enable various braking devices such as thrust reversers and spoiler/speed brakes, "aero-braking" could easily lengthen stopping distances by preventing timely use of the devices that are intended to slow and stop the aircraft.
From the current 777/787 Flight Crew Training Manual:
" After main gear touchdown initiate the landing roll procedure. Fly the nose wheels smoothly onto the runway without delay..".......
" If nose wheels are not promptly lowered to the runway, braking and steering capabilities are significantly degraded and no drag benefit is gained"..
(my emphasis)
First officers who do that will get a very sharp comment from me. Don’t you just love it when the aircraft weathercocks into the wind as there is no direction from the nose wheel keeping things straight. The slam when the front gear hits the ground once the airspeed runs out is fun as well. Not to mention the risk of a tail strike.
"… when the aircraft weathercocks into the wind as there is no direction from the nose wheel keeping things straight."
Then use the rudder !
Why is there much focus on NWS which might be ineffective on wet or icy runways - fly the aircraft.
Then use the rudder !
Why is there much focus on NWS which might be ineffective on wet or icy runways - fly the aircraft.
Last edited by PEI_3721; 8th Feb 2020 at 06:33.
Use the rudder! You’ve obviously never tried it..needs the nosewheel steering at low speeds.
(Airflow is partially blanked by fuselage).
In my brief career with Britain’s Excuse for an Airline there were a few guys who did the aerodynamic braking but I left it too long and paid the price with a resounding bang.
As to the poor copilots I once after a long Bolloxing having been told what I should want when I got my command on the gripper, I asked if there was a course in sarcasm involved...his briefcase hurt.
Many years later with a know all Swede who had been on the death cruiser three times as long as moi offered me the stateside landing which I excepted with glee (he was probably too tired). On the way back to Zurich which is where I normally got the landing although often lost it due to low viz I was asked where he should start the descent.
Give up.
No I’m serious.
Luxeil.
20 miles before hand he started down leaving some power on.
When he was 1,000ft high I mentioned the throttles.
I know I started down early.
3,000 ft high.Peter you are getting high.
Do you want to fly the Effing aircraft yourself.
Sorry just doing my Job.
At the last possible point where I knew I could get into Zurich I pointed out height and distance and then the s**t hit the fan. Ended up doing an unnecessary 360 and dragging it in.
Finished with I hate it when effing copilots are right.
Ten years later bumped into him after visiting the london boat show..still wouldn’t talk to me.
In hind sight I would have watched him doing a go around at 6am and said “you should have listened to your copilot”.
(Airflow is partially blanked by fuselage).
In my brief career with Britain’s Excuse for an Airline there were a few guys who did the aerodynamic braking but I left it too long and paid the price with a resounding bang.
As to the poor copilots I once after a long Bolloxing having been told what I should want when I got my command on the gripper, I asked if there was a course in sarcasm involved...his briefcase hurt.
Many years later with a know all Swede who had been on the death cruiser three times as long as moi offered me the stateside landing which I excepted with glee (he was probably too tired). On the way back to Zurich which is where I normally got the landing although often lost it due to low viz I was asked where he should start the descent.
Give up.
No I’m serious.
Luxeil.
20 miles before hand he started down leaving some power on.
When he was 1,000ft high I mentioned the throttles.
I know I started down early.
3,000 ft high.Peter you are getting high.
Do you want to fly the Effing aircraft yourself.
Sorry just doing my Job.
At the last possible point where I knew I could get into Zurich I pointed out height and distance and then the s**t hit the fan. Ended up doing an unnecessary 360 and dragging it in.
Finished with I hate it when effing copilots are right.
Ten years later bumped into him after visiting the london boat show..still wouldn’t talk to me.
In hind sight I would have watched him doing a go around at 6am and said “you should have listened to your copilot”.
bp, you appear to have missed the point in the context of this thread.
Aero braking - pitch control has no advantage; directional control with rudder has advantage over NWS in many situations.
Aerodynamic controls loose effectiveness as airspeed reduces; the arguments above strongly advise lowering the nose while there is sufficient control. This should 'un-blank' the rudder according to aircraft type, which can be used until rudder effectiveness reduces, thence use NWS.
Consider the failure case of landing without NWS, or abnormal operations on a wet, contaminated runway; there is advantage of prior knowledge from everyday use of rudder.
Aero braking - pitch control has no advantage; directional control with rudder has advantage over NWS in many situations.
Aerodynamic controls loose effectiveness as airspeed reduces; the arguments above strongly advise lowering the nose while there is sufficient control. This should 'un-blank' the rudder according to aircraft type, which can be used until rudder effectiveness reduces, thence use NWS.
Consider the failure case of landing without NWS, or abnormal operations on a wet, contaminated runway; there is advantage of prior knowledge from everyday use of rudder.
Having the nose wheel on the ground on a tricycle undercarriage aircraft improves control as it is forward of the CofG and allows the pilot to have a better view along the runway. On the A320 forward side stick is recommended below 100kts on take off to aid in maintaining direction.
With a tail wheel aircraft, the rear wheel is behind the CofG and often assists the rear end in trying to overtake the front end, similar to a lorry jackknifing. Many a tail dragger pilot has enjoyed a 360’ panoramic view of the airport during a misjudged landing and subsequent ground loop. On take off, the idea was to get the tail up, improve the forward view and steer aerodynamically using the rudder. Landing had two schools of thought, one was to three point the aircraft which generally resulted in a shorter ground run, the other was to land on the main wheels first and lower the tail as the speed decayed.
With a tail wheel aircraft, the rear wheel is behind the CofG and often assists the rear end in trying to overtake the front end, similar to a lorry jackknifing. Many a tail dragger pilot has enjoyed a 360’ panoramic view of the airport during a misjudged landing and subsequent ground loop. On take off, the idea was to get the tail up, improve the forward view and steer aerodynamically using the rudder. Landing had two schools of thought, one was to three point the aircraft which generally resulted in a shorter ground run, the other was to land on the main wheels first and lower the tail as the speed decayed.
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Spoilers and full reverser are the same as auto brakes 2.75 (+/-) at touchdown. At approx 90 kts the effectiveness has reduced to approx autobrakes 2. You can check that as the speed decreasing below 90-100 kts, with full reverse, you'll start to feel the brakes being applied if auto brakes 2 was selected.
Aero braking is not going to give you the same effect as auto brakes 2.75 (full reverse and spoilers). And the additional risk is slamming the nose wheel on the ground. That doesn't always end well.
Aero braking is not going to give you the same effect as auto brakes 2.75 (full reverse and spoilers). And the additional risk is slamming the nose wheel on the ground. That doesn't always end well.
The above also depends on the aircraft type. On the A320 auto-brake is designed to achieve a calculated deceleration rate.If you land with MED set and don’t select any reverse thrust the brakes are applied hard which sends everyone forward in their seats and the brake temperatures soaring. Selecting full reverse thrust as well greatly reduces brake demand and gives a much smoother arrival.
Obviously auto brake MED is normally used on shorter runways in conjunction with full reverse anyway.
Airline interview question:
What is the most effective way of stopping an aeroplane?
A. Reverse thrust
B. Wheel brakes
C. Spoilers
Correct answer - B.Wheel brakes
Get the aircraft on the ground, the weight on the wheels and let the brakes do their job.
Obviously auto brake MED is normally used on shorter runways in conjunction with full reverse anyway.
Airline interview question:
What is the most effective way of stopping an aeroplane?
A. Reverse thrust
B. Wheel brakes
C. Spoilers
Correct answer - B.Wheel brakes
Get the aircraft on the ground, the weight on the wheels and let the brakes do their job.
