Do we “bump down” these days? I was taught to land……
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Dehavillanddriver,
I'm not certainly going to get into a debate about long, greaser, short and hot landings as this is outside my sphere of expertise (pity Dick Smith didn't do the same).
However, I must reiterate that weight of the vehicle has no effect on the aquaplaning speed, according to the experiments conducted by NASA. Whether the mass (weight) of your acft is partially supported by the lift of the wings, this should not affect the aquaplaning speed of the acft...according to the theory I was taught.
I'm not certainly going to get into a debate about long, greaser, short and hot landings as this is outside my sphere of expertise (pity Dick Smith didn't do the same).
However, I must reiterate that weight of the vehicle has no effect on the aquaplaning speed, according to the experiments conducted by NASA. Whether the mass (weight) of your acft is partially supported by the lift of the wings, this should not affect the aquaplaning speed of the acft...according to the theory I was taught.
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DirtyPiere,
You are quite correct - this applies once the wheels have spun up, untill then you must take rotational inertia into account - it's quite simple, the greater the mass of each wheel, the more it will resist 'spinning-up', and of course, untill it has reached full rotational speed the tyre is by definition hydroplaning or aquaplaning (even on a dry rwy - it's called reverted rubber hydroplaning) - instead of getting caught up in the formulae, consider the basic physics. The extreme example of this effect would be landing with the park brake on - does that clear things up?
You are quite correct - this applies once the wheels have spun up, untill then you must take rotational inertia into account - it's quite simple, the greater the mass of each wheel, the more it will resist 'spinning-up', and of course, untill it has reached full rotational speed the tyre is by definition hydroplaning or aquaplaning (even on a dry rwy - it's called reverted rubber hydroplaning) - instead of getting caught up in the formulae, consider the basic physics. The extreme example of this effect would be landing with the park brake on - does that clear things up?
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Cloud Cutter,
I'll take your word for the effect of rotational inertia. I think the formula might be just a rough guide you can use to calculate aquaplane speed mentally. It certainly works for cars, and it doesn't matter the weight of the vehicle, whether you're driving a Ford F350 or a Fiat Bambino.
I'll take your word for the effect of rotational inertia. I think the formula might be just a rough guide you can use to calculate aquaplane speed mentally. It certainly works for cars, and it doesn't matter the weight of the vehicle, whether you're driving a Ford F350 or a Fiat Bambino.
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Please don't take my word for it, think about this - given your car example, that formula gives you a speed at which the car will hydroplane if you drive over a big enough puddle, if you put the anchors on, and give the wheels resistance to rotation, you can get the car to hydroplane at a much lower speed, particularly when your talking reverted rubber hydroplaning (when the surface of the tyre melts to form a liquid film) - this is essentialy a skid.
Moderate, Modest & Mild.
but the wings are still producing sufficient lift to support part of the weight. This has the same effect as a lower tyre pressure i.e. lower and wider range of speeds for aquaplaning.
My impression has always been that the speed at touchdown is faster than it is towards the end of the landing roll.
Do you know something the rest of us don't, Wiz??
Touching down firmly (a good idea at all times) puts all the load on the wheels and deploys the speed brakes in the shortest time
DirtyPierre, the formula of 9 times the square root of the tyre pressure to give aquaplaning speed (in mph) was always the one I had used as well, but I seem to recall reading (somewhere) recently that there was now more of a range (something along the lines of 7-11) with 9 still the median.
Anyone else seen this reference?
Cloud Cutter, rubber reversion is the phenomenom that occurs when the water trapped between the wheels and the runway heats up (to form steam) and dissolves the rubber into smallish tacky "blobs", further reducing braking effectiveness through the tyre to pavement contact. Well that was my understanding of it, at least.
Anyway, avoid speeds around 80-90 kph in your car on days when it's p!ssing down - I experienced aquaplaning in my car several years ago (by not following my own advice
) and ended up off the freeway in a gully. It's a strange sensation, you can turn the steering wheel full lock both ways with just an index finger, and NOTHING happens....I just kept going straight ahead foot off the accelerator, at the SAME speed (until I hit the grass) 
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My belief of the theory has always been to do with
the efficiency of the wheel brakes i.e to get the weight
of the aircraft on the wheels asap (hence spoilers)
If the runway is wet, a greaser will not deliver the
true weight of the a/c but an apparant weight significantly
less which in turn will cause the wheels to lock-up and
engage the anti-skid system which will, due to less
braking efficiency will increase the landing roll.
If Im completely wrong..so be it!
the efficiency of the wheel brakes i.e to get the weight
of the aircraft on the wheels asap (hence spoilers)
If the runway is wet, a greaser will not deliver the
true weight of the a/c but an apparant weight significantly
less which in turn will cause the wheels to lock-up and
engage the anti-skid system which will, due to less
braking efficiency will increase the landing roll.
If Im completely wrong..so be it!
or better still get the FO to pay.
Kaptin M
Can’t see that that is one of the requirements for Ground Spoiler extension. Boeing might be different but the A330 FCOM 1 section 27 states that full extension of the Ground Spoilers will occur at landing if both main landing gear have touched down and:
· They are armed, and
· All thrust levers are at idle, or
· Reverse is selected on at least one engine (other engine at idle).
I have always been told that “greasing” it on is to be avoided, not because it increases the risk of aquaplaning but because it increases the risk of touching down outside the “zone”. If you know the runway is going to be slippery, it is best to get it on the ground, allow the spoilers to auto deploy and use full reverse thrust as these devises are most effective at higher speeds. Once the aircraft has slowed enough, the auto brakes with anti skid working should start to become effective. Obviously allowing the aircraft to float down the runway because you were after a “greaser” is a bad move in this situation and should be frowned upon.
speedbrake deployment is dependant upon main wheel spin up
· They are armed, and
· All thrust levers are at idle, or
· Reverse is selected on at least one engine (other engine at idle).
I have always been told that “greasing” it on is to be avoided, not because it increases the risk of aquaplaning but because it increases the risk of touching down outside the “zone”. If you know the runway is going to be slippery, it is best to get it on the ground, allow the spoilers to auto deploy and use full reverse thrust as these devises are most effective at higher speeds. Once the aircraft has slowed enough, the auto brakes with anti skid working should start to become effective. Obviously allowing the aircraft to float down the runway because you were after a “greaser” is a bad move in this situation and should be frowned upon.
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It would appear that "bumping down" is still alive and well in a small town 300km to the east of Perth...
The local aviators (worried about avian flu these days I imagine) carefully "bumpdown" by the first or second wire on the runway... (oh, sorry, Rwy 10 doesnt have a cable arrester system, well what were you aiming for?)
Who needs a chiropractor after you have been shown a "bumpdown" reminiscent of Maverick in Top Gun (they all wear the glasses as well)... Even a chiropractor couldnt salvage what would be left of your spinal column...
It is rumoured that these pilots are so adept at "bumping down" that on many occasions they do this with such vigour that ones eyes retract in their sockets and end up somwhere around the anal region, hence the outlook achieved by many a young aviator in their employ...
If "bumping down" is an art, then they should all be bloody picasso... But then again, he put the one ear he had to good use...
The local aviators (worried about avian flu these days I imagine) carefully "bumpdown" by the first or second wire on the runway... (oh, sorry, Rwy 10 doesnt have a cable arrester system, well what were you aiming for?)
Who needs a chiropractor after you have been shown a "bumpdown" reminiscent of Maverick in Top Gun (they all wear the glasses as well)... Even a chiropractor couldnt salvage what would be left of your spinal column...
It is rumoured that these pilots are so adept at "bumping down" that on many occasions they do this with such vigour that ones eyes retract in their sockets and end up somwhere around the anal region, hence the outlook achieved by many a young aviator in their employ...
If "bumping down" is an art, then they should all be bloody picasso... But then again, he put the one ear he had to good use...
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404
How do you think the aircraft decides the mains are on the ground? On all the Boeings I'm familiar with, an armed spoiler pops up automatically when one of the wheels (eg 727 right main) reaches a certain RPM - of course manual deployment can be done at any stage but is usually not the norm. Sounds like the 330 may be different, maybe olio extension - but then, who know's with Airbus (donning flack jacket)
How do you think the aircraft decides the mains are on the ground? On all the Boeings I'm familiar with, an armed spoiler pops up automatically when one of the wheels (eg 727 right main) reaches a certain RPM - of course manual deployment can be done at any stage but is usually not the norm. Sounds like the 330 may be different, maybe olio extension - but then, who know's with Airbus (donning flack jacket)
Kaptin M, I know what you mean about the differing formulae for calculating the aquaplaning speeds. Apparently it is 7.7 if the wheel is not 'spun-up' and 9 if it is
.
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Cloud Cutter
I haven’t flown the B747-400 or the B777 but I have just looked up the relevant section of their FCOM 1’s and nowhere does it refer to the wheels having to spin up before the Ground Spoilers deploy. Maybe it is just a B727 thing or something? It make far more sense to me to have the Ground Spoilers deploy on a squat switch or reverse thrust when you are aquaplaning than on tire spin up which make not occur until you are off the far end of the runway.
Ground Spoilers B747-400 (FCOM 1)
On the ground, the Speedbrake lever stop retracts allowing the Speedbrake lever to be moved fully aft to UP position. All six spoiler panels on each wing extend to their full travel positions.
When the Speedbrake lever is in ARMED position, thrust levers 1 and 3 are near the closed position, and the main landing gear touch down, the Speedbrake lever is driven to UP position, extending all spoiler panels. If the Speedbrake lever is in DN position with the main gear on the ground and thrust levers 1 and 3 near the closed position, and reverse thrust levers 2 or 4 are pulled up to idle detent, the Speedbrake lever is raised out of DN detent and driven to UP position. This provides an automatic ground spoiler function for RTO and provides a backup automatic ground spoiler function for landing when the Speedbrake lever is not armed during approach.
Spoiler Speedbrake Operation B777 (FCOM 1)
In the ARMED position, the speedbrake lever is driven aft to the UP position when the landing gear is fully on the ground (not tilted) and the thrust levers are at idle.
The EICAS memo message SPEEDBRAKE ARMED is displayed when the speedbrake lever is armed.
I haven’t flown the B747-400 or the B777 but I have just looked up the relevant section of their FCOM 1’s and nowhere does it refer to the wheels having to spin up before the Ground Spoilers deploy. Maybe it is just a B727 thing or something? It make far more sense to me to have the Ground Spoilers deploy on a squat switch or reverse thrust when you are aquaplaning than on tire spin up which make not occur until you are off the far end of the runway.
Ground Spoilers B747-400 (FCOM 1)
On the ground, the Speedbrake lever stop retracts allowing the Speedbrake lever to be moved fully aft to UP position. All six spoiler panels on each wing extend to their full travel positions.
When the Speedbrake lever is in ARMED position, thrust levers 1 and 3 are near the closed position, and the main landing gear touch down, the Speedbrake lever is driven to UP position, extending all spoiler panels. If the Speedbrake lever is in DN position with the main gear on the ground and thrust levers 1 and 3 near the closed position, and reverse thrust levers 2 or 4 are pulled up to idle detent, the Speedbrake lever is raised out of DN detent and driven to UP position. This provides an automatic ground spoiler function for RTO and provides a backup automatic ground spoiler function for landing when the Speedbrake lever is not armed during approach.
Spoiler Speedbrake Operation B777 (FCOM 1)
In the ARMED position, the speedbrake lever is driven aft to the UP position when the landing gear is fully on the ground (not tilted) and the thrust levers are at idle.
The EICAS memo message SPEEDBRAKE ARMED is displayed when the speedbrake lever is armed.
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Hey!...do we really need all this bloody hi-tech mumbo jumbo?
Everybody with their bloody ego hang ups trying to out-ego every one else with their super duper mathematical formulas about how to land a bloody aeroplane with a bit of bloody water on the bloody runway!
For crying out loud!...just read the bloody Ops Manual!!!
It's all there, you silly bloody Donkeys!!
Everybody with their bloody ego hang ups trying to out-ego every one else with their super duper mathematical formulas about how to land a bloody aeroplane with a bit of bloody water on the bloody runway!
For crying out loud!...just read the bloody Ops Manual!!!
It's all there, you silly bloody Donkeys!!
Kap,
Others (including yourself) with a greater understanding of this phenomina have made this a very educational thread. Thanks and I stand corrected on my misunderstanding.
This is known as admitting error-try it some time.
Amos,
If you have no interest in how Aeroplanes work, B***** off back to your fishing and but out of conversations between people who have something worthwhile to contribute.
Others (including yourself) with a greater understanding of this phenomina have made this a very educational thread. Thanks and I stand corrected on my misunderstanding.
This is known as admitting error-try it some time.
Amos,
If you have no interest in how Aeroplanes work, B***** off back to your fishing and but out of conversations between people who have something worthwhile to contribute.
Claret,
Yes I was the odd man out, and would land in the touchdown zone and taxi to the apron rather than hover taxi..
I was a big critic of the practice and was very disappointed that the check and training people in Perth actually encouraged it.
Yes I was the odd man out, and would land in the touchdown zone and taxi to the apron rather than hover taxi..
I was a big critic of the practice and was very disappointed that the check and training people in Perth actually encouraged it.
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It is more than two years since I left aviation, and I may be wrong, but I understood that, to have spoilers deploy automatically on touchdown of either Boeing OR Airbus, the following were necessary:
1. "Spoilers" lever to "ARMED"
2. "Weight-on-wheels" (squat) switch made
3. Both power levers at "Ground Idle" position
Spoilers will then deploy automatically, or have I got it wrong?
Kind regards,
TheNightOwl.
1. "Spoilers" lever to "ARMED"
2. "Weight-on-wheels" (squat) switch made
3. Both power levers at "Ground Idle" position
Spoilers will then deploy automatically, or have I got it wrong?
Kind regards,
TheNightOwl.
Well, the way I see it....everyone that doesn't know anything about flying (ie most pax) will always judge the skill of the pilot by their landings. So, if they fly with company X and find their landings a bit "firm" and then fly with company Y who grease em on....me thinks that they'll think that these pilots are better and will wanna fly with them.
I've got friends outside the industry that live by this rule....the better the landing...the better the pilot...therefore I'm flying with them always!!!
So, if runway is available and weather conditions ok, then why not grease it on? In saying that though if it's raining or there's crosswind or on a short runway then by all means a positive touchdown is the saftest option.
My two cents worth anyway.
I've got friends outside the industry that live by this rule....the better the landing...the better the pilot...therefore I'm flying with them always!!!
So, if runway is available and weather conditions ok, then why not grease it on? In saying that though if it's raining or there's crosswind or on a short runway then by all means a positive touchdown is the saftest option.
My two cents worth anyway.
Moderate, Modest & Mild.
"more than two tears since I left aviation" - Freudian slip there, TNO?
You are pretty much right - from the B737-400 Boeing manual
During landing, the auto speed brake system operates when these conditions occur:
- SPEED BRAKE lever is in the ARMED position
- SPEED BRAKE armed light is illuminated
- both thrust levers are retarded to idle
- main landing gear wheels spin up (more than 60 kts) - SPEED BRAKE LEVER automatically moves to the UP position, and the flight spoilers deploy
- right main landing gear strut compresses on touchdown, causing the mechanical linkage to open the ground spoiler bypass valve, and the ground spoilers deploy.
If a wheel spin-up is not detected, when the air/ground system senses ground mode, the SPEED BRAKE lever moves to the UP position, and all spoiler panels deploy automatically.
You are pretty much right - from the B737-400 Boeing manual
During landing, the auto speed brake system operates when these conditions occur:
- SPEED BRAKE lever is in the ARMED position
- SPEED BRAKE armed light is illuminated
- both thrust levers are retarded to idle
- main landing gear wheels spin up (more than 60 kts) - SPEED BRAKE LEVER automatically moves to the UP position, and the flight spoilers deploy
- right main landing gear strut compresses on touchdown, causing the mechanical linkage to open the ground spoiler bypass valve, and the ground spoilers deploy.
If a wheel spin-up is not detected, when the air/ground system senses ground mode, the SPEED BRAKE lever moves to the UP position, and all spoiler panels deploy automatically.
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Umm, back on topic, (Surely you do more dry landings than wet anyway).....
If it is too hard to land decently, and you must dump it onto the runway.. surely you would need better training to land it decently on the right spot then? My dear old dad would never forgive me if i had that excuse doing circuits...
If it is too hard to land decently, and you must dump it onto the runway.. surely you would need better training to land it decently on the right spot then? My dear old dad would never forgive me if i had that excuse doing circuits...