Practical Hydroplanning Advice
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Practical Hydroplanning Advice
I just realized something the other day. I know the types of hydroplanning and formulas. However, no one has really taught me practical techniques to use while facing hydroplanning in real-life during Takeoff and Landing.
The only advice I have ever received was that while facing hydroplanning during landing, you would want to plant the aircraft firmly on the ground. No advice about use of thrust reverse.
The are three types of hydroplanning. Dynamic, viscous and reverted rubber. There are two scenarios that we can encounter. Take off and landing. So, that should mean that there should be 6 scenarios we can face. So, what techniques would you use in these 6 scenarios?
Look forward to your responses
The only advice I have ever received was that while facing hydroplanning during landing, you would want to plant the aircraft firmly on the ground. No advice about use of thrust reverse.
The are three types of hydroplanning. Dynamic, viscous and reverted rubber. There are two scenarios that we can encounter. Take off and landing. So, that should mean that there should be 6 scenarios we can face. So, what techniques would you use in these 6 scenarios?
Look forward to your responses
ok, just 'cause it's low hanging fruit...
I'm glad you're "..planning" about hydroPLANING".
Sorry, just couldn't resist. I'm sure someone here has something relevant to say.
I'm glad you're "..planning" about hydroPLANING".
Sorry, just couldn't resist. I'm sure someone here has something relevant to say.
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Techniques will vary with the type of airplane (light/heavy), installed equipment (antiskid brakes, thrust reversers, etc), and Operating Manual procedures. Also, there is no way for you to analyze and identify the type of hydroplaning you might encounter in real time.
On takeoff, hydroplaning should not be a factor except in a significant crosswind. Use normal crosswind techniques. If you think controlability will be a problem, don't take off!
On landing, there may be 2 significant factors that affect hydroplaning: crosswind and braking. Again, use standard crosswind techniques when applicable. Use the longest runway available and use charts for "poor" braking conditions if you think hydroplaning will be a problem. If landing distance is marginal, go somewhere else. If you encounter controllability problems on the runway due to hydroplaning, consider a rejected landing.
Use aerodynamic braking if allowed. If you have thrust reversers, use them to minimize wheel braking. If you have anti-skid brakes, use them, because they will work to minimize the effects of hydroplaning. If no anti-skid brakes, use them judiciously and release them if you start skidding.
On takeoff, hydroplaning should not be a factor except in a significant crosswind. Use normal crosswind techniques. If you think controlability will be a problem, don't take off!
On landing, there may be 2 significant factors that affect hydroplaning: crosswind and braking. Again, use standard crosswind techniques when applicable. Use the longest runway available and use charts for "poor" braking conditions if you think hydroplaning will be a problem. If landing distance is marginal, go somewhere else. If you encounter controllability problems on the runway due to hydroplaning, consider a rejected landing.
Use aerodynamic braking if allowed. If you have thrust reversers, use them to minimize wheel braking. If you have anti-skid brakes, use them, because they will work to minimize the effects of hydroplaning. If no anti-skid brakes, use them judiciously and release them if you start skidding.
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A couple of additionals.
Fly the airplane down the runway...meaning those flight controls still put out a lot of effort even though all three gear are on the ground.
Discontinue all reverse thrust IMMEDIATELY if yaw is anything other than down the runway. The reversers will suck you sideways if a skid starts. Once straightened out again, you can go back to them, but beware the sideways yaw in T/R.
AntiSkid is your best friend.
Fly the airplane down the runway...meaning those flight controls still put out a lot of effort even though all three gear are on the ground.
Discontinue all reverse thrust IMMEDIATELY if yaw is anything other than down the runway. The reversers will suck you sideways if a skid starts. Once straightened out again, you can go back to them, but beware the sideways yaw in T/R.
AntiSkid is your best friend.
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There is that rough old formula for determining the hydroplaning speed of a pneumatically tyred vehicle, be it a bicycle or an A380.
Speed in MPH = 9 X (the square root of the tyre pressure in PSI).
That means that you will lose it in your car, having tyre pressures of 36 PSI, at any speed over 54 MPH when you try to traverse across sheet water on the road.
There is no function for weight so planting your aircraft hard on to a water covered runway or smooth lake at speeds above the hydroplaning speed will not get your tyres through a water layer. Give this myth to the Mythbusters.
Regardless I don't want to be the first to skim a lake with a heavy heavy.
Speed in MPH = 9 X (the square root of the tyre pressure in PSI).
That means that you will lose it in your car, having tyre pressures of 36 PSI, at any speed over 54 MPH when you try to traverse across sheet water on the road.
There is no function for weight so planting your aircraft hard on to a water covered runway or smooth lake at speeds above the hydroplaning speed will not get your tyres through a water layer. Give this myth to the Mythbusters.
Regardless I don't want to be the first to skim a lake with a heavy heavy.
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A Hydroplane is a kind of speedboat. Did you by any chance mean to ask about "Aquaplaning"????
Hydroplane - Wikipedia, the free encyclopedia
Never mind. Accuracy has never been seen as particurlarly important on PPRuNe.
Hydroplane - Wikipedia, the free encyclopedia
Never mind. Accuracy has never been seen as particurlarly important on PPRuNe.
Last edited by Agaricus bisporus; 19th Sep 2009 at 19:22.
you would want to plant the aircraft firmly on the ground.
Speed in MPH = 9 X (the square root of the tyre pressure in PSI).
This is also why grooved runways are so effective - water sitting in the grooves doesn't count, and braking on a wet grooved runway is considered by Boeing as equivalent to that on a dry runway. (As an aside, "chevron cuts" - the V-shaped cuts you see on tyres are caused by overly-heavy braking on a grooved runway.)
In 12,000 hours, I have only aquaplaned twice, both times in jets, both times landing in tropical downpours on flooded runways. The experience is much like landing a taildragger - in that, as above, you must constantly "fly" the aircraft by staying lively on the controls (ailerons into wind, rudder to keep straight) until the speed drops (which happens veeerrrryy slowly
) below the aquaplaning speed and the brakes become effective. The aircraft skitters about just like driving on ice at high speed .It is also important that your crosswind landing technique is good enough that you are certain you will touch down with the aircraft tracking down the runway centreline - any drift on touchdown on a flooded runway will probably see you off into the bushes.
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Lots of HP incidents result from crews not spotting contaminated conditions early enough (sudden heavy downpour after preceeding has landed...but before runway inspection takes place). Practical tip ....if your windscreen wipers are on high and still not clearing ...smell a rat.
A Hydroplane is a kind of speedboat. Did you by any chance mean to ask about "Aquaplaning"????
Hydroplane - Wikipedia, the free encyclopedia
Never mind. Accuracy has never been seen as particurlarly important on PPRuNe.
Hydroplane - Wikipedia, the free encyclopedia
Never mind. Accuracy has never been seen as particurlarly important on PPRuNe.
Agaricus bisporus, may I recommend something less flavour of the day but more practical in terms of not looking like an idiot: a dictionary. My copy of the Oxford English Dictionary contains the following entry:
hydroplane
- noun 1 a light, fast motor boat. 2 a fin-like attachment which enables a moving submarine to rise or fall in the water. 3 us a seaplane
- verb another term for aquaplane
Most people are familiar with the 9*square root formula from D. P.Davies excellent "Handling the big jets", however, if you want to read the original NASA research paper, gathering together and fully explaining the research from both NASA and the Royal Aircraft Establishment, it's here:
You can skip the maths, but the rest is an excellent easy to understand description of the entire event, under each of the controlling conditions.
PHENOMENA OF PNEUMATIC TIRE HYDROPLANING (1963)
By Walter B. Horne and Robert C. Dreher
By Walter B. Horne and Robert C. Dreher
You can skip the maths, but the rest is an excellent easy to understand description of the entire event, under each of the controlling conditions.
Last edited by Checkboard; 20th Sep 2009 at 12:18.
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2 caveats to posts above:
1)
- remember that once the reversers have deployed (which should be quickly!) a 'rejected landing' is not a good idea and is forbidden in most operations.
2) As you all reach for your calculators and tech notes, remember that 9 root p is only valid for PSI in the tyre and knots on the ASI
1)
Originally Posted by Intruder
If you encounter controllability problems on the runway due to hydroplaning, consider a rejected landing.
2) As you all reach for your calculators and tech notes, remember that 9 root p is only valid for PSI in the tyre and knots on the ASI
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For Info
There were a series of trials done by Cranfield on aquaplaning
using a Hunter (there was a gap left between the ponds for the nose wheel to run in so the pilot had a steering function) so there should be a report on them somewhere.
There were a series of trials done by Cranfield on aquaplaning
using a Hunter (there was a gap left between the ponds for the nose wheel to run in so the pilot had a steering function) so there should be a report on them somewhere.
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Reverse thrust aside (that may disrupt water level tension). Just like a car ,the first wheel that is in the breaked position will become the pivitol point of contact. Anti skid is great.
Landing distance being degraded, the goal is to break the water tension. There are several methods to do so.
Landing distance being degraded, the goal is to break the water tension. There are several methods to do so.
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My opinion....
Only my opinion.....take it for what it's worth. Feel free to throw rocks at me. I won't get upset, nor will I respond.
Fundamentally, there are three kinds of hydroplaning (as mentioned). The formula mentioned is also valid, but misleading.
The 9 times the square root thing applies to a tire that is already spinning at the correct speed. If the tire is stopped (as just prior to landing), and you make a really nice touchdown, the tire may never reach the proper speed, and, at that point, hydroplaning can occur at speeds as low as 6 to 7 times the square root. Firm touchdowns will get the wheels spinning at the proper speeds.
The above formula applies only to "Dynamic" hydroplaning.
Reverted rubber hydroplaning occurs when the tire is allowed to skid. Steam (from boiling water) develops and changes the surface characteristics of the rubber. This new surface characteristic doesn't do as well in stopping the aircraft.
Finally, there is viscous hydroplaning. It occurs when there are contaminants on the runway, such as oil, fuel, rubber deposits, etc.
It is important for you to touchdown firmly at the proper speed and the proper point on the runway. Use maximum reverse thrust immediatley upon touchdown. It is also important to touch down with no lateral drift AND with the aircraft aligned with the runway. No crab. (In some cases, some aircraft, some circumstances, it is necessary to land with some crab, I know....)
If you begin to drift toward the downwind side of the runway, steering to get back to centerline is proper, but, with maximum reverse, you will drift even more. This is because the thrust vector has a lateral component when the aircraft is not perfectly aligned with the runway. So, steer to get back on centerline, and, at the same time, go into idle reverse. Once you're back on centerline and aligned with the centerline, go back to maximum reverse.
The new anti-skid systems are great. The older generation ones are not. You don't want to skid....that's the idea. If you do, you get into a reverted rubber problem. (And, possibly a control problem.)
It's quite possible to experience all three types of hydroplaning in the same landing. First, you make a really nice, smooth landing....the tire really never makes good, solid contact with the runway (dynamic). Then, you skid, for one or many of a number of reasons, and you get reverted rubber. Then, as the other end of the runway comes up, you get into a viscous hydroplaning problem....all the rubber build up from the landings coming the opposite direction...take offs in the opposite direction (oil, fuel, exhaust, etc.).....
Be aware that with reverted rubber...and most especially viscous hydroplaning, hydroplaning can and does occur at any speed...even as low as ten knots. And, many aircraft anti-skid systems do not function at slow speeds. So, this makes things worse.
Again, the idea is to use reverse thrust at max and as soon as possible after touchdown. You want to take advantage of this, as best you can, so the brakes and tires don't have to do as much work at these high speeds. As the speed decreases and reverse thrust effectiveness diminishes, the brakes, tires, and anti-skid system will have to do more of the work...which is OK, since, ostensibly, you're going slower....less chance of dynamic hydroplaning.
Follow SOP with regard to reverse thrust use....but, keep in mind, if you need it, use it. If the end of the runway is rapidly approaching, and your deceleration is not so good...use max reverse...to a full stop if necessary. While this may not comply with SOP, it's far more desirable to the alternative.
By the way, unless your aircraft tires have fancy tread designs (as automobiles have), the tread on your tires has little effect on dynamic hydroplaning. Proper inflation pressure is the critical factor. And, runway grooving is critical, as well.
As I re-read this for typos, I noticed I failed to mention the importance of getting the speed brakes out immediately upon touchdown, as well. The reason for this should be obvious.
Your company's SOP is a good benchmark for operation in adverse weather. Use of autobrake (Today's systems are great!) is desirable. Typically, autobrake, coupled with a good anti-skid system, will allow you to get maximum deceleration (for the conditions given to you), minimizing skidding, maximizing control. Again, follow your company's SOP.
Many times, under adverse conditions, you'll exit the runway at the end or a turn off near the end, where contaminants can be heavy. And, with ATC constraints, you'll be asked to 'expedite' to the next available turn off. Be careful with this, as you'll find that when it's time to slow for the turn off, you'll be unable to slow....anti-skid system is not active because of the low speed (20 Kts for the Bus)....a lot of rubber and oil, etc., on the runway....and you'll slide right past your turn off. (If you were planing to expedite to the last turn off, you'll have problems....obviously.) So, resist the 'go along, get along' with ATC. They know (or should know) to give a bit more spacing on aircraft on approach, as it'll take a bit longer for aircraft to decelerate and clear the runway under adverse conditions. If the aircraft behind you has to go around, it won't be your fault....it'll be ATC's fault. In other words...one of flying's golden rules: Don't let ATC fly your aircraft!
Just my two cents...
Fly safe,
PantLoad
Fundamentally, there are three kinds of hydroplaning (as mentioned). The formula mentioned is also valid, but misleading.
The 9 times the square root thing applies to a tire that is already spinning at the correct speed. If the tire is stopped (as just prior to landing), and you make a really nice touchdown, the tire may never reach the proper speed, and, at that point, hydroplaning can occur at speeds as low as 6 to 7 times the square root. Firm touchdowns will get the wheels spinning at the proper speeds.
The above formula applies only to "Dynamic" hydroplaning.
Reverted rubber hydroplaning occurs when the tire is allowed to skid. Steam (from boiling water) develops and changes the surface characteristics of the rubber. This new surface characteristic doesn't do as well in stopping the aircraft.
Finally, there is viscous hydroplaning. It occurs when there are contaminants on the runway, such as oil, fuel, rubber deposits, etc.
It is important for you to touchdown firmly at the proper speed and the proper point on the runway. Use maximum reverse thrust immediatley upon touchdown. It is also important to touch down with no lateral drift AND with the aircraft aligned with the runway. No crab. (In some cases, some aircraft, some circumstances, it is necessary to land with some crab, I know....)
If you begin to drift toward the downwind side of the runway, steering to get back to centerline is proper, but, with maximum reverse, you will drift even more. This is because the thrust vector has a lateral component when the aircraft is not perfectly aligned with the runway. So, steer to get back on centerline, and, at the same time, go into idle reverse. Once you're back on centerline and aligned with the centerline, go back to maximum reverse.
The new anti-skid systems are great. The older generation ones are not. You don't want to skid....that's the idea. If you do, you get into a reverted rubber problem. (And, possibly a control problem.)
It's quite possible to experience all three types of hydroplaning in the same landing. First, you make a really nice, smooth landing....the tire really never makes good, solid contact with the runway (dynamic). Then, you skid, for one or many of a number of reasons, and you get reverted rubber. Then, as the other end of the runway comes up, you get into a viscous hydroplaning problem....all the rubber build up from the landings coming the opposite direction...take offs in the opposite direction (oil, fuel, exhaust, etc.).....
Be aware that with reverted rubber...and most especially viscous hydroplaning, hydroplaning can and does occur at any speed...even as low as ten knots. And, many aircraft anti-skid systems do not function at slow speeds. So, this makes things worse.
Again, the idea is to use reverse thrust at max and as soon as possible after touchdown. You want to take advantage of this, as best you can, so the brakes and tires don't have to do as much work at these high speeds. As the speed decreases and reverse thrust effectiveness diminishes, the brakes, tires, and anti-skid system will have to do more of the work...which is OK, since, ostensibly, you're going slower....less chance of dynamic hydroplaning.
Follow SOP with regard to reverse thrust use....but, keep in mind, if you need it, use it. If the end of the runway is rapidly approaching, and your deceleration is not so good...use max reverse...to a full stop if necessary. While this may not comply with SOP, it's far more desirable to the alternative.
By the way, unless your aircraft tires have fancy tread designs (as automobiles have), the tread on your tires has little effect on dynamic hydroplaning. Proper inflation pressure is the critical factor. And, runway grooving is critical, as well.
As I re-read this for typos, I noticed I failed to mention the importance of getting the speed brakes out immediately upon touchdown, as well. The reason for this should be obvious.
Your company's SOP is a good benchmark for operation in adverse weather. Use of autobrake (Today's systems are great!) is desirable. Typically, autobrake, coupled with a good anti-skid system, will allow you to get maximum deceleration (for the conditions given to you), minimizing skidding, maximizing control. Again, follow your company's SOP.
Many times, under adverse conditions, you'll exit the runway at the end or a turn off near the end, where contaminants can be heavy. And, with ATC constraints, you'll be asked to 'expedite' to the next available turn off. Be careful with this, as you'll find that when it's time to slow for the turn off, you'll be unable to slow....anti-skid system is not active because of the low speed (20 Kts for the Bus)....a lot of rubber and oil, etc., on the runway....and you'll slide right past your turn off. (If you were planing to expedite to the last turn off, you'll have problems....obviously.) So, resist the 'go along, get along' with ATC. They know (or should know) to give a bit more spacing on aircraft on approach, as it'll take a bit longer for aircraft to decelerate and clear the runway under adverse conditions. If the aircraft behind you has to go around, it won't be your fault....it'll be ATC's fault. In other words...one of flying's golden rules: Don't let ATC fly your aircraft!
Just my two cents...
Fly safe,
PantLoad
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If anyone is searching I'm pretty sure it was a 'down-and-welded' Supermarine Swift they used for the trials.
From flight archive: 1971 | 1620 | Flight Archive
However, the department also undertakes research
and development flying under contract to the Ministry of
Aviation Supply, and recent projects have included
aquaplaning trials using a Hunter and variable stability
research for which a Bassett and, more recently, a Twin
Comanche have been the vehicles.
Also mentioned in this blog:http://viewfromthecockpit.**********...1_archive.html
The Department of Flight, which operated the Doves, also had a French Morane-Saulnier MS 760 Paris jet for flight testing. The department also operated a Supermarine Swift jet fighter (later replaced by a Hawker Hunter) for aquaplaning trials carried out on the main runway. To facilitate these trials the runway was checker-boarded with rubber dams which formed artificial lakes. Cranfield also had a gliding club and in addition the Department of Flight operated a Training Flight using Auster Aiglets. This was my idea of heaven.
b l o g s p o t/2009_07_01_archive.html (without the spaces)
The Boeing FCTM makes an interesting point about releasing the brakes if you are going sideways in reverse during the landing run on a slippery runway with crosswind. Among other things it states: "To correct back to the centreline, reduce thrust to idle reverse and release the brakes". It also says "Main gear tire cornering forces available to counteract this drift are at a minimum when the antiskid system is operating at maximum effectiveness for the existing conditions."
So you have the situation where a slippery runway has a crosswind and normally the pilot would select an appropriate autobrake setting depending on landing weight and runway length. You plant the aircraft beautifully at the 1000 ft markers and apply full reverse (reverse is most effective at high speed) and you think the autobrakes are working but it is initially hard to tell on a slippery runway. They are probably working but the decelleration is hard to feel although you could have a quick glance at the green line going backwards on your glass cocpit ADI.
A sideways drift hits and the aircraft weathercocks. The book says to go to idle thrust (ever tried to reduce to idle thrust quickly without coming out of reverse completely - you need lots of practice I tell you).
The N1 is spooling down and you quickly dab hard on the downwind brake in order to straighten up. That dab immediately disconnects the autobrake system and the aautobrake disarm light comes on. Chances are the PNF does not notice the autobrake light illuminate because he is sweating on you straightening the aircraft before it slides off the edge. You didn't see the light come on either, because you too are sweating on trying to straighten up.
The aircraft now is hopefully straightening up under the influence of your dab of the downwind brake pedal and you relax knowing the autobrake is working hard to pull you up - except it has been inadvertently disengaged by your little dab. Now tracking straight you rip back into reverse but it takes a long time from 23 percent N1 in idle reverse to wind up to 89 percent or full reverse. No problem with a long slippery runway but a real bind if it is a limiting length runway.
Let's go back to the advice contained in the FCTM. How would you interpret that advice with regards to the words "Reduce reverse thrust to reverse idle and release the brakes."
Does this mean you switch off the autobrakes? If so, what is the fastest way of doing that? Override by depressing hard on the brake pedals - or maybe having the PNF turn the autobrake selector off? Or perhaps put the speed brake lever in the down detent which turns off the autobrakes? The latter is a bit of a risk because you need spoilers to dump lift and put weight on the mains.
It all becomes a bit convoluted doesn't it. The tricky part as I see it is deciding in a flash how to take the brakes off as you are going sideways. Makes for a good discussion.
So you have the situation where a slippery runway has a crosswind and normally the pilot would select an appropriate autobrake setting depending on landing weight and runway length. You plant the aircraft beautifully at the 1000 ft markers and apply full reverse (reverse is most effective at high speed) and you think the autobrakes are working but it is initially hard to tell on a slippery runway. They are probably working but the decelleration is hard to feel although you could have a quick glance at the green line going backwards on your glass cocpit ADI.
A sideways drift hits and the aircraft weathercocks. The book says to go to idle thrust (ever tried to reduce to idle thrust quickly without coming out of reverse completely - you need lots of practice I tell you).
The N1 is spooling down and you quickly dab hard on the downwind brake in order to straighten up. That dab immediately disconnects the autobrake system and the aautobrake disarm light comes on. Chances are the PNF does not notice the autobrake light illuminate because he is sweating on you straightening the aircraft before it slides off the edge. You didn't see the light come on either, because you too are sweating on trying to straighten up.
The aircraft now is hopefully straightening up under the influence of your dab of the downwind brake pedal and you relax knowing the autobrake is working hard to pull you up - except it has been inadvertently disengaged by your little dab. Now tracking straight you rip back into reverse but it takes a long time from 23 percent N1 in idle reverse to wind up to 89 percent or full reverse. No problem with a long slippery runway but a real bind if it is a limiting length runway.
Let's go back to the advice contained in the FCTM. How would you interpret that advice with regards to the words "Reduce reverse thrust to reverse idle and release the brakes."
Does this mean you switch off the autobrakes? If so, what is the fastest way of doing that? Override by depressing hard on the brake pedals - or maybe having the PNF turn the autobrake selector off? Or perhaps put the speed brake lever in the down detent which turns off the autobrakes? The latter is a bit of a risk because you need spoilers to dump lift and put weight on the mains.
It all becomes a bit convoluted doesn't it. The tricky part as I see it is deciding in a flash how to take the brakes off as you are going sideways. Makes for a good discussion.