Pulling a Stop to Runway Overruns
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Not Losing Sight of the Aim.....
RatherbeFlying said:
Can't disagree with that. It's manifestly the distilled essence of the underlying theory. I might have said: "plus the aerodynamic downforce." Seeing it as the resultant of two moments or a type 2 lever acting upon the nose-gear as a dynamic fulcrum is also valid. But what is obvious (and missed by most) is that there is an "effective" weight shift towards the nose. i.e. We are getting side-tracked by static Center of Gravity computations saying that only about 5% of an aircraft's mass acts through the nosewheel. May be true but it's a red herring in this dynamic flight context. RBF's succinct statement also doesn't address (but obviously accepts) the reason why the nose stays down (a nose-down pitch is induced by reverse and whatever braking you are achieving courtesy of spoiler lift-dump when the progressive backstick input commences). As the backstick increases, wheel-braking becomes more effective, thus allowing more backstick etc etc. Eventually you do end up on the backstops, but by that time you will have killed that speed increment above the min aquaplaning speed -as well as any directional control or cross-wind induced problems that you may have otherwise had.
The process is dynamic and what is being advocated is an early accelerated rate of deceleration. That dynamic process compares with the Air France, QF1 and SWA pregnant pause hiatus where there were interlock problems entering reverse and indecision/mind-changing. The latter process eats up landing real-estate at a great rate of knots and kills your options - whereas the backstick braking uses those knots to achieve very early efficient deceleration before the aircraft reaches that last 2000 odd feet of rubberised runway remaining. Chalk and cheese. Success and failure/disaster. I suspect that, in the fullness of time, Airbus (at least) will be automating the advocated process.
MFS said:
MFS then goes on to draw invalid comparisons of parked a/c and the effect of significant winds, disregarding the nose-down pitching moments that result from reverse and spoiler-assisted early braking. His conclusions are invalid because we are talking about 2 completely different scenarios:
a. static parked weight distribution with nose-up stab trim combatting local wind effects and
b. a 1.1.Vs or greater handling technique with engines running and reversing, spoilers up and a pilot making appropriate control inputs).
.
It is difficult to clearly discuss the nuances of handling techniques with engineers (even flight engineers) - or so I've found. Handling is not like placing a switch at A, B or centrally OFF. Handling is about moderated input tempered by observed reaction. An OFF/ON selection of instant full backstick is not what's being advocated at all. However MFS does introduce (and remind us of) that all-important "square of the speed" factor - which is also a player when considering the effect of early backstick after touchdown. It is certainly what empowers that backstick-induced early breakthrough (to the bitumen) for the main-gear wheels. "EARLY" is also the point at which the effect of reverse thrust (and its pitchdown moment) is maximal (then gradually tapering off).
A mite harum scarum -but that has been your [MFS] underlying theme. I'd suggest that it's only MFS with the trepidations. All the Xperimental TP's that I've known in the RAF, BAe and elsewhere would say: "well let's do some sums and then go find out. Anything that can stop this wasteful "off the end" bizzo is worthwhile exploring and exploiting. It may even be a great marketing tool if it was automated. Let's go talk to some aerodynamics people and perhaps get them to write a program for the iron bird. The simulator should tell us what's what."
RBF said:
Bravo for keeping an open mind and identifying the unsubtle difference.
MFS said:
Five bucks for whoever can get MFS off his FULL backstick bandwagon.... and start entertaining the full vista of forces at play during the dynamics of landing deceleration. i.e.
,
a. REVERSE - greatest effect at the outset => strong nose-down pitch (NDP)
.
b. Braking - It is agreed that despite spoilers assisting, that braking is minimal at the outset on a slippery surface (but then again, that is the actual problem) but still =>(NDP) (initially only equivalent to only another +5% of a/c mass - according to MFS)
.
c. Center of Gravity - I won't venture whether this is MUCH more pro or con at landing (versus take-off) but I suspect that in the landing configuration it's in most cases helping our quest (for a counterbalance to introduced backstick). But no matter how far it's moved as fuel burns off, it will still be telling the nose firmly "to stay down" => (NDP)
.
d. Spoilers will be up and, per the T-W/L-D couple, should also be helping kill lift and admonishing the nose to stay down. i.e. =>(NDP)
.
a+b+c+d => a powerful counterbalancing (but varying) total nose-down force against which we can introduce our proposed progressive backstick
.
So throughout the early landing evolution, speed dissipates at "some rate" and braking will improve "somewhat". Once in reverse, early pilot introduction of progressive backstick will have the desired effect and will improve braking effectiveness (which will in turn enable more backstick, etc etc). Certainly "forward" stick has more than its fair share of perils (link) ("..it appeared that the captain’s technique for landing at Gibraltar differed from that at other destinations, with an evident, if unconscious, propensity to apply full nose-down elevator right after main landing gear touchdown. Immediately after the incident, Monarch modified its FDM software to include nose-down elevator as an "event."). G-MONC was out of service for over 2 months and required >$6M in repairs.
.
The "effective" weight-shift toward the nose will be that imparted by aircraft momentum and retardation forces acting around various axes (and thus summed in ft/lbs). Overall, the early "stickiness" of the nose very much depends upon the total magnitude of the nose-down couples mentioned above. MFS chooses to ignore the cumulative effect.... and why that should be is a mystery - but perhaps it just helps his argument. It is conceded that the diminishing effect of reverse as the a/c slows will be countered by the increased effectiveness of braking.... probably making it a zero-sum game. However that's of no real consequence because the pitch-up authority of the (by that time) full backstick will have faded to insignificant.
.
The theory disregards all the other factors acting for and against a successful stop within runway available as being irrelevant - however it should be noted that it will be particularly effective at combating high groundspeeds caused by landing with the wind (rather than against it). Sometimes it is expedient to accept a tailwind component, but always it is less safe to do so. At such times, the value of backstick braking will be to restore the balance in favour of the pilot not running out of career or runway. Not to be forgotten (also) is the stabilizing effect of getting the weight shift redistributed to the tricycle geometry that gives best directional control. Stick forward can be destructive (G-MONC) but the wheel-barrowing effect of any unopposed weight-shift forward can also cause great directional instability, particularly on a wet runway in a crosswind.
.
Ultimately the aim is to have the theory revalidated and assessed for effectiveness. It is nothing more than a handling technique that seeks to minimize the intervention of anti-skid on inhospitable surfaces by increasing the weight-on-wheels as soon as possible in the landing roll. If it is assessed as worthy, then everybody is better off....and at nil cost. It's a principle called regrets management....and it contrasts well with risk management (which lets us down more often than not).
Overtalk
Pilot Retard Advocate
The fulcrum on the ground is the maingear axle. Backstick produces down force at the tail which:
Adds to the total load on all gears
Produces a nose-up moment which relieves a portion of the load on the nose-gear such that the maingear supports a larger portion of the total weight plus any aerodynamic downforce.
Adds to the total load on all gears
Produces a nose-up moment which relieves a portion of the load on the nose-gear such that the maingear supports a larger portion of the total weight plus any aerodynamic downforce.
This may result in a change in AOA and lift....
MFS said:
"assuming that there is NO aerodynamic download, which is an optimistic assumption for this method...."
a. static parked weight distribution with nose-up stab trim combatting local wind effects and
b. a 1.1.Vs or greater handling technique with engines running and reversing, spoilers up and a pilot making appropriate control inputs).
.
It is difficult to clearly discuss the nuances of handling techniques with engineers (even flight engineers) - or so I've found. Handling is not like placing a switch at A, B or centrally OFF. Handling is about moderated input tempered by observed reaction. An OFF/ON selection of instant full backstick is not what's being advocated at all. However MFS does introduce (and remind us of) that all-important "square of the speed" factor - which is also a player when considering the effect of early backstick after touchdown. It is certainly what empowers that backstick-induced early breakthrough (to the bitumen) for the main-gear wheels. "EARLY" is also the point at which the effect of reverse thrust (and its pitchdown moment) is maximal (then gradually tapering off).
I'm as certain as I can be that you WILL lift the nose under those conditions. Well if it wasn't for the four additive factors producing the strong (and opposing) nose-down pitch during deceleration, I might concede that point. But MFS is single-mindedly stuck in his engineer's view of the airplane as a static entity. After all, that's how you achieve rotation, no? Well no, not really. You have to consider that there's a Thrust/Weight-Lift/Drag couple at work there during lift-off, ably assisted by leading- and trailing-edge devices (and minus spoilers, braking and reverse). If you fuel-chopped all four at the point of pre-rotate (V1) would it still rotate??
"We are scared of someone trying this out with pax in the back and either departing the side of the runway due to loss of NWS/directional control, or raising the nose and actually losing braking effectiveness."
RBF said:
"Static loads while parked and dynamic loads while braking are different cases with greater nose wheel loadings under braking."
MFS said:
1. "The problem is that the case where the nosewheel is most heavily loaded by the braking forces is the case where the brakes are ALREADY WORKING WELL!" MFS -Please see a+b+c+d below for your illogical sequitur
2. "Not enough to overcome full back stick; not even close for some types."
2. "Not enough to overcome full back stick; not even close for some types."
,
a. REVERSE - greatest effect at the outset => strong nose-down pitch (NDP)
.
b. Braking - It is agreed that despite spoilers assisting, that braking is minimal at the outset on a slippery surface (but then again, that is the actual problem) but still =>(NDP) (initially only equivalent to only another +5% of a/c mass - according to MFS)
.
c. Center of Gravity - I won't venture whether this is MUCH more pro or con at landing (versus take-off) but I suspect that in the landing configuration it's in most cases helping our quest (for a counterbalance to introduced backstick). But no matter how far it's moved as fuel burns off, it will still be telling the nose firmly "to stay down" => (NDP)
.
d. Spoilers will be up and, per the T-W/L-D couple, should also be helping kill lift and admonishing the nose to stay down. i.e. =>(NDP)
.
a+b+c+d => a powerful counterbalancing (but varying) total nose-down force against which we can introduce our proposed progressive backstick
.
So throughout the early landing evolution, speed dissipates at "some rate" and braking will improve "somewhat". Once in reverse, early pilot introduction of progressive backstick will have the desired effect and will improve braking effectiveness (which will in turn enable more backstick, etc etc). Certainly "forward" stick has more than its fair share of perils (link) ("..it appeared that the captain’s technique for landing at Gibraltar differed from that at other destinations, with an evident, if unconscious, propensity to apply full nose-down elevator right after main landing gear touchdown. Immediately after the incident, Monarch modified its FDM software to include nose-down elevator as an "event."). G-MONC was out of service for over 2 months and required >$6M in repairs.
.
The "effective" weight-shift toward the nose will be that imparted by aircraft momentum and retardation forces acting around various axes (and thus summed in ft/lbs). Overall, the early "stickiness" of the nose very much depends upon the total magnitude of the nose-down couples mentioned above. MFS chooses to ignore the cumulative effect.... and why that should be is a mystery - but perhaps it just helps his argument. It is conceded that the diminishing effect of reverse as the a/c slows will be countered by the increased effectiveness of braking.... probably making it a zero-sum game. However that's of no real consequence because the pitch-up authority of the (by that time) full backstick will have faded to insignificant.
.
The theory disregards all the other factors acting for and against a successful stop within runway available as being irrelevant - however it should be noted that it will be particularly effective at combating high groundspeeds caused by landing with the wind (rather than against it). Sometimes it is expedient to accept a tailwind component, but always it is less safe to do so. At such times, the value of backstick braking will be to restore the balance in favour of the pilot not running out of career or runway. Not to be forgotten (also) is the stabilizing effect of getting the weight shift redistributed to the tricycle geometry that gives best directional control. Stick forward can be destructive (G-MONC) but the wheel-barrowing effect of any unopposed weight-shift forward can also cause great directional instability, particularly on a wet runway in a crosswind.
.
Ultimately the aim is to have the theory revalidated and assessed for effectiveness. It is nothing more than a handling technique that seeks to minimize the intervention of anti-skid on inhospitable surfaces by increasing the weight-on-wheels as soon as possible in the landing roll. If it is assessed as worthy, then everybody is better off....and at nil cost. It's a principle called regrets management....and it contrasts well with risk management (which lets us down more often than not).
Overtalk
Pilot Retard Advocate
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Moderately Speaking....
JT
I recognize your MFS and alf5071h and apologize for any perceived brusqueness. However intolerant I might seem, I am interested in stopping the pointless overruns. The frustrations arise from "knowing how to" being just drowned (in typical Pprune fashion) by a sea of doubting thomases, many of whom need more than simple convincing. Argument for argument's sake normally sends me scarpering. However I've stuck with this one because I'd like to see somebody somewhere move convincingly on the overrun problem.
However I will also raise you a John Farley and a Tony Spence (ETPS grad) from amongst my familiars. Anthony Brown the well-known Canadian aerodynamicist was a one-time copilot of mine. We've corresponded on major accident causes.
I've previously fought this one out with the famed poisoned dwarf (Bo Plummer, the longest serving RAF A1 QFI) and "Farmer" Rod Brown (2nd longest) - and was not found wanting. Prof Peter Ladkin and I often agree as much as we disagree, but he knows who I am. Ray Hudson (MD-11 and F35 flt control designer) and I have often sparred - and always find middle ground. I've often corresponded with Graeme Braithwaite (Cranfield). I also write for ASW. I could go on.... but won't.
I base my theory on practice - and that's as close as anybody can ever hope to get to a working hypothesis.
I recognize your MFS and alf5071h and apologize for any perceived brusqueness. However intolerant I might seem, I am interested in stopping the pointless overruns. The frustrations arise from "knowing how to" being just drowned (in typical Pprune fashion) by a sea of doubting thomases, many of whom need more than simple convincing. Argument for argument's sake normally sends me scarpering. However I've stuck with this one because I'd like to see somebody somewhere move convincingly on the overrun problem.
However I will also raise you a John Farley and a Tony Spence (ETPS grad) from amongst my familiars. Anthony Brown the well-known Canadian aerodynamicist was a one-time copilot of mine. We've corresponded on major accident causes.
I've previously fought this one out with the famed poisoned dwarf (Bo Plummer, the longest serving RAF A1 QFI) and "Farmer" Rod Brown (2nd longest) - and was not found wanting. Prof Peter Ladkin and I often agree as much as we disagree, but he knows who I am. Ray Hudson (MD-11 and F35 flt control designer) and I have often sparred - and always find middle ground. I've often corresponded with Graeme Braithwaite (Cranfield). I also write for ASW. I could go on.... but won't.
I base my theory on practice - and that's as close as anybody can ever hope to get to a working hypothesis.
Moderator
Re: Pulling a Stop to Runway Overruns
My friend ... no-one is saying that your position is wrong, only that the analysis may be more complex than you suggest.
I would suggest that the others are NOT purporting that the braking loads case is equivalent to the stationary aircraft .. indeed, to do so would make us consider them in a rather strange light.
As you would be aware, no doubt, JF is a regular in these halls and I imagine that he has been following the thread and may well choose to wade in at an appropriate time. The venerable Milt, likewise, probably is finding it hard to restrain himself.
So long as we observe the normal civil niceties, go your hardest with the argument .. this sort of thread is the single most valuable aspect of this forum.
And we are all on the same team .. and all have an equal interest in reducing the abort/landing risk scenario.
I would suggest that the others are NOT purporting that the braking loads case is equivalent to the stationary aircraft .. indeed, to do so would make us consider them in a rather strange light.
As you would be aware, no doubt, JF is a regular in these halls and I imagine that he has been following the thread and may well choose to wade in at an appropriate time. The venerable Milt, likewise, probably is finding it hard to restrain himself.
So long as we observe the normal civil niceties, go your hardest with the argument .. this sort of thread is the single most valuable aspect of this forum.
And we are all on the same team .. and all have an equal interest in reducing the abort/landing risk scenario.
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Re: Pulling a Stop to Runway Overruns
Gentlemen,
I bow to your obvious superior knowledge of aircraft braking effectiveness. However, I have landed an Electra on a dime with an "in ground effect flare maneuver." The aircraft came to a complete stop upon touchdown. I had to add power to taxi off the runway! This is just an extreme example of momentun control before touchdown, which is not utilized in todays flight operations, to the detriment of flight safety.
I bow to your obvious superior knowledge of aircraft braking effectiveness. However, I have landed an Electra on a dime with an "in ground effect flare maneuver." The aircraft came to a complete stop upon touchdown. I had to add power to taxi off the runway! This is just an extreme example of momentun control before touchdown, which is not utilized in todays flight operations, to the detriment of flight safety.
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A Momentun of Your Time
Wsherif said: "This is just an extreme example of momentun control before touchdown, which is not utilized in todays flight operations, to the detriment of flight safety."
Perhaps you should elaborate on your point.
.
As I understand it, OVERTALK's suggestion (by contrast) is to propose a straight-forward means of stopping contaminated runway overruns (ie. accidents) by enhancing post-touchdown braking effectiveness. That might indeed be an example of something:
<<<which is not utilized in todays flight operations, to the detriment of flight safety.>>>
.
Would you not agree? Or are you disputing that backstick braking works? i.e. as a means of achieving effective braking on slick runways. That doesn't appear to be the case. But perhaps you didn't review the whole thread.
.
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Re: Pulling a Stop to Runway Overruns
Simple question.
Is the nose landing gear oleo FULLY COMPRESSED under braking?
If not then ANY reduction in nosegear download WILL raise the nose, by an amount equal to the reduction in download times the effective spring stiffness of the oleo. I would suggest that there are very few types which completely compress the nose oleos, if for no other reason than to completely compress on an oleo risks mechanical damage and significantly affects nose gear damping behaviour.
If that is a significant distance - and on some types it will be, you may rest assured of that, especially at more aft cgs and lighter weights - then there will be an increase in AoA and corresponding increase in AoA and REDUCTION in load on mains due to increased aerodynamic lift.
Just to be clear: I recognise that OVERTALK and others are suggesting a progressive increase in tail download. The reasons I will CONTINUE to harp on about "full back stick" are:
(1) a procedure which requires modulation of input will ALWAYS carry the risk of someone pulling full back on the "if a little is good, a lot must be better" reasoning
(2) in order to obtain a significant improvement in braking a LOT of tail download is required - to the extent that full back stick will be used at some point
There is already a nominal 67% planning margin between your "landing field length" and "actual landing distance". Unless a technique is going to make a significant impact relative to that 67% margin, it's not going to do much. That means a lot of redistribution of reactions, and that means a lot of tail load.
Is the nose landing gear oleo FULLY COMPRESSED under braking?
If not then ANY reduction in nosegear download WILL raise the nose, by an amount equal to the reduction in download times the effective spring stiffness of the oleo. I would suggest that there are very few types which completely compress the nose oleos, if for no other reason than to completely compress on an oleo risks mechanical damage and significantly affects nose gear damping behaviour.
If that is a significant distance - and on some types it will be, you may rest assured of that, especially at more aft cgs and lighter weights - then there will be an increase in AoA and corresponding increase in AoA and REDUCTION in load on mains due to increased aerodynamic lift.
Just to be clear: I recognise that OVERTALK and others are suggesting a progressive increase in tail download. The reasons I will CONTINUE to harp on about "full back stick" are:
(1) a procedure which requires modulation of input will ALWAYS carry the risk of someone pulling full back on the "if a little is good, a lot must be better" reasoning
(2) in order to obtain a significant improvement in braking a LOT of tail download is required - to the extent that full back stick will be used at some point
There is already a nominal 67% planning margin between your "landing field length" and "actual landing distance". Unless a technique is going to make a significant impact relative to that 67% margin, it's not going to do much. That means a lot of redistribution of reactions, and that means a lot of tail load.
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the writing's already on the wall......
MFS said:
I think that we have lost the physics bubble here. The four retardation scenario factors discussed (a-b-c-d above) are producing a strong nose-down pitching moment. By opposing that moment with progressive backstick soon after spoilers are up and reverse kicks in, we must end up with an effective weight increase on the main-gear - which helps the "rubber more intimately meet the road" so to speak - instead of glissading over the wet and slippery surface. It makes early braking much more effective by minimizing the intervention of anti-skid; and it's even got the improved directional control bonus. If you multiply that tyre/bitumen area interface increase on one tyre by all the tyres on a plane's main-gear, you can appreciate that the overall effect will be worthwhile.
This is a little confusing but I imagine that you meant to say that up elevator would cause the nose oleo to extend and consequently the wing's AoA to increase, thereby acting in an opposite sense to what is being claimed (i.e. reducing the weight upon the main-gear). That that is a fallacy can be exposed by a simple illustration. Put a soft pea (or jelly-bean say) under the midpoint of a 12" rigid ruler and press down on both ends of the ruler. Do it with roughly equal force, simulating a pilot tempering his backstick input to just below what "could" (not saying "would") possibly cause the nose to rise. In other words, braking "for effect" by flying the attitude out the front window. The pea gets squashed of course. That simple experiment replicates the 4 retardation factors producing a nose-down moment at one end of the ruler and, at the other end, the opposing nose-up (i.e. tail-down) moment induced by the backstick. It adequately demonstrates that the resultant will be a down-force upon the maingear (the pea). Now do it with a new "soft pea" yet without the simulated pilot's up-elevator input. The nose drops, tail rises and the pea is unsquashed. That simulates the lack of anything other than the ruler's weight acting upon the "maingear" pea. It emphasizes the need for early introduced backstick braking when the chips are down (i.e. you suspect that you may have landed too far in on a slippery runway and urgently need max effective braking ASAP).
If I was in the RHseat and the reverse had cut in and I knew that we were "down, come what may", yet running short of bitumen - well I'd be urgently calling for backstick and double-checking that the spoilers were up. I have a mind's eye image of both SWA 737 pilots urgently tromping their toe-brakes at Midway recently, the end looming large - yet salvation having been only a pole-grip away. That's the needless futility of not understanding the logic behind backstick braking.
Disagree with your point (1) because I've been there and done that. Pilots that I have trained are told to introduce toe-braking first and then (but almost simultaneously) progressively feed in the backstick, ensuring that the nose stays down. Unless they soon ease up significantly on the brakes while maintaining "the pull", the nose won't rise - in part because, by that time, you will have slowed significantly. It is the hard braking that keeps the nose down (as well as the airspeed loss). The danger of teaching it in a jet without maxarets or anti-skid on a wet runway is perversely that BLOGGs will overcook on the toe-brakes without having adequate backstick in. It's the backstick that keeps the wheels loaded up and the tyres rotating. If you don't stop the wheel, you don't blow the tyre. I can recall writing that across the top of whiteboards in my briefing cubicle for many early type-conversion handling briefs. With autobrakes and anti-skid, the whole exercise is just too easy (unless you're ignorant of the technique and/or don't mind motoring mindlessly off the end). I reiterate that pilots are taught to use two controls at once (in fact directional rudder inputs plus toe-braking, aileron into wind and steering with cocked throttles to compensate for wind is a normal pilot activity that has four unique and discrete inputs). And if challenged, most could probably make an R/T call at the same time. You seem to have a picture of pilots as motor morons incapable of coping with a simple manipulative task. Landing a heavy-weight asymmetric airplane on a wet runway with 50 kts across used to make me salivate with anticipation..... not dread.
(2) <<<....to the extent that full back stick will be used at some point. Agreed (that full backstick may be used), but if that occurs more latterly in the piece, where's the harm? I reiterate that once heavy braking is underway, with or without reverse, that nose-rise just won't happen.
Unfortunately that 67% is roll-out, if I'm not mistaken. Few pilots manage to get to grips with the first few feet of runway. Indeed many PAPI's and glidepaths would have you landing over 1500ft in. When pilots misjudge and make a name for themselves, it's usually because they've grossly misjudged. That can happen as a result of an optical illusion or down-sloping runway or a tail-wind. It's relatively easy to discard 2 or 3 thousand feet of bitumen, yet be unaware of it. Why? Because we haven't got eyes in the backs of our head and a touchdown too far in is not readily apparent. Distance-to-run marker boards are usually only found at military airfields. Landing 1/3rd into a runway at night off a low ceiling in poor vis? That's easily done. When the runway is additionally greasy and ATC has arranged a tailwind for you, don't start any wishful thinking after you've touched down and ripped it into reverse. At that point the writing's already on the wall at the far end of your marginal runway.
Is the nose landing gear oleo FULLY COMPRESSED under braking?..............................................
....then there will be an increase in AoA and corresponding increase in AoA and REDUCTION in load on mains due to increased aerodynamic lift.
....then there will be an increase in AoA and corresponding increase in AoA and REDUCTION in load on mains due to increased aerodynamic lift.
<<<"then there will be an increase in AoA and corresponding increase in AoA and REDUCTION in load on mains due to increased aerodynamic lift.>>>
If I was in the RHseat and the reverse had cut in and I knew that we were "down, come what may", yet running short of bitumen - well I'd be urgently calling for backstick and double-checking that the spoilers were up. I have a mind's eye image of both SWA 737 pilots urgently tromping their toe-brakes at Midway recently, the end looming large - yet salvation having been only a pole-grip away. That's the needless futility of not understanding the logic behind backstick braking.
Just to be clear: I recognise that OVERTALK and others are suggesting a progressive increase in tail download. The reasons I will CONTINUE to harp on about "full back stick" are:
(1) a procedure which requires modulation of input will ALWAYS carry the risk of someone pulling full back on the "if a little is good, a lot must be better" reasoning
(2) in order to obtain a significant improvement in braking a LOT of tail download is required - to the extent that full back stick will be used at some point
(1) a procedure which requires modulation of input will ALWAYS carry the risk of someone pulling full back on the "if a little is good, a lot must be better" reasoning
(2) in order to obtain a significant improvement in braking a LOT of tail download is required - to the extent that full back stick will be used at some point
(2) <<<....to the extent that full back stick will be used at some point. Agreed (that full backstick may be used), but if that occurs more latterly in the piece, where's the harm? I reiterate that once heavy braking is underway, with or without reverse, that nose-rise just won't happen.
There is already a nominal 67% planning margin between your "landing field length" and "actual landing distance". Unless a technique is going to make a significant impact relative to that 67% margin, it's not going to do much. That means a lot of redistribution of reactions, and that means a lot of tail load.
Last edited by OVERTALK; 11th Jan 2006 at 07:51.
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Re: Pulling a Stop to Runway Overruns
(a) the landing distance factor is applied to the demonstrated flight test/aerodynamic model data as accepted by the Regulator and applies to the total demonstrated distance from 50ft, not rollout distance.
(b) may I suggest that, if the approach is flown accurately to a predetermined aiming point, few pilots with any experience to speak of will fail to detect that they have floated significantly beyond the planned touchdown zone ...
(b) may I suggest that, if the approach is flown accurately to a predetermined aiming point, few pilots with any experience to speak of will fail to detect that they have floated significantly beyond the planned touchdown zone ...
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Re: Pulling a Stop to Runway Overruns
<<<total demonstrated distance from 50ft,>>> by test pilots, probably in good weather in a pristine jet.
<<<<if the approach is flown accurately to a predetermined aiming point, few pilots with any experience to speak of will fail to detect that they have floated significantly beyond the planned touchdown zone ...>>>>
Must be another explanation for all the overruns then, although most that I have read about or heard about seem to have landed well down the runway and frequently hot. Usually there's a weather component or tailwind. The Air France A340 in Toronto touched down around 2000m in.
Rejecting a proposed technique on the basis or with the assertion that pilots wouldn't have problems if they did everything correctly is to deny that fatigue, illusions, CRM breakdowns and mishandling regularly occurs.
That ruler and pea analogy above (in OVERTALK's post) works for me. What further proof does anybody need (beyond flight test)?
<<<<if the approach is flown accurately to a predetermined aiming point, few pilots with any experience to speak of will fail to detect that they have floated significantly beyond the planned touchdown zone ...>>>>
Must be another explanation for all the overruns then, although most that I have read about or heard about seem to have landed well down the runway and frequently hot. Usually there's a weather component or tailwind. The Air France A340 in Toronto touched down around 2000m in.
Rejecting a proposed technique on the basis or with the assertion that pilots wouldn't have problems if they did everything correctly is to deny that fatigue, illusions, CRM breakdowns and mishandling regularly occurs.
That ruler and pea analogy above (in OVERTALK's post) works for me. What further proof does anybody need (beyond flight test)?
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Re: A Momentun of Your Time
Originally Posted by UNCTUOUS
.
Perhaps you should elaborate on your point.
.
As I understand it, OVERTALK's suggestion (by contrast) is to propose a straight-forward means of stopping contaminated runway overruns (ie. accidents) by enhancing post-touchdown braking effectiveness. That might indeed be an example of something:
<<<which is not utilized in todays flight operations, to the detriment of flight safety.>>>
.
Would you not agree? Or are you disputing that backstick braking works? i.e. as a means of achieving effective braking on slick runways. That doesn't appear to be the case. But perhaps you didn't review the whole thread.
.
Perhaps you should elaborate on your point.
.
As I understand it, OVERTALK's suggestion (by contrast) is to propose a straight-forward means of stopping contaminated runway overruns (ie. accidents) by enhancing post-touchdown braking effectiveness. That might indeed be an example of something:
<<<which is not utilized in todays flight operations, to the detriment of flight safety.>>>
.
Would you not agree? Or are you disputing that backstick braking works? i.e. as a means of achieving effective braking on slick runways. That doesn't appear to be the case. But perhaps you didn't review the whole thread.
.
Re: Pulling a Stop to Runway Overruns
There is general agreement about the theory of how progressive back stick during landing should increase main wheel load and assist braking, although there are some interesting and debatable explanations of the physics, actually mechanics, of how this is achieved.
There have been several parallel inputs about the overall effectiveness of the technique when applying it practically to a wide range of aircraft and operations, and many issues have been identified which could negate any improvement or even be detrimental to safety, especially in crosswinds.
Given these inputs, it is difficult to understand how individuals can persist with the view that their specific experiences on one or a few aircraft will apply universally to all aircraft and operations. There is an overwhelming need to remind operators to heed manufacture’s advice to ensure continued safe operations; the doubters should read the thread on the Emirates A340 incident.
I had hoped that from the posts of 10th Jan alternative aspects of the ‘interest in stopping pointless overruns’ would be explored.
There have been several threads on the hazards of contaminated runways (where 67% margin may not be available), and then there are the issues of landing long and / or fast, for which there are approved solutions with proven safety benefits.
In recent years, there has been more focus on human factors, particularly the frailties in awareness and decision making. Therefore, perhaps the safety focus that we require is ensuring pilots’ use of their ‘superior judgment’ before landing, rather than the superior skill on the runway, which some would claim.
There have been several parallel inputs about the overall effectiveness of the technique when applying it practically to a wide range of aircraft and operations, and many issues have been identified which could negate any improvement or even be detrimental to safety, especially in crosswinds.
Given these inputs, it is difficult to understand how individuals can persist with the view that their specific experiences on one or a few aircraft will apply universally to all aircraft and operations. There is an overwhelming need to remind operators to heed manufacture’s advice to ensure continued safe operations; the doubters should read the thread on the Emirates A340 incident.
I had hoped that from the posts of 10th Jan alternative aspects of the ‘interest in stopping pointless overruns’ would be explored.
There have been several threads on the hazards of contaminated runways (where 67% margin may not be available), and then there are the issues of landing long and / or fast, for which there are approved solutions with proven safety benefits.
In recent years, there has been more focus on human factors, particularly the frailties in awareness and decision making. Therefore, perhaps the safety focus that we require is ensuring pilots’ use of their ‘superior judgment’ before landing, rather than the superior skill on the runway, which some would claim.
Re: Pulling a Stop to Runway Overruns
Mad (Flt) Scientist said:
My understanding of the margins built in to the Landing Distance Required (for the B737 at least) are:
DRY RUNWAY: Actual demonstrated landing distance from 50 ft to complete stop multiplied by 1.67.
WET RUNWAY: (no more than 3 mm of standing water): Actual demonstrated landing distance (on a dry runway) multiplied by 1.67, multiplied by 1.15.
CONTAMINATED RUNWAY: (more than 3 mm but no more than 13 mm of standing water, compacted snow, ice): "Calculated" landing distance for either Good/Fair, or Poor reported braking action multiplied by 1.15. So the margin for error and variables is only 15%, not 67%.
Interestingly, our manual states that contaminated runway performance data is only "Guidance Information".
So with the contaminated runway scenario in mind, any technique that improves the actual landing distance by just 1.5% increases the safety margin by a whopping 10% (1/10th of 15%)!!
It's been a very interesting thread so far. Thanks everyone.
There is already a nominal 67% planning margin between your "landing field length" and "actual landing distance". Unless a technique is going to make a significant impact relative to that 67% margin, it's not going to do much. That means a lot of redistribution of reactions, and that means a lot of tail load.
DRY RUNWAY: Actual demonstrated landing distance from 50 ft to complete stop multiplied by 1.67.
WET RUNWAY: (no more than 3 mm of standing water): Actual demonstrated landing distance (on a dry runway) multiplied by 1.67, multiplied by 1.15.
CONTAMINATED RUNWAY: (more than 3 mm but no more than 13 mm of standing water, compacted snow, ice): "Calculated" landing distance for either Good/Fair, or Poor reported braking action multiplied by 1.15. So the margin for error and variables is only 15%, not 67%.
Interestingly, our manual states that contaminated runway performance data is only "Guidance Information".
So with the contaminated runway scenario in mind, any technique that improves the actual landing distance by just 1.5% increases the safety margin by a whopping 10% (1/10th of 15%)!!
It's been a very interesting thread so far. Thanks everyone.
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Re: Pulling a Stop to Runway Overruns
Re BLIP's Post
Book figures for landing are good for planning and inflight review (except for contaminated runway performance data).
Unfortunately when flight crews get it wrong, they seem to do it big-time, with or without CRM. Or maybe it's just that many of the variables are actually indeterminants. As OVERTALK said in his first sentence at post #1 on this thread, landing overruns are happening all the time. It's only when they have a nasty outcome that goes beyond embarrassment, lost jobs and muddy, scrubbed or flattened tires, that we get to hear much about it. The fact that the industry is (or was) unaware of the value of progressive backstick braking on nasty surfaces is unsurprising. Offhand I can think of numerous things that the industry was apparently unaware of:
.
a. the dangers of certain types of wiring and neglecting wiring husbandry (EAPAS NPRM comments close 03 Feb 06)
b. the dangers of Concorde tire failures (court-case soon to begin)
c. the perils built into faux redundancy (two computers each empowered to take over from the other when it is assessed that the primary computer has failed) i.e. G-VATL's fuel transfer double-flameout.
d. the dangers inherent in forgetting to ARM spoilers (AA1420)
e. the lethal unpredictability of SLD icing (freezing rain)
f. the flammability of heated tank ullage
g. the dangers inherent in resetting CB's (because ensuing arc-tracking faults won't re-trip them)
h. the hazards of designing identical interchangeable fuel gauges for different models (ATR42/ATR72)
i. the hazards of sandpaper textured rime ice on supercritical wing sections. (CL-600)
j. the pitch-up illusion (GulfAir A320)
k. the flammability of metallized mylar thermal-acoustic blankets
l. the idiocy of having a take-off configuration warning horn identical to a pressn warning horn. One oft heard, the other rarely heard - and every chance that a hypoxic crew wouldn't make the right choice. Inaccessible hypoxic pilots behind an impenetrable reinforced door.
m. Software that can allow a fatigued crew to leave previous take-off calc figures in place (and operable) for their next departure (HFX 747)
n. A closed runway with lethal WIP that can be mistaken for the duty runway due to insufficient markings (no active alerting/just passive cues) SQ006
o. A bogus FMC fuel usage consumption that would suck in a crew transiting with the gear down (Hapag A310) or an FMC that allows a crew to enter nonsense take-off parameters (SIA 744 Auckland).
p. Fuel leakage scenarios and checklists that can sucker a crew into believing it's fuel imbalance
q. the ability to down a modern airliner by just bugging the pitot or taping over the static ports
r. A CRJ engine that requires a massive sustained speed increase to achieve sufficient fan rotation for an inflight relight
s. A rudder handling and RTL design flaw that allows a vertical fin to be torn off in the blink of two eyes. A rudder that can disintegrate in flight with little more than a shudder/shake (and no pilot input - Air Transat ex Cuba)
t. The design of a runway incursion system that is useless in rain and doesn't warn pilots directly (AMASS)
u. A Beech 1900 maint manual error that was ancient but would sucker engineers into fatally misrigging an elevator (Colgan and Air Midwest)
v. Standby horizons that are panel central nowhere near the scan of PF or PNF (aka "twinning, where any anomaly between roll or pitch-rate of an immediately adjacent STBY instrument and primary attitude reference is immediately apparent - KAL747F Stansted, Air India 747 Bombay and many others).
w. Using an a/c NAV configuration that is open to auto-resetting to a VOR operating on TEST (A320 North Africa)
x. Jeppesen databases that could dial up a distant NDB in error (AA 757 Cali) long enough to CFIT the crew
y. A speedbrake that wouldn't auto-retract in response to a full power GPWS response. (AA 757 Cali)
z. bits falling off shuttles and NASA conveniently assuming that high-speed light-weight foam was harmless (despite ample evidence over many flights that tile damage was occurring).
.
etc etc etc. Yes we're in great shape. Unawareness is blissful ignorance. But this thread has adequately demonstrated also how some people will argue on quite specious grounds for their right to not know or be told.
The only sure thing is that nobody will be surprised at the next jaw-dropping fatal revelation.
Book figures for landing are good for planning and inflight review (except for contaminated runway performance data).
Unfortunately when flight crews get it wrong, they seem to do it big-time, with or without CRM. Or maybe it's just that many of the variables are actually indeterminants. As OVERTALK said in his first sentence at post #1 on this thread, landing overruns are happening all the time. It's only when they have a nasty outcome that goes beyond embarrassment, lost jobs and muddy, scrubbed or flattened tires, that we get to hear much about it. The fact that the industry is (or was) unaware of the value of progressive backstick braking on nasty surfaces is unsurprising. Offhand I can think of numerous things that the industry was apparently unaware of:
.
a. the dangers of certain types of wiring and neglecting wiring husbandry (EAPAS NPRM comments close 03 Feb 06)
b. the dangers of Concorde tire failures (court-case soon to begin)
c. the perils built into faux redundancy (two computers each empowered to take over from the other when it is assessed that the primary computer has failed) i.e. G-VATL's fuel transfer double-flameout.
d. the dangers inherent in forgetting to ARM spoilers (AA1420)
e. the lethal unpredictability of SLD icing (freezing rain)
f. the flammability of heated tank ullage
g. the dangers inherent in resetting CB's (because ensuing arc-tracking faults won't re-trip them)
h. the hazards of designing identical interchangeable fuel gauges for different models (ATR42/ATR72)
i. the hazards of sandpaper textured rime ice on supercritical wing sections. (CL-600)
j. the pitch-up illusion (GulfAir A320)
k. the flammability of metallized mylar thermal-acoustic blankets
l. the idiocy of having a take-off configuration warning horn identical to a pressn warning horn. One oft heard, the other rarely heard - and every chance that a hypoxic crew wouldn't make the right choice. Inaccessible hypoxic pilots behind an impenetrable reinforced door.
m. Software that can allow a fatigued crew to leave previous take-off calc figures in place (and operable) for their next departure (HFX 747)
n. A closed runway with lethal WIP that can be mistaken for the duty runway due to insufficient markings (no active alerting/just passive cues) SQ006
o. A bogus FMC fuel usage consumption that would suck in a crew transiting with the gear down (Hapag A310) or an FMC that allows a crew to enter nonsense take-off parameters (SIA 744 Auckland).
p. Fuel leakage scenarios and checklists that can sucker a crew into believing it's fuel imbalance
q. the ability to down a modern airliner by just bugging the pitot or taping over the static ports
r. A CRJ engine that requires a massive sustained speed increase to achieve sufficient fan rotation for an inflight relight
s. A rudder handling and RTL design flaw that allows a vertical fin to be torn off in the blink of two eyes. A rudder that can disintegrate in flight with little more than a shudder/shake (and no pilot input - Air Transat ex Cuba)
t. The design of a runway incursion system that is useless in rain and doesn't warn pilots directly (AMASS)
u. A Beech 1900 maint manual error that was ancient but would sucker engineers into fatally misrigging an elevator (Colgan and Air Midwest)
v. Standby horizons that are panel central nowhere near the scan of PF or PNF (aka "twinning, where any anomaly between roll or pitch-rate of an immediately adjacent STBY instrument and primary attitude reference is immediately apparent - KAL747F Stansted, Air India 747 Bombay and many others).
w. Using an a/c NAV configuration that is open to auto-resetting to a VOR operating on TEST (A320 North Africa)
x. Jeppesen databases that could dial up a distant NDB in error (AA 757 Cali) long enough to CFIT the crew
y. A speedbrake that wouldn't auto-retract in response to a full power GPWS response. (AA 757 Cali)
z. bits falling off shuttles and NASA conveniently assuming that high-speed light-weight foam was harmless (despite ample evidence over many flights that tile damage was occurring).
.
etc etc etc. Yes we're in great shape. Unawareness is blissful ignorance. But this thread has adequately demonstrated also how some people will argue on quite specious grounds for their right to not know or be told.
The only sure thing is that nobody will be surprised at the next jaw-dropping fatal revelation.
Moderator
Re: Pulling a Stop to Runway Overruns
Dagger Dirk indirectly highlights a very important consideration ... SOPs seek to address the fact that the guy on the line doesn't have all the information or answers and, to a significant degree, can insulate himself from embarrassment by sticking with the published words of wisdom .. not a guarantee, just an example of sensible risk management/minimisation.
So far as landing is concerned, the principal hazards which the pilot can influence include
(a) approach profile control, minimising float .. ie land shortly after the aiming point ... ALL the time, even if the runway has 15000 ft to play with.
(b) getting the configuration/speed correct - autobrake, autospoiler, flap setting, speed additives, manual brake, reverse and spoiler use, and so on.
At the end of the day, the pilot is paid to think and be aware of what is going on around him .. the enquiry will never be complimentary if the aircraft was hot, incorrectly configured, floated way in (how about a miss ?), boards/autobrake/reverse failed to operate .. but the pilot just sat there with a dazed expression on his face.
Some of us wonder whether this will become an increasing philosophical problem as/if the depth of training and knowledge is watered down in the pursuit of profit ?
So far as landing is concerned, the principal hazards which the pilot can influence include
(a) approach profile control, minimising float .. ie land shortly after the aiming point ... ALL the time, even if the runway has 15000 ft to play with.
(b) getting the configuration/speed correct - autobrake, autospoiler, flap setting, speed additives, manual brake, reverse and spoiler use, and so on.
At the end of the day, the pilot is paid to think and be aware of what is going on around him .. the enquiry will never be complimentary if the aircraft was hot, incorrectly configured, floated way in (how about a miss ?), boards/autobrake/reverse failed to operate .. but the pilot just sat there with a dazed expression on his face.
Some of us wonder whether this will become an increasing philosophical problem as/if the depth of training and knowledge is watered down in the pursuit of profit ?
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Re: A Momentun of Your Time
Originally Posted by UNCTUOUS
.
Perhaps you should elaborate on your point.
.
As I understand it, OVERTALK's suggestion (by contrast) is to propose a straight-forward means of stopping contaminated runway overruns (ie. accidents) by enhancing post-touchdown braking effectiveness. That might indeed be an example of something:
<<<which is not utilized in todays flight operations, to the detriment of flight safety.>>>
.
Would you not agree? Or are you disputing that backstick braking works? i.e. as a means of achieving effective braking on slick runways. That doesn't appear to be the case. But perhaps you didn't review the whole thread.
.
Perhaps you should elaborate on your point.
.
As I understand it, OVERTALK's suggestion (by contrast) is to propose a straight-forward means of stopping contaminated runway overruns (ie. accidents) by enhancing post-touchdown braking effectiveness. That might indeed be an example of something:
<<<which is not utilized in todays flight operations, to the detriment of flight safety.>>>
.
Would you not agree? Or are you disputing that backstick braking works? i.e. as a means of achieving effective braking on slick runways. That doesn't appear to be the case. But perhaps you didn't review the whole thread.
.
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Re: the writing's already on the wall......
Originally Posted by OVERTALK
I think that we have lost the physics bubble here. The four retardation scenario factors discussed (a-b-c-d above) are producing a strong nose-down pitching moment.
a. Reverse thrust on our aft-mounted types causes a strong tendency for the nose to rise; for that very reason our advice to pilots is moderate forward stick force to prevent the nose from rising.
b. Braking. As I noted above, the best you can hope for is 5% or so additional mass on the nose - under relatively good braking action. With poor braking action - say 0.10'g' or lower decel - you'll be lucky to see more than 1 or 2% mass 'transfer' occur.
c. c.g. - not sure exactly what you allude to here. Are you assuming that the landing cg is further forward than at takeoff? It hardly matters, for most practical aircraft configurations this is basically the static nosewheel load - usually, as discussed above, of the order of 5-10% of aircraft weight.
d. spoilers. Depends on their location on the wing, degree of sweep etc; entirely possible to have a nose UP moment due to spoilers, since they are AFT of the cg and above or aft of the main gear.
The best you could hope for is the 5-10% basic, static, nose loading, plus an additional 5% due to decel 'weight transfer' under good braking. There are other factors acting to raise the nose, on our types at least, so that represents an OPTIMISTIC assessment of the force on the nose gear.
If you multiply that tyre/bitumen area interface increase on one tyre by all the tyres on a plane's main-gear, you can appreciate that the overall effect will be worthwhile.
This is a little confusing but I imagine that you meant to say that up elevator would cause the nose oleo to extend and consequently the wing's AoA to increase, thereby acting in an opposite sense to what is being claimed (i.e. reducing the weight upon the main-gear).
That that is a fallacy can be exposed by a simple illustration. Put a soft pea (or jelly-bean say) under the midpoint of a 12" rigid ruler and press down on both ends of the ruler. Do it with roughly equal force, simulating a pilot tempering his backstick input to just below what "could" (not saying "would") possibly cause the nose to rise. In other words, braking "for effect" by flying the attitude out the front window. The pea gets squashed of course. That simple experiment replicates the 4 retardation factors producing a nose-down moment at one end of the ruler and, at the other end, the opposing nose-up (i.e. tail-down) moment induced by the backstick. It adequately demonstrates that the resultant will be a down-force upon the maingear (the pea). Now do it with a new "soft pea" yet without the simulated pilot's up-elevator input. The nose drops, tail rises and the pea is unsquashed. That simulates the lack of anything other than the ruler's weight acting upon the "maingear" pea. It emphasizes the need for early introduced backstick braking when the chips are down (i.e. you suspect that you may have landed too far in on a slippery runway and urgently need max effective braking ASAP).
Put the "mainwheel jelly baby" in the middle, and stick something fairly heavy on top of the ruler, pretty much right above it. Say a coffee mug or something. That squashed the baby a bit - representing the bulk of the aircraft weight on the mainwheels.
Now put a smaller jelly baby - just a head, perhaps? - near the "front" of the ruler, to represent the nose gear, and then slide the mug forward a little until there's a little bit of load on the "nosegear jelly baby" too. That represents the aircraft under normal static conditions.
Now take a small glass - say "shooter glass" sized and place it above the nose gear. That's our "weight transferece" due to various effects. Fill it with water (it might tip off, so don't risk alcohol, no sense in wastefulness) to simulate the effect of increased braking/increased nose weight transfer. What should happen is that the "nosegear jelly baby" gets more squished due to this increased load.
Now, apply back stick by pushing down at the back of the ruler with your finger. As you do so you will both squish the "mainwheel jelly baby" AND "unsquish" the "nosewheel jelly baby". The only circumstances under which you will NOT unsquish the "nosewheel jelly baby" is if the load was so high that it totally flattened it first. In which case you'd have some ability to apply tail download before affecting the angle of the ruler.
And THAT is why I mentioned complete nosegear oleo compression.
You seem to have a picture of pilots as motor morons incapable of coping with a simple manipulative task. Landing a heavy-weight asymmetric airplane on a wet runway with 50 kts across used to make me salivate with anticipation..... not dread.
And, incidentally, let's assume that I'm wrong, and that a reliable and simple technique can be demonstrated to provide a, say, 10% reduction in landing distance. Then what would happen next is that we (the OEMs) would take credit for the technique in our published distances which would result in every landing becoming potentially more marginal. The technique wouldn't be something in your back pocket for a bad day when you need it; it'd be something you'd have to use every day, and would be assumed to use.
Do a Hover - it avoids G
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Re: Pulling a Stop to Runway Overruns
This thread has become rather personalised – but that so often happens here.
It started with an excellent proposal – pull the stick back to improve braking in the landing run.
This simple idea is in danger of being lost so (if I may be allowed) I will start the thread all over again.
A suggestion to reduce the chances of an overrun accident
On a tricycle gear aircraft pulling the stick back increases the effective ‘weight’ on the main wheels and in many circumstances this will increase the retardation available from the brakes. It will never make the brakes less effective. The military use this technique widely so does anybody know why the civil manufacturers apparently ignore it?
My guess is that they ignore it because the precise effect would be too difficult to quantify due to the many variables that would be involved between different landings. So therefore they say if you can’t actually quantify the benefit it has no place in the manual.
Anybody know?
Any civil testers out there care to comment?
It started with an excellent proposal – pull the stick back to improve braking in the landing run.
This simple idea is in danger of being lost so (if I may be allowed) I will start the thread all over again.
A suggestion to reduce the chances of an overrun accident
On a tricycle gear aircraft pulling the stick back increases the effective ‘weight’ on the main wheels and in many circumstances this will increase the retardation available from the brakes. It will never make the brakes less effective. The military use this technique widely so does anybody know why the civil manufacturers apparently ignore it?
My guess is that they ignore it because the precise effect would be too difficult to quantify due to the many variables that would be involved between different landings. So therefore they say if you can’t actually quantify the benefit it has no place in the manual.
Anybody know?
Any civil testers out there care to comment?
Re: Pulling a Stop to Runway Overruns
Civil practice is generally straightforward enough.
You define the practice used to achieve the scheduled field performance in the manual, and describe that in the POH.
It's actually common to have aircraft where it's known that the POH scheduled performance could be improved upon - but a conscious decision was made to use a more conservative (and thus predictable) set of handling actions to safeguard the company from liability in the event that the pilot failed to take the actions exactly as the company TP had.
Incidentally, the last light aircraft I test flew (a new French model) had all three wheels braked - it was like hitting a brick wall!
G
You define the practice used to achieve the scheduled field performance in the manual, and describe that in the POH.
It's actually common to have aircraft where it's known that the POH scheduled performance could be improved upon - but a conscious decision was made to use a more conservative (and thus predictable) set of handling actions to safeguard the company from liability in the event that the pilot failed to take the actions exactly as the company TP had.
Incidentally, the last light aircraft I test flew (a new French model) had all three wheels braked - it was like hitting a brick wall!
G
Moderator
Re: Pulling a Stop to Runway Overruns
.. as with the nosewheel brake mod to the 727 ... gets the pilot's attention smartly if the pedals are pushed harder than intended in normal operation.
More Fun with Figures
Have finally been driven to pull out my '72 edition of Kermode's Mechanics of Flight. Appendix 2 presents acceleration formulae in various units.
Taking 4b. F = (W/g)a:
a 744 at 644,000 lbs with autobrakes producing a 10 ft/s/s deceleration and g of 32.2 ft/s/s produces a braking force of:
F = (644,000/32.2)10 = 200,000 pounds
Wildly assuming a CG 15 ft above the ground for this tall a/c (pending a better figure from the more knowledgeable) produces a nose-down moment of 3,000,000 ft-lb.
Assuming a mlg to nosewheel distance of 100 ft. produces a corresponding nosewheel loading of 30,000 (3,000,000/100) lbs from braking.
Assuming a static nosewheel loading of some 5% produces some 30,000 lbs of loading from the CG before the mains.
So braking near autobrake max potentially doubles nosewheel loading.
Poor braking action can drastically reduce the extra loading on the nosewheel, but there remains a potential that as deceleration increases as a result of some backstick, greater amounts can be progressively applied.
The maximum case is nosewheel loading reduced to zero by back stick with good braking action. The mlg loading will in this case be increased by:
I would welcome the application of precise numbers for any type.
Taking 4b. F = (W/g)a:
a 744 at 644,000 lbs with autobrakes producing a 10 ft/s/s deceleration and g of 32.2 ft/s/s produces a braking force of:
F = (644,000/32.2)10 = 200,000 pounds
Wildly assuming a CG 15 ft above the ground for this tall a/c (pending a better figure from the more knowledgeable) produces a nose-down moment of 3,000,000 ft-lb.
Assuming a mlg to nosewheel distance of 100 ft. produces a corresponding nosewheel loading of 30,000 (3,000,000/100) lbs from braking.
Assuming a static nosewheel loading of some 5% produces some 30,000 lbs of loading from the CG before the mains.
So braking near autobrake max potentially doubles nosewheel loading.
Poor braking action can drastically reduce the extra loading on the nosewheel, but there remains a potential that as deceleration increases as a result of some backstick, greater amounts can be progressively applied.
The maximum case is nosewheel loading reduced to zero by back stick with good braking action. The mlg loading will in this case be increased by:
- the static and dynamic loading previously on the nose wheel
- the tailplane downforce (approximately equal to the nosewheel loading)
I would welcome the application of precise numbers for any type.