Aerofoils in heavy rain

[BOAC]

If I could drag folk off their soapboxes and axes to grind, may I remind all that in post #1 I said:

"I believe there has been 'advice' in the past on increasing speeds on approach in these conditions, but I am not aware of any specific guidance in Ops Manuals (in my time). Is it in place now? Should it be?"

Judging by the responses I detect that no-one so far:

a) Thinks it should be in the Ops Manual
b) That it IS in any Ops Manuals
c) Thinks approach speeds need to be considered

Thus case closed.

[john_tullamarine]

.. from a report just read .. it may be that the recent LionAir mishap involved some very heavy rain ?

[de facto]

The mechanics of the weather radar and wind shear alert system. Doesnt the windshear alert use the weather radar? I am aware that some models use a l@ser system for windshear, I am just not positive about the connection between the 2 systems.
If the settings for the weather radar had been to look up, with the windshear system auto engage at 2500 feet, does this automatically reposition the dish?

The Predictive windshear is independent of the wx swith on the B737 NG.
It engages during take off when thrust levers are past the vertical position(wx radar on or off) and during descent when below 2300 AGL.

[Mr Optimistic]

From my noddy perspective, how about it's got nothing to do with a wet wing but rather the increase in effective density/inertia of the air ? When accelerating over the top of the wing the water particles add inertia and hence reduce speed/increase local pressure. Would expect this to be most pronounced when acceleration/shear at maximum ie high alpha so giving reduced Clmax.

[911slf]

If you should fly a hang glider

The higher performance hang gliders get a ten knot increase in stalling speed when wet (from 20kt to 30kt), that's 50% . My intermediate performance hang glider was entirely unaffected because it had a textile leading edge rather than one with a shiny coat. On occasion I got the whole hill to myself. On the other hand it is a miserable experience flying a hang glider in the rain.

[lomapaseo]

from a report just read .. it may be that the recent LionAir mishap involved some very heavy rain ?

I seriously doubt it had any effect, more likely it was the effect of hitting the surf.

course I don't have any data, but I doubt the veracity of most of what has been reported so-far (it's outside historical data and engineering comprehension)

[CISTRS]

Energy management

Big fast jets against slow small gliders?

The total energy of an airliner compared to a glider at approach speeds makes it prudent practice for the glider to increase speed with wet wings. A glider will typically aim to deploy a setting of half-airbrakes for the planned approach to give a plus or minus tolerance on approach slope and speed.
I suspect that the effects of wet wings on a commercial aircraft will be less significant.

[Bye]

For what its worth, in Formula 1 we did a lot of studies into the effects of rain on the cars wings and bodies.

the basic rule now as a result is that when its dry we use a hydrophobic coating to resist water and dirt as much as possible.

however when its wet, we use a Hydrophillic coating. The reason being that the Hydrophobic coating causes the beading together of droplets which cause greater drag with them having to be pushed off the surface as beads. The beads also cause more surface disruption and them moving about under vibration disrupts the optimum wing tuning frequencies.

BUT with the hydrophillic coating we found that the water forms a nice thin (wetted ) slippery film over the surface with lower drag and better boundary conditioning.

Not flying i know but thought someone might find it interesting.

GB

[lederhosen]

Interesting post from Bye. The slippery film he describes makes me think of the effect we get from de-icing fluid.

The most I have noticed the effect of rain in over thirty years of gliding was in the Libelle. A beautiful early glass glider which really did not like wet wings. The rate of sink increased markedly.

On the Boeing I fly there is no noticeable difference. However a basic understanding of practical aerodynamics suggests any contamination must effect performance. However the difference between a glider where you may at times be only few knots over the stall speed and a jet where at the slowest point you should be some twenty to thirty knots over the stall speed mean you do not notice it.

The only time it is an issue is with flaps 15 vref ice. I understand Boeing discovered in testing that the margin was reduced in this configuration which is the reason for the add on. Presumably one could expect a similar but lesser effect from rain.

[safetypee]

“… a similar but lesser effect from rain”, re de-icing fluid.
IIRC some old studies of the effects of de-icing fluid on lift and drag concluded that any deterioration was minor. However more recently, several manufacturers evaluated the new higher-viscosity de-icing fluids, which depending on aircraft type showed some deterioration or the need to adjust configuration / speeds to maintain controllability standards.
Rain, in comparison with de-icing fluid, has relatively low viscosity and thus might not be such a problem.

[PantLoad]

I remember....

I remember years ago....like 30 or 35 years ago....NASA was doing
a study about the effect of bugs on the leading edges of wings....
how the bugs affect lift. No kidding. Our tax dollars at work.

Never heard what conclusions they came to, if any. Maybe someone
can Google this.

Anyway, I was a flight engineer on the 727...doing my walk-arounds...
along with some NASA guy with a ladder counting bug splats on
the leading edges.

Fly safe,

PantLoad

[Piltdown Man]

NASA was doing a study about the effect of bugs on the leading edges of wings.... how the bugs affect lift. No kidding. Our tax dollars at work.

That was well spent money. Understanding bug contamination on wings leads to a better understanding of airfoils with improved stall characteristics and reduced drag in the cruise. Let's face it, aerodynamically there's not much difference between a well spattered aircraft and one with ice on the leading edges. One contaminant we get rid of, the other we don't.

PM

[john_tullamarine]

I seriously doubt it had any effect, more likely it was the effect of hitting the surf.

A second report suggests that there may have been a crew interaction problem/deficit which had very predictable results. Premature to discuss the details I suspect.

[lomapaseo]

A second report suggests that there may have been a crew interaction problem/deficit which had very predictable results

that fits about 75-80% of accidents, now to find the other causal factors because all we can do is minimize the 75-80% by a few percentage points

to err is human

[Turbine D]

JT,
According to Flightglobal's Special Safety Bulletin regarding this accident,
the co-pilot was in control of the landing. The aircraft hit a pocket of heavy rain at a fairly low altitude (flaps and slats out for the landing) and lost sight of the runway, at which point the Captain took over the landing. The Captain then elected a TOGA missed approach but the aircraft did not respond to the climb quick enough or as expected and settled into the water. If true, it might suggest that heavy rain does indeed affect lift capability of the wings with slats and flaps out at slow speeds.

TD

[asc12]

Originally Posted by PantLoad

I remember years ago....like 30 or 35 years ago....NASA was doing
a study about the effect of bugs on the leading edges of wings....
how the bugs affect lift. No kidding. Our tax dollars at work.

On highly laminar wings this has a major effect, actually.

The Piaggio p180 POH contains this text and reduced figures are available for performance calculations:

"This airplane is characterized by extensive natural laminar flow over the forward and main wings. Insect debris, dirt in general, or rain may force the boundary layer to become turbulent prematurely and the performances are affected by the loss of laminar flow.

The extension of laminar flow as a function of surface contamination is very difficult to determine. However, loss of performance, substantiated by flight test data, ... are indicated if significant in each performance graph..."

Emphasis mine.

[de facto]

+5 knots for the wife

+5 for @ kid

+10 for the girlfriend

So 20 kts in the overrun for your pax?

[tggzzz]

I remember years ago....like 30 or 35 years ago....NASA was doing
a study about the effect of bugs on the leading edges of wings....
how the bugs affect lift. No kidding. Our tax dollars at work.

Some glider pilots like to wipe the bugs off the leading edge while flying, typically in a competition.

Don't believe me? Have a look at this (or any of the other vids on that page):

Bugwiping during flight - YouTube

[lomapaseo]

Some glider pilots like to wipe the bugs off the leading edge while flying, typically in a competition.

Where do they get the power to operate it from?

From some sort of RAT or battery?

I wonder what the trades in performance vs weight are?

[mm43]

Where do they get the power to operate it from?

"One distinctive feature that is incorporated in the LS10 fuselage is the bug wiper garage. Even though the wing of the LS10 has been designed to be bug tolerant, fitment of bug wipers does not result in a drag penalty as they fit perfectly into the fuselage garage. The distinctive aluminum-carbon design of the bug wiper goes one step further to make the LS10 a distinctive high tech glider.

In addition to the integral bug wiper garages, solar panels are also integrated into the fuselage turtle deck to provide continual battery charging. Two normal batteries are sufficient to provide the required electrical demand for flight inclusive of (optional) bug wiper and turbo operation."

The full article is at www.dg-flugzeugbau.de.