Why use a firm landing on wet runway

[getonit]

I have heard that when landing a jet on a wet runway you should use a firmer landing. Is that true and if so why? I can't find anything that explicilty says to do that, I have the formula for hydroplaning but nothing there that helps. Only thing I could think of (ie guess) is it might compress the tire more and get more surface area but I don't see how that would help.

 

[Andy Neill]

Remembering that the Force of Resistance for Friction (Fr) is equal to the coeeficient of friction (u) times the Normal Force (Fn) or the force pressing perpendicular toward the surface, I can see where a firm landing will minimize the time where lift is reducing Fn making the Fr (the force necessary to overcome the force that keeps your tires effective in keeping you on the runway) relatively low.

Fr = Fn * u

 

[avbug]

Also, it aint' gonna slide around so much.

 

[C172Heavy]

Although it seems if you smack too hard on the runway the frictional force would be high for a second and then when the plane started to rise up again the force would actually be much lower again for a while whether you bounce or not.

 

[avbug]

The goal isn't to bounce. It's to put the airplane down and keep it there.

As the mains touch, the nosewheel is lowered smoothly to the surface while deploying reverse thrust. As the nosewheel is lowered, angle of attack is reduced, settling the weight of the airplane on the wheels.

Another neat trick is to make all the passengers jump in the air just before touchdown, such that they land just as the mains touch.

At least three participating ICAO countries are experimenting with giant tracts of fly paper on the runway. This greatly increases the coefficient of friction, and to date, not a single case of a fly hydroplaning has been observed.

 

[bigD]

At least three participating ICAO countries are experimenting with giant tracts of fly paper on the runway. This greatly increases the coefficient of friction, and to date, not a single case of a fly hydroplaning has been observed.

This is SO impractical. Everyone knows that the solution is to cover the runway with uneaten cake donuts. By my math, it'll take just over 12 million cake donuts to cover a 9000'x150' runway.

 

[avbug]

Plain might work, but if it's got sprinkles, glaze, or powdered sugar, the coefficient of friction of donut (Dfc) goes down considerably, especially in the presence of rain, milk, or any heavy weight petroleum oil.

For gear up emergencies, or emergencies in which potential threat to life or property may exist due to fire, hazmat spill, or starvation, covering the runway in day-old donuts may be a very appropriate soloution.

 

[Brother Francis]

Donut etiquette

You get a bunch of pilots around 12m donuts and within 3 minutes there will be 1/4 donut left. (No one wants to be the pig that eats the last one so they break it in half, then someone breaks the half in half because they don't want to be the pig either. Pride overcomes greed with the remaining 1/4.)

Uneaten donuts; phffffyeahright Now I've heard it all.

As an aside:

Avbug- My hat is off to you. I have been in this business in various capacities for 25 years. I learn something from you every time you post.

 

[TurboS7]

You need to get the wheel spin up as fast as possible so that the anti-skid will be working properly and immediate braking can occur. This also insures operation of the auto-spoilers, and auto-brakes if they are installed.

 

[dogman]

A firm landing will also disssipate your kinetic energy faster.