soft landing because wheels have spun up more smoothly

After landing in wet grass I'm sometimes afraid to deplane even when we're parked at the tiedown, since no sensation of landing was evident and I fear the airplane has yet to touch down. I just attribute it to my superior flying skills and deft touch. Skeptics might call it something else.
 
wabower said:
After landing in wet grass I'm sometimes afraid to deplane even when we're parked at the tiedown, since no sensation of landing was evident and I fear the airplane has yet to touch down. I just attribute it to my superior flying skills and deft touch. Skeptics might call it something else.
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Sometimes I have to hop out, grab a rope and lasso the tail to pull mine down the last three inches, as it's still floating on those spun up wheels...
 
So Kryponite is your only real threat as well?

dmccormack said:
Sometimes I have to hop out, grab a rope and lasso the tail to pull mine down the last three inches, as it's still floating on those spun up wheels...
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Gerhardt said:
"When you do not feel the touchdown, it often means that the runway surface was not dry, which allows the wheels to spin up more smoothly. "

====================

huh.
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Think how much force it takes to almost instantaneously take several large, heavy airliner tires and wheels from not spinning at all to spinning at touchdown speed. That is a huge backwards kick on the landing gear and has to be felt distinctly by the whole airplane. If the surface is wet (slick), that spin up is streched out over a considerably longer time resulting in much less backwards kick given to the landing gear.

I've always thought that some sort of anemometer type cups on the landing gear to spin them up in the air would save a lot of rubber when the tires hit the runway.
 
Graueradler said:
Think how much force it takes to almost instantaneously take several large, heavy airliner tires and wheels from not spinning at all to spinning at touchdown speed. That is a huge backwards kick on the landing gear and has to be felt distinctly by the whole airplane. If the surface is wet (slick), that spin up is streched out over a considerably longer time resulting in much less backwards kick given to the landing gear.

I've always thought that some sort of anemometer type cups on the landing gear to spin them up in the air would save a lot of rubber when the tires hit the runway, even though they would burn out wheel bearings and fry the tires at alarming rate.
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FTFY;)
 
wabower said:
FTFY;)
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I'm always open to learning - explain please.

On airliners, the tires are in the well when not lowered for landing so the tires aren't spinning all the time. Wheel bearings on cars last 100s of thousands of miles running while loaded. A few extra minutes per landing unloaded isn't going to do a lot to aircraft wheel bearings. It should be possible to size the cups to get near the right rotational speed on the wheels to match touch down speed. There would be additional gyroscopic forces to deal with on retract unless automatic braking was incorporated on retract.

If it was worth doing, someone would have already done it so I'm sure it isn't as simple as it sounds. Share your thoughts on issues with the idea.
 
Are you familiar with the term "whether the hare is worth the chase?" Is the rabbit trail of "smoother landings" worth following?

Graueradler said:
I'm always open to learning - explain please.

On airliners, the tires are in the well when not lowered for landing so the tires aren't spinning all the time. Wheel bearings on cars last 100s of thousands of miles running while loaded. A few extra minutes per landing unloaded isn't going to do a lot to aircraft wheel bearings. It should be possible to size the cups to get near the right rotational speed on the wheels to match touch down speed. There would be additional gyroscopic forces to deal with on retract unless automatic braking was incorporated on retract.

If it was worth doing, someone would have already done it so I'm sure it isn't as simple as it sounds. Share your thoughts on issues with the idea.
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wabower said:
Are you familiar with the term "whether the hare is worth the chase?" Is the rabbit trail of "smoother landings" worth following?
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The secret to PERFECT LANDINGS is so simple that even student pilots know it................. The pilot must be the sole occupant of the aircraft!:D:D
 
wabower said:
Are you familiar with the term "whether the hare is worth the chase?" Is the rabbit trail of "smoother landings" worth following?
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Maybe the rabbit trail of "longer lasting tires" is ? :wink2:

How much is a set of re-treads for your typical airliner MLG and how many landings are they good-fer?
 
An old jet jock told me that the touchdown wasn't what wore out airliner tires; it was the braking forces. The touchdown spinup takes a few feet; the heavy braking near the end of the landing roll takes many more feet and the tires are skidding just slightly as ABS kicks in and holds it that way. The use of reverse thrust saves tires much more than wheel spinners would. They have been tried, you know. See the input on this forum: http://www.eng-tips.com/viewthread.cfm?qid=293321

Dan
 
N747JB said:
The secret to PERFECT LANDINGS is so simple that even student pilots know it................. The pilot must be the sole occupant of the aircraft!:D:D
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With absolutely no one around......
 
Graueradler said:
I've always thought that some sort of anemometer type cups on the landing gear to spin them up in the air would save a lot of rubber when the tires hit the runway.
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They experimented with that early on in the jet age. Forget what airplane. Turned out it wasn't all that feasible, over all.
 
Dan Thomas said:
An old jet jock told me that the touchdown wasn't what wore out airliner tires; it was the braking forces. The touchdown spinup takes a few feet; the heavy braking near the end of the landing roll takes many more feet and the tires are skidding just slightly as ABS kicks in and holds it that way. The use of reverse thrust saves tires much more than wheel spinners would. They have been tried, you know. See the input on this forum: http://www.eng-tips.com/viewthread.cfm?qid=293321

Dan
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Great thread. Thanks for the link.
 
Well, if the runway was a giant treadmill matching the planes touchdown speed there would be no bump, then the pilot could simply lock the brakes, cut the throttles, and let the treadmill do the braking thereby saving mucho dollars on tire treads, eh...
I am always amazed that they have never put me in charge of things like this..

denny-o
 
I'm not sure what the problem was with the original article. Landing on a wet runway will definitely help out with the smoothness of the touchdown.
 
And here I was thinking that the rate of descent had more to do with it than the wheels being spun up.
 
Gerhardt said:
And here I was thinking that the rate of descent had more to do with it than the wheels being spun up.
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As I said, all other things being equal (including descent rate at touchdown), a wet runway provides a smoother landing than a dry one. If you plant it on, it will be firm anyway.

FWIW you don't really want to roll it on when the runway is wet. You want to get the wow switches activated so you can get the spoilers out as soon as possible and t/rs deployed to aid in braking.

A wet runway also does a great job of smoothing out touching down in a crab. On a longer airplane it can be very noticeable when you are aligned with direction of travel.
 
Dan Thomas said:
An old jet jock told me that the touchdown wasn't what wore out airliner tires; it was the braking forces. ,,,,,,
Dan
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If that is true, why do you see lots of rubber build up in the touchdown zone and almost none on the roll out and turn offs?

I can see most of the wear coming from taxiing and sharp turns scrubbing off a significant amount.
 
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Rex Kramer said:
As I said, all other things being equal (including descent rate at touchdown), a wet runway provides a smoother landing than a dry one. If you plant it on, it will be firm anyway.
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I wasn't discounting what you said. Sorry about my implication, it wasn't meant to come across that way.
 
maddog52 said:
If that is true, why do you see lots of rubber build up in the touchdown zone and almost none on the roll out and turn offs?

I can see most of the wear coming from taxiing and sharp turns scrubbing off a significant amount.
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The big black marks on the touchdown zone are smeared into the pavement by heat. They build up. Taxiing and braking forces, on the other hand, don't generate that much heat. In the link I posted earlier, an airport maintenance guy says they find many small rubber balls that have been rubbed off the tires at places where airplanes turn sharply, and I imagine they would find rubber powder farther down the runway where braking takes place.

Dan
 
Gerhardt said:
I wasn't discounting what you said. Sorry about my implication, it wasn't meant to come across that way.
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No worries..! :cheers:

Text isn't the best form of communication at times.
 
I've seen pre-spinning the wheels for landing come up on the Engineering Tips message boards (there are a couple aerospace forums).

I believe it's been tried and determined that it's not worth the weight and added complexity.
 
Bingo. A weight penalty (wheel spinners) not worth carrying and maintaining.
 
kontiki said:
I've seen pre-spinning the wheels for landing come up on the Engineering Tips message boards (there are a couple aerospace forums).

I believe it's been tried and determined that it's not worth the weight and added complexity.
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Might be real fun if one side spun up and the other side didn't.
 
gismo said:
Might be real fun if one side spun up and the other side didn't.
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When I was a little guy I learned something cool from my dad. We were shopping for a new kitchen sink... found one with all kinds of cool do-dads on it. Mom was all for it (automatic temp selector for washing foods or washing hands, a built in cutting board over the disposer, deep bucket sinks, very high quality manufacturer). All dad said was.... "Great, more **** to break and have a hell of a time trying to fix".

He was really right, I think to replace a faulty sensor (for the water temp control) cost about half of what the new sink price was, and required you to take the sink out of the counter to remove the sensor. Cool? you betcha.... but I guess sometimes what you get in return is not worth the extra effort to have it.

Any rate - I've had a couple landings where passengers said they didn't know we landed till the pops came back. They were on dry runways, but for the majority of my experience the wet runways were all grooved and didn't have enough water to fill them (grooved and crowned). So it really wouldn't have mattered anyway.

Bob
 
Graueradler said:
Think how much force it takes to almost instantaneously take several large, heavy airliner tires and wheels from not spinning at all to spinning at touchdown speed. That is a huge backwards kick on the landing gear and has to be felt distinctly by the whole airplane. If the surface is wet (slick), that spin up is streched out over a considerably longer time resulting in much less backwards kick given to the landing gear.

I've always thought that some sort of anemometer type cups on the landing gear to spin them up in the air would save a lot of rubber when the tires hit the runway.
Click to expand...

Like this?

http://www.google.com/patents?id=w7CSAAAAEBAJ&zoom=4&pg=PA1#v=onepage&q&f=false
 
I've found that I get smoother landings and less tire wear if I land in the same direction the Earth is rotating.:idea:
 
Red Air Rambo said:
I've found that I get smoother landings and less tire wear if I land in the same direction the Earth is rotating.:idea:
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Rather than add all that complexity to so many airliners, why not just install treadmills in the landing zones?;)
 
gismo said:
Rather than add all that complexity to so many airliners, why not just install treadmills in the landing zones?;)
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That would be a problem, since they could no longer do a rejected landing - since we all know you can't take off from a treadmill! :D
 
N747JB said:
The secret to PERFECT LANDINGS is so simple that even student pilots know it................. The pilot must be the sole occupant of the aircraft!:D:D
Click to expand...

Darn it this happened to me last week, at ten pm, at a deserted airport, in pitch black! How did you know???? Three perfect touchdowns and nobody to witness it.
 
jhausch said:
Maybe the rabbit trail of "longer lasting tires" is ? :wink2:

How much is a set of re-treads for your typical airliner MLG and how many landings are they good-fer?
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On the 737 i flew which was an IGW (Increased Gross Weight) model, 171,000# Takeoff weight and 134,000# max landing weight they would make it about 100 takeoff/landing cycles.

On the Lear 55 I used to fly 21,500# Takeoff weight and 18,000# max landing weight they would make it about 150 takeoff/landing cycles.
 
kimberlyanne546 said:
Darn it this happened to me last week, at ten pm, at a deserted airport, in pitch black! How did you know???? Three perfect touchdowns and nobody to witness it.
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No, I was there, you just couldn't see me on account of the darkness being so, well, dark. I had IR goggles. But yes, I will provide independent verification that those indeed were absolutely perfect. So gentle *I* couldn't even tell she touched the ground, standing to the side.
 
Think how much force it takes to almost instantaneously take several large, heavy airliner tires and wheels from not spinning at all to spinning at touchdown speed. That is a huge backwards kick on the landing gear and has to be felt distinctly by the whole airplane. If the surface is wet (slick), that spin up is streched out over a considerably longer time resulting in much less backwards kick given to the landing gear.

I've always thought that some sort of anemometer type cups on the landing gear to spin them up in the air would save a lot of rubber when the tires hit the runway.
Click to expand...
Steve said:
Like this?

http://www.google.com/patents?id=w7CSAAAAEBAJ&zoom=4&pg=PA1#v=onepage&q&f=false
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There's a gravel kit available for older Citations that spins up the nose wheel:
1008326.jpg


I believe similar kits exist for some Lears. There's the notable 737 Gravel Kit, but that doesn't include any wheels being spun up prior to landing...just gravel deflectors.
 
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