Whats the actual force of landing jet?

[NYCDooDahMan]

Hey JC'ers, hope everyone's enjoying the lovely summer. So I remember reading somewhere (I think it was here) that a when a bird hits an airborne aircraft the force can be compared to a 10 pound brick being hurled at the plane..or something along those lines.
Here's my question, I was doing some reading about the design and construction of runways. I was reading that some are compacted with concrete over 20 feet deep to absorb the impact of a landing jet. So, anyone have any idea what...say.... a 757 fully loaded landing on a runway, what kind of actual force is being put onto that runway.
I also remember reading that it takes mutliple years to build just a runway from scratch...any thoughts?

[pilot602]

[ QUOTE ]
I also remember reading that it takes mutliple years to build just a runway from scratch...any thoughts?


[/ QUOTE ]

It takes so long because there are very few (if any) Federal or state guidlines and thus every single little whiny NIMBY group complains and thereby slows the process down. In other words it's the politics involved that cause it to be so slow.

To physically build a runway, it would take not much longer than to build a road of compareable length.

[USMCmech]

Force of impact when an airplane touches down.

Vertical speed at touchdown. (not very much)

x

Weight of airplane (a whole lot)

x

Enginering fudge factor (4-5X)

=

A whole lotta concrete



The touchdown zone must be thicker than the rest of the runway.

The rest of the paved area is rated for the static weight of the airplanes that will be used there.


I was in El Salvador when an Air Force C-130 sank into the hot soft asphalt up to it's belly.

Getting that thing out was a royal pain in the A$$!

[flyover]

[ QUOTE ]
I was in El Salvador when an Air Force C-130 sank into the hot soft asphalt up to it's belly.

[/ QUOTE ]

Does this mean the force of a stationary airplane is greater than a landing one? Because I don't believe you can hit even the softest asphalt hard enough to sink up to the belly.

Dave

[Minuteman]

Normal touchdown forces reach a peak load factor between 1.2-1.5 G's. So take the weight of the plane, multiply it by the load factor and there's the force on the runway.

And here're some pics of that C-130...

[USMCmech]

[ QUOTE ]
[ QUOTE ]
I was in El Salvador when an Air Force C-130 sank into the hot soft asphalt up to it's belly.

[/ QUOTE ]

Does this mean the force of a stationary airplane is greater than a landing one? Because I don't believe you can hit even the softest asphalt hard enough to sink up to the belly.

Dave

[/ QUOTE ]

No it was sitting still.

When asphalt gets really hot it melts, and a heavy load can sink into it. This happens really slowly, but fast enough that you can walk into the hanger to find out who is suposed to unload your cargo, and walk out to a "booted" airplane.

If an airplane is too heavy for the pavement, you must keep moveing in order to avoid getting stuck.

[Kristie]

[ QUOTE ]
[ QUOTE ]
I also remember reading that it takes mutliple years to build just a runway from scratch...any thoughts?


[/ QUOTE ]

It takes so long because there are very few (if any) Federal or state guidlines and thus every single little whiny NIMBY group complains and thereby slows the process down. In other words it's the politics involved that cause it to be so slow.

[/ QUOTE ]actually, there are a ton of federal guidelines (mostly FAA) and sticky red tape, but getting the FAA to agree with the state, county and so forth is usually what the political hotseat is all about.



[/ QUOTE ] To physically build a runway, it would take not much longer than to build a road of compareable length.

[/ QUOTE ]not necessarily...it depends on the depth of concrete in the runway.. the deeper the concrete, the longer it takes to cure... I know PHX has a good 18-20" of asphalt on their runways.. we have a construction guy that's out there building the new runway now and i know a couple of structural engineers that work out there... I'll ask them and see what they say.

[ QUOTE ]
The touchdown zone must be thicker than the rest of the runway.

The rest of the paved area is rated for the static weight of the airplanes that will be used there.

[/ QUOTE ] The runway has to stay the same depth along it's entire length because the plane will have the same force upon landing as it does running down the runway for takeoff... the runway itself has a certain amount of compacted soil underneath it and it also must stay level.

the taxiway(s) and terminal locations are the only concrete areas that are able to take the weight of a stopped plane (static force), but the runway is never supposed to have a static plane on it -> it's only use is for takeoff and landing...The taxiways have less concrete depth than the runways but have more compacted soil in order to accept the weight of a stationary plane.

if that didn't make much sense, it's understandable.. it's easier to show via diagram...which is why plans are created! haha

[Kristie]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
I was in El Salvador when an Air Force C-130 sank into the hot soft asphalt up to it's belly.

[/ QUOTE ]

Does this mean the force of a stationary airplane is greater than a landing one? Because I don't believe you can hit even the softest asphalt hard enough to sink up to the belly.

Dave

[/ QUOTE ]

No it was sitting still.

When asphalt gets really hot it melts, and a heavy load can sink into it. This happens really slowly, but fast enough that you can walk into the hanger to find out who is suposed to unload your cargo, and walk out to a "booted" airplane.

If an airplane is too heavy for the pavement, you must keep moveing in order to avoid getting stuck.

[/ QUOTE ]uhh.. i hate to say this.. but as far as I know, the asphalt would never get sooo hot that it would melt... when they lay down asphalt, it's at a good (shoot, i can't remember the exact temperature and i don't have my specs book here) 200+ degrees.. i'll have to find that info...

have you actually seen that happen? because i've asked my construction people before and they say it would never get hot enough to melt the asphalt.. it takes a lot to get to the threshold point of asphalt. it might be more of the fog seal that melts vs the asphalt (there's always some sort of seal that's put over the asphalt to protect the asphalt as much as possible).

[Doug Taylor]

If you sit on a taxiway for too long, the wheels can somewhat sink a bit into the surface. I think LGA is especially bad with this and it takes a disporportionate amount of thrust to get the aircraft rolling again sometimes.

[Kristie]

[ QUOTE ]
[ QUOTE ]
I was in El Salvador when an Air Force C-130 sank into the hot soft asphalt up to it's belly.

[/ QUOTE ]

Does this mean the force of a stationary airplane is greater than a landing one? Because I don't believe you can hit even the softest asphalt hard enough to sink up to the belly.

Dave

[/ QUOTE ]could be... because the weight/force of a stationary plane is at that location longer than a moving plane...the force of a moving plane probably wouldn't be as much because the plane's force is only at that point for a split second at most and then the weight is lifted off of that point.

[Kristie]

[ QUOTE ]
If you sit on a taxiway for too long, the wheels can somewhat sink a bit into the surface. I think LGA is especially bad with this and it takes a disporportionate amount of thrust to get the aircraft rolling again sometimes.

[/ QUOTE ]are you sure that it's not the tires though? because I think the heat threshold of a tire is lower than aspahlt...and a tire has more "give" than asphalt and esp concrete.

[Doug Taylor]

Aww geez hon you KNOW I'm just a layman! I dunno!

I don't have all of those fancy schmancy degrees on the wall!

[MikeD]

I don't even know why airports have ANY asphalt surfaces on movement areas. Should all be concrete. Cost maybe? You can always tell the old mil bases that are now civil fields since they all have the huge ramp made of concrete squares, as well as a normally all-concrete runway.

[mtsu_av8er]

[ QUOTE ]
I don't even know why airports have ANY asphalt surfaces on movement areas. Should all be concrete. Cost maybe? You can always tell the old mil bases that are now civil fields since they all have the huge ramp made of concrete squares, as well as a normally all-concrete runway.

[/ QUOTE ]

The cost of concrete has apparently risen quite a bit lately...any construction folks have any real world numbers for us - maybe a cost comparison with asphalt?

Kristie?

[mastermags]

Oh really, how much can a few thousand bags of quickcrete really cost?

[mastermags]

Hey lloyd, that picture is of you correct? Kinda looks like Bill Cosby.

[mtsu_av8er]

[ QUOTE ]
Oh really, how much can a few thousand bags of quickcrete really cost?

[/ QUOTE ]
I know a guy with a private concrete strip up in KY...over 5,000 feet. I won't quote the numbers, but it's alot!!!!



[/ QUOTE ]
Hey lloyd, that picture is of you correct? Kinda looks like Bill Cosby.


[/ QUOTE ]

Yeah, it's the man before he became the man!!! My, how times change! I still do wear the leisure suits from time to time, though....

[USMCmech]

[ QUOTE ]
uhh.. i hate to say this.. but as far as I know, the asphalt would never get sooo hot that it would melt... when they lay down asphalt, it's at a good (shoot, i can't remember the exact temperature and i don't have my specs book here) 200+ degrees.. i'll have to find that info...

have you actually seen that happen? because i've asked my construction people before and they say it would never get hot enough to melt the asphalt.. it takes a lot to get to the threshold point of asphalt. it might be more of the fog seal that melts vs the asphalt (there's always some sort of seal that's put over the asphalt to protect the asphalt as much as possible).

[/ QUOTE ]

It doesn't acctually melt, it just becomes very soft. Melting is just the common term for when that happens.

The acctuall surface temp of asphalt can easily reach 140-150 on a hot summer day. That is why concrete, not asphalt is the material of choice in the desert. All through the south you will see rutts in asphallt from heavy trucks driving over it when it is really hot.

Like I said we helped pull that C-130 out in El Salvador, and I've seen tractor trailers sink into parking lots.

[Bryan]

Current asphalt pavements use oil graded for the area it is being placed. For example in Minnesota we use maybe a PG58-34, which means the pavement will perform adequately from -34C (prevent cracking in cold temps) and up to 58C (prevent rutting). Placement temperature can exceed 300F.

The departing aircraft weight is the main factor in determining taxiway and runway pavement thickness. Landing weight is much less and the impact is not that hard (at least it's not supposed to be).

Concrete prices are really going up because China is really booming and using all of their cement. We used to import from them and now it isn't available.

[Kristie]

[ QUOTE ]
[ QUOTE ]
I don't even know why airports have ANY asphalt surfaces on movement areas. Should all be concrete. Cost maybe? You can always tell the old mil bases that are now civil fields since they all have the huge ramp made of concrete squares, as well as a normally all-concrete runway.

[/ QUOTE ]

The cost of concrete has apparently risen quite a bit lately...any construction folks have any real world numbers for us - maybe a cost comparison with asphalt?

Kristie?

[/ QUOTE ]ok.. got some answers...

the cost of concrete right now is $75/cy (cubic yard).. it's up about 10-$15/cy

it's true that the planes can get "stuck" in the asphalt because the heat from the engines in the previous plane heats the asphalt up enough that a sitting plane can end up being a sitting duck on the taxiway!

the only reason asphalt is used on the taxiways is because of cost..that's it...

it is true that the concrete on the runway is at different depths depending on take off location, landing location, taxi locations... most have 1' of compacted ABC (subbase) depending on the type of soil underneath.. then they put down a layer of asphalt so they have a nice level surface to work with when laying out the different depths of concrete. The runway at PHX is 18" in most locations and 20" in the landing location... apparently, we have a couple of really huge Russian cargo jets that fly in and out... so they design for those rather than the 777's.. yes, actually bigger than the 777's...

our construction guru just told me they're switching out all the asphalt at PHX to concrete... they'll be replacing S(ierra), D(elta), E(cho) and R(omeo) soon and will be extending C(harlie)....They're talking about a 4th runway but it will probably never happen because of the environmental cleanup disagreement that's going on between COP (city of phx) and Honeywell right now....

[mtsu_av8er]

Thanks!!!!

[Kristie]

No... thank you for thanking me! I wondered how many hours it would be before someone even noticed the thread and mentioned a thanks.. i had to go way out of my way to get that info from our construction engineer...he's not easy to reach -> hence, airport construction engineer.. always AT the job...

let me know if you want to know anything else, i'd be glad to try and hunt him down again!

[Doug Taylor]

Having a cool wife just rocks man!

[I_Money]

Kristie I am inpressed - I know it is your job, but pilots would have argued this for days - you set us straight.

[Doug Taylor]

But the nature of pilots is that someone is probabaly going to want to argue it anyway!