Airliner Rollaway Gradient
Airliner Rollaway Gradient
(OP)
The FAA limits airport aprons (parking areas) to 1% maximum in any direction for aircraft approach categories C, D, and E (all jet airliners). What is the exact gradient in which aircraft of the following categories start rolling with all engines off and all brakes released in the absense of wind or seismic action? They are:
turboprop airliners
narrow-body jet airliners
mid-size wide-body airliners
jumbo jets
turboprop airliners
narrow-body jet airliners
mid-size wide-body airliners
jumbo jets
RE: Airliner Rollaway Gradient
RE: Airliner Rollaway Gradient
You see "strongmen" contests pulling big planes so clearly not much is needed to get them moving relative to their weight. go to 1:26 in this one https://www.youtube.com/watch?v=B-4NuNeIk3Q
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RE: Airliner Rollaway Gradient
another day in paradise, or is paradise one day closer ?
RE: Airliner Rollaway Gradient
To expand slightly on what others have stated. Even though aircraft are heavy and tires are small... inflation pressures are remarkably high so that heavy aircraft have relatively small tire bulging/drag... and the wheels have very high precision roller bearings packed with grease. These design aspects alone are intended to minimize tire/wheel rolling friction. I have seen a couple of mechanics move a 40,000# jet with just a 'little sweat' [on dead-level surfaces]
A gradient is built into all large parking/apron/taxiways, simply for necessary rain/slush-water drainage.
As I recall, runways have a 'slight crown'... higher on the centerline and slightly lower on the edges [like most roads/freeways] for rain/slush-water drainage to the sides [water stagnation on a runway is bad news].
The only mandatory gradient of 'dead level' that I know of [~0+/-5-minute Deg, all orientations, as memory serves me poorly], is on parking/maintenance 'pads' intended for...
Outdoor aircraft jacking for maintenance or structural alignment inspections... under strictly enforced weather conditions.
Compass calibration... on compass-rose pads... under strictly enforced weather conditions.
Parking pads, under a open 'flow-thru' parking rain-shelter.
You have not been in maintenance, for real, until you've witnessed...
[A] An aircraft slowly rolling towards the edge of a parking apron and the keystone cops trying to stop it with chocks up to the last possible moment to prevent something bad happening. Most aircraft are balanced to a point just forward of the Main Gear tire contact point... so can easily tip-up/backwards onto the tail-cone/feathers... under many circumstances.
[B] An aircraft 'jumping' off one-or-more jack-pads, when elevated... bad things happen.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: Airliner Rollaway Gradient
If it's not perfectly flat, it can move is the conservative answer. Even then chocks and or chain it anyway... because reality.
Definitely going to be a civil engineer/code question.
If you're the guy writing the code... find a recent airport project of similar scale to your project, look up who the engineer/architect of record is and start making calls to them and the contractors who built the place. There is a guy who drives a white truck with yellow flashing lights on it that knows the answer.
RE: Airliner Rollaway Gradient
But I can certainly understand the amazement when a runaway plane has its nose wheel pop over a hastily thrown chock.
RE: Airliner Rollaway Gradient
RE: Airliner Rollaway Gradient
1. small piston-engined 2-to-3-row plane (such as Cessna 172)
2. turboprop minibus-sized 2-per-row airliner
3. turboprop bus-sized 2+2 per-row airliner
4. narrow-body 3+3 per-row jet airliner (such as Airbus A320 and Boeing 737)
5. mid-size wide-body jet airliner (such as Boeing 787 Dreamliner and Airbus A330)
6. large wide-body jet airliner (such as Boeing 777, Airbus A350, and Airbus A340), and
7. jumbo jet airliner (such as Boeing 747 and Airbus A380)
RE: Airliner Rollaway Gradient
RE: Airliner Rollaway Gradient
Explain yourself.
RE: Airliner Rollaway Gradient
Some math is appropriate/necessary for this discussion.
A 1-degree slope will translate to a small thrust vector.
TAN or SIN 1.000-Degree are virtually identical = 0.01745
Example of 'gravity thrust' due to a 1.000-Deg slope... EXAMPLE ONLY... for a 100,000 [pounds or Kilos static weight]
so...
0.01745 X 100,000 [pounds or Kilos] = 1745 [pounds or Kilos] gravity thrust for a 1.000-Deg slope-thrust vector.
NOW, factor this slope vector from wheel-tire-rolling orientation, around 90-deg to wheel-tire-side-load orientation [0-to-90], in 1-Degree increments.
NOTE1. This assumes 'perfectly still air'.
Try this simple math for any aircraft.
NOW...
Add in the effects of 'wind-drag loading' and this problem gets pretty hairy.
NOTE2. Determine wind [drag] forces on a 'static aircraft', 0.0000-deg slope. Wind orientation can be from any compass direction. Airframe wind-drag forces will vary dramatically, depending on 360-Deg wind-orientation to the airframe.
See what we've been talking about?
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: Airliner Rollaway Gradient
https://youtu.be/MeGlm_2da5M
RE: Airliner Rollaway Gradient
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Airliner Rollaway Gradient
Is the coefficient of friction going to depend on the class of airplane ?
or upon the weight of the airplane, the ground pressure area of the tires (which probably accounts for the weight), the type of concrete surface, the thread and wear of the tires, the "greaseiness" and/or wetness of the surface, the type of tire, the pressure of the tire ? the CBR of the surface ??
Again, why do you want this ??
another day in paradise, or is paradise one day closer ?
RE: Airliner Rollaway Gradient
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Airliner Rollaway Gradient
Then you can calculate slope based on weight.
Please let us know when you've done it!
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.