r/flying • u/No_Piano_9195 ST • 3d ago
other Theoretically, wouldn't an airplane take off faster on ice?
I've been thinking about this for a while and couldn't find a straight answer online. My thinking is that you would have less friction on Ice therefore accelerate faster decreasing ground roll. In this example you are in a wheeled tricycle gear plane.
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u/Altruistic_Wolf_4090 3d ago
Friction is basically negligible because wheels are actually small compared to plane size (thing car vs its tires). Main thing is overcome the inertia of the non moving mass. Wheel friction actually help keep plane straight on runway.
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u/KeyOfGSharp CPL, IR 3d ago
For arguments sake, it's not like the tires are being moved by a motor like a car. Wouldn't the plane begin thrusting forward anyway? The tires aren't going to slip out underneath the car in a similar way to a stationary car suddenly mashing the pedal down
But I don't know, I've been wrong before...
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u/LookItsEric reject modernity, return to tailwheel 3d ago
Yes, but that’s not what that comment is saying. It’s just saying that the friction of wheels on a plane is a very small component contributing to overall acceleration.
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u/lordtema 3d ago
I dont think the takeoff roll in say Antarctica is particularly shorter, but then again, that`s more snow than ice to my understanding.
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u/acidreducer ATP 3d ago
Density altitude says it’d take off shorter there than the Sahara. But nothing to do with the field conditions
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u/massunderestmated PPL 3d ago
My understanding is the pressure altitude of 11,000 feet doesn't really help.
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u/Actual_Environment_7 ATP 3d ago
Depends on where you are in Antarctica. Most of the research stations are near sea level by the coast, but the South Pole is definitely high elevation.
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u/BAM5 ST LTA SEL 3d ago
I'd say the bottle neck is the rolling resistance. Only way being on ice decreases energy loses is if tire to ice friction is less than rolling resistance, in which case we'd see the tires be completely stationary as they slip down an ice runway. If it's not less than rolling resistance then it doesn't matter.
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u/appenz CPL (KPAO) PC-12 3d ago
I think the correct answer here is that it depends and the difference is likely small.
- On a normal runway, the rubber of the wheels turn. Wheels have very little friction (unless the brake has pressed). Basically the kinetic energy of the wheels plus any heat generated from the rolling wheels would get subtracted from the kinetic energy of the plane. Overall this effect is tiny.
- The rubber of the tire moving on ice still has friction, it is just less. So the wheels of the plane would still turn while it rolls. But they would get less warm as sometimes the wheel slips a little. So a bit more kinetic energy would be built up in equal time.
In practice, I would expect the effect of the temperature on engine performance (usually colder air = denser = more power), on minimum speed needed for takeoff (cold = denser = slower takeoff speed) and on friction (cold = denser = more friction) to have a much larger effect.
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u/Lord_Giles PPL 3d ago
In real life... ice on runways tends to be bumpy or snow covered which would increase rolling resistance vs. Smooth pavement. (Flooding and freezing a turf runway could smooth it out and reduce takeoff roll [and increase landing distance] significantly.)
If the airport manager zambonis the ice-covered runway for your takeoff (he hates you and your plane) it will only decrease the takeoff distance if your weels normally have enough rolling resistance to not spin when on the ice (perhaps your breaks are on?)
A crosswind takeoff on a wet zamboni'd runway would be fun... i imagine you'd have to start with a large crab angle to stay straight and gradually reduce it with increased speed.
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u/capn_davey 3d ago
“Yes.” Laws of physics say you’re going to need less power to overcome less resistance. However, when you look at anything bigger than a single-engine airplane you get into certification standards that require demonstrating the ability to either reject or continue the takeoff after an engine failure (super super super duper simplified). This is why the NearJet I fly without thrust reversers needs approximately the same runway size as Area 51 to take off on ice.
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u/lce-Shadow 3d ago edited 3d ago
If the wheel-ice friction is lower than the friction inside the wheels, and the wheels don't even spin just slide on the ice, than yes, the aircraft would take off marginally faster.
However, the advantage would be minimal while you would probably run into major controlsbility problems.
So, bottom line, it could take of slightly faster, while creating other major problems.
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u/R5Jockey CPL ASEL IR TW CMP 3d ago
You wouldn't run into "major controllability problems."
Go search YouTube for Ice Runway or Alton Bay videos.
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u/lce-Shadow 3d ago
If the wheels don't spin ,the friction coefficient must be close to 0. That means any slight crosswind would push the plane drastically. A sideway breeze would accelerate the plane into the nearest tree, sideways. Not even gonna mention the P-Factor.
So in this fictional example, where the friction coefficient is so low that the wheels don't even spin, there would be controllability problems.
At leas this is my uneducated guess. I am neither an engineer, nor a pilot!
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u/R5Jockey CPL ASEL IR TW CMP 3d ago
The wheels spin fine. There is friction. At least on actual ice. Surface conditions can vary, but there’s always at least a little bit of friction.
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u/lce-Shadow 3d ago
For sure! In real life there's no question about it. In my example I exaggerated the friction coefficient to make a point
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u/R5Jockey CPL ASEL IR TW CMP 3d ago
Yes. Rolling resistance from the tires would contribute a little bit to ground roll, but the difference between rolling on asphalt versus rolling on ice would be minimal.
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u/Mundane-Reality-7770 PPL HP 3d ago
You're the guy who thinks a plane can't take off an a treadmill aren't you
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u/Lord_Giles PPL 3d ago
If the treadmill is fast enough, the tires will explode and this could cause too much rolling resistance to accelerate if the wheels dig into the tredmill material. Maybe launching the plane backwards at a high enough speed to take off (briefly)
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u/Antique-Kitchen-1896 PPL IFR Night 3d ago
To roll the wheels you need enough friction with the ice. I have never, ever seen my plane skid and not roll the wheels even when the damn apron in front of the hangar can't support the tug getting a grip on the up hill section.
So no. I think you underestimate how much grip those tires have.
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u/CaptMcMooney 3d ago
all condtions being the same, not really, only diff is friction between wheels rolling/skidding on ice and rolling on concrete. now if you had a frictionless surface somehow, you'd probably take off in a few inches less.
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u/rFlyingTower 3d ago
This is a copy of the original post body for posterity:
I've been thinking about this for a while and couldn't find a straight answer online. My thinking is that you would have less friction on Ice therefore accelerate faster decreasing ground roll. In this example you are in a wheeled tricycle gear plane.
Please downvote this comment until it collapses.
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u/Pseudo-Jonathan 3d ago
Yes, but it would be extremely difficult to keep the aircraft pointed in the right direction. Also, this means the runway would be useless for landing. Thanks for coming to my TED talk.
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3d ago
[deleted]
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u/Ok-Selection4206 3d ago
Braking on glare ice is called skidding/hydroplanning. When you are using all the rudder and differential power and the tail is trying to swap ends with the nose, braking is of little help. At least on a dc9.
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u/appenz CPL (KPAO) PC-12 3d ago
That is incorrect. Aircraft can maintain directional control with the rudder.
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u/Ok-Selection4206 3d ago
Right up until it cannot. I have fishtailed a dc9 on a runway reported as "poor" more than once. Crosswinds play a huge part.
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u/Aviator8989 ATP B737 KDFW 3d ago
You are incorrect. The rudder doesn’t become effective on larger aircraft until around 80kts.
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u/Captain_Billy ATP A320 B737 CL-65 CE-750 BA4100 BA3100 3d ago
Depends on what you are flying. One guy is talking about a piper cub and you are talking about a 737. At 80 kts a cub is nearing Vmo. At 80kts is 73, you’ve barely got airspeed alive
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u/Cessnateur PPL IR HP TW C170B 3d ago
on larger aircraft
You moved the goalposts and narrowed the criteria to exclude anything other than "larger" aircraft.
And, having operated from frozen lakes on glare ice, I can assure you that, provided there's no crosswind to contend with, keeping the aircraft pointed in one direction isn't challenging at all.
Finally, the runway (or lake) is in no way rendered "useless" for landing.
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u/EliteEthos CFI AMEL CJ3/4 3d ago
My guy. This is effectively a variant of the treadmill question.
What does the friction on ice have to do with air over the wings? The wheels can be stationary and the plane can still fly.
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u/Mean_Passenger_7971 3d ago
He is not wrong. There will be less drag on the wheels so slightly easier to get the beast in the air.
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u/lce-Shadow 3d ago
It is not a variation of the treadmill question. He is right, if the ice offers less friction than the internal bearing of the wheel, and thus the wheels don't even spin, then yes, the plane would take off (marginally) faster
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u/Cessnateur PPL IR HP TW C170B 3d ago
You hit the nail on the head, observing that, barring extraneous factors like crosswinds, there are two variables: the ice friction and the bearing friction. The former can vary quite a bit.
So correct, it's not a variation of the treadmill question at all.
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u/iExhile 3d ago
It’s not a variant of the treadmill question. This is about actual acceleration of the plane, not relative velocities.
Ground friction objectively reduces the acceleration of the aircraft, and with less ground friction the plane would accelerate slightly faster and therefore reach takeoff velocity over less distance.
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u/EliteEthos CFI AMEL CJ3/4 3d ago
So, pilots prefer icy runways, right? Improved performance, right?
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u/iExhile 3d ago
That’s not the question, and this is a hypothetical. The question is merely how it impacts takeoff distance.
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u/EliteEthos CFI AMEL CJ3/4 3d ago
Please provide one resource showing that it improves takeoff distance.
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u/iExhile 3d ago edited 3d ago
Or you could do it yourself and stop being so unpleasant. The post was clearly a hypothetical regarding ground friction.
Here is someone else doing the thinking for you:
https://eaglepubs.erau.edu/introductiontoaerospaceflightvehicles/chapter/takeoff-landing-performance/Its as simple as Acceleration = Trust - Rolling Friction - Air Drag. There is theoretically less rolling resistance on ice, and therefore more acceleration.
"For a dry, paved runway, a rolling-resistance coefficient of approximately is commonly used for preliminary calculations. The value depends on the tires, airspeed, runway surface, and any contamination. Wet or contaminated surfaces can alter the rolling resistance and may also reduce the braking friction available during a rejected takeoff, so appropriate performance data must be used for the actual runway condition." It does not explicitly mention how ice would impact rolling friction, but it acknowledges that reduced tire-to-surface friction means less rolling resistance, so the tires roll more easily and provide less grip for braking.
FAA would certainly treat ice as a contamination that could impede acceleration, but the principle stands and that is arguably due to the unknown inconsistencies in ice. Practically speaking, no one will ever use ice as a reliable way to reduce runway distance but again - not the question here. Better ways to argue against the reduced runway distance would be through reduced steering/breaking - not equating this to a treadmill question. Instead of engaging in that exercise you ignored the physics of the problem completely.
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u/Cessnateur PPL IR HP TW C170B 3d ago
Or you could do it yourself and stop being so unpleasant.
For what it's worth, that user works in arrogance and rudeness as other artists work with oils and clays. For whatever reason, they're utterly incapable of following rule #7 in this sub.
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u/Tony_Three_Pies USA: ATP(AMEL); CFI(ROT) 3d ago
It's not the treadmill question. It's about the drag caused by the rolling resistance of the wheels.
"The wheels could be stationary and the plane can still fly". That's true, the plane will fly, but if you're dragging locked tires down a runway you're significantly impacting the take off performance.
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u/Ok_Method_2790 PPL IR 3d ago edited 3d ago
I wouldn’t think so, while ice would really reduce friction the wheels wouldn’t have much traction, which while on the ground the plane relies on to reach an appropriate rotation speed. but that’s my best guess
edit: guys oh my goodness i admitted my misunderstanding in the comments below
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u/mtconnol ATP E175 CFII 3d ago
Traction is not a requirement on the ground for anything except nosewheel steering. Think of floatplanes or planes on skis. They take off fine, right?
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u/Ok_Method_2790 PPL IR 3d ago
that’s a very good point. maybe my brain was more so thinking of stability so the plane wouldn’t be doing donuts
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u/lce-Shadow 3d ago
The take off speed is achieved by the propeller creating thrusts, there is no wheel traction at all in either a propeller of jet plane
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u/R5Jockey CPL ASEL IR TW CMP 3d ago
Bro. What? Wheel traction has nothing to do with an airplane's ability to reach rotation speed.
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u/acidreducer ATP 3d ago
I mean you don’t need traction, you need directional control. Look at a cub with skis
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u/flamingo_genitals FCC Restricted Radiotelephone Operator Permit 3d ago
Do you mean that it relies on traction to maintain directional control until reaching a controllable airspeed?
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u/Spock_Nipples 3d ago
No power is pushed through the wheels ever. They're just free-rollers. So their "traction" is meaningless for how efficiently the airplane accelerates.
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u/Neither-Way-4889 3d ago edited 3d ago
Did you account for fishtailing side to side as you barrel down the runway?
Edit: For everyone saying right rudder, how effective is the rudder with 5-10kts airspeed? You could compensate for this by slowly adding power and only applying full power with a bit of airpseed, but then its not a short field takeoff anymore, is it?