High Speed Climb
Why is it then some airplanes, after t/off and when given high speed
climb reply by saying " ok on passing 5000ft high speed" Any reason for this? :ok: |
Company speed limit to 250 below 5,000 ft
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Thanks everyone for the replies.
Ok i understand that a heavier aircraft has more energy but how does it take a longer time to slow down? Is there a better analogy? If i were to compare a lorry to a car, you would say the lorry will coast further than a car. But can i not argue that gravity will pull the heavier lorry down more than the car and effectively slowing down the lorry faster? Can anyone counter this? Pardon me, i don't possess any physics knowledge, just logic. Pls advise. Cheers |
Originally Posted by extricate
But can i not argue that gravity will pull the heavier lorry down more than the car and effectively slowing down the lorry faster?
But your original question was about aircraft, not cars and lorries, and the physics are somewhat different. |
simple analogy.
i throw a ping pong ball at your head at 20 MPH. then i throw a snooker / Billiards / pool ball at the same place at the same speed (20 MPH ) which one hurts the most ?? Or if i roll a bowling ball down the alley will it knock over the pins. now if i roll a balloon down at the same speed what happens ????? sorry but you have to accept that the physics for now is correct and that the formula's and explanations you have are enough for you to understand why a heavier aircraft takes more slowing down than a lighter one. Hope this helps. But if you really want to get into the physics, you really need to start at the beginning and build your knowledge up, rather than jumping in at some random point. GB |
Originally Posted by Bye
you have are enough for you to understand why a heavier aircraft takes more slowing down than a lighter one.
Regards, HN |
I'm wondering if your simple analogy explains that the heavier aircraft slows down more rapidly than the lighter aircraft below the minimum drag speed. http://home.anadolu.edu.tr/~mcavcar/htk224/MinDrag.pdf GB |
Bye,
Post #2 states the 'basic physics'. F/M is 'basic' aerodynamics. Your analogy doesn't address either one. |
Inertia, momentum weight and mass and all that !
DaveReidUK
Join Date: Jan 2008 Location: Reading, UK Posts: 856 Quote: It is worth remembering that at a given weight you will always have the same inertia Inertia is a function of mass, not weight. On its way to the Moon, Apollo had a lot of inertia but weighed nothing at one point If that is true, would inertia in zero gravity space be equivalent to Vsquared ?:bored: ?:rolleyes: It seems to me that there is not much attention paid to the cleanliness of aerodynamic profiles in modern heavies and that is also a contributing factor to it taking longer to slow down. My high performance glider, when loaded with water has a longer slowing down time when decellerating in level flight (vs a Schweitzer 222, which is a big drag queen in the gliding world !);) |
post #2 states "some" basic physics but is not the correct formula to explain why a heavier object has more kinetic energy than a lighter one at a given speed and drag.
F/M is that some code to describe movies of a certain type. certainly not a formula or basic aerodynamics of any kind. I look forwards to your explanations and analogies of why a heavier aircraft below Vmd slows down quicker than a lighter aircraft. GB |
Originally Posted by Bye
F/M is that some code
Extricate's questions in posts #1 and #5 are about A, which equals F/M. F is aerodynamic drag, and it is related to mass M by the aerodynamic lift which equals weight. So a question about A=F/M is about aerodynamics. I look forwards to your explanations and analogies of why a heavier aircraft below Vmd slows down quicker than a lighter aircraft.
Originally Posted by Microburst2002
The heavy one, flying at max L/D (green dot speed) would make, say 240 kt, whereas the light one would be making only 210 kt. But they are both flying at 300 kt, so the heavy one is 30 kt closer to green dot that the light one. Its L/D ratio is better. Its AoA is closer to min Drag, to green dot.
Regards, HN |
If you load up the same truck with more weight, keeping the same brakes, then it takes longer to stop. If there's the same braking force, energy to dissipate scales with mass.
It's a little bit more complex with an aircraft, as if it's heavier, it needs more lift, which means a different speed, height or attitude to fly level. More lift usually means more drag, both in approximate proportion to weight, and so more power is required to cruise heavier. When losing energy descending though, if you try to shed speed deliberately with speedbrakes, that amount of braking isn't affected by weight, just by the speed and spoiler setting, and so a heavier aircraft will need more energy throwing away, and a longer deployment. The energy required to drop from 10,000m would make you travel at 440m/s in addition to your 300m/s cruise speed, so you need to lose a lot of energy on descent to land at 50m/s. That scales with mass, whereas the speedbraking force doesn't. |
Originally Posted by awblain
If you load up the same truck with more weight, keeping the same brakes, then it takes longer to stop.
(a) the brake pressure equals the maximum brake pressure, or (b) the tires start skidding. In this context 'brakes sufficiently powerful' means that condition (b) applies. The braking force is then proportional to the load on the wheel. |
Energy doesn't come into it. i give up :ugh::ugh: |
We're not talking forces or accelerations here, we are talking inertia which is velocity and mass related.
Remember the equation M1V1=M2V2 (numbers should be in subscript) Therefore if M1 > M2 then V1 < V2 |
(a) the brake pressure equals the maximum brake pressure, or (b) the tires start skidding. The friction of Carbon Carbon brakes increases as they get hotter, so for the same brake pressure as they heat up they get grippier. (b) not true, Depending on the Mu and the surface texture the maximum retardation is just before the skid onset. |
Bye,
How do your remarks make untrue what I wrote, that the maximum braking force is determined by either the maximum that the brake can produce, or the maximum that the tire/runway friction can produce, and that the latter is proportional to the load on the wheel? |
because that is not what you wrote.
What you did actually write is not true. My remarks do not make what you wrote untrue, what you wrote that is untrue makes it untrue. I have merely pointed out that what you wrote is untrue. GB |
Ms 39,
You're right - I was assuming progressive braking: dumping of heat in the truck brakes at some acceptable level without locking the wheels. If you keep maximum braking force applied, limited by rubber-road friction, then the braking force would rise linearly with weight (until you ripped the tread off the wheel or set fire to the brakes). |
Originally Posted by Bye
I have merely pointed out that what you wrote is untrue.
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