Calculating a descent
 

Is there any rules of thumbs about how you calculate TOD or TOC quickly for a jet??

How do you calcuate when to start the descend?? or to be level at a certain point??

How do you achieve the descent down to MDA if you dont fly level at that point

Programme the computer mate and it does it for you - assuming that you trust VNAV of course.

Otherwise 3 x thousands of feet to use with small allowances for wind component, use of engine anti-ice, and anticipated speed variations according to airspace.

Constant descent to MDA based upon notional glidepath bearing in mind any requirement for mimimum altitude at FAF.

The thouands of feet to lose X 3 plus a few miles to get established in descent and make a gentle level off works well enough as a TOD point. A rate of descent in FPM equal to 5 times your ground speed in knots will keep you aproximately on profile. Add a few more miles if you want to level off early to meet a speed restriction. Works well enough in Jurrasic jets and is a good crosscheck in the robot jets.

Best regards,

Westhawk

A reasonable allownace for an idle deceleration in level flight is 1 kt per sec clean. So if you have to decel from 320 to 180kts allow say 2 and half minutes at midpoint GS of 4 miles per minute and 10 miles is close enough. WIth a tailwind add say 5 miles, use the HW as a bonus.

The equations below describe the motion of a falling body, assuming that the acceleration due to gravity is a constant, g (in which case Newton's law of gravitation simplifies to F = mg where m is the mass of the earth). This assumption is reasonable for objects falling to earth over the relatively short vertical distances of our everyday experience, but is very much untrue over larger distances (such as spacecraft trajectories).
Galileo was the first to demonstrate and then formulate these equations. He used a ramp to study rolling balls, the ramp slowing the acceleration enough to measure the time taken for the ball to roll a known distance. He measured elapsed time with a water clock, using an "extremely accurate balance" to measure the amount of water. 2
The equations ignore air resistance, which has a dramatic effect on objects falling an appreciable distance in air, causing them to quickly approach a terminal velocity. For example, a person jumping headfirst from an airplane will never exceed a speed of about 200 mph due to air resistance. The effect of air resistance varies enormously depending on the size and geometry of the falling object – for example, the equations are hopelessly wrong for a feather, which has a low mass but offers a large resistance to the air. (In the absence of an atmosphere all objects fall at the same rate, as astronaut David Scott demonstrated by dropping a hammer and a feather on the surface of the Moon.)
The equations also ignore the rotation of the Earth, failing to describe the Coriolis effect for example. Nevertheless, they are usually accurate enough for dense and compact objects falling over heights not exceeding the tallest man-made structures.
Near the surface of the Earth, use g = 9.8 m/s2 (metres per second per second), approximately. For other planets, multiply g by the appropriate scaling factor. It is essential to use consistent units for g, d, t and v. Assuming SI units, g is measured in metres per second per second, so d must be measured in metres, t in seconds and v in metres per second. To convert metres per second to kilometres per hour (km/h) multiply by 3.6. In all cases the body is assumed to start from rest.
Distance d travelled by an object falling for time t:http://content.answers.com/main/cont...1e7423c898.png
Time t taken for an object to fall distance d:http://content.answers.com/main/cont...c8bb9fc14d.png
Instantaneous velocity vi of a falling object after elapsed time t:http://content.answers.com/main/cont...94bd5a5425.pngInstantaneous velocity vi of a falling object that has travelled distance d:http://content.answers.com/main/cont...76d6ee7e97.png
Average velocity va of an object that has been falling for time t (averaged over time):http://content.answers.com/main/cont...3e7cacb3b9.png
Average velocity va of a falling object that has travelled distance d (averaged over time):http://content.answers.com/main/cont...a28d1178d2.png

Well - that explains why I am always high:)

Cashking, That's truly amazing! It stuns us all into silence........except me. You didn't answer the question. You did the politicians answer, which is: if you can't answer the question, answer another one like it, but throws you into a favourable light, and hopefully as well gets a dig in at '13 years of Tory misrule', and if you can get a good word in for Tony B as well, well one day you may inch up the promotion ladder!

The actual question was So when you feather, travelling initially at 560mph and 35,000' commences descent, how far horizontally will it have travelled when it flutters to the ground?

Ha! I Have to say that I'm enjoying the torrent of science that Cashking has been unleashing on so many threads this morning. Can't say I understand it of course but all very impressive.

Well, he's on an ASBO straight away :mad: :mad: :mad: