Quite simply you cannot. It is widely stated you would need to be at a height of at least 40,000 ft to get even a hint of curvature if earth were round. Commercial aircraft are not allowed to fly this high. They are only allowed to fly just under this altitude. 36,000ft might be typical. In addition, the windows on commercial aircraft are small and heavily curved. Even if they flew high enough for a person to see curvature, it would still not be visible to passengers.
The earth isn't pulled into a sphere because the force known as gravity exists in a greatly diminished form compared to what is commonly taught. The earth is constantly accelerating up at a rate of 32 feet per second squared (or 9.8 meters per second squared). This constant acceleration causes what you think of as gravity. Imagine sitting in a car that never stops speeding up. You will be forever pushed into your seat. The earth works much the same way. It is constantly accelerating upwards being pushed by a universal accelerator (UA) known as dark energy or aetheric wind.
What must be the angle of incidence for total internal reflection to occur? Let medium 1 be the medium with the higher index of refraction. As θ1 increases, θ2 also increases, albeit at a faster rate. When θ2 reaches 90 degrees, there is total internal reflection, and there is no transmission of light. The corresponding angle of incidence, θ1, is the critical angle where total internal reflection occurs. Let the critical angle be θc. Substituting into Snell’s law:
The aeronaut can see for himself that Earth is a Plane. The appearance presented to him, even at the highest elevation he has ever attained, is that of a concave surface - this being exactly what is to be expected of a surface that is truly level, since it is the nature of level surfaces to appear to rise to a level with the eye of the observer. This is ocular demonstration and proof that Earth is not a globe.
The surveyor's plans in relation to the laying of the first Atlantic Telegraph cable, show that in 1665 miles - from Valentia, Ireland, to St . John's, Newfoundland - the surface of the Atlantic Ocean is a LEVEL surface - not the astronomers' "level," either! The authoritative drawings, published at the time, are a standing evidence of the fact, and form a practical proof that Earth is not a globe.
In consequence of the fact being so plainly seen, by everyone who visits the seashore, that the line of the horizon is a perfectly straight line, it becomes impossible for astronomers, when they attempt to convey, pictorially, an idea of the Earth's "convexity," to do so with even a shadow of consistency: for they dare not represent this horizon as a curved line, so well known is it that it is a straight one! The greatest astronomer of the age, in page 15 of his "Lessons," gives an illustration of a ship sailing away, "as though she were rounding the top of a great hill of water;" and there - of a truth - is the straight and level line of the horizon clear along the top of the "hill" from one side of the picture to the other! Now, if this picture were true in all its parts - and it is outrageously false in several - it would show that Earth is a cylinder; for the "hill" shown is simply up one side of the level, horizontal line, and, we are led to suppose, down the other! Since, then, we have such high authority as Professor Richard A. Proctor that the Earth is a cylinder, it is, certainly, a proof that the Earth is not a globe.
63) In a second experiment Dr. Rowbotham affixed flags 5 feet high along the shoreline, one at every mile marker. Then using his telescope mounted at 5 feet just behind the first flag looked over the tops of all 6 flags which lined up in a perfectly straight line. If the Earth were a ball 25,000 miles in circumference the flags should have progressively dipped down after the first establishing line of sight, the second would have descended 8 inches, 32 inches for the third, 6 feet for the fourth, 10 feet 8 inches for the fifth, and 16 feet 8 inches for the sixth.

The remark is common enough that we can see the circle of the Earth if we cross the ocean, and that this proves it to be round. Now, if we tie a donkey to a stake on a level common, and he eats the grass all around him, it is only a circular disc that he has to do with, not a spherical mass. Since, then, circular discs may be seen anywhere - as well from a balloon in the air as from the deck of a ship, or from the standpoint of the donkey, it is a proof that the surface of the Earth is a plane surface, and, therefore, a proof that the Earth is not a globe.
100.) The Sun, as he travels round over the surface of the Earth, brings "noon" to all places on the successive meridians which he crosses: his journey being made in a westerly direction, places east of the Sun's position have had their noon, whilst places to the west of the Sun's position have still to get it. Therefore, if we travel easterly, we arrive at those parts of the Earth where "time" is more advanced, the watch in our pocket has to be "put on"or we may be said to "gain time." If, on the other hand, we travel westerly, we arrive at places where it is still "morning," the watch has to be "put back," and it may be said that we "lose time." But, if we travel easterly so as to cross the 180th meridian, there is a loss, there, of a day, which will neutralize the gain of a whole circumnavigation; and, if we travel westerly, and cross the same meridian, we experience the gain of a day, which will compensate for the loss during a complete circumnavigation in that direction. The fact of losing or gaining time in sailing round the world, then, instead of being evidence of the Earth's "rotundity," as it is imagined to be, is, in its practical exemplification, an everlasting proof that the Earth is not a globe.

Most of us in the Western world have been taught from birth that we are living on a spherical earth that spins daily and goes around a giant sun once a year. This is taught as an absolute truth that we should never question. It is “scientific fact”! Or is it? Most Christians are taught that God created a spherical world and that this is what the Bible also teaches. We have learned through public schools and the controlled media that we came to existence through the Big Bang and Evolution, the opposite of what the Bible Teaches. Modern science leads us to believe that the Bible should not be taken seriously as a scientific source. Since the Bible teaches that we were created in six literal days, not by millions of years of evolution, the Bible must be false and allegorical, according to modern “science”. Is the Bible just an allegorical book of stories that are not to be taken seriously? Is the heliocentric model (spherical earth) Biblical? What kind of earth is actually described in Genesis and consistently throughout the Bible? Is there physical and scientific proof to support the Biblical Earth model?
72) October 16, 1854 the Times newspaper reported the Queen’s visit to Great Grimsby from Hull recording they were able to see the 300 foot tall dock tower from 70 miles away. On a ball-Earth 25,000 miles in circumference, factoring their 10 foot elevation above the water and the tower’s 300 foot height, at 70 miles away the dock tower should have remained an entire 2,600 feet below the horizon.

Mr Hind speaks of the astronomer watching a star as it is carried across the telescope by the diurnal revolution of the Earth." Now, this is nothing but downright absurdity. No motion of the Earth could possibly carry a star across a telescope or anything else. If the star is carried across anything at all, it is the star that moves, not the thing across which it is carried! Besides, the idea that the Earth, if it were a globe, could possibly move in an orbit of nearly 600,000,000 of miles with such exactitude that the cross-hairs in a telescope fixed on its surface would appear to glide gently over a star "millions of millions" of miles away is simply monstrous; whereas, with a FIXED telescope, it matters not the distance of the stars, though we suppose them to be as far off as the astronomer supposes them to be; for, as Mr. Proctor himself says, "the further away they are, the less they will seem to shift." Why, in the name of common sense, should observers have to fix their telescopes on solid stone bases so that they should not move a hair's-breadth, - if the Earth on which they fix them move at the rate of nineteen miles in a second? Indeed, to believe that Mr. Proctor's mass of "six thousand million million million tons" is "rolling, surging, flying, darting on through space for ever" with a velocity compared with which a shot from a cannon is a "very slow coach," with such unerring accuracy that a telescope fixed on granite pillars in an observatory will not enable a lynx-eyed astronomer to detect a variation in its onward motion of the thousandth part of a hair's-breadth is to conceive a miracle compared with which all the miracles on record put together would sink into utter insignificance. Captain R. J. Morrison, the late compiler of "Zadkeil's Almanac;" says: "We declare that this "motion" is all mere 'bosh'; and that the arguments which uphold it are, when examined with an eye that seeks for TRUTH only, mere nonsense, and childish absurdity. "Since, then, these absurd theories are of no use to men in their senses, and since there is no necessity for anything of the kind in Zetetic philosophy, it is a "strong presumptive proof" - as Mr. Hind would say that the Zetetic philosophy is true, and, therefore, a proof that Earth is not a globe..
34) Ship captains in navigating great distances at sea never need to factor the supposed curvature of the Earth into their calculations. Both Plane Sailing and Great Circle Sailing, the most popular navigation methods, use plane, not spherical trigonometry, making all mathematical calculations on the assumption that the Earth is perfectly flat. If the Earth were in fact a sphere, such an errant assumption would lead to constant glaring inaccuracies. Plane Sailing has worked perfectly fine in both theory and practice for thousands of years, however, and plane trigonometry has time and again proven more accurate than spherical trigonometry in determining distances across the oceans.
Astronomers have never agreed amongst themselves about a rotating Moon revolving round a rotating and revolving Earth - this Earth, Moon, planets and their satellites all, at the same time dashing through space, around the rotating and revolving Sun, towards the constellation Hercules, at the rate of four millions of miles a day! And they never will: agreement is impossible! With the a Earth a plane and without motion, the whole thing is clear. And if a straw will show which way the wind blows, this may be taken as a pretty strong proof that the Earth is not a globe.
 179) If the Earth were constantly spinning Eastwards 1000mph then airplane flight durations going Eastwards vs. Westwards should be significantly different. If the average commercial airliner travels 500mph, it follows that Westbound equatorial flights should reach their destination at approximately thrice the speed as their Eastbound return flights. In reality, however, the differences in East/Westbound flight durations usually amount to a matter of minutes, and nothing near what would occur on a 1000mph spinning ball Earth.
94.) In " Cornell's Geography" there is an "Illustrated proof of the Form of the Earth," A curved line on which is represented a ship in four positions, as she sails away from an observer, is an arc of 72 degrees, or one-fifth of the supposed circumference of the "globe" – about 5,000 miles. Ten, such ships as those which are given in the picture would reach the full length of the "arc," making 500 miles as the length of the ship, The man in the picture, who is watching the ship as she sails away, is about 200 miles high; and the tower, from which he takes an elevated view, at least 600 miles high. These are the proportions, then, of men, towers, arid ships which are necessary in order to see a ship, in her different positions, as she "rounds the curve" of the "great hill of water" over which she is supposed to be sailing: for, it must be remembered that this supposed "proof" depends upon lines and angles of vision which, if enlarged, would still retain their characteristics. Now, since ships are not built 500 miles long, with masts in proportion, and men are not quite 200 miles high, it is not what it is said to be – a proof of rotundity – but, either an ignorant farce or a cruel piece of deception. In short, it is a proof that the Earth is not a globe.
God's Truth never - no, never - requires a falsehood to help it along. Mr. Proctor, in his " Lessons," says: Men " have been able to go round and round the Earth in several directions." Now, in this case, the word " several will imply more than two, unquestionably: whereas, it is utterly impossible to circumnavigate the Earth in any other than an easterly or a westerly direction; and the fact is perfectly consistent and clear in its relation to Earth as a Plane.. Now, since astronomers would not be so foolish as to damage a good cause by misrepresentation, it is presumptive evidence that their cause is a bad one, and - a proof that Earth is not a globe.
If the Earth were a globe, there certainly would be - if we could imagine the thing to be peopled all round - "antipodes:" "people who," says the dictionary, "living exactly on the opposite side of the globe to ourselves, have their feet opposite to ours: - people who are hanging heads downwards whilst we are standing heads up! But, since the theory allows us to travel to those parts of the Earth where the people are said to be heads downwards, and still to fancy ourselves to be heads upwards and our friends whom we have left behind - us to be heads downwards, it follows that the whole thing is a myth - a dream - a delusion - and a snare; and, instead of there being any evidence at all in this direction to substantiate the popular theory, it is a plain proof that the Earth is not a globe.
If the circular motion of the Sun is a wider circle in December and Shorter in June and it still completes a circle in 24 hours, that Must mean the Speed of the Sun's travel changes accordingly right? Now a fixed spinning record will have one speed but depending on where on the record you are your linear motion will be different. Does this mean then, to achieve the change in speed for a FE Sun, it would need to be affixed to something unseen that is rotating?
If the earth is a sphere like we’ve been taught, with different layers of rock and a molten core, where did all the water of “the great deep” come from? The “great deep”, a giant reservoir of water going to great depths below the earth, does not fit into the globe earth model at all. It does, however, describe perfectly the Biblical Ancient Hebrew model of the flat earth.