High-Speed Turns and the Oldest College Graduate
Posted June 10th, 2008 at 02:03 by Minuteman
I went out for a run tonight and the mind was wandering:
Why did the SR-71 need ¾ of Arizona to make a 90º turn?
If the aircraft is traveling at M=3.0, that's roughly 30 miles a minute. A standard-rate 90º turn should take 30 seconds, or about 15 miles. 2-pi-r is the circumference of a circle, so a standard-rate turn at Mach 3 should be roughly a 5 nm circle, not 300 nm.
Something don't compute, and its probably that the SR-71 doesn't do standard-rate turns at 80,000 feet.
Assuming the horse is a sphere, the equation for the radius of a turn is:
r = V² / (g · tan(L)), where L = bank angle
I figure they were doing well to make between 105% and 110% load factor for straight-and-level flight. That means L = acos( 1/LF ) ... or about 20º.
So r = (3040 ft/s)² / (32.3 · tan(20º) ) = 788543 ft, or about 130 nm for a turn at M=3.0 at 80,000 feet.
Not exactly ¾ of a state, but still pretty big and it would take almost seven minutes. Incidentally, if they wanted to do a standard-rate turn, they'd need about 68º and pull 2.7g ... which is probably quite impossible with only a lifting surface.
The oldest college graduate.
Then I passed a public service billboard that advertised the merits of being the oldest college graduate: Nola Ochs is 95 years old and spent the last four earning earning her bachelor's in history.
In the afterglow of achieving something and setting a new record, one might wonder, "What's the point?"; a valid question since the cost of schooling probably won't be recouped in gainful employment and college was probably pretty stressful (maybe not so much if the rest of your life, statistically speaking, is minus 15 years).
But, reading beyond the inane billboard, I see she attended school with her grand-daughter and intends to be employed as a storyteller on a cruise ship (where having studied history would probably be an asset).
So, the lesson is -- jeez, I can't believe I'm saying this -- if you think something is a lemon, think how to make lemonade ... work with the ideal/best-case scenario. It's at least a first-step in a beneficial direction.
(Stupid advertisement.)
Why did the SR-71 need ¾ of Arizona to make a 90º turn?
If the aircraft is traveling at M=3.0, that's roughly 30 miles a minute. A standard-rate 90º turn should take 30 seconds, or about 15 miles. 2-pi-r is the circumference of a circle, so a standard-rate turn at Mach 3 should be roughly a 5 nm circle, not 300 nm.
Something don't compute, and its probably that the SR-71 doesn't do standard-rate turns at 80,000 feet.
Assuming the horse is a sphere, the equation for the radius of a turn is:
r = V² / (g · tan(L)), where L = bank angle
I figure they were doing well to make between 105% and 110% load factor for straight-and-level flight. That means L = acos( 1/LF ) ... or about 20º.
So r = (3040 ft/s)² / (32.3 · tan(20º) ) = 788543 ft, or about 130 nm for a turn at M=3.0 at 80,000 feet.
Not exactly ¾ of a state, but still pretty big and it would take almost seven minutes. Incidentally, if they wanted to do a standard-rate turn, they'd need about 68º and pull 2.7g ... which is probably quite impossible with only a lifting surface.
The oldest college graduate.
Then I passed a public service billboard that advertised the merits of being the oldest college graduate: Nola Ochs is 95 years old and spent the last four earning earning her bachelor's in history.
In the afterglow of achieving something and setting a new record, one might wonder, "What's the point?"; a valid question since the cost of schooling probably won't be recouped in gainful employment and college was probably pretty stressful (maybe not so much if the rest of your life, statistically speaking, is minus 15 years).
But, reading beyond the inane billboard, I see she attended school with her grand-daughter and intends to be employed as a storyteller on a cruise ship (where having studied history would probably be an asset).
So, the lesson is -- jeez, I can't believe I'm saying this -- if you think something is a lemon, think how to make lemonade ... work with the ideal/best-case scenario. It's at least a first-step in a beneficial direction.
(Stupid advertisement.)
Total Comments 1
Comments
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The myths about supersonic airplanes taking half a country to make a turn are pretty common, I've heard them before. Just like a myth that north star is the shiniest star etc, they come from uneducated folks...
On the other hand, I have nothing but respect for the lady deciding to graduate college at the age of 95. I completely understand, and had I not graduated already I would have graduated eventualy even if I was 105. I think it's awesome. A lot of people see college just as an instrument that helps in getting a better job, but I see it as it is supposed to be seen, as education and personal improvement. Anyway, this is just my few cents.
Posted June 23rd, 2008 at 11:53 by skidz 
