Corsair 115
Penultimate Amazing
- Joined
- Apr 18, 2007
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- 14,519
Relevant word bolded and capitalized.At 35,000 feet, they are CRUISING at the best atainable speed while facing less air resistance than at 1,000 feet.
Best crusing speed does NOT mean fastest speed possible. Best cruising speed means the fastest speed the aircraft can go while still being efficient in using its fuel. The aircraft can always go faster, but then it would become much less fuel efficient. Since fuel is one of the biggest costs for an airline, using fuel efficiently is of prime importance to both the airline and the aircraft manufacturer (look no further than the fuel-saving measures put into the design of the forthcoming Boeing 787 for evidence of how important fuel efficiency has become).
The B-17G, for example, had a maximum speed of 287 MPH at 25,000 feet, though it could reach a maximum of 302 MPH if war emergency power was used. The cruising speed, however, was 182 MPH at 10,000 feet.
The Lancaster B.Mk.I had a maximum speed of 281 MPH at 11,000 feet. The maximum weak mixture cruising speed was 227 MPH; the most economical cruising speed was 216 MPH at 20,000 feet.
Is that 500 miles per hour or 500 knots? Though some assume the terms are essentially interchangeable, there is in fact a big difference between the two, since a nautical mile 15% longer than a statute mile (and knots and nautical miles are the traditional measurement system for distance and speed in the aviation world).500 mph[/B] agrees with 570 mph?
No, they wouldn't, because: A) delays can happen for a variety reasons, so it's not an unusual occurrence, and B) fuel is expensive. Going faster generally means burning more fuel, and airlines hate it when flights have to use more fuel than is necessary, since that means more fuel is needed to refuel the aircraft for the return trip, and that additional fuel costs money.I understand that tail winds and head winds at 35,000 feet do effect arrival times which means they have a push or drag effect and since I'm sure airlines try to keep to schedule, if they had reserve speed that could overcome opposing winds, they would utilize this speed instead of stating the delay was unavoidable!
But it doesn't become a major threat to the aircraft, depending on the design, until you're going really fast. Read up on the development of the P-38 fighter to learn how compressibility issues were discovered, and the threat it posed to fighter designs."As an aircraft moves through the air, the air molecules near the aircraft are disturbed and move around the aircraft. If the aircraft passes at a low speed, typically less than 250 mph, the density of the air remains constant. But for higher speeds, some of the energy of the aircraft goes into compressing the air and locally changing the density of the air. This compressibility effect alters the amount of resulting force on the aircraft. The effect becomes more important as speed increases."
10,000 feet per minute is a very substantial descent rate. Consider that a Boeing 757, for example, has a normal descent rate of 1,400-1,800 feet per minute depending on the altitude and speed.It was not in a power dive and 10,000 feet per minute is 113 mph.