How do you find out the cruise altitude that will be most efficient? I'm attempting some long distance flights in a 747 but am worried about fuel. I heard that a 747 made it from UK to Australia non-stop.
What I've always done is to actually fly to some reasonable altitude, say FL 290, fly straight and level for a few minutes, then start recording the fuel consumption. If your plane displays PPH on the panel, that's good, otherwise you watch the fuel gages and record the time, and calculate PPH for yourself. Leave the autothrottle set at the same speed, but climb a couple thousand feet, let it stabilize at speed, then record fuel consumption again. Do it again until you can't climb anymore, then pick the best altitude for the best fuel economy.
Most of the time, higher is going to be faster and more efficient, but you need to pick an altitude that you can get up to reasonably efficiently.
I've done this a few times in the Lear Jet, and I find that I will burn about 600 pounds of fuel climbing from sea level to FL415, then if I cruise at mach .81, I'll burn 850 pounds per hour in level flight. That gives me 6.35 hours of cruise, at a ground speed of 490 kts, so my level flight range would be about 3000 nm. If I keep my flights to under 2500 nm, that gives me plenty of margin, since the fuel consumption goes way down on descent. Of course, if I ever get diverted to another airport an hour away, I am going to run out of fuel and crash!! 😳 I suppose real pilots need to be a bit more conservative!
Do not think you will make UK-Aus in one hop...if you do let BA/Virgin know how you did it!
I think .85 is the economical cruise speed at around 38000 feet according to a 747 training manual 😉
Thanks guys. I'll use Eds technique and measure my fuel consumption at 38000 and see if it is reasonable.
... I heard that a 747 made it from UK to Australia non-stop.
That trip is around 10,000± miles. The range on a fully loaded 747-400ER is 7670 nautical miles according to Boeing specs.
Was the Flight Quatas or BA ❓
A good cruise altitude would depnd on the weather and other traffic. There are a few other specs but they wouldn't properly in the current FS.
Quantas used a 747-400 to set the world distance record for a commercial airliner by flying from London to Sydney non-stop. This record stood until 1993. I know it seems to defy the rules but it happened.