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Old 01-08-2008, 09:34 PM   #11 (permalink)
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I don't know nothin' 'bout flyin' no boeings. But I do know that ATC has made me get outta the way of a scheduled, faster aircraft especially if it was on an IFR flight plan. Usually ATC frowns on planes touching each other so most of their priorities yield to the less maneuverable and faster hunk of flying metal. I've also been on my own instrument approaches (even in VMC) and been given priority landing clearances over VFR traffic. This makes sense because doing a mere prelanding checklist on a fixed gear single-engine plane for a VFR landing is trivial compared to say setting up a full ILS approach and then doing all the prelanding preparation of a complex aircraft while trying to keep the glideslope and centerline needles centered. Needless to say, holds are very expensive for folks flying the big iron.

Now something I can speak to a little better is the power required curve (or just power curve) of a plane. In non-accelerating flight, a plane must make enough thrust to equal aerodynamic drag. Drag is made of parasitic and induced drag:

Parasitic drag goes with speed squared and induced goes with the reciprocal. Look at these two curves. Where they meet is the least drag. This is where the plane will climb the at the highest rate, and will glide the longest.

Now, look a the power required:

The power required curve is the least where the drag is. Notice that going slower and going faster will both require more power. There is a speed called minimum controllable airspeed (MCA) where it takes full throttle to keep the plane in the air and yet the wing is right on the edge of stalling.

Ideal speeds of an aircraft are determined and published by the manufacturer after tests nearly as extensive as those that Darin does on his metro. Pilots are trained to know what to do with these speeds and to memorize them for the particular plane at hand.

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Old 01-09-2008, 02:59 PM   #12 (permalink)
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I had no idea there were that many pilots here.

Thanks for the info everyone - very interesting stuff.

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Originally Posted by Silveredwings View Post
Ideal speeds of an aircraft are determined and published by the manufacturer after tests nearly as extensive as those that Darin does on his metro.
If the quality of their data is comparable to the quality of mine... I'm never. Flying. Again.

Those drag curves are fascinating. Thanks for posting them.
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Old 01-09-2008, 09:10 PM   #13 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
Those drag curves are fascinating. Thanks for posting them.
The induced drag is exactly why spoilers and wings will not help FE on a car (especially because their angle of attack don't go down with airspeed the way a plane's wing does). VGs create drag the same way but can be helpful in a few rare cases where there is an advantage to prolonging laminar flow instead of (earlier) airflow separation into turbulance.
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Old 01-09-2008, 11:07 PM   #14 (permalink)
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Flyer

I do a lot of flying -- mostly as a airline passenger, but also on Flight-Sim (cheaper that way)

I read an article that American Airlines went on a quest to reduce fuel consumption a few years ago. The plan: reduce as much weight as possible.

This translated to removing non-essential equipment such as food warmers, calculate the proper amount of fuel + reserve (no more), and going as far as to justifying a profit from the in-flight magazine, or it was to get the boot.

Lightening the fleet saved the company loads of expenses. IIRC, about 10% fuel savings. As Laz mentioned, single-engine taxi is very common among all airlines. I've been in cases where the on-board power unit (a turbine-powered auxiliary power unit, or "APU") isn't used to cool the aircraft in the summer, and passengers are asked to pull the shades to help keep the cabin "hot" instead of "blistering". The big, yellow ground-air-con hose can't often handle the demand. It gets toasty, but fuel is saved...

Here's the biggest problem: With the current Air Traffic Control setup, a flight isn't "direct" -- meaning a flight from Chicago to LA isn't a straight line. So controllers can track flights with their antiquated technology, airways have to be followed, which are like "expressways in the sky". The final route will look like a jagged edge instead of a straight line. This process leads to congestion, overworked controllers, delays, vectors off-course for spacing the aircraft for landing, and speed restrictions. All of this adds up to more fuel consumed. A priority needs to be placed on updating this system, or it's only going to get worse.

Every transportation industry is feeling the fuel price pinch, and that is passed down to the consumer. Baggage weight limits have decreased, with surcharges for over-weight bags increasing. This is all with the average American weighing more every year.

Same goes for the engine itself. Northwest is the best example. I often fly on the old Douglas DC-9. The engines are old, loud, and inefficient -- but I'm sure the 35-40 year-old aircraft are paid off (they use the "Low-Bypass Turbofan" engines -- very cylindrical in appearance). In contrast, the newer Airbus A319 (similar to the Boeing 737) has a quieter, high-efficiency, "high-ratio bypass turbofan" engine. They're have the more common large intake. I'm sure they still carry a note on those...

To survive, I'm sure the trend will continue...

RH77
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Old 01-09-2008, 11:30 PM   #15 (permalink)
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It's no accident that AA planes' livery is bare skin with a stripe down the side. That much paint weighs literally hundreds of pounds.

Big iron flies almost exclusively at and above flight level 180 (18,000 feet), where IFR is required (including following airways). One of the reasons for religiously flying the airways is that the redundancy of the system. Even if ATC and all ground radar goes down or if the plane loses radio and/or transponders, traffic will still maintain minimum separation. Contrast that to South America where the radar coverage is spotty and pilots aren't so 'religious.' It's like the wild west down there and planes occasionally have mid-airs.

However we eventually update our antiquated system, it will have to account for newer and more efficient procedures that don't sacrifice safety.
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Old 01-09-2008, 11:54 PM   #16 (permalink)
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I took the controls in a 4 seat Cessna once!

(Just had to say that. Kinda feeling left out.)

Oh - and I sucked! I had quite a hard time holding steady altitude.
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Old 01-10-2008, 12:00 AM   #17 (permalink)
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Quote:
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I had quite a hard time holding steady altitude.
Once you have the altitude/attitude you want, just set the elevator trim for zero yoke force. It really minimizes the workload of holding the yoke. Then you need only make minor adjustments, and to climb or descend, you adjust the throttle for that.
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Old 01-10-2008, 09:21 AM   #18 (permalink)
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True hypermiling for naturally aspirated piston-powered aircraft would require flying in ground effect. Imagine skimming across a lake with the lowest part of your fuselage maybe 1 to 5 meters above the water depending on visibility, responsiveness of the aircraft, marine traffic and your own bravery / stupidity level. You’re brave if it works out for you, stupid if it doesn’t.

Aircraft manufacturers don’t publish consumption specs for this but pilots are trained how to take advantage of this when doing short field take-offs. The idea of a short field take-off is to get the wheels off the ground as soon as possible since the amount of drag once airborne is greatly reduced. Then the key thing is to keep the nose as close to the ground as possible. Firstly because an airplane can so easily get into ground effect – think of Bernoulli’ principle and that piece of paper being blown across a table – and secondly because an airplane that gets off the ground quickly can easily lose lift and stall a wing. You effectively lift off too soon and then force it to stay close to the ground.

Once off the ground flying in ground effect, the aircraft accelerates at its fastest rate so that you can use the speed to pull up and clear taller obstacles, or just get clear of a short or rough runway quickly. The toughest part is trying to stay close enough to the ground because as you accelerate the aircraft goes more and more out of trim and it takes a serious effort just to keep the nose down – the aircraft is fighting you to climb and you are pushing the yoke very hard towards the ground. Fun stuff… but I sure wouldn’t have wanted to be a bomber transport pilot in WWII flying 50’ above the Atlantic doing deliveries to England… no wait, that would sure be more fun than sitting at my desk job.
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Old 01-10-2008, 10:55 AM   #19 (permalink)
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Who: is ground effect so noticeable? While landing the Cessna, the pilot told me the plane doesn't easily descend through those last few meters above the runway to touch down. I've heard of the phenomenon, but I wasn't sure how much my leg was being pulled or not.
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Old 01-10-2008, 11:41 AM   #20 (permalink)
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He wasn't pulling your leg. Check out the ratings for helicopters hovering in ground effect (IGE) vs out of ground effect (OGE) - major difference.

I'm not sure what the mileage improvement from skimming across a lake would be but 30% wouldn't surprise me at all and the optimal speed for skimming would likely be faster than the maximum endurance (most economical) flying speed as well.

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