TimePilot From Japan, joined Sep 2005, 284 posts, RR: 0 Posted (3 years 1 month 2 days 13 hours ago) and read 973 times:
Most people know that stop & go traffic is bad for cars. Brakes, for example, usually perform their best when warmed-up (at least carbon fiber racing brakes.) Most parts on racing cars are at the best when constantly running and at high temps. Always stopping and starting puts lots of stress on parts and causes them to wear-out quickly.
Is this the case with aircraft? Do aircraft engines perform their best when constantly running? Someone once told me that after take-off, at around 400ft, engines are spooled back to abate noise and reduce the chance of failure. Is this true? Is this only for props or all aircraft in general? If an aircraft engine is run at 100% all the time, does it increase its chances of wearing out and possibly breaking?
How about the airframe? Does the airframe of an aircraft receive more stress from landing and taking-off or from bumps and jolts while in the air? Does the average airliner spend more time in the air or on the ground? (I would say air, but I'm not sure.)
Jush From Germany, joined Apr 2005, 1617 posts, RR: 5 Reply 1, posted (3 years 1 month 2 days 12 hours ago) and read 967 times:
Of course an engine would wear out at 100% quite quickly. In fact most engines are limited to a timeframe in which maximum thrust can be used.
Today almost all takeoffs from normal airports are derated and are suited to temperature weight and so on. Engines are often spooled back when in air cause you don't need all the thrust that you need for takeoff. It's usually when they change the computer from takeoff mode to normal climb. That, as you said, could happen at 400' but it can happen at any height around this point.
Regds
jush
There is one problem with airbus. Though their products are engineering marvels they lack passion, completely.
Squakin1200 From United States, joined Oct 2006, 17 posts, RR: 0 Reply 2, posted (3 years 1 month 2 days 12 hours ago) and read 967 times:
There is a saying, "one flight hour a day keeps the mechanic away" this applies to flying your plane often as it is better on the airplane than sitting.
On piston engines at least, runnig a 100% power all the time would reduce the life of the engine. Generally, 100% is for take-off and it must be reduced to 75% power for cruise.
Usually power reductions after takeoff are to reduce noise, but also to get the prop speed and manafold pressure out of the red line.
Bond007 From United States, joined Mar 2005, 4510 posts, RR: 11 Reply 3, posted (3 years 1 month 2 days 6 hours ago) and read 927 times:
Remember, the 'age' of an airframe is often reported in cycles (landings/takeoffs). An 8 hr flight is not 8 times as 'bad' as a one hour flight as far as the airframe goes. Much wear and tear is due to the pressurization/depressurization. In fact one might argue that an aircraft that does 4 1hr flights/day is much 'older' than one that does one 8hr flight/day.
Engine 'age' is usually reported as Total Time...hours in use.
Piston engine aircraft usually work off the Hobbs meter...this tracks hours when the engine is running...whether taxiing or flying.
Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
Vikkyvik From United States, joined Jul 2003, 3805 posts, RR: 26 Reply 4, posted (3 years 1 month 2 days 5 hours ago) and read 915 times:
Quoting TimePilot (Thread starter): Does the average airliner spend more time in the air or on the ground? (I would say air, but I'm not sure.)
For airliners, while the engines are running, they typically spend more time in the air. At least, I'd say this is the case for airplanes that typically do flights of over an hour or two. As a professor put it to me, "Airplanes like to be in the air. They don't like to be on the ground."
Quoting TimePilot (Thread starter): If an aircraft engine is run at 100% all the time, does it increase its chances of wearing out and possibly breaking?
As has been said, absolutely. Kind of like running your car's engine at 7000 RPM all the time.
I believe many engines are limited to 5 or 10 minutes or so at maximum thrust.
Quoting TimePilot (Thread starter): Brakes, for example, usually perform their best when warmed-up (at least carbon fiber racing brakes.) Most parts on racing cars are at the best when constantly running and at high temps. Always stopping and starting puts lots of stress on parts and causes them to wear-out quickly.
As far as airplane braking upon landing is concerned, a lot of the time, only idle reverse thrust is used. For one thing, using more than idle reverse puts more wear on the engine, as it has to spool up again. Also, there's the risk that the reversers could blow some FOD into the intake (which is one reason why the reversers are only used down to a certain speed). Thirdly, modern carbon brakes, as you said, work better at higher temperatures, so it's not a bad idea to use mostly the brakes.
The spirit of Massachusetts is the spirit of America!
Vikkyvik From United States, joined Jul 2003, 3805 posts, RR: 26 Reply 6, posted (3 years 1 month 2 days 5 hours ago) and read 903 times:
Quoting Kaddyuk (Reply 5): The operators like them to be in the air, the airplanes, along with gravity and the rising cost of fuel like to remain on the ground!
Haha, all I meant was that airplanes, all else being equal, are designed for the regime of flight through the atmosphere. Tons of time and development (and money!) go into perfecting the wings and other flight surfaces.
Of course, time and money are spent getting them into the air and back down to the ground; but all else being equal, they are designed to fly through the air, not to roll along on the ground.
The spirit of Massachusetts is the spirit of America!
Bond007 From United States, joined Mar 2005, 4510 posts, RR: 11 Reply 7, posted (3 years 1 month 2 days 5 hours ago) and read 900 times:
Quoting Vikkyvik (Reply 4): As far as airplane braking upon landing is concerned, a lot of the time, only idle reverse thrust is used.
One important thing about reverse thrust, is that it has little effect on braking, even though it might make a lot of noise. On a dry runway, the extra braking force is 15% at best. It's more effective on a wet runway, but in this case it wouldn't be reducing much less of the wheel braking force (due to the lack of friction on the wheels/brakes anyway).
Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
SOP for light props(my Cessna ) is full power for takeoff. Now, there is a golf course at one end of the runway and we will sometimes pull the power back just to watch all the golfers look up as the engine sounds stop.
Quoting TimePilot (Thread starter): If an aircraft engine is run at 100% all the time, does it increase its chances of wearing out and possibly breaking?
Small Cessna's run at very high power settings coninuously. I'll keep a 172 around 2100 RPM for cruise, 2400 being the max. Thats about 88% power continuously. For a 152 it sits around 2400 RPM, 2450 being max, with me at the controls. Or about 98% power continously. The engines are extremely reliable and I dont worry about breaking them.
Quoting TimePilot (Thread starter): Does the airframe of an aircraft receive more stress from landing and taking-off or from bumps and jolts while in the air?
Small a/c definately recieve more damage on t/o and landing then in cruise. Bumps in flight never seem to bother the a/c, but God knows I've had my share of tail strikes and some, um, touchy, landings. Thats for a different thread though.
Sorry, I know you wanted Airliner answers, but I gotta speak up for us pilots of small a/c now and then.
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) is full power for takeoff. Now, there is a golf course at one end of the runway and we will sometimes pull the power back just to watch all the golfers look up as the engine sounds stop.
Thats for a different thread though.
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