by PhantomTweak » Mon May 26, 2014 12:26 am
A lot depends on the T/O weight, Take Off Weight or total gross weight of the aircraft as it starts the take off run. That's fuel, passengers, cargo, toilet paper, etc etc, and most important thing, COFFEE! The greater your t/o weight, the faster you need to go to establish the plane in a climb. Remember, above the first or second flap setting, say 15° or threabouts, the flaps provide more drag than lift and shouldn't be used. The bombers that flew off the carrier for Dolittle's raid on Toykyo had one big advantage to what they were trying to do that plane on land-based runways do not: The carrier was plowing through the water at max speed, and was turned directly into the surface wind. This gave the planes a boost of 35-45 kts airspeed with 0 groundspeed. The boat was also pitching quite a bit, so with proper timing it helped, literally, to throw the planes into the air a little bit. Shortened the t/o roll quite a bit, and even so, the first few birds barely made it into the air. Their rolling distance was almost too short, given the weight they were carrying.
As for your A380, there are two schools of thought an sitting on the runway and running the engines up. One says is shortens the take off roll, by having the engines at full bore before you start to roll. True, up to a point. However, watch the thrust of the engines as you roll...they can't suck air fast enough at slow speed to develop full thrust. They need the ram effect of moving forward through the air to get up to full thrust. Also, they airport doesn't care for the noise and exhaust fumes created by heavy jets powering up at the end of the runway. The normal proceedure I think, is for the pilots to spool up to about 85%, release the brakes, and once the bird starts to get some airspeed, go to mil, or 100% thrust. This lets the engines work properly, gulping down air that's getting rammmed into the the front a lot more efficiently than by trying to do so sitting still. It also moves the noise and exhaust on down the runway and into the big open areas of the airport rather than the more densly occupied areas at the end of the runway. The propeller driven planes, mentioned above, don't have this limitation. THEY can develop full thrust sitting still. Once the manifold pressure, mixture, prop pitch and so on are all set, release the brakes and you are at full thrust!
So, weight, noise, acceleration and so on all are part and parcel of t/o calculations. The more weight, the higher the t/o speed must be. etc
Pat☺
Have fun, fly high, far, and free!
Pat
2S7, Chiloquin OR
