When I was working under contract to Hamilton Sundstrand, I built and helped design all nine of the ECS (Environmental Control System) fans and did the wiring in the APU (Auxilary Power Unit). In the engine start sequence, the 1,100 horsepower APU provides power to the starter generators to start the jet engines. The wiring on the APU was custom teflon over pure silver.
Pretty cool to see it finally leave the ground after two years of delays, and I guess my shit worked because it didn't crash
i'll start with the wire. silver is the best conducting material known. why would such a thing be needed on an engine? to transfer power with? why not copper? it doesn't seem needed/cost effective in the least bit...
the APU sounds like its a generator all in it's own, since it produces power, therefor it must be driving an alternator. you said it powers the "starter generators", so i'm assuming that device is an electrically driven "generator".
whats getting at me is the 1,100hp genset powering yet another genset. an 1,100 hp engine has the ability to produce well over 500kW, and is very large in size. it might require multiple starters just to crank over. the again i'm not sure if frequency is critical in a starting system for aircraft, so size might not be a factor (gens need to run at 1,800rpm to produce 60hz, and need size/torque to do so (for all those who didn't know and are reading this)). being said, that powering another generator sounds a little odd. i'm not sure how electric based generators can be productive to the point where they're logical to use, but i don't work on anything of that nature, all i know is an alternator is needed.
to me it sounds like there would be a starting device for the APU, which powers the starting device for the turbines.
are the starter generators basically... just starters? what exactly do they generate besides torque to get things up to speed? sounds ridiculous i'm poking around at it this much but being in the career field i'm in just got me thinking...
on a different note, sweet plane. some big @ss turbines on that thing.
Ok Eric, let me answer these questions as best I can. Quite a few aspects of the design and build of the 787 were strictly classified, and only the crews in the areas where specific components were built were privy to any information. This is what I personally know:
Silver wire, usually teflon wrapped, has been used in aircraft for many years for three main reasons:
1- Extremely low resistance combined with near perfect current flow and very high reliabilty.
2- Silver has a higher melting point than copper.
3- Weight. Although silver is heavier than copper, the amount of copper required to match the performance of silver would make it heavier on a wire-by-wire basis.
Also, the APU used on the 787 is a $600,000+ unit. Boeing engineers demand every single component to be of the absolute highest quality available at the time of build. Since, potentially, millions of lives are at stake during the lifetime of a given aircraft, they do not cut corners on anything at all, and cost is never a priority. When I did work for military aircraft companies (Boeing, Lockheed, McDonnell Douglas, Hughes) and Government agencies (NASA) the attention to quality control and materials was even higher. Not suprisingly, weight is an extremely important aspect of aircraft manufacturing, with even a couple ounces here and there adding up to a considerable reduction in overall weight.
The APU has a few duties. One is to run the onboard heating, cooling and ventilation before the main engines are started. It sits in what is called the tailcone, which is the "pointy" part of the fuselage at the very rear of the aircraft, just below and behind the fin. The APU automatically shuts off once the main jet engines are running at speed. The APU also acts as an emergancy power generator in the rare case that both (or all 4) engines were to fail. The Boeing 787 requires roughly 200 kilowatts of electrical power. The Hamilton Sunstrand APC 5000, which is used on the 787, is basically a gas powered jet (turbine) engine.
The starter generator is responsible for two tasks. When the jet engines are started, it receives the current from the APU and acts solely as a starter. Once the engines are up to speed, they switch to being generators, using the rotation of the engines to power the electrical needs of the aircraft.
Yes they are very powerful main turbines. The Rolls-Royce Trent 1000 engines which were on the 787 at the time of this maiden flight (Boeing will also use the General Electric GEnx engines) are capable of creating 75,000lbf (pounds of thrust) each.
I agree, Nice info post. I like watching those yt plane vids as well as large locomotive ones.The northern snow plow trains are crazy. And the 747 doing a roll over..
