Jet engine response. Newer pax jets have more & better safety features. Faster throttle response is handy?

Question

Faster throttle response would be an important safety feature if suddenly becoming aware of a need to climb over terrain?
A reduction from 10 secs to 5 to 6 secs could be crucial in avoiding a crash? How long have the better fuel control units been available in newer turbofans?
Mike Tyson said;
Lots of guessing here as usual... if you guys are talking about the CFM56 and saying 10 seconds you're a bit off. 5-6 seconds tops... not sure about the old JT8Ds but I can't imagine even them taking 10 seconds. As Grumpy Geezer said, the Fuel Control Units in these newer turbofans make a world of difference... but he was voted down so that pretty much sums up our knowledge base here.

Answer 1

Its not really a FCU issue - even the oldest of Gas Turbine engines have FCUs that can throw in fuel as fast as the combustion chambers can burn it. It is a matter of the engine design - old single spool engines had a rotating assembly that was heavy and needed to overcome inertia, also the air moving through the engine has its own inertia to be overcome. Modern engines 'slam' accelerate faster because they have two or even three co-axial rotating assemblies (spools). A twin-spool ducted fan has a low pressure and a high pressure compressor/turbine assemblies (sometimes an intermediate pressure system). The lower mass HP system will spin-up a lot faster than the LP system. As most of the thrust is from the LP by-pass system - which has the higher mass - it still takes some time to power-up. The compressors can only take an airflow increase that will maintain compressor blade angle-of-attack, in old engines, the FCU had to actually restrict the fuel flow on acceleration to a predetermined profile, or the engine would surge.

Answer 2

The engines are designed to meet operating requirements. One of those is throttle response. Making the engine respond faster when it is not required by the system engineers would add significantly to the cost of the engine while making minimal difference to safety.

An Air India A320 slammed in to a berm because the pilot relied on the side stick controller to put him into go-around mode, including automatically advancing the throttles. But that delayed advancing the throttles by several seconds, during that time they continued to sink below the glideslope and that made all the difference.

But 99.9999999999% of the time a couple of seconds off the acceleration time from idle to full power wouldn't make any difference. Acceleration from 60% to 100% (power, not rpm) is already fast. The engines are only slow to respond from low rpm areas, like ground idle to takeoff power.

There's always something that could be done to improve safety, but you have to spend your money on the ones that would actually make a difference.

Answer 3

iwould say that theengines are too limited in torque to manage such rapid accelerations. The old fashioned combustion engines were doing much better in acceleration just because give it enough fuel to blast and it will start spinning.
The jet engines on the contrary use a fluent flow and in case you add too much fuel, you just overheat the turbine blades. the stopped/ not rotating jet engine still provides a lot of "holes" for the combustion gasses to leak out. thus the increase in RPM has to be received through efficient flow increase. notice that the fuel burning chambers of jet are not that sturdy like the cyllinder heads of a car or aircraft engine.

having a turbine that would be able to incerease its RPM like the comb. engines do, you will need to redesign the engine shaft that transfers the energy in the form of torque to the compressor and turbofan. these have very different mass distributaion when compared to the propeller. they are bulkier and a lot of mass is quite far from the rotatin axis. this make is a giant gyro, with enormous momentum.

result is that the construction problems linked to the faster RPM increase would not be worth of doing it.

Answer 4

A quicker response to the throttle would have prevented this crash, but jet engines just don't respond as quickly as piston-engined planes. That unfortunately is an economic fact of life.

http://www.youtube.com/watch?v=a5NXpar4Ouw

Answer 5

The best answers aren't usually the correct ones. I've gotten "Best" ratings with flippant BS and collected a bunch of "thumbs down" for answers based upon over 30 years of exprience.

That's probably why guys like john b and Cherokee Flyer bugged outta here.