3 ms·

A friend in the industry explained to me recently that part of the problem is requirements creep while the engines are being designed. I am definitely _not_ a m

by rossng 7y ago

A friend in the industry explained to me recently that part of the problem is requirements creep while the engines are being designed. I am definitely _not_ a mechanical engineer - so take what I say with a grain of salt - but I did think there were some interesting parallels to software development. New engines are normally designed alongside a particular aircraft. The aircraft manufacturer optimistically estimates how much thrust will be required. Over years of development, the predicted weight of the aircraft increases and the aerodynamics get slightly worse. To compensate, the engine manufacturer needs to find a way to squeeze more thrust out of the engine - but without changing its size or overall architecture. This can be resolved by adding extra complexity in the form of extra compressors or stages. Alternatively, you can try to run the engine at higher temperatures and pressures. While it's still possible to certify the engine and run it safely, you will probably experience many more maintenance issues than if the engine was running inside its original design parameters.

aunty_helen 7y ago
When an aircraft is released engine development doesn't stop. These things are always undergoing revisions, performance upgrades, ADs, and even just performance upgrades / downgrades / operating procedure changes based on data from in field running. I doubt an engine would undergo the addition of a stage as that's pretty major but there's no reason a mfc couldn't charge you a mil for better compressor blades and give you a thrust rating upgrade for your patronage. Edit: I'll keep talking as more info is coming to my head. Jet engines have fadec computers that get to decide what your maximum power level is. This maximum is programmed into the engine as a thrust rating. Let's say you engine has 8 possible power levels to configure, when you test the engine when new or after maintenance, you will look up a chart based on parameters that your test cell has logged, ie thrust vs EGT (exhaust temp) is a big one, so too is vibration at the different bands. This chart will tell you what to program the ECU with (forgot the actual acronym, its analogous to an ECU on a car). So to your point, when you get more performance out of an engine, you can set these levels higher, so you wouldn't expect more degradation from you engine for a higher power level as the manual will tell you what power level the engine can be set to which will keep everything within its maintenance limits. (Sorry if that's not super clear) Edit 2: Funny implementation detail of setting a thrust rating, it's literally a jumper based system similar to old motherboards, except you manually wire a blanking plug to bridge the connections. A blanking plug is an electrical connector that has a cap on it with a little bit of space to run wires from one pin back to another. Also the correct acronym is EEC.
einpoklum 7y ago
If this happens "normally", that means the engine manufacturer can predict they will be asked for X% more thrust with the same size/arch/features - so they can plan for this in advance.

by rossng 7y ago

aunty_helen 7y ago

When an aircraft is released engine development doesn't stop. These things are always undergoing revisions, performance upgrades, ADs, and even just performance upgrades / downgrades / operating procedure changes based on data from in field running. I doubt an engine would undergo the addition of a stage as that's pretty major but there's no reason a mfc couldn't charge you a mil for better compressor blades and give you a thrust rating upgrade for your patronage. Edit: I'll keep talking as more info is coming to my head. Jet engines have fadec computers that get to decide what your maximum power level is. This maximum is programmed into the engine as a thrust rating. Let's say you engine has 8 possible power levels to configure, when you test the engine when new or after maintenance, you will look up a chart based on parameters that your test cell has logged, ie thrust vs EGT (exhaust temp) is a big one, so too is vibration at the different bands. This chart will tell you what to program the ECU with (forgot the actual acronym, its analogous to an ECU on a car). So to your point, when you get more performance out of an engine, you can set these levels higher, so you wouldn't expect more degradation from you engine for a higher power level as the manual will tell you what power level the engine can be set to which will keep everything within its maintenance limits. (Sorry if that's not super clear) Edit 2: Funny implementation detail of setting a thrust rating, it's literally a jumper based system similar to old motherboards, except you manually wire a blanking plug to bridge the connections. A blanking plug is an electrical connector that has a cap on it with a little bit of space to run wires from one pin back to another. Also the correct acronym is EEC.

einpoklum 7y ago

If this happens "normally", that means the engine manufacturer can predict they will be asked for X% more thrust with the same size/arch/features - so they can plan for this in advance.