What design differences are there between the post-ww2 and the modern jet engines – quora electricity khan academy

The first generation of turbine engines were very simple machines. I know, its odd to call a Jet Engine, literally one of the most complex pieces of machinery man has devised, as simple. Yet those early Jet engines compared to modern jet engines is like comparing a 2-stroke weed wacker motor with a Formula 1 engine.

So lets dive right in. First gen jet engines came in two flavors, axial flow compressor and centrifugal flow compressors. The Whittle engine, and then the GE-IA which was the American carbon copy, both used centrifugal compressors. The Germany engine on the Me-262 used an axial flow compressor. Centrifugal can provide more pressure ratio with a single stage, but axial flow can be much more efficient at high flow rates. Contrary to what some seem to think these days, centrifugal compressors have not disappeared in the modern age. The last stage of the T700, which powers the UH-60 Blackhawk, the AH-64 Apache, and a small army of other Rotorcraft, is centrifugal flow compressor stage. However, just about every large flow turbojet and turbofan today is purely axial flow.

One major difference between then and now are the materials used. Those early jet engines had steel compressor blades, steel turbines, steel combusters…. Steel steel steel. Steel does not hold up well in jet turbine conditions. In fact, the combusters of the GE-IA and the Me-262 engines (Junker Jumo 004) both had “can” combusters with a total life of 50–100 engine flight hours. After that, you threw them away. Today combusters are made from Nickle alloys, or ceramics. They are also cooled by compressor air with very well defined cooling holes through the liner designed to lay down a specific pattern of cooling air. This has allowed us to push T4 (combustion temp) much higher without throwing away engine parts after 100 hours. Other materials include Titanium alloys (Fans rotors, front end compressor rotors, cases, frames, shrouds), nickle alloys (back end compressor stages, diffusers, combusters, turbine blades disks and nozzles, exhaust liners, etc) as well as ceramics (thermal barrier coatings, ceramic matrix composites) and organic matrix composites (with carbon or glass fibers).

So materials is a biggy, but there is more. We understand the physics behind the engines better than we did then. Things like compressor operability, 3D-Aero design of blades and stators, and aeromechanics are all things that were not well understood back in the first gen days. This means we can push the limits of the operation envelope without blowing up our engines. Whcih in turn lets us run them more efficiently, in higher speeds and altitudes than were previously possible.

Since the early jet engines were exclusively military engines, I am going to focus my comparison on military engines here. Early jet engines had fixed nozzles. Most high bypass turbofans also have fixed nozzles, but not military turbofans. Once we started opening up the operating envlope, more controls of the cycle were desired. So one of the big differences that was added as the engines devloped were variable area nozzles. The first step were variable convergent nozzles, like that found on the J85 engine.

See that ring, conected to all those little rotating arms? Those are each attached to a stator vane, and this enables them to change vane angles while the engine is running. This is a HUGE advantage to the compressor. It allows much better off design point efficiency and operation. In fact, without them, compressors can not operate within the entire flight envelope we fly in today.

Today’s jets are designed with the benefit 3/4ths of a century of experience operating them. Dangers to jet engine operation like bird ingestion and Foreign Object Damage (FOD) are now baked in design considerations. An F110 engine can eat group of small birds at take off and still fly a mission. They can eat a medium sized bird and still maintain control of the aircraft and ingest a large bird and keep things together long enough for a pilot to point himself in the correct direction and punch out. An Me-262 eating a medium bird at take off would result in one dead German pilot. A GE-IA eating some kicked up stones would likely result in a spectacular end of flight.

In addition, if an F110 eats enough of a problem to liberate portions of its blades, it can contain these portions up to a certain size. Also, it is designed to not tear itself apart from the large imbalance loads. again this is to provide a stable platform for the pilot to eject from, but it is by no means a trivial consideration.

So there are a few things off the top of my head. I didn’t even mention FADECs, an telemetry driven operation. Or maintenance aspects like bore scope inspection features, or engines that can be taken down into modules. There are dozens of other things we could point out… Maybe I will update my answer down the road.