Yup. I acquired very little knowledge of engines and such over my life, so I’m a little proud that I figured out myself that jet engines and internal combustion ones are doing the same things.
I mentioned this to a pilot friend, and she said, “yup, we like to say ‘same actions, just in a different order’.”
just throwing a complimentary piece of info into this concerning combustion feedback-loops:
diesel engines … the (positive) feedback loop becomes really evident if you think about a runaway-diesel-engine - which miraculously keeps running even if you cut the diesel-supply
and more evidenter if it runs in reverse, sucking air in through the escape system and evacuating fumes through the air-box …
yes, fun can be had with diesel engines, (especially if it is not yours and you are at a safe distance)
Somewhere in the couple of biographies I’ve read about Frank Whittle was the claim that the conceptual idea, in the form of a “gas turbine” had been around for decades. Whittle ran with this, but it was extremely tough going for him. The RAF was hesitant about funding his work, progress was slow and the metallurgy at the time was only just barely up to the job.
I agree, and it had occurred to me that there was a certain rough analogy with piston engines of whatever number of cylinders, in that there’s a “parasitic” component that steals energy rather than making it – in piston engines, it’s the non-firing cylinders that are being compressed and readied for firing, in jet engines, it’s the compressor stages.
I would note that one of the important operational differences is that a piston engine can respond almost immediately to increased fuel flow and start producing more power. As you know better than anyone, in a turbine, power increase has to be gradual so the compressor blades have time to spool up and prevent compressor stall and backflow.
That was in fact one of the problems with the Chrysler Turbine car. Contrary to rumours at the time, hot exhaust was not an issue as Chrysler went to great lengths to avoid this. The two main issues were slow acceleration response and the fact that it guzzled gas. As marvelous as turbines are, they’re not efficient at small scales.
Yep. In your first paragraph you mention “non-firing cylinders”, implying a multi-cylinder engine. The same is true of a single cylinder ICE engine. The stealing is all the inertia and energy required to spin through the other 720-180 = 540 degrees of crank rotation and perform the work of compression. So the creation of power and internal consumption of “stolen” power is sequential.
For sure a multi-cylinder engine overlaps e.g. 8 such events, so any given power stroke is doing part of the work over time on each of the other 7. But each of those other 7 are, in their turn, helping the first to fire get around to firing time again. It’s still not continuous, but it’s more continuous. If we made 1000 cylinder ICE engines we’d be sorta kinda close to continuous.
From the other POV, and this goes a bit towards explaining gas turbines’ slow acceleration…
In crude analogy, you can look at a turbine engine compressor as an engine with however many stages times however many blade count worth of “cylinders” = compression modules. Each of which is pretty small, and each of which has a very low compression ratio. Such that they have to be daisy chained together to add up to meaningful end-to-end compression.
In an ICE metaphor, imagine a first cylinder with no fuel or ignition which simply mechanically compressed the air a bit, then fed it into a second similar but smaller cylinder that did the same. Etc., for 5 or 10 or 15 stages of ever-shrinking cylinders, finally followed by a fuel + ignition cylinder. Whose firing had to power the whole shebang. Acceleration / deceleration also becomes limited by the sheer inertia of all those moving parts. And the time taken for an air charge to get from the first inlet to the outlet into the combustion cylinder.
Not to get too far off the topic of aviation, but one time when I had my old Dodge Caravan, I started it up and heard a loud bang. One of the spark plugs on the V6 had self-destructed. The surprising thing was that one cylinder out of 6 being out of commission did not result in 1/6 loss of power as one might expect – the engine could barely limp along with a tiny fraction of its normal power while making a racket like a steam locomotive. I made it to a Chrysler dealership but just barely.
I’ve always been amazed that he received funding. It was a miracle the Mosquito made it into production. To say money was tight was a gross overstatement. I think the wisdom behind the Tizard Mission was a major factor in the success of the Allies.
I think you probably meant the Gloster Meteor.
No I meant the Mosquito. Those in controlled of what went into production did NOT want the Mosquito. It was the antithesis of a bomber. It was small, fast, and unarmed. It’s survival from attack was based on outrunning the pursuer. De Havilland believed in it enough to go it alone until someone saw reason.
The Meteor didn’t exist without a jet engine and the funding for that engine was an uphill battle they couldn’t afford to lose. It meant diverting time and money from the war effort when both were at a premium.
It was a poorly worded response that should have been broken up into 2 separate thoughts.