this post was submitted on 22 Jan 2024
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To me it was F14. F15 is cool and all, but... I definitely saw Top Gun while way too young.
I mean, even without watching Top Gun the retractable wings were the coolest thing ever for a kid. It was the aviation equivalent of Mad Max flipping on the supercharger on the V8 Interceptor.
(I know, I know. You can't actually spin up a supercharger like that, but it's still fuckin cool.)
Funny story. Nowadays you could feaseably run a dual forced air like turbo and super charging and use an electric clutch to disengage the super. But the intake would be convoluted with some way to bypass the stupid charger or the turbo depending on rpm. it just makes it not worth it.
In real life conversation I'd laugh and pretend I understood that. I'm glad the internet makes ignorance more comfortable.
Imagine you're breathing through a big straw, and at the other end of the straw is a device that pumps air faster whenever you're breathing faster, say when you're running fast. If you turn off power to the pump, you can't breathe through the straw anymore because the pump isn't spinning, so you'd need a second straw that opens up only when the pump is off.
You are the engine, and the pump is the supercharger. When the engine doesn't need to breathe fast, turning off the supercharger would conserve energy use at the expense of power output. But the design of the pump doesn't let air bypass it when it's off, so you'd need to engineer something (overly complex) to do it.
Technically you could design a supercharger with a clutch (like the one for the car's A/C compressor) , but it'd be dumb because there's no good reason not to have it active all the time.
Superchargers come with massive parasitic losses, in many cases 10-20%, and there’s a decent handful of cars with clutches on the supercharger pulley. The MR2 is one.
Not running the extra 20kg or whatever of rotating blower mass would increase efficiency for cruising. A supercharger doesn't have a good way of doing active bypass when you don't need boost like a turbo wastegate so just turning it off can save some mpgs.
If the size of the turbo on my VW is anything to go by, I think the rotating mas of an automotive supercharger would be more likely on the order of 2 kg, not 20 kg. In my mind, that has two implications: (a) the gain from bothering to disable it is perhaps not actually all that significant, and (b) the additional mass that would come with attaching a clutch to it might be large compared to the total mass you're trying to control, so maybe it wouldn't be worth it. Then again, the Previa supercharger the other reply gave (which certainly wouldn't be a very large supercharger) might be a counterexample...
Turbos spin far faster than (Roots-type) superchargers, and can therefore be much smaller.
Besides that, I don't think rotating mass is really the issue. Yes, more inertia is like having a bigger flywheel so the engine will be slower to spin up/down, but that doesn't consume much energy, especially in steady-state cruising.
Superchargers compress air - that takes energy. You then restrict it through the throttle body, because you're not cruising with a wide-open throttle. That throws away all the compression.
You also have pumping losses and bearing/gear/belt losses.