New engine design could muffle roar of fighter jets
uc.edu
uc.edu
But the title is pretty misleading. This article is about an attachment nozzle. Unless I missed it, it is nothing resembling a "new engine design."
This could make more sense for jetliners, especially for late night take-offs.
Granted, this would help people who live next to active airbases, but noise form commercial traffic is a bigger issue as more people are exposed to it and are usually closer to dense cities.
Growing up in the DC area in the post-9/11 era fighter jets were quite a common experience. Except for 9/11 every other time there was really nothing to worry about. Obviously this might be different if you live in say Syria or Palestine.
And if you have fighter jets buzzing by, the least of your problems is noise.
More importantly, as the article mentions it would also help protect the hearing of sailors, airmen, and marines that help operate those airframes.
A major winner would be the communities near airbases. Hornets, in particular, are quite loud.
https://www.stripes.com/branches/navy/2021-08-19/naval-air-s...
You only hear the jet after it passes you.
The ground crews at the target had to be very vigilant.
Are they going to report anything they hear from any source along the whole border? Imagine the control center having to match every hearing with every domestic and recognized flight
Further down on my list would be a bunch of nations bordering those three, a handful of African nations, and two or three south American nations.
I'm not sure if Taiwan should be on the list, as the People's Army does not currently have operational stealth aircraft.
"JET PILOT tries 3 different attachment nozzles from Wish"
They are starting with an attachment as it means it can easily be retrofitted to existing planes and tested. If it works there is a good chance it will be the default design on a new generation of engines.
I don’t think this is misleading.
Except that in the case of a jet engine, this is more like the exhaust, transmission, and differential.
Look into tech like thrust vectoring.
It's WAY, WAY more than a muffler
I'm perfectly familiar with typical ICE and the design of jet engines. Exhaust is no less important in ICE. If you block it, the engine doesn't run.
Jet engines use exhaust as propulsion, so it just moves the mechanism from inside to out, in a way.
A muffler is a device that baffles air to quiet it. That's -exactly- what this device does. You can argue, rightly, that more is at stake and more considerations must be made here. But it's still, by definition, a muffler.
Exhaust systems can be tuned, as in using wave propagation to scavenge the exhaust gasses out of the combustion chamber much more efficiently. Intake manifolds are tuned for the opposite effect. The dyno tests on my Dodge V8 showed adding a 3/4" spacer between the carb and the manifold added 40 HP at the peak power rpm.
Also on exhaust side. Too big of exhaust, such as 'open exhaust', is worse in most cases than restrictive. Apparently a restrictive exhaust provides both accounted for backpressure, and at times a bit of a vacuum effect.
Anymore, I just trust the makers know what they are doing and go with it. But 40 years ago, very different story. My 2019 Colorado would outrun my old 66 mustang, both in stock forms.
Was this measuring at the flywheel or at the wheels? I'm genuinely interested, it's been a long time since I've had grease under my fingernails.
The guy doing it remarked that it really made a dramatic difference, it seems the original parts configuration was a pessimizer. I'm not too surprised, because the engine was heavily modified and so would exhibit very different flow characteristics from the stock configuration.
I don't remember the RPMs. It's a bored, stroked, and rollered 340 engine, and peaked at just under 400 hp. The dyno guy normally worked with drag engines, and told me I was an idiot because I had the stock heads modified rather than getting aftermarket performance heads, a mistake that likely cost me another 40 hp.
The engine was built as a sleeper, so the only way you can tell there's some monkey business going on is the oversize aluminum radiator, but nobody notices that :-) But they notice when I start it.
The average person can’t even draw bikes that work[1].
[1] https://twistedsifter.com/2016/04/artist-asks-people-to-draw...
For example when a 737 has a broken light, then it is not in compliance with the approved type design and any aircraft in such a state is legally not airworthy.
Fortunately we have provisions in airworthiness to defer rectifications of unserviceabilities that have no/marginal effect on actual airworthiness, but the point stands. The light is part of the aircraft's design.
If you change a light to a new kind of light, then you're embodying a Design Change which is a Big Deal (tm) even though it seems minor, and that piddly little light will go through the same design approval process as, say, a new wing. Less structural analysis will be conducted (obviously) but it's still the same process.
In aerospace, changing the nozzle on an engine changes the design of the engine. "Design" in that context is an industry term and it doesn't have the same nuance as in other contexts.
https://scholar.google.com/citations?hl=en&user=0FYKxIYAAAAJ...
Because a lot of commercial jets have an issue with loudness. In the Netherlands there is a lot of push by residents to reduce the number of (nighttime) flights because of noise pollution.
Military craft have low bypass engines, while large civilian craft have high bypass. These different designs trade off engine size and efficiency; large jets are willing to have large engines if they’re more fuel efficient, while military craft have high needs and very little room to spare.
My suspicion is that these techniques will need significant tweaks to work on the very different large engines. Already we’re seeing external nacelle changes to wide body aircraft for noise reasons, rather than the internal design shown here.
Yes, high bypass: With a jet engine, what you pay is kinetic energy, and what you get and want is momentum. For mass m and velocity v, the kinetic energy, that costs you (1/2)mv^2, and for the momentum you get mv.
So, you want to maximize the resulting momentum mv for the paid kinetic energy (1/2)mv^2. So, you want to select m and v to maximize momentum for a given kinetic energy.
Since for a given velocity v, in kinetic energy are paying for v^2 but in momentem getting only v, clearly want to make mass m large and velocity v small.
So use the kinetic energy of the pressure of the burning fuel to turn a big turbine that moves a large mass m by a small velocity v.
That works so well that GE took one of their early jet engines and put on an aft-fan, that is, put a fan, a turbine, free wheeling, not driven by any shafts, on the back of the engine. So the blades of the fan played two roles: (1) Close to the axis of rotation, the blades got hit with the fast, hot gas from the engine, and (2) the rest of the blades, that extended past the engine, pushed on cold air.
The Dassault FanJet 20 used these GE fanjet engines, and those were the planes, modified for carrying cargo, used at the start of FedEx.
BUT! My understanding is that this whole story only works for subsonic flight! So, jet engines developed for military fighter jet planes and supersonic flight didn't have fans.
But when the US military wanted a really big cargo airplane, the C5A, they paid for the development of high bypass turbofan engines and used them. With the engines developed (took big bucks), commercial aviation took advantage.
After a certain point changes are incremental. We're at that stage with jet engines.