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I'm not knocking what they are doing, at all. Really nice progress.
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."
The design of the nozzle is part of the design of the engine.
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.
That's pretty loose. It's akin to saying that headers are a part of car engine design. Technically, literally, perhaps correct, but not what is thought of when hearing the words.
In aerospace engineering, we take that kind of thing seriously.
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.
I see, interesting, thank you for clarifying.
Exhaust is a VERY important part of engine design.
Except that in the case of a jet engine, this is more like the exhaust, transmission, and differential.
It's a muffler for a jet engine. Mufflers are great things for humanity, there's nothing wrong with that. They are not even included in drawings if you asked the average person to draw an engine.
> average person
The average person can’t even draw bikes that work[1].
[1] https://twistedsifter.com/2016/04/artist-asks-people-to-draw...
Attachment nozzles sound more economical though. Maybe it starts a new trend.
"JET PILOT tries 3 different attachment nozzles from Wish"
A fighter jet is just a fancy hairdryer, really.
And if you have fighter jets buzzing by, the least of your problems is noise.
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.
I live 1 km away from an air base (Misawa, Japan, for those curious). Just a few minutes ago a couple jet fighters took off. I don't really care so much, but they are loud as fuck. I'm pretty sure the whole city would appreciate quieter engines.
Parents live very close to Damiano but the runway is at an angle so they don't have it as bad as, say, people at cavalese had.
The article discusses many advantages to quieter planes. Including stealth, plane longevity, and health of the crew around the planes. It would be a big deal to the military to "instantly" have things be 1/2 as loud.
Indeed -- the only loser for a quieter fighter aircraft is the enemy. If fighters could be made silent, they'd be even more effective. The 'sound of freedom' can take on many interpretations.
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...
My dad flew ground attack jets in the Korean War. He said it was easy to sneak up on a target, as you were traveling close to the speed of sound and so the sound didn't get there before you were in firing position.
You only hear the jet after it passes you.
The ground crews at the target had to be very vigilant.
Audio stealth doesn't seem a big deal, missile won't lock to sound and by the time you hear the sound plane is already not there.
You don't think that the guardposts at the border will report the jets they heard screaming overhead in the direction of the nation's nuclear reactor or capital 1200 km away?
If you don't have radar systems detecting them long before the border guards hear them, then you can't do anything about it anyway. Accurate detection is the key part of any anti-air system - if you're sitting at the controls of an anti-air system and your first notification of an enemy jet plane is a call from someone who literally heard it, then you still can't fire anything at useful at it, and the only thing that you can do is walk away before your (apparently useless) anti-air system gets bombed.
How convenient for them the jet flew so near a checkpoint. And how do they know they have to report something, if they hear the plane but can't identify it since it's long gone anyway?
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
I imagine a quieter jet also helps marginally improve its war fighting capability by making the enemy less aware of its presence, although
More importantly, as the article mentions it would also help protect the hearing of sailors, airmen, and marines that help operate those airframes.
Reducing noise from training runs would be welcome in many communities.
Yeah, UPS bought out my entire childhood neighborhood because of all the noise they generate.
It did say in the article it could be applied to other jet engines. I'm guessing the military is bankrolling the research.
While we do have larger problems in San Francisco it would still be nice if the fighter jets buzzing by weren’t quite so loud.
From engines or from sonic booms? I think this is to make take off quieter for personnel and people in the vicinity of activity ANG/airbases. SF flyovers going after incursions occasionally have booms.
When was the last time a military airplane actually caused a sonic boom near SF?
Growing up in Kansas in the 60s, I heard window-rattling sonic booms all the time. I enjoyed them :-) I'm sure the pilots were having a good time, too.
Here's a recording of the F-35 making one in 2019, and this also serves as a reminder to all San Francisco residents that fleet week is coming up. I don't think they'll get these upgrades installed in time, which sucks for anybody that lives here that hates disruptively loud airplanes, however.
Notice the gradual fade-in of the sound. That's not a sonic boom, those are a sudden pressure change with lots of sound waves packed together in a single wavefront.
There is no sonic boom visible or audible in that video.
> And if you have fighter jets buzzing by, the least of your problems is noise.
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.
They do need to train in the airspace. Would you want pilots unfamiliar with the terrain to show up when they’re needed in a hurry?
When I lived in Germany in the late 60s, it was commonplace to see NATO fighters hedge-hopping over the countryside. My dad said the Germans didn't complain about it, they knew why the fighters were training that way.
I assume they were responding to:
And if you have fighter jets buzzing by, the least of your problems is noise.
I think the work is related to the "micro vortex generator" papers, here's the Google Scholar list for the lab:
https://scholar.google.com/citations?hl=en&user=0FYKxIYAAAAJ...
Yeah looks like they're generating vortices to mix high and low velocity air better. The problem here is this will decrease the efficiency of the engines as it's adding drag to the flow coming through the nozzle.
Fighter planes have tiny wings because of aerodynamic drag and so require very powerful engines to keep the plane in the sky. Since the engines are running at high output, they are very noisy. The fact these are also low bypass engines, contributes to the noise as well.
Is this unique to fighter jets?
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.
Turbofan engines have two exhaust components: high pressure/temp exhaust coming from the turbine, and unburnt low pressure air coming from the bypass, which is forced through by the first turbine but not actually burned.
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.
Here's some of the story on bypass for jet engines:
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.
For what it's worth, the article says "UC’s preliminary lab results hold promise for reducing jet noise in both commercial and military aviation."
Is it mainly about Schiphol or other airports as well?
Slightly around Eindhoven, but the real hot-button issue is Lelystad. The plans are to move a lot of passenger and short distance flights there, to give Schiphol more capacity for long haul flights. People are against Lelystad both because of extra noise aswell as because of CO2 emissions.
How is shaving 8 decibel from 150 a game changer? It's sure nice, but it's still deafening at 142
I just checked, everything beyond 110dB for 1.5min per day will lead to a permanent hearing loss
10 decibels is a 10x reduction in energy. An 8dB reduction is a factor of 10^(8/10) = 6.3 times less energy radiated. Good luck getting a 6.3x improvement in any other parameter in an aircraft design without major sacrifices elsewhere.
At what distance? Sound takes quite a bit of power to generate. It's likely this saves a noticeable amount of fuel (maybe over multiple flights). If it's an attachment this may not apply.
After a certain point changes are incremental. We're at that stage with jet engines.
A 10 dB reduction is half the perceived loudness, so 8 dB is quite significant. 142 dB (SPL) will make you deaf instantly if you are right next to the sound source, but at a distance the 8dB reduction will make it sound much softer.
not particularly new, although maybe newly applied to combat aircraft (https://en.wikipedia.org/wiki/Hush_kit)
Thank god; my fighter jet keeps waking up the neighbors every time I take off toward the office.