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.
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.
This stuff makes for easy virtue points on the internet an is pretty true for civilian aviation.
The military doesn't give two shits what the people who wrote the service manual say is "correct" if someone else comes along with something better and testing/operational reality bear that out. The military is not deathly afraid of holding the liability bag the way private companies are.
>The military doesn't give two shits what the people who wrote the service manual say is "correct" if someone else comes along with something better and testing/operational reality bear that out. The military is not deathly afraid of holding the liability bag the way private companies are.
Speaking as someone who worked in military airworthiness and aircraft maintenance, I disagree.
We follow rules or aircrew die. It's that simple. You find something that works better through operational testing? Okay. Then your next step is to change the maintenance program.
Military maintenance has a separate category for aircraft battle damage, hot refuelling, stuff like that. But it still takes airworthiness seriously.
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.
I'm seriously not trying to be confrontational and say you're wrong, you're not.
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 on ICEs are much more than simply a muffler and directing exhaust gases away from the driver.
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.
As someone with lots of experience on small block Fords, but nothing Chrysler, I would say that a 3/4" spacer under a 600-750 CFM double pumper adding 40 HP just solved either the manifold leak or the throttle cable binding. Did peak power occur at the same RPM (i.e. was it really putting out more torque)? How fast was it spinning, and at what RPM did the power really start dropping off?
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 engine had just been built and I took it to a dyno company to be tuned. It was mounted in their machine, so it was at the flywheel.
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.
Sounds nice. Yeah, a lot of engines of the era were detuned at the factory for regulatory and other (supposedly e.g. insurance, later emissions) reasons. If you already had other top end mods, e.g. good headers and ported heads (seems you did) then sometimes a small change could open up a bottleneck. Thanks for sharing!
I always found it all interesting. We've all heard of 'hemi', but now pent roof across the board, that found adding just the right amount of turbulence on the intake side led to power gains.
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.
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.
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.
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.
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
You’re replying like you think this is some kind of wacky idea, but it was literally what they did in the Cold War to counter low flying strategic bombers.
I infer that you live in a nice stable country who isn't worried about foreign jets attacking their infrastructure and doesn't have their entire borders dotted with posts. I'm happy for you!
no, I'm not googling things around, your point is that they have "people hearing planes" as part of their defense system, you provide evidence of your claims.
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.
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.
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.
> 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.
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.
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.
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.
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.
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."