In this installment of NASA's Aeronautics and Space Report No. 67 we see the research that was going into trying to reduce the noise of jet aircraft around 1970.
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#NASA #Engine #Jet
- Intro Music by Fran Blanche -
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Join Team FranLab!!!! Become a patron and help support my YouTube Channel on Patreon: http://www.patreon.com/frantone
#NASA #Engine #Jet
- Intro Music by Fran Blanche -
Fran's Science Blog - http://www.frantone.com/designwritings/design_writings.html
FranArt Website - http://www.contourcorsets.com
Having flown on a 707 in the 70's I can confirm it is freaking loud at take off. Anyone flying on most current jets don't know what they missed 😊An A380 at takeoff is almost silent in comparison.
The Boeing 727 was the noisiest plane in my opinion. When the wide body planes like the L-1011 and DC 10 with their fanjet engines appeared they were much quieter. In the 1980's when the 757 and 767 became the new wide bodies their engines were even more quiet.. Now the noise level is so much better than ever that it doesn't seem to be so much of a concern. The type of noise has changed and it's nowhere as irritating as before.
Loved the wowing music backing track…. I have some very fond memories stored away of times at Primary School in the 60s being given 16mm movies on similar subjects like this with the backing track music becoming a laugh feast for 30 other very young classmates.
In the late 80's early 90's we lived near an AFB still running straight turbo jets on KC 135s. Want to hear noise, wow! when they used water injection on TO the dishes rattled in the cupboards. We lived under the practice pattern, so some times when on the phone, we' say hold on a second a planes going over. But we were used to it, no big deal. When they started to switch to bypass fan engines in the mid 90's, amazingly quiet! You almost didn't notice the planes at all.
Strange they didn't mention at all the private sector manufacturers such as GE and Prat & Whitney.
I'm sure there was plenty of co-operation between them and NASA as part of these improvements, because it would impact the sales of engines to Boeing, Airbus and other aircraft makers.
I work at an airport and have worked at airports for close to 30 years. Just a few weeks ago I paused to watch a newer 747 takeoff and was shocked how quiet it actually is. It almost sounded as if the engines were barely above idle when it leaped into the sky. I remember 30 years ago that would have been an entirely different story.
This film was underwritten by the RealEstate Speculators Association of America in hopes of lowering jet noise sufficiently that they can sell a crap load of homes built on cheap land that is directly in the flight path of major airports!
Concorde had turbojets and afterburners and consequently was noisy as heck, but ironically resulted in quite a lot of reduction in noise around New York. As Concorde flew over certain communities, they would turn their engines right down and coast, and then turn them back up again once they'd gone past. The kicker was- other aircraft had to follow suit because Concorde was so quiet it made them look bad!
Yikes, your wow problem is back. Sometimes it's caused by a dried out dash pot damper in the stabilizer. Maybe you could watch the stabilizer in the sound flywheel loop while running to help determine what's going on. I've never seen this caused by film shrinkage and don't know why it should. Good luck!
The Birmingham Al. airport had to purchase entire neighborhoods to expand the runways, and build rolling hills that deflect the sound upward instead of outward. It really seems to help with noise pollution. Living less than a half mile from that airport we saw many changes, most memorable was the pollution from jet engines. When I was very young I recall thick grayish white smoke coming from all jet engines then watch as that smoke settled across the ground. It seemed heavier than air by how quickly it settled. Not sure of what physics are at play here, I assumed the exhaust was lighter from the heat generated from combustion. My high school was near the top of RED MTN. and on bad pollution days we were above the layer of low pollution clouds. The tops of the tall buildings rose from that smog. Birmingham had an angry red hue overhead on bad pollution days anyway, the air quality improved with each step with industry and aeronautics. I moved to S.w. Florida in mid 70's and had trouble trusting air I couldn't see. I moved back in mid 90's and the air is now clean. The actions taken worked.
You have to be around back in the 60's and 70's to remember just how ear splitting some of the commercial jets used to be. Totally different today with the much quieter turbo fan engines. But yep, I remember just how high pitched some of them were back then.
For some reason, my town is at a spot where airliner engines are often mostly inaudible, then you'll suddenly hear them in a high pitch WHOOSH that, over the course of about 3 seconds, smoothly pitches down until it's low for about 30 seconds to a minute, then pitches back up high and disappears in about 3 seconds just like it came in
The greatest noise reduction improvements came, in order of decreasing effect, from 1) increasing the bypass ratio (providing an "air blanket"), 2) adding serrations to the core section exhaust (breaking up exhaust resonances and pushing the sound energy into short-range ultrasonic vortices), and 3) improved turbine blade designs (via CFD).
Split-spool designs (which run the compressor, or sections of the compressor, at different speeds than the power turbine) were also effective, but the added mechanical complexity was problematical until ever-greater engine inlet diameters made it mandatory in order to keep inlet blade tip speeds subsonic.