sound relativity to speed and pressure

[streetbeater07 0]

ok, see if you can follow me, to create a sonic boom an object has to travel 720mph rite? A driver displaces air to make sound rite, so if I had a sub that would displace air at 720mph could I create a sonic boom in my car? Or would it create an ungodly amount of db's? Also, how loud is a sonic boom? Or is speed and sound not relative to pressure? Or would the sub make no sound at all since it would be traveling faster than the speed of sound or would it just be delayed? would the car explode? just trying to keep those good minds working. lol

[audio-neon 34]

ok, see if you can follow me, to create a sonic boom an object has to travel 720mph rite? A driver displaces air to make sound rite, so if I had a sub that would displace air at 720mph could I create a sonic boom in my car? Or would it create an ungodly amount of db's? Also, how loud is a sonic boom? Or is speed and sound not relative to pressure? Or would the sub make no sound at all since it would be traveling faster than the speed of sound or would it just be delayed? would the car explode? just trying to keep those good minds working. lol

IIRC we have already discussed this before. The rate of acceleration needed to get a subwoofer cone to move to 720mph, stop and return etc. Is impossible.

[///M5 2,833]

Definitely impossible.

[helotaxi 46]

Search, we really did discuss this at length a bit over a year ago.

[MikeS 0]

That's easy....just drive the car 730 miles per hour......

I remember when in the '70's when I was a kid riding my bike around, and would get blasted by a sonic boom when they still had fighter aircraft at the local AFB. They would hit mach 1 before they left the area.

I'd be riding my bike along and WHOMP!! A big pressure wave with a loud thump like a cannon with a muted kinda sound.

They had a SR71 blackbird here about 10 years ago, it hit subsonic when it left the area. Thumped the apartment I was in pretty good at the time.

Trimmed grass for groundskeeping at the local AFB once. Don't ever trim grass without hearing protection at the head of the flightline when a pair of those damn dual engine F18's or whatever take off in a pair......even at 150-200 yards.

Caught me off guard.....I just seen some jets taxiing on the flightline......kept trimming, nose to the ground......next thing I know my ears are getting trashed.....look over and see two F18's and four jet engines pointed at me, taking off.

Low frequencies beating off my chest with high frequencies that make you wanna run away in fear.

That was about sick loud. Wore hearing protection from then on.....

[dave_Edwards 1]

being an Airforce vet....I know some of the statements you have just made are not true.....it is against AF regs. to break the sound barrier with-in 20 miles of a residential area(bases included)and also they can not do so under 20,000ft....I know F-16's take off at 3/4 throttle.....F-18's(Navy jets) take off at 3/4 throttle also.....I know they are loud and they may seem to be "breaking the sound barrier" but BELIEVE me....they are not, pilots do not want to be grounded for something as stupid as that.

I highley doubt you will see this at an altitude you can see......without being a pilot yourself.

as for the SR-71....they have been retired for 10years....they do not take off at sound barrier breaking speeds.....they have enough fuel to reach their cruising altitude then need to be refueled THEN they take off from the refueling jet(KC-135[the planes I worked on] or a KC-10[guicci boys]).....PS.....taxi ways are for that....taxing, not take off....and I do not EVER recall seeing ANYONE near the ramp when ANY jet was landing or taking off....hell most civies were not even allowed on the pad let alone with in 1000 yards of a plane.

[MikeS 0]

"being an Airforce vet....I know some of the statements you have just made are not true.....it is against AF regs. to break the sound barrier with-in 20 miles of a residential area(bases included)and also they can not do so under 20,000ft....I know F-16's take off at 3/4 throttle.....F-18's(Navy jets) take off at 3/4 throttle also.....I know they are loud and they may seem to be "breaking the sound barrier" but BELIEVE me....they are not, pilots do not want to be grounded for something as stupid as that"

Maybe the Air Force regulations were a little different back in 1972, because I recall hearing sonic booms quite often back then.

"I highley doubt you will see this at an altitude you can see......without being a pilot yourself.

as for the SR-71....they have been retired for 10years....they do not take off at sound barrier breaking speeds.....they have enough fuel to reach their cruising altitude then need to be refueled THEN they take off from the refueling jet(KC-135[the planes I worked on] or a KC-10[guicci boys]).....PS.....taxi ways are for that....taxing, not take off....and I do not EVER recall seeing ANYONE near the ramp when ANY jet was landing or taking off....hell most civies were not even allowed on the pad let alone with in 1000 yards of a plane."

Who knows about the SR71, that was just what I was told. Trust me, I was top of the old bomber alert building (which is half covered with grass) when the fighters took off.

The base used to be a B52 bomber base, but now is just a KC135 tanker base.

The fighters taxied to the end of the runway, (the end of the actual flightline) and then took off when they were cleared.

It couldn't have been more than 200 yards behind them.

I wasn't on the actual flightline, on was top of the bomber alert building about 20 feet up above them. The bomber alert building is directly behind the end of the flightline about 200 to 250 yards max.

Whether they were F16 or F18, I dunno.....but they were dual engine fighters......Tomcats?

I know I wasn't no 1000 yards behind them.

Edited June 18, 2008 by MikeS

[helotaxi 46]

If you were on an Air Force base and they were dual engine fighters, they were either F-15s or F-15Es. They were nowhere near the sound barrier, they fly around at about 250kts (around 300MPH) below 18,000ft and they take off much slower than that. I'm guessing that you were at Fairchild?

Dave-all aircraft use full throttle for take-off, especially fighters. Period. 11 yrs as an Air Force pilot speaking.

For the record, the SR-71s had their own fleet of KC-135s that were specially equipped to carry the JP-7 that they burned. The fuel would eat through the tank liner in a regular tanker. No KC-10s were ever modded because they weren't fast enough and there weren't any to spare.

[KU40 173]

I'm jealous of you Helotaxi. I've always thought it would be amazing to be a pilot. But it also scares the chit out of me. I'm 6'3" anyways, which I think rules me out of being a pilot doesn't it? So I guess I'll just have to play Ace Combat on my PS2 to get my fighter fix .

Maybe you were hearing the afterburners light up? I dunno. I didn't think they could do supersonic around urban areas either. But F-15's sure can go fast. Mach 2.5 I believe. Awesome, awesome planes.

[helotaxi 46]

I'm 6'3" myself. Not terribly restrictive at all.

As badass as the F-15 is (we used to refer to it as God's jet) the F-22 makes it look like an amatuer's tool. Friend of mine was flying an F-16 against an F-22 during the testing. 4xF-16 against 1xF-22. The F-22 won 4 of 4 and no engagement lasted longer than 1 min from "fight's on." The 16s tried every dirty trick in the book and it was like clubbing baby seals for the Raptor. They saw him once. Never got him on radar.

[KU40 173]

I'm 6'3" myself. Not terribly restrictive at all.

As badass as the F-15 is (we used to refer to it as God's jet) the F-22 makes it look like an amatuer's tool. Friend of mine was flying an F-16 against an F-22 during the testing. 4xF-16 against 1xF-22. The F-22 won 4 of 4 and no engagement lasted longer than 1 min from "fight's on." The 16s tried every dirty trick in the book and it was like clubbing baby seals for the Raptor. They saw him once. Never got him on radar.

dang. I knew the Raptors were awesome but didn't know they were THAT awesome. Don't they have some partial stealth? I hope the US doesn't sell some of these planes or the plans for them to other countries like they have with other jets. Even if they are our allies.

I've heard that nowadays fighter jets more or less do almost all of the work and the pilot is just another input for its computers.

[dave_Edwards 1]

I will admit I don't know it all on flying the jets....I left the break the jets to the officers and us enlisted guys fixed them....

[MikeS 0]

"If you were on an Air Force base and they were dual engine fighters, they were either F-15s or F-15Es. They were nowhere near the sound barrier, they fly around at about 250kts (around 300MPH) below 18,000ft and they take off much slower than that. I'm guessing that you were at Fairchild?"

Right. I was civilian groundskeeping twit there from roughly 1999-2003. They took off in a pair under the typical guidelines/restrictions I would assume.

I just happened to be up on bomber alert building behind them at the time, which is a little too close with respect to noise with fighter aircraft on takeoff. One may have not been that bad....two was too loud...

With the typical KC135's that would take off, the noise levels were a lot less up on that bomber alert building. Not enough to be a concern at all.

I trimmed that area weekly, (along with most of the base) and KC135's are the typical norm. I got caught off-guard with the fighters that week, and learned a lesson in hearing protection.

They didn't take-off wide open...or did they? I went to a air show at FAFB about two years back, and they had a pair of the same fighter aircraft.

One did a demo where it sat there with the brake on or whatever cranking the thing full blast to where there is gray smoke just chuffing out the ass-end off the thing. Something akin to the jet cars at the drags, but with the option of being able to go straight up in the air for three miles.

I don't recall gray death smoke when I was trimming grass at that one time the pair took off, but they didn't have the brakes on either.......I dunno......I remember real loud noise....I wouldn't lie about that...

I never heard any sonic booms in the years I worked there. But I do remember sonic booms back when I was a kid in the '70's when the place was a B52 bomber base. They had fighters stationed there back then....I couldn't tell you what type they were, but there is one at Heritage park. I trimmed the grass around the beast.

This is back when they used to fire up the air raid sirens every wed at 12:00PM in Spokane. Duck and cover.....

Mike

Edited June 18, 2008 by MikeS

[KU40 173]

I don't want to dig up the old thread so I'll post it here. I remember on the older version of winISD (the beta version I think), the port velocity was measured in mach. It recommended you stay under mach .14 to not have port noise. I don't know if that is true mach or if their calculation for the mach number is correct, I'm just throwing it out there.

[helotaxi 46]

Yep, the old WinISD referenced true Mach.

Modern jets don't smoke, makes it too easy for the enemy to spot you. Depending on the time frame you're talking about, they could have been F-4s which smoke like crazy and won't get off the ground with less than full power.

[MikeS 0]

Yep, the old WinISD referenced true Mach.

Modern jets don't smoke, makes it too easy for the enemy to spot you. Depending on the time frame you're talking about, they could have been F-4s which smoke like crazy and won't get off the ground with less than full power.

I understand that, but it was a air show. There wasn't any enemies.....

The time frame would be 2006.

Have you watched jet cars at the drags where they kick out tons of smoke, and then they ignite the burner where the smoke stops and then flames appear with big "Booof!" And It'll surge the car forward a bit.....but the guy is hanging on the brakes so he doesn't end up 1500 feet down the track.

It was pretty much the same the same thing with the fighter aircraft at the airshow. It sat there and billowed out gray smoke (excess fuel?) with the guy holding the brakes. Then he must more than likely kick on the igniters and lets go of the brakes. The smoke goes away, he starts to boogie, and as soon as he is airborne he goes straight up for 3 miles.

Does that make any sort of sense? I'll admit I am a bit touched in the head.......

[TSDIZ.COM 0]

I'm agree with MikeS... MikeS you have very good brain:))

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[vladd 26]

you're going to get banned so quickly.

[helotaxi 46]

Modern fighters don't smoke. Even when lighting up the afterburner. As soon as the first stage of the AB starts dumping fuel into the exhaust, the ignitors have it lit. Even at an air show (unless it is a specific smoke generator like the T-birds and Blue Angels use) there is no smoke on a current gen fighter.

The jet cars at the drags smoke because they use old generation engines and you are watching them start the engine at the end of the track.

It was most likely an older fighter. The F-4 held the time to climb record for years and it's a smoky bastard.

[Godsmack 360]

While i know pretty much dick about planes i remember being in Kuwait and being woken at 0645 (it was a sunday leave me alone LOL) by a series of loud ass booms, and my place rattling like all hell. Went outside and talked to a friend. He said South Korea had pilots down the road and they were flying jets.

He said they were breaking the sound barrior. Is this possible? i mean it did rattle a 1L water bottle off my bedside table and it hit me in the head (henceforth waking me up) I believe the guy cause it happened about 4 more times and u could hear them flying over head all day and the booms were constant.

J

[KU40 173]

Sure it's possible. I bet over there they don't have rules like the US does about not breaking the sound barrier around cities, though.

[shizzzon 461]

How accurate is WinISD though?

I just got it to tell me this design i made up would push 911mph out of a single port that would need to be 1.25" if using 3\4" mdf. That's over MACH 1. you guys say it is impossible so i am asking if it is then why is this software saying it isnt impossible?

Box specs-

5 cuft box using 1 single 3" diameter port off of 5,000w of power tuned to 30hz.

[QuestionMan 0]

So while i have some people with a little knowledge on the subject, how does a plane not move with all that force being exerted behind it? Ex: mythbusters, when they make a truck drive from behind a 747(?), they have the thrust on, but the plane remains still, and even throws a bus 100 yards. Are brakes the only thing holding it from moving?

i've always wondered.. lol

[Acidburn 10]

yep, really good brakes, and they might put chocks on it for those tests too