Sonic Boom

I would appreciate your comments regarding mach speed rockets with regards to sonic booms.

Having never seen one fly I would like to know if rockets that break the sound barrier produce an audible sonic boom. If so how loud ect.

Thank You!

Todd Bright

Not unless they hit sonic sideways over your head. The thing about sonic booms is that they spread out in a cone, not down. Because of this, unless you are quite far from the pad when it launches, you cannot hear an audible sonic boom, simply because you are inside of the "cone of sound"

a Cone of Silence???
sorry, Chief!!!

Its to bad! It would be great if there was an audible sonic boom as the rocket broke the sound barrier!!!

This one always starts a debate. If I were a betting man, I'd wager very few if any people have heard a sonic boom from a hobby rocket. Many will claim to have heard one. Someone else will come along and explain the science explaining why that's extremely unlikely.

Yes you can hear one.
You do have to be off to the side a ways; how far depends on how high the rocket is when it reaches mach.
Is it loud?
No, not like an F-4; was the target of one of those in 1992 and my toenails are still vibrating.
Thing is, our rockets are not that loud to begin with so the resulting "boom" is more like a thud.
The boom is the accumulated sound waves all reaching you at once so the louder the source, the louder the boom.
OK, it's a little more complicated than that, but that'll work for starters.
Those at MWPIII last weekend were treated to more than a few, IF they were far enough away.

Greg

I posted a drawing (trying to find it) in a similar thread. It shows the rocket breaking mach and the sonic boom radiating in the form of a cone from the tip fo the rocket. When this sound wave hits the ground it inscribes a circle. Unless you are on that circle you won't here it.

I have heard what I beleive to be the sonic boom a few times. Conditions have to be just right and surounding *quiet* is key as it isn't much of a *boom*...

I beleive I heard one this past year (NERRF perhaps?) where, according to the flier, his rocket broke mach shortly after leaving the rail, about 20 feet in the air. In that respect I could see the sonic boom wave hitting the ground and radiating/bouncing with quite a bit of force as it is so close to the ground. Everybody in the area heard it. It was either the sonic boom or a coincidental sound when the rocket cleared the rail...

I beleive it was Centuri reported being able to hear it when they were doing some work (can't recall who it was involved with, maybe a movie set) where they were launching rockets horizontal along a guy-wire. In this mode, the sonic wave would strike the ground at a much more oblique angle making it more likely to hear. I can't remember if I saw this report in one of their catalogs or one of their publications... Anyone remember this?

jim

There have been reports of people actually hearing the Aurora Borealis (northern lights). I saw the display in 89 that resulted from the flare that took out the power grid in Quebec and I'd have to say that there is something to this. I believe your brain is trying to fill in the sensory experience. I think what I'm getting at is if you expect to hear something, you might...

Originally posted by MetMan
There have been reports of people actually hearing the Aurora Borealis (northern lights).

Click to expand...

And everyone who believes this should go stand outside and stare at the sun until they can hear it too?
(Kids: dont' try this at home without adult supervision)

Originally posted by powderburner
And everyone who believes this should go stand outside and stare at the sun until they can hear it too?
(Kids: dont' try this at home without adult supervision)

Click to expand...

I'm actually not making this up:

https://www.northern-lights.no/english/what/sounds.shtml

https://www.churchillmb.net/~cnsc/ab-attrac-lights.html

It's a perception thing. The 89 display was so wild that I think it was my brain's attempt to make sense of it. (Something this freakin' wild must have a sound that goes with it!)

Where's Dr Dynasoar when you need him...

?Yes you can hear them....myself, mike denton of cesaroni and 5 others heard them at the ldrs in lethbridge canada this year....from about midnight to 3am we watched and HEARD them....I was outside the motor coach watching and walked out to the pad area to get a better view away from the lights at the campsite.....as the curtains would shoot over my head I heard a crakeling sound like ice cracking or static electricity......I hollered for the others to come out......we all heard it! .......two of them said they had heard it before.....you must be in a perfectly quiet area away from all ambient sound to witness this and close enough for them to be shooting right over your head.....most people only get to view them from a distance....it was an experience myself and the others will never forget!

Originally posted by jflis
I beleive I heard one this past year (NERRF perhaps?) where, according to the flier, his rocket broke mach shortly after leaving the rail, about 20 feet in the air. In that respect I could see the sonic boom wave hitting the ground and radiating/bouncing with quite a bit of force as it is so close to the ground. Everybody in the area heard it. It was either the sonic boom or a coincidental sound when the rocket cleared the rail...jim

Click to expand...

I've heard this one before. No way, no how, it's impossible.

The speed of sound is about 1100 fps at sea level. The equation that determines acceleration if you know the velocity change and distace is:

a = v^2/2d = (1100^2)/(2*20) = 30,250 fps2 or in G's 32,250/32 = 945 Gs! A big rocket will have a hard time hitting 100 Gs, never mind 10 time that.

More than likely they heard the ignition shockwave. The rocket exhaust plume is supersonic. When a motor ignites promptly, you can hear the initial shock wave generated as the exhaust plume first interacts with the atmosphere. After that you hear the multiple shocks as the roar of the motor.

It takes ~0.2-0.3 s for the sound to travel the ~200-300 ft that one might be away from the launch pad. A rocket accelerating at 25-30Gs would be about 20 ft in the air when the ignition shock arrives at their vantage point. A far more realistic senerio.

Bob

werks fer me

So let's just say that there is in fact a sonic boom (or thud or crack) where is the best place to locate one's self or others to hear it?
I guessing you would want to know the time hacks for when the rocket accelerates through and decellerates through mach1.
Then position yourself that number x the speed of sound in your chosen units away.
That didn't come out well; try this instead:
If the rocket will break mach 1 at 2 seconds into the flight and stay supersonic for one second, the choice area to hear the boom would be between:
2 (seconds) x 1116 ft (I choose feet) = 2232 feet and
3 x 1116 = 3348 feet away from the point of launch.
This is of course at STP.
Any thoughts?

Greg

im guessing that at that distance, unless you've got a huge rocket, you wouldnt hear anything.

Originally posted by 11Bravo
Any thoughts?

Click to expand...

The best location would have to be in front of the rocket.

A location off to the side, X thousand feet away, could well get you absolutely nothing. An object that is barely supersonic will produce only a weak shock wave toward the sides. Plus, at several thousand feet to the side, any shock wave that *is* somehow generated will be greatly dissipated by the time it travels that far.

It takes a pretty large supersonic body, more like airplane-sized, to create a strong shock.