This ia an F-18 going sonic. I bring this to you so you can visualize the power of the pressure wave when breaking the sound barrier. This is something you should know not just with my SC but any rotating machine. If you go even close to 1100 Ft/sec. Turbos may not get there because they feel the resistance and are not locked to the engine. But other blowers that are belt driven could get there if you don't follow the builders guidlines.

BTW this has to be a one in a million lucky shot by the photog. Where the hell was he standing??

 

holy shitzer, that had to hurt

 

charlie, i really think that is inappropriate as I don't know Jim, but I'm pretty sure richard likes wom... oh.. you said aFs.. my bad..

 

Good one.......

 

...

i know.. it was lame... i'm sorry..

 

I have seen video of a jet transonic that was 100ft off the water. In the right light as a passanger jet approaches M.80 or more, you can see a shock wave develouping on top of the wing. This also occures in the blades of a turbo as well as a prop plane. Next time you are at an airport you may notice some small planes, ie Cessna 210, have a loud raspy sound. that is actually the prop tip going supersonic. these proptips or turbine blades loose efficency in this state. therefor the idea is to keep them subsonic.

John

 

When you "crack" a buggy whip or bull whip what is it that makes the noise?
You know, like when you're training a lion, or your girlfriend.


Kidues to Hymee

 

the crack is actually a sonic boom caused by either :

a. the tip of the whip acclerating to a speed greater than the speed of sound
or
b. the tip of the whip displacing air at a speed greater than the speed of sound

 

Well I admit I didn't think anyone would get that.
zoom44 you win, a date with Brittney Spears. If your older, Bo Dereck.

 

but which is actually correct? i have known this little fact(first man made object to breach the speed of sound) for a long time but i really dont know which of a or b is correct or if both are. and i have always had a thing for Bo so you can just send her on her way how to explain that to the wife hmm.....

 

Because the whip will be displacing air faster than the speed of sound if it is accelerating faster than the speed of sound the test would be to flick the whip in a vacuum. Vacuums are noiseless so that would lead me to think Option B, that the air particles being displaced would be the source of the sound.

I also heard Liza Minelli is single again, if you're older

 

Ya but she fell out of bed the other day, probably drunk. I think she may still be in hospital. Also never a bathing beauty.

I think I'm going to write a little lecture for the forum in order that all these things might get clear to members. The speed of sound is a condition of tempreture. I'll just put this in a thingie that can be opened if one wants and doesn't have to be bored if not.

 

The speed of sound is faster with increasing pressure or density isn't it? That seems to make the most sense. If this holds true then I would think that the blade tips on the rear stage of the supercharger where pressure is higher would be more at risk than the front ones for going supersonic. I could just be talking out my *** too. Am I close or is there no effect?

 

Yes, sound travels faster in a denser medium.
The air in the rear stage is denser than that in the front stage.
Ergo: the speed of sound is faster at the rear stage than at the front stage.

So the front blade tips will reach transonic speeds earlier than the rear blades (because the speed of sound is slower there).

 

Bob you are almost right. It is not dependent on the density though.The speed of sound is dependent on the temp only. If i remember right it is 49 x the sq root of the temp in degree R. At standard cond sea level it is 1117 ft/sec or 761 MPH. And at abs zero or -460F there is zero speed and there is no pressure

Pressure depends on the molecules hitting the side of the container. That pressure is the result of said force, being 2mc=force. c=velocity m=mass

The density is the number of molecules in a given space. the more molecules the more times they strike the walls. giving more pressure.

TEmpreture changes the speed of the moles therefore changing the force or pressure.
If the temp goes up the speed goes up and the pressure goes up. But this has not changed our mass.

Experement: We have a closed chamber with a temp probe and a press gauyge. around this chamber we have a "water jacket" in this jacket we have crushed ice. The temp gauge reads 32F the pressure gauge reads 10 psi.

Now we boil the ice in the jacket. The temp gauge reads 212f and the pressure gauge reads 19 psi. Is there any more mass in the chamber? Of course not it is sealed.
This is known as Boyle's law.

Then comes Charles' law. This states that if the pressure is held constant the volume varies
with the absolut temp. Here our test device has a piston held by a constant pressure so the volume can change. if the starting temp is again 32f the volume is 10 cu ft. we then raise the temp to 212 f the piston has retreated so as to allow 13.6 cu ft. Still the same mass.

Ijust know I'm being to breif and not getting out the foundation but I always said I'm a poor teacher, I tend to jump around. That's how my mind works, constantly wandering around.

I had thought of going into this with a paper that I took alot of time writing and rewriting until it made sense. So go ahead ask, maybe then I'll realize what I left out.

Oh yeh, I left out the sonic boom thing. It's the moving of the pressure wave away from the object that is going faster then it's pressure wave. OK OK I need to write that one over. Let me think on it for awhile. I'll make it more understandable.

 

I know it's confusing on the surface but if I could draw some diagrams it would be easier.


SOUND BARRIER


This is a better stab at telling you what happens when you break the sound barrier.
We have already discussed the way molecules act and why temperature effects the speed of sound and that effects pressure. Moving an object through the air creates a pressure wave in front of itself because we are compressing the air. The air propagates through the air at the speed of sound and at sub sonic speeds stays in front of the object.

So the influence on the air is immediately in front of the object going negative mach but when going supersonic it cannot stay ahead because it can only travel at Mach one. ( the word Mach is so named for the Australian physicist Ernest Mach)Therefore we can assume that a supersonic object is not penetrating disturbed air because the compressed wave is now going slower then our object.

So what we have just done is penetrate a wall of air compressed to an incompressible medium. This displaces the shock wave out at oblique angles to the object. I’m going to stop calling this an object, it’s a wing. In fact this is why the supersonic wing is so sharp compared to the subsonic.

Simply put, a sonic shock wave is the accumulation of sound wave energy developed when the sound moving away from our wing is stalled by the pressure of the air coming from the opposite direction. The speed of the airflow across the shockwave will decrease because the molecules are moving with the sound wave against the air velocity. This decrease in speed is accompanied by a rise in pressure, because the sound wave motion will convert most of the kinetic energy into a pressure rise. This is a sharp rise in pressure and temp creating a violent shock wave to be diverted obliquely off the wing.

Now that is perfectly clear, right?er. You can suffer by re-reading it and you'll get it.

 

hmm interesting...as i am not into areonautical science (or whatever you would call it...hmm physics :p) i'll have to say that i got the meaning after reading it a few times...but reading things like that on a post are sometimes hard........just b/c of the context in which they were written..but i go tthe meaning and now i feel more intelligent...oh crap...nope i just forgot it...lol...ah well. You almost got me feeling good about my brain..thank you for that:D

 

OK, I guess I misremembered some stuff.
I thought that the speed of propagation of a sound wave depended on all of the factors that you mentioned as well as the density of the medium. Thus explaining why sound waves travel faster in water than in air, at the same temp & pressure.
Obviously Boyle's Law and Charles's Law don't apply in an incompressible medium. Could be a whole different set of rules govern sound propagation in incompressible media.

Or I could just be full of it.

 

Good explanation Richard.

For a similar explanation but with pictures, check out the Wikipedia article on sonic booms at http://en.wikipedia.org/wiki/Sonic_boom

I love the picture of the F/A-18 pushing the Mach. Can your supercharger do that? :D :D :D

 

Hey that site has the same picture of the Fa-18 as I posted.
Guess there's not to many that show that point of flight.
Had to be one lucky shot. Truth is I know how it was done.

 

Fun subject.

Here's a couple videos for more amusement:

F-14 #1 (you can see the shockwave from condensation)

and

F-14 #2 (you can see shockwave on the surface of the water)

 

Thanks Ranger, I do love those. Wouldn't it be great to be able to play with Uncle Sams war toys?? I guess that is small consolation for those boys that serve to protect us all. They should get all the fun that is due them. Yet I still think I should get a ride in something, anything as long as it's fast.

Most fun I've had was a ride in a P-51 and that only screws it's way through the air. We need something that blows it's way.

 

Screws or blows... either is fine by me if it can get the job done.

 

The screw job can't take you supersonic. Or pull anywhere near the G's.

HEY, I need help. My Eldorado will not let me go to work. It thinks I'm stealing it. It flashes "anti theft system trouble, car may not restart". And it will not.
Any Cad mechanics out there??

Oh Lord, Please give me a carb and distributor. With those I can make a fart run.

 

is the eldorado passkey 1 or 2?
gm had a big problem with the wires doming off on the inside of the ignition switch.

and can i buy one of the sc's for a pj?