So, what did Bluebird sound like?

[KW Mitchell]

The sound, I can tell you, will sound mightily more impressive than that, Mike. In those latter days of '66/early '67 when DC was doing static tests at full bore with the uprated Orpheus, and, when he opened the cocks to start a run it would have been ear-rending - not unlike standing at the end of a runway when a jet is throttled-up!

The thing we must realise, too, is that the exit area of the nozzle in a jet engine is critically related to the velocity of the ejected gases. It would have been designed to match the Orpheus's max. thrust not the enhanced thrust conditions we know it was being operated under at that time. Thus the exhaust velocity would have been even higher and would have been around 500mph i.e.approaching sonic velocities. Now sound intensity is proportional to velocity to the power four i.e. if velocity doubles sound intensity increases 16 fold !!

Now let's make an assumption that velocity increased by 10%, the effect upon sound intensity would be to increase it by almost half! It must have been ear-splitting at the jetty -----------------.

The other big factor is configuration. BB's jet-pipe venting but a few inches above the water surface enhances acoustic reflection (particularly of low frequencies - a bit like the effect of having the bass woofer on the floor in your sound system). The roar would be tremendous plus the not insignificant acoustic emission from the water spray e.g. an almighty pressure-washer.

Of course, we may not get the full effect as then due to the derated Orpheus I believe is to be fitted, but thunder-freaks won't be disappointed I'm sure --------------!

[rob565uk]

I was privileged to hear K7 in late 1966 and can confirm Keith Mitchell's observations and assertions. The first day I heard it was from a distance of several miles, when staying at the Tarn Hows hotel and I can still remember clearly it's note echoing off the hills early on that first morning. At close quarters it was truly awesome and I can still recall the excitement as K7's engine spooled up with the boat lying low in the water before planing and then -whoof!, she would get up on the plane and accelerate away unbelievably quickly, trailing the characteristic rooster tail of spray and accompanied by the unique sound of the Orpheus. It was absolutely stunning and no less exciting each time I experienced it.

[Renegadenemo]

Will you lot shut up! The friends of the ant brigade probably read this and next we'll have old Mrs Miggins from the top of Tarn Yeat Fell bleating on about us possibly compromising her peace and tranquility. K7 will be whisper quiet and unless you were run over by it you'd not know it was there - OK!

[rob565uk]

Will you lot shut up! The friends of the ant brigade probably read this and next we'll have old Mrs Miggins from the top of Tarn Yeat Fell bleating on about us possibly compromising her peace and tranquility. K7 will be whisper quiet and unless you were run over by it you'd not know it was there - OK!

Point taken, but my mind is working overtime on the images suggested by the above- fertile ground for a Mike Bull cartoon perhaps ...

[Grant]

I'm sure that's overdubbed with the sounds of me having a bath. I distinctly heard a sniff half way through?

[klingon]

Well put it this way-I'm trying to beg some ear defenders for the crew from the brylcreem brigade and they're major items-I got pretty severe hearing damage from sticking my ear up Lightning jetpipes!-theres also lower spectrum sound from the engine to contend with as well-that "rumble" from a running jet is deeper than you think!- how will K7 sound?-one word-FANTASTIC!

[Renegadenemo]

Nothing is as loud nor as damaging to the ears as when I get let loose with the panel saw in the workshop!!!

he's not kidding either. The noise is paralysing. It's even loud with ear defenders on. But our new compressor arrived today and according to the manual it makes only 70db when running. The lads will be able to hear my hair growing at that level.

[KW Mitchell]

I did say it was the best we could do for now!

Keith's technical archive, earlier today;

If you look on the second tier, upper left corner (the beginning of the 'A' section) there's a textbook 'Laws of Acoustics ' ---------------!

[KW Mitchell]

[/quote]

---- But our new compressor arrived today and according to the manual it makes only 70db when running. The lads will be able to hear my hair growing at that level.[/quote]

It'll need to be 10dB to hear mine ------------.

[bluebirdsback]

Our old compressor wasn't the problem as we had prety much sound proofed that. Its that bloody noisy Welshman that will ruin our hearing to the point us on the team will never know what the orpheus sounds like. People in the workshop fight for ear muffs when he sets that saw away