Lotus Elan and Lotus Elan Plus 2 Forums

Anyone remember the Howmet Turbine racer in the late 60s? It made as much noise coming toward you as it did after it passed. Exciting car!! What a great era in racing!

http://www.youtube.com/watch?v=49vkeGchF-o

John

Thanks, John. This one's even better!! http://youtu.be/x24c-7pJZeM

It is built of a large quantity of rare alloys including large amounts of Titanium, Aluminium etc and weights in excess of 12000lbs.

No problem shoehorning it in then? Brakes via reverse thrust, add lightness by venting some of the thrust through a vertical nozzle, how hard could it be

AHM wrote:The Olympus 593 with full reheat produces 34,000 lbf the J58 only 32,000lbf. Concorde has 4 engines the SR-71 has only 2. So Concorde was roughly twice as noisy!

I don't like to quote myself, but it would appear that I am incorrect in my assumption..... Not much of an engineer!! (pun thought about!)

I read Stanley's book. It would appear that 2 equal noise sources are just a little bit noisier than 1. So 4 engines are a bit more noisy than 1.

"Not Much of an Engineer" by Sir Stanley Hooker. Well worth a read. A fascinating story... a brilliant man.

AHM wrote:

AHM wrote:The Olympus 593 with full reheat produces 34,000 lbf the J58 only 32,000lbf. Concorde has 4 engines the SR-71 has only 2. So Concorde was roughly twice as noisy!

I don't like to quote myself, but it would appear that I am incorrect in my assumption..... Not much of an engineer!! (pun thought about!)

I read Stanley's book. It would appear that 2 equal noise sources are just a little bit noisier than 1. So 4 engines are a bit more noisy than 1.

"Not Much of an Engineer" by Sir Stanley Hooker. Well worth a read. A fascinating story... a brilliant man.

It depends what you mean by a "bit noisier".
4 engines versus 2 of a similar type will put out twice the level of sound power energy.
This will equate to a 3dB rise in measured sound level e.g for a SR71 versus Concord aircraft at take off flying maybe 100 metres over you head an increase in measure noise level from 120 dB to 123 dB. The decibel sound scale is a logarithmic scale on sound power levels so a doubling of power equates to a 3 dB step on the scale.

Perception of what constitutes a doubling of noise to the human ear is even more complex and very subjective and at these high sound power levels you probably cant distinguish between 120 and 123 dB - both planes would be just "deafening"

cheers
Rohan

Rohan is correct, doubling sound power creates a 3 db increase in sound intensity. To double the perceived intensity requires an increase of 10 db. The perception of sound intensity becomes non-linear (even in a logarithmic sense) at high intensities, probably over 90 db. Get a Radio Shack SPL meter and use it to measure your sound system to see the differences in SPL and perceived loudness. The perception also changes with frequency.

Getting close to either of these aircraft was dangerous to your aural health. Even the best ear protection cuts SPLs by around 30 db. Both of these aircraft were substantially over 120 db, so the user was subjected to over 90 db, even with ear protection, and that leads to hearing loss if subjected to the noise for more than a few minutes. The damage is greater with high frequencies, not so much with low frequencies. The SR-71 was so loud the earth would shake for quite some distance from the aircraft, so the SPLs were very substantially over 120 db. I do not know of any published SPL readings at any distance for either aircraft.

Supersonic aircraft had many problems as a result of exceeding Mach 1, the problems became substantially worse the higher the speed, and noise was only one of them. There were quite a few military aircraft that would perform in the range of Mach 2, but these aircraft generally were away from population centers, so most of the noise complaints were from the Concorde taking off on either side of the Atlantic.

A small handful of aircraft even attempted to get close to Mach 3, and the number of hours at that speed were very limited. So, the SR-71 is the only aircraft that flew at a sustained Mach 3, and did so for thousands of hours over 25+ years. But most of its sorties were away from population centers, or were closely controlled demonstrations so we do not hear of many complaints about noise (plenty of sonic booms though).

So, we probably will never really know which aircraft was "noisier".

Cheers,

David
1968 36/7988 (not a Mach 3 vehicle)

When studying Gas Turbine theory at Brunel, three of us decided it would be a good practical to go and stand at the end of the runway at Heathrow while Concorde took-off and compare to other aircraft.

The easiest place to stop was by Hatton cross Tube station, but they only take-off going into London (09R) infrequently and there is a massive car rental carpark before you get to the petrol station here:
http://www.youtube.com/watch?v=7zDDru0IRrE

The closest you could get was the old emergency gate on the (inner) Western perimeter road at the west end of the northern runway (27R) - now next to terminal 5.

There is a dual carriageway further out... where these people are standing. Tthey are at the end of the southern runway (27L) which isn't quite as close, and the Police would never let us stop there.
http://www.youtube.com/watch?v=QHe8R4tx_eU

I've been much closer than that! The Police used to move us on regularly, and they didn't like it when the IRA were making threats, but if you were prepared to stand there waiting for an hour on a cold February night you were obviously nuts.

To describe how close we were. They release the noisy aircraft in groups, so we would be treated to a real show. Often that would include an old 747-200 Cargo - not exactly quiet either. I vividly remember running for my life on one occasion, when one of those used the whole runway - More brown trousers than taking the rear hubs off an elan!

Rohan, David,

That is exactly the way that Stanley describes it in his book. The only difference is that he was writing in the late 70's when the entire world banned her for being too noisy - They couldn't think of a better excuse. So it is written in a casual way that the French did a great job on the noise suppression, and 4 engines are only 6 dB louder than one .... so it isn't much noisier than a 707

The Mach 2 limit is a metallurgical limit for Aluminium - Beyond that things get too hot, and a lot more expensive in Titanium.

More impressive than the noise, watching from the end of a runway, is watching the wing tips. As the plane approaches takeoff speed the wing tips start to "fly" much sooner than the rest of the plane. When the body starts to lift, the wing tips unload a bit and the wings appear to flap as the bird takes to the air. Now, that's not going to happen with either of these aircraft, but I think the B-52's wings "flapped" about 26 feet, full down to full up, IIRC. We used to stand at the end of the runway and watch them launch less than a minute apart when I was in Thailand in '69. Crap, that was a long time ago....

Bud,
You can still see that in a 747.. I think also that Boeing have more flexible wings than Airbus, which makes for a smoother ride.