Thick Heavy Black Smoke
 

Hello,

I was watching a G4 take off. From the engines spooling up to, till as far as I can see her disappear, I can see thick trail of black smoke out of both engine. It used a good amount of rwy so knowing she's heavy I realise. Can someone explain what this usually means? I was first thinking maybe that's an indication of service times are coming up. What else? This is got me curious.....

It was probably not a G4, but actually a G2. From a bit of a distance, they look pretty much the same. G2's usually blow stacks of smoke and use a bunch of runway.

Smoke
 

Nothing wrong with it at all. Back in the 70s the whole world stank of kerosene... newer designers are leaner.. better combustion.

older jet engines have a lower bypass-ratio. of even maybe "direct-jets" where all the air goes thru the combustion process.

Standard call with the old engines was "smoke on" when setting T/O thrust.

If it was a G-IV, then it would be RR-Tay powered, and I've never seen them that smokey on either Fokkers or Gulfstreams...just the usual light mist....:ok:

So can someone explain why low by-pass ratio engines produce so much black smoke?

B-707, B-727, B-52! come to mind.

Thanks.

Nothing to do with bypass ratio. Look at photos of, say, F-86 and B-47, both powered by straight jets. Black smoke is unburnt carbon from incomplete combustion. The US engine technology of the time was not capable of full combustion. Compare British engines of the same time, e.g. Derwent, Ghost, Avon, Sapphire - little or no smoke because of better combustion technology.

Standing by for incoming from the West!

Generally agree:ok:

The smoke thing was a nusisance visually like chemtrails :} but of more serious concern in the military.

From an engine cycle effiicency (lb of fuel per lb of thrust per hour) it had little impact.

The designers addressed it by moving holes arround in the burner cans inside the engine. In the end, same internal pressures and temperatures and same fuel efficiency, just turned up the heat in local areas inside the burner.

B-52s thru the G model, like the KC135As used water injection on take-off. No water, no take-off. Water ran out at about 400 feet, which someone here said is how 400 became the end of Zone I or level-off height.

GF

Admittedly slightly O/T, but I've always wondered why Sud/BAC and RR didn't do something sooner about the smoke of the prototype Concorde engines, and in particular before sending 001 and 002 on world tours.....
By the time the preprod aircraft flew, with annular combustion chambers and very much less smoke, all the tree-huggers were already out in force.

CJ

The 1-11 also used water injection. Not a lot of smoke
from them. But they compensated for that by producing
a hell of a racket!!! The Crackle was painful at times.

Black smoke is unburnt fuel.

By lower bypass ratio I believe the above poster was referring to blade clearances.

Other factors such as burner section design and nozzels that spray fuel to atomize better in conjunction with higher pressure ratios burn a much larger percentage of fuel resulting in increased engine efficiency and lower emissions.

High bypass engines become more efficient and burn less fuel because a larger percentage of thrust is created by the fan. But remember this, higher tolerance engines become less tolerant, we counteract this by creating tougher materials to make these engines less susceptable to failure. Progress and failure in the desire to progress are just a factor of life.

Storm...
The Caravelle was not so much a 'crackle' as a screeching, tearing noise.
Concorde may have produced more decibels, but it was a lower-pitched roar.
The Caravelle was 'ear-splitting'....

CJ

and other Spey favorites....
 

I always enjoyed our pre-stage II Gulfstream II at T/O power. From the inside. ;)

Then we got banned at TEB and had to "upgrade", sigh.

No, that 400 feet is a holdover from CAR4B and the pistion airliner era.
Also consider screen height, jets 35 feet, piston aircraft, 50 feet.
Why the lower figure for jets?
Believe it or not, some of the early types (B707-120 for example), simply could not meet the fifty foot requirement anticipated, performance-wise, so the screen height was lowered to 35 feet.
Some of those early models were...lead sleds, in the extreme.

Yes, that was the reason for the lowering to 35 feet.

I can recall quite a few accidents in the KC-135 caused by the failure of the water injection system. One of the worse was in Wichita, Kansas. They lost water injection right at rotation, they immediately started dumping fuel out of the refueling probe, but to no avail. The aircraft crashed and the flames from the resulting crash followed the stream of dumped fuel and caused a lot of homes to be burned down causing the deaths of a lot of people on the ground. A total of 30 people were killed, the seven crew members and twenty three people on the ground.

City of Wichita - 11 - The Reawakening 1965

A G2 smoke? Naw mate, this is smoke. :D

http://i100.photobucket.com/albums/m...footprint2.jpg

OMG I wish I was in aviation in the early 70's!

He wasn't messing around getting the gear up was he!!!