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Enthusiast Joined: Aug 02, 2006 Posts: 62 Status: Offline

Hello everyone. It is me again.

When I asked at this forum few things about Viper's afterburner I realized that one thing bothers me still. I was told that the engines kicks out some smoke when raw fuel is pushed there. Well I have seen that engines kicks out black smoke right after when the afterburner is turned off. Next video shows it quite well. 1:39-1:42 and 2:34-2:42 are these parts when it is seen quite clearly.
http://www.flightlevel350.com/Aircraft_ ... -5750.html
When at military power the engines doesn't smoke that badly. Now I would like to know what might cause this. And I have also seen this to happen in various jets too like F-15, F-22 and Eurofighter. It's strange, isn't ? At least for me Razz

Thanks for your time. Thanks

Best Regards _Viper_

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The smoke comes from the engine when it is at or near MIL power. (Which is top shaft speed/power the engine can run.)

It has nothing to do with the afterburner. Even in SEC (Secondary) mode (Where the augmentor is inhibited) there will be smoke at MIL power.

Just before the engine goes into AB it nears MIL, at this point it is running almost wide open. The engine is trying to accelerate at the fastest possible rate. To accelerate a turbine engine you add fuel. When the burner kicks in, the smoke goes away as the flame of the augmentor cleans up the exhaust of the engine. (The smoke still enters the augmentor duct, but it burns off before it can emerge.)

When you cancel 'burner, the smoke will return as it is still pouring from the engine at MIL. When the throttle is pulled back towards mid-range the smoke does subside as the engine isn't trying to make so much power.

"Older" engines, ones with more cycles/hours on them, tend to smoke a little more than "newer" ones. This is do to more excessive clearances within the compressor section. To compensate for the lower efficiency of the compressor, the engine's temperature is increased by it's control system. This is done by adding more fuel into the combustion chamber. You have a less efficient compressor (lower compression) and you add more fuel for heat to compensate, and you'll get more smoke... Wink

Follow?

You need to find a video of a Viper taking off in MIL. No augmentor plume, but the engine will smoke. Or maybe find a video of an A-6, A-4 or perhaps the P-80 or F-86. None had 'burners, but they all smoked at MIL power during takeoff. Cool

I'll try to find one...

Keep 'em flyin' Thumb

Watch this F-86 video, 1:00-1:20, you'll see how the older jets smoked at MIL too.
http://www.youtube.com/watch?v=Bq110lI-Ot8

Even older commercial engines smoke. (Unlike modern High-Bypass Ratio engines)
http://www.youtube.com/watch?v=wE_Nwczq7ps

Now you want smoke? Watch this one!
http://www.youtube.com/watch?v=gsJmZzKZl-A

Water injection causes the engine to run WAY rich... Twisted Evil

Man I miss seeing that! Crying or Very sad

Enthusiast Joined: Aug 02, 2006 Posts: 62 Status: Offline

Well I think that I managed to follow your text's intrigue although there were few odd words Very Happy

But that is not your mistake in any case. If I understood correctly the engine won't smoke as much when it isn't at MIL power or let say about 80 % of thrust without burner.So when at MIL power it is going to smoke like in the video untill the throttle is moved. As far as I know the military power means full power without the AB.

Earlier on I linked a video clip in the other thread. i was told that the smoke was caused by raw fuel being pushed to the engine. Now after this explanation I would like to know has the MIL power smoking, whose you explained very well, something to do about that. Actually I have thought that rapid throttle movements at any thorttle area can cause puffs of smoke.

PW and GE engines apparently are pretty powerful even without the 'smoking'. I mean in dogfight situation a big trail of smoke would be quite problematic when flying at MIL power. I could guess that the pilot could select the AB or to save fuel and fly at MIL power depending on situation.

That_Engine_Guy wrote:

Watch this F-86 video, 1:00-1:20, you'll see how the older jets smoked at MIL too.
http://www.youtube.com/watch?v=Bq110lI-Ot8

Even older commercial engines smoke. (Unlike modern High-Bypass Ratio engines)
http://www.youtube.com/watch?v=wE_Nwczq7ps

Now you want smoke? Watch this one!
http://www.youtube.com/watch?v=gsJmZzKZl-A

Water injection causes the engine to run WAY rich... Twisted Evil

Man I miss seeing that! Crying or Very sad

I've seen 12 fully loaded (internal gravity and 12 underwing ALCMs) G models do that many times at Barksdale. Not quite that close, but close enough to feel the downwash from the wingtips. Notice how they kept taking off after a shorter takeoff run than the ones before them? After the 6th plane the following ones have about a 50mph headwind to help them. I do miss them too.

R.I.P. 57-6491 "Lil' Patches"

_Viper_ wrote:

If I understood correctly the engine won't smoke as much when it isn't at MIL power or let say about 80 % of thrust without burner.So when at MIL power it is going to smoke like in the video until the throttle is moved. As far as I know the military power means full power without the AB.

Yes, the engines will smoke at MIL more than any other setting. MIL is the point at which the maximum amount of fuel is being fed to the engine's combustion chamber. This is the point when the engine is running the hottest.
Yes, the smoke will subside when the throttle is reduced. (or AB is selected)
Yes, MIL is full power on the basic engine without AB. AB only adds fuel downstream of the actual gas turbine engine. It is (in effect) like a rocket being fed oxygen by the jet engine, and raw fuel that is mixed and ignited for extra heat. (thrust)

Idea

Point to remember. Engines and Afterburners were considered separate items early in their history. If you changed an engine, you would often use the same afterburner, or vise versa. Now the augmentors stay with the engine most of the time unless there is a problem with the augmentor that can not be repaired, or it is due for overhaul. It can then be removed and replaced in a shop or on a flight-line. The augmentor is considered a "line replaceable unit" or LRU that can be changed on the line, after the engine is partially removed for access.

Here is a good explanation: http://science.howstuffworks.com/question374.htm

_Viper_ wrote:

Earlier on I linked a video clip in the other thread. i was told that the smoke was caused by raw fuel being pushed to the engine.

Not exactly. It is a rich fuel condition within the engine that causes the smoke. There is a bit of unused fuel when the AB is canceled, but that only lasts a second or two. If the throttle is moved rapidly from AB to IDLE, you see almost no visible smoke.

_Viper_ wrote:

Now after this explanation I would like to know has the MIL power smoking, whose you explained very well, something to do about that.

Any engine will smoke more at full power. GAS, DIESEL, GAS-TURBINE, RADIAL etc. It is the point at which the maximum amount of fuel is being pushed into the engine to make the maximum amount of power.

_Viper_ wrote:

PW and GE engines apparently are pretty powerful even without the 'smoking'. I mean in dogfight situation a big trail of smoke would be quite problematic when flying at MIL power. I could guess that the pilot could select the AB or to save fuel and fly at MIL power depends on situation.

The PW-229 can make about 17,000lbs of thrust at MIL, so if you backed off a bit so that the engine were running about 80-85% you may be getting 12-14,000lbs. At MAX AB, the engine will exceed 29,000lbs of thrust, but will reach 50,000lbs/hr fuel flow. Twisted Evil

When a Viper only has 12,000lbs of fuel it doesn't last long at that power setting! Shocked

Now if you see white/gray smoke trailing your engine (and it's not a T-bird) you have an oil leak. Land immediately, if not sooner! Sad

Keep 'em flyin' Thumb

Nothing like a pair of J79's and JP-4 for smoke!

http://www.youtube.com/watch?v=ApM_f-jB ... ed&search=

Applause

ACMIguy wrote:

Nothing like a pair of J79's and JP-4 for smoke! Applause

Yes the JP4 did tend to smoke more than the JP8 does now-a-days. Twisted Evil

And you gotta' miss the Phantoms... In Love

Such a lovely howl...

Enthusiast Joined: Aug 02, 2006 Posts: 62 Status: Offline

_Viper_ wrote:

When a Viper only has 12,000lbs of fuel it doesn't last long at that power setting! Shocked

Yep. I have read that PW 200 burns about 800lbs of fuel per minute at maximum power. I wouldn't pay that fuel bill Very Happy

Quote:

Actually I have thought that rapid throttle movements at any throttle area can cause puffs of smoke.

Apparently my deduction about the next sentence was correct because I actually watched some more videos and I certainly noticed this during a high alpha pass in a display flight. I mean the plane was still advancing slowly.
A thousand thanks for your patient answers.

That_Engine_Guy wrote:

Now you want smoke? Watch this one!
http://www.youtube.com/watch?v=gsJmZzKZl-A

And I thought my uncle was smoking too much Shocked

I've seen the "older" smoking smoking Pantoms we have here, but it doesn't come anywhere close to these BUFFs Shocked

What model B-52 is that ??

seat_dreamer wrote:

What model B-52 is that ??

All of them had J57s with water injection up to the 'G' model. Cool

The B-52H had TF33s with more thrust than that of the J57s with water.
(But you have to consider water injection on any engine only lasted a specific amount of time before it ran out... typically 1 minute or less.)

KC-135A and Qs had J57s with water too.
B-47/J47 engines had water injection.
F-105s had J75s with water injection AND afterburners! Shocked

Just to name a few... Wink

In 1956 the J75-P-19W of the F-105 made 26,500lb (118.3 kN) of thrust with water injection and afterburning on take-off. In 1978 the F-16A with the F100-PW-200 engine (Much lighter than the J75) only made about 24,000lbs; also consider the F-105 weighed in at 27,500lbs where the F-16 was only 16,000lbs The 'Thud' did not have the performance of the Viper, but did have awesome power! Twisted Evil

Early jet-airliners often had water injection for added thrust as well. The water injection's increased thrust was used for hot day or high altitude take-off performance. It was even optional for early Boeing 747 engines. (JT9D-3A in 1969)

The AV-8B/F402 still in active service with the US is the only aircraft/engine I know that still has water injection.
(I think about 40 seconds worth for hot/high/heavy hover capability)

Enthusiast Joined: Aug 02, 2006 Posts: 62 Status: Offline

_Viper_ wrote:

Quote:

Actually I have thought that rapid throttle movements at any throttle area can cause puffs of smoke.

Apparently my deduction about the next sentence was correct because I actually watched some more videos and I certainly noticed this during a high alpha pass in a display flight. I mean the plane was still advancing slowly.

Finally I found that clip which hopefully proves it's. Please take a look at 2:05 and 2:11. I could guess that the pilot isn't using the MIL power at all. http://video.google.com/videoplay?docid ... &plindex=5
Oh and those BUFFs are pretty insane when it comes to the engine smoke Razz

Yes, a rapid throttle advance will cause smoke. It is more evident at high throttle settings.

High-Alpha passes have a pretty high throttle settings too...

Air Shows are a poor place to observe "normal" engine operations. The point of the demonstration is to showcase the "limits" or "extraordinary" capabilities of an aircraft. During most of the show the throttle is slammed to MAX, MIL, or IDLE. If the aircraft were flown this way all the time, the cycles put on the engines would be very high, and would not last long.

Enthusiast Joined: Aug 02, 2006 Posts: 62 Status: Offline

Yep, that was exactly what I thought. According to my eyes I could almost swear that the pilot wasn't running at MIL power power during that pass Wink

Most civilian's only chance to see some fighter planes are air shows. But as you said it won't tell the whole truth.

That_Engine_Guy wrote:

KC-135A and Qs had J57s with water too.
B-47/J47 engines had water injection.
F-105s had J75s with water injection AND afterburners! Shocked

Just to name a few... Wink

In 1956 the J75-P-19W of the F-105 made 26,500lb (118.3 kN) of thrust with water injection and afterburning on take-off. In 1978 the F-16A with the F100-PW-200 engine (Much lighter than the J75) only made about 24,000lbs; also consider the F-105 weighed in at 27,500lbs where the F-16 was only 16,000lbs The 'Thud' did not have the performance of the Viper, but did have awesome power! Twisted Evil

[/i]

The Thud's water injection was used only for takeoff and then only when the burner was lit. It never smoked using water. The water injection system was good for 2,000 lbs of thrust over the J-75-P17 in the F-106. The pilot had to dump the water tank when he was done with the water in it because the tank was not stressed to handle g-loads when not empty.

Jet engines smoke due to incomplete combustion of the fuel that goes through it. The burner completes the combustion, ergo you don't see smoke in AB. Jet engine technology has come a long way from the old F-4C/D and KC-135A days. The F-4E had a smoke kit TCTO on it that reduced the smoke output considerably. The -135A was the smokingest airplane I ever saw in my life. I remember being at Minot watching the SAC boys do a mass takeoff and really feeling sorry for the poor BUFF drivers who had to make instrument takeoffs after the 4 -135s took off in front of them. The eight TF-33s of the H-model BUFFs didn't smoke half as much as the four J-57s on the tankers.

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