Visible Turbine Flames

[Obi Offiah]

Visible Turbine Glow/Flames

I was just wondering, under what circumstances are flames visible (from the rear end of course) around the turbine blades, excluding turbine fires?

This video shows a centrifugal jet with visible flames: YouTube - Jet Engine Backyard - Episode 2

This photo shows flames in the turbine sections of an F414 powered Super Hornet (I think the engines are set to military thrust not minimum reheat):


Here is the link for a high res version of the photo: http://www.news.navy.mil/management/...-6106R-140.jpg

Thanks
Obi

[muduckace]

High Temperatures....

[lomapaseo]

I seem to recall that we covered this in the last 3 months in this forum, the subject had something to do with flame arrestors etc.

[Intruder]

Depends on the engine.

The old J-65 with a single turbine stage threw visible flame outside the tailpipe on start in daylight. These days, with multiple turbine stages, you'll likely see them only at night at high power, or when looking directly down the tailpipe as in your photo.

[Tmbstory]

Reminds me of the old joke about two eagles sitting on a branch, side by side,as a jet went by with afterburner on. One said to the other " you would scream too if your ar.e was on fire like that".

Tmb

[henry crun]

Obi Offiah: Please resize that photo so we don't have to scroll to the right to view it, thank you.

[18-Wheeler]

Not quite what you're after, but I've seen right up the tailpipes of a 747-400 a couple of times, when they were taking off out of Cairns on runway 15. The procedure there has you starting the turn at 400' so very early, and where we parked the plane in the morning it was perfectly placed so we could see right up the back of the engines as the aeroplane banked around.
Just for a second of two, I could clearly see four bright-orange glowing donuts, one per engine.

[Obi Offiah]

Originally Posted by 18-Wheeler

Not quite what you're after, but I've seen right up the tailpipes of a 747-400 a couple of times, when they were taking off out of Cairns on runway 15. The procedure there has you starting the turn at 400' so very early, and where we parked the plane in the morning it was perfectly placed so we could see right up the back of the engines as the aeroplane banked around.
Just for a second of two, I could clearly see four bright-orange glowing donuts, one per engine.

No no 18-Wheeler thats pretty interesting. You mentioned that you observed this in the morning, under what sort of lighting, was it low light or dim conditions?

[lomapaseo]

Thanks for resizing the pic

The flame you see is the afterburner lit (behind the engine turbine) and is typical for an afterburning engine at high power.

Most flames that you may see in the back end of non-afterburning engine under power are abnormal and pretty much signal a sudden loss of power while the flame is visible.

Flames during startup or shutdown are completely different thing,

[Obi Offiah]

Originally Posted by lomapaseo

Thanks for resizing the pic

No problem

Originally Posted by lomapaseo

The flame you see is the afterburner lit (behind the engine turbine) and is typical for an afterburning engine at high power.

I'm pretty sure this it is not an afterburner flame because firstly it is too deep within the bypass duct, i.e upstream of the spraybars. Secondly for a carrier launch (particularly this far down the bow), either the engines are at military thrust or maximum afterburner. In either case due to the possibility of a flameout/stall the afterburner igniters would be energised and visible. Thirdly when set to low/minimum afterburner it is the central circular V gutter channel that is lit as well as the igniters as in the following picture:

High Res version here: http://www.news.navy.mil/management/...-2838C-003.jpg

The following is another picture in which the turbine flame is visible (just barely) possibily due to the brighter ambient light condition:

High Res image here: http://www.news.navy.mil/management/...-6854D-001.jpg

Obi

[lomapaseo]

Obi

I'm pretty sure this it is not an afterburner flame because firstly it is too deep within the bypass duct, i.e upstream of the spraybars. Secondly for a carrier launch (particularly this far down the bow), either the engines are at military thrust or maximum afterburner. In either case due to the possibility of a flameout/stall the afterburner igniters would be energised and visible. Thirdly when set to low/minimum afterburner it is the central circular V gutter channel that is lit as well as the igniters

Well you seem to have a lot of experience in this from reading the above. So I had to go back to your original questiom to form my answer

I was just wondering, under what circumstances are flames visible (from the rear end of course) around the turbine blades, excluding turbine fires?

The only time that flames would be visible that far forward arround the turbine blades at high power would be in the event of simultaneous dual engine failures which seems not to be the case in your photos. So I chalk it up to optical allusion.

What do some of the others carrier deck folks see? Is it normal or not? Are these really flames or just glowing hot?

[Obi Offiah]

Originally Posted by lomapaseo

The only time that flames would be visible that far forward arround the turbine blades at high power would be in the event of simultaneous dual engine failures which seems not to be the case in your photos. So I chalk it up to optical allusion.

cheers, I'm starting to think the same. Also it could be that visually it is very sensitive to ambient lighting which has a huge impact on the appearance of the flame, perhaps a little like how an afterburner flame changes appearance depending on ambient light. It looks completely different in low light conditions as to broad daylight.

Obi

[Will Fraser]

Generally the Iris is fully open with any AB setting??

[18-Wheeler]

No no 18-Wheeler thats pretty interesting. You mentioned that you observed this in the morning, under what sort of lighting, was it low light or dim conditions?

I think it was about 6am or so, so call it low-ish light I guess. I'm pretty sure the effect could have been seen under full daylight though if you were at just the right angle.

Must upload some vids I have of starting the Garretts on the rattly old Metro's I used to fly - They get up a frighting glow.

[Obi Offiah]

Originally Posted by Will Fraser

Generally the Iris is fully open with any AB setting??

Hi Will
The VEN variable area nozzle/Iris has an area that varies depending on throttle settings, flight conditions, atmospheric conditions and engine condition. Generally speaking the nozzles are fully open (or close to fully open) at ground idle. At military power they are near fully closed. As the afterburner is selected they begin to gradually open from mil setting and continue to do so as maximum afterburner is selected. At maximum AB they are near fully open under optimal conditions.

The reason the nozzles at max AB are not fully open under normal circumstances is that additional 'margin' is needed to ensure the engine can operate safely with require performance throughtout the flight envelope. Also on a hot day an engine will make less thrust so the nozzles are set with a smaller area than on a cold day where more thrust is avaliable.

Obi

[Obi Offiah]

Originally Posted by 18-Wheeler

I think it was about 6am or so, so call it low-ish light I guess. I'm pretty sure the effect could have been seen under full daylight though if you were at just the right angle.

Hmmm....so there must be some other factor at play here, because sometimes you can get very similar lighting conditions and view the engine/s from a very similar angle yet not witness a glow.

muduckace mentioned high temperatures, so perhaps an engine running hot due to a low EGT margin could be a contributary factor?

Originally Posted by 18-wheeler

Must upload some vids I have of starting the Garretts on the rattly old Metro's I used to fly - They get up a frighting glow.

Please do, I look forward to seeing those.

Obi

[John Marsh]

JT4 flickers

What can produce flickers of light visible from the front of a JT4? I saw some whilst on a B707-320. There were no accompanying noises.

[lomapaseo]

What can produce flickers of light visible from the front of a JT4? I saw some whilst on a B707-320. There were no accompanying noises.

Wow you must have a long memory

I have seen similar flickers associated with reverser operation and reingestion of ground debris into the outboard engines while turning off the runway . This went away quite a few (50) years ago with better reverser techniques.

[MarkerInbound]

Are we really seeing flames? Metal glows red hot a bit above 700C, I think it's just the last turbine wheel. I've taxied behind 727s and 737s and seen the engine light up when the power is puched up.

[18-Wheeler]

Good timing for the thread to come back up, I found a video of the Metro starting, and here it is.

YouTube - Starting a Garrett turboprop engine

That's a nice, quick start as well.

Hmmm....so there must be some other factor at play here, because sometimes you can get very similar lighting conditions and view the engine/s from a very similar angle yet not witness a glow.

I guess it would depend on the amount of derate used as well. Full derate has the engines running a fair bit lower EGT.