Moderators: richierich, ua900, PanAm_DC10, hOMSaR

Topic Author
Posts: 2495
Joined: Sat Jun 18, 2016 7:29 am

Jet Engines "Backfiring"?

Tue Apr 03, 2018 2:47 pm

Listening to the beautiful music that are the afterburners of some (or one?) F-16, there were a series of semi-loud bangs. Definitely not loud enough to alarm me (compared to the basic engine noise) but nevertheless powerful enough to make me feel the sound pressure in my body - some 3 km away. While the engine(s) were kept at that power level for maybe 30-60 seconds those bangs occured intermittently (the aircraft was presumably stationary, I couldn't see it). Reminded me of a back-firing piston engine or engine knocking / pinging.

What would be the cause of this? I've only experienced this on engines with afterburners. Regular high-bypass civil engines only have that deep rumble coming from behind but it's much more constant.

On another note, the sheer loudness of the engine surprised me. Going with typical descriptions, I would assume that this was around 90-100 dB, maybe more. Normal F-16 takeoffs are much quieter and their landings are basically silent.
Posts: 4094
Joined: Fri Apr 12, 2013 2:27 pm

Re: Jet Engines "Backfiring"?

Tue Apr 03, 2018 3:59 pm

Lighting the burners I suspect will cause this.
Posts: 7402
Joined: Fri Jan 01, 2016 4:44 am

Re: Jet Engines "Backfiring"?

Tue Apr 03, 2018 5:39 pm

Compressor stalls during an engine run.

User avatar
Posts: 624
Joined: Sun Aug 23, 2015 9:14 am

Re: Jet Engines "Backfiring"?

Tue Apr 03, 2018 6:34 pm

The term 'backfire' actually refers to an engine that blows back through the carburetor, especially if the timing is too far advanced. Unfortunately the public use this expression for a miss fire, which is unburnt fuel, due to a fouled plug, that accumulates in the exhaust and subsequently explodes on the next cylinder firing. In the old days the backfire could cause engine fires in the carb and inlet manifold and is why they always had a fire extinguisher handy on start up. Also opening the throttle fully would also help to stop the fire. :)
Licensed Aircraft Maintenance Engineer (retired).
Posts: 2126
Joined: Tue Feb 26, 2013 2:26 am

Re: Jet Engines "Backfiring"?

Tue Apr 03, 2018 6:54 pm

mxaxai wrote:
Regular high-bypass civil engines only have that deep rumble coming from behind

Not always --
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
Posts: 2529
Joined: Fri Sep 09, 2011 8:46 pm

Re: Jet Engines "Backfiring"?

Wed Apr 04, 2018 6:04 pm

I remember USAF F106s would emit a loud bang when the afterburners were lit. Not sure if the F16 noise is similar.
Posts: 241
Joined: Fri Jun 06, 2014 9:33 am

Re: Jet Engines "Backfiring"?

Wed Apr 04, 2018 9:14 pm

Sounds like a compressor stall. When the afterburners are lit the exit nozzle needs to expand to match the increase in mass flow rate. Sometimes the compressors can briefly stall as the ABs are lit before the nozzle expands fully emitting loud bangs.
I'm sure this thread will take off soon
Posts: 3928
Joined: Sun Dec 05, 2004 6:50 am

Re: Jet Engines "Backfiring"?

Sat Apr 07, 2018 10:45 pm

GalaxyFlyer wrote:
Compressor stalls during an engine run.


Sounds probable to me.

Compressor stalls can occur during ground runs if the airplane inlet is not directly oriented into the prevailing wind. The off axis wind vector plus the engine induced "sucking" vector causes the flow to separate and the fan face pressure to drop. The loss of mass flow causes the fan/compressor flow to reverse and the engine surges.

This is less often a problem for a subsonic airplane like a jet transport because the inlet lip can be fat and is more forgiving of off centerline airflows.

On supersonic airplanes, like the F-16, the inlets need to be sharp, making them prone to separation for off centerline ground run airflows.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
Posts: 306
Joined: Fri Nov 20, 2015 2:53 am

Re: Jet Engines "Backfiring"?

Thu Apr 12, 2018 9:02 pm

Was on an AA 727 coming into DFW some years ago that suffered a compressor stall. We heard a very loud bang from the empennage and felt the a/c drop. While recovery was quick it was definitely a pucker moment, that's for sure, given our low altitude.

Who is online

Users browsing this forum: ILikeTrains, United857 and 25 guests

Popular Searches On

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos