(OT) The physics of afterburners (OT)

***PRB*** · December 20th, 2009, 15:56

So I was watching a YouTube video which featured the McDonnell F3H Demon fighter (among others) landing and taking off from aircraft carriers during what appears to be flight testing. At some point in the video the Demon lights off its huge after burner, and it got me to thinking about these devices.

The only airplanes I've worked closely around that had after burners (re-heaters for our friends across the pond?) are F-14s and FA-18s. Now, both of these planes had this fancy multi-stage AB system whereby the full force of the AB is not applied instantly, but in “stages” as you advance the throttles forward. I'm told this type of system is not nearly as dramatic as, say, the RF-8 Crusader, which, like most planes of the era (like the F3 Demon...) had only one “stage” of AB. It was either off, or it was on, and if it was on it was “OFF” (On Full Force) Hehe. I'm told the “audio/visual” effect of this, if you were nearby, was somewhat “attention getting”. When the AB “lit off” there came an almighty and earth shaking “BOOM!” from the offending airplane. This, of course, is what we call “cool”.

Being such a youngster, the RF-8 Crusaders were gone from the fleet by the time I sailed on my first aircraft carrier in 1982. But (but...(as Lionheart would say)) when in 1990 our FA-18 squadron went on a visit to Holloman Air Force Base in New Mexico, I witnessed an engine test of what I think was a QF-100. That's a radio controlled target drone version of the famous North American F-100 Super Sabre fighter. The F-100 had one of the old style (1-stage) AB systems. The engine test was going on quite a distance away, and I would never have even noticed it had it not been for the fact that they tested the AB at some point... What I heard (and felt) was a deep base-component heavy “thud” through the ground, and through the air. It wasn't loud, because the plane was far away. But the power that was delivered through the air and through the ground was amazing. As I watched, they shut off and lit off the AB several more times over ten or so minutes. Amazing! Stuff we just can't get from FSX!

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**warchild** · December 20th, 2009, 16:31

I remember one time when i was in Nam.. I was walking to my post one afternoon, and all of a sudden the ground started shaking, then some seconds later there was this god awful roar.mind you, i still couldnt see anything till all of a sudden this huge streak flashed across in front of me about 500 feet off the deck. It was some F-4 haulin ass back to cam rahn. I'll never forget that though. Not knowing what it was, i dont know if i was more scared or just plain curious..

***Navy Chief*** · December 20th, 2009, 17:24

I can tell you first hand, having ridden backseat in F-4 Phantoms.....the feeling of the AB kicking in is incredible. I remember it felt like it was hitting right against my back. The sense of power was unlike anything I had ever felt; then, or since. My last back seat ride was in a F/A-18D, but nothing, repeat nothing came close to what rides in Phantoms felt like.

NC

***jmig*** · December 20th, 2009, 18:45

The Phantom was a multistage AB. It didn't kick like the "hard" light AB of the early Century series jets. The F-4's AB was most dramatic in going from around 0.75-0.8 mach to supersonic. It was incredibly fast.

Silver Fox · December 20th, 2009, 20:14

425 Sqdn of the Canadian Air Force used to do airshows with 4 CF-101s as 'Warlock Flight'. Min altitude, banked so the belly was toward the crowd... at about 500 Knots. Stage centre and they went burner with the most frightening sound in creation. At the London Airshow they caught an F-16 jock by surprise one day and he blurted something rather... inappropriate in front of the gathered crowd.

Good Times!

***falcon409*** · December 20th, 2009, 21:30

When I took my backseat ride in the F-16 in '02, we did a max climb to 10,000. I remember him saying "ok, here we go". . .then a faint recollection of some added thrust, an unforgettable realization that I was traveling down the rwy at slightly over 300kts with the gears up and then in almost the blink of an eye we were rolling out at 10,000. There was never the "slam you into your seat" AB, but a very real "pin you to your seat" sensation of super speed in such a short span that it took my breath away.

**Wingnut172N** · December 20th, 2009, 21:40

In the Rhino (F/A-18F) the acceleration at Mil was pretty similar to a lightly-loaded airliner. As soon as we were rolling and the blowers kicked in the acceleration got much more sprited.

I'll agree with the above poster, in that the burners didn't slam me back in the seat, but the acceleration was noticibly increased and I felt pinned back in my seat. Both flights were in a clean jet without pylons or stores, but with full internal fuel. It was still pretty impressive.

***modelr*** · December 21st, 2009, 06:46

While I never got a ride in an aircraft while I was in the USAF, (bomb dump personel didn't fit the "need") I did get to work around many different aircraft on the flightline. As Pam said, the F-4 had a fantastic sound, but nothing, and I mean NOTHING compares to the sound of the SR-71 when it lights 'em up!! The ground just shakes, and buildings on the far side of the base (Kadena, on Okinawa, in this case) just rattle. Since we had 5 of the Blackbirds based there, we had to make sure we had nothing near the edge of bookshelves or they would fall off. The sound, and feel, is something you would never forget.

It was not unusual for one to fly low and slow over the runway and light 'm up near center and point the nose up at around 60-70 degrees and climb till out of sight, before returning for landing. They would be out of site in seconds.

**GT182** · December 21st, 2009, 10:46

The Mig-23 has a heck of a roar to it in AB... and a 30 foot flame to boot. You can feel the vibration a good 600 yards away.

Off to the 4 o'clock of a Mig-21 the AB will rattle yer cage from the shockwave when it lights up. 2 of our ground crew found that out a couple of weeks ago. Next Sunday I'll get to experience it trying to get some footage of the takeoff.

**peter12213** · December 21st, 2009, 11:45

I'll never forget the first time I stood next to the runway at work a Tornado went past a full chat and I've honestly never felt anything like it, It almost knocked the air out of my lungs it was unbelievably brilliant! Great Vid too!:salute:

**dharris** · December 21st, 2009, 12:38

http://www.youtube.com/watch?v=H02iF...eature=related Interesting afterburner sound and low level flight on f16's amongst mountain passes full screen and HQ

**JO_Wingnut** · December 21st, 2009, 13:06

That comment about the SR-71 is so true. I spent a lot of years working around F-4d/e/g planes, and when I saw an SR take off it was awsome. I was riding a motorcycle along the takeoff pattern and this thing flew by. The sound was so loud and rummbled so much it almost felt like it was going to blow me off my bike. When it lights up that AB you would swear there was a large rocket taking off.