F16 in afterburner on ground test video link.

[Leo]

Re: F16 in afterburner on ground test video link.

LOUD
I once got tasked with climbing down into a row of manholes on a runway edge at Travis AFB. Purpose was to dip the elevations for a survey. Being 6 feet underground when a KC-135 took off was actually nauseating. The vibrations echoing off the walls were that severe. This was back when they still used the water injection on takeoof and the outboard engine passed almost overhead of the holes I was in. After a day of this I was deaf until the next day!

[SkyvanDelta]

Re: F16 in afterburner on ground test video link.

There have been some interesting responses from people who have been there and seen tethered jets in afterburner. What an obscure but interesting topic.

Some more questions.

1. How long can a tethered jet run in afterburner? Can they run for hours providing they have fuel or is there a limit to how much an engine can take?

a. Does outside temperatures limit the testing of engines. Can they run equally well in hot or cold temperatures? Do they prefer a certain temperature range and what would that be?

2. Are there varying degrees of afterburner or is it an all or none proposition?

3. Regarding sound, is there a cone shape of sound coming out of the exhaust, (pointy end of cone forward and broad end of cone aft both inline with long axis of engine) where if standing off to the side of the motor (like the people shown in the video), is the sound quieter than if you were directly behind the motor say, 200-300-400-500' directly behind the exhaust? In other words, is it louder directly behind the exhaust as compared to standing off to the side but closer?

4. What type of hearing protection do people use who work around such noises? Is it something very unusual or unique with noise suppresion and electrical components/batteries or is it just plain old hearing protectors?

5. Do these motors ever explode while testing like this? What would be the outcome of such?

6. Is the expandable exhaust in the open or closed mode when in afterburner and what determines whether it is open, medium or closed? What is it's purpose?

[Peashooter]

Re: F16 in afterburner on ground test video link.

One more -- do the shock diamonds move or are they static?

[Inverted]

Re: F16 in afterburner on ground test video link.

There has been some interesting responses from people who have been there and seen tethered jets in afterburner. What an obscure but interesting topic.

Some more questions.

1. How long can a tethered jet run in afterburner? Can they run for hours providing they have fuel or is there a limit to how much an engine can take?

a. Does outside temperatures limit the testing of engines. Can they run equally well in hot or cold temperatures? Do they prefer a certain temperature range and what would that be?

2. Are there varying degrees of afterburner or is it an all or none proposition?

3. Regarding sound, is there a cone shape of sound coming out of the exhaust, (pointy end of cone forward and broad end of cone aft both inline with long axis of engine) where if standing off to the side of the motor (like the people shown in the video), is the sound quieter than if you were directly behind the motor say, 200-300-400-500' directly behind the exhaust? In other words, is it louder directly behind the exhaust as compared to standing off to the side but closer?

4. What type of hearing protection do people use who work around such noises? Is it something very unusual or unique with noise suppresion and electrical components/batteries or is it just plain old hearing protectors?

5. Do these motors ever explode while testing like this? What would be the outcome of such?

6. Is the expandable exhaust in the open or closed mode when in afterburner and what determines whether it is open, medium or closed? What is it's purpose?

1. I used to run the F-18 in afterburner untill I would get flameouts if we we had to defuel the aircraft to work inside the fuel system. On the Carrier we would carry 2 drop tanks, and the Hornets would tanker with the Air Force and they used JP-8 if I remember correctly. Well we couldnt defuel JP-8 into the ships JP-5 tank because of the different flash points. So I would go up , chain it up and burn 14,000 lbs of fuel up in about 20 min heeheehehe.

a. I have ran engines in 120 degree temps in the Gulf to in a Snow Blizzard at Top Gun. We have some cold temp procedures. But I dont remember not being able to fire the engine up because of cold temps. We didnt have a high temp limit but we had to watch ourselves. In hot weather the heat exchangers would heat soak pretty quick and we would get fuel hot cautions.

2. The Hornet is all or none. MIL power is max power without AB. Then you bump the throttle past the Military power detent and boom there the AB lights.

3. Not really understanding this question so forgive me if I dont answer it right. To answer the last part no the quietest part is directly behind the exhaust. The loudest would be directly in front of the intake or abeam the intake opening. I remember when I was a line rat, when refueling aircraft on the cold days I would stick myself on aft fire bottle(worst position because of exhaust and heat) because it was nice and warm, sometimes I would fall asleep on the fire bottle after long days because it was so quiet.

4 I havent seen any ANR type of noise suppression used in Military ground crews. We used a Cranial which consists of PNR ear cups and protective plastic to protect the head.

5. I have never seen one explode in the sense of a huge fireball. But I have seen plenty of what we would call a catastrophic engine failure. Basically the engines just eat their own internals and shut down or seize. They may shoot huge fireballs of metal and crap but never seen one explode explode.

6. The VEN(variable exhaust nozzle) on the hornet is controlled by the main fuel control and the electronic control assembly. All afterburners are regulated for the age old velocity vs pressure idea. In burner, the VEN is full open because there is a tremendous amount of velocity. Idle VEN position is 73-84%. Then as throttle is increased it closes until either 80% N2 or Mil power which if I can remember correctly is fully closed. Then it opens for AB. All the big wigs with degrees figured out where the nozzle position should be for the optimum power setting to give the most efficient pressure/velocity .

here is a cool picture that was taken by the Carl Vinsons bridge cam of one of our birds launching. I was working on an aircraft just to the right outside of the picture when I heard a huge bang. All I could remember thinking was damn I hope that wasnt our bird cause I am gonna have to fix it. Sure enough 20 min later I get called up into maintenance and get shown the pic. I thought it was so cool and wanted a copy of it. I ended up getting my ass chewed for thinking the pic was cool lol. Anyway sometimes the pilot can be in front of the main fuel control and give the imput to AB too quickly. Combine that with maybe the incorrect air or any other million variables and you get an AB hiccup. The best is when the compressor stalls and shoots that flame out the intake lol.

[SkyvanDelta]

Re: F16 in afterburner on ground test video link.

Inverted, thanks for your response. Your answers have triggered more questions.

"I used to run the F-18 in afterburner untill I would get flameouts if we we had to defuel the aircraft to work inside the fuel system."

1. Are you saying you run the engine in afterburner until it runs out of fuel? Is that considered acceptable or hard on such an engine?

"So I would go up , chain it up and burn 14,000 lbs of fuel up in about 20 min."

2. Any idea how many gallons or the cost of such getting rid of unwanted fuel? Is 14,000 lbs considered a full load with 2 drop tanks?

3. What's the going price on a new or rebuilt engine?

4. How many hours can they be used before they are scrapped out?

5. When you throttle up an engine, suppose it is warmed up to proper temperatures, can you quickly push the throttle into afterburner like in a second or two or do you have to slowly throttle it up so you don't damage the engine?

[hattend]

Re: F16 in afterburner on ground test video link.

Nothing was as loud as the SR-71 on takeoff out of Beale at 4AM.

It woke up the whole base.

Don
Weather Observer
Beale AFB, 1981-84

[Inverted]

Re: F16 in afterburner on ground test video link.

Inverted, thanks for your response. Your answers have triggered more questions.

"I used to run the F-18 in afterburner untill I would get flameouts if we we had to defuel the aircraft to work inside the fuel system."

1. Are you saying you run the engine in afterburner until it runs out of fuel? Is that considered acceptable or hard on such an engine?

"So I would go up , chain it up and burn 14,000 lbs of fuel up in about 20 min."

2. Any idea how many gallons or the cost of such getting rid of unwanted fuel? Is 14,000 lbs considered a full load with 2 drop tanks?

3. What's the going price on a new or rebuilt engine?

4. How many hours can they be used before they are scrapped out?

5. When you throttle up an engine, suppose it is warmed up to proper temperatures, can you quickly push the throttle into afterburner like in a second or two or do you have to slowly throttle it up so you don't damage the engine?

I always appreciate answering questions.

1. More specifically I would run it in burner till about 800 lbs then let it idle out. at about 600 lbs the engines would start flaming out. I have had to go from full AB to immediate shutdown due to some Bleed Air cautions which I am sure was hard on the engine. I dont know how bad it is to go from AB to shutdown.

2. This is strictly off of memory but I believe the cost of jet fuel back then was around 7 bucks a gallon. JP-5 I think is 6.8 lbs per gallon. Now this is really tasking my memory. Full internal load I think is 10.5, 1 drop tank is 12.5 sometimes 12.6, and 14.5 for 2 tanks. So just gasing a Hornet up can be very expensive.

3. The F-404-GE-400 was a Million new. When we need an engine we send the bad one to AIMD who repairs it. We basically get one in exchange that is serviceable that we can put in the aircraft. And the squadron pays what it costs to fix the bad engine we turned in. So if it didnt fail and just needs an overhaul, then the squadron pays for an overhaul in exchange for that serviceable engine.

4. I think the TBO is 1000 hours on the F-404. And thats a big I think. They never or hardly ever last that long. And the engine is modular. So say we turn an engine in that had problems. And they found a problem in the compressor section. Well they overhaul the compressor mod and slap her back together. So the compressor section has 1000 hours left but the fan section may only have 300 hours. So that engine will come back out and get turned in, in 300 hours. On the boat we would go through motors like crazy. FOD was a huge issue. One little bolt would destroy a motor. I think in the 8 months we were on deployment we changed at least 20 engines. I would say close to 30. Heres what a 1/4 in nut will do:




5. When we would do new engine tests and if a pilot experienced a problem we couldnt duplicate. I would go out there literally with the mindset of being the crap out of it. On one of our tests you have to check the transient throttle time from idle to full AB. I think it was 3 seconds. So you just sit at idle then pop them into AB and wait. Should take no more than 3 seconds. I remember if you could make the jet go in and out of AB just right you could bounce the main wheels off the deck. Because the jet is only secured by the high power chain on the nose wheel.

[Stevo]

Re: F16 in afterburner on ground test video link.

Since exploding enigines was brought up here are a video from YouTube showing just that... and one that show's what can happen when an engine comes loose in the test cell.

http://www.youtube.com/watch?v=5F-I08xLWqM

http://www.youtube.com/watch?v=T4bn1WG5LS0

[Randy Haskin]

Re: F16 in afterburner on ground test video link.

2. Are there varying degrees of afterburner or is it an all or none proposition?

2. The Hornet is all or none. MIL power is max power without AB. Then you bump the throttle past the Military power detent and boom there the AB lights.

I don't have any time in the F-18, but I don't think that's correct. I would be surprised if the Hornet was much different than the jets that I've flown -- T-38, F-15, and F-16 -- all of which have varying degrees of burner. With the Hornet being a McDonnell Douglas product like the Eagle, I'd have to guess that they work very similarly.

Although the throttle position does not directly control (or tell the pilot) how many stages of afterburner are being used, there is variation in how much thrust the burner gives.

We generally talk in terms of "min burner" which is just over the hump, "mid burner" which is in the middle of the AB section of movement, and "max" which is all the way to the northwest part of the throttle quadrant. On the PW-229 that I fly currently there are 11 different stages of burner. I used to fly with the PW-220 which had 5 stages of AB.

sometimes the pilot can be in front of the main fuel control and give the imput to AB too quickly.

Again, I don't have any Hornet time, but this hasn't been the case with any other jet with AB that I've ever flown. None of them have had any limits on how fast you could move the throttle or how rapidly you could put them in/out of AB. Even a low-bypass, low-tech motor like the J85 in the T-38 doesn't have problems with throttle-bursts from stop to stop so long as you're in the heart of the flight envelope.

This was certainly an issue with engines of the generation before the F404 and the F100, but with the advent of the DEEC it is "smarter" than the pilot and keeps things like that from occurring.

[Peashooter]

Re: F16 in afterburner on ground test video link.

Randy: This vid from last year's GOML shows the Raptor doing a tail slide. What have they done to avert compressor stall in the F-22? There seem to by many F-22 maneuvers that would cause problems with other engines/inlets. Thanks! Peas

http://www.airshowbuzz.com/videos/view.php?v=40c6c112

[Randy Haskin]

Re: F16 in afterburner on ground test video link.

Randy: This vid from last year's GOML shows the Raptor doing a tail slide. What have they done to avert compressor stall in the F-22? There seem to by many F-22 maneuvers that would cause problems with other engines/inlets. Thanks! Peas

http://www.airshowbuzz.com/videos/view.php?v=40c6c112

Well, other jets have been doing tail slides for years. The first time I saw one was the Frecce Tricolori at the 86 Abbostford airshow. The Russians have been doing it in MiG-29s and Su-27s at airshows since the 1990s. I fully believe that F-15s and F-16s could do it if we were allowed to (it's a tech order prohibited maneuver in the Eagle at least). We do tactical maneuvers that effect airflow in the inlet similarly, however -- lots of high-alpha maneuvering with lots of stagnant and disturbed airflow -- and have no problems with compressor stall.

It's all about the DEEC. I don't know what they call it on the Raptor's motor, but digital engine control technology is pretty phenomenal. Compressor stalls are VERY rare in the current PW-229 and GE-129 engines, so I can only imagine the leap in technology over the last 15 years since those were introduced.

I've had two compressor stalls in my career -- one in the T-38 and one in a PW-220 powered F-15E. In the T-38, which has a manual fuel control and nozzle control, the result was catastrophic -- a compressor blade from the 6th stage broke off, taking numerous other blades on successive compressor stages and turbine wheels with it as it travelled down the engine. The thing quit and never restarted.

In the F-15E, there was a gigantic fireball that came out the intake and a tremendous bang that accompanied it. By the time my eyes got to the engine instruments, the engine had all ready recovered and the indications were completely normal.

The difference is that the 220 was a DEEC controlled engine and the J85 was all manual.

[Peashooter]

Re: F16 in afterburner on ground test video link.

Isn't the T-38 failure in your SUPT Journal? Thanks for the informative reply!

[Randy Haskin]

Re: F16 in afterburner on ground test video link.

Isn't the T-38 failure in your SUPT Journal? Thanks for the informative reply!

Yep, the very same incident.

[Inverted]

Re: F16 in afterburner on ground test video link.

I don't have any time in the F-18, but I don't think that's correct. I would be surprised if the Hornet was much different than the jets that I've flown -- T-38, F-15, and F-16 -- all of which have varying degrees of burner. With the Hornet being a McDonnell Douglas product like the Eagle, I'd have to guess that they work very similarly.

Although the throttle position does not directly control (or tell the pilot) how many stages of afterburner are being used, there is variation in how much thrust the burner gives.

We generally talk in terms of "min burner" which is just over the hump, "mid burner" which is in the middle of the AB section of movement, and "max" which is all the way to the northwest part of the throttle quadrant. On the PW-229 that I fly currently there are 11 different stages of burner. I used to fly with the PW-220 which had 5 stages of AB.



Again, I don't have any Hornet time, but this hasn't been the case with any other jet with AB that I've ever flown. None of them have had any limits on how fast you could move the throttle or how rapidly you could put them in/out of AB. Even a low-bypass, low-tech motor like the J85 in the T-38 doesn't have problems with throttle-bursts from stop to stop so long as you're in the heart of the flight envelope.

This was certainly an issue with engines of the generation before the F404 and the F100, but with the advent of the DEEC it is "smarter" than the pilot and keeps things like that from occurring.

Again this is tasking my memory. But from what I can remember the AB on the F-404 was fixed. I honestly dont remember.

As for the second part I didnt mean there was a time limit for how fast you can move the throttle. But the MFC takes over scheduling at 80%. If you can catch it just right when moving the throttle and move it fast enough the ECA to MFC transition dumps a buttload of fuel in because it thinks burner is about to occur. If you do that without putting it into burner 2 or 3 times then but it in burner, all that excess fuel is ignited and blown out the back causing a huge fireball hehe.

[Peashooter]

Re: F16 in afterburner on ground test video link.

Hold onto your hats!