approach speed question? (and strange whistle?).

I live in Sun City AZ, near LukeAFB, and play a lot of golf.
My buddies and I have a dispute about the approach speeds of the f-16's as they fly over us on the golf course (approx 3mi out from Luke).

I keep telling them that even though they look LOW/SLOW as they fly over, that I'm sure they're going at least 100mph(guessing), or they would stall...(depending upon weight/load.)

Without giving away classified data, can someone tell me if I'm correct.
I've seen other data talking about 250kt approach speeds, but I just can't believe they are traveling THAT fast. (isn't 250kt equal to appx. 280mph?).
I'm refering to all this at estimated 1000-1500 altitude(I'm guessing).
They look like 500ft, but I'm sure they must be at least 1000+

AND another question that comes up is WHAT THE HECK is the short, high pitched whistle that we hear occassionaly as they pass over on approach?
Is it some kind of hydraulic pump? Sounds sorta like a short hight pitched "ffffffffffffffftttt!" (okay, quit laughing!!!) I know that's not a very technical description...but that's the only way we can describe it!

Thanks!

Ty Dale
a1aztours@yahoo.com

The sound that you hear would be the pilots putting on the air brakes back by the tail. and adjusting the engine at the same time. I take it that you play at the Flacon course.

Sounds like the CENC , moving the nozzle,if flying a Pratt, and they are going faster than 100 kts.

Ty

Our typical approach speed 3 miles back from the runway on a 3 degree approach (normal straight in or ILS) would be from around 140 knots to 180 knots. The speed depends on the fuel and stores remaining on the jet (weight).
A 3 degree approach will give 300 feet pr mile from the runway. Therefore 900-1000 feet would be pretty close as you guessed.
With regards to the high pitch whistle, I must say that I never heard it inside the cockpit so I just don't have a clue..........

Guy

I think vinnie nailed it, the sound probably the turkey feathers opening and closing. This video http://www.youtube.com/watch?v=GcFWP_TvNjM at about 45 seconds in you can hear the sound clearly before the rapid throttle up. The sound is a little out of sync, but you get the idea.

vinnie wrote:Sounds like the CENC , moving the nozzle,if flying a Pratt.

Yes; what you hear is the CENC "Convergent Exhaust Nozzle Control" that moves the actuators for the engine's exhaust nozzle.

If it 'zip-zips' (wistles) when the throttle is moved it is a F100-PW-2XX. The F110-GE-1xx engines use hydraulic (engine oil) actuators to move their nozzle, which is silent.

The CENC uses high-pressure air from the 13th stage of compression, the highest in the engine, to move the nozzle. The CENC is akin to an "air-motor" As the air moves through the CENC in one direction the nozzle is "driven" open by flexible-shafts that turn screw-jack type actuators. In less than a second, the CENC can turn 341 revolutions to fully open or close the nozzle. When air is directed through the CENC the opposite direction, the nozzle will close as everything spins in reverse.

The CENC controls "nozzle position" or Aj (Area Jet) which is the primary method of maintaining proper EPR (Engine Pressure Ratio) and N1 (Fan RPM) Whenever the pilot moves the throttle, or PLA (Power Lever Angle) the engine adjusts for the requested thrust, and Aj is the most evident adjustment made. (Nozzle opens/closes and the zip of the CENC is heard)

The CENC has an exhaust port that dumps the used air overboard. It is located about 5 o'clock on the engine just aft of the 'H-Flange' where the augmentor duct attaches to the aft-fan duct. On the Viper the exhaust port would be located between the ventrals, more towards the one on the right.

Every PW F100 engine has used a CENC to drive it's nozzle. Even the prototype F100-PW-100 made this sound. Some rumors say that this sound is the "screech" that gave the F-15 the name "Eagle"

Ah what a wonderful sound...

Keep 'em flyin' (edit for spelling sorry guys... ):

Guys,
Thanks for the excellent and quick response to my questions!!!
That video was amazing, and that is exactly the sound (at about 50sec into the video!), so now I can research air break/"turkey feathers". for further knowlege.


Also, it's amazing that you're doing 140kts at 3mi out! It looks like so much lower/slower...but that's just an illusion based on the fact that we're so used to seeing them screeming by at airshows/on TV, I guess.

That video was amazing, and you can imagine how LOUD it must have been in real life! It's pretty much a consensus around the Sun City/LUKE AFB area that we all LOVE that sound. (ie: "sound of freedom" is the typical local quote!)

I don't get to play at Falcon Dunes as much as I'd like to, but play a lot Sun City (about a 5 handicap) but I sure do Love the Falcon Dunes course!
It's funny because when I'm playing golf, I get distracted by the sound of a mower or weedwhacker, but the sound of an F-16 never bothers me!!!
But I grew up around it (Elmendorf AFB, Alaska) so it's always MUSIC to my ears!

Ty

a1aztours wrote:so now I can research air break/"turkey feathers". for further knowlege.

Here are 2 photos.

One is the PW nozzle showing the Speed Break open. The "Turkey Feathers" are the External Nozzle Segments. The parts that run horizontal around the nozzle and say "NO PUSH" at the aft end and "NO STEP" at the forward end. The newest PW-229 engines have black carbon-fiber Turkey Feathers.

The other is the GE nozzle. Same situation but no stenciling on the feathers. Open Speed Breaks, and detail of the "Turkey Feathers"

Note the appearance of the respective nozzles. GE's nozzle is shorter and has more curved feathers when viewed from the side. The PW nozzle is longer, and it's feathers are more straight when viewed from the side.




(Edit - Sorry the photo links didn't work, so here they are.)

Awsome pictures!
Man, I can't believe what a great site this is!!!
I have to tell you folks that you are very much admired and appreciated around the Sun City retirement community...especially on the golf course where we all get to watch the 16's fly over.

I'm young for Sun City, (46) and have had to take care of my parents (Alzheimer's) for the last 6 years, but back when I had a life, I grew up and worked in Alaska around aviation (all my life). I have to say that this site impresses me! Not just the technical expertise, but the pride that shows through!!! I miss the sound of Alaska Floatplanes soooo much, but the 16's have almost taken their place in my psych.

I am prior Air Force (avionics), and you guys make me only wish I could have some of my years back again, to be able to work with folks of your caliber.

Keep up the good work, and drop a line if anyone here in AZ needs to hit a golf ball!

ps: Thanks to you guys, I will now be the hero amongst my buddies when I am the FIRST person to have the REAL answer to what the h___ that whistle really is!!!
Thanks again Guys!!!
Awsome!
pss: I've got some pretty good aviation pic's (parttime hobby) so I'll try to get a couple Alaska Bushplane shots uploaded in the next couple days!

Ty Dale
a1aztours@yahoo.com

That_Engine_Guy wrote:Here are 2 photos.

One is the PW nozzle showing the Speed Break open. The "Turkey Feathers" are the External Nozzle Segments. The parts that run horizontal around the nozzle and say "NO PUSH" at the aft end and "NO STEP" at the forward end. The newest PW-229 engines have black carbon-fiber Turkey Feathers.

The other is the GE nozzle. Same situation but no stenciling on the feathers. Open Speed Breaks, and detail of the "Turkey Feathers"

TEG--Does that mean that GE Viper maintainers are smarter than their PW counterparts? Smart enough that they can figure out on their own that they can't walk on the tail feathers?

Hadda ask, y'know?????

TEG--Does that mean that GE Viper maintainers are smarter than their PW counterparts? Smart enough that they can figure out on their own that they can't walk on the tail feathers?

Naw... GE Viper Maintainers can't read, so the stenciling is a mute point.



Hadda dig back, y'know????

FYI, the new carbon-fiber PW-229 feathers don't have the stenciling either. Guess ALL maintainers have figured it out after the first few decades of use?

Reading or not