F-16's - did you know they can whistle?

I just experienced something very strange, at least it was strange to me as I'd never heard anything like this before.

I work very close to an Air National Guard Base in NW Ohio. Every day, sometimes a couple of times per day, anywhere from 2 to 5 F-16's fly over my building on approach to landing.

If I were to guess I'd say that when they cross my building they're 500 feet or so off the ground? ( total guess ).

It's always a very neat sight to be outside on break when they're landing, as they're close and loud. However today, a co-worker and myself experienced something neat but strange.

I hear the planes coming, look up, they're about, oh I don't know 1000 ft or so away, and flying about 500-600 feet in the air. Once they're about 500 ft closer to us and still about the same altitude, we hear it...

A very loud, high pitched "whislte" or "squeeking" sound. It sort of sounded like someone was "cat calling" at a woman, type whistle, but very loud.

Do F-16's have external speakers that they can "communicate" through?
Could this be a test of some type of "sound" weapond?

No. It most likely was a hydraulic pump. We used to hear it with the F-15s when they were going overhead sometimes too. Occasionally the hydraulic system needs a "boost" and the pump will kick on and it makes an odd sound when it does.

Air brakes.

If they came in a little hot and ATC told them to cut airspeed to landing/holding pattern airspeed you can get that sound... Shouldn't last to long though.

Yeah, we no longer heard the sound once they flew past us...

Yeah, anything involving the hydraulic system makes that odd whistle. It really freaks you out when you first hear it.

The whistle you hear is engine bleed air moving the variable exhaust nozzle. The exhaust nozzle's diameter changes automatically based on several variables (such as throttle position) to maintain proper engine parameters.

The Pratt & Wimpy engine uses engine bleed air while the General Electric engine, which powers nearly all active duty Vipers except those used in training, uses engine oil as the pressure source. You do not hear such a whistle with the GE engine. The bleed air or engine oil is not vented overboard.

You would also hear the same sound from all F-15s (except the GE-powered F-15K). The Ohio ANG unit in question flies the Block 42 F-16CG powered by either the P&W F100-220 or P&W F100-229. The ANG and AF Reserve decided to reengine their Block 42s with the higher-thrust -229 as the Block 42 with the -220 was (and still is) a PIG.

Originally posted by fulcrumflyer
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the whistle you hear is engine bleed air moving the variable exhaust nozzle. The exhaust nozzle's diameter changes automatically based on several variables (such as throttle position) to maintain proper engine parameters.

You're probably correct and you know a lot more about than I do. But when I take my grandson to the bike park the final approach path to Nellis AFB is exactly 200 feet above us. I hear that exact same whistle every single time. Now if it was engine bleed air moving the variable exhaust nozzle don't you think one, just one approach wouldn't need an adjustment of the throttle at 200 feet. Like its every single time.

Great thread, thanks for the answeres everybody. I have noticed this all the time aswell. Now I know, or somewhat know, what it is.

The reason I gave as "engine bleed air" is not "probably correct" but absolutely correct. [1000+ hours in the Pratt-powered F-15, 2400+ hours in the F-16 (mostly GE-powered though)]. Please don't confuse the whistle at 200 feet with the pilot making huge throttle movements and not precisely flying the jet. It doesn't take more than a few percent chage in engine RPM to induce a change in the nozzle position. Besides, at 200 feet they're most likey making last second corrections to on-speed conditions before pulling the throttle(s) to idle.

Well, all I know is that that engine has to loudest noise ever.

thanks for all the answers guys, but the more I think it over....

This was the first time I've heard it, I've worked at this building for 8 years and been outside while lots of landings were taking place, this was the first time ever.

Also, as I play the event over in my mind, the "whistle" sounded more electronic than mechanical....

I think it's safe to say that fulcrumflyer knows what he's talking about. If he says that's what it is, you can pretty much take it to the bank that the noise was caused by that.

Whoa wait a minute. thats the first time you have heard it, a pilot and air crewman tell you its hydraulic, plus ive heard hydraulic whistles from all kinds of machinery, and you think its electric. Please tell me what type of electronics you think can cause that kinda whistle, since i work in electronics, id like to know myself.

I would take fulcrums and Zaphods explanations long before an electronic cause. Im curious of your basis for that decision.