I was watching an airshow in Rome, GA a few weekends ago and noticed something interesting during the aerobatic routine flown by an A-10 Thunderbolt. During high-speed dives, the aircraft made a high-pitched buzzing noise once it got up to speed, and the noise would disappear as it slowed down during climbouts. My first thought was flutter... but considering the pilot wrung this thing out for nearly 20 minutes, and the noise was heard dozens of times, I figure flutter would have destroyed something before he was done!

So anyone who is very familiar with the A-10... is this a "normal" noise? If so, what causes it?

FWIW, I was watching from outside the airport due to the $130.00 (per carload, but I was by myself) entry fee. One of the most thrilling moments came when the pilot did a high-G knife-edge turn right over my head at just about tree-top level! It took the rest of the day to get the grin off of my face! LOL

It's the turbofan engine. You're hearing the fan.

Also the doppler effect...

And if you ever hear a "BRRRRIIIPPP!! sound, it's too late.

quote:

Originally posted by M-11:
And if you ever hear a "BRRRRIIIPPP!! sound, it's too late.

I think if YOU hear it, it means he’s not shooting at you.
Yet.

I saw a pair fly at an air show many years ago. Was very impressed at an attack pattern in the shape of 4 leaf clover where the diving A-10 could be shooting as the other was coming about out of the line of fire. Right after the climb out and standing on wing-tip bank left the 2nd was ready to dive and fire. This pattern could put ordinance on target 15 out of every 30 seconds! I was impressed

The A-10 has a type of aileron called a “deceleron.” It’s a two-part device that functions like an aileron for roll control, or can be split to function like a dive brake. Since you described the Hog as being in a full power dive, you certainly could have heard the decelerons in dive brake mode.

Hog farts. The least of your worries is methane in the atmosphere...

quote:

Originally posted by sns3guppy:
It's the turbofan engine. You're hearing the fan.

This. A-10s fron the ANG unit in Ft. Wayne overfly our area every now and then and the engines make a very distinctive sound. I can tell it's the A-10s before I even look up. They're always a treat to watch, I wish they were around more. This summer my son and I were out fishing on the lake and 2 of them came in low over the lake and banked right over our boat. It was awesome!

^^^
(what sns3guppy said, it's the fan)

The fan "whine" is different from the fan buzzing.
You know it when you hear it, and if your in an aircraft that is doing it, it is very obvious. (Bombardier CRJ and Embraer E type use the civilian version of the engine)

The A-10 fans make the buzzing (that people hear on the ground) partly because it is moving pretty fast in dense air, and near the ground, and the fan blade tips are trans/supersonic, so it is more pronounced.

Like this I recorded at the Sanford Lockheed Air Show....




Link to original video: https://www.youtube.com/watch?...u.be&ab_channel=SCox

Yes, between the :22 and :28 mark, then again 33 to 38 and 1:45-1:55 is the fan "buzz".

The ducted fan produces most of the engine thrust, not the jet effluence or exhuast stream. At lower altitudes, the fan thrust accounts for most of the thrust, with an increasing component of jet thrust contributing to overaall thrust s the aircraft climbs higher.

The fan is a free spool, meaning that under a load, making thrust, it's being driven by the turbine section. In idle conditions, the airflow through the fan is different; the engine isn't driving the fan so much as the slipstream.. In a descent, the aircraft is operated at idle, or close to idle thrust. The sound from the engine is very different, because the fan speed, and the airflow, and angle of the airflow through the fan is very different.

The fan is essentially a propeller with multiple blades. Unlike turbojet engines found on many tactical aircraft in which the inlet blades for the engine are internal to the engine and are compressor blades that feed air to the engine, the fan on the turbofan engine is external, and is a big propeller driven by the turbine engine.

A propeller is inefficient, with a big loss of thrust around the tips. In a ducted fan, the engine nacelle or case (duct) eliminates this problem, and also creates a unique sound when the fan is under a load; the sound in a propeller driven airplane would be a loud "braaaaaap" sound as the prop tips go supersonic. The ducted fan produces a very different sound, but you can hear elments of that in the unique signature when at higher power settings and lower speeds. You'll hear the unique signaature at low speeds, high angle turns, and climbs, and of course, on takeoff.

You'll hear the whistle in descents, at idle thrust, when the fan is being acted on more by the slipstream than by the turbine section of the engine.

There are also other sounds you may hear, which are actuators, and of course, the aerodynamics of the aircraft.

I think most Hog Drivers will attest that their Turbofans could use a little more Turbo, and a little less Fan...

Still my all time favorite aircraft though! My first sight of one was static at an air show at Westover AFB, Massachusetts back in '77 or '78.

Todd

HRK, you weren't too far from Hopkins Meat Market!

They have some very fine sausages, brats, and cuts of meat.

quote:

Originally posted by rsbolo:
HRK, you weren't too far from Hopkins Meat Market!

They have some very fine sausages, brats, and cuts of meat.

You are correct, been there bought stuff, bacon is awesome as well....

quote:

Originally posted by phxtoad:
I think most Hog Drivers will attest that their Turbofans could use a little more Turbo, and a little less Fan...

Years ago, I listened to one of the demo pilots addressing room full of civil air patrol cadets, on the A10. The demo driver said that the A10 was his idea of a fighter, meaning single seat, and single engine.

One of the cadets raised his hand and said, "Excuse me, sir, but the A10 has two engines."

"No," the pilot replied, "It's got two half-engines."

I love nothing more, nothing I can think of, more then the roar of a fighter engine. I dont care what model, they all have that distinct sound.

It puts a smile on my face every time.

That's the sound of freedom.

.

quote:

Originally posted by HRK:
Like this I recorded at the Sanford Lockheed Air Show....




Link to original video: https://www.youtube.com/watch?...u.be&ab_channel=SCox

Yup, that's the noise I heard! LOVE IT!!!