We were at Ocean City, NJ this past weekend and there's always lots of aircraft flying by parallel with the beach, including lots of helicopters.

We saw the iconic Coast Guard orange helo go past quite a bit and also 3 Navy Sea Hawks plus a few civilian and a NJ State Police chopper.

What struck me is how I could tell the military ones before I even saw them; they just have a much lower, more powerful sound and the rotation speed of the blades also seems much faster. The civilian ones sound slower and higher pitched just less powerful.

Is this because the military helos have basically a helicopter version of a V-8 or V-12 in them while the civilian ones are 4 cylinders?

Military ones are bigger, have more powerful engines, often two of them, and bigger, four-bladed rotors.

The military birds definitely all have turboshaft (jet) engines, but it is the rotor blade number and design that is most different.

A Blackhawk/Seahawk for example has a 4 blade rotor and the tips are re-curved to reduce tip speed and noise. I believe the CG Dolphin is similar and they have UH-60s as well.

A Chinook has a dual rotor system with each having just 2 massive blades with no re-curved tip so they go WHUMP, WHUMP, WHUMP!

If the NJ SP bird was a probably a Jet Ranger so similar engine, but if it had a 2 blade straight tip rotor that would sound a lot different.

The CG Dolphin is commonly referred to as "the whistling shitcan", it has a much higher pitched engine than any other jet powered helicopter...

it also has straight tipped rotors...

The HH-60 is the same helo as the Blackhawk...the CG just calls them Jayhawks....dunno why

The Navy Seahawks, and the USCG J hawk and Tangos, use 2 GE T700-401 engines. They have a maximum of about 1600 continuous Shaft Horse Power and a Max contingency power rating of over 1900 SHP at sea level. Of course that all depends on operating conditions and how "healthy" the engine is.

IMO, it's mostly in the rotor blades.

quote:

Originally posted by MikeinNC:
The CG Dolphin is commonly referred to as "the whistling shitcan", it has a much higher pitched engine than any other jet powered helicopter...

it also has straight tipped rotors...

The HH-60 is the same helo as the Blackhawk...the CG just calls them Jayhawks....dunno why

Because its the HH-60J model

quote:

Originally posted by 229DAK:
IMO, it's mostly in the rotor blades.

Rotors do make a difference in how they sound. On the Navy Hawks the rotors weigh 210 lbs and turn at 258 rpms. They sound different depending on how much power the pilot is pulling, pitch of the blades and a much of other stuff.

<<<<<been working on/with Navy H-60's since 1984

The military helicopters you hear are heavier with wider blades, and have two engines; most civilian helicopters are single engine and weigh less.

The number of blades makes a big difference in the sound, as does the blade type and design of the rotor system. The most distinctive sound is the classic huey; a slap-slap or whop-whop sound of "blade slap" in a heavy, wide, two-blade teetering system. A deaf person can hear them landing in the next state.

I think I could still tell you if it was a Cobra, Huey, Blackhawk or a Chinook by sound.

Sorry, don't have any answers for you

CH53's are the loudest to me. Nothing else sounds like them.

My understanding of the Dolphin is that the whistle is primarily an effect of the geometry of the blades in the fenestron (or windowed) tail rotor system. The blades on the Dolphin and it's civilian counterpart the Dauphine are spaced equally around the axis. This creates some aerodynamic effects between the blades and the stirred up air from the previous blades. Since all the blades are the same distance apart it creates a sound wave on the same frequency. The EC-135 a civilian helicopter has the blades spaced at differing intervals around the disk so it creates multiple, but quieter frequencies.

At least that's how I remember it. I'm 20+ years out of my helicopter days now.

Power and lifting capacity. In addition to the variations in engine number, blade number and blade tip and tail rotor configuration, which have a lot to do with radiated noise level, there are significant differences in capability and lifting power.

Bell Jet Ranger (typical police chopper) one engine, two blades, 1,600 lbs. lift; 420 shp.

Eurocopter Dolphin (Coast Guard small bird) 2 engines, 4 blades, 2,400 lbs. lift; 1,700 shp.

UH 60 Blackhawk/Jayhawk (medium lift) 2 engines, 4 blades, 9,900 lbs. lift; 3,800 shp.

CH 46 Chinook (Army heavy lift) 2 engines, 2 rotors w/3 blades each, 25,500 lbs. lift; 9,400 shp.

CH 53 Super Stallion (Navy/Marine Corps. heavy lift) 3 engines, 7 blades, 40,000 lbs. lift; 13,140 shp.

My first Army assignment was in the 101st at Fort Campbell. You quickly learned to tell the difference between helicopter sounds - Kiowa, Huey, Blackhawk, Apache, Chinook and even the ubiquitous CH-54 Tarhe (Skycrane). The latter moved our 155mm howitzers several times - it was a real blowjob underneath that 72' diameter rotor blade system, hooking up & lifting a ~13,000 pound howitzer.

This message has been edited. Last edited by: 229DAK,

Military helos are beating the air into submission to stay aloft while their civilian counterparts are asking nicely not to drop out of the sky, ergo, military helos are mean sounding and civilian are nice?

Or....... the rotor blades in military helicopters are tuned precisely so as not to induce harmonic vibrations that would set off the rocket motors in the ejection seats out of sync with the rotors? Civilian helos don't have ejection seats?

Anecdotal trivia.....

In the course of a 6mo deployment you have a 1 in 75 chance of launching the orange from a flight deck lunch through the turning blades of a CH-46 in flight.

A golf ball dropped from 1000ft onto the deck of a cargo ship bounces really high but makes a tiny splash.

No matter how much weight you put inside a triwall strapped to a pallet and kick it out the back of a CH-46, when using it as your target for aerial gunnery quals for the crewman if that shit doesn't sink someone gets an asschewing.

Real trivia....

On average 75% of available engine power in a helicopter is used just to keep the drive system turning with only 25% used for actual flying.

My son does V-22's. Neither airplane nor helicopter.

It's all kinds of fucked up.

Sounds like an eight year old driving a deuce and a half up a mountainside in the wrong gear mated with a polar bear that got the sniffles. Just wrong.

quote:

Originally posted by BigSwede:
I think I could still tell you if it was a Cobra, Huey, Blackhawk or a Chinook by sound.

Same here.

I can add: Kiowa/Kiowa Warrior, Apache, Hind, Hip and Hoplite.

Number of blades, blade length, blade surface, number of engines, type of engine, RPM and probably weather or not the blades are fixed or pivoted and dampened all change the sound.

Two massive fixed rotor blades, like those on the old AH-1W Cobras, chopping the air generates a different sound that seemed more intense to me than a 4+ rotor blade helicopter.

My beloved CH-53E had seven massive 500 pound rotor blades with a 75 foot main rotor arc, a titanium leading edge and a composite pressurized body for rigidity. Our main rotor blades also pivoted fore and aft as it spun around. I think we called it lead and lag.

We had huge hydraulic dampeners that would control the lash of the blades. As the blades would spin and pass the 6 o'clock position and approach the 12 o'clock position, they would cut into the air and angle back as it encountered resistance. As the blade passed the 12 o'clock position and had no resistance, the blade would speed up and lash forward until it hit the 6 o'clock position and repeated the cycle all over again.

It's been almost 20 years since I've been out, so the memories are a little fuzzy.

When a helicopter is flying at max forward air speed, the main rotor is tilted as far forward as it can be, directing the sound waves forward.

Then you take something like a CH-46 or a CH-47 with a front and rear rotor head and you have two sets of rotor heads running opposite directions which creates a completely different sound.

It's not really civilian vs military. Every kind of helicopter sounds different from another. They all have a unique sound frequency. Some are similar, but they are all different.

A 2 bladed cobra doesn't sound anything like a 4 bladed super cobra.

Tony.

What always amazed me was the difference in the sound from being on the inside and hearing them from the outside. On the inside it was the transmission whine, turbine whine, I don't remember any blade noise, it has been awhile though.

The most important difference is that civilian helicopters are built as light as possible to save weight, gas etc.

Military helicopters for the most part are built as big and heavy as needed for the mission.

I miss flying them!

I'm down in SW Virginia and we mostly hear the small civilian medevac helo. I run to the nearest window when something bigger than that flies by.