How far away can you hear a helicopter?

[Mahatatain]

This obviously varies between models of helicopters and the weather conditions but does anyone have any examples or suggestions or thoughts?

For example does anyone know how far away a transport helicopter like the Mi-8 Hip can be heard from on a clear night?

Any rough ideas would be of help.

Thanks,

Mahatatain.

[Legbreaker]

A LOOOONG way if it's as quiet as it should be on a night time battlefield! (i.e. noise discipline is being enforced)
Only takes a poke of the head out the front door when there's a heli in the area to get an idea of distance and time.

[Mahatatain]

A LOOOONG way if it's as quiet as it should be on a night time battlefield! (i.e. noise discipline is being enforced)
Only takes a poke of the head out the front door when there's a heli in the area to get an idea of distance and time.
Thanks for this.

Do you have any esimates for what a long way is though? 10 miles? More? Less?

I have no idea (apart from it being a long way.....) :D

[HorseSoldier]

My last deployment our FOB was visited frequently by ANA and UN Mi-8/17s (plus assorted other flavors of US, ISAF, and contractor helicopters). There was masking terrain about 6-8 km out from the flightline side of the FOB and once incoming aircraft cleared that ridge line you could hear them the rest of the way in, unless there was background noise drowning it out. That's the only time I can think of off the top of my head where I dealt with hearing aircraft coming where I had a known distance terrain feature to index on.

Not sure on a solid figure for how far out you could pick them up if those ridge lines weren't in the equation. Besides masking aircraft on the far side, I'm not sure if the ridges didn't help hear aircraft on the near side by reflecting sound waves back towards the FOB.

[raketenjagdpanzer]

When somebody rabbits from the local cty pokey, or when there's a life flight to the hospital up the road from us, the helo noise will wake the dead: and we're surrounded on all sides by trees and traffic noise.

[stg58fal]

I think there are too many variables to give you a hard number. Helo altitude, model, weather, terrain, background noise, etc. I'd say for game purposes you can hear it as far out as you, the GM, need it to be heard. Or with failures on Perception, Awarwness, whatever, rolls, it can get as close as one ot two hundred meters before someone realizes the bird is there.

[Grimace]

I live near a fort that uses Chinooks for training. Montana National Guard.

You can hear Chinooks flying during the day at about 5-6 miles. During the night you can add a couple 2-3 miles.

Blackhawks are about 2 miles shorter during the day, so you can hear them when they're about 2-3 miles distant. At night it's around 5 miles away you can hear a Blackhawk.

And just for reference, we've got a couple of old Hueys that fly around here (not for the military). You can hear those coming from probably 10-12 miles during the day. Strangely, during the night it seems like you don't hear them from as far away. So nighttime for a Huey is probably 9-10 miles away before you can hear it. Might be my imagination, but it really seems like nighttime stifles the Huey's chop.

The big Sikorsky Skycranes can be heard during the day about 3-4 miles distant. I've never heard one at night, so I can't guess.

And I can't speak for any Russian helicopters.

[Graebarde]

Can't speak for the Russian choppers, but the Huey I can. I have been on a dirt bike and 'sensed' the chopper. I stopped and started scanning for it. Now my eyesight wasn't all that good even then, but I had to use binos to spot the dot of the bird. It was high and a LONG ways out. Like I said, I really didn't 'hear' it, rather got vibes in my neck hairs from it long before it was visible. Eerie feeling it were at the time.

[raketenjagdpanzer]

Not sure if I've told this one, but here goes...

One Saturday morning (back when I was a teenager, in the late 80s) I was barely awake and out walking the dog when suddenly, almost out of nowhere, this ... "sound" is wholly inadequate for the nigh-fortean event that happened. It was this...it was like God himself was having a morning gargle. It was like Gabriel pointed his trumpet directly at my abdomen and set for "disrupt". This...rumble started ricocheting off the concrete walls of the apartment complex around me and shaking me to the very core of my being. I was being physically pushed around by sound waves. Prying my eyes open (it was about 7 or 8 AM and I was - and am - a night owl so it was the crack of dawn as far as I was concerned and I was as I noted barely awake), I looked up to see a phalanx of 5 UH1 (unsure of series) all bearing Air Cav markings, flying at about 500ft over residential Central Florida, hell-bent for leather.

It was only one Robert Duvall and a PA-blared rendering of die Waulkere from being straight out of Apocalypse Now. I don't recall per se that they were armed, but good Lord it was impressive nonetheless.

I went back in and asked my dad if he'd heard it and he said "What, the Hueys? Yeah, they're probably headed over to Martin Marietta for an electronics upgrade or something."

It was even more impressive than a similar tableau I witnessed about ten years later - out in Apopka, FL, a string of AH64Ds (the radomes were clearly visible) hauling ass out over the campground we were at. That flight seemed to go on and on forever, two helos here, another four there, coming in waves over us. Easily a dozen or more birds. But their sound was almost disappointing - this sort of dull shriek with a soft "poppoppoppop" of main rotors overlaid.

The noise of the Hueys was a force of nature; the Apache's rotor sounds weren't much different from a TV station or sheriff's department Bell Jetranger.

But with that said, the Hueys seemed almost to creep up on me. I didn't really notice until they were almost right on top of us. It might have been the weather, the acoustics of the buildings around me, etc. etc.

[Grimace]

Yeah, the more helicopters in the air, in the same area, the more impressive, and noticable, they are. I was working at a place that was en route to the fort and one day I heard this strange rumble. It wasn't clearly distinguishable what was making the rumble, but I could hear it, inside a building.

I wandered around the building, attempting to determine the source of the rumble, and realized it was coming from outside. I went out, just in enough time to see a flight of 14 Blackhawk helicopters, all in a fairly tight, cluster formation, going overhead.

Now, I heard these helicopters coming, even though I didn't know what they were, for about a minute and a half to two minutes before I saw them. They weren't moving at a leisurely pace, so I have to assume that they were moving at normal cruising speed. That means that a cluster of 14 of them could probably be heard at 10-14 miles distance, possibly more.

So if you get enough of them, helicopters can be pretty impressive.

Oh yeah, I forgot to mention the A-Star helicopters and the "Jolly Green Giant". I worked as an aircraft refueler for a while, so I get very familiar with their sounds. A-Stars are pretty quiet, at least the type I refueled. They flew over the city on tourist flights, so they may have been modified to be quieter. A-Stars can be heard at probably 2-3 miles during the day. A mile or so more at night. The lone Jolly Green that I refueled was plenty loud up close, but I'd estimate that the sound pretty much disappeared after about 4-5 miles. I only saw it during the day, never at night, so I don't know how it sounded at night.

[Legbreaker]

Do you have any estimates for what a long way is though? 10 miles? More? Less?

What they all said. :)

In most military situations, it's extremely unlikely a helicopter is going to be able to sneak up on a unit on the ground, unless that unit is making a lot of noise (tank engines, weapons fire, etc). As a general rule of thumb (and to be stretched and altered as the GM sees fit) a 30 second warning would seem appropriate, possibly more if the helicopter is slow moving/large/flat, open terrain, etc, etc, etc

And that's just using the Mark I Ear & Eyeball - throw in some tech (radar, acoustic sensors, etc) and it can get "interesting".

[Trooper]

Finnish air force still has an observer corps (like UK:s former Royal Observer Corps). Unlike cold war ROC their main war time duty is visual detection, identification, tracking and reporting of aircraft over Finland. (Yes FAF + Army AA has more than 100 radars, but observing teams can spot cruise missiles and other low flying targets. And there is also serious doubts how long radar network is going survive (SEAD + ARM:s.))

Anyway FAF tried to replace some observing companies near eastern border with automated acoustic detection systems in 90s. It was great idea- use modern microphones to pick up sounds and use computers to calculate bearing , distance and filter out unwanted background noises. Army paid part of project- they would use passive microphone arrays as warning device against low flying helicopters like Mi-24.

Fine idea, but it didn´t worked out. Acoustic detection of aircraft is unreliable. Computers and modern microphones couldn’t change complex systems of local air flows and winds.

Sometimes you can only hear the plane (jet plane flying over clouds). Sometimes you can`t hear noisy Mi-8 flying less than a mile away.
You should never trust that you can hear choppers or planes. Yes you can hear subsonic jets, but if you detect them by hearing its usually too late. Modern prop planes are quite silent. In motorized or mechanized units there are usually so much background noises, that it makes hard to hear even choppers.

In normal conditions you can spot fighter plane in 3-4 km distance. Aircraft observing is very tedious work, even a single observing post needs a 6-7 men crew.

(Yes serving in Anti-Aircraft Regiment isn´t the most glamorous job in armed forces…):D

[Legbreaker]

Of course in a T2K type scenario where there are few to no vehicles moving about (even if they are available, fuel might restrict them to just an hour or so of operation a day), the sound of a helicopter will attract a lot of attention. It's something so out of the ordinary that even the slightest indication of their presence will cause people to sit up and take notice, even if just on a subconscious level.

All in all though, it comes back to the individual situation. There's just too many factors to account for.

[pmulcahy11b]

I live in a city with air force aircraft (ranging from small trainers to C-5s), Army helicopters, and commercial and civil aircraft.

(and godammit, they all seem to want to fly over my house!)

I've heard police R-44s and EMS AirLife helicopters that were so far away I've actually need binoculars to spot them. But I could still hear them decently.

I've also seen, but not heard, C-5s and C-17s until they're right on top of me.

As for how far you can hear an aircraft, I think it probably has more to do with air and weather conditions or the terrain the aircraft is flying over than anything else.

Oh, that sterotypical Huey "whop-whop"? That's also characteristic of just about every twin-blade helicopter. Again, air movement and suchlike is involved.

[TrailerParkJawa]

I can't speak to helicopters but San Jose airport is three or four miles from my house. Under certain conditions, I can hear the aircraft bring their engines online as they sit on the tarmack in the morning. Once in a while late at night I can hear the C-130s at Moffet taxing on the runway which is maybe 8-10 miles.

[Mahatatain]

Thanks for all the replies people - very interesting and useful information/experiences. :)

Mahatatain.

[ArmySGT.]

A Huey doesn't fly, so much as it beats the air into submission.

[WallShadow]

Not sure how far, but Radar O'Reilly always had about a 30 second lead on the normal human ear when it came to the incoming wounded.

[bobcat]

drunk and dead tired on the sunday night of a four day weekend in korea i could still ID blackhawks, huey's, and shithooks 5 miles out so it would take an awareness fumble for anything in a helo to be sneaky.

[Graebarde]

A Huey doesn't fly, so much as it beats the air into submission.

I definately like that.. lol

[Adm.Lee]

Altitude may have something to do with volume, the lower to the ground, the louder it gets.

The house I grew up in was under the small-plane landing pattern for the city airport, and an Army Reserve Huey company was based there. If they were climbing away from a take-off, it was a sedate bup-bup-bup-bup. If they were descending for a landing, it boomed a lot louder, echoing off the houses. If they were really low (I can remember on at least one clear day in my side yard, being able to see the pilot's feet on the control bar through the nose glass), the windows rattled, the house shook, and the freestanding bookcases in the living room would rock back and forth. BAMABAMABAMABAMABAMABAM! It could drown out the lawnmower I was pushing.

We felt a small earthquake once and I saw the same bookcases rocking, but couldn't hear the chopper.

Strangely, I can remember once they landed one of the choppers at my elementary school for a special Bicentennial event (remember 1976?), and I don't remember the bird landing in the same schoolyard being as loud as a few of the times they came over my house.

[ArmySGT.]

air temperature affects too

Cold dense air carries sound better.

[Sanjuro]

I get a lot of helo traffic over my house; mostly civilian, a good number of Chinooks passing to the North, plus police, HEMS, etc: the surprisingly quiet visitor turned out to be an AH64D! I guess a lot of work has gone into that rotor to keep the noise down...