Not even the Hood Blimp? If it’s not based in Boston then it sure comes to visit often.
You may have a point. The ones I saw landed at Hanscom for sure and I know that they don’t live there. I am not sure where the Hood blimp shacks up when she’s not up whoring around.
Hood Blimp is in Beverly (see post #19).
I can assure you that choppers fly at night and do so frequently – think air ambulance and military. I can also tell you that riding in a military chopper in a combat or maneuver area with ground-support high performance (jets) whooping around is no bowl of cherries, especially under black-out conditions.
Jinx, ain’t you never seen no traffic report on the evening news? 
Half the year it’s already dark when those choppers are broadcasting live feed of the freeways.
I’ve forgotten what sporting event was taking place when we moved to this area but the MetLife blimp cruised the coast line at night; the advertising marquee was lighted and as someone has mentioned, it was kinda pretty.
Helicopters certainly do fly at night. If they don’t – then the local cops have some damn good sound effect going at 11 pm up in the skies above my suburb.
My high school science teacher won a contest and got to go up in the Goodyear blimp. She came back with a bunch of goodies and gave a great lesson on helium and aerodynamics and lots of stuff I don’t remember from 20 years ago.
When I lived in center city Philadelphia I could see the roof of Hanniman (sp?) hospital from my kitchen window. The air ambulance would come and go all hours of the day and night. Neat to watch from the patio we made on the roof.
Why are non-essential helicopter flights allowed at night – or in the day for that matter – over populated areas? I’m thinking of the tourist flights in New York. I assume safety issues are negligible but it’s the noise I’m talking about. They are extremely loud and they go on well into darkness hours, seeming to buzz very near tall apartment buildings. I can only imagine what the noise is like to the tenants because it is bothersome on the ground, wherever you are. You need not be anywhere near them. They’re endlessly and predictably repetitive, increasing their nuisance quotient.
A related question: can a helicopter be made quiet? Why aren’t they?
In my experience non-essential flights are not annoying at all. It’s the essential ones that disturb me. I used to live in L.A. under the traffic pattern to Santa Monica Airport. No worries with the civilians flying around. But at night (there was a curfew) the cops came out. They would orbit for an hour over my neighbourhood. Transient flights are there and gone. ‘Essential’ flights, such as the LAPD looking for a miscreant, are there… and there… and there… Very annoying when one is trying to sleep and has to get up early in the morning! This is my experience and YMMV. But transient flights = not annoying; essential flights = frequently annoying.
Most of the noise from helicopters come from the tail (anti-torque) rotor. Helicopters can be made quieter by eliminating it. But it’s much too expensive a solution for people who rent. The McDonnell Douglas MD-500 NOTAR is very quiet. But not many people can afford to rent a multi-million dollar helicopter. (I did find a 1999 MD600N for just a little over $1.6 million; so you can get used ones that are not ‘multimillion dollars’. 
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Blimps do get more lift when it’s warm.
Not just miscreants. A couple years ago I was in my backyard when the mother next door came out, calling for her 12-13-yr-old daughter. At first calmly calling out, soon she escalated to shouting, then shouting with obscenities. Within 5-7 minutes a helicopter started buzzing around and continued about 15 minutes. The little girl was located – whether by the helicopter I don’t know – at a schoolyard a block away. I thought to myself, “How much, monetarily, did that little incident just cost us, because this woman can’t find her child instantaneously?” Low-lifes I live around.
I’m pretty sure most helo noise is generated by the main rotor. Here’s a linky.(Scroll to ‘tail rotor noise’)
Last summer I heard the distinctive WOP-WOP-WOP of a Huey. In looking any helo in flight you’ll notice that the frequency of the WOP-WOP will correspond with the main rotor speed.
On the other hand:
Note: Blade slap does not always happen. While it is 'helicopter noise, it’s not constant like the rest of the noises such as the tail rotor. From personal experience I can say that blade slap occurs at higher speeds during a relatively shallow descent.
I’ll remember that next time Mr. Huey flies over and the windows rattle a the same frequency as the main rotor and can hear the distinctive ‘blade slap’ long before I can see it.
A tiny Robertson, a ‘Huey’ and H-37 Mojave are all very different.
Most folks dislike high frequency sound the most. Some folks love the sound of ‘Huey’ blade slap. It is the first and last sound you hear as they go over.
What choppers were used for the tests? where was the sound measured? Was it in flight or from the most often position of the usual observer? Piston or turbine engines?
Ever been around a straight pipe H-21 or etc…
I love me ‘big loud round’ engines…
You must live in a safe neighboorhood! Come to Baltimore any night of the week, you’ll see the police choppers out and about.
From my own observations: When I lived in L.A. I could see and hear many types of helicopters. You get so you can say, ‘That’s an R-22’ or ‘That’s a JetRanger’ or whatever without looking up. (Although I always did. At a family reunion a cousin said, ‘You can tell the pilots in the family. Every time an airplane flies over you all look up!’) Different types of helicopters do sound different. UH-1 types seem to always be in blade-slap mode. All of the others, not so much. Anyway, the best way to observe the difference are to observe the same type of helicopter; one with a tail rotor and one without. That is, the MD-500 and the MD-500 NOTAR. The NOTAR is noticeably (NOTARiceably?) more quiet than the tail rotor-equipped MD-500.
I was taught that most of the noise from a helicopter comes from the tail rotor (as has been cited), and I have personally observed the difference in noise from similar helicopters (the MD-500s) with and without tail rotors. But is it the tail rotor itself making the noise? Or is it the interaction of the vortices of the tail rotor and main rotor? (I’ve noticed that Fenestron™-equipped helicopters tend to be quieter than similar ones with conventional tail rotors.) If it’s vortex interaction, and that interaction relies on the presence of a tail rotor, it it ‘tail rotor noise’? And what is ‘noise’? Is it amplitude? Or is it frequency? A low-frequency sound may have greater amplitude than a high-frequency one, but the high-frequency sound may be more annoying and thus ‘noisier’.