This is interesting, isn't it?

Perhaps this effect should be taken into account during rotor blade design, as it obviously makes helis an easier night target.

There can't be many armies without night sights these days.

Blackhawk Halo
 

The Blackhawk main rotor blade has a fiberglass end cap. Only the Leading edge of the tip cap is Titainium, I was told on my NVG qual course that the lights you see are static discharge from the blade to the dust.
Funny Story, on that same course whilst conducting CCT's at Oakey (Queensland Aust) I eagerly warned my instructor of some inbound traffic that I had spotted far away, feeling quite smitten that I had picked up the moving pos'n lights of the said Acft out of the stars.
I was then informed by my hysterical QFI that the acft did not pose a threat to our operations, as it was in the holding pattern for a approach into Brisbane Int'l over 150kms away.
NVG's very effective..........:eek:

Bigdog1971,

I don't think that your instructor was right that the flashes we see are static electricity. The effect has been recorded several times that I have seen, and is seen as discrete sparks like glowing objects (a whole trail of them to be sure). Static disharge would be firey glow type stuff, like St Elmo's fire.

The blades on Black Hawk are well grounded to the head and fuselage, so charge will not build up unless the jumpers are misinstalled. I'll have our H-60 Chief Pilot communicate with the IP's at the Qual course to understand how they formed the opinion that static electricity is the cause.

Also, the Black Hawk does not have Titanium strips, they are nickle, even on the fiberglass tip caps. Looks like Ti, as it is a dull gray.

I guess the thing I'd like to understand is - Are the Black Hawk and Chinook different that other helos under the same conditions?

there was a huge post about this in late 2001 but I cannot seem to locate it for you. Will keep trying.

Nick,

I think that we "narrowed" down several factors on that last thread:

Airborne Dust density (related to downwash velocity, dust material and airspeed/height)
Dust material
Blade material
Air moisture - humidity

With all these variables, I think only a test pilot like youself could afford the time effort to find out if its different on different machines.:)

I have noticed that the Black Hawk has it heaps, with little dust required. The Chinook obviously has it, but it often seems to require more dust than the Black Hawk, the UH-1 has it but it seems to need heaps of dust. I have rarely, if ever, seen it with a B206. So in short - ******ed if I know!!

:D :D

Edited to add the previous thread:
http://www.pprune.org/forums/showthr...threadid=18985

That is the link (not good with these). other way to find it is to search in rotorheads for Icing - and other wx nasties

If you are brave enough to read through the pages, there is a lot of info hidden amongst the banter.

This is an about face for myself. The previous thread had someone wondering whether this effect lit up helicopters enough so that someone on NVG could find a helicopter that was trying to hide close to the ground. I went with the consensus and thought that there was not enough light to be a problem. I'm now reconsidering.

Two things changed my mind. One was the CNN footage. I was amazed how bright it was. Of course, the cameraman knew where the helicopter was, and was zoomed in on him, so at first I didn't think it was a problem. Then I remembered SAR Coad.

SAR Coad was a mission I was on right after I converted to NVGs. Two guys in a Cessna crashed in highly mountainous area in April. Aircraft was found and two sets of footprints walking downhill away from the crash site. Two problems with this. One, they weren't dressed for it, and two they were headed for a river. That survival thing about following rivers doesn't work in many mountainous areas. The rivers are too carved out and thus too steep for easy travelling. Anyhow, nightfall approaching, their injuries still undetermined and hypothermia is a real possibility.

We got on scene at dusk, donned NVGs enroute, and started searching. One crewmember noticed an unusual flashing light about three miles from our location. Investigating, we found the two survivors and pulled them out with only scratches, bruises, and a little bit cold.

Good story, huh? What does this have to do with blade sparks? The flashing light was a Bic lighter that had no fluid in it. He wasn't signalling us, just trying to get the lighter lit to start a signal fire. We saw the spark of the flint from about three miles through tall trees.

Makes me think that this blade spark show might just provide enough illumination for someone overhead to spot you.

Night Vision Goggles
 

I saw an advertisement by Bell offering a course in the use of NVG's. I'm not thinking doing it, but it got me wondering how they work.
I know the AAC use them - can any mil pilots explain how they work etc.
Bell say low level, middle-of-the-dark-night missions have become routine with NVG's, you 'can literally see in the dark', and night ops can be completed 'nearly as normally' as during the day.
True or advertising blurb?

What are the limitations?

Virgin, a detailed reply to your question would take up most of the pprune mainframe memory so i'll try to keep it short!
NVGs work on the image intensification principle, ie, amplifying light energy. Within each tube is a photocathode which receives the incoming light radiation and after impact, a stream of electrons accelerate away from the photocathode and strike a phosphor screen. The power supply creates an electrical field which produces the means of acceleration. Essentially, the phosphor screen emits light in proportion to the amount of electrons that strike it. When voltage is applied, the electrons brighten creating an image that can be seen.

The current generation of NVGs produce superior amplification of somewhere in the region of 3000 times from the ambient conditions. Good enough for low level flying in low light level conditions of perhaps less than 1 mililux.
Limitations:
NVG performance is directly related to the ambient conditions. they will let you down if there is not enough light!
Bright lights will close down, or whiteout the goggles.
Fields of view are in the region of 40 degs so head movement is important to substitute peripheral vision.
Depth perception can be difficult.
No colour, a green image is tiring.
Wires are difficult to see.

Will that do for now?

A basic page, but fufills your question on how they function.

http://www.morovision.com/howset.html

Virgin -
NVG flight has been the norm for military hels for years now (I believe that they were first used by the French helicopter crews in Vietnam) to the extent that non NVG flight is known as 'reversionary' night flying. It is pretty much true that, if you are a REGULAR user, you can do most things visually at night on goggles. There is no secret to the technology, it is just two TV screens placed in front of your eyes that have had the electrons in the tubes amplified by about a thousand times. In terms of limitations they are bloody heavy, they 'bloom' out if exposed to too much light and they have poor peripheral vision leading to a lack of near field visual clues at low speed/height. The biggest limitation of all however is that a thousand times **** all is still **** all and therefore they will not help you on a dark night over the sea/desert or in the mountains.

:cool:

Night Vision Goggles
 

NVG are excellent aids but must be used wisely and with caution. The number of NVG related accidents amplify this adequately.

I had the great fortune whilst flying low level, solo, on goggles, over the sea from Anglesea to Carlisle, to see the "Northern Lights" on the goggles but not with the naked eye - very spectacular!

I would not go anywhere without them but am very aware of their limitations and mine.

A very wise pilot once asked me to consider what the doctor would say at my next aircrew medical if I told him that my vision was limited to a 40 deg field in varying shades of green...

hh

I believe Devon & Cornwall Police use NVG in their 117? Anyone any knowledge of this?

The D&C BK117 is I believe the only aircraft currently CAA approved for night operations. The Alan Mann Group did the work.

slightly off topic...
 

... but a policeman was sitting beside the A1M (a local motorway) late at night was surprised when two cars flashed by at considerably more than 100mph without lights on a dark night on an empty, unlit road.

Turned out it was local heli pilots from a military base using NVGs to drive their cars in "stealth" mode.

could be an urban myth, but heard it from a usually reliable source.

I've used Litton M949 Night Vision Goggles with ANVIS white LED-based auxiliary lighting system installed in a 206BIII at Bell. They're now using that combination for the factory NVG course.
I thought it was pretty good, but didn't use it on a live mission.
Anybody else used that gear?
Anything out there better?

Main points been highlighted, heavy, poor (no) periph vision, poor depth.

I have had difficulty getting the right focal plane when using them as well - admittedly they were cheap ex-Russian stock, not the modern 3rd gen US stuff - does anyone have any experience of how to look at the instruments (close up) and then at a long distance?

And they bleach badly with a Nite-Sun!!

By the way, does the D&C 117 fly with two pilots, or just one at night?

Anton

NVG photograph through one lense:
 

This will take a while but is worth the wait:



http://www.artistic.flyer.co.uk/nvg.jpg

Anton,

You can't look at the instruments through the goggles. The goggles are focused to infinity, and are used for looking outside the cockpit. It is best to set them about 1 inch away from your eyes, and you look under them with the mark 1 eyeball to look at your instruments. Of course, you need NVG compatible lighting in the cockpit (blue), or the glare will prevent you from seeing anything through the goggles.

Now I was always taught that it is red light that affects night vision the least, so why do all NVG's produce a green image ?

Just an idle thought

Cheers all

NVGs are worth the effort and expense. They make night flying without them downright frightening.
They are heavy at first, however if used correctly, with a good mounting system and the battery pack fitted to the rear of the helmet with a weight bag (max 450gm) you should not have too many problems. Weight bags are a personal option where I come from. If you do it properly you probably won't need one. I don't use one anymore.
The key is to ensure your helmet is a nice snug fit. If you cannot wear your helmet for hours without getting 'hotspots' and general discomfort then sort that out first. Wearing NVGs without a helmet is fraught with frustration and discomfort!
As for the rest of fit, the manufacturer's handbook should be ample advice. Other posts on this thread have covered the salient points. Ensure though that they are focused to infinity.
Flying with NVGs is a perishable skill. Conversely, the more you do it, the better you get. IMHO, to maintain your skills at tip top condition, at least 5hrs/mth. That is the ABSOLUTE minimum. 10hrs/mth would be more realistic. The course would likely be 10-20hrs of ICUS type supervision.
Using NVG with 'white light' eg a NiteSun, is not good. Avoid it as their resolution falls away rapidly. It is better to have an Infra-Red filter over a searchlight of about 250W. The later model NVGs don't flare out too badly around external white light, and work well for urban ops.
Many of the civil authorities appear to have a great fear of legalising NVG, however I believe that those fears are only partially founded.
NVGs are one of the best things around for night ops, have no doubt.

3D, the green monochromatic colour is due to the type of phophor screen used within the tube. A usual after effect when using nvg for extended periods is 'brown eye'. This is evident when you remove the nvg and look unaided. This afterimage is called chromatic adaptation and goes after a while, normally as you get to the bar!