In response to LEDagent's original question back in the beginning of this thread ...
Snip ON - Author Topic: airplane lights?
LEDagent
- posted 11-27-2001 06:08 PM I live in the city and i constantly see airplanes fly-by at night with their headlights on?
2 questions. WHY do airplanes nead headlights other than for take-off and landing? I can imagine the importance of blinking lights at night...but why headlight?
And what kind of lights do they use? BOY are they bright!
Snip OFF
Just a moment . . . Putting on CFI hat here -Certificated Flight Instructor-
LEDagent,
?#1
You appear to be referring to the aircraft's landing light. Yes, typically these are normally thought of as being used for takeoff and landing.
These are also much easier to distinguish from the lower wattage navigation lighting -FWIW same general configuration as on boats, red = left, green = right, white = rear-.
The landing lights, and on bigger aircraft, the taxi lights as well are used for collision avoidance. During flight training with my students, I generally take a moment on night flight orientation/training to show them just how far away the landing lights can be seen versus just the nav lighting. This makes a major difference in metropolitan areas that have much light pollution from city lights/highways etc. particularily when the observed aircraft is relatively close to the ground.
Many times it is virtually impossible to pick out aircraft from the "light clutter". Before the advent of strobe lights marking airspace obstructions and larger radio towers, it was a bit easier to see the flashing "anticollision white and/or red strobe beacons on the planes, but...
Airlines typically will have their landing/taxi lighting on very early in the approach to landing process. Many times traveling 20 plus miles with them on before landing, and the same for takeoffs. When you're traveling at anywhere from 80 to well over 250 mph indicated airspeed in two aircraft you can have a VERY RAPID rate of closure as can be seen by adding the speed of both aircraft, particularily if they are approaching on rapidly converging courses.
So, a 500 mph closure speed = how many seconds of travel time to travel the total distance of, oh lets say 25 miles to use a night of good visibility and expecting our two intrepid captains to see each other at relatively the same time? Then there is reaction time to consider.
It may take 7 to 12 seconds of reaction time to actually determine that you are looking at an approaching aircraft due to the fact that if it is really coming at you, it will have very little apparent motion relative to those inside the cockpits looking out the window at it. Hmmm, hey is it a plane or is it a star? "...
hey Joe!, lookit 12 o'clock, between the horizon and that funky cloud ..." ticktock, ticktock more reaction time...
Sorry, CFI hat off now
Basically its the same thing now with the ever more prevelant use of automotive Daytime Running Lights or DRL's which automatically turn on the cars headlights when the engine is started.
?#2
Can't really speak about the airline landing lights, but the smaller planes that I deal with use either 12 or 24 volt systems and a reflector type lamp about 3-4" diameter.
My experience is that they have a lamp life of about 15-25 hours of operation, depending upon how many bounces the pilots make in their landings, as well as the amount of vibration in the particular lamp location.
Filament orientation makes a difference as well, generally horizontally oriented filaments seem to last longer than those oriented vertically.
There are some aftermarket light flasher kits which have been through the FAA approval process that allow the landing/taxi lamps to be flash. These also make a marked difference in the recognition distances both day and nightime.
There are some relatively recent developments in the use of HID lighting in general aviation aircraft as well, and I've seen ads for LED'S as nav lamps, although I have not personally been close to either the HID or LED lamps in these two applications.
FWIW there has been a marked increase in sales booths at the Lakeland flyin for electroluminescent and LED cockpit/instrumentation lighting.
Hope this helps.
LH