taxi and landing light focal point distances

[wantobe]

Help me out and provide the calculation supports the assertion "It will take more than 5 degree down".

If you draw a proper diagram, then it is self-explanatory. In this diagram, you have the glide path line at a slope of 3 degrees. One end of this line is the numbers on the runway, the other end is the airplane. At the aiplane end of line draw two more lines: the longitudinal axis of the airplane and a horizontal line. The angle between the horizontal line and the glide path is 3 degrees as advertised earlier. The angle between the horizontal line and the longitudinal axis of the airplan will be the pitch angle of the airplane at final approach, and let's assume it is 2.5 degrees. Thus the angle between the glide path and the airplane longitudinal line will be 3 + 2.5 = 5.5 degrees. And this is the angle you need to have the landing light down (relative to the airplane longitudinal line) to reach the numbers on the runway.

[FlyingRon]

If you aim your approach at the numbers, you're never going to use the full length of the runway.
Do not assume that the angle of the aircraft on approach equals the glide slope. I can almost assure you that you are at a positive angle of attack.

[martymayes]

If you draw a proper diagram,

Might be overthinking this. Just select a couple points and try them out. Unless you have a spotlight from a tugboat mounted on your plane, you're not going to see much further than ~100 ft ahead of the plane.

[FlyingRon]

Not sure I buy that. Admittedly I have two landing lights but they certainly light up part of the runway further away than 100'. That would mean that I'd only be looking 3/4 of a second ahead of me. Frankly, given some amount of reflectivity on the ground, you can see from much further a way. The rocks off the end of my runway light up pretty bright a half mile out on final.

[martymayes]

Fortunately, the light is moving at the same speed. Low beam on a car shine ~150' ahead. That is usually adequate to drive at 60 mph because there are street lights and other light to aid in seeing. (Motorist on a dark road start reaching for high beams at that speed which double the lighted distance to ~300'). At an airport there's runway lights, surrounding environment, etc. Light plane lands at ~60 mph, usually has one landing light that pales compared to a car headlight, shining ~100' in front of the plane is adequate.

Doesn't really matter if the light is aimed at the numbers when on a 1 mile final cause it don't shine that far. With light we're taking 100's of feet, not miles. I've flown with a lot of folks on a really clear night where they reach final, turn on the landing light, there is nothing within a few hundred feet to reflect light and they think the bulb is burned out cause they can't see the beam.

[Kyle Boatright]

Might be overthinking this. Just select a couple points and try them out. Unless you have a spotlight from a tugboat mounted on your plane, you're not going to see much further than ~100 ft ahead of the plane.

I have HID lights on the RV. Not street legal. Brighter than the sun. The landing light has a fairly narrrow beam.

I did the HID install one winter, so after work one day I took the airplane up for the first flight with the improved lights. It was stunning. From pattern altitude, I was following automobiles down roads known to me, and with the flaps deployed to achieve the proper deck angle, I was literally spotlighting cars on the move. I was at 800 feet, following cars a quarter or half mile ahead, and lighting up the cars and the landscape around them. Just amazing, and probably generated UFO reports. The lights were so bright I was literally laughing in the cockpit.

Anyway, with the narrow beam HID, you can generate a reasonable amount of light out to at least a quarter mile, maybe a half mile.

[FlyingRon]

Car headlight beams have a distance of close 200' at low beam and nearly 500 on high beams. The standard GE4509 has about 2000 lumens output and your 9006 typical car headlight around 1000. So your aircraft landing light is twice as bright and a tighter beam. I don't buy any of Marty's analysis.

[Cary]

Lots of "over-thinking" going on here. The only way to actually aim the lights is to install them, decide what you want them to show, and then go from there. It'll probably take you a number of landings in the dark to aim the landing light so that you like what it lights up. The taxi light you can aim while the airplane is sitting on the ground. Here's how I did it, when I had my IA install HID lights in my P172D some 8 1/2 years ago (these are a pair of lights in the left wing--both on for landing, one on for taxiing):

First, aim the taxi light. Easiest way: park your car next to the airplane with the low beams shining on a flat surface, such as a hangar wall a couple hundred feet away. Then turn on your taxi light and adjust it to match the car lights in height and centered. A couple hundred feet works very well for taxiing speeds.

Now aim the landing light, so that the top of the beam is at the base of the wall you shined the other light on, and center it. Yup, that points it way down compared to the taxi light, but that's what you want for the landing light.

Then go fly. On a 60-65 knot approach, I like the beam to pick up the numbers as I'm still above flaring height. Then as I start to flare, it will light up the runway a long way down, and in the flare itself, it will be a bit high, but the broader beam of the taxi light will make up for it somewhat.

In my case, it took 4 landings before I was satisfied. I haven't re-aimed the lights since that time, and I'm still totally satisfied with how they are aimed.

Cary

[Richard Warner]

This is for wantobe's post: Is that pitch angle the angle of the fuselage ot the angle of the wing taking into consideration the wing's angle of incidence. Actually, trial and error are the only way any of us will be satisfied with the final setting of the Landing & Taxi lights.

[wantobe]

This is for wantobe's post: Is that pitch angle the angle of the fuselage ot the angle of the wing taking into consideration the wing's angle of incidence.

By convention the pitch angle is the angle between the longitudinal axis of a fuselage and the horizontal plane. Usually a pitch angle is of an airplane, rather than a wing.

I am interested in the final installation angles of Cary and others after all their hardworking trial and error. I expect them to be very close to each other, maybe within 0.5 degree.