taxi and landing light focal point distances

[wantobe]

I am calculating the installation angles for a taxi light and a landing light. For that I need to know how far ahead of the vehicle I need to focus these lights. I assume the focal point for the taxi light should be closer than that of the landing light, but have no idea what should be the numerical values of these two distances. I think the landing light focus distance should depend on the approach speed, for that my airplane has a 60 knot approach speed. Please help.

[WLIU]

I will suggest that my ideal landing light points right at the numbers as I fly my stabilized approach.

I do not have my Cessna 100 Series service manual handy, but my hazy recollection is that you can fine adjust the lights but the gross aiming is fixed by the way the supporting structure is riveted in place. So if you are building the structure, you likely want to first, set the landing light to be aimed parallel to the aircraft longitudinal axis, and then guess that you will fly maybe a 4 degree approach path, at an airplane attitude of maybe 5 degrees nose up in relation to your flight path?

Digging into the trigonometry text, your line of sight from your cockpit to the numbers is 4 degrees below horizontal. Adding your pitch attitude to that says you might aim your landing light down 4 - 5 = 1 degrees. If you mount the light on your wing, add in the angle of incidence to the calculation. Build an adjustment mechanism that allows maybe 5 or 10 degrees of fine tuning. Check by flying some night approaches.

Now for the taxi light, I want it to show me the yellow stripe on the taxi way maybe 60 feet in front of me. So using some more trigonometry, you will need to look at horizontal and vertical aiming. For the vertical aiming, look at the attitude that your airplane sits at on the ground, how high above the ground the light is, and the distance in front of the airplane that you want the beam center to be. A bunch of triangles to compute and turn into angles. For the horizontal aiming, you look at the triangle that is the distance of the light from the aircraft centerline and the distance in front of the airplane that you want the beam center to be. You can eliminate this calculation by mounting the light on the front of the cowling, but your Piper and Grumman friends will warn you that lights do not last that long at that location due to vibration and maybe engine heat. Better put them out on the wing.

Best of luck,

Wes
N78PS

[wantobe]

I will suggest that my ideal landing light points right at the numbers as I fly my stabilized approach.

you will fly maybe a 4 degree approach path, at an airplane attitude of maybe 5 degrees nose up in relation to your flight path?

Digging into the trigonometry text, your line of sight from your cockpit to the numbers is 4 degrees below horizontal. Adding your pitch attitude to that says you might aim your landing light down 4 - 5 = 1 degrees.


Wes, are you suggesting to aim the landing light 1 degree down relative to the longitudinal axis of the airplane in the above example? I think the current answer is to aim the landing light 5 degree down relative to the longitudinal axis of the airplane, so the light will be parallel to the glide path and reach the numbers.

I appreciate your many replies which help me a lot. By the way, you use a 4 degree glide slope instead of the conventional 3 degree in the above example. Any particular reason behind it?

[martymayes]

I am calculating the installation angles for a taxi light and a landing light.

If it's a homebuilt, adjustments will be through trial and error. Aiming the taxi light will obviously be easier than the landing light. I would just find a comfortable spot for the taxi light, then aim the landing light ~50' in front of that, for starters.

[Kyle Boatright]

I fly a taildragger. The airplane has both landing and taxi lights. The landing light is a narrow beam HID light and is directed parallel to the ground with the airplane in a 3 point attitude. That is perfect for final approach, IMO, and gives very good visibility down the runway as you flare and touch down. The taxi light is a wide angle HID and is pointed where it hits the ground about 50' in front of the airplane with the airplane in a 3 point attitude. It provides a lot of light along the periphery of the landing area and gives a good view for taxiing.

The HID lights give an amazing amount of light compared to the halogen lights they replaced.

[WLIU]

The last post is great info for one type of airplane. What airplane are you talking about. If the original poster has the same type of airplane, he may now know exactly where to start. If he is building a different airplane, it may sit on the ground in a different attitude.

On the topic of 4 degree approaches - If you are not doing the ILS, you will find that the typical final approach following the pilot handbook numbers is steeper. Typically, flying a 3 degree ILS is a power approach. Power off, different airplanes glide more or less steeply. I say that as a guy who flys airplanes with glide characteristics that resemble a falling manhole cover. My power off approaches are VERY steep. Cessnas are sailplanes in comparison. So factor that into your landing light mounting, or don't. Maybe you will always fly a power approach at night.

Best of luck,

Wes
N78PS

[Kyle Boatright]

The last post is great info for one type of airplane. What airplane are you talking about. If the original poster has the same type of airplane, he may now know exactly where to start. If he is building a different airplane, it may sit on the ground in a different attitude.

On the topic of 4 degree approaches - If you are not doing the ILS, you will find that the typical final approach following the pilot handbook numbers is steeper. Typically, flying a 3 degree ILS is a power approach. Power off, different airplanes glide more or less steeply. I say that as a guy who flys airplanes with glide characteristics that resemble a falling manhole cover. My power off approaches are VERY steep. Cessnas are sailplanes in comparison. So factor that into your landing light mounting, or don't. Maybe you will always fly a power approach at night.

Best of luck,

Wes
N78PS


The last post was intentionally generic. The intent was to point out what I want to see when I'm on final, in the flare, and on the ground and how to select and aim lights to meet those needs. The OP should consider what he wants to see in a particular phase of flight and install a lighting system that meets those needs. Mine was a simple example of how I accomplished that.

[wantobe]

I would just find a comfortable spot for the taxi light, then aim the landing light ~50' in front of that, for starters.

If we aim the landing light further than the taxi light, then it will not aim at the numbers during the stable final approach. As an example, Cessna 172's lights are about 3 feet above ground, if we choose taxi light focus point to be 50 feet ahead of the airplane, and landing light focus point 100 feet ahead of the airplane, then the landing light beam will be about 1.7 degree down relative to the longitudinal axis and the taxi light beam will be about 3.4 degree down relative to the longitudinal axis. It will take more than 5 degree down (3 degrees for the glide slope and at least 2 degrees for the airplane pitch angle) for the landing light to reach the numbers during approach. Here I assume the landing light beam as a single line without an angular spread in vertical plane.

Should we expect the landing light to reach the numbers during final approach?

Another question is how does the new LED light compare with the HID light? Anybody tried the LED?

[WLIU]

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

Thanks,

Wes
N78PS

[Jim Rosenow]

Another question is how does the new LED light compare with the HID light? Anybody tried the LED?

We put a PAR46 LED on the 172 last annual. It was an amazing difference from the standard light. Much better from the cockpit on final and everyone on the airport noticed it was easier to acquire as traffic. Went from 16 amps to 2.6 if memory serves correctly. Around $250 from Spruce.

[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.

[Flyfalcons]

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.

Flying at night into an unfamiliar airport, I'd rather be on the proper glidepath (aiming even further down the runway) and have obstacle clearance assured than worry about dropping the wheels right on the numbers.

[WLIU]

The statement "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." doesn't apply in my world. We look at the angle of attack of the wing, its angle of incidence with the fuselage, and then the glide path and where on the runway the glidepath takes us. The horizontal plane is irrelevant and reference to it possibly misleading.

And the statement "I'd rather be on the proper glidepath" is missing information. That glide path is different for a C-150 vs a DHC-6, or a Pitts and additionally depends on the type of operation. I will suggest that any pilot who thinks that there is a one size fits all answer needs broader experience.

After 21 posts, I hope that when the original poster gets the light installed and test flown, he reports what the final answer was.

Best of luck,

Wes
N78PS

[Flyfalcons]

Not really, each runway with visual glidepath lighting has just one glide path, and going below it at night can be hazardous to your health no matter what airplane you're in.

[WLIU]

Well, other folks experience may be different, but unless I am flying the ILS, I can report that a power off, full flap, approach in the C-150, C-172, C-180, C-182, C-205, C-206, C-207, C-208, C-310, PA-28R, King Air, DHC-6, and a bunch of other airplanes all use different glide paths day or night. There is certainly a minimum glide path that keeps you out of the obstacles, but most of us fly a steeper glide path depending on the runway, the aircraft, and how it is configured. And I live on an airport where flying a 3 degree glide path WILL put you in the trees. 4 degrees is the minimum.

Best of luck,

Wes
N78PS

[Flyfalcons]

Understood Wes, that different airplanes glide differently with the power at idle. That has little to do with obstacle clearance at night, where aiming for the runway numbers, instead of the touchdown zone, takes away the safety net of the visual (or instrument) glide slope. That last little bit of ducking below the visual or instrument path to "make the numbers" probably isn't the best idea at an unfamiliar airport at night. If you really want me to list the types I've flown to impress you then I guess I could, but like I said earlier, trees and power lines don't really care what you're in.

[WLIU]

I just realized that reading post #23 that you are talking about big airports with VASI or PAPI. I operate out of little airports that do not have those conveniences. Working in and out of 1900' you do not have extra runway to waste, day or night. You try to fly the same pattern and final day and night for consistency that helps you see if you are going low on the planned profile. A tip - if the runway end lights look like they are flickering, there are trees between you and them.

Folks have different experiences and in aviation it is unwise to assume that the rules of thumb for your environment work everywhere else.

Thanks,

Wes
N78PS

[Flyfalcons]

Wes, I think you'd find I have very similar experience background to you, based on the aircraft types you have listed as flown. As you have stated, if the runway lights are flickering, it means there is something between you and them. Unfortunately in a totally dark environment you have no idea exactly how far away that impediment is. It could be a mile away, or the flickering lights in front of you could be the last thing you see before suddenly hitting trees. In the case of going into runways at night with no visual approach path given, familiarity of the area is the only thing you have going for you. Notice the very important qualifier I have stated in my posts, unfamiliar airports. It's very important to understand the context of my statements. Aiming straight for the threshold at night at an unfamiliar airport is playing with fire. A very important part of my job is to fly to unfamiliar, mountainous airports at night, so I do have the experience to back up my assertions.

[Cary]

I'd like to say this thread is generating more heat than light, but I won't say that. :) However, it does contain some issues which need clarifying.

How you aim the lights is as much a preference thing than an absolute. In other words, different strokes for different folks.
How you safely fly a night approach does not necessarily reflect how you will want your lights aimed. For instance, I said that I like the landing light to pick up the numbers before I begin to flare on final--that's not the same thing as saying that I like to land on the numbers at night, but that's how it was interpreted.
Really bright lights aren't very helpful unless they're aimed in such a way that they show what the pilot needs to see to safely land.
I've suggested to students and BFR clients in past years that staying a minimum of 400' AGL until in a position to land power off is a good idea for safety. When I aimed my landing light so that it lights up the numbers, I took that into account.
Someone said that you'll never use all the runway--but I can think of many runways I've landed on over the years which were short enough that I sure wouldn't want to touch down at the 1000' mark, leaving half the runway behind me.
Having PAPIs or VASIs or an ILS is wonderful, and it's a good idea to use them if they're there, for safety--but they aren't on every runway.

Just some of my thoughts--but keep in mind that the only way to safely land at night is to practice landing at night. Everyone's thoughts here or elsewhere doesn't substitute for being properly trained and regularly practicing night landings.

Cary