Winter Swappables Part 2: Landing Lights

Last year I shared the idea of simple skis that can be easily swapped with the wheels to allow flying from snow. But there are times when it's not enough. Many of us could not take advantage of that simply because of very short days - it's already dark when we are done with our daily duties. Fortunately, there is a solution for that, and we all know it: LIGHTS. What many of us don't know (until they try to land an airplane in the dark) is that seeing the plane is just one part of the equation. The other one is seeing it's surrounding, especially the distance from the ground. In this article, we'll try to learn some basics of both, and find some nice, effective and cheap solution.

(For the impatient ones: the video can be found in the middle of the article)

THEORETICAL BACKGROUND

Most of us already saw an RC vehicle illuminated in that way or another, and we know what's the purpose of that: it allows the pilot to see where the plane is and to recognize it's orientation/attitude. This type of illumination can be established in two ways:

- point light sources, usually steady/blinking LED lights mounted on the surface of the airframe. This category also includes light sources mounted inside the airframe in cases where there is very few of them and they don't lit much of the surface.

- spread light sources, in most cases done in one of two ways: either by using strong external light sources, mounted on a boom/arm and pointed at the airplane itself, or by installing a large number of light sources inside the airframe and making large parts of it "glow".

There are other methods available as well, but those are more rare and usually not as effective. The best examples of such can be found in the RC heli world, where various limitations (weight limit, lack of the actual fuselage) are mixed with an opportunities (large surface of the rotor disc) resulting with unique and spectacular solutions.

But that's not in the scope of this article.

Point light sources work best for showing plane's location. High-intensity light emitted from a small surface can be easily spotted on the dark background, even from quite long distances; and can help with airplane's identification. They are also required for scale airplanes since all "full scale" airplanes have them installed (and for the same reasons). But they are not very useful for the orientation since all you see is "a group of points flying in loose, constantly changing formation". This is where spread light sources come to play. They make the whole plane visible by either pointing a light source at the airframe (often used for large balsa/plywood aerobatic planes), or by illuminating partially transparent airframe from the inside (works best with foam planes). This type of light does not look scale at all, but makes the whole plane visible just like (or even better than) during the day.

There are tons of sources about how to install both point and surface lights all over the internet. I did explain my own way of doing that in the Depron Storch build article, combining both types of lights in one plane to get the best of both worlds. The lights were tested on various occasions, both in the summer and on the snow, and they work great as you can see in the pictures below.

Now there's the other group of lights: the ones meant to illuminate the airplane's surroundings rather than the plane itself. Such lights can be useful for various purposes, but the most common one is to make the landing easier, safer and/or even possible. That's why those are referred to as "landing lights" and usually are installed in a similar way to the "full scale" planes.

This way of installing lights works great for the scale look but is not very useful for their intended purpose. "Full scale" planes are usually way faster than RC planes, and the beam of their landing lights can reach much further and cover much more surface. RC landing lights have to be much less powerful and should have a much wider beam to cover enough space to actually work. The plane type I'm using as a test bed - FT Simple Storch - is almost as far from the real plane as you can get in terms of speed and thus required light beam range. This renders "scale-like" landing lights useless but creates additional opportunities I'll try to describe later.

Two more things need to be explained before we'll jump into technical details, and those are: goals and restrictions. Landing lights are used for two main goals: altitude/glide path assessment and obstacle detection. In "full scale" planes both of those goals are achieved by one light source (or group of those) pointed forward and slightly below the horizon. With the visual clues provided by this light, the pilot sitting inside the cockpit can see everything he or she needs to safely bring the plane down. But that's not true for RC pilot. Due to a different point of view, one forward-facing light source may work for obstacle detection but is not very useful in terms of altitude assessment. For that purpose, RC plane does require a second light source (or the first one with wide enough beam) pointed more down than forward, with the angle adjusted according to the approach speed (slower the plane, the angle should be more vertical). In terms of restrictions: some of them are obvious, like weight and power consumption. But one more thing that needs to be considered is the fact that landing lights should not be too strong to avoid over-shining other airplane lights or even blinding the pilot, especially during the most demanding flight phase: landing.

When you decide to install landing lights on your plane, you need to start with answering few simple questions:

1. Should you be able to turn the light on and off independently from the rest of power system, and if so: in flight (remote controlled) or on the ground only? The answer to this question is obviously related to power consumption and the light output limitation. From the most complex solution to the most simple one:

- radio controlled lights definitely look great. They can also be turned on only when needed, using less energy and thus limiting the impact on flight times. This solution allows them to be a bit on the strong side. Even if the light itself may be too strong to see the plane when staring directly at it, you can mitigate this risk by simply not turning it on when flying straight in. The obvious disadvantage is the wiring complexity, with one more part - RC switch - you need to buy and one more part that can fail.

- manually operated switch is slightly more simple and cheap. It can also preserve the battery when flying during the day. But it can't be used to avoid staring at the bright light, and it also does not provide this "blink factor" RC switch definitely have.

- constantly powered lights are theoretically the most simple ones, but they lack all the advantages mentioned above. This can be improved to some extent by using additional power source (rather than connecting the lights to the main battery), but in my opinion, it doesn't make much sense.

2. What the power and beam angle should be? The answer is related to the one for the previous question to some extent, but in the most part, it depends on the intended use. The power should be appropriate to the range the beam should have to fulfill its purpose. Faster planes need to have the landing strip illuminated way before the plane reaches runway threshold, slower planes can deal with relatively dim lights and still work well enough. Beam angles (both horizontal and vertical) needs to be restricted in two cases: when the light is very strong and can disturb the pilot/observer view or bother spectators, or - on the contrary - when the light source is very weak and you don't want to waste the light going where you don't need it.

3. Where and how you want to install the light source? This is actually the least important and the least specific question, even though at the beginning it may seem the easiest to answer. What you decide at this point determines the limit of light source size and weight, and the amount of work you will need to do to actually perform the installation. But it doesn't have much to do with the actual light performance, and thus the answer can and should be changed if you can't find proper light source that will fit in the original spot.

PROPOSED SOLUTION

My answers were as follows:

1. Radio controlled switch for the landing lights. This is due to the fact that my plane has other lights already controlled by manual switch, and I really wanted the additional "blink factor" :)

2. The light intensity should not exceed my other external lights by much. My plane of choice is very slow and thus does not require large beam range; while I'm going to fly the plane in places where very strong light may actually bother other people. Limited intensity practically removed beam angle restrictions. I wanted to have the light cover almost a full quarter of the vertical plain (from straight forward to straight down), but didn't care much about the horizontal coverage.

3. At first, I wanted to have the lights installed in the wings, but the answer to second question (especially the angle part) combined with the wing structure would make it very labour-intensive and much more expensive. I then settled on the fuselage-mounted lights, leaving the number of light sources to be determined later.

For the switch, I already had Turnigy Receiver Controlled Switch lying around, so this part was a no-brainer.

It was slightly more difficult for the light source. My "orientation lights" are made of "standard led strip" lights, which are using 3528 SMD LED modules (three on each wing tip). That, plus a lot of similar LEDs inside the wings, provide a relatively large amount of light; yet definitely not enough in terms of landing aid (tested in flight). Knowing that, and having some basic knowledge of what's on the market, I decided to look for SMD LED modules intended for car use, most well-known as "LED bulb replacements". What immediately caught my attention was 24x 5050 panel described as "roof/reading light": a flat piece of 24 LED modules designed to operate on a 12v power supply and provide enough light to read in a car, but not disturb the driver. Sounds like a perfect fit for the purpose, so I got two of them.

Originally, this type of light source is designed to provide uniform stream of light in the whole area, distributed evenly for the entire 180 degrees angle in both plains. This task is partially achieved by using diffuser lenses - basically a semi-transparent cover that reduces the intensity, but spreads the light beam. The LED panel itself emits most of it's light in the 90 degrees angle (both plains), with some residual light emitted outside the main beam up to 180 degrees. This is exactly what I need: with two such panels, I can cover the designed area with the main beam and still have the light visible at any angle from the front/down.

The panels came with thick, double-sided adhesive foam, but after removing it, the whole thing turned out to be pretty thin. I decided to glue the down-facing light to the bottom of the fuselage, which did not require any airframe modification other than cutting out the hole for wires.

The forward-facing one was a little more tricky, because there is no surface the light can be glued to. I had to glue in a piece of depron in front and below the firewall to create such surface, making sure it will not make the battery installation more difficult.

I connected both of those lights in parallel, and then passed the wires trough the "electronics rack". The wires were then connected to the manual switch, with the remote switch installed (as instructed) on the positive wire. This way of connecting landing lights make them work only when all other lights are turned on, which is perfectly fine - I don't need to use landing lights when it's bright enough to fly with no lights at all.

TESTING

A couple of tweaking and bench-testing hours later, it was finally the time to test the lights "in the real-life scenario". Luckily, I do have a camera operator "contracted" for all of my test/maiden flights (one day my girlfriend said: "don't you dare flying new planes without me! I want to see them in the air at least once, and you always crash them when I'm not around!"). Thanks to that, I can gladly share the experience with all of you:

I started flying in the early evening just to make sure everything is ok with the plane and the "standard" set of lights is working as expected. I also needed to refresh my skills a bit because I just completed the rebuild of this plane after one unfortunate event (mid-air collision with 3D balsa plane).

After the short flight I made the very first approach and landing with the landing light turned on. It didn't change much at this point because the light was barely visible on the ground, but it definitely looked awesome.

After the second take-off I made one longer flight, trying out some slow precision flying with the landing light on and off to get used to the idea and the look of the plane and the light spot on the ground.

With the evening slowly crawling in, I was still exploring the benefits of having the ground below the plane illuminated - it raises the altitude judgment to the whole new level.

When the night fully settled in, I did some "free flying" with mild aerobatics - again with the landing light on and off - to learn how the bright light source changes the feel and orientation.

Just after that, I made a several take-offs and landings - it was the easiest and most precise landing practice I ever did, even compared with flying with the clear skies during the day.

At the end of the battery (yes, I did all the flying on single charge of 2200mAh 3s LiPo) I tried to make one landing with the landing light turned off...

... but that was a big mistake, so I quickly turned it on again (the frames above and below are less than a second apart).

SUMMARY

Testing results were much better than expected. As you can see above, the solution I choose was more than enough to ensure safe take-offs and landings even at the darkest night. Low power consumption and the ability to turn the lights off mid-air ensure the lowest possible impact on the flight endurance, and the additional "blink factor" cannot be overlooked. The added margin of safety, combined with the low cost and ease of installation makes the landing light a "must have" for everyone who wants to enjoy this hobby regardless of the time of day. Especially in winter, when many of us cannot enjoy the hobby during the daytime.

BONUS FACTS

The airplane used in this project is modified in more ways than the one just described. In the order of significance:

 - main LG supporting struts (the lower ones) are now hinged, allowing much more flexibility for LG legs and thus softer landings;

- tail feathers are removable (!);

- the fuselage is 3/8" / 9mm wider than the original allowing easier battery replacement and improving access to the internals;

- magnetic hatch added to the nose to allow access to motor/ESC connections for easier component replacement;

- large "cargo" opening on the bottom of the fuselage is covered by another magnetic hatch.

All of those are being tested and - if they turn out to be successful - will be described in another article.