CHAPTER 8
Make Your Plane Look Good at Night
Night flyers are entities with a super powerful impact on human perception. There has to be some vestigial part of the human brain that harkens back to when we were tiny mammals very worried about what might swoop down from the night skies and eat us. In Manhattan, an alien portal to dimension X could open on Broadway, and people would assume that it was just some marketing stunt—but fly a bit of electroluminescent wire (el-wire) with a wiggly tail 50 feet up, and you introduce jaded New Yorkers to the notion of awe and curiosity. There’s nothing like it.
Overall Considerations
There are lots of different ways to illuminate an aircraft. Illumination has to satisfy two criteria: (1) It must convey to the pilot sufficient information about pitch, yaw, and roll orientation to control the aircraft, and (2) it must impress anyone watching—otherwise, what is the point? Fortunately, satisfaction of point 2 generally takes care of point 1. Choice of illumination is largely determined by the design goal because the illumination effects of the various technologies are so different. Another consideration is use of autostabilization equipment, which makes night (and day) flying much less stressful because the aircraft will right itself when the sticks are released. Chapter 12 covers this technology in detail.
Major Ways to Illuminate Aircraft
At the night-flying balloon pop competition at the 2012 NEAT (Northeast Electric Aircraft Technology) Fair, all but one competitor used strip lightemitting diodes (LEDs) for illumination. You can already guess that it was the Brooklyn Aerodrome that was the outlier by sticking it out with el-wire, but the visual contrast was remarkable between el-wire and LED lit aircraft. The LEDs could be blindingly bright and very effectively provided wonderful-looking aircraft, but the regularity of the pinpoints of lighting made it very clear that the flying object was engineered. In contrast, the el-wire approach presents as a far more organic shape that cannot help but invoke the biological. The Brooklyn Aerodrome uses both, and Figures 8-1 and 8-2 shows examples of each. Figure 8-3 shows the lighting sources discussed in this chapter.
FIGURE 8-1 The Crystal Towel: strip LED edge-lit polycarbonate night flyer.
FIGURE 8-2 Flying Jelly Fish: el-wire-illuminated night flyer.
FIGURE 8-3 Various sources of light: 3-millimeter LED, 5-millimeter LED, Acolyte battery-powered LED, strip LED, 2.5-millimeter high-brightness el-wire, 2.3-millimeter standard-brightness el-wire, 1.2-millimeter angel-hair el-wire.
Color at Night
Because of how the human eye is constructed, some colors are much more clearly perceived than others at night. In my experience, green really pops at night, with yellow and aqua following closely. Less effective are blues and reds. White light is not particularly effective, but it is fine for 100 feet or less.
Electroluminescent Wire
The most effective overall solution for night flying is electroluminescent wire (el-wire) in my experience. It looks like thin neon. It is difficult to solder but very flexible and really adds the “alien” to “alien abduction craft.” In daylight, el-wire is hardly noticeable, but at night it is a different story. I have flown planes at Burning Man where people saw them more than a mile away and ran to find me. The only downside is that soldering el-wire is a considerable hassle. Ready-to-go kits are available, but they will not be able to run off the airplane’s power without modification, and modification requires soldering.
How El-Wire Works
El-wire is made from a phosphorescent coating applied to a core conductor wire with two very thin excitation wires on the outside of the phosphor (Figure 8-4). On application of alternating current (ac), the phosphor coating glows in ultraviolet blue. This color is the source of all el-wire colors. To get other colors, the enclosing sheath is made from various wavelength-sensitive dyes that convert to white, reds, yellows, oranges, and greens.
FIGURE 8-4 Properly stripped el-wire ready for soldering. Visible are the outer sheath, inner sheath, two fine excitation wires, phosphor coating, and exposed inner wire.
The only sizes of el-wire we use at Brooklyn Aerodrome are the 1.2- and 2.5-millimeter High Brite from coolight.com at about $1.50 a foot. You will want at least 12 feet, preferably 8 feet of one color and 4 feet of another.
Powering El-Wire
El-wire requires an inverter to apply the appropriate ac current. The inverters have a broad range of input voltages and lengths of el-wire they will drive. Length estimates are based on the 2.3-millimeter size. Inverters tolerate overdriving (more wire than rated) better than being underdriven (shorter than specified). Leaving an inverter powered up for long periods of time without a load from el-wire will destroy it. The brightness of the el-wire depends on the voltage of the inverter’s output as well as its ac switching rate. An output of 2 kilohertz is considered on the bright side of the distribution at 125 volts. If you touch the bare power coming from an inverter, it will shock you quite solidly, but it is low amperes, so it should not pose much of a danger. Figure 8-5 shows a range of inverters. Coolight.com is our standard vendor for inverters.
FIGURE 8-5 A range of inverters that work with 12-volt input voltages down to 1.5 volts. Lengths that can be driven vary from 15 meters to 80 centimeters.
The Easy Way to Get Night Flying
Ready-to-go el-wire kits powered by AA batteries are available for around $25, and that is the easiest way to get night flying. The Flack should be able to handle the extra weight of the inverter and batteries. Get around 12 feet of el-wire, and look at the section on how we route the wire for maximum visibility. A web search should turn up a bunch of options, or check this book’s website for the latest information.
IFW 3294BL Inverter
Choice of inverter depends on the length of wire to be illuminated and available power sources. Our standard inverter is the IFW 3294BL from coolight.com for around $9 that will drive 5 to 15 feet of 2.3-millimeter wire at 1.7 kilohertz. This needs around 0.3 ampere at 5 volts of input. The 2.5-millimeter High Brite wire requires more energy, so we use no more than 12 feet total per inverter for the best brightness. As lengths get longer, the inverter drops voltage, and the wire is less bright. The 5-volt input at low amperes allows for very clean installations because power can be drawn from the battery eliminator circuit (BEC) on the speed controller via unused channels on the receiver, as shown in Figure 8-6.
FIGURE 8-6 Inverter set up to draw power from the receiver and power two lengths of el-wire.
Soldering an Inverter for BEC Power
The IFW 3294BL inverter arrives with a 9-volt battery connector and bare wires on the el-wire side. Do not attach a 9-volt battery to the connector! You will fry the inverter. Cut the 9-volt connector off and save it for future 9-volt battery projects. The tools you will need for this include
1. Wire stripper
2. Soldering iron
3. Helping hands
4. Hot-glue gun
5. Heat gun or cigarette lighter
6. Bamboo skewer (useful for manipulating the delicate excitation wires)
Remote-control (RC) receivers are based on 0.10-inch header pins that can be found at various electronics vendors. A website for the desired headers is www.futurlec.com/ConnHead.shtml. Other sites include digikey.com and allelectronics.com. The male versions are described as 0.025-inch square posts on 0.1-inch centers. Female versions can be found by searching on “header” at those sites. There are lots of options.
All that nice, clean 5-volt power coming from the BEC is mighty tempting for powering the inverter. But do visit the “BEC-Powered Lighting” section below to be sure that you are not overwhelming the BEC. The easiest way to access that power is to use a spare RC connector from a stripped servo. There are also two-pin 0.10-inch female header pins that fit the receiver male pins perfectly from electronics suppliers. I don’t use the three-pin connectors because the connectors with heat shrink tend to be bigger than the slot in the receiver. These instructions assume that 0.10-inch female headers are used. Instructions for soldering inputs/outputs are given below.
Adding 0.10-inch Connectors to Inverter Inputs and Outputs
The typical Flack setup for night flying uses one 8-foot and one 4-foot section of el-wire that we wire in parallel. El-wire can be wired up in series, but nearly every illumination job I have done has had parallel implementations. The steps include
1. Strip and tin the black and red wires.
2. Tin a female 0.10-inch header pin.
3. Solder the black and red wires to the female header, and heat-shrink it all up.
4. Strip the white wires and tin them.
5. Using helping hands, solder two female 0.10-inch headers as shown in Figure 8-7.
FIGURE 8-7 Two female 0.10-inch header pins soldered to outputs of an inverter.
6. Trim any extra wire on the top.
7. Put blob of hot-melt glue on the wires to insulate them.
8. Slide heat shrink over the bare wires and hot melt. Apply the heat gun.
Never run the inverter without el-wire attached or it will burn out. In my experience it will tolerate brief moments without an el-wire load.
Soldering El-Wire
El-wire is tricky stuff to work with, but with patience, it can be done. Matt, our test builder for this chapter at Brooklyn Aerodrome, got all the el-wire done, but it was challenging. I highly recommend that you consult this book’s website for videos showing the process. Take your time, and keep in mind all the cool stuff you will be able to do if you can master this. The following steps take you through stripping the el-wire and then attaching it to the inverter.
Stripping the El-Wire
The most difficult part of soldering el-wire is stripping the insulation off without breaking the two very fine wires that wrap the phosphor-coated inner wire. This can be very tough to do with standard wire strippers and may take many tries before you succeed. Do not cut el-wire to length until you have soldered it because you may lose considerable amounts trying to get it properly stripped and soldered. Below are some techniques to try depending on what kinds of equipment you have.
Option 1: Standard Wire Stripper
The standard wire stripper can work quite well, but it takes skill not to break the fine wires. This works for me about 50 percent of the time. Each failure eats up about ¾ inch of el-wire. Steps include
1. Using a larger stripping size, remove ¾ inch of outer sheath, as shown earlier in Figure 8-4.
2. Using a smaller stripping size, remove ½ inch of inner sheath. It may help to warm the inner sheath with a cigarette lighter. Try to keep the fine wires away from the jaws as you strip to avoid tearing them off.
3. If you get the inner sheath off without breaking the two fine wires, declare success; otherwise, try again. If this goes on too long, try the lighter method below.
Option 2: Using a Cigarette Lighter to Strip El-Wire
This approach should be done with good ventilation because it really stinks the place up with burned-plastic smell. However, it works well and has a high probability of success.
1. Use a stripper to remove ¾ inch of the outermost sheath.
2. Take a cigarette lighter and burn off the inner insulation so that ½ inch of the small wires are exposed. If you are brave, you can get the inner sheath really hot and just pull off the sooty length, but watch out for burning fingers!
3. Gently clean any soot off the fine wires.
This approach doesn’t get much use because option 3 is so effective.
Option 3: Using the Hobbico 2-in-1 Wire Cutter/Stripper to Strip El-Wire
Figure 8-8 shows the tool that gave me back a month of my life by making stripping el-wire quick and painless. I have a nearly 100 percent success rate with it. It works by gripping the insulation with a cutting set of jaws, and then a pulling set of jaws is actuated with a firm squeeze of the hand. Steps include
FIGURE 8-8 Hobbico 2-in-1 wire cutter/stripper.
1. Use the stripper to take off ¾ inch of the outer sleeve.
2. Reposition so that the inner sleeve will be have ½ inch stripped. Try to align the fine inner wires away from the cutting jaws and strip.
3. Be in awe at how easy that was.
The only weakness of this tool is that the handle will break eventually. I use it only to strip, not cut. I have repaired mine with a bit of reinforcement, epoxy, and a coat hanger to hold it all together.
Once you have the fine wires exposed, it is time to solder.
Soldering the El-Wire to Male Header Pins
Next up is how to connect the el-wire using 0.10-inch header pins, as shown in Figure 8-9. There are lots of other ways to connect el-wire to wire that can be found on the Internet, but I find them slow to execute. The way shown here has served me very well over the years in demanding environments. The steps include
FIGURE 8-9 El-wire soldered to 0.10-inch male header pins.
1. Scrape off ¼ inch of the phosphor coating on the inner wire of the el-wire with a knife, wire cutters, or whatever works for you. The wire needs to be completely clean and shiny.
2. Break off a section of male header pin with two pins.
3. Insert the one side into a female connector, and place in the helping hands. The female connector helps the male connector keep its shape when being soldered. This is the same trick I used for soldering the battery connector in Chapter 3.
4. Tin the exposed posts of the male connector.
5. Put el-wire in the opposite jaws of the helping hands.
6. Tease out the two fine conductors from the el-wire, and put them off to the side. I find that a bamboo skewer helps with this. You also should tug gently to verify that the wires are still attached.
7. Tin the core wire.
8. Solder the core wire to one of the header pin posts.
9. Solder the fine wires to the other post.
10. Inspect the wires carefully to ensure that both fine wires are soldered and that there is not a short circuit between the core wire and the fine wires.
11. Put a blob of hot-melt glue on the solder joints and extend it down to the insulation, as shown in Figure 8-10.
FIGURE 8-10 Hot-melt glue applied to a new el-wire joint. The next step is to slide heat-shrink tubing over glue and shrink it all up.
12. Quickly, before the hot-melt-glue cools, slide heat-shrink tubing over the header pins, and squish the glue around a bit.
13. Apply the heat gun to shrink the heat-shrink tubing. Ideally, you should see a little of the glue ooze out the back. This will make for a very strong joint.
Always test the inverter and el-wire before attaching them to an airplane. It is much easier to debug problems on the bench than on the airplane. Steps to vivify the el-wire include
1. Insert the el-wire leads into the female header pins on the output side of the inverter (white wires). Since there is no polarity, there is no way to screw this up. The one mistake you can make, but not a disaster, is to put one el-wire onto one output lead and the other onto the other output lead, thereby not creating a circuit.
2. Connect the direct-current (dc) power side of the inverter to a spare channel of the receiver. Make sure to get the polarity right, or the inverter may be fried. Brief moments of incorrect polarity do not seem to hurt the inverter, however.
3. Power up the airplane, and the wire should light.
That’s it! Time to decorate the airplane.
Simple Decoration
Make up a 4- and an 8-foot length of High Brite 2.5-millimeter el-wire in contrasting colors. If you only have one color, go ahead with what you have on hand. The suggested placement conveys plenty of orientation without needing color. Figure 8-11 shows a typical installation of the inverter and el-wire. Things to note are that the inverter has zip ties protecting against the direction of crashes, as was done with the receiver and speed control, and the connectors between the inverter and el-wire are well secured with zip ties on both sides of the connection. Also be careful not to make the el-wire turn too tight a corner. The minimum diameter of a turn should be ½ inch, or you risk cracking the phosphor coating, which will short out the entire length of el-wire and keep all el-wire from the inverter from illuminating.
FIGURE 8-11 Inverter is powered from the receiver. El-wire starts at the stabilizer.
Figures 8-12 and 8-13 show Bill Suroweic’s technique of attaching el-wire. It works very well as a way to convey the airplane’s orientation and looks great in the sky—the key bit is to have a strand of el-wire go across the tops of the stabilizers. Note that the el-wire is “sewn” through the various surfaces. I prefer this approach for the simpler airplanes because the el-wire stays put better than if tape is used. It also can be done very quickly.
FIGURE 8-12 A good distribution of el-wire for beginners developed by Bill.
FIGURE 8-13 Better-lit version of the Flack rigged according to Bill.
Next up is the world of LEDs.
LED-Based Approaches
Light-emitting-diode (LED) technology is advancing continually at a brisk pace. The simplest is a single-point LED, followed by strips of LEDs and high-power LEDs that can be used to overdrive optical fiber for beautiful flowing effects. The intense points of light are not as compelling on their own. For example, the Crystal Towel (shown in Figure 8-1) gets much of its visual impact from the reflections in the polycarbonate wing rather than from the LEDs in the edges by themselves. Done correctly, though, LEDs can really make a flying object pop in the sky. Let’s start with the simplest approaches.
Single-Point LEDs
When most people think LEDs, they think of the lights shown in Figure 8-14. These LEDs are very cheap (10 cents each) and easy to work with. If the desired effect is the navigation lights found on full-scale aircraft, then LEDs are an excellent choice. Early Brooklyn Aerodrome night flyers had single-point navigation lights that mirrored full-scale aviation lights for night flying. We have since found that well-articulated designs provide more than enough information about orientation of the airplane for night-flying control.
FIGURE 8-14 Navigation lights using single LEDs.
LEDs run off dc voltage, and they require current-limiting resistors to prevent their burning out. The formula for calculating the required resistor is
Resistance = (power-supply voltage – LED voltage drop)/LED current
Typical values for running off the BEC are 5 volts for power-supply voltage, 2.4 volts for LED voltage drop, and 20 milliamperes of current, yielding a needed resistance of
(5 – 2.4)/20 = 0.13 ohm
If the calculated resister value is not available, pick the next-higher value. There are many online calculators for calculating the resistor values. You can wire them in series, in which case you add the drop voltages. Two of the preceding LEDs in series would not need a resister at all.
Battery-Powered LEDs
The simplest version is an LED attached to a watch battery. LEDs are so power-efficient that they will burn for days off a watch battery. They are available commercially at www.wholesaleflowersandsupplies.com/reusable-floral-led-light-III-safety-light.html for less than $1 each, and they turn on and off. There are do-it-yourself (DIY) sources that provide the raw materials as part of the “throwable” culture where magnets are included for urban “decoration.” Do a web search for “LED throwies” to go this route.
A major advantage of the watch-battery power source is that the LED stays on no matter what happens to the airplane. I have used them as backup lights that will not turn off if the battery pack is knocked off on a hard landing or crash. This is very useful for airplane recovery if you are flying in large, open dark areas such as Burning Man.
Strip LEDs
Figure 8-15 shows strip LEDs up close on the Crystal Towel refracting off the polycarbonate flutes in the greenhouse roofing from which it is made. The best prices to be had are from e-Bay or direct import from China, which can be as low as $2 per meter from http://www.aliexpress.com. The good prices start at 5-meter-long rolls, and the range of choices is truly impressive. Strip LEDs can be impossibly bright to look at directly for any period of time, and their uniformity makes them look like Christmas lights. The strip lights are only really flexible in one dimension but will tolerate limited twisting and no flexibility in the width of the ribbon.
FIGURE 8-15 Strip LEDs reflecting off 6-millimeter polycarbonate.
The only issue around the use of strip LEDs is that they require 12-volt power, drawing 2 to 4 amperes for 5 meters, which, in turn, requires a three-cell lithium-polymer (LiPo) pack to power. The voltage range will be from 12.6 to 9.0 volts, which I have found sufficient to keep the strip LEDs lit. There are a couple of solutions to consider:
1. Have separate three-cell pack with sufficient capacity for a few flights. If the power draw is 2 amperes per hour and flights are 6 minutes, you can expect to draw 200 milliamperes. With some margin, a 300 milliampere-hour three-cell pack could work well. Note that there is no overdischarge protection built into this system, which is one reason that I generally avoid separate power.
2. Convert the airplane to three-cell operation, and draw from the flight battery. The extra voltage will translate into more revolutions per minute for the motor. You may be able to keep the two-cell motor if the prop size is dropped by 1 or 2 inches. Check the motor for overheating. Otherwise, get a lower-kilovolt motor, which turns the prop more slowly per volt supplied. Power from three cells is my preferred route for strip LEDs because there is no danger of overdischarge, and every time I fly, I know that the power to the LEDs is from a battery that should be freshly charged. Even if a discharged battery is used, the motor will shut down before the lights go out.
High-Power LEDs and Fiberoptics
I was introduced to high-power LEDs by the costume artist BriteLite. I have collaborated with him over the years, and his current bleeding-edge technology is high-power LEDs focused into fiberoptic cable, as shown in Figure 8-16. There is a very high-power LED that has all its light driven into a bundle of fiberoptic cable that leaks light from the sides of the fiberoptic strands as well as the intended route of the ends of the fibers. The results are subtle but stunning.
FIGURE 8-16 Details of a high-power LED and fiberoptic cable.
This setup requires 12-volt dc at 0.5 ampere, and the housings need to be in decent airflow. I have yet to use this setup, but I am really looking forward to the moment of creative clarity when my design will take to the skies. Check this book’s website for more information as I learn more about these sources.
Other Illumination Options
The limiting factors in illumination break down to weight, power needs, robustness, and visual impact. Lighting techniques change all the time, so it make more sense to understand these limitations for evaluation rather than to guess where lighting may go.
Weight Considerations
The Flack weighs about 15 ounces and can easily carry 4 to 8 ounces of payload. This then becomes the weight budget for any lighting technology. More weight than this will affect flying performance significantly and generally should be avoided for safety reasons, if nothing else. Another factor is where the lighting weight will be with respect to the airplane’s CG. The Jelly Fish in Figure 8-2 was initially decorated with el-wire tendrils hanging from the elevon hinge line, which meant that as the tendrils moved, they changed the CG, constantly making the airplane a challenge to fly. It was pointed out by Mike Phillips, whom we met at Burning Man, that the CG would be more constant if the tendrils were concentrated at the CG. The tendrils were moved, and we had a much better flying plane.
Any uniformly lit airframe will have the lighting tend to make the airplane tail-heavy because 75 percent of the wings’ surface area is aft of the CG. A heavily decorated Flack will have all nondisplay parts of the lighting (i.e., inverters, extra batteries, etc.) as far forward of the CG as possible to counteract this tendency for tail heaviness. The motor/battery/prop also can be moved forward, which is seen often in our semicircle planes and the bat from Chapter 9.
BEC-Powered Lighting
The BEC from the speed controller typically supplies between 2 and 3 amperes of power at 5.0 volts, which means that we have between 10 and 15 watts to work with from that source. Servos can draw 1 ampere at stall with much less at rest. With a 2-ampere BEC, we keep the lighting-power draw down to 0.5 ampere, and with a 3-ampere BEC, we will allow 1.5 amperes for lighting. It is easy to see whether the BEC is struggling if the attached lighting is flickering when it should not, particularly when maneuvering hard. If the plane ignores control for a second or two when the lights are flickering, then there is clearly a power issue because the receiver is rebooting on low-voltage brownouts.
If you are dedicated to a BEC-driven solution and need more amperes, then get a separate BEC circuit from companies such as Castle Creations, which offers a 10- and 20-ampere BEC.
Robustness
I have tried to use halogen bulbs on airplanes to very limited success because the bulbs kept burning out from hard landings and vibration of the plane. Other fails include single LEDs, which tend to get torn off on landings, and glow sticks, which are hard to attach and don’t give much illumination. A downside of strip LEDs is that they are hard to repair, and el-wire can get stress fractures that will shut down the entire wire. Keep in mind that the airplane lands on its belly and vibrates constantly when evaluating new technologies.
Conclusion
Lit planes look great in the sky, are not hard to fly, and the ability to fly at night increases the amount of time that you can fly. In summer, nighttime is one of the better times to fly in parks in Brooklyn. It is also an exciting time to be creating night art because of the innovations that are coming to lighting, and a bit of awe and curiosity is a great gift to a jaded world.