"Since the beginning of time man has dreamed of flying". How many times have you heard that one?! Too many? As overused as it may be, IT'S TRUE! I don't know about everyone else, but since the beginning of my time I've dreamed of it, and re-dreamed of it, and... There's only one major problem (other than it being too expensive for the average Joe), it's loud and polluting (alright, so that's three problems). To me, real flying is the kind birds do, silent, graceful, and natural (much like the solar powered Challenger at the left, except for the 'natural' part)! But since we weren't born with wings we need some sort of propulsion method, right? Enter the Wright Brothers and the dawn of the age of flight. Without going through a history lesson, let's just say that if it hadn't been for the gasoline piston engine they wouldn't have made that flight. To take a step further, had it not been for the jet engine the US may not have been able to maintain air superiority and consequently the cause of freedom (or at least the cause of oil) throughout the world for all these years. Certainly mass transcontinental travel would be nearly non-existent without the jet airliners of today. Laurels and accolades aside, it is also the most polluting form of transportation. With all the hooplah about auto pollution, the aviation industry had been sneaking by relatively unnoticed. Zero emission mandates for cars in California abounded until one day someone mentioned that a jet airliner produces about as much air pollution as 1 million cars on an average flight! What to do, what to do?! Society as we know it would cease to function without air travel, but continuing with the status quo would eventually kill off everyone from toxic air, and then society would certainly cease to function. It was then that the DOE asked NASA to look into ways to make air travel more eco-friendly. As it turns out, not only NASA, but many other companies worldwide had done research into hydrogen powered aircraft (artist's conception at right) as early as the 1950's.

Can hydrogen really power a jet aircraft?... Hydrogen has been used as rocket fuel since the dawn of space flight. From early research it was clear that jet engines could also be altered to run on liquid hydrogen. Although they're still just as loud, at least they don't spew out toxic gases. Right? Well, not completely. It turns out that the high temperatures inherent in jet-type combustion cause the production of copius amounts of nitrogen-oxides. You'll remember from our hydrogen combustion page that, in hydrogen burning automobiles, various techniques are employed to avoid the high temperatures (above 4000 degrees Celsius). This isn't as easy with a jet engine, but it's not impossible. Already researchers have found ways through fuel injection technology to help the NO2 problem and greatly reduce it's production. Unforturnately, it doesn't seem that NO2 production is completely avoidable. Even so, emissions are still only 20% of that of kerosene burning engines. Other than that, the only other emission is water vapor. At ground level this isn't a problem, but at high altitudes (above 10km) water vapor is a greenhouse gas. This may seem alarming at first, what with all the talk about CO2 and global warming, but on second glance we discover that hydrogen powered jets could easily be re-routed to altitudes lower than 10km. (Hydrogen powered craft produce about 2.6 times the amount of water vapor than a kerosene jet, except the kerosene has a whole bunch of carbon and sulphur added in for fun.) So, with the NO2 problem solved, hydrogen aircraft are indeed the eco-friendly solution we've been looking for, right? Not so fast. Turns out that there are a few technical problems that must be solved first. Principle among those is the large volume that hydrogen occupies. Even as a liquid, hydrogen occupies almost 3 times the volume of kerosene. The upside to this is that hydrogen is also much lighter and has 3 times the energy density of kerosene. These two things together make for a lighter aircraft that can carry greater payload, or extra fuel to fly longer distances, or use smaller engines to reduce noise, but that also have very large fuel tanks (see the odd looking Cryoplane above left). Jet engines aren't the only types of aircraft engines looking to use hydrogen. At the right you can see a piston type aircraft engine called the Larsen Radax (Radial and Axial) engine. It was designed from the ground up to run on hydrogen. It uses what's termed the 'Larsen cycle' which, unlike traditional 2 and 4 stroke engines, is such that every stroke is a power stroke. It has 8 cylinders, 4 opposing pairs on each end, and develops 561 hp @ 2000 rpm while only weighing 250 lbs! All that and it's zero emissions too! It operates on the stratified charge principle which throttles via direct fuel injection and a free-breathing air intake. The geometry is such that all 8 cylinders fire 3 times on each shaft revolution (every 30 degrees) which makes for super smooth and silent operation with virtually no vibration (also due to the use of cam rollers on the pistons). This is an amazing engine and anyone wanting further information may contact the American Hydrogen Association.

So what about electric powered aircraft?... Electric aircraft? Are you crazy?! How could an aircraft possibly be powered by electricity? I was hoping you'd ask! If electricity can drive automobiles and large buses then certainly it can power an aircraft. This is a realm which is diametrically opposed to combustion-based aircraft. An electric aircraft uses an electric motor to turn the propeller and is powered by on-board electrical energy storage such as batteries or solar panels. Electric aircraft have been around for a fairly short time. NASA has been the biggest player in this arena, but the world's record for the longest continuous human-piloted electric-powered flight was held by a non-NASA-ite. On July 7, 1981 Steve Ptacek flew a solar-electric aircraft across the English Channel from Pointoise, France to Kent, England. The plane, the Solar Challenger (at left), was sponsored by Dupont and designed with the help of a Mr. Boucher of Astroflight. One year prior to that, a fellow by the name Eric Raymond flew a solar-electric aircraft, the Sunseeker, on a transcontinental flight across the US (non-continuous). You can see a picture of it (basically a glider retrofitted with solar cells, a Ni-Cd battery, and a propeller) on the cover of the advertised book by Michael Hackleman on the upper right of this page. NASA has also built a number of solar electric aircraft. The Penguin at the right is one of their earlier attempts. More recently they teamed up with a company called Aerovironment to design and build a solar-electric aircraft that could fly at low-earth-orbit altitudes and stay up indefinitely while carrying a payload. These seem to be destined to replace satellites for communications as they are cheaper and far more maneuverable. This is all well and good, but you might notice that these aircraft don't seem to be designed to carry lots of people, nor do they seem fitted to travel very fast. In this you would be right. As any good aerospace engineer could tell you, the challenge in designing any aircraft is to maximize the power-to-weight ratio. The problem with electric aircraft is the same problem with electric cars, the batteries. The motor itself is really no problem as there are many electric motors light enough and powerful enough to power an airplane at typical airplane speeds. The problem is that the batteries have a very low energy density, specific energy or Whr/kg, and in some cases a low specific power too (W/kg). This means the batteries are very heavy and don't store enough energy to power the motor for very long. The partial fix for this has been to use fewer batteries, but ones that have a high specific power (can deliver high currents). This helps the weight problem but makes for very short flights. The other method has been to use extremely light, but strong, materials for the fuselage - such as carbon fibers. SunWater designed, built, and flew a radio controlled electric aircraft (above left) that was built out of carbon fiber rods and powered by Ni-Cd batteries. The plane met all of the design requirements except one, good aerodynamics. This made for flight times of about 5 minutes. Designs with lower drag coefficients achieve much better results. The radio-controlled aircraft market has all but perfected small electric aircraft nowadays. With excellent motors and high capacity batteries these aircraft often achieve greater flight times than their noisy, dirty gasoline counterparts! Not only that, but they are also capable of flying faster in many instances. All this and they're quiet and clean too. Please see a small lineup of commonly available electic RC aircraft below. From jets to flying platforms to flying saucers (see above right), these amazing little aircraft demonstrate the future of eco-friendly flight. You might wonder why we don't see their full-sized, piloted, passenger carrying counterparts quietly flying around our blue skies? It turns out that the batteries don't scale up as easily as the rest of the aircraft does. Making larger motors is relatively easy, but making bigger batteries is another problem altogether. Only recently have high capacity batteries become available in big sizes, mostly thanks to the push from the electric and hybrid car industries. But certainly batteries aren't our only hope! Read on...

The most amazing electric powered flying craft we've ever seen! This RC flying platform is available from Draganfly.

Electric jets are hot items these days! This is an RC replica of the A10 Warthog. It's powered by dual ducted-fan electric jets. This is available from the Electric Jet Factory.

The PicoCopter is the smallest available electric helicopter. Available from Tower Hobbies.

Electric hovercraft, although not exactly aircraft, are super fun to "fly"! Many different models are available from Kinetics.