Types of R/C Planes

Here's some tips on converting a gas kit to electric power .
Below is a sampling of the kinds of electric model planes one often encounters.

Powered Sailplanes

Sailplanes are popular choices for electrically-powered planes since a relatively low amount of power is required to sustain flight. This corresponds to long flight times of 10-20 minutes and more. Some gliders are capable of high speeds and advanced aerobatics, others are designed for seeking and circling in hot air pockets called thermals.

The smallest sailplanes are about 4-5 feet in wingspan and can fly effectively as pure gliders or with .049 engines or 50-100 watt (035 class) motors. They require the smallest radio equipment due to their small fuselages.

The most popular type of sailplane is the 2-meter (6.3 feet) class. This size of plane responds faster to control input than its larger siblings, and is easier to see at high altitudes and is more resistant to gusty wind conditions than smaller sailplanes. Powered 2-meter sailplanes are usually propelled with 05 class motors (100-200 watt).

Standard-class sailplanes are the next largest at slightly over 9 foot wingspans. Sailplanes larger than this are classified as open class gliders. Relatively few of these planes are powered, but could be modified to accept 200-400 watt (15 to 40) electric motors as desired.

Trainers

Although the easiest way to learn to fly R/C planes is through sailplanes, many opt for the more traditional Cessna-like trainer approach. Most trainers are gas-powered, but several kits also come in an electric flavor. Most of these planes are designed for 100-250 watt (05-15) motors and have wingspans of 3-5 feet. They generally fly somewhat faster than the typical sailplane, but still slowly enough for the novice to comprehend the situation and respond correctly. Trainers are generally high-wing planes with flat-bottom airfoils and plenty of dihedral for positive stability and high lift at low speeds. Most good trainers, if placed in an unusual or hazardous attitude, will recover on their own if there is sufficient alititude.

Sport and Aerobatic Planes

After mastering the basics of flight, many modelers seek planes that are less overtly stable than trainers and hence make better aerobatic planes. Such planes range from 3-9 foot wingspans with 100-1500 watt (05-90) motors. Unlike sailplanes and trainers which utilize a flat-bottom airfoil, most sport planes use semi-symmetrical and symmetrical airfoils. This can sacrifice some lifting capability but usually improves handling in gusty wind conditions and during aerobatic maneuvers. The plane tends to be neutrally stable -- they "go where they're pointed"; i.e. they don't self-recover from bad situations as readily as trainers.

Some pilots choose to design low drag planes that will go as fast as possible. Such planes typically have 3-4 foot wingspans and use 200-400 watt motors, reaching speeds well in excess of 100 mph! Some gas kits can achieve speeds of 200 mph. By comparison, typical sport planes fly at 40-60 mph, sailplanes from 20-60 mph.

Scale Models

Exact scale models of all varieties of civilian and military planes are also popular targets for model airplane enthusiasts. Details are easier to implement in larger models, so such planes tend to be above 5 feet in wingspan and have high power requirements (300+ watts). Civilian planes with light wing loadings, such as the classic J-3 Cub, and multiengine models as displayed above, are excellent electric flyers.

Ducted Fan Models

Text and picture(s) contributed by Martin Lagerstedt, etxmlag@kk.ericsson.se

For those who like special challenges, you can model jet aircraft with electrics as well! Electric ducted fan models are a new exiting and challenging part of the hobby. Ducted fan models powered by an electric motor have only been possible for a couple of years. Contrary to typical prop planes, where a "slow"-turning, high torque motor is desired, in ducted fan models high RPMs are needed on relatively few nicads. Fortunately, R/C car afficienados use high speed motors for racing purposes often with "only" 6-7 cells. Also, motors used in pylon racers are also frequently suitable for ducted fans.

Why would anyone want to use an electric motor in a DF plane? There are many reasons! First, the fan unit is usually mounted inside the fuselage -- for a gas plane this often means that you have to have a complex, inaccessable fuelsystem with separate fueltanks. The starting procedure of the motors is more complicated -- which is only compounded if you have two fan units as you must work hard to make both run reliably. All this is solved with an electric motor. The fuel problem is solved by having a battery. There are no problems starting the motors and if you run the two (or more) fan units on the same battery pack and speed-controller they will have the same rpm.

Another reason is the sound! With a gas plane you have a loud engine that does not sound scalelike at all. In contrast, the high-revving motor and its corresponding fan create a sound/scream that is very close to a real jet engine (or vacuum cleaner).

The challenge with electric ducted fans is to get the highest thrust from a fan unit/motor/cell combination. After much experimenting with a variety of fan units from all over the world, now several commercial units are available on the market.

The first commercial unit was designed by David Chinery (editor of the Flying sparks column in RCM&E). He first experienced with hairdryers (yes, you read that right) and different car motors. He wanted to use on-the-shelf equipment and not expensive cobalt motors and 20-30 cells. The final design is called the Jet-elec unit and is manufactured by Morley (diameter 63mm). Experiments with this unit have shown that it is best suited for podmounted application as airliners or in profile models. When mounted in a long duct, too much thrust is lost.

Several fan units from Germany are available in the Speed 400 size. These small but high-speed motors are a great match for small twin ducted-fan models.

Kurt Grosse of Electro Jet Technologies has designed three good fanunits. The sizes are: 400 (speed400 or AP29 and 7cells), 540(540 and 7cells) and Cobalt (300-500 watt motor and 10-14 cells).

Recommendations: The 400 size units and the Jet-elec units are perfect for podmounted models and short ducts. If you want to build in your fan unit in your fuselage or in along duct the EJT 540 and EJTCobalt version is more suitable (diameter 89mm).

If you are interested in electric models and want a challenge and people's attention and admiration at your flying field, then build yourself an electric ducted fan model. If you have experiences or want to discuss electric ducted fan please feelfree to contact me or if you want to do it more public post to the newsgroup: rec.models.rc.air

Martin Lagerstedt
etxmlag@kk.ericsson.se

Helicopters

Image courtesy of Martin Lagerstedt, etxmlag@kk.ericsson.se

R/C helicopters are an interesting aspect of the hobby. Such models can hover and move exactly like their full-size counterparts -- in addition to non-scale abilities such as inverted flight and stunning aerobatics. Relatively few electric helicopters have entered the market due to the short flight times (you can't exactly glide a helicopter). Helicopters tend to be more complicated and costly to build and maintain, a trait which R/C helis also inherit.