M2 (oz15129)

About this Plan

M2 (Minimal #2). Simple electric biplane model for micro RC. Uses some foam construction.

Quote: "FLIGHT PERFORMANCE: M2 is the pure definition of a slow flyer. In calm air, it is a stable flyer at slower than walking speeds.The speed needs to be kept up a bit In light wind. I have looped M2 but have not tried any rudder tricks. This plane is for lazy flying and touch-and-gos. My favorite trick is to head it into a slight breeze and 'helicopter' It down. I fly the M2 on 5 or 6-cell packs. The cells from a 9V rechargeable battery (110mAh AAAA) seem the best and provide 3-minute flights. M2 will ROG in about 20 feet unless the battery pack is freshly charged - then it leaps up (the thrust lifts the plane, not the wings). Quickly gaining altitude and then throttling back can provide long flights, as M2 will definitely thermal.

THE M2 IS A TEST BED FOR SEVERAL IDEAS:
• Minimal wing construction with 8 single-surface airfoil.
• Cheap motors, servos and radio gear.
• Bamboo parts,
• Simple, fast construction.
• Hands off flying.

My interest in micro flight began back in the days when we could build our radios from kits. A very light, small aircraft has a grace that is not duplicated in its bigger brethren and brings a different experience to flying. Needless to say, in recent years we have redefined 'micro' flight. Not long ago, my interest in small planes was rekindled, and I was overwhelmed by the intricate construction and the expensive components. I wanted a cheap, easy-to-build plane that I could experiment with.

Using typical framed-up construction or hot-wired foam wings seemed to be overkill for our little planes. Their small scale should be able to take advantage of the inherent strength of all of the downsized components; their slow flying speeds are less critical of the aerodynamics.

The wing is the plane; it provides lift and makes a pile of scrap parts fly. The wing needs shape to accomplish this, but how much strength is needed? Using the inherent strength of wallpaper insulation or Depron (foam meat-packaging trays), a single-surface (modified Jedelski) wing can be made with a few ribs using a leading edge (LE) and spar to provide durability and stability. A trailing edge (TE) is not needed if the single-surface material is sufficiently stiff.

A long wing (long aspect ratio) will need rigging (M1 proved that!) unless a stout, heavy spar is used. A long wing will also tend to warp easily. Two shorter wings (short aspect ratio biplane) of the same surface area may not need rigging and would take advantage of a strong, light spar. The first airplanes in history took advantage of this.

Good motor/gearbox/prop combinations are available for $10 to $20, and you won't cry when the prop breaks or the shaft bends. For the M2, I used a Mini-6 HiLine geared motor, Gunther push-on prop, 2 Cirrus CS-20BB servos, Hitec Feather receiver and Cirrus GFS speed control. Rechargeable cells from a 9V Ni-Cd battery are light and handle current well, and a 9V battery costs only 55. You can charge a 3- to 5-cell pack using a standard wall charger or a larger 8-cell battery pack if need be.

Pull/pull controls are very precise when the distance between the control surface and servo stay consistent (stiff fuselage). A package of unwaxed dental floss will give you a lifetime supply of non-stretch control cable that's strong enough to use for micro applications. Make sure the control horns are at the same distance from the hinge line and are the same width as the servo arm; otherwise, one side will pull more.

A properly balanced plane will need less control input and put less load on the motor. With the light weights and sizes of micro planes, a 1/8-inch shift of battery position can make a marginally flyable plane into a pussycat. Experiment with the CG before you decide that the plane design is unworkable. The weight of the components of a micro-size plane is not always consistent, and the differences are much more significant than in larger planes. The airfoil shape is also more difficult to keep consistent throughout the wing compared with that of a larger plane. This all has an impact on the CG.

CONSTRUCTION: The wing consists of two spars; one also serves as the LE. I took a 1/4-inch-thick balsa stick and cut it at a 45-degree angle to provide the LE for two wings without a lot of sanding to shape. The ribs space the spars apart and shape the foam surface into an airfoil. New builders need to be reminded that most CAs attack foam unless they are designed specifically not to (for example, odorless CA). White glue works well on wood and foam but can take several hours to dry. Hold the front edge of the foam to the LE with a pin. Place a few straightedges across the foam on top of the ribs to hold the foam to the ribs while the glue dries.

The dihedral is provided by the TE stock that you attach the wings to. Bamboo struts that are exactly the same length maintain the upper wing's dihedral. I stripped the struts off of bamboo skewers. The wing is held on with screws for easy transport, CG and incidence adjustment.

The tail is built flat and is covered on one side with foam. The LEs of the elevator and rudder are beveled and have tape hinges. After you've built the tail, glue it onto the fuselage..."

Direct submission to Outerzone.

Supplementary file notes

Article.

Corrections?

Did we get something wrong with these details about this plan (especially the datafile)? That happens sometimes. You can help us fix it.
Add a correction