Build It: Eindecker

Written by Dick Sarpolus
A simple, fun profile model
Construction feature
As seen in the Winter 2017 issue of
Park Pilot.

Download free plans

Click here for full-size plans 40" x 28"
Click here for tiled plans 8.5" x 11"


Type: Sport model
Wingspan: 37 inches
Wing area: 250 square inches
Length: 28 inches
Weight: 12 ounces
Power system: BP Hobbies BP 12 outrunner; 8 x 4 GWS propeller; BP 15-amp ESC; 3S 1,000 mAh LiPo battery

Construction feature

Dick Sarpolus with the Eindecker.

My longtime friend, Bob Peru, has been active in RC aviation since the days of glass tube radios. He’s always been a scratch builder with traditional materials and techniques. In other words, he makes a lot of balsa sawdust and wood chips.

He’s recently been competitively flying Old-Timer Free Flight RC with ignition engines. That’s why I was so surprised when he told me that his latest project was built from sheet foam and was electric powered—quite a change of pace. Because I’ve been flying a bunch of electric foamie stuff lately, I jumped at the chance to do some flying with his Eindecker.

This little park flyer is fun! Unlike the World War I original Eindecker, this one has ailerons, ample aerobatic capability, and a good power-to-weight ratio for some active flying. With a 37-inch wingspan, it’s not for indoor gym flying but is a good size for a baseball field.

The lightweight model’s good performance comes from the use of a brushless motor and LiPo batteries. Low-priced components are used to keep the cost of this project to a minimum.

The aircraft has roughly 250 square inches of wing area and weighs less than 12 ounces. Depending on the battery used, the wing loading is approximately 7 ounces per square foot, which makes for easy flying. This Eindecker isn’t for aerobatic 3-D fliers, but it’s also not for slow, stable, cruise-around pilots. This aircraft is more for aerobatic, fun park flying.

The brushless motor used is a BP Hobbies (bphobbies.com) BP 12 outrunner with an 8 x 4 GWS (gwsprops.com) propeller. The ESC is a BP 15 amp. There are plenty of small, low-cost, lightweight servos on the market these days. The ones used in this project were Blue Bird (blue-bird-model.com) 306s.

The Eindecker uses an inexpensive power system and radio gear, but provides a lot of enjoyment in flight.

There are several small, lightweight receivers from which to choose. Bob used a Blue Bird receiver with his Futaba transmitter, and a 3S 1,000 mAh LiPo battery pack for power.

Building instructions are brief because this is an easy project. Any of the popular sheet foam construction materials can be used, such as BP Hobbies foam, Midwest Cellfoam 88, Depron foam, or blue fanfold insulation foam. The parts are cut to shape with a sharp modeling knife and/or a razor blade.

The fuselage is made up of two foam layers for more rigidity, and Bob used a spray-on contact cement to laminate them. The wing is perfectly flat—no undercamber and no dihedral—with a 5mm carbon-fiber tube epoxied in place as a spar. Be sure to sand the carbon-fiber tube well so the epoxy holds.

All of the needed foam parts are cut to shape with a sharp modeling knife and are ready to start building.

The leading edges of the ailerons, rudder, and elevator are beveled for hinging, and clear packaging tape is used on both sides as hinges—a popular and proven method. A small plywood firewall is epoxied in place for the motor mounting.

Holes are cut in the foam for the servos, and they can be retained with a few drops of hot glue. Commercial small, lightweight nylon control horns can be used, or you could make your own from thin plywood. Control linkages are thin wire pushrods that attach to the elevator and rudder using a few short pieces of plastic tubing as guides. The ESC and receiver are mounted with Velcro tape, and the LiPo battery pack is also held in place with Velcro.

The wire landing gear is held in place by wrapping it with some thread, applying glue to a small block of wood, and then gluing the block into the foam fuselage with epoxy or hot glue.

Any lightweight wheels can be used, but they should be fairly large if you want to fly from a grass field. This Eindecker gets off of the ground quickly and easily. If the grass is too high, hand launching is easy.

The final finishing could be done a number of ways. Most construction foam for projects such as this is white, and some World War I-style German insignia crosses could be cut from vinyl or low-temperature iron-on material and applied. Bob chose to finish his Eindecker with sprayed-on red enamel. Be sure that the paint you use is compatible with the foam. Water-based acrylic craft paint could also be used.

Dick chose to paint the model using red enamel, which makes it easy to see in the air.

I’ve flown this little Eindecker with 7 x 6, 8 x 6, and 8 x 4 propellers. Performance is good with all of them, but the 8 x 4 might be best. It pulls well and high speed isn’t needed. The motor on the 3S LiPo battery pack draws roughly 9.6 amps and provides approximately 90 watts—plenty for lively performances.

For small, easy-build projects such as this, sheet foam has been adopted by modelers as an alternative to traditional balsa. Hey, whatever material is used, I know flying these airplanes is fun and that’s what it’s all about.

Try a little WW I Eindecker for some up-to-date flying fun!

--Dick Sarpolus




Looks like fun! One question -- what thickness is the sheet foam used for construction of this plane?

Hi Mark! Here is the response from the author, Dick Sarpolus:
Answer - Insulation foam at places like Home Depot or Lowe’s is usually available in ¼”/6mm thickness. Sheet foam sold through hobby dealers is usually available in 5mm thickness, sometimes 6mm. Either 5mm or 6mm/1/4” foam will be fine for our airplane modeling. For reinforcement we can use 5mm or 6mm fiberglass tubing, or basswood or spruce strips of the same thickness as the sheet foam. Even if the wood is slightly thicker than the sheet foam, the planes will fly fine.

For the airplane shown in the article, Bob had used ¼” thick foam intended for house insulation. It worked fine.

Good luck with your project!

I do not know why people think motors provide or produce watts. Motors produce rotational energy. Wattage is the base amount of energy "consumed or used" by electrical motors.
As an electrician I can provide insight into this.
For the above mentioned plane you state the motor draws 9.6 amps on a 3s li-po pack. For the said amperage and using a 12 volt nominal voltage this equals 115.2 watts of electricity consumption. Now if you are happy with that amount of thrust and do not want more or less, you can change your battery voltage up or down and determine how many amps the motor will need. Remember if the motor is effecient, the wattage will be nearly the same. I say nearly, because I have yet to find any brand or size of hobby motor with efficiency above 95%. Say you only have a 10 amp ESC and need the same thrust you will divide the wattage by amperage and get the needed voltage.
So with the motor needing 115.2 watts divide that by 10 amps and you find you will need a battery that can provide 11.52 volts minimum for the full 10 amp esc capacity. Since we don't like to run anything at maximum capacity it would be better to use a 4s battery. 115.2 watts divided by 14.8 nominal volts and you get 7.78 amps.
To make a long boring and poorly worded example simple, MOTORS PRODUCE NOTHING MORE THAN ROTATIONAL MOVEMENT, NOT WATTS.

If a motor does not provide power to the propeller than it is 0% efficient. I am very interested in the power output of an electric motor as that implicitly include the efficiency of the motor. (and ultimately the system efficiency through the propeller as well - a four prop climbs faster but a three prop will move faster in level flight. Each is more efficient in different work situations, right?)

A watt is a simply measure of power. A great example is a manner in which electric cars are rated in both horsepower and watts, A watt is equivalent to 1.341 × 10^–3 horsepower. This power is translated to work by the wheels on the car, through the drivetrain, or the propeller on an aircraft.
To further clarify a joule is the amount of energy "consumed or used" by electrical motors, or any machine. A watt is the RATE of energy use - a joule per second.

It seems that the writers are forgetting one function, which is that amperes are the result of the voltage being applied divided by the resistance of the load. The resistance of the motor is a constant at a given speed (RPM) with a specific load (prop diameter and pitch). Therefore, increasing the voltage, (or increasing the load) will increase the amperes, thus increasing the wattage drawn by the motor. Let's assume that 10 volts being applied by the ESC results in 8,000 rpm with a given prop. The current drawn by the motor
is 15 amperes, which is 150 watts (10v x 15a). This makes no difference if the source is 11volts, or 14 volts. However, note that with the 11 volt source, the ESC has to absorb the difference, (11v. - 10v) x 15a=15 watts. With the 14 volt source, set for 8,000 rpm, this becomes (14v – 10v) x 15a = 60watts. So by the foregoing you can see that increasing the source voltage will increase, not decrease the wattage drawn by the motor/ESC circuitry. As an aside, note that with both cases, the ESC being set for the 8,000 rpm load,the amperage drawn will be the same, so flight time will be the same if both batteries have the same madc rating. When does one increase battery voltage (S )? Reducing excessive ground runs for take off, or higher airspeed required or desired are the two main reasons, just be sure you stay within the ESC and motor wattage and voltage (s) ratings.

Good morning, I went to the BP Hobbies and wanted to order the BP12 out runner motor and BP15 amp ESC and I couldn't cross reference those parts. Have you more detailed specs. on the motor and esc?

Looks like a winner!

Any angle on the firewall to compensate for torque?

Any thoughts on using a "Kline-Fogleman" airfoil design? Step on top of wing - about 1/2 chord length.

My Eindecker flies beautifully! However, I have damaged it twice while landing in uncut grass. The landing gear gets caught in the grass immediately and the plane flips on its nose. I broke one prop and broke the motor mount off. Both easily repaired. Any thoughts on landing technique?

stall it in.

just try a hay field to brake the inpact and hand launch

Kevin is WRONG. David is CORRECT.
Battery provides energy; which can be converted to mechanical energy (potential or kinetic).

It always bothers me when I see statements like “yhis motor produces (x) watts. A watt is a measurement of energy consumption. IE 1 watt =1 joule per second 1W = 1J / 1s. To say that something produces a watt to me is wrong. To say it consumes is more correct. This comes from over 40 years as an industry certified professional electronics engineer. :-)

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