How long the propeller will spin the propeller before completely unwinding is limited to how many turns can be stored in the length of rubber. This will determine how long the power phase of the flight will be. If the airplane can climb and then level off on with a limited amount of thrust required, the propeller can turn slower and use up the turns slower. Propellers for rubber powered airplanes will normally be larger than propellers that would be on a similar sized airplane using an electric or gas motor which would spin the propeller faster. To fly the airplane on less thrust, the model airplane needs to be built very light which means less lift needs to be created to counteract the weight. The rubber motor can provide a good amount of energy for it’s weight.

The loop of rubber strip that powers a model airplane appears to be a pretty simple power source but without understanding the basics it will not work very well. First if you can select a width of rubber either 3/32” width or 1/8” rubber strip will most likely be used to turn a plastic propeller that is either 5 ½” or 6” diameter. The next decision is how long the loop of rubber will be. It is possible to use a loop that is much longer than the distance from the rear of the propeller shaft to the rear hook which results in the rubber hanging down with lots of slack. With a longer rubber motor which can be 1 ½ times the length from propeller shaft to rear hook this will give a longer duration of motor run. In actual practice with kids this never seems to work very well unless they are using a mechanical winder and doing “stretch winding”.

To wind a longer motor by hand you need to be holding the slack rubber with part of one hand while winding the propeller with the index finger in the other hand until the slack is drawn up. From experience for planes that will be wound by hand it is best to make the loop the same length as the distance between shaft and rear hook. Lubricating the rubber motor will prolong the life of the rubber motor but for most of the workshops I skip this step. To wind the rubber motor spin the propeller clockwise, it is best to count the turns or at least observe the layer of knots that have been created in the rubber. Maybe it is because we live in a digital world but I find the need to clarify that clockwise is to the right. The model airplane does not fly well when it is launched with the propeller trying to push it backwards because rubber was wound the wrong direction.

Another issue which may seem like common sense but kids have a problem with is having the knot in the rubber motor attached to the propeller shaft. It must be on the rear hook, or the propeller shaft will not turn smoothly. Even with the rubber placed correctly it can sometimes move up the loop in the rear of the propeller shaft causing the motor to bind and not spin easily.

Lubricating Rubber Motors

For longer life and better performance of the rubber motor it helps to lubricate the rubber motor. I use a spray used for cleaning and protecting car interiors such as Armorall or Son of a Gun.

Using a Winder
 Although it is possible to wind the rubber motor by turning the propeller with your index finger clockwise, it is much more efficient to use a device known as a “winder”. The winder has a crank that turns gears, this turns the rubber motor faster than you turn the hand crank. Rubber is stretched so that it becomes thinner and more turns can be cranked into the rubber.

 

For example: maximum turns per inch for 3/32″ rubber is 129, for our rubber motor 10″ long, maximum turns would be 1290. For sport flying 80% would result in 1032 turns.

Rear Hook for Rubber Motor
In every rubber powered model airplane there needs to be a method to attach the rubber motor at the opposite end of the rubber motor from the propeller. It is preferable that it is easy for the rubber to be easily attached or detached at this spot but that the rubber does not fall off as the tension slackens. This part of the model airplane is commonly known as the “rear hook”. In kit airplanes this will often come pre-bent from music wire but I normally make rear hooks by bending up paperclip wire. Straight pins can also be bent up although some airplanes show just using the straight pin inserted into the balsa motor stick at an angle.

 

 

 

Using Glue Instead of Tape 

In my first article on Foam and Straw Gliders I showed using masking tape to assemble the glider. This will also work for the rubber powered foam airplanes but it might be better to use some type of adhesive to keep the parts together especially if it is a larger airplane. For the classes I have taught we have used the low temperature hot melt glue guns.  This is hardens fast – maybe a couple of minutes before glue joint is solid but there is the danger of coming in contact with the hot tip of the glue gun or the glue.

 

There are foam safe versions of CA or what is commonly known as “super glue” but this is expensive and can be dangerous.  Model cement types of glue of sold in hobby shops or hardware stores will actually attack the foam.  If glue drying time is not an issue a white glue or the white tacky type of glue sold in craft stores will work.

News Flash 4-22-2015

Check out my new webpage on the Guillow’s Model Airplanes

Images of Rubber Powered Foam Plane Activities

College for Kids Class Built Plane Pictured on the Right	Balsa Motor Stick used With Foam Plates Flying Surfaces

Rubber powered airplanes climbing high at summer camp.	Campers built two planes; FPG-9 and rubber powered foam plane.

Foam Planes on Display at STEM Day at MN State Fair	In Front of my booth at STEM Day at MN State Fair

What Other People are Doing With Foam Model Airplanes

Rubber powered foam airplane by Neil Dennis designer of the Denny Dart series of balsa and tissue covered airplanes.	Denny Dart II in flight, I have had many students build this airplane.

Gary Hinze Sierra Nevada Special check out article from link below.	Foam Squirrel in flight also by Gary Hinze.

Recently Created Foam and Balsa Plane by Paul Lachance 

Ken Achee had grandsons building and flying some foam airplanes.

Links to Additional Information on Foam Model Airplanes

Gary Hinze article on foam Sierra Nevada Special Foam Plane
Gary Hinze VERY Detailed article on Foam Squirrels (Model Plane)
Gary Hinze article Simple Hand Launched Foam Plate Gliders
Darcy Whyte Foam Squirrel Article
Blog Article About Neil Dennis and the Denny Dart
Blog Article on College for Kids Class Using Foam Planes

Want to learn More and Connect With Others on Simple Foam Free Flight Airplanes
Click Here to Join Facebook Group for these types of model airplanes.

 

College for Kids 2014 Pictures

 

Foam Rubber Powered Planes Sold in Stores

Craft stores and hobby shops often sell foam rubber powered airplanes and foam gliders that are easy to assemble.  The main problem I have seen in these airplanes are they are too heavy, the rubber motor provided might not be suitable also.

This planes sold by Estes has full width fuselage but could use more wing area and larger propeller.

This plane from Lyonaeec can be flown as a monoplane or as biplane the motor stick and plastic parts are rather heavy.

 

 Video of First Plane I Built, Rather Amazing How Well it Flies