Rubber Powered Foam Model Airplanes


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First rubber powered airplane was converted from glider.

Rub3LeftFoam rubber powered plane with propeller made from cottage cheese container.

New 8-3-2015 New Foam with Balsa Fuselage Airplane With Great Promise

Check Out Article Here: Fantastic Foam Flyer

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Video of Test Flight

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Video of Phases of Flight – 75 second Flight

 

 

 

Note:  For details on constructing the airplane refer to the article on this website Foam and Straw Gliders.  I would suggest using a balsa strip 1/8″ thick by 3/8″ wide for the fuselage. Using a bamboo skewer inside of the plastic straw will work for the fuselage but it will be more difficult to attach the propeller assembly.

Refer to that article also for suggestions on how to adjust the airplane.

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Combine a lesson of the basics of flight and practical math in
Basic  Aerodynamics With a Lesson

I am mentioned in this new book available from Amazon:

Components for This Project

Propellers for Rubber Powered Airplane

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Guillow ,Midwest, and Sig propellers with nose piece included. The last batch of propellers purchased from  Sig Manufacturing, I called for volume price on
200.

Most people will purchase a commercially manufactured propeller distributed from Sig Manufacturing or Midwest products. Guillow’s also sells propeller assemblies but these tend to be heavier but they certainly will work well. If you have a damaged Guillow’s all balsa airplane that is damaged beyond reasonable repair that could be a source for a propeller, some of these come with landing gear assembly with wheels. Silver colored Peck propellers are sold from a number of sources but these propellers do not include the nose piece. Some people carve their own propellers from balsa or make a propeller from a plastic bottle.

Rubber Motor

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Rubber strip comes from FAI Model Supply. It can be purchased by weight or in smaller packages. 1/8″ or 3/32″ is the suggested width. For hand winding it is easiest to make the loop to fit from rear of prop shaft to the rear hook with little slack rubber hanging down.
Duration of the Rubber Motor Run
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.


Rubber Width
Rubber strip is sold in a number of various widths but the most useful for use in the foam planes will be either 3/32” width or 1/8” width preference would be 1/8” for hand winding. Rubber strip can be purchased in packages of a certain length or by weight in a box of ½ or 1 pound weight.

Winding the Rubber Band

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

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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.

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Left 5:1 winder  Right 10:1 winder
Winders are commercially available in ratios of 5:1 , 10:1, or 15:1, the 15:1 winder is quicker, but 5:1 winders are generally less expensive.

 

Power Burst of a Rubber Motor
If the rubber motor is wound near the maximum turns the rubber motor will release most of the power in the first few seconds, this has been called the “power burst”. It is possible that two or more times the power of the cruise power is released during the power burst. This is good in that it accelerates the airplane in a climb but often there is so much power that the plane climbs too steeply until it hangs briefly on the propeller and then stalls.
Stretch Winding
To get maximum turns in rubber, the rubber is stretched to a length of 3 to 4 times the un-stretched length. To extend the life of the rubber and for smoother unwinding, the rubber should be lubricated before winding. Many things have been tried but silicone based rubber protectant such as Armorall or Son of a Gun are easy to find and use. The rubber motor is placed in a plastic bag and then the rubber protectant is sprayed in the bag, the rubber is worked inside the bag.

Calculating How Many Turns Can be Wound in the Rubber Motor
The number of turns that can be wound in a rubber motor is proportional to the width of the rubber, Smaller rubber more turns, larger rubber, fewer turns. Charts have been created relating the width of rubber to the maximum number of turns per inch. Multiplying by the length of the rubber motor, the total turns that can be wound into the motor can be found. For sport flying it is better to wind to less than 100% of maximum turns, as the rubber will not lose power as quickly.

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.

129 x 10 = 1290 1290 x .8 = 1032
Can you do the math for 1/8″ rubber, Turns Per Inch is 97?


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.

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Balsa Motor Stick
With the evolution of my airplanes from foam and straw gliders to rubber powered airplanes I decided that using balsa for the motor stick would make things easier. For the rubber powered conversion a bamboo skewer was placed inside of the plastic straw to give it stiffness needed to resist the tension of the rubber motor trying to buckle the plastic straw. This does work but attaching the propeller nose to the plastic straw can be problematic. Balsa wood can be selected to fit tight into the nose.

 

The Sig and Midwest propeller assemblies are 1/8” wide so either balsa strips can be purchased to fit the nose or sheet balsa can be cut into strips. Balsa strippers are available which make the task of cutting the balsa into a specified width easier. Otherwise a straight edge and a sharp blade can be used to slice the widths.

 

Normally balsa comes in 36” long lengths, by using motor sticks 9” long, more can be cut from a single sheet if the motor stick was 10”. My second building session for the rubber powered planes included some younger kids out of close to 30 model planes built the balsa motor sticks were broken in five of them mainly just from handling before the airplane was built.

 

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.

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News Flash 4-22-2015

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

Images of Rubber Powered Foam Plane Activities

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 College for Kids Class Built Plane Pictured on the Right  Balsa Motor Stick used With Foam Plates Flying Surfaces
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 Rubber powered airplanes climbing high at summer camp.  Campers built two planes; FPG-9 and rubber
powered foam plane.

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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

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

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Recently Created Foam and Balsa Plane by Paul Lachance 

New 5-6-2015    Rubber Powered Foam Airplanes in Indonesia

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Riyadi Lembang Pictures from His Blog :  Lembang Aeromodelling

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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

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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

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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.

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

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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

21 thoughts on “Rubber Powered Foam Model Airplanes

  1. Right here is the right web site for anyone who wants to
    understand this topic. You understand a whole lot its
    almost tough to argue with you (not that I personally would want to…HaHa).

    You certainly put a new spin on a subject which has been discussed for years.
    Excellent stuff, just great!

  2. Thanks for the thorough guide. My brother’s physics class had a contest of the longest flying plane and there was one contestant with foam flying surfaces. His plane was a bit slower but flew more stable and floated longer than the others.

  3. Thank you Aubrey for your comment I really need to add to this article with more details and a sample plan. Foam models can really fly well if designed properly.

    Bill Kuhl

  4. Hi,

    Excellent advice and inspiration for helping kids to get into planes. I started as a kid in the early ’70’s buying stick rubber powered balsa planes. I forget the make but they were very light with very efficient propellors, looking like the SIG you show here. The wings and tail were 1/32″ thick and clipped into a simple plastic fitting which slid back and forth on the 1/4″ x 1/8″ medium balsa fuselage for balancing. The duration was pretty good and I used to experiment with making different sized wings and rubber motors. I used castor oil for rubber lubricant. I remember warping the wings and tail using my hot breath to create aerofoil lifting shape for the wings and making the tail turn or lift / dive. Great memories which in the fullness of time took me into a career in science and engineering. Keep up the good work. Steve

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