Indoor free flight model airplanes can weigh as little 400 milligrams and can be as heavy as 7.00 grams.  These models are powered by a loop of thin rubber strip which can be wound with over 2000 turns, and the flight times can vary from a few minutes in duration to over one hour!  For maximum flight times and consistency, accurate record keeping is important.  The length, weight, thickness, and even vintage of the rubber band motors used is critical in how long the model flies.

F1D is an international event flown in many countries throughout the world, and every two years the Indoor World Championships are held.  Here each competing country is represented by the top three fliers of their country.  These models have a wingspan limit of 55cm, a minimum weight of 1.200 grams, and fly approximately 35 minutes per flight.  Additionally, there is a restriction that the rubber motor shall not weigh more than 600 milligrams.  Because of this restriction, each milligram of rubber band not used results in about 3 seconds of lost flight time.  At world competition level, three seconds can be the difference between first and third place!

To ensure rubber motors are as close to possible to the 600 milligram limit, modelers need to be able to size the rubber motor accurately and quickly at the contest site during the event.  To be able to do this, an accurate scale is needed.  Additionally, because many of the flying sites do not have easily accessible electrical power outlets, if they have any at all, the scale must have the feature of being both battery powered and easily transported.  After trying many types of scales, both of the mechanical and digital variety, a vast majority of the modelers have now settled in on the Tanita 1210-100 as their preferred choice for weighing rubber motors. The Tanita1210-100 offers a 20 gram capacity, double the capacity of the Tanita 1210-50, as well as a .002 gram resolution.  This pocket scale combines all the desirable features needed.  It is very accurate, small in size, portable, and very economical.  All this makes it the perfect match for indoor modelers around the world.

But the scale is not only used for this one event, there are over 30 types of indoor free flight models, and the scale has applications for all of them.  Not all events have restrictions on the weight of the motors, but the weight of the motor is a critical factor nevertheless.  A typical rule of thumb for best performance is to have a rubber motor which weighs between 1.2 and 1.5 times the weight of the model.  So if your model weighs 1.0 gram, then your motor should weigh between 1.2 and 1.5 grams for best flight potential.  Generally a motor which is too light will not provide enough torque, and result in shorter flight times because the model does not climb high enough and lands with too many unused turns.

A common phrase in the indoor community is ‘matching the prop and rubber’.  This means that the rubber motor needs to be sized accordingly to the propeller on the model.  Some models have large slow spinning propellers, and other have smaller faster spinning propellers.  ‘Matching the prop and rubber’ in these cases would mean a short thicker loop for the slow spinning prop, and long thin loop for the smaller faster spinning prop.  Interestingly, the motors may weigh exactly the same, but the length and thickness varies because of the size of the prop being used.  This is why knowing the weight of the motor being used is very important during test flights and trimming, and the Tanita 1210-100 is an essential tool during this process.

After looking at many web sites, Precision Weighing Balances had the lowest cost anywhere for this scale.  They also had the widest selection of scales I have seen anywhere.  Many modelers have a selection of different scales with different capacities and resolutions for use in different segments of the model building process.  For example, the Ohaus SC2020 portable toploading scale offers a 0.01 gram resolution and a 200 gram capacity which makes it excellent for weighing large sheets of balsawood at the hobby shop. The weight of the sheet wood is used to determine the density of the sheet, and is a key factor in the final weight of the model.  The wide selection offered, and the low cost makes Precision Weighing Balances a one stop shop for all our modeling needs.

Additional web sites relating to indoor free flight model aircraft include:

    http://www.indoorfreeflight.com
    http://www.indoorduration.com

    You can also join us on the indoor free flight mailing list on Yahoo at http://groups.yahoo.com/group/indoor/join

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