India Class Helpful Information for Teams and Teachers

The Speedfest organizers have compiled some additional information that India Class teams may find useful.  Expect this page to be updated as questions arise.


Advisors, mentors, and team members must make sure they are working and operating their aircraft safely.  It is recommended that advisors and mentors ensure that the teams always comply with the Speedfest Safety Requirements and General Aircraft Requirements.  Even when not at the Speedfest event.


Building Advice
Additional learning ideas for team advisors
How to be more competitive


Building Advice

Before you begin!  Read the complete India class rules page from top to bottom carefully.  Then, read the instructions for the kit from cover to cover carefully.  We receive multiple questions about the rules, procedures, and the kits, that need not have been asked if the team would have done some careful reading beforehand.

Before beginning construction, consider making full size copies of the plans, or at least tracing kit parts to make templates.  That way if you want to build another airframe, or if you need to make major repairs, all you need to do is buy wood, and not another complete kit.  This will be significantly less expensive, and eliminate the need to rely on the continued availability of the kit (which are manufactured in small batches).  It will also allow for mistakes, or the opportunity to have different teams build multiple airframes if you have a large class and want to get more people involved.  There are plenty of places to buy wood for building RC airplanes.  Here is one example.  Here is another.

One source of useful information is "build threads" which are forums where people share their experiences building a particular plane.  It is often a nice way to supplement the instructions.  Also, you may submit questions and comments yourself, and people are often eager to help.  Note that there are different ways of doing things, and all of the information may not be appropriate, but many find it helpful .  Here is a build thread on the Dazzler
http://www.rcgroups.com/forums/showthread.php?t=1403724  and here is another for the Uproar:  http://www.rcuniverse.com/forum/kit-building-121/9228805-tower-hobbies-uproar-40-build.html

If you are new to building RC airplanes, you may like to search for images of different types of covering schemes for the Great Planes Dazzler or the Uproar, to give you some ideas.  Remember to keep it simple until you have some experience covering.

Tips for using Monokote covering can be found here.  You can also find some very helpful videos on how to apply coverings such as Monokote.  If you would like a good DVD for purchase, I recommend this one: "Secrets of Great Covering with Top Flite Monokote" If you are applying covering properly, there should be very little need for a heat gun.  By gently stretching the film when applying it, and properly using the iron (with sock), the film can be stretched appropriately.  Be careful when applying covering film, that you do not warp your wing or tail structures.  The fact that the film shrinks makes this possible.  Also note that if you leave your airplane in a hot car, the covering can sag, and possibly warp.

For larger teams you may want to consider splitting the team up into subgroups.  For example, wing, fuselage, tail, propulsion.  This will allow things to be completed more efficiently, while allowing more people to get involved.  Just make sure there is good communication between the teams.

Single cylinder engines create a great deal of vibration.  This can cause problems for the mounting of the engine.  When attaching the engine to the mount, and the mount to the firewall, use Locktite on the mounting threads to prevent vibration from loosening the mount.  Blue Locktite which is the type that can be more easily removed, will usually be sufficient.

Carefully read the complete manual for the 46LA engine.  There are directions for every aspect of engine mounting, break-in, starting, operating, tuning, and troubleshooting.


Some additional learning ideas for team advisors

The Speedfest India Class project can be considered scalable.  Small teams can compete working after school, and also teachers could incorporate the project into their curriculum as an aerospace engineering project for larger teams.  Small teams may have the time to just complete the kit and perform some basic flight testing before competing.  Teachers of larger teams may want to incorporate more supplemental learning activities appropriate for their classes.  This section is intended to provide some ideas for subjects that will enhance student understanding as well as possibly assist the team with competitiveness.

A word of advice:  Within the RC hobby world, there is a wealth of information.  Unfortunately there are also a lot of myths, legends, and inaccurate science and engineering.  Consider this when searching for information.

The Academy of Model Aeronautics (AMA) has an education section on their website that contains useful information for teachers and students.  The information include such topics as; the basics of flight, scholarship opportunities, grant opportunities, educator materials, etc.

A technique that we have found to be very useful to teams working on competitive projects like this, is to conduct a rules test prior to commencing the project.  A lot of time is saved, mistakes reduced, and team communication improved, when all team members are equally aware of the requirements for the project.

Propulsion
Two subjects in propulsion are key for the India Class planes: engines, and propellers.  The engines being used are examples of 2-stroke, glow ignition engines.  The advantages of these type of engines are: excellent power to weight ratio, simplicity, reliability, and cost.  The only real disadvantage of these engines are that they are not as efficient as 4 stroke engines, and because the lubrication oil is mixed with the fuel, the exhaust is a bit messy.  Neither of these play any factor in racing, and in this they excel.  The propellers that are used are examples of fixed, constant pitch propellers.  There are a several manufacturers of propellers, and a variety of materials used in their construction.

Engines

Internal combustion (IC) engines operate very differently than electric motors.  An electric motor will continue to draw whatever power is necessary to drive the load while trying to maintain a constant rpm.  Conversely, the power of an internal combustion engine is based on the rpm which will vary significantly with the load.  So, on an electric propulsion system, increasing propeller size will increase the power draw, but on an IC engine, increasing propeller size beyond a certain point will actually decrease power.  This is why it is so critical to run a variety of tests in order to select the optimum prop for a particular mission.  The propellers provided with the Uproar kits from Speedfest II were a general purpose propeller, more optimized for aerobatics than racing.

For a given specific propeller, rpm is a direct indicator of power.  As you make adjustments to the engine, measure rpm with a device like this which is called a tachometer or "tach".  More rpm = more power.  See the propeller section for more details.  Do not use the tach in a room with fluorescent lighting or you will get inaccurate readings.

Engines have an rpm operating range.  At the lower limit, the engine cannot continue to turn and develop power.  The high end of the rpm range is the redline limit.  This is the mechanical limit of the engine.  Operation of the engine above this limit will result in engine damage.

Fuel:  2-stroke glow ignition engines require a special fuel  The fuel has a base of methanol, and contains a percentage of nitromethane to increase power.  The fuel must also contain oil to lubricate the engine.  Without this, the engine would overheat and seize.  The oil in the fuel is the reason for the residue that comes out of the exhaust, and covers parts of the plane.  It is harmless, but should be cleaned off of the airplane after each flight.  This can be done with paper towels and a general purpose spray cleaner like 409.  The fuel provided during Speedfest contains 15% nitromethane as well as 17% synthetic lubricant, so no additives are necessary or allowed.

Engine Break-in:  Start with the engine manual.  Properly breaking in the engine is very important and can give you an advantage.  Dont be afraid to run through several tanks of fuel with your engine.  As long as you are not running too lean and overheating the engine, it will help further break in the engine.

Engine Tuning:  Start with the engine manual.  

You can build a small engine test stand to test engines.  This can be a very useful diagnostic as well as teaching tool.  A test stand can be as simple as a wooden frame on which to mount a motor for testing, to as complicated as a full dyno that will measure power.  Examples of simple test stands that you see online, usually are made to measure thrust.  Unfortunately, static thrust is not very useful in determining the power output of the engine.  To measure engine power, you need to measure torque.  This may be done by mounting the engine on a spindle that is free to rotate.  An arm is then connected from the spindle to a scale.  Knowing the force and moment arm, torque may be calculated.  Then by measuring the rpm, power output of the engine is simply calculated.

Engines are relatively inexpensive.  It may be useful to purchase one to take apart to learn how it operates, and then learn how to reassemble.

Propellers

The propeller is one of the most complicated and nonlinear devices on the airplane.  Small changes in propeller can have very large effects on thrust and power.  For example:For safety, it is a good idea to paint both sides of the tips of the propeller a bright color.  This will significantly increase the visibility of the propeller when spinning, and reduce the chances of someone inadvertently putting thier fingers through the blades.

Make sure you balance your propellers using some type of balancer.  An out of balance propeller can cause excessive vibration, and can be dangerous.

There are a wide range of propellers available for radio control airplanes.  They are also made of different materials including; wood, nylon, glass fiber, and composites.  Do NOT use propellers made for electric airplanes in the India class.  They can not handle the vibrations and rotational power pulses of an internal combustion engine.  At least they will be less efficient due to deformation.  At worst, they will disintegrate while spinning, and can be very dangerous.  Here is a link that includes 26 pages of propellers for RC airplanes that you can purchase:  Propellers.  At this scale, even the more expensive composite propellers cost less than $3 each.  Test a variety of propellers made by different manufacturers and different materials.  Start with the propeller recommended in the manual which is an 11x6  (That is 11 inches in diameter, with a pitch of 6).  Test different 11x6 props.  Then you can iterate from there by selecting props with smaller diameter, different pitch, etc.  Dont change pitch or diameter too much at one time.  Make sure to check rpm of the engine to make sure it is not over redline.  The only way you will be able to compare these propellers is to fly with them to see which will give you the fastest lap time.  To make a fair comparison, make sure all other variables during the flight are held constant.  If you are a returning team, you could actually perform these tests early on with your Uproar since the airplane is very similar aerodynamically to the Dazzler.  Once you find your optimal propeller, purchase several of them since they can chip or break sometimes.

Aerodynamics

Since the kit is fixed, significant aerodynamic changes are most likely not beneficial.  However accuracy and care in construction can have a beneficial effect:

Teams should do what they can to reduce drag in order to increase speed.  Properly applying covering material is one way to reduce drag.  Make sure covering is tight with minimal wrinkles.

When sanding aerodynamic surfaces and shapes, take care to avoid discontinuities and other types of bumps or protrusions.  Accurately shape and round the aerodynamic surface leading edges.  Avoid gaps as much as possible.


Structures

Aerospace structures are designed to be lightweight and strong.

Use the materials in a way that takes advantage of the nonhomogeneous nature of wood.  For example, cut the shear webs for the wing spar such that the grain runs vertical.  In this way the structure will be much more resistant to shear loads with no increase in weight.

Follow instructions carefully when putting parts together.  Make sure the fit together well.  Gaps reduce strength of the structure and the adhesive bond.

Make sure epoxy and CA are used properly and cured completely.  It is best to "jig" the structure in some way as the adhesives are curing so that the structure does not deform.

Flight Stability and Control

Make sure that the center of gravity (cg) for the airplane is where the manufacturer recommends.  Take care to accurately measure the CG location.  An aft cg will reduce the stability of the airplane, a forward cg will reduce turning ability.  It is a good idea to mark the required cg location on the airframe so that it is easy to quickly check it.

"Slop" in control surfaces make airplanes more difficult to fly, and can even make the airplane feel unstable to the pilot.  Make sure control surfaces and control actuators are firm.

Control surface throws have a significant effect on how the plane "feels" to the pilot.  This is called "handling qualities."  Control throws that are too small do not allow the plane to be fully controlled.  Conversely, control throws that are too large, reduce handling qualities, and make the airplane too sensitive to input.  Test turn rate by decreasing and increasing elevator throw.   Turning faster will reduce lap time.  Turning too fast will increase drag too much and possibly stall the wing and can lead to loss of control.


How to be more competitive

Some basic rules of thumb