Sooner or later, every pilot will encounter a situation where something within fails during flight. Even though you may not be able to predict all types of malfunctions, it is important to know some common problems and how to react when a malfunction occurs. Let’s explore some unknowns — electrical and structural failures, pre-flight problems, and common engine issues. While not every situation can be prevented, it is best to be ready for when, and if, they do arise.
It is important to always use good-quality equipment. Today, manufacturers usually list the components they recommend for their specific airframe. These can include heavy-duty switches, redundant battery systems, voltage regulators, and so forth. This is a good place to start but if you have any doubts, seek the advice of other experienced giant-scale enthusiasts.
Generally, I think it’s best to use electrical accessories from the same manufacturer of your radio system so everything is consistent throughout your aircraft. Dual battery packs are preferred to power the receiver with two separate switches and heavy-duty servo extensions throughout the entire airframe. For those that prefer 4.8V or 6V (4 or 5-cell) Ni-Cd or NiMH batteries, a voltage regulator is not needed. Newer LiPo and lithium ion packs require the use of a voltage regulator for power. Using higher amounts of voltage to power a servo will increase the overall torque, if the servo is designed for higher voltages. Using higher voltages with servos intended for 4.8V can lead to servo damage and failure. Always check the specifications for your electrical components and follow the factory-recommended settings.
Also, when it comes to airborne battery packs, you should always charge, cycle and/or balance them properly for maximum performance and lifespan. It is also important to routinely check all the electrical connectors and monitor battery voltage between flights including the engine’s ignition battery. Engine vibration can take a toll on the aircraft, and can lead to electrical components becoming disconnected or fail.
Over the years, I’ve had situations arise where either a battery, or a voltage regulator failed. As voltage begins to decrease, you’ll find that the aircraft’s response is becoming rather sluggish in the air. Should this happen to you, decrease throttle and prepare for an emergency landing. Keep control surface corrections at a bare minimum and once safely on the ground, check your battery voltages. It is not uncommon for one of the two battery packs in a redundant setup to fail. Don’t push a bad situation.
Wing failure and flutter
While building a giant-scale model, it’s important to follow proper build practices to ensure a structurally sound aircraft. Wing panels have to withstand the forces that act upon it during any given flight so don’t take shortcuts with wing construction. Ensure the spars are installed properly. If the plans show the use of shear webbing that connect the upper and lower spars, ensure that the balsa grain is in the proper direction. For the best strength, the grain should be in an orientation that is perpendicular to the spar and not running span-wise. Since giant ARFs have become so popular, I think it is very important to really check out all the critical areas within the wing, and the airframe. If you feel an area on an aircraft appears questionable, don’t be afraid to reinforce that area. Spending a few extra hours reinforcing a spar, a servo mount, or any other area can save a lot of grief down the road.
One summer, while pulling out of a vertical down-line, I experienced “wing flutter” on an all-composite aircraft. The wingtips began to flutter which resulted in stripping out both aileron servos in flight. One servo was locked at full deflection! Immediately, I throttled back and the aircraft began to roll. I was able to stabilize the aircraft while it was in a constant roll and applied the inputs to perform a 180-degree rolling circle to bring the model to the outer edge of the runway. Decreasing altitude with throttle management and various rudder and elevator corrections, I waited for the airplane to be in an upright position and forced it onto the ground. Post flight inspection showed that the wing’s trailing edge and the ailerons’ leading edges had de-laminated in flight. A crack was also evident on the wing at the end of the wing tube. Surprisingly, the fuselage and the tail were in perfect condition! It was difficult to predict this type of failure as the entire aircraft had a full-composite fiberglass, Kevlar, and carbon-fiber airframe. The important thing is to keep flying the plane and don’t just give up.
Far too many pilots have lost their models as a result of having the control surfaces reversed. To prevent this, perform a control surface check before takeoff. Check the direction of each control surface and from behind the aircraft. Don’t perform the check with your plane inverted on a stand. It’s too easy to get confused about what’s up and what’s down. If you sent your radio system in for service, perform a ground check for all your planes using that transmitter to ensure no settings have been accidentally changed.
Finding reversed controls once in the air is a bad thing. Only an experienced pilot can react quick enough and apply the control inputs needed to safely return the aircraft back to the runway. As a tip, let’s say you notice the ailerons are reversed after takeoff. It is crucial to switch to using only throttle, rudder, and elevator to get the airplane back on the ground if it is too difficult to use reversed ailerons inputs.
Gasoline engines have a strong reputation of being reliable. However, proper setup is key for the engine to perform properly. Always ensure the throttle linkage is firmly secured and that the throttle travel volume is similar between the high and the low throttle setting. A reliable idle and a smooth transition to maximum power is also mandatory.
A variety of synthetic oils exist today that have a recommended mix ratio of 100:1. It is extremely important to precisely measure the oil and gasoline quantities. Always go through the proper engine break-in process and if an engine is not performing as desired, don’t attempt to fly the aircraft. Also use fresh fuel and high-quality fuel filters to ensure that debris does not find its way to the carburetor. While all giant-scale gasoline engines will exhibit some level of vibration, excessive vibration is typically caused by an unbalanced propeller or an engine that is inadequately secured. Always check the engine is properly mounting bolts and that the firewall is properly glued in place.
When an engine abruptly quits, you have to react quickly. Get the nose down relation to the horizon and keep the airspeed at a moderate setting to avoid a tip stall. Speed is important! Occasionally, the engine will quit when the aircraft is too far from the runway or too low to the ground. If this occurs, quickly observe the surroundings to find an area that is flat and safe for the model. Don’t try to stretch the approach! Attempt to land the aircraft in that area with a minimal flight speed as it contacts the ground. For a giant aerobatic model, flaring the aircraft at a 20-degree angle of attack before it touches the ground will help minimize any damage.
As an RC pilot, you must always be ready for the unexpected, as a failure can occur at any point during the flight. Try to figure out what’s wrong, make your decisions quickly and maintain airspeed. The best way to avoid problems in the air is to set up your airplane and its equipment properly while still on the workbench. BY JOHN GLEZELLIS