Engine Break-In
How and why should we break-in our new helicopter engines? That is the most common question asked by everyone who buys a new engine. The responses to both of those questions are somewhat controversial, and everybody has their own method and reasoning for how and why. Just a few weeks ago, I had a hot and intense debate with a fellow RC heli pilot who happens to build full-size car engines for a living about this very topic. The conclusion that both of us came to was that a new engine needs the piston and ring to seal properly, and therefore you need to break in an engine. If you do not break in a new engine properly, you reduce its power and life.
What do I mean by sealing the piston and ring? Well, when you look at an engine sleeve with the naked eye, you see a smooth shiny surface. You see the same thing in the ring and piston, but if you ever look at these three components under a microscope you will see something completely different. You will see valleys, peaks, grooves and imperfections on the ring, piston, and sleeve. During the break-in process, oil will get in these grooves and valleys to allow the ring to glide over these areas as the piston and ring go up and down in the sleeve. While this is happening, the peaks and imperfections are being smoothed out in all three components. This is the goal of breaking in an engine: to create the largest possible surface area of contact between the ring and sleeve. So why do you say this is necessary? Well, the answer is simple. A properly sealed engine will produce maximum power with the least amount of fuel consumption. When the piston and ring have properly seated, they do not allow combustion gases to escape from the combustion chamber into the crankcase where that energy ends up going to waste. In addition to the previous statement, an improperly seated ring will allow too much fuel to get into the cylinder and the excess oil and fuel will be pushed out of the exhaust port, causing the engine to run improperly due to the fuel not burning completely. This, in my opinion, is one of the reasons why people have tuning issues with their engines.
The Basics
To break in an engine I usually fire up the heli and let it idle for one tank's worth of fuel. I keep it as rich as possible to allow for extra lubrication. The reason for this is while the ring grinds away any imperfections, I want the metal debris to be ejected into the exhaust port easily so that I do not have any unnecessary scarring of the sleeve which could reduce compression. The extra oil will also help the engine cool while it's sitting on the ground idling. Once the first tank is almost empty, I shut off the engine and let it cool. During the cooling phase I make sure the piston is at the bottom of the sleeve. This way when the ring cools, it can go back to its normal shape as there is less compression at the bottom of the sleeve compared to the top section. Tanks two through four are just hovered with the engine still running rich. After every tank I make sure the piston is at the bottom of the sleeve during cool off. During break-in, I also check the temp of the engine to make sure it isn't running abnormally hot. For tanks five and six, I lean out the engine just a bit and do some casual forward flying. Once this has been completed, I tune the engine to my liking and consider the engine to be properly broken in.
Step-By-Step Engine Break-In
Step 1: Install a new glow plug in the engine.
Step 2: Fuel the heli with your pump, but make sure to close the end of the fuel tubing leading to the engine with some fuel line clippers. You do this to keep the engine from flooding during the fueling process.
Step 3: As a general rule, you can start with these settings. Close all needle valves and open them back up by turning the high end needle counter clockwise by two full turns, and open the low end by 1 3/4 turns. If your engine features a mid-range needle, it should also be two turns out. This should be a good starting point, but make sure to consult the manual that comes with your engine for specifics. You will adjust this as needed later.
Step 4: Turn on the radio and heli, and make sure that the carb is in the fully closed position while the throttle stick is in the down position.
Step 5: Prime the engine by unclipping the fuel line clipper and turning the engine over briefly without the glow igniter plugged in.
Step 6: Hold the heli by the rotor
blades and put a foot on the skids. Connect the glow plug igniter and start the heli using your starter.
Step 7: Once it has been started, make sure the engine will idle on its own when the igniter is removed. Let it idle like this and use your temp gauge to monitor the temp of the engine. With the settings above, the engine should be relatively cold.
Strep 8: When the first tank is 90% empty, shut off the engine by pinching the fuel line leading to the carb and let the engine cool down. Make sure the piston is sitting towards the bottom of the sleeve during cool down.
Step 9: For the next 3 tanks I start the heli using the above procedures and I begin to hover the heli. If the heli dies when idling, I lean out the low end needle by turning it 1/8 of a turn clockwise.
Step 10: On the 5th tank I am ready to lean out the engine. I turn my low end needle in 1/8 of a turn at a time until I can pinch the fuel line for at least 7 seconds before the engine dies. On the high end, I lean it out enough so that I still see a nice smoke trail during hover.
Step 11: After the 6th tank, lean out the high end a bit more but keep the smoke trail visible. And then have fun!
Note: Some engine run hotter than others, some run best below 200�F while still others may get up to 260�F or more before they make power. Consult you manual for specifics.
CONCLUSION
I do this to all my engines. I have an O.S. 50 that I've had for almost 3 years; it was originally bought for my Hirobo Evo but now resides in my Raptor. It gets about 6 flights per weekend and the engine still runs great. I opened it up this past weekend just to look it over and all seems good. So if you take the time to break in your engine properly over the course of the first few tanks, it should give you long lasting flying enjoyment for years to come.
Tuning For Training
There's no doubt that the RC helicopter industry is one of the fastest growing segments of the radio-controlled hobby world. Not only has the overall quality of kits increased over the years, but prices for "entry level" helis have come down and ARF's (Almost Ready to Fly helicopters) have become a dominant fixture on the heli scene. All in all, it's a great time to get into the hobby.
One obstacle that helicopter newcomers must overcome is knowing whether they have a good setup. A helicopter can be tuned to be extremely sensitive and quick-responding to control inputs (ideal if you're an avid, aggressive 3D pilot), or it can be tuned to feel much more "dead" and deliberate on the controls (which is much better for the beginning pilot). Oftentimes, newcomers to the hobby don't have a clear understanding of how to tune a helicopter's control response, and don't have immediate access to an experienced pilot who can help them sort things out. Thankfully for you--the reader--you have RC Heli magazine!
This installment of Buddy Box will take a look at some of the basic adjustments a pilot can make to his or her helicopter in order to make it a more ideal tool for learning. Three separate categories will be covered: mechanical adjustments (meaning adjustments to the machine itself), software adjustments in the transmitter, and "accessories," meaning additional items that can be purchased for training.
MECHANICAL ADJUSTMENTS
Flybar and Paddles • Proper selection of paddles and flybar tuning will have one of the greatest effects on overall handling. In Issue 9 of RC Heli, we featured an article on the effects of paddle tuning. (This is a great excuse for you to purchase your subscription to RC Heli if you haven't done so already, or you can check our website and download the article.) For a beginning pilot, the name of the game is "stability," so the thicker and heavier the paddle, the better.
For machines like the Hirobo Evo 30/50, the stock paddles allow the pilot to adjust the weight via removable brass and lead inserts in the leading edges of the paddle. If your helicopter has adjustable weight paddles like this, it's best to leave all the weights in while learning to fly. For other helicopters that don't have adjustable weight paddles, the stock paddles are usually on the heavier end of the scale, and are suitable for training. Be aware, though, that some kits are offered with lighter, more aggressive paddles that may not be the best choice for someone just starting out. If this is the case, then a simple visit to a local hobby shop or favorite online retailer can help yield a more appropriate paddle selection. If in doubt about the paddles that were included with any given helicopter, information can be found from local flying buddies or a visit to any of the fine Internet forums available, like the one at www.rchelimag.com
For mini electric helicopters, a slightly different approach may be required. Since paddle selection for mini electrics can be a little more sparse than for larger machines, the use of flybar weights can be a valuable tool. As discussed in our Issue 9 article, moving the flybar weights out to the ends of the flybar makes the helicopter behave the same as if it had heavier paddles.
One advantage of using flybar weights is that it allows a change in the effective weight of the paddle/flybar system without buying any additional parts. Beginning pilots can start with the flybar weights all the way out, and as their skills progress, the weights can be moved in--which gives quicker control response. For this reason, lighter paddles in conjunction with flybar weights may be a viable option to heavier paddles.
Bell-Hiller Mix Ratio Adjustment • Not all helicopters have this capability, but on those that do, this is a very useful adjustment. Bell-Hiller mixing refers to the ratio of direct pitch input from the swashplate (Bell mixing) versus the amount of pitch control from the flybar (Hiller mixing). A pure Bell-type control system is one where the swashplate is directly connected to the main blade grips, thereby controlling the blade pitch entirely. This yields a highly maneuverable helicopter, but doesn't have as much of a stable feel. A pure Hiller control system is one where the swashplate controls the flybar, and the flybar controls the pitch of the main blades. This yields a more stable helicopter, but at the expense of a solid, direct control feel. By changing the ratio of Bell input vs. Hiller input, a helicopter can be fine-tuned to the pilot's desired control feel.
For a beginning pilot, a high Hiller ratio is often desired. Each helicopter model that offers this adjustability goes about it in a different way, so it's important to consult the owner's manual to see if this adjustment is available, and how to do it. Oftentimes, higher Hiller ratio settings will be referred to as the "stability" setting or the "training" setting. As stated earlier, not all helicopters have this particular kind of adjustability, so consult the owner's manual to see if your particular helicopter does.
Washout Arm Adjustment • This is another adjustment that not all helicopters have, but it's useful on those that do. One end of the washout arm connects to the flybar control lever. If this end of the washout arm has more than one place to mount the control ball, then moving the ball to the inside position (the one nearest the mainshaft) gives less leverage to the flybar control arms. As a result, the total amount of paddle deflection is reduced, which helps to slow down the helicopter's cyclic response.
Rotor Head Damping • Softer damping gives a helicopter a softer feel during hovering, which is ideal for a beginning pilot. Many ARF helicopters come standard with soft durometer dampers, and most manufacturers offer a variety of dampers in different durometer ratings. "Durometer" is a numerical reference to the relative hardness or softness of a damper; higher durometer dampers are harder, and lower durometer dampers are softer.
Some helicopters utilize shims between the blade grips and the head dampers to adjust the stiffness of the damping. When this is the case, removing shims will effectively soften the head damping. Check the owner's manual to see how your helicopter's damping is adjusted.
SOFTWARE ADJUSTMENTS
Exponential • This is an adjustment that changes how much the servo moves around the center portion of its travel, in relation to the stick input. By increasing the amount of exponential, the sensitivity of the control response around center stick is reduced, while still retaining full servo travel at the extremes. For a beginner, a modest amount of exponential on cyclic (aileron and elevator) will help the helicopter feel less twitchy during a hover, while still allowing enough travel for loops, rolls, and the like. A good place to start is with 10%-15% expo on cyclic. A word of caution: Using too much exponential (40%-50% or more) can cause the helicopter to feel almost "dead" around center stick, and then suddenly the control inputs will come in with a rush as the transmitter stick reaches maximum.
Each radio manufacturer is different in how they measure exponential. Some transmitters need a positive numerical value to decrease sensitivity around center stick, and some transmitters use a negative number for the same thing. Be sure to check which is needed for your particular brand of transmitter, since using the wrong value will cause the servos to move more around center stick instead of less, and this will cause the helicopter to feel very twitchy.
End Point Adjustment (EPA) or Auto Travel Volume (ATV) • These adjustments are essentially the same; the only distinction is the title a particular manufacturer uses (some manufacturers call it EPA, and others call it ATV). This adjustment limits the maximum
amount of servo rotation for a given stick input. Once a helicopter is fully assembled, EPA/ATV can be used to reduce the total amount of cyclic throw that a helicopter has--for example, from 7 degrees total cyclic pitch down to 5 degrees. Doing this will reduce the total amount of paddle deflection available, much like using the washout arm adjustment listed earlier.
A word of caution: Using too much EPA or ATV on cyclic can create a situation where the helicopter doesn't have enough control authority to adequately handle certain conditions. For example, a pilot could use EPA to reduce the paddle throw to only 2 degrees, which will make for a very docile helicopter, but at that low a setting, the helicopter may not have enough control authority to handle a strong gust of wind or an "emergency" situation.
Do not use EPA /ATV to tame a CCPM heli, instead use the percentage value in the swash menu.
EPA and ATV are used as "global" adjustments, which means that a change in EPA typically affects all flight modes. EPA can be used as a training aid, but it's best thought of as a way to limit total servo rotation to prevent binding up of control surfaces on the helicopter. What follows is an alternative to EPA.
Dual Rates • Think of dual rates as a sort of switchable EPA. Dual rates allow a pilot to set a lower amount of servo travel when the dual rate function is activated, but still retain full servo rotation when the switch is turned off. A common way to use dual rates would be to set a lower percentage (70%-80%) in Normal/Hover mode, and 100% in Idle-Up, which would effectively turn off the dual rates. In doing this, the pilot can have reduced sensitivity during their hovering, and full control authority during aerobatics.
The main thing to remember when using dual rates is that there is such a thing as "too much." If too low a percentage value is used for dual rates, a situation could arise where the helicopter doesn't have sufficient control power to overcome an adverse situation. Much like spices in a food dish, dual rates should be used sparingly.
One advantage of dual rates over exponential is that dual rates allow for a consistent, linear feel to the controls. Don't be afraid to experiment with dual rates and exponential to see which method you prefer.
ACCESSORIES
Training Gear • For a beginning pilot, one of the more "cheek clenching" times can be in the transition between flight and landing (or vice-versa). As the helicopter gets light on the skids, it's easy to have a tip-over accident. To address this, a pilot can use training gear, which in many cases is little more than whiffle balls on the ends of sticks that are attached to the skids. The goal with training gear is to give the helicopter a wider footprint on the ground, so that the chance of tip-over damage is reduced. As the pilot gains confidence in his flying abilities, the gear can be removed and flight can be continued without any additional adjustment to the helicopter.
Wood Blades • While not a "training tool" in the strictest sense, wood main blades do offer a couple of significant advantages for a beginning pilot. First, they're much less expensive than carbon fiber or fiberglass blades, so repair costs are minimized. Second, wood blades typically have a thicker airfoil than fiberglass or carbon fiber blades, resulting in more subdued flight characteristics that are an asset to the new pilot. Third, the lowered replacement costs of wood blades makes the prospect of flying a helicopter (and possibly crashing it) a much less intimidating prospect for a new pilot than having to repair a $2000 carbon fiber and aluminum masterpiece. Additionally, learning how to correctly balance a set of wood blades teaches skills that are useful in other aspects of helicopter ownership.
Plastic Vs. Aluminum Parts • It's tempting to spend the extra money on the aftermarket aluminum pieces for any given helicopter. However, for the new pilot, it's best to stick with the stock plastic pieces while learning to fly. They're less expensive to replace after the inevitable crash, and as with wood blades, the prospect of replacing inexpensive plastic parts is much less intimidating to the beginner.
Computer Flight Simulators • The importance of a good flight simulator cannot be overestimated. A flight sim is a great tool that helps a new pilot learn orientation skills without the worry of crashing a real helicopter. Most flight simulators today offer very realistic flight physics, and most either provide the owner with a dummy controller to use with the simulator, or offer adapter cords for use on the pilot's own transmitter. Either way, all that's required to get a crashed helicopter simulation back in the air is a simple press of the reset button.
There are several good simulators on the market these days. The most common ones in the U.S. are the RealFlight G3.5 simulator, Reflex XTR and FS One. There are also some free simulators available on the Internet for download, but be aware that most of these do not possess very realistic flight physics, so they might not be the best choice as a training tool. Save up the money and buy a well-known, commercially available simulator. You'll be glad you did. A good computer simulator pays for itself after just a couple of simulated crashes. [11]
CONCLUSION
As you can see, it's not necessary to accept a helicopter in the condition in which it arrives from the factory. With a little bit of tweaking, it's possible to set up nearly any helicopter to provide a much less intimidating experience for the new pilot. So don't be afraid to tinker!
