Diagnosing Radio Control Problems
Have you ever noticed that some flyers planes always fly great no matter what they are flying? Part of this may be they are better pilots but there is more to it than that. These flyers have learned how to fine tune or trim in their planes. If your plane is not flying as well as you think it should, or once did, you need to make some adjustments both on the ground and in the air to get the plane back to peak performance.
Simple things like center of gravity and amount of movement in the elevons need to be correct for your plane to fly well. We use big elevons on our planes and they don't have to move as much as you may think because of their size. Make sure you plane is set up correctly. Read our Ten Mistakes to Avoid article.
Trimming your plane is one of the first things you do after you take off. By clicking the trim tab sliders on your transmitter you can make minor adjustments in the elevons and elevator and rudder while the plane is in the air. If the plane is trimmed properly, it will fly predictably with the stick in a neutral position. Trimming is the process of making the fine adjustments that let your plane maintain flat and level flight with your hands off the radio. You may adjust the trim several times in a flight.
I have seen new pilots struggle with trimming. Some make no attempt to trim the plane at all and just try to keep the plane in the air. Some look down at their transmitter and then are disoriented when they look back. I even saw one flier accidentally turn off his transmitter when he thought he was adjusting the elevator trim. Practice finding the trim adjustments without looking before you have your plane in the air.
After you land adjust the push rods. After you have flown your plane and are back on the ground, look at where the trims are set on your radio, and make mechanical adjustments to the push rods to match. You should be able to move the trims on the radio to be centered again. This will sometimes take several flights to get the plane fine tuned in. Successfully trimming a plane takes a little experience. Once you understand what you are doing it is easy to do. A good teacher can help you learn.
Diagnosing electrical problems
If your motor isn’t running like it should:
1. Is your prop on frontwards with the lettering or fat part of the propeller facing the direction your plane will be flying?
2. Is your battery charged and does it have enough power for your motor? If not you won't have enough power.
3. Is the throttle trimmed on your transmitter so the motor doesn't have maximum RPMs at full throttle?
3. Look for broken wires, especially in plugs and motor wire connections.
4. Look for broken solder joints if motor kicks in and out or won't start.
5. Rebind your receiver with the throttle off.
6. Is the wiring in your motor damaged especially where the wires exit the motor?
7. Use throttle down trim to stop prop if prop is turning with throttle off.
Motors and ESCs can burn out. Batteries lose their peak performance and battery chargers may not be fully charging your batteries. Without a lot of diagnostic equipment you can easily trade your motor, battery and speed control one at a time so you will know which one fixed the problem. Occasionally a servo goes bad or breaks a gear. Since our servos are glued in servo replacement is a more difficult field repair but it can still be done if you have a portable glue gun that can plug into your car.
Throttle problems can be a worn out or bad motor, or ESC but is often a weak or damaged battery that isn't giving enough power. Your ESC is designed to cut out when a battery voltage drops to a certain level. Many flyers mistake this for a motor problem. A weak battery can also cause the ESC to do strange things, like cutting out as you feed in throttle or the motor fading out within seconds of launching. Batteries are usually the weakest link. Often, the quickest way to diagnose more complex problems is to start trading parts. I carry extra motors, ESCs, servos and batteries with me. If I can't find a cause for a problem I will trade the parts out one at a time at the flying field and see if the problem is resolved.
I have a three-wire extension cord so I can run a motor on one plane off of the battery, receiver, and ESC that is still in another plane. I don’t even hesitate to trade the ESC and battery to see if the problem continues. The antenna is usually secured, so I usually end up leaving the receiver in the plane and testing it in place. As you get to know your equipment, diagnosing problems is easier.
Motor thrust angle and torque
When you adjust the throttle you may see that the plane pulls up or down. If this is the case, then either the motor thrust angle or the center of gravity needs to be adjusted. Flying wings have reflex, which means the elevons are set slightly upward to help the plane fly straight at half throttle. This little bit of up-trim may pull the nose of the plane up at higher speeds but is normal and expected for all flying wings.
To correct the motor angle, fly the plane to a safe height for a test and trim the plane during a glide to fly flat and level. Give the plane some throttle and see if the plane pulls up or down. If the plane pulls up with increased throttle, you need to tip the motor down. (This is the same for motors in the front or back.)
You will notice the plane may fly level, but will start to roll when the throttle is changed. This is usually due to prop torque and will have to be accounted for by the pilot as he flies. There’s not much to do mechanically to change it. Fliers will ask why their plane is rolling or turning better one way than the other. Because your prop is turning one direction the plane tends to turn easier the other direction.
If your plane rolls over as you loop, the center of gravity may be too far back, or you may have too much movement in one elevator, or a warped wing. If the plane stalls easily or you can’t pull the nose up when gliding, you may not have enough power, your servos may be too small for your plane or you might have the center of gravity too far forward.
Trimming the Slow Flyers are a little different (Pelican, Albatross, Storm Chaser)
The slow flyers are designed to be launched with a harder toss at half throttle and then throttled up. This is to help them be amazing at self stabilization at any throttle setting. Self stabilizing occurs when the plane speed and the trim on the rudder and the angles of the wing and elevator pull the plane to a flat and level flight form any position if they have enough altitude. For example: The Pelican polyhedral wing trainer will pull down until it is up to speed if you launch at full throttle or throttle up from a slow glide too rapidly. This design will then stabilize itself in flight as it comes up to speed and can be trimmed with the elevator to keep their nose on the horizon at any throttle setting.
You can decrease the amount of downward pull if you give a faster toss on the launch to help the plane get up to speed more quickly. You can permanently decrease the amount of pulling by tipping the motor up 3 to 5 degrees by putting two or three 3/16" washers under the bottom motor mount screw which makes it easier to launch, but then the plane is a little slower to self stabilize. The plane will still fly well once it is trimmed with the modified motor angle.
The Pelican has a shorter fuselage than the Albatross so it is more sensitive to the motor angle especially if it is over powered. The down pull on the Albatross and Storm Chaser is minimal due to their increased size.
Why does this happen? When the motor is angled down on the nose of the plane it pulls down more as it is throttled up. As motor speed increases so does the speed of the plane and the lift on the wing, so, the downward angle of the motor pulls down harder to compensate for the increased lift from more air moving over the wing.
When the motor is on a pod it still pulls down because the thrust of the motor is elevated above the rotation point of the wing giving the same effect. I prefer the pod on the slow flyers to protect the motor and prop. Once trimmed in it is hard to tell a difference in how the plane performs in the air other than at wide throttle the plane is a little slower to recover in a dive.
We angle the nose mounted motor to the right because it is below the wing to compensate for prop torque.. We angle the motor on the pod to the left since it is above the wing to compensate for prop torque. It seems odd I know but it works. We point the motor that is on the pod at the front left corner of the fuselage.
This is not unique to our planes. You will notice many planes that have the tail, wing and motor angles set to help trim of the planes. We chose to do it this way to simplify the build and increase the strength of the plane.
Too much movement in the elevons is often diagnosed as the plane being tail heavy because the plane has similar instability problems. It is important to have the right amount of movement in the ailerons and elevator and rudder. Not enough movement and the plane is hard to control. Too much movement makes the plane seem wild and out of control and can cause stalls and snap rolls especially for beginners. Please follow the instructions for your plane, and only change the amount of throw incrementally and when you’re comfortable doing so. Control surfaces and linkages need to be solid, without flutter. With the radio off you should be able to rotate the servo by gently moving the flap by hand. Make sure the push rods do not flex. You need solid linkage.
Lighter planes fly better. If a plane is heavy, it struggles to fly, It won't glide well so it lands fast, it is hard to take off, it can snap roll whn you pull back on the elevator and is likely to have more damage in a hard landing. I have seen several new fliers that try to build their planes strong so they won’t break, and in the process, make them so heavy they won’t fly.
Wing loading is usually measured in ounces per square foot. The lighter a plane is, the less power it will take to carry it into the air. The relative weight of a plane is adjusted by it’s size. Weight is more important than most fliers think. It takes a lot less power to fly a feather than a brick. Heavy planes are not fun to fly. In fact they are work. It is a challenge to keep them in the air at slow speed.
Which is best, hand launching or landing gear? A plane has to get up to speed before it will fly. Wheels or skis allow you to take off with both hands on the radio, but add weight to the plane, affecting flight characteristics. I’ve owned many of both types of planes. I like my bigger planes with landing gear, but I hand launch my wings, and small planes. If your flying field is a grass field, you will have trouble with wheels. Landing on pavement is hard on planes without wheels, so consider your flying site to help decide. Once in the air, the wheels are a liability because they give added weight and drag, and often need straightening or repair after landing. Full size planes often use retractable landing gear, but retracts add even more weight, and frequently malfunction or break. In a wreck landing gear tends to tear and puncture the plane. Don’t put them on your first planes.
If you are going to hand launch, hang on to your plane at about the CG. Throw it at the horizon, not up, or it will stall right out of your hand. Small planes and flying wings can be launched by a wingtip, but launching at a wingtip takes some practice. Don’t spin the plane or make a Frisbee toss as you let go; make sure the wings are level. I launch by a wingtip all the time. Most flyers learn to launch a flying wing by launching from the center of the wing with a finger on each side of the prop. They give the plane a hard toss and then throttle up after the plane is out of their hand. We see occasional injuries when someone gets their hand in a turning prop while hand launching. You have to be careful and think through the process. Some flyers have a hard time getting their hands back on the transmitter after launching their plane. I find this to be more of a problem if it is cold and I am flying with gloves on.
Center of Gravity
The Center of Gravity (COG) is the point at which the plane should balance front to rear. It is usually around 33% back on the wing (including ailerons) of a conventional plane and 23% back on a flying wing or delta. If you don’t get the CG right, the plane won’t fly well and may not fly at all. Don’t just go by the instructions for your plane to get recommended COG fly it and see if it is in the right place. Some planes will fly much better if you experiment with a minor change in the balance.
When we buy and build planes here in Utah, it is important to not under power our planes or build them too heavy. Planes do not fly as well at our 4500 ft altitude as they do at sea level. Most kits are designed for sea level. We have recommended motors that fly well at our altitude.. When I went down and flew at lower elevation in California, my planes flew better. So what do I do? I try to build light. I look for motors that are light but still give enough power for the plane design
It is critical that the flight surfaces move in the proper direction. You will need to make sure, as you program your radio, that everything is moving correctly. See the Tx & Rx article for more details.
Build it Strong
We had a flyer who had a Vertigo flutter and break apart in flight. In our communication we learned he had done some things in his build that resulted in his plane structure failing. I hope this will help some of the rest of you understand how to build the basic structure and build a tough plane that will last.
The building errors he made was to save weight he left out the E-Tape and then he cut into the back of the plane to give more prop clearance because he had used a shorter motor and the prop was likely to hit the back of the wing.
Here is some of the communications:
You have to use the Extreme tape, especially in an FPV plane that has so many cut outs for all of your gear.
E-tape is what makes our planes rigid so they won't flutter. E-tape doesn't stretch and has a breaking strength of 150 lbs per inch so a 2" wide piece of tape has a breaking strength of 300 lbs. This is part of what makes our planes so indestructible.
In the instructions we show a 2" center strip over the top of the spar and another 2" strip under the spar on the bottom and a another 2" strip wrapped around the leading edge. The 1" top and bottom E-tapes built into the hinge line also adds another 300 lbs of strength to the elevons. With this tape as shown in the instructions you would have 1200 pounds of breaking strength with just the addition of the E-tape. The E-tape does not stretch so it adds extreme rigidity to the plane. That is why we use it in all of our planes.
The lack of E-tape is why your plane fluttered and ours do not. The laminate alone stretches so the wing is not going to be as stiff even if you double up on the laminate.
You will also notice on all of our small and medium planes (including the Scythes, Widowmakers, Assassins, Vertigos, Titans, Reapers, Reaper XLs) that we don't make prop cut outs to increase the prop clearance. Every time a plane with the prop cut out tears it always starts at the corner of the cut out and rips through the servo holes and radio and battery holes in some combination. This is because they are weakened areas because we have cut into the foam and E-tape. The prop cut out is a necessity on the Gladiator and on the Hercules because of their size but we avoid it like a plague on the smaller planes because of how it weakens the plane.
I think one of the biggest problems is the cut-outs for radio that weaken the center of the plane. I like to spread electronic parts out in the wing. Make sure the E-tape over the spar and the E-tape under the spar is not cut into so you have a continuous strip from one side of the wing to the other then tie it in with the E-tape around the leading edge of the wing. You will be able to feel the rigidity of the wing when there is E-tape top and bottom over the spar.
We have had several similar comments about the smaller motors not being long enough to get the necessary separation of the prop from the back of the plane. This has become more common as people are trying to use quad-copter motors to fly our planes. No one says that the motor mount has to be pushed all the way up to the back of the wing. You can leave it poking out a ways with a bigger gap between the motor and the wing. I have seen some flyers build a triangle that fits in the angle that is built into the plane that also moves the motor mount back. If you do build up the angle just remember the CG will remain the same so you will have to shift weight farther forward to compensate for the motor being farther back.
I frequently get asked about the science of putting a forward fuselage under a flying wing so it is easier to balance.
My question is why do you want a flying wing? If you are going to put a nose on it why not put a tail on it and it will be easier to balance and not so sensitive to CG. All of the advantages of the flying wing start to disappear when you have a front fuselage to break off of the plane.
It is always a challenge to get the CG far enough forward on a heavier flying wing unless the motor is on the nose of the plane without adding big batteries or lead to the nose. To resolve this problem some flyers want to add a hollow fuselage under the nose to move more of the electronics and battery weight forward to help with the CG.
The CG on a flying wing is back at about 23% so there is 77% of the wing behind CG which includes the motor, motor mount, fins, elevons and hinges. The nose of a flying wing has the battery and as many of the electronic components as you can get forward but often it is still difficult to get some wings to balance. This is especially true for wings with deeper chords and blunt noses because the blunt nose moves the CG even farther forward and the deep chord moves the motor farther back behind the CG.
Our Titan with its long narrow swept wing is the only flying wing I have seen that is easy to get nose heavy. Deeper wings like the Gladiator and Herc Pusher are harder to get the CG correct because they have deeper chords. On these deeper chord wings we have to have motor cut outs to move the motor farther forward and bigger batteries to help get the CG right unless you put the motor on the nose.
Smaller planes like the Assassin, Vertigo and Scythe are fairly easy to get the CG far enough forward without added weight. The Grim Reaper isn't too hard partially because I use a bigger motor and bigger batteries and they balance out OK. I usually have to add about 1 oz of lead to the nose of a normal Widowmaker and 2 oz of lead to a Pinata to get them to balance. The Grim Reaper XL is a longer range plane that does balance out with a 4500 mA 3S battery but it is designing what we wanted it to do.
Summary: Keep your flying wings as simple and indestructible as possible and you won't regret it. Putting a nose on an EPP flying wing defeats the reason most of us have flying wings in the first place. The chance of breaking it off in a moderate accident or hard landing is very high. It is a fix to a problem that comes with the way you build a plane, set up your electronics and also to the basic design of the plane.
Build the back of your plane light. Lighter planes are easier to balance. Lighter planes also fly better. Don't put anything behind the CG that you don't have too. You will notice that even our spars on most of our wings are on or in front of the CG so they don't make the plane harder to balance.
I hope this helps you build your next plane. Watch our build videos for more ideas.