RC helicopter will not lift off?: Common reasons & fixes

By V Kadamatt | RC Helicopters

Feb 07

For sure many of you already know – for any object to be able to lift, the amount of gravitational force that pulls the object down has to be overcome. Helicopters achieve this by the application of Bernoulli’s principle. That is, by rotating the rotor blades, it creates lower pressure air at the top of the blades (consecutively, at the top of the helicopter itself) relative to the bottom of it, generating that upward push or ‘thrust’. If your RC helicopter will not lift off, then it somehow falls short of the physics!

That’s all well and good. But if you already built a working model helicopter which used to fly, or if you have an RTF model that used to function well up until yesterday, what could be causing this weakening of ability to produce that upward thrust?

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The following are some common reasons for the ‘toilet bowl effect’ and things you could do to fix them:

Weakened battery

RC helicopter will not lift off

The most common reason your RC helicopter will not lift off (toilet bowl effect) is because your batteries have been weakened or unbalanced. The first thing to check is of course, that your batteries are charged in the first place.

Charging your batteries however, doesn’t mean that they are working at its fullest. Especially if they are sort of old have run a few cycles, expect it to weaken and have issues.

Use a multimeter to check the voltages. A fully charged battery cell should have a voltage of 4.2V (not above nor below) .If you find that the voltages are out of whack, we recommend you go ahead and do a storage discharge and recharge the battery with a balance charger. Check the voltages again.

If the problem still persists, it might be time to get some new batteries. Make sure to properly care for your LiPo this time around!

Here is a nice guide on LiPo batteries.

Toilet bowl effect due to loose or broken shaft

Toilet bowl effect - heli shaft

 

If your RC helicopter does not lift off even if the battery is good, check if your shaft linkage is weak. having a loose shaft linkage is one of the most common reasons for weakening of upward thrust causing that toilet bowl effect.

If you try to rotate the hollow shaft, the inner shaft should move along with it. If it feels loose and wobbly, you might have to fix it. The same is true with the blade holder. The looseness can cause a significant amount of rotational force transfer from the motors to the blades to be lost.

Make sure the screws that hold the blade holder and the outer, hollow shaft are aligned and tight with the inner shaft. If your model has the glued version instead of screws, you might want to re-glue it.

If you find that the inner plastic has worn out causing the looseness, you could fill the gaps by adding in super glue but if that doesn’t work, best get a replacement. Make sure that the shafts of both blades are sturdy and firm.

Another closely related reason is a broken shaft. Here is a video that might be of help to repair a broken shaft:

Worn gear

toilet bowl effect

Another reason why your RC helicopter will not lift off is due to worn gear. Slowly spin the prop blades around and see if you can feel any resistance. Any resistance is an indication that there is extra power being drawn from the motors. This can also have an additional negative effect of wearing the batteries over time. The most plausible culprit? The gear.

Here is a video that might help you with fixing a worn/damaged gear:

Worn blades

Take a closer look at your RC helicopter’s propeller blades. Do they seem worn out or worse, are they cracked/broken? Even the slightest crack can damper the propeller’s overall ability to have a strong angle of attack on the surrounding air which is another reason why your RC helicopter will not.

A worn out propeller blade can also affect the angle of attack and possibly increase the amount of turbulence and drag, ultimately limiting an upward thrust movement.

If you think you need a propeller blade replacement, you should definitely go ahead and get one.

Worn motor brushes

Brushes within the motor is essentially the backbone of it. If it shows any signs of weakening, it is time to get a replacement because the motors are what powers the lift in the helicopters in the first place. No wonder your RC helicopter will not lift off!

Unlike brushless motors, motors with carbon brushes lose power over time as it wears it quicker. It can be difficult to detect which of the motors is the malfunctioning one because the gyroscope within the craft tries to keep the motors spinning at the same RPM. If you aren’t sure, replace both the motors.

Here is a video that might help with replacing your motors:

Weakened receiver connections and range

Transmitter - rc helicopter will not lift off

Overtime, the receiver within your copter and/or the connections and transistors on it can weaken. If you have tested for every issue above and your RC helicopter will not lift off then almost surely, it is a receiver problem and you better get a replacement.

However, a receiver isn’t the only culprit when there is a decreased signal. Batteries within your transmitter can also lose charge and wear out. Make sure to check that out!

If that doesn’t work, you should try and increase the range of your antennas by unwrapping it and adding additional wires to it.

Conclusion

That’s all folks! Hope this helps! If your RC helicopter will not lift off within your first few flights and you have have just bought your RC helicopter , it is recommended that you contact the seller get a replacement when you can. If you have no choice, don’t just throw away that craft into the trash just yet. Try and get it fixed no matter what, we assure you it will be a fun learning experience!

If you have any comments, questions or suggestions, please, please do not hesitate to drop them below!

RC helicopter will not lift off?: Common reasons & fixes was last modified: August 2nd, 2017 by V Kadamatt

About the Author

Artificial Intelligence , UAV and RC enthusiast. Software professional, part time philosopher and star gazer. Also loves physics, mathematics, economics, psychology, fantasy, Sci-Fi and futurology.

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