CX2 Heli: Important Blade Selection Tips

After a lot of trail and error, I have discovered some interesting things about the stock eFlight blades. Some of this has been covered in forums, but I wanted to put this together with pictures. I hope this is helpful to you.

When your blades break and you replace them, use the following steps to maximize the performance of your heli.

I discovered that most stock eFlight blades vary in both weight and pitch. Even when they are made identical, they are likely stuffed in boxes in hot warehouses long enough to deform the blades slightly.

BEFORE MOUNTING THE BLADE:

Make sure it's the right blade
First be sure you are two lower or two upper blades. They rotate in opposite directions yet still have upwards thrust , so the leading and trailing edges are reversed. If you get them mixed up on your bench, the blades with the larger balls are the upper blades, the smaller balls are the lower blades.

Check the weight
Pairing blades of unequal weight will cause vibration of the rotor shaft. This is obvious at lower throttle positions when the heli is on the table, as the shaft and body will shake. In the air, the tail will vibrate. To avoid this, be sure your blades are balanced. Snap two blades together and balance them on their balls with two cups. They should balance pretty close to horizontal. Keep the heavy and light blades in different bags for easier selection next time. Mark them with an "H" and "L".

Check the pitch
Pairing blades of unequal pitch causes all sorts of issues. I have experienced TBE (toilet bowl effect), vibration, and even not being able to develop enough thrust to take off! The flatter the blade the less lift it has. Blades with more pitch have more lift. Place the blade on a table, with the tip pointing towards you. Look at the trailing edge. It's obvious that some blades have more pitch. Match blades with the same pitch, and the ones that are almost flat I discard, you simply need the curvature to develop thrust!

Lastly, with your blades off, check to be sure your outer and inner rotor shafts, and flybar, are not bent. This is important before mounting the blades in the next step. Throttle up just enough to rotate the shaft. It should have little to no wobble (keep in mind this is a mass produced model, so it's never going to be perfect). If there is wobble, you may need an new outer shaft. You can find details on how to do this from other postings (you need to be sure to correctly reinstall retaining collars, bushings, and other items in the right positions and orientations). To check the inner shaft, remove the drive gear on the bottom of the heli (two set screws) and pull it out from the top rotor head. Roll it on the edge of a level table. It should be not wobble and the plastic drive gear should also spin mostly in line. Lastly check the flybar. It's critical it's as straight as possible.

AFTER MOUNTING BLADES:

Check the tracking of the blades. Throttle up 75% and look at the heli from the side (I wear goggles, I value my eyes just in case a blade seperates or a flybar weight flys off... it happens). Look at the tips of the blades. The two sets of blades should each rotate in a plane. The room lighting needs to be right.

- upper blade
If you see two tracks, that means either one blade is higher than the other due to unequal pitches, the flybar is not balanced, or both. Try the flybar first since you already choose two blades with the same pitch. The flybar should be straight. Then remove the flybar linkage from the large ball on the blade. Give it one turn either clockwise of counterclockwise. Put back on, did it get better? If not, go the opposite direction. Adjust until the blade is rotating in the same plane.

- lower blade
If you see two tracks, that means either one blade is higher than the other due to unequal pitches. Go back and select another pair of blades with the same pitch. If you have TBE or little lift, choose a set of weight and pitch paired blades with more pitch.

Note: you will notice that replacing blades, especially the lower blades, may cause the heli to drift in the yaw direction (it will slowly spin in one direction of the other). This is normal due to the pitch differences in the blade sets, and you can you trim it out with the transmitter, or using the mixing POT on the helicopter.

Great writeup! Even with our own blades, we have to explain to customers the same things you've pointed out. No matter how hard you try, you can only make the blades similar or at best, nearly-identicalin mass production.