Calming 450 sized heli's

Written by Ashley Davis Thursday, 28 April 2005 00:00

This article is for both experienced nitro pilots and beginners with micro helicopters. One of the initial problems when either starting out with the T-Rex as a first micro helicopter or starting out in the hobby with a T-Rex as your first machine is that of cyclic sensitivity.

For the total beginner, what do I mean by cyclic sensitivity?

Cyclic pitch is the method by which you introduce different angles of attack to the flybar paddles. The flybar paddles cause the helicopter to rotate on it's axis and fly off in one direction or another. Cyclic pitch is the elevator and aileron controls on your helicopter.

OK, so what's the deal with sensitivity?

The T-Rex from stock has washout mixer arms that turn a very small movement on the swashplate into a much bigger movement on the flybar paddles. This differential makes the T-Rex very sensitive to elevator/aileron or cyclic pitch as explained above. Which is great for those fancy high speed 3D moves but not so good for learning.

This means that for someone new to the hobby, new to the T-Rex or new to micro helicopters the T-Rex will feel very sensitive to elevator and aileron stick inputs, which will make the T-Rex harder to fly than it need be. The good news is that you get used to it the bad news is that for total beginners it often leads to that first crash. This article tells you how you can get over that sensitivity by the use of what is often referred to as flybar weights.

Flybar weights are very often just wheel collets (round brass collars used to hold under carriage wheels on planes in place). Wheel collets come in various internal diameter sizes, the T-Rex requires 2mm (inside diameter) wheel collets for secure fitment to it's flybar. Flybar weights work by adding weight to the flybar which in turn increases the gyroscopic effect of the flybar and paddles when in motion. This means a much larger force is required to move the helicopter in any direction to overcome the gyroscopic effect. Adding weight to the flybar slows down the responsiveness of the helicopter.

Right that's the theory, so what amount of weight needs to be added and where. My experimentation showed that around 4g of weight at the outer edge of the flybar was enough to keep a reasonable level of responsiveness but also dramatically increase stability. See the pictures below for detail ....

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The pictures show two 2g collets at the base of the paddle. Both paddles should have this weight added, otherwise the head will be unbalanced and severe vibration will occur. Once this is done make sure that as per the other setup instructions on T-Rex Tuning the control rods should be set up to run on the inner most holes on the servos. This reduces the overall movement going to the swashplate per set deflection of the aileron/elevator stick. Care should be taken to tighten down the wheel collet grub screws correctly and to use loctite on the grub screws to stop them working loose over time.

With this new weight on the flybar and the servo horns configured correctly the T-Rex should feel a very tame helicopter to hover with none of the sensitivity normally associated with the T-Rex. Best of all this is a very cheap upgrade and almost essential for the total beginner to calm down their T-Rex enough to make it a very good beginners machine. As your flying progresses you can remove the wheel collets, so long as the head remains balanced to avoid vibration.

My current preference for beginners is just one collet on either paddle, which makes the T-Rex much less unpredictable and more of a joy to fly.

 

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