This is the beginning of a series of articles related to flying F3C style hovering and aerobatic maneuvers. F3C is the class defined by the FAI (Fédération Aéronautique Internationale) for model helicopters.

F3C flying is a series of hovering and aerobatic maneuvers that are judged by a panel of judges sitting behind the pilot. Emphasis is placed on precision, position and symmetry.

In order to do well, the model must fly straight, perform aerobatics accurately, be very stable in the hover and as resilient as possible to wind conditions.

There is a lot more setup required for F3C than there is for 3D simply because the model must hover well but also perform aerobatics well, whereas a 3D model is mainly concerned with radical aerobatics.

A well setup model will be the difference between night and day in how you perform in a competition, however unless you know where to start with setup, it's very difficult to make any progress.

The points that I'm going to cover here are tips and tricks that I've picked up and experimented with. All helicopters are different, what worked on my Vigor doesn't work on the Tempest. Take what you can from this article and draw your own conclusions.

Headspeed
Curtis runs his hovering headspeed around 1750rpm which for a mortal like myself is pretty tough to deal with. A high speed can give a helicopter the following properties:
· Jumpy collective response.
Some blades just don't hover as well at high speeds as others no matter what you do with your pitch curve. You have to find the sweet spot for your blades.
· Nervous cyclic response.
A high headspeed will naturally give the cyclic controls more power which is not always what you want when hovering. You'll be downgraded for jerky collective movements.
· Jumpy reaction to winds.
I have no explanation for this, but some blades tend to bounce more in wind when at high speeds than low. I don't know why this is, but I've experienced this. Having a high headspeed though will increase the 'gyro' effect of the blades and in theory should make the helicopter more resistant to lateral movement due to winds.

I tend to run lower headspeeds. On the Vigor I have good results at 1500-1550rpm, on the Tempest I leave it at 1450. The Vigor is different in that it seems to like a highish hovering headspeed before it will 'lock in', whereas the Tempest is quite happy with a low speed. I hovered a Sylphide the other day that sat rock solid at 1130rpm. The headspeed you can use is determined by the following (amongst other things):
· The temperament of your blades.
I am not qualified to say why a blade likes a certain speed or not, but different blades like different headspeeds, experiment to find the best for your blade.
· Dampening.
The harder the dampening of your head, the higher the headspeed you'll have to run to prevent 'nodding' (where the helicopter oscilates at a lower headspeed).

For aerobatics, aim for a headspeed of between 1750 and 1900. Most tend to run at about 1850. Often the reason for this is to allow the helicopter to still roll fast enough even with a very stable rotor system. The higher head speed often allows a higher forward speed which can be used to complete larger maneuvers.

Dampening
Softer head dampeners will often yield a better hover than harder ones, however this will often be at the expense of accuracy in aerobatics. Softer dampening allows the helicopter to better absorb the effects of gusts than hard dampeners. Hard dampeners can show up every little cyclic movement as well which is not good, however, you have to strike a compromise in order to get good hovering and acceptable aerobatics performance.
Adjust your dampening by getting harder o-rings/rubbers and/or using shims.

Paddles and flybar weights
Paddles make a big difference to the performance of your helicopter all by themselves. Sharp, light, aggressive paddles are not the story here. Instead you want a stable paddle that can either have weights added to it, or an adjustable weight on the flybar.
A loose description for a stable paddle is one that doesn't have too sharp of a leading edge and that the leading edge isn't a long way in front of the flybar. A good example of a great paddle is the Hirobo Freya paddle. I used it to great effect on the Vigor and the Tempest in F3C. It has adjustable weights and is secured to the flybar by threading and also grub screws that grip from the top and bottom. A great paddle for the price.
Increasing the amount of weights on the flybar will yield a stable hover, however the more weight you put on the more ineffective the flybar will become in the wind as it becomes too heavy to react to wind gusts. With flybar weights though, you can move the weights in to make the system more effective, or out to make it less effective.

Flybar length
Increasing the length of the flybar also makes the helicopter more sensitive especially around the center of the cyclic controls and vice versa.

Flybar ratios
Flybar ratios determine the amount of influence the flybar has on the main blades to compensate for factors such as wind conditions. For example a flybar ratio of 0.9:1 means that the flybar has a greater impact on the mainblades than a ratio of 0.65:1 which means the flybar is more powerful at 0.9:1 than at 0.65:1. Now depending on your paddles, flybar length, blades, flybar weights etc this may or may not be a good thing.

Blade length and weight
For ages, I thought the answer was always the longest blades you could get, I'm now having to rethink that theory. After talking with guys who are more experienced with this than myself, I decided to give it a go. I took the 720's I had off the Tempest and bolted on some 680's and immediately noticed the heli seemed to 'sit' better and was a bit more resistant to wind gusts. The theory behind this is simple, the larger blades you put on the heli, the lighter the blade loading will be (ie the weight of the helicopter divided by the area of the rotor disk). This means that there is more of an 'umbrella' for wind gusts to act upon.
Now when you make the rotor disk smaller, the blade loading has gone up which means the helicopter has become 'heavier' to wind gusts.
The downside of this is that you loose a little bit of performance in the aerobatics and you can definitely lose some autorotation performance depending on your blades.
Heavier blades are obviously more stable (due to the increased gyroscopic effect), but they roll slower, which isn't necessarily a bad thing in F3C, you will also get a lot more vertical penetration. Lighter blades will make the heli more nimble (ie roll quick) but often you will lose vertical penetration.
Here's an example. When I competed in Australia, I had a set of FAI MS 710 blades which were great in aerobatics but weren't optimum in the hover which was annoying me. A guy lent me a set of MAH 710 tapered blades which were a good improvement in the hover but they absolutely sucked in the aerobatics (I couldn't get anywhere near the vertical penetration). However because they were better at hovering (and hovering is worth double the points of aerobatics) I decided to stick with the MAH's.

Pitch curve
After trying many different variations, I have now settled on using a straight line pitch curve in normal mode. However I seem to be a bit different from many of the setups I have seen in that I use less positive pitch, but more negative pitch in my setup.
I generally set my curve from about -4 through to about +8 degrees pitch in hover. My reasoning is that in the hovering, you never need more than 8 degrees in the hovering maneuvers, and in windy conditions, you often need quite a lot of negative pitch to pull the machine down.
However one thing I do with my 9Z is utilize one of the sliders to allow me to change the top and bottom end points on my hover pitch curve. Now the reason I do this is because if I find that all the wind has gone when it's my turn to compete, I move the slider so I reduce the top end pitch and also the negative pitch, this means less pitch movement for the same amount of stick travel. This makes the heli less sensitive to pitch change which in my case makes it smoother. However if I find part way through the hovering that the wind comes up, I move the slider to give me more pitch range so I can drag the heli down. It's proved very useful.

Weight balance
If you pick the helicopter up by the flybar you'll want to see that the helicopter balances level or with a slight nose down attitude. This will ofcourse depend on whether your model has a forward mounted tank or if it is aft mounted. A slightly nose heavy helicopter will penetrate better than one that is tail heavy. There is often talk that a nose heavy heli will hover better too.

Weight
Weight isn't as big of an issue with a contest heli as it is with a 3D machine. Once again it comes down to blade loading. A slightly heavier machine will sit better in the hover than a lighter one, hence the reason why gas helicopters hover well, they're so damn heavy. Don't be scared to add a heavier battery if necessary to achieve the correct weight balance.

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