Setup for F3C
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
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
· 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
· 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.
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.
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.
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 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
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
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
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 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.