Hi Guys,
I've been enjoying getting back into flying F3C competition this season and I am also enjoying flying my SOXOS helis for my club flying so I decided to work with the designer/owner at Heli-Professional on a model that was suited to F3C flying. There are no specific plans to have this as a new model in the lineup but if there is interest it wouldn't be out of the question to see it as an option of some sort in the future. All of the parts used here are current production parts so anyone could piece this current setup together.
The Heli-Professional range of SOXOS helis includes several models from 550 to 800 size and in discussions with the factory we selected parts from the range that would optimise the platform for F3C.
We started with a DB7 model as the base as it has a strengthened main frame, heavy duty gears set and carbon front frame.
We then swapped out specific parts shown in this photo which I will cover one by one:
The DB7 has main frames that are raked forward so clearly not suitable, but the standard SOXOS 700 has larger side frames that keep the mainshaft vertical so these were the first parts required to be replaced.
Fitting these frames also mean a larger canopy is required, which I think suits the model size better than the smaller DB7 canopy so again one of the standard 700 canopies was selected.
As the boom is no longer raked upwards the longer tail fin (and matching horizontal fin) from the standard 700 heli is also fitted.
As I want to try several blade sizes on the model I opted to fit the boom for the 800 setup, which will allow me to try several configurations from 710/720 up to 760/780 blades.
The SOXOS has a very high Centre of Gravity and very compact weight distribution, in order to slow the response down a little and improve stability and hovering performance the standard 700 headlock is used. It is 8.5mm taller than the DB7 headblock and interchangeable. This head does not have a centre pivot in contrast to the DB7 head, which will also give softer damping in the head.
The taller head requires some longer top links, unfortunately the DB7 turnbuckles are not long enough to use, so for now I have the standard links fitted but as the links are all M3 sized threads (including the servo to swash) I have some Lundsford turnbuckles on the the way to replace the rods. This will give me the fine adjustability required to get a perfect mechanical setup in place.
The new head also uses dual washout arms instead of the single on the DB7 head so these are also added to the configuration.
I won't detail the build in this thread as it is almost the same as the standard DB7 I have already written up
here.
One picture from the build is showing how the mainframes level the heli so the mainshaft is now vertical, it also provided an additional 20mm of depth for batteries, which gives it enough room to fit 10,000mAh packs if you really wanted too. :shocked!:
Here are some pictures of the finished heli before the maiden.
The initial setup I am running is:
Scorpion HK4530-450kv (17t pinion)
YGE 160A ESC with 150A current sensor fitted (YGE Gov Store mode)
Futaba BLS273 swash and BLS274 tail servos
CGY750
2600mAh 35C Rx pack
Jeti RSat2 with SBUS firmware
6000mAh 12s 35C flight packs
Rotortech 760mm main blades and Rail 116mm tails for the maiden
+-12 degrees pitch
Weight of the airframe without packs and battery tray = 4.0kg
Pack weight with tray = 1.80kg
RTF weight = 5.8kg
The maiden flight was uneventful with the head speeds at 1400/1800/1900 the heli felt really nice in the idle up heaspeeds but had a slight elevator nod at the lower hover head speed. I bumped the hover head speed up to around 1480rpm and the nod disappeared. This is probably a better hover RPM anyway but as the dampers wear in I would expect to be able to go lower in the head speed without a nodding, there is also the option of shortening the boom down from 800 to 760 size which should reduce the tendency to nod. There is still a lot of testing to do but straight off the boards the aero performance feels very good, with excellent tail hold and if anything too much collective authority (power). I swapped to some 716 F3C blades which were more manageable but could drop the head speed or collective range with the bigger blades to calm the heli down a little. The hovering side felt fine with flat pirouettes but I will need to work on the feel some more as it is more reactive than the 766 I have been flying.
Overall a good starting point but one of the joys of F3C is spending time working on tuning the heli, and there is a lot of testing still to come as well as a few more parts being developed that I can't talk about yet which I will also be fitting and testing over the next few months.
//Dennis.
