General looking for a new heli head

Derek

Derek

Well-Known Member
I've been looking at various rotor heads for my helicopter at various different websites. I've seen some heads are listed as "flybarless" and some are listed as "dfc". Is there a difference?
 
Tony

Tony

Staff member
DFC has solid links going to the blade grips, means Direct Flight Control. FBL has regular linkages with swash drivers seperate. The DFC actually drives the swash with the linkage arms.
 
P

pvolcko

Well-Known Member
DFC heads often are shorter than swash driver FBL types, both because they can be (no need for extra room for the swash driving links and arms) and also to reduce the torque experienced by the DFC blade links (shorter they are the less lever advantage the torquing forces get against the link to blade grip connection). As a result DFC seems to have higher incidence of boom strikes and they have the potential for faster acceleration into a roll due to the shorter rotor to CG distance (i.e. "snappier"). They also put a lot of strain on the connection point to the blade grip arms and where the lower ball link attaches to the metal of the DFC link, which can be a failure points if the design isn't right. While they can be used with a standard swash (link balls inline with the radius) many newer head designs have swashes with link balls tangential with the radius, allowing for more direct transfer of rotational energy into the swash from the DFC link and less chance of the link popping off the swash due to torquing forces.
 
Lee

Lee

Well-Known Member
Derek said:
So, other than the boom strikes, DFC is better than flybarless?
Click to expand...

They are both FBL Derek.
The difference is the DFC heads are "direct to swash" (more stress on servos
The more conventional style is with a swash driver. Linkages between swash and blade grips.

A lot of the companies are going back to the older style (Goblin, Compass). I'm no expert as to why, but it seems people prefer the older style.
 
Tony

Tony

Staff member
They are still a clone, but a little better than HK.

The reason I put a DFC head on the 600 is for the lower stance. I know that in a crash, it's going to take out the servos. If I had left the FBL head on that had the swash drivers, then it would be less likely to strip servos in a crash. YOu have to have a part that fails in a crash to save other parts. On the FBL head, it's the linkages, on the DFC, it's the servos.
 
coolgabsi

coolgabsi

Super Mod & DEAL KING!
I was all about dfc till I saw (after my flying style and maintenance) my heli didn't like it... I wasn't getting that lower of a stance on my 600.. So I went back to v2 design.

I definitely like the swash follower type design better in the way it tracks and stress on the servos and stuff like that. No there isn't a flaw .. But it's just preference that I have developed by trying things out. Love the looks of dfc and the fact that it rides low.

My 700 and 600 are both swash follower design. Miniature aircraft helos are good, and they don't even make a dfc head for these.

My compass warp is the only one with dfc but the heli and swash mechanics were designed FOR it.. So it works very well
 
Lee

Lee

Well-Known Member
I had a Tarot head on My 500 Derek. It was a very well made piece of kit.
Tarot is made in the same factory as Align by the same people. It used to be that they just rebranded Align stuff, but now they are a company in there own right, and coming out with some good product. There Tarot Ironman hexicopter is a sweet machine.
 
Derek

Derek

Well-Known Member
coolgabsi said:
My 700 and 600 are both swash follower design.
Click to expand...

What is this "swash follower design"? There is so much that I'm trying to wrap my head around. Gaba, you also mentioned that you went back to the v2 design. What do you mean by that?
 
coolgabsi

coolgabsi

Super Mod & DEAL KING!
Derek said:
What is this "swash follower design"? There is so much that I'm trying to wrap my head around. Gaba, you also mentioned that you went back to the v2 design. What do you mean by that?
Click to expand...
V2 design is the align's name for it. It is another name for swash follower design. It's the non dfc flybarless system. There is only two types.

http://m.ebay.com/itm/270927003113

This is swash follower type design. The thing in the middle of the head yoke and swash is swash follower.

Dfc is "swash follower less " design :)
 
Last edited:
Tony

Tony

Staff member
Derek, did you get my text? If so, that head that I have has swash drivers. Otherwise knows as radius arms or washout arms. Depending on what kind of head they are on.
 
P

pvolcko

Well-Known Member
On a non-dfc FBL head, the swash followers (I learned them to be called swash drivers or radius arms, as Tony mentioned) are what actually transfer rotational energy into the top half of the swash from the head. The links in this kind of design should have practically no side/tangential force on them, only up/down force imparted by the swash and blades. In a DFC design the links both have up/down forces on them from the swash and blades, as well as rotational force that they impart onto the swash to spin it with the head. Due to blade/spindle flapping there are some small non-up/down forced on the links in both designs, but on a standard/V2 style FBL head they are not an issue since the links connect to the blade grip arms via a ball. They will cause some long term wear on these connections, but in general it is not an issue.

With DFC designs the links are rigidly connected to the blade grip arms, which means flapping and torsional forces can cause this connection point to wear dramatically in a short period of time, resulting in catastrophic failures if the connection isn't designed to take the forces applied to it. Bolts strip out or simply fatigue and sheer. The aluminum the bolts thread into can strip out or the holes can be widened by poorly fitted bolts, etc. This same force gets transmitted down the link as skewing side to side which can cause the plastic to metal link arm connections to fail too, if not designed for properly. Generally this is why plastic links on the bottom of DFC arms will have long threads and may actually countersink right into a cup in the bottom of the link arm. Other designs actually embrace this vibrational tendency and will go with well threaded but relatively "loose" link to arm connections so this loose joining of the two parts will be free to move and absorb the higher frequency side to side movement of the link arm. These two areas were the most frequent trouble spots in early DFC designs and are the most common failure points even in today's designs so far as I can tell.

Aside from higher boom strike probability, I think this pair of critical failure points is why manufacturers have begun moving away from DFC head designs as of late. It's a difficult problem to solve fully and when the failure occurs it is catastrophic for the heli, costly, and potentially quite dangerous. I'm sure DFC will live on for some time, as it is fewer parts to deal with and there are certain applications in which it makes a lot of sense, such as speed helis, high end aerobatic helis, etc., but I think it is a fad that is going out for most of the mainstream heli designs. May be wrong. Will have to see. :)
 
Derek

Derek

Well-Known Member
Oh wow! I'm gonna have to come back later and reread this just that I can absorb it all. However, something I did understand is that since I'm not looking for just speed and I'm not a high impact 3D pilot, maybe I should be looking at the v2 flybarless heads instead of the DFC heads.

Choices, choices, choices!!!
 
You must log in or register to reply here.
Top Bottom