Hi, I heard somewhere that for hardcore 3D flying n hovering the rudder should be on positive exponential, ie much more sensitive in the center than at greater stick movement.

To me it sounds strange as i fly all my surfaces with negative expo and its fine. What do the pros say?

Cheers b_p

Originally Posted by baja_patient

Hi, I heard somewhere that for hardcore 3D flying n hovering the rudder should be on positive exponential, ie much more sensitive in the center than at greater stick movement.

To me it sounds strange as i fly all my surfaces with negative expo and its fine. What do the pros say?

Cheers b_p

If your using negative expo then I assume you have a Futaba radio?On Spektrum it would be positive expo.I use full rates with about 60% expo depending on the size of the plane,bigger plane,less expo,a slightly lower rate for ailerons on 60'' and smaller planes.I used to fly at 75% but have lowered it & Im starting to drop it down to 50% next.Most manuals say to use 70-75% on full rates & as much travel as possible.

I'm no pro, but I don't think having your rudder more sensitive around neutral would be a good idea for any 3d flying. Whether you use pos or neg is driven by the radio you use but I cant imagine doing it as has been suggested. I am curious to hear more responses from others.

Daryll

I use less expo on my rudder, but don't go on the other side of zero. I prefer to have more movement around center when 3ding.

There is only one time I've ever used reverse expo. I had a Direct Connection Ultimate Bipe (ARC). It had a 60" wingspan and was a very pretty and well built model but it was heavy as hell. I had a very strong OS 1.08 glow on it, but performance was aenemic. There was something odd with the ailerons on the model. For some reason, even with no expo (and 4 aileron servos) the ailerons were extremely slow around center. Past half deflection on the stick and the roll rate was insane, but it was so soft and mushy around center that it was almost impossible to fly. I fixed it with reverse expo, making the throw around the center of the stick more sensitive. I never discovered the root cause of the strange aileron issue. I sold the plane a few years later.

As to the OPs originally question about reverse expo on rudder... it doesn't sound like a good idea to me at all. I fly with 3D rates all the time and I'm typically about 60% expo on elevator, 40% on aileron and 50% on rudder.

I think the others have covered it, I'd be very surprised if giving it the opposite to the other surfaces will help. It's normal to have negative(fut) Positive(JR/Spek) apart from unusual cases as mentioned.


One reason why it doesn't sound right is that the reason we use expo is to compensate for the rotational movement of the servo so the control surface moves in a more linear way. Basically when the servo starts to rotate the surface moves quite a lot, more servo travel means a straighter link between the arm and horn so the surface moves less despite the servo moving more.


Another is that for most people getting into 3D, rudder is one surface that takes quite a bit of getting used to. Many times during rolls people(myself included of course ) will input the wrong rudder, if you have a very sensitive rudder this will highlight your mistake. If you are down scraping the deck this can end nasty!


Setting the percentages is a very personal thing, I used to use quite a lot, however this can cause issues as you move the stick a little and nothing happens, move it a little more then BANG, too much! I find now using less is a nice balance, but this is a very personal thing, set up a few rates with different values and see what feels comfortable.


I'm probably repeating stuff you all ready know but hopefully it's helped anyway.


Cheers
Chris