What is coupling?
 

Ok everybody, this is probably the worst question to ever been asked. What exactly is coupling? I hear a lot of guys at the field talking about this during rolls and turning.

RE: What is coupling?
 

An example is a down aileron causes more drag than an up aileron (or vice versa i'm not 100 percent sure at the moment) so as you roll the plane the nose turns into the aileron with more drag so you dont get perfectly straight rolls.

Or if you give full rudder for knife edge and the nose pulls up too so you have to give down elevator to keep it straight.

RE: What is coupling?
 

Coupling is using 2 (or more ) functions at the same time. For instance, rudder and elevator or rudder, aileron and elevator.

Computer radios have the ability to do this through the programming. MOST computer radios refer to it as "mixing". Check the manual for your radio to see how it is done for your radio.

I have a couple of planes where I have coupling/mixing activated. One uses elevator with the flaps, another uses rudder and elevator with the ailerons (scale 30's era plane).

Hope this helps.

RE: What is coupling?
 

Generally when most mention coupling, they are talking about a non-pure control issue with the plane, due to the plane design or setup. By non-pure, I mean that if you give one input (say aileron), the plane does more than roll (like yaws too.) This is the coupling, i.e. a pure aileron input imparts a yaw as well as the expected roll, yet the rudder was never moved. As touched on in a prior post, in this example, the yaw is due to one aileron producing more drag (it would be the downward or lift generating aileron that produces more drag, i.e. the process of generating lift causes drag.)

Common coupling issues are ailerons causing yaw, and rudder causing roll and pitch, but other issues can occur. These couplings occur because of plane design.

Some coupling is desired in some models. For example, if you have dihedral, rudder input will cause a roll in the same direction, by design. In that case, the coupling might actually be desired as it helps coordinate turns, i.e. left rudder would also cause a little left roll.

However, a lot of coupling is not desired. A standard sport aerobatic model might have some very noticeable coupling issues. Even the best competition aerobatic models often have some very minor coupling issues. In the first example where ailerons cause yaw due to excess drag on the downward aileron. The yaw is actually in the opposite direction as the roll, i.e. a left aileron roll would cause right yaw. As you can imagine, this is generally not desired. There are several ways to fix that specific issue, such as decreasing just the downward travel of the ailerons (called aileron differential.) This can be done either mechanically or with a mix on the radio. But you could also setup a radio mix that applied a little rudder when you moved ailerons such that it offsets the yaw from moving the ailerons.

So, when you hear pilots talk about coupling, mixes, knife edge mixes, aileron differential, and the like, most likely they are discussing unwanted coupling effects and the mixes and/or setups to used to eliminated these issues such that the plane is “honest” to the control inputs.

Hope that helps. Cheers.

RE: What is coupling?
 

Campy, you are describing "mixing" not coupling. Coupling refers to the plane reacting on another axis when a different axis is commanded. The previous example of knife edge is a good one. Practically every plane will show coupling to the canopy or the wheels (pitch axis) when given rudder for the KE. Some flyers use transmitter mixing to blend a correction for the coupling so the pilot doesn't have to manually make the flight correction.

RE: What is coupling?
 

crabbing into a crosswind landing... if i give Right rudder the plane wants to roll instead of "crabbing" do you mix alieron in to the mix w. a flip of a switch if its programmed?

RE: What is coupling?
 

I just hope they were talking about flying airplanes:D

RE: What is coupling?
 

lmao
[X(] [X(]

RE: What is coupling?
 

I think this would create more problems that it would solve. To crab a model on a cross wind you need to cross couple the controls and you need to adjust it since your mix would have to change with the differant wind speeds and gusts.

keep the wings level with the ailerons and hold the heading with the rudder. You can practise this on calm days by side slipping the model

RE: What is coupling?
 

I want to practice 'slips', but do they have to be on approach? When I do it high, I can't actually see the plane slipping, so I guess I'm not really practicing.

Oh...and just so I don't hijack the thread, .....Your parents should have explained 'coupling' to you when you were younger, this is not really the place for that kind of talk.

;););)

RE: What is coupling?
 

Sure you can practice without the actual approach,
from medium alt:
reduce throttle and drop the nose some to get a glide slope
start your slip
keep it stable in glide & heading for 5 or 6 seconds
now get out of the slip & start a slip in the other direction

You can practice this reversing the slip controls till you can keep the plane stable in its glide slope... wherever that glide may be: up 2 mistakes high or on final 20' up. Just remeber that the slip is a drag monster, and you will lose speed- watch out for stalling! But practicing at high speed doesnt give you the right feel for the rudder at landing speeds, so practice slow, but HIGH UP. Will also help get the feel for the slipping stall speed & corrective actions... something not availible when practicing low, where corective action involves CA, Sticks, & Ironing

Even if you cant see the plane 'slipping', you know it must be from the TX being max Rudder & some Aileron, but the plane is going straight on the slope.

RE: What is coupling?
 

LOL...my UCD is hard to stall, but any added drag would certainly do it. Thanks for the tip...I need lots of practice...my slips um...SUCK....for now, that is. I use my foamies for risk-taking...I'll try slips higher and reversing them sounds like great practice.

Later,

Mark