Question About Differential Ailerons

[leccyflyer]

3 minutes ago, Nigel Heather said:

 

BTW - though if all the mass-produced Ruckuses are the same as mine then it is impossible to set up the aileron throws of '8mm up and down' as specified in the manual.

If you really had your heart set on the aileron throw being 8mm up and down you could probably do so using your transmitter's servo travel/end point adjustment to compensate for the incorrect mechanical set up.

[Nigel Heather]

13 hours ago, leccyflyer said:

If you really had your heart set on the aileron throw being 8mm up and down you could probably do so using your transmitter's servo travel/end point adjustment to compensate for the incorrect mechanical set up.

I’m not, I was just commenting on the statement which suggested that I was the only one out of thousands of customers that has noticed the issue.  So I was saying that as the instructions say that the ailerons should move 8mm up and down that others must have noticed that was impossible - without the use, as you say, of a computer transmitter.

 

Just to reiterate, I’m not bothered, it was just something I noticed when replacing the clevises and wanted to understand why it was like that - that’s all, as others say the plane flies okay as it is and I wouldn’t have been any the wiser had I not changed the clevises.

[Jonathan M]

Re aiming for perfection in general...

 

Of course most sports fliers aren't good enough to really notice the difference in travels of a couple of mm here or there, and your typical foamie certainly isn't tight enough to deliver full accuracy, but half the fun of this hobby is noticing these things and seeking to improve them!

 

Getting better at flying and getting more out of one's models is an iterative process overall... made up of scores of smaller iterative improvements in understanding and implementation... where worthwhile of course! 😉

[Simon Chaddock]

Although an aerodynamic effect may not be significant on a current model it can be worth understanding the "what and how" as it might well be important a bit further down the line.

Remember "adverse yaw" no matter how  it is created can in some situations lead to a serious crash. A low slow final turn as an example.

[Martin McIntosh]

You will probably laugh at this, but when I was flying F3A around 50 years ago, we mistakenly raked the horns forwards, even though the wing section was symmetrical. When I came back to the hobby with computer sets they said to rake the horns back. I made up a simple test jig and they were correct. In the old days, servo outputs tended to be square and to change the centre was not always easy but now they are splined so you have the choice of mechanical or Tx controlled differential.

My Stampe and Tiggys have 2:1 up/dn, mostly mechanical.

For a general fly everyday model you probably would not notice a slight barreling of rolls.  

[Nigel R]

15 hours ago, Martin McIntosh said:

You will probably laugh at this, but when I was flying F3A around 50 years ago, we mistakenly raked the horns forwards, even though the wing section was symmetrical.

 

If that was using torque rods on a low winger, then some forward rake of the horns (as in, the torque rods themselves) is correct for that setup.

 

 

 

 

[Robert Welford]

On 14/09/2024 at 13:35, Martin Harris - Moderator said:

In case anyone is misled by John’s jest, adverse yaw is produced by the increase on drag caused by the “downgoing” aileron modifying the wing section, producing more “lift” and in consequence, induced drag. In the case of inverted flight, that increased lift is acting downwards from the aileron increasing the wing’s angle of attack. 

 

Whether john's comment was made in jest, or not, his comment is correct in the sense that correcting for adverse yaw when in sustained inverted flight requires the opposite rudder input. For an aircraft that exhibits adverse yaw a roll to the right from upright flight requires input of right rudder. From sustained inverted flight a roll to the right requires left rudder to counter adverse yaw. Ask any pilot of full-size aircraft - an aerobatic pilot would be better. 

 

Thus, the effect of setting up differential aileron will cause the opposite desired effect when flying inverted when the wing section is producing lift in the opposite sense. 

So using aileron differential clearly works for countering adverse yaw for aircraft that do not sustain inverted flight - gliders, scale aircraft. However, for aerobatic aircraft we (me included) tune the aileron throws with different aileron throws up vs down - aileron differential. Why?

 

An axial roll is achieved when the roll axis passes through/along the fuselage  - if not the aircraft wobbles around the pure roll axis. It is possible that tuning up vs down aileron movement (differential) on an aerobatic aircraft shifts the roll axis up or down so the roll axis more closely intersects the centre of mass. This matches my observations.