Aileron Differential?

[Steve W-O]

Posted by Steve Houghton 1 on 05/12/2011 14:15:50:

Can someone explain why we use aileron differential? What are the benefits of having less down movement than up?

 

 

Maybe the answer should have been something like:

 

It prevents adverse yaw

It helps prevent tip stalling

It can help rolls to be neater

[Olly P]

Posted by Steve W-O on 07/12/2011 16:08:53:

Posted by Steve Houghton 1 on 05/12/2011 14:15:50:

Can someone explain why we use aileron differential? What are the benefits of having less down movement than up?

 

 

Maybe the answer should have been something like:

 

It prevents adverse yaw

It helps prevent tip stalling

It can help rolls to be neater

 

On some, but not all aircraft...

[Andy Gates]

Ult

 

Is it not 3 Ahhhhhs and you are out? Just joking.

 

I too would not suggest that an inexperienced flier attempt slow low flying anymore than doing slow aileron rolls, flying inverted or prop hanging.

Edited By Andy Gates on 07/12/2011 16:33:39

[Ultymate]

You can have models where "negative" aileron diff is necessary to correct adverse yaw where the downgoing (relative to the airframe) has more travel than the upgoing one. This is nothing to do with reducing tipstall but relates to keeping rolls axial. Personally if I had a model that was inclined to tipstall on landing I would rather plumb in some slight up trim into both ailerons thus simulating washout.

[Steve W-O]

Posted by Ultymate on 07/12/2011 16:58:44:
You can have models where "negative" aileron diff is necessary to correct adverse yaw where the downgoing (relative to the airframe) has more travel than the upgoing one. This is nothing to do with reducing tipstall but relates to keeping rolls axial. Personally if I had a model that was inclined to tipstall on landing I would rather plumb in some slight up trim into both ailerons thus simulating washout.

 

 

 

And the effect of doing that?

 

Exactly the same as differential when you move the ailerons, so I would rather have the differential than your added drag of uptrim in normal flight.

 

[Ultymate]

The up trim (washout ) can be switched if the transmitter is capable and don't forget the differential may be counterproductive on some models, of all the aerobats I've had and there have been many only one has needed differential.

[Steve W-O]

Posted by Ultymate on 07/12/2011 18:16:36:
The up trim (washout ) can be switched if the transmitter is capable and don't forget the differential may be counterproductive on some models, of all the aerobats I've had and there have been many only one has needed differential.

 

 

Fair enough, but the original question?

 

It wasn't about why we don't use it, it was why is it used.

 

All the personal opinions/interpretations/experiences are interesting, but are not directly answering the original question, and as others have commented, some confusion has been introduced. If the question had been answered and the further questions asked, it might have less so.

[Ultymate]

Steve do you not fly aerobatics at all, as I see in your post no3 that you advocate 25-50% differential on all your models?

[Paul Adams]

I have been pondering BEB's reasoning and my reasoning and I can see the logic in both. So what is different between them?

 

Then it struck me, BEB's reasoning takes the view that as the model rolls the angle of attack of the wings in respect to the air flow is constant, and in that case the lift increasing wing will always have added drag. In my test cases the angle of attack of the wings has reversed as such the differential required would also need to reverse when the model is inverted.

 

In practice I would suggest that it is impossible to determine the angle of attack of the wing throughout the roll by theoretical processes and as such differential is best determined by trial and error.

So I suppose what I am saying is that we are both right.

[Simon Chaddock]

After a lot of Googleing on full size plane web sites the answer to my question

"Would the effect of reducing aileron yaw by differential aileron movement (more up than down) work the same in inverted flight"

The answer is an emphatic no.

Conventional differential movement when in inverted flight adds to any aileron induced yaw.