Question About Differential Ailerons

[Nigel Heather]

I have noticed the aileron servo arms my on my low-wing foamy (Max Thrust Ruckus) are both off centre by the same amount at neutral - the arms are angled forward (towards leading edge) rather than being at right angle.

 

These are pre-installed and set-up in the factory.

 

Because they are angled by exactly the same amount I assumed that it was deliberate to create differential ailerons mechanically, but when I check operation they are the opposite to what I would expect - they move more down than up, I thought it should be the other way round.

 

What are your thoughts?

[Mike T]

The setting at the aileron you describe should give more up than down (assuming your Ruckus is standard with the servos and control horns are installed on the wing underside). 

 

How are the servo horns positioned?  Is there a stray mix in your Tx that you haven't got rid of?

[Nigel Heather]

10 minutes ago, Mike T said:

The setting at the aileron you describe should give more up than down (assuming your Ruckus is standard with the servos and control horns are installed on the wing underside). 

 

How are the servo horns positioned?  Is there a stray mix in your Tx that you haven't got rid of?

 

Yes that is what I thought- guessing that I must have reverse on.

[MattyB]

Just take a pic of the linkage and add it that will really help us. To know whais going on

Edited September 13 by MattyB

[MattyB]

15 minutes ago, Nigel Heather said:

 

Yes that is what I thought- guessing that I must have reverse on.

Probably just some negative diff in the Tx I am guessing but we need a pic of the linkage first to truly understand

[Simon Chaddock]

The angle of the aileron horns will depend on the relative position of the aileron hinge line.

In this case the angled horn is to is to get the horn pivot point perpendicular to the hinge line and not to create differential. The differential movement (more up than down) is created by the forward angle of the servo arm. 

A simple diagram of your Ruckus aileron linkage would help establish what is happening.

[MattyB]

40 minutes ago, Simon Chaddock said:

The angle of the aileron horns will depend on the relative position of the aileron hinge line.

In this case the angled horn is to is to get the horn pivot point perpendicular to the hinge line and not to create differential. The differential movement (more up than down) is created by the forward angle of the servo arm. 

A simple diagram of your Ruckus aileron linkage would help establish what is happening.

Agreed or even just a simple photo would do! 

[Nigel Heather]

1 hour ago, MattyB said:

Just take a pic of the linkage and add it that will really help us. To know whais going on

 

Here you go

 

 

[John Rickett 102]

There's your answer, the aileron horn is set further back from the hinge line than the servo arm is in front of the servo pivot. You would need to add more servo differential, easily done with replacing the push rods with slightly longer ones. 

[Nigel Heather]

6 minutes ago, John Rickett 102 said:

There's your answer, the aileron horn is set further back from the hinge line than the servo arm is in front of the servo pivot. You would need to add more servo differential, easily done with replacing the push rods with slightly longer ones. 

 

Got it - so what you are suggesting is that they haven't pitched the servo arms forward to introduce differential ailerons but to try and get rid of of unintentional differential from having the servo horns too far back?

[John Rickett 102]

Nigel,

 

I don't know what the manufacturer's intentions were, though it looks as if the aileron horns couldn't be positioned any further forward due to the chamfer. It would have helped if they had fitted horns which were raked forward so that the holes were directly under the hinge line. You may be able to find some and fit them yourself. Failing that, if you move the servo horn to be 30- 45 degrees, instead of the 15 degrees or so  it is now, it will give you the more-up-than-down movement you're seeking, you'd just need some longer pushrods, which you can bend to the desired length.    

[john stones 1 - Moderator]

There's no differential intent there, maybe the spline won't allow 90% if it does do it and adjust pushrod, just lazy work by worker under time pressure, piece work.

[MattyB]

Given the Pandora of this model for now I would just tweak the differential settings the Tx at for the maiden so that you don’t see any +ve or -ve diff at the surface. It may not be the optimal mechanical setup like that but you n at least get the maiden done without raising with bending up a new set of linkages. 

[john stones 1 - Moderator]

Not sure what I said that's funny, nor why new rods are needed ? Enlighten me ?

 

[Nigel Heather]

The more I think about it, I think the manufacturer is just trying to offset the horn position to make the aileron movement equal rather than to introduce differential ailerons.

 

One reason is the setup in the manual specifies equal up:down throws for the ailerons.

 

The simplest solution would be to move the horns a little more forward, but I would need new rods for that as they are only barely long enough at the moment for my liking.  But I’ve been unable to find any 1.2 threaded rod.  The alternative would be to replace it with 2mm.

 

Another possibility is to find different horns or modify the existing ones - but I have never seen any where the clevis holes are well forward of the mounting plate.  I have this problem to solve with a kit (a gangster 63 lite) which has sloped top hinged ailerons so the underside front edge of the aileron is miles away from the hinge line.

[Jonathan M]

I think you're right:  the manufacturer is correcting for the rearward aileron horn position, so as to achieve zero differential as per spec settings.  (Had they used angled horns this wouldn't have been necessary, but I don't suppose anything more than bog-standard horns are available at the extreme budget end of things.)

 

Re your Gangster Lite, the supplied horns do rake forwards to bring the leverage point forward, but not quite as far as to be perpendicular to the hinge-line.  On mine I tweaked computer differential independently to bring each aileron to zero actual differential.

[John Lee]

....or just fly it inverted when the differential will work the right way😀

[Nigel Heather]

Anyone know of any horns that have a larger than normal offset - I've looked at all the online stores that I can think off but haven't be able to find any.

 

My preference would be to get the horns in the proposer place rather than increasing the rake of the servo arms.

 

Of course it may not be possible as the horns on the foamy do seem to have bespoke mounting plate.

[Martin Harris - Moderator]

2 hours ago, John Lee said:

....or just fly it inverted when the differential will work the right way😀

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. 

[Jonathan M]

53 minutes ago, Nigel Heather said:

Anyone know of any horns that have a larger than normal offset - I've looked at all the online stores that I can think off but haven't be able to find any.

 

My preference would be to get the horns in the proposer place rather than increasing the rake of the servo arms.

 

Of course it may not be possible as the horns on the foamy do seem to have bespoke mounting plate.

 

Maybe suss a way to adapt the existing ones?  e.g. insert a balsa wedge under the horn-plate to angle the whole thing?

 

To be honest though, the plastic horns on my recently-bought Riot are terrible!  I knocked an aileron lightly the other day putting the model back into the car and the brittle horn just broke!

 

PS - they must all be really bad!  I've just looked at every retailer for replacement Max-Thrust horns and they're sold out everywhere!

 

Edited September 14 by Jonathan M

[John Lee]

Hopefully this will be a bit more helpful than my last suggestion!

 

Have a look at the Multiplex control horn part no MPX703457 maybe from Sussex Models among others, shown here on my RaceWulf:

 

 

[Chris Walby]

22 hours ago, Nigel Heather said:

I have noticed the aileron servo arms my on my low-wing foamy (Max Thrust Ruckus) are both off centre by the same amount at neutral - the arms are angled forward (towards leading edge) rather than being at right angle.

 

These are pre-installed and set-up in the factory.

 

Because they are angled by exactly the same amount I assumed that it was deliberate to create differential ailerons mechanically, but when I check operation they are the opposite to what I would expect - they move more down than up, I thought it should be the other way round.

 

What are your thoughts?

TBH and IMO its a case of overthinking this in a really major way. IIRC the wing was derived from the Riot, so perhaps the designers had something in mind for a high winger model. The Rucus is just a mid wing version and if you can tell the difference between differential and non differential on a Rucus then you are better man than me.

 

Check model, put battery in and go fly... repeat until next time and save your time and effort for something else. 🤣

[Eric Robson]

The Ruckus is one of the most popular models in our club and I have never heard of anyone having to modify the ailerons. Being a mass produced kit I would imagine the fittings to be jig aligned. As Chris said just fly it. All the ones I've seen fly very well and are quite aerobatic. 

[leccyflyer]

Good point Eric, frankly, given the use to which the models are typically put,  I'd be very surprised if anyone would even notice any difference in the handling with the ailerons set up exactly as they come from the factory.

[Nigel Heather]

3 hours ago, Eric Robson said:

The Ruckus is one of the most popular models in our club and I have never heard of anyone having to modify the ailerons. Being a mass produced kit I would imagine the fittings to be jig aligned. As Chris said just fly it. All the ones I've seen fly very well and are quite aerobatic. 

 

I'm not really that bothered - I didn't notice it at first, it was only when I decided to replace all the clevises after I had two just snap on me - they are made of a hard plastic, like Airfix kit polystyrene which is very brittle.  Both the rudder and elevator clevises snapped while in use - still hanging on but it was lucky that I noticed.

 

It was only when I went to change the aileron clevises for good measure that I noticed that the servo horns were raked forward - and I just wondered why - I assumed that it was for mechanical differential but but the symmetry seemed wrong, more down than up, so I asked on here - that's all.

 

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.

 

But as you say, at my skill level, I won't be able to tell the difference.

 

The reason I am asking about different horns is primarily for the Gangster to be built over the winter that I would like to set up more accurately.