Any pros or cons to an extreme rudder pivot angle?

[Chuck Plains]

I'm rebuilding my first ever scratch built jobby. It's a 1.3mtr slow stick, with about 20 degrees of diherdal and I'm adding ailerons, because I can.

So my thought this evening was about an interesting rudder pivot angle. I know some aircraft and models have some mild angles at the rudder pivot, but I was wondering about a more definite angle like 20 or 30 degrees.

If the angle is forward at the top I assume there is a relative amount of force directed downwards when the rudder operates.

Are there benefits, I'll admit I have realized that it would be used to advantage if there was any. So I thought I'd ask.

[Geoff S]

My Eezee Peezy has an angled rudder though it slopes backwards rather than forwards. The main problem is the operating mechanism which needs to allow for the slope. Not insuperable but it needs a little thought.

I once had a model racing yacht that had an angled rudder pivot which was a swine to steer downwind in a blow. Because there was so much area behind the pivot the Futaba 148 servo was unable to hold it straight. I changes it for one with a vertical pivot and with some area forward of it to help reduce the load. I suppose the same would apply in the air as it does in water.

Geoff

[Former Member]

[This posting has been removed]

[PatMc]

With the bulk of the area so high it will increase the rudder's rolling effect - in the wrong direction.

[Simon Chaddock]

As drawn the swept forward rudder hinge line will tend to push the nose down in a rudder turn. Whether this is good or bad will depend on the characteristics of the plane.

It is more conventional to sweep back the rudder hinge line,

**LINK**

I fear 20 Degrees dihedral will tend make the ailerons rather in effective.

[Chuck Plains]

Thanx guys, I suspected the detriment rather than a benefit, to be honest.

Heh, when I tried googling angled rudder pivot, all I got was stuff about racing yachts etc. And it seems to me that would possibly cause the rudder itself to twist somewhat. And this is only foamboard, so let's treat it gently, well a bit anyway. Vertical pivot it is then.

The ailerons are more like a mini comfort zone for me as I've not flown anything successfully without them, not even when even when switching the rudder to the right stick. I'll build some mechanical differential in them to give a little more down aileron for the upward pointing wing.

We'll see how it goes. I've crashed this one before, so I'm sure I have the skills to do it again. :D

[Chuck Plains]

Posted by Simon Chaddock on 03/04/2016 22:52:43:

I fear 20 Degrees dihedral will tend make the ailerons rather in effective.

Well I think it's 20, I haven't actually measured it. Maybe it's 15 but there's a little bit of flex in there too.

[Rosco]

If you go with your angled rudder for experimental reasons, as has been mentioned, the operating mechanism will bind if you attach the control horn in a parallel orientation to the fuselage. You will need to angle the horn and control linkage so that it operates at 90deg to the hinge line. I would also attach it higher up on the rudder where there is more 'meat' which should prevent any twisting when the rudder is used.

Apologies if I'm stating the obvious.

Rosco

[onetenor]

I think forward area at the top of the fin would tend to force the rudder over more than intended and might overpower the servo. Of course I could be entirely wrong

John

[Don Fry]

When you march in a different direction to the rest of the world, they may have good reason to go where they go. Chinese proverb.

[Biggles' Elder Brother - Moderator]

Posted by PatMc on 03/04/2016 22:13:45:

With the bulk of the area so high it will increase the rudder's rolling effect - in the wrong direction.

Yeap - that was my first thought to. Put in right rudder and its going to try to roll you left! Mind you with 20 degrees of dihedral maybe a bit of "opposite" wouldn't be a bad idea.

BEB

[IanN]

Back in single channel days it wasn't unusual to hear it said that people slanted the rudder hinge line back a little to get some "up elevator" effect

I remember David Boddington writing that he had experimented with this, using increasing angles, and that he found no discernible elevator effect at all but did experience progressively deteriorating rudder authority

[PatMc]

Posted by Biggles' Elder Brother - Moderator on 04/04/2016 13:27:34:

Posted by PatMc on 03/04/2016 22:13:45:

With the bulk of the area so high it will increase the rudder's rolling effect - in the wrong direction.

Yeap - that was my first thought to. Put in right rudder and its going to try to roll you left! Mind you with 20 degrees of dihedral maybe a bit of "opposite" wouldn't be a bad idea.

BEB

A bit less rudder area would be better.

Assuming that 20° dihedral means 10° per side then it's slightly less than the Junior 60 (23° total) - so not really that bad.

[Chuck Plains]

Hehe, calculated it properly now and it has 14deg total dihedral, (Specsavers at the end of the month) No flexing will be occurring, due to the application of some 6mm carbon tube and a suitably bent aly tube joiner glued to the dihedral brace.

I guess you could call these ailerons 'trim tabs' as they are quite narrow, but they do cover the outer half of the span. The wing has a 24cm chord (9.5" and the control surfaces are the width of my straight edge at 28mm

23deg? That's almost a wannabe boat hull!

[Chuck Plains]

Posted by Biggles' Elder Brother - Moderator on 04/04/2016 13:27:34:

Posted by PatMc on 03/04/2016 22:13:45:

With the bulk of the area so high it will increase the rudder's rolling effect - in the wrong direction.

Yeap - that was my first thought to. Put in right rudder and its going to try to roll you left! Mind you with 20 degrees of dihedral maybe a bit of "opposite" wouldn't be a bad idea.

BEB

I'm left footed when I kick a ball, but right handed when I do anything else. All that's left after that are my politics.

[Chuck Plains]

Posted by Donald Fry on 04/04/2016 06:26:01:

When you march in a different direction to the rest of the world, they may have good reason to go where they go. Chinese proverb.

I like that.

[Chuck Plains]

Posted by Rosco on 04/04/2016 01:12:21:
If you go with your angled rudder for experimental reasons, as has been mentioned, the operating mechanism will bind if you attach the control horn in a parallel orientation to the fuselage. You will need to angle the horn and control linkage so that it operates at 90deg to the hinge line. I would also attach it higher up on the rudder where there is more 'meat' which should prevent any twisting when the rudder is used.

Apologies if I'm stating the obvious.

Rosco

I would have used a micro servo at the tail.

[Simon Chaddock]

Chuck

"I'll build some mechanical differential in them to give a little more down aileron for the upward pointing wing."

Doesn't aileron differential work the other way? More up than down,

"a suitably bent aly tube joiner glued to the dihedral brace"

Be careful just simply bending ally tube. It is normally cold drawn extruded which means it has been pretty well 'worked' already so even a small bend (14 degrees!) can stretch the ally beyond its yield point and it looses much of its strength.

The plane sounds very interesting. Any chance of a picture?

[Denis Watkins]

Just to add, although a high angle rudder angle can look racey, they do cause a bank when sustained rudder is held in. This is amplified with the rudder pivoted above the main plane. Rudder authority is improved when designed similar to F3a models, with much of the rudder surface above and below the main plane pivoted at right angles, and does fly with much less of a tendency to bank

[Chuck Plains]

Posted by Simon Chaddock on 04/04/2016 21:27:38:

Doesn't aileron differential work the other way? More up than down,

"a suitably bent aly tube joiner glued to the dihedral brace"

Be careful just simply bending ally tube. It is normally cold drawn extruded which means it has been pretty well 'worked' already so even a small bend (14 degrees!) can stretch the ally beyond its yield point and it looses much of its strength.

The plane sounds very interesting. Any chance of a picture?

Differential to me just means one different to the other. I realize that the tradition is as you say. But my logic in this case says that the downward wing produces more lift and has more control, so needs less up aileron than the upward wing needs down aileron. Anyhoo, seeing as the maximum total movement at the trailing edges of the control surfaces will only be about 25mm I'll only be giving it a few mm extra down to begin with.

I hear you about the ally joiner. But this isn't a stunt plane, it's a slow flier and has already flown with no joiner and just two 4mm carbon rods, each shoved right through into the opposite wing a bit at the center. It didn't eve have a ply wing brace. Don't forget this was only the second set of wings I ever made.

Picture?

Oh all right then. Phone cam only though.

Wing and repared stick

Not an Armin wing, but intentional undercamber.

[Chuck Plains]

Oh yes and some other bits and bobs.

Tail feathers with edges pinched.

Edges pinched? I hear you ask.

Just a rapid demo for this thread. (seeing as how you asked for pics)

Foam pinched in vice 15mm deep from edge. No close focus available.

15 second squeeze.

2 minute squeeze at half depth to finish.

That was rapidly done just to demonstrate this process that I discovered last year. More care was taken over the tail feathers and they are a bit better that what is shown here, more central to the foam. But foamboard is foamboard and it's not an exact process. I just don't want too much sanding of foam or balsa in my front room-workshop as my cat is always around and I don't want him to be grooming himself and ingesting it.

[Chuck Plains]

Posted by Denis Watkins on 04/04/2016 22:14:41:

Just to add, although a high angle rudder angle can look racey, they do cause a bank when sustained rudder is held in. This is amplified with the rudder pivoted above the main plane. Rudder authority is improved when designed similar to F3a models, with much of the rudder surface above and below the main plane pivoted at right angles, and does fly with much less of a tendency to bank

What you have said has confirmed in my mind why so many wing and stick gliders and DLGs have fin and rudder above and below the fuselage line. Yes, flat turns can be advantageous if you are attempting to maintain altitude. I learned to use my ailerons to negate the banking while using the rudder to effect a turn with my trusty Bixler. (now retired)

[Chuck Plains]

Sorry, no video or flight pics, all I had was my phone in my pocket.

First time flying the stick was at Little Haldon. I surprised myself by taking it home in one piece after 3 flights with 3 battery packs. I had taken two 2200 3s and two 1300 3s packs but the 2200 turned out to be too heavy. The wind was about 8mph or maybe less generally and the 3 glider guys were finding good thermals. But those same thermals made it a bit tricky from ground level to 50 feet, which is where I was flying.

The stick did ok, considering my lack of skills and kept itself off the ground except when I wanted to land. Yes the ailerons give a sluggish response as expected and the rudder was more effective than anything I've flown before by rudder! So much so that I was 'trim tabbing' like mad at first to compensate!

Great weather though.

[Chuck Plains]

That was Sunday if I'm not mistaken.

I was only giving it 5 minutes at a time then.

But on Tuesday, I did the stupid thing with the battery and forgot how long I had been flying. And, having not set the ESC to go to 50% power on sensing low voltage, I dumped the Lipo to 1%. Doh! It seems to be recovering, somewhat and is in storage mode now after accepting a full charge this evening, finally. I'm certain that it won't be back to full spec this time around, but it still seems it will be useful after all thanks to everyone's advice on this thread >> Can I recover this Lipo?

That time it dumped itself in the 6 inch grass in the field behind work and broke my last serviceable 9x5 cheap orange prop.

Yesterday I did the noob type thumbs thing and broke the stick while using a 10x7 prop on the same motor. But it was a bit too windy and the prop gave so much more thrust, that I didn't control it properly and stuffed it in.

The metal skid is an offcut gleaned from the scrap bin at work. It's approx 1mm thick and 10mm wide. I just have to rub the sharp edges off, cut to length, drill tow holes and it's done. It bends a bit, but then you straighten it. Home made motor mount too, also from scrap.

The stick, at 600g flight ready isn't heavy enough for 15 mph winds. Ironically I would have been better off using the 2200 Lipos that time.