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Jul 08, 2016, 12:57 PM
Endurance, Altitude, and Range
daBKLYNdoorman's Avatar
Thread OP
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Dihedral Effect on Aileron and Rudder


If my plane has a large dihedral (~10 degrees) and long wings and cruises slow, which is the better surface to use for turning: aileron or rudder? Should there be any mixing of the two?

I am under the understanding that a rudder is used for yaw and the aileron for roll - does this change in any way in a large dihedral configuration?
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Jul 08, 2016, 01:06 PM
AndyKunz's Avatar
If you have lots of dihedral, ailerons don't work well. The rudder will provide plenty of roll.

Andy
Jul 08, 2016, 01:19 PM
Endurance, Altitude, and Range
daBKLYNdoorman's Avatar
Thread OP
Quote:
Originally Posted by AndyKunz
If you have lots of dihedral, ailerons don't work well. The rudder will provide plenty of roll.

Andy
Do you recommend still doing some aileron-rudder mixing to make turns more stable?
Jul 08, 2016, 01:37 PM
AMA 537620
ChillPhatCat's Avatar
If you have that much dihedral, you don't even need ailerons. Simply put, with lots of dihedral, when you use the rudder to yaw, the outboard wing in the turn faces it's underside toward the oncoming air and it pushes the wing into a bank.
Jul 08, 2016, 01:39 PM
Registered User
Clive66's Avatar
With lots of dihedral, I would fly it 3 channel (no ailerons)


What plane are you talking about ?
Jul 08, 2016, 01:50 PM
Endurance, Altitude, and Range
daBKLYNdoorman's Avatar
Thread OP
Quote:
Originally Posted by Clive66

What plane are you talking about ?
Bearospace Gemini V2
Gemini V-2 Custom UAV with Extensive Modifications (25 min 37 sec)
Jul 08, 2016, 02:19 PM
A man with too many toys
For UAV both ailerons and rudder would be good. Since that’s a UAV airplane that is to be flown by an autopilot it should have been build with about 1 degree of dihedral but I expect that it will fly ok as is.

If you use a good autopilot like the Pixhawk it will put in the correct rudder to control the yaw automatically. It does need to be set up to do that. I have that on several UAV airplanes and it’s easy.

That should be a very nice airplane. Don’t cut corners, get a full Pixhawk setup. PM me if you need advice.


BTW why does it have two rudders?

.
Jul 08, 2016, 02:51 PM
Endurance, Altitude, and Range
daBKLYNdoorman's Avatar
Thread OP
Quote:
Originally Posted by RC Man
For UAV both ailerons and rudder would be good. Since that’s a UAV airplane that is to be flown by an autopilot it should have been build with about 1 degree of dihedral but I expect that it will fly ok as is.

If you use a good autopilot like the Pixhawk it will put in the correct rudder to control the yaw automatically. It does need to be set up to do that. I have that on several UAV airplanes and it’s easy.

That should be a very nice airplane. Don’t cut corners, get a full Pixhawk setup. PM me if you need advice.


BTW why does it have two rudders?

.
Yeah, I have a Pitlab AP+OSD inside it right now. Great system so far but the true test will be when I fly it soon.

I was thinking about Pixhawk but my main turn off was (1) the need for an extra antenna for telemetry and (2) low power telemetry TX. I also use 1.2Ghz for video and noticed anything transmitting on the 900-1800Mhz frequency will completely destroy my video signal (or vice versa). Invested too much in 1.2Ghz video system to switch and plus it is the most robust for video penetration and range. Can't use 433Mhz for Pixhawk telemetry either because I use Dragonlink V3 for RC control.

Any ideas?

BTW - where is the store for Pixhawk stuff? 3DR only sells Pixhawk itself and the GPS and they are out of stock!
Jul 08, 2016, 03:04 PM
Registered User
glidarflyar's Avatar
Ailerons on a dihedral wing very probably need differential. Otherwise when deflected they actually create forces that oppose any turn the ailerons are supposed to help. When using those ailerons to facilitate a turn, the wing outboard on the turn experiences significantly more drag than the inboard wing. That tries to yaw the plane away from the turn, not into it.

Differential ailerons usually are rigged to go up more than they go down. That erases some of the stupid drag that comes when using ailerons on a wing that has significant dihedral.
Jul 08, 2016, 05:29 PM
Registered User
Yes - I would add aileron differential with a flat bottom wing with lots of dihedral. Add it until you don't get a yaw in the wrong direction when you apply a bunch of aileron.
Jul 08, 2016, 06:16 PM
A man with too many toys
Differential is very easy to tune with FPV. If you don’t have enough you will see the nose swing in the wrong direction when you first apply ailerons. You should first see roll with no yaw then the nose will start to swing as it enters the turn.

.
Jul 08, 2016, 06:59 PM
Endurance, Altitude, and Range
daBKLYNdoorman's Avatar
Thread OP
So let's say I want to make a left hand turn:
The ailerons should move as they would normally without dihedral (left aileron up, right aileron down).
Would the rudder move towards the right aileron or towards the left aileron?
Jul 08, 2016, 07:43 PM
AMA 537620
ChillPhatCat's Avatar
Quote:
Originally Posted by daBKLYNdoorman
So let's say I want to make a left hand turn:
The ailerons should move as they would normally without dihedral (left aileron up, right aileron down).
Would the rudder move towards the right aileron or towards the left aileron?
The surfaces always need to move in their appropriate respective directions. You need to set the up travel more than the down travel on the ailerons so that there is no yaw in the opposite direction when you apply the ailerons, otherwise the surfaces are just fighting each other and you need even more rudder to bring the nose around.
Jul 08, 2016, 09:38 PM
Registered User
Quote:
Originally Posted by daBKLYNdoorman
So let's say I want to make a left hand turn:
The ailerons should move as they would normally without dihedral (left aileron up, right aileron down).
Would the rudder move towards the right aileron or towards the left aileron?
To counteract adverse yaw from the ailerons you add rudder in the same direction as the aileron input.
Jul 08, 2016, 09:56 PM
Registered User
DustBen's Avatar
Quote:
Originally Posted by daBKLYNdoorman
Do you recommend still doing some aileron-rudder mixing to make turns more stable?
If you got that much dihedral in the wings, just nail the ailerons shut and plug the rudder servo into the aileron port.

I will never understand, after 50 years in this hobby, why any designer specifies so much dihedral in a full house (that's elevator, rudder, aileron, and throttle, for the kiddies in the audience) model.

The PT-40 called for lots of dihedral.
I used the aileron port for rudder, and the rudder port for nose gear...


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