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Maximum Control Deflection

#1
What is the maximum effective angle of deflection for a plane’s control surfaces? As a naval architect I know what it is for a vessel. But, since water is about 800 times denser than air my concepts may be way off.
A boat’s or ship’s rudder never exceeds a maximum deflection of 35 degrees. Beyond that it acts like a brake rather than a steering device. At that point it loses a smooth flow of water on each side, with the stern side living in pure turbulence. Actually, the average designed deflection is closer to 32 degrees. It all depends on the rudder and how it is mounted.
 

Merv

Well-known member
#3
I’ve been told there is no point going above 45 degrees. I usually set mine somewhere between 35 & 45, but I can’t say I’ve ever measured. With a new plane, I start with much lower throws until I get the plane trimmed out. Then slowly crank up the throws.

When you turn up throws, you will discover you have a whole new plane. It will eventually become unstable. I set throws more by how the plane fly’s than by a fixed number (always 35 degrees). I want enough instability to have some fun but yet be flyable. How much instability you want is a matter of personal choice.
 

Hai-Lee

Old and Bold RC PILOT
#4
The other thing that does not compare well between hydrodynamic modelling of ships and aerodynamic modelling of aircraft is the mass/inertia of the craft involved and the viscosity of the medium through which they travel. Then there is the simple fact that air is compressible whereas water is not!

Relative to naval vessels the control surfaces on an aircraft are massive! Also the speed range is relatively vast for aircraft.

Slow speed aircraft can have very large control surfaces and large deflection angles just to maintain controllability whereas the same plane at high speed may require only the slightest of control surface movement for extremely high "G" maneuvers.

The real issue for an aircraft is not the maximum possible deflection but rather the appropriate amount of control deflection to suit its mass, wing loading and speed. To this end RC model aircraft have features like Dual Rates and Expo to enable a variable control surface movement for when the change in airspeed requires more delicate control surface movements.

The forum is littered with those new to the hobby/sport who have great struggles learning that with model aircraft control surfaces, less, (control surface movement), is more, (control).

Have fun!
 
#5
Found this: "On the Boeing 767-300 aircraft (I happened to have the aircraft maintenance manual handy) the total rudder deflection is about 26 degrees left and right, the total elevator deflection is about 28 degrees up and 20 degrees down, the total inboard aileron deflection is about 21 degrees up and down, and the total outboard aileron deflection is about 30 degrees up and 15 degrees down."

Not exactly our kind of plane. But some further research shows that a common Cessna 180 uses 24 degrees, while a C-130 Hercules cargo plane has 35 degrees--which is the greatest deflection that I've found.

Still love to know if guys flying 3D planes really need as much deflection as they are using.
 

Hai-Lee

Old and Bold RC PILOT
#6
Still love to know if guys flying 3D planes really need as much deflection as they are using.
There are different categories of flight! A bullet is said to fly through the air and so does a airship but they do not use aerodynamic lift to stay in the air.

3D flying also does not really require aerodynamic lift but rather is best considered as a "Vectored thrust" flying platform in the same way that a quadcopter flies. The good thing about a 3D plane though is that you can markedly reduce the control deflections, (using dual rate) and fly them as sport aircraft as well.

As the motor thrust is used to control and support the plane in 3D flight large control surfaces and serious control deflections are required for rapid responses to control inputs.

As for the maximums you quoted for full-sized aircraft try to find out the effects of full control surface deflections at maximum flying speeds. (The on-board flight computers are now programmed to prohibit such structurally dangerous situations). The maximums are only available when the plane is travelling quite slowly.

Just my thoughts!

Have fun!
 

quorneng

Well-known member
#7
As Hai-Lee pointed out air flow is rather different to water flow.
Air flow over a smooth surface tends to go fully turbulent at quite a small sudden change in angle so most control surfaces are turbulent on the 'low pressure' side well before 30 degrees. The surface will still produce a force at 45 degrees and beyond although the drag increases compared to smaller deflections.
It worth remembering that moving a plane's control surface not only creates drag but the effect of the surface makes the plane alter its angle in the air stream so increasing the total drag further. Selecting the best size and deflection of a control surface for a particular manoeuvre can be quite a complex compromise.
 
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mayan

Well-known member
#8
I agree with all that was said and must mention that the control surface size can influnce the amount of deflection required to achieve the same goal. The speed has an effect on how the smallest defelction will effect the plane manvuerabilty. And all this needs to be considered when deciding what the chracteristics of the desired plane.