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# Control Surfaces Hinge Moment Calculation

## Control Surfaces Hinge Moment Calculation

(OP)
Firstly, this isn't my area but got dragged into this project. In these hard and lean times, you have to do what is needed to survive.

Primary objective is to find a way to optimize control surfaces hinge moments and ultimately bring down size of Control Surfaces.

Currently, for prelim design ESDU data sheets are used and for further iterations data from CFD is being used. As a first step, trying to find out if there are any newer & better alternative ways to calculate hinge moments. Project is in very early research & exploratory stage...so any inputs are welcome.

Just thought I will put it out here since this site has been a valuable & helpful resource for me in the past.

### RE: Control Surfaces Hinge Moment Calculation

Which control surface? Aileron, spoiler, flap, elevator, rudder? All are driven by different aspects of the aircraft configuration and flight maneuver requirements.

### RE: Control Surfaces Hinge Moment Calculation

"Primary objective is to find a way to optimize control surfaces hinge moments and ultimately bring down size of Control Surfaces."

The size of control surfaces are determined by the aerodynamic force required for control, not by hinge moments.

### RE: Control Surfaces Hinge Moment Calculation

Not sure is this a new design or a modification, large or small aircraft, don't forget aeroelastic effects, those horrible piano hinge control surfaces can have high hinge moments due to wing flex under G.

### RE: Control Surfaces Hinge Moment Calculation

Do you have Raymer's book?
Have you examined Roskam's book series and the DARCorp design modules?

I have a personal story to recount as well. A few years ago I was looking at a prototype aircraft being made by a firm trying to grow from the LSA market to the GA market. They had in some ways copied a homebuilt aircraft, in some ways extended the manufacturing processes of their LSA's, and hired a bunch of kids fresh from school to analyze it. I got to see it about 1 month after the "supposedly" successful first flight.
Aside from several other characteristics that worried me, one of the major concerns I raised was the authority of the elevator to control the aircraft at high angles of attack, low speed, generally all of the corners of the envelope. In my opinion, given the power of the engine and the likely wide range of the CG, the elevator was too small by half.
The reason for this turned out to be that the designers wanted a sidestick control. For that to work, the elevator could not be too big or the stick force would be unmanageable.
Completely backwards thinking. That, and for other reasons, I could not give my support to their project.

Kind of the same thing Compositepro just said.

### RE: Control Surfaces Hinge Moment Calculation

Huh, there are a lot of ways to keep the stick force and the hinge moment low - balanced controls or flying them by the trim tabs. Not sure how it changes feel, but balanced surfaces were used by the Wright brothers and trim tabs can't have been much later.

Doesn't stop people from failing to learn from history.

### RE: Control Surfaces Hinge Moment Calculation

#### Quote (3Ddave)

Doesn't stop people from failing to learn from history.

Exactly what was going on during my site tour.

### RE: Control Surfaces Hinge Moment Calculation

(OP)
So the application is for a UAV. The control surface is a combination of elevator & aileron.

I will try to go through the traditional approaches. But as I've mentioned, the prelim design of control surfaces sizing (hinge moments were the primary driver as I understand) we are using ESDU sheets.

Anyways, thanks for replies folks. I will update this post as when I get a little bit more finer clarity on how we went to proceed.

### RE: Control Surfaces Hinge Moment Calculation

Agree with others ... hinge moment is an "odd" design driver ... unless you're looking solely at the structure of the surface, in which case it is key !

but you can't separate things in design like this. A key problem with particularly aircraft design is that some many things are so interrelated by usually non linear relationships and with many variables changing daily, so "all" we can do is make decision based on experience and hope they are good ones ... else spend an enormous budget analyzing the heck out of millions of variations of a design.

A control's surface primary job is to control the airplane. Aerodynamics defines the effectiveness of a control surface, and the aero loads on the surface. Size of the surface is off-set by deflection angle. The onboard control system (the cables controlling the position of the surface) define the onboard loads, the reactions to the aero loads. Design restrictions here are stick force and deflections angles. On top of these design constraints you have a tonne of other controls (like aero-elastic stiffness, mass balancing, etc). Some of these you may side-step with a (small?) UAV. Weight of the surface is driven as much by the assembly process.

A control surface doing double duty (as elevator and aileron) isn't unheard of, though it is untraditional (so some of the traditional approaches won't work well). One idea (thought d'heure) would be to combine the traditional aileron and elevator weights, maybe 0.75 of the combined weights (so you get some advantage from combining them). Setting the weight budget is an early design consideration. The area of the surface is another, and there should be traditional approaches that may not be directly applicable to your project!

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