Trying to scale an actuator

[boffin5]

Hello,

I have a design problem: I have a known large airplane and aileron actuator definition, and would like to scale the actuator down for a smaller aircraft study. If the ratio of the aileron areas times their centroid distance from the centerline is, say 2, how do I apply this to scale down the actuator size?

If it was by volume, it would be the cube root of 2. If it was by piston area, it would be the square root of 2.

I just need a rule of thumb.

Any ideas? Thanks if so.

 

[GregLocock]

Soince the difference between the cube root of 2 and the square root of 2 is bugger all, in rule of thumb terminology, then it doesn't matter in that case.

More generally, I'd avoid taking that approach, just reverse engineer the original installation and then use the same sums for the new one. I think one of your assumptions is very dodgy.





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[rb1957]

how to the rolling moments compare, since this is the thing that ailerons control ? maybe you have roll rates and Ixx (moment of inertia about the roll axis)

 

[debodine]

Should you not also take into consideration airloads, which will differ not just because of the difference in area but because of the likely difference in airspeed between the two aircraft?

 

[boffin5]

Thank you all for the help.
Let me simplify the question:
If I have a known actuator that is capable of 10,000 lb of force, and I want to scale it down to a notional one capable of 5,000 lb force, what will be it's size? I know it won't scale linearly, that is be half as big.
Careers must have been built on scaling laws, but I'm having trouble getting info on this now.

 

[israelkk]

Assuming the oil pressure is the same, the inside diameter of the scale down cylinder will be smaller by the square root of 2. However, there is the matter of the cylinder wall thickness calculation, the construction material of the cylinder. etc. If you could not know this by yourself by now I suggest you study some engineering books (assuming you have an engineering degree) and do not even try to continue. An explosion or a burst of cylinder driven by 3000 psi hydraulic oil can take humen life.

 

[israelkk]

To clarify, the inside area of the scale down cylinder will be half therefore, the inside diameter will be scaled down by SQRT(0.5)=0.7071

 

[rb1957]

if you are trying to get an actuator for your design (rather than designing an actuator, i'd try contacting people who make them.

if you are trying to design an actuator, see israelkk's first post ... i'd suggest not proceding with caution, rather don't proceed at all ... designing an actuator isn't something to be taken lightly.

 

[tbuelna]

Actuators for control surfaces are usually sized for power rather than torque or force. So you should be concerned about actuation times/frequencies and system inertias. These requirements do not scale easily.

Also be aware that aircraft control surface actuators are typically designed with very generous power margins (>100%), to account for unusal conditions such as icing, hinge binding, or jamming.