Sizing and mass of aircraft surface controls

[icyplanetnhc (Steve)]

Hi everyone,

I'm currently performing component research for our senior design project. Our mission requirements currently call for a fairly small UAV with a takeoff weight in the neighborhood of 100 lbs, with a Vmax of 120 mph, and a service ceiling of less than 10,000 ft. In our preliminary design, we are performing a component weight and drag buildup, but the equations for such buildup found in our design books, such as Fundamentals of Aircraft Design by Leland Nicolai and Aircraft Design: A Conceptual Approach by Dan Raymer, don't scale particularly well for an aircraft of our weight class. Specifically, using Nicolai's small aircraft weight estimation for surface control weight (given below), our iterative methods resulted in surface control weight accounting for about 40% of our takeoff weight, which is not reasonable. To address this issue, I've been researching individual actuators, but I believe an aircraft of our size is too large to employ typical hobby servos, and my research of UAV in our weight class, such as the RQ-15 Neptune or even somewhat larger aircraft such as the RQ-2 Pioneer hasn't yielded much useful information regarding surface control mass. For an aircraft in our weight class, are there general rule of thumbs for estimating the mass of surface controls?

- Steven

 

[AeroFranz]

1- Look up Pegasus servos. They should have military-grade servos in the torque/speed range you need.

2- for control surfaces you might be better off either assuming a lbs/ft2 value, or try to do a mass buildup of the elements making up the surfaces. in your size and speed range, you are probably looking at minimum gauge construction. I'm assuming composite construction, right?

 

[icyplanetnhc (Steve)]

1- Look up Pegasus servos. They should have military-grade servos in the torque/speed range you need.

2- for control surfaces you might be better off either assuming a lbs/ft2 value, or try to do a mass buildup of the elements making up the surfaces. in your size and speed range, you are probably looking at minimum gauge construction. I'm assuming composite construction, right?

Thank you AeroFranz.

Composite construction may be better for weight reduction, but the equations for mass buildup from Nicolai appears to apply for an aircraft of traditional construction methods. We've been applying these equations to known aircraft and trying to match their weight by modifying the coefficients. Hopefully that will make them more applicable to an aircraft of our weight class. That being said, I believe most modern UAVs are of composite construction, right?

Furthermore, our research of different reconnaissance UAVs show that they carry a payload, such as a 20 lb payload for the 135 lbs WTO RQ-15 and 75 lbs payload for the 450 lbs WTO RQ-2. What would typically constitute as payload? We think it should include cameras and surveillance devices, but does it also include the avionics?

Side note: is there anywhere that I can find a component weight breakdown of a small UAV?

 

[AeroFranz]

Composite construction may be better for weight reduction, but the equations for mass buildup from Nicolai appears to apply for an aircraft of traditional construction methods. We've been applying these equations to known aircraft and trying to match their weight by modifying the coefficients. Hopefully that will make them more applicable to an aircraft of our weight class. That being said, I believe most modern UAVs are of composite construction, right?

yes, use Nicolai, Roskam, or Ramer and apply fudge factors. Small UAVs are definitely all composite these days. Or at least they should be!

Furthermore, our research of different reconnaissance UAVs show that they carry a payload, such as a 20 lb payload for the 135 lbs WTO RQ-15 and 75 lbs payload for the 450 lbs WTO RQ-2. What would typically constitute as payload? We think it should include cameras and surveillance devices, but does it also include the avionics?

depends what your mission is. Typically EO /IR cameras area a basic fit. Larger UAVs have larger cameras. The size is dictated by how high you are flying and what kind of resolution you need. Other payloads could include mini-SAR, more radios, precision munitions, etc. Avionics are book kept separately, it's a fixed part of empty weight.

Side note: is there anywhere that I can find a component weight breakdown of a small UAV?

Sadly i'm not aware of any detailed weight breakdown.

 

[icyplanetnhc (Steve)]

Thank you very much. If this had been an even smaller UAV then I might have been able to use our school's Design/Build/Fly aircraft as references for weight breakdown. But I'm not sure if balsa wood and monokote structure can count as composites. ;D