Assignment #1: Attributes to consider for fixed wing UAV
“According to all known laws of aviation, there is no way that a bee should be able to fly. Its wings are too small to get its fat little body off the ground. The bee, of course, flies anyways. Because bees don't care what humans think is impossible.”
Steering entirely away from the obvious science that makes flight possible, or the mechanics behind flight dynamics, and the whole avionics or auto-pilot package let’s focus on the mission, the comms and the payload. UAV design teams also need to consider the following attributes such as
Takeoff – Will the UAV use a high energy launch system ie catapult, or vehicle mounted take off? How about Vertical Take Off and Landing (VOTL) but that’s not for Fixed Wing models. In some cases, hand launching is possible though too unpredictable
Landing – Parachutes, Deep Stall (free falling drop from the sky!), Belly Landing (hard), Wheeled landing, Net Recovery, or high precision hook catch (Scan Eagle by Insitu)
Positioning of payload – The actual payload or delivery capability. Some experts would say that the most important consideration in designing the UAV _IS the payload, without the payload the UAV has no purpose [3]. Depending on the structure of the UAV and purpose of the payload and load balancing, possible positions could be belly mounted (for cameras or munitions) vs nose positioning.
Comms Path – more to follow.
A Complete UAV package design would typically include [2]
- The baseline aircraft be it fixed wing or rotary series
- Optional manual control backup, by remote control link for collision avoidance
- GCS system for remote monitoring the UAV in flight status, intervention
- Onboard flight control
The communications link between UAV and GCS (ground control station) may theoretically be established by laser, fiber optics or radio but the RF- based communications is by far the most practical and widely used. Comms link is required for sending flight control data and analysis back to the control station, and depending on the mission, sending the data logging and interaction with on board sensors. Navigation sensors provide measurement of the UAV inflight status. Mission oriented sensors complement the nav sensors, can provide real-time and first person view.
ITU and IEEE names the designated frequency bands for small-scale UAV comms operation to
L band 405-425 MHz, 915 MHz, and 1.35 to 1.39 GHz
S band 2.45 GHz, C band 5.8 GHz all in LOS
Signal modulation – the wide usage of frequency hopping, spread spectrum has made it highly unlikely to lose comms between a UAV and GCS from signal interference. Spread spectrum is spreading the signal across the frequency spectrum and repeats the freq switching to minimize the chance of intercept or jamming.
Here is a really great example for a complete fixed wing UAV in operation, the Aerosonde.
Interesting facts about Aerosonde by AAI Corporation, a catapult-launched UAV with a typical takeoff weight 39 or 55. It lands by a net recovery catch or a soft belly landing in the snow.
It was initially designed to collect weather and atmospheric data over oceans, at a high altitude (over 5,500 ft) and endurance of over 10 hours. Example of other uses include missions by the US Navy and the US Special Operations Command.
In August 1998, it was the world’s first smallest aircraft to traverse the Atlantic Ocean, the first UAV for sure, launched from the roof of a moving car from Newfoundland, Canada and flew for over 26 hours to a small island off the coast of Scotland through stormy weather. Aerosondes have been known to fly through tropical storms since 2001. [1]
[2] G. Cai, J. Dias, L. Senevirantne, “A Survey of Small-Scale Unmanned Aerial Vehicles: Recent Advances and Future Development Trends” Unmanned Systems, Vol 2, No 2 (2014) pg 1 – 25.
