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BARNARD MICROSYSTEMS LIMITED helping you keep an eye on things... |
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Unmanned Aircraft design
We provide design guidelines for a Unmanned Aircraft based on a payload and a range specification:
The Unmanned Aircraft data used was first checked in detail for consistency using our UAV Analysis Utility. If you have additional, or, better, suggestions in respect of design guidelines for a UAV, we would be pleased to add your contribution and credit you for the information. |
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UAV Designer Version 1.4 This is the first prototype UAV Design Utility. It will give you a rough idea of the UAV characteristics based on the UAV payload weight in kilograms and on the range required. Note that we have converted a Microsoft EXCEL spreadsheet to an HTML script using the SpreadsheetConverter software, and have incorporated the resultant HTML script in this web page. Consequently, depending on the security setting on your computer, you might be asked whether you would like to allow your computer to run the following HTML script. I have noticed that the UAV Design Utility can become corrupted. If you find it is not working, please drop me an email and I will upload a working copy of the utility. My email address is:
These are design guidelines based on trends identified from the best data we can get for existing Unmanned Air Vehicles. These guidelines are for UAVs fitted with either four stroke or Wankel engines. Two stroke engines are not very fuel efficient, although they do have a high power-to-weight ratio. I have left off two stroke engines because we are mostly interested in long range UAVs that can be used in geophysical survey work. UAVs powered by gas turbines tend to be the larger UAVs, and these are at present not considered since we are in this case mostly interested in the smaller UAVs. The design process for a UAV to be used in a survey application starts with the weight of the PayLoad Wpl and the Range. From the plot below we have deduced a relationship that allows one to estimate the take off weight, Wto. Remember these are guidelines for use with UAVs in which either four stroke or Wankel engines are used. The data used in the trend analysis has been based on:
Given the scatter in the above data, simply assume an endurance speed of 100 Kph.
For a flight at constant speed, we have assumed the power required to keep the plane moving is directly proportional to the total weight of the plane, which decreases in a non-linear manner with time as the fuel is used up. The weight of the plane at a distance = x is given by W(x) = Wto * exp( - x / D ), where Wto is the take-off weight of the plane, and D is a figure-of-merit for the plane we call the " characteristic distance" . Through a simple integration, it can be shown that: D = R / ln (Wto / Wnf) where R is the range, Wto is the take off weight and Wnf is the weight of the of the plane with no fuel on board. For simplicity, it is assumed that at the end of the UAV flying a distance = R, there is no fuel left on the UAV.
Above is a plot of D figure-of-merit values for several well known UAVs. There is quite a spread. The higher the D value, the more efficient the UAV. The average value is 6,966 Km if we ignore the low values for the Shadow 200 and the Hermes 180. The Characteristic Distance " D" figure-of-merit value, or efficiency measure, for the UAV, is the distance the UAV flies per Kg of total, time dependent (since the UAV gets lighter as it uses up the fuel), aircraft weight, per Kg of fuel used. Inverting the above relationship, we can calculate the weight of the fuel = Wf from:
If we plot a histogram, as shown above, comparing the actual versus the predicted weight of the fuel for several UAVs, and then perform a least squares minimisation of the sum of the errors as a function of the D value, we conclude that we minimise the errors for the above UAVs when D = 7,200 Km. We have ignored the comparison for the Shadow 200 and the Hermes 180 since these two UAVs have low Characteristic Distance figures-of-merit.
For a four stroke engine, Pout = 0.073 * x + 0.031 for Pout in KWatts, where x is the engine capacity in cc. The engine capacity = CAP is given by:
Derived from some data in the US DoD uav_roadmap2005.pdf document.
This is one of the most difficult charts, since we wish to remove the costs associated with the sensor systems that are typically to be found on military UAVs. Consequently, we have removed the data points for the Predator UAV and the Global Hawk UAV, since these UAVs carry very expensive avionics, communications and sensor systems.
So, here you have the basis for a rudimentary Unmanned Air Vehicle design based on relationships derived from some existing UAVs. Additionally, you have a rough price guide, albeit based on FY02 $K values. Treat these estimates as very approximate guidelines: we have derived the data from the US DoD uav_roadmap2005.pdf and have no way of knowing any of the details about the financial arrangements.
Above from the presentation by Peter Bockelmann on " The importance of logistics for all lifecycles of a UAV system" at the UAV 2007 Conference in Paris. © Barnard Microsystems Limited 2006 - 2008
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