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We're designing a new 200kg VTOL drone, but have hit a problem with wing-propeller interaction. We need someone to help us understand the issues - and then to help us scope out the range of solutions that are available to us.

Compendium of Results

The slides below summarise a few findings of potentially more general interest that we have extracted from our work on various projects* for various clients - we hope you find them interesting!


more examples
Wake geometry and and associated partitioning of the thrust between the rotors of a compound-coaxial helicopter, as predicted by the VTM.

More information

A problem that is often encountered with helicopters and other aircraft that are designed for vertical takeoff and landing is the impingement of the wake produced by the propulsion system on some part of the airframe over a range of flight speeds or with the aircraft at certain attitudes to the oncoming flow. These aerodynamic interactions are associated with unexpected trim changes, noise, vibration, and a range of other more-or-less subtle, but nonetheless unwanted, physical effects on the airframe.

This figure shows the results of a computational analysis of the aerodynamic interactions that might be present in a very compact helicopter design that has a stiff, coaxial main rotor together with a tail-mounted propulsor to provide thrust in forward flight. Longitudinal stability and trim of the helicopter is augmented by a tailplane that is mounted on the fuselage just forward of the propulsor.

The interaction between the wakes from the two main rotors, the propulsor at the rear, and the horizontal stabiliser of this complex rotorcraft design is clearly apparent in the diagram at right. The diagram at bottom left shows how the changing nature of this interaction strongly influences the relative contribution to the overall thrust that each rotor must make as the forward speed of the helicopter is increased. A particular problem with this design is evident at low forward flight speed (i.e. at advance ratios less than 0.10) where, in order to trim the vehicle, the main rotor must provide a force that is in opposition to that provided by the propulsor.

Capturing effects such as this requires accurate characterisation of the aerodynamics of the vehicle down to a very fine level of detail. It is clear that, in the example presented here, the design will likely consume more power in practice than might have been suggested by a more simplistic analysis where, for instance, the effects of the aerodynamic interactions between the components of the aircraft were neglected.



* Except where explicit permission has been obtained to release actual data, geometries and test conditions have generally been changed to protect the intellectual property of the sponsors of the original work.

News

Use the tab above to access the latest news from Sophrodyne Aerospace!

Articles

The tab above leads to a page containing various articles on aeronautical topics that we have written over the last years.

These are in addition to Dr Brown's published academic articles, a list of which can be found here.

Useful tools and downloads Coming soon!

For the moment this tab will take you to our "Articles" page.

The tab above leads to a page containing some simple tools and downloads that may be of use to you in performing your own investigations.


Sophrodyne's Fundamental Approach

Our years of experience in combining numerics and theory lies at the core of Sophrodyne's way of working. We understand that an analysis of a problem using a brute force approach (such as is obtained for example with a pre-packaged general-purpose CFD code) is often necessary and useful in order to obtain basic data - for instance for evaluating a parameter or to validate a model - and we have the tools to do that.

We believe though that this approach only becomes cost-effective and valuable once these individual data are abstracted into a sensible mathematical framework which clearly expresses one's current understanding of the problem. Unlike "ideas" or "hunches", an explicit, simple mathematical model is a tangible object with which the human intellect can engage and interact. A good model allows the strength of your understanding of the problem to be exploited directly in being able to predict the properties of the system that are of interest to you. But often even more important is the fact that predictive errors in the same model are very often an indication of a deficiency somewhere in understanding the problem properly. The key advantage thus of the model-building process during the development of a product is that it invariably promotes the sort of interaction with the problem in which these lapses in understanding can be exposed and rectified before they can cause too much harm.

This is where the experienced practitioner will save you time and effort in achieving your goals.

We understand from first principles the methodologies that underpin most current commercial aerodynamic tools, and can advise regarding both their strengths and their weaknesses. In many instances we have our own analogue methodologies that we have written in-house and understand down to the last line of code. We can use these to perform genetically-independent sanity checks on, and independent verifications of, the data coming out of your models, or to perform the relevant analyses on your behalf. Indeed, over the years we have built up a series of models that work from very limited data to give reliable estimates of the most salient performance characteristics of a wide range of flight vehicles - from subsonic drones and helicopters, through mid-sized commuter aircraft, through to supersonic jets and even hypersonic re-entry vehicles!

We can also help you upgrade and develop your internal modelling capabilities, starting from a clean sheet of paper or based on what you already have available. You may be surprised to find out how broadly used our methodologies are within the aerospace community.

Most importantly, and this is where we specialise in bringing value to organisations such as yours, we can help you understand and generalise your proprietary data into models that can be used over and again, not only today but also in your future products, adding to your reserve of intellectual property and know-how as you develop your product line.

Please feel free to contact us to discuss your problems and requirements.

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