All bespoke development performed by FOSS UAV Ltd retains copyright by the author and is covered by the GPLv3 licence agreement - https://www.gnu.org/licenses/gpl-3.0.en.html. Why is this and why don’t sponsors of the work own the code?
Open Source products such as ArduPilot only exist through the generous contributions of individuals and companies - if these parties were not prepared to give away work that they either performed or paid for then ArduPilot would not exist and your company would not even be thinking about owning code. A conservative estimate of the development effort that has gone into ArduPilot is $35m - if your company had to develop this from scratch it is certain that your business plan would not be viable. So in working with Open Source it is important to recognise the quid pro quo of the arrangement that makes the whole thing possible in the first place.
Open Source results in fewer bugs and higher quality software due to its open nature - https://en.wikipedia.org/wiki/The_Cathedral_and_the_Bazaar. More people are looking at the code and using the code and thus problems are found and fixed more rapidly. In flight control software, where safety is paramount, this is extremely important. Thus developing features in the open means that you benefit from the experiences of others with the code.
If you are lucky enough to get your enhancements into the main codebase then you also have much lower support costs. There is no cost to upgrades as the code is carried release-by-release and in fact maintenance costs of upgrades can completely dominate development costs if done in a close source manner. You are likely using ArduPilot due to its features - but those features only exist because of the rapid development of the flight stack which you will then have to maintain if you want to benefit from later features.
All existing code is covered by GPLv3, this requires that modifications be made available as source code to the customers of the modifications if they ask for it. Thus supplying any kind of product to a customer requires that you also provide the software modifications for free under the GPL if they ask for them - anything else is a violation of the licence agreement. Thus, trying to retain IP on modifications to Open Source software developed in this manner is both legally disallowed and practically unmanageable. There are other subtleties which are explored more here - https://fossa.com/blog/complying-gpl-v3s-user-product-clause/
How do you make money? The answer is that people generally pay for products rather than software. They want a solution rather than a collection of proprietary pieces. So many companies are entirely successful in selling products that are built on open source components. Even in the pure software space companies make available the source code for free, but few customers try and build the software themselves because it is far more convenient to buy a solution from a vendor. In the context of UAVs, customers want to buy UAVs, not the software that is running on the UAVs.
Is copying a risk? Copying is certainly a risk, but copying will occur whether you keep software closed or open. If you develop a closed source piece of software then someone somewhere will develop the same functionality in the open and at that point any competitive advantage you might have will be gone - and worse other users will be using the open version rather than your version creating a maintenance headache for you. The advantage of sponsoring code in the open is that you get to determine the direction that suits your business and you will get a head start on others trying to achieve the same goal.