Unfortunately RadChart does not have the ability to create a Ternary Chart and it is not in our near plans for development. We have logged your feature request in our public issue tracking system
so we can monitor the interest in such feature (and eventually raise its priority if it is commonly requested).
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.