Build a lightweight delta with a fast, symetric airfoil and give it better than 1:1 power to weight. 3 pounds with a strong .45 engine and roughly 500 sq inches, for example.
Get the model trimmed and balanced for hands off flight wherever it's pointed at full speed, then land it and take note of where your elevon trim is.
If everything goes to plan [in this example] the amount of up trim in the elevons will hardly be measurable.