Hi charlieuk

I think I can see what you're trying to do there, but correct me if I'm wrong. You're trying to get the tips to go from a "point" or line to the curve you have already established in the main body. So what you are actually doing is two blended curves one in the X and one in the Y axis, which filleting won't cope with iirc.

I would try deleting the fillets you have at the bottom of the leading and trailing edges of the wing tip sections and then use Modify - Loft tool to try and do the compound curve I think you're after.

Compound curves are a pain in fusion (and most CAD for that matter).

Hope that helps, but give me a PM and access to a copy of the model, if you get really stuck and I'll try and help directly in Fusion.

Chris