Hello on the current hovercraft the lift duct is a bit more fancy its made out of threee seporate bits a cone a straight section and cone but i am having trouble marking out the cone any tips (see attachments)

Use the super ultra handy Shroud Calculator.

http://www.realmcommunications.com/r...shroudcalc.htm

No favorite link folder should be without one.
[8D]

thanks for the link but the cone made is too steep it needs to be a shallow cone

That's what the calculator,...uhhh... calculates

Input the large diamter of the cone,
Input the small diamter of the cone,
Input the height of the cone, then
pushe calculate.

The calculator will give you the dimensions to draw flat so
you can cut it out, and roll the piece into the cone you want.

I use the calculator to make all sorts of differnt height and sloped cones.