The is the best video I have seen of a helitorch in action. Unfortunately, there is no more information available, other than it was posted on YouTube by “brimaviation” about six years ago.
A helitorch uses gasoline, or a mixture of gasoline and diesel, that has been thickened. Land managers don’t like to use the term napalm, but that’s what it is. It’s made by mixing a gelling agent with the fuel. Running a helitorch operation and mixing the stuff without blowing yourself up is very complex.