Can you Weld Models to a Player?

I am trying to weld a model and I tried it without modeling it and they both don't work. It only welds one part of it when I try it without modeling it, but it just says an error when I try to weld the whole model, saying that CFrame is not a part of Model.

function weldToHuman(a,b)
    b.CFrame = a.CFrame
    local  weld = Instance.new("Weld")
    weld.Part0 = a;
    weld.C0 = a.CFrame:inverse()
    weld.Part1 = b;
    weld.C1 = b.CFrame:inverse()
    weld.Parent = a;    
    return weld;
end
game.Players.PlayerAdded:connect(function(player)
    print(player.Name .. " Welcome");
    player.CharacterAdded:connect(function(character)
        game.Lighting.JetPack:Clone()
        game.Lighting.JetPack.Parent = game.Workspace
        print(character.Name .. "  character")
        wait(2);
        weldToHuman(character.Torso,game.Workspace.JetPack.MainPart)
    end)
end)
print("loaded welding")