Add ExternalProjects with for loop :

 var fd = new FormData();

 for (var i = 0; i < ExternalProjects.length ; i++) {

     fd.append("ExternalProjects["+i+"].Name",ExternalProjects[i].Name);
     fd.append("ExternalProjects["+i+"].Body",ExternalProjects[i].Body);
     fd.append("ExternalProjects["+i+"].Url",ExternalProjects[i].Url);
     }

Add ExternalProjects with for loop :

 var fd = new FormData();

 for (var i = 0; i < ExternalProjects.length ; i++) 
     {
        fd.append("ExternalProjects["+i+"].Name",ExternalProjects[i].Name);
        fd.append("ExternalProjects["+i+"].Body",ExternalProjects[i].Body);
        fd.append("ExternalProjects["+i+"].Url",ExternalProjects[i].Url);
     }