Looking at the village of Kout Na Sumave in the 1840's, I came up with one Joseph Vogeltanz. Born in 1844. A few years off of date for your grandfather. It's not uncommon for the date of a immigrant relative to be incorrect. I'd say it's almost the norm (of my g-grandfather's family, none of the eight people were the date that their descendants thought it was). But five years is the outer edge of the margin of error.
Joseph was the son of Georg Vogeltanz & Margaretha nee Hallada. Georg was the son of a Thomas Vogeltanz & Magdalena Stefek.
And this was the only Joseph Vogeltanz that appeared in the Kout Na Sumave index for the 1840's. The next one born is 1857. Even further off the date. And obviously someone immigrating at the age of eight isn't the same thing as a sixteen year old immigrating.
This Thomas is dead in 1833, so if that guy immigrated, that's pretty much a dealbreaker, it's not them. If that's the case, you may need to start looking in other villages near Kout Na Sumave. There are a lot of Vogeltanzs in Mrakov and Klicov. I have several in my family. But none match the names/years you're looking for. Although at some point "yours" likely connect to "mine".
Below I've give the basic information and the webpages to check out the records that would give you all of this information.http://www.portafontium.cz/iipimage/30063730/kdyne-29_0960-n
19 Apr 1844
fath: GeorgeVogeltanz, farmer from here
moth: Margaretha Hallada, dau of Mathias Hallada from Kout #75 and Katharina born Vachal from Zahorzan #44http://www.portafontium.cz/iipimage/30063717/kdyne-16_0220-o
29 Jan 1833
groom: residence Klitschau (Czech = Klicov) #44, Georg Vogetlanz, legitimate son of deceased Thomas Vogeltanz, hausler of Klitschau and Magdalena born Stefek from Uzejd #_ ,age 22
bride: residence Kauth (Czech = Kout Na Sumave) #75, Margaretha, legitimate daughter of deceased Matthaus Hallada, hausler from here and deceased Katharina born Wachal from Zahorzan #35, age 23 (notation looks like her birthday of 05 Dec 1809