[quote=Toaw]
Well technically if you look at it the first hot air balloon was invited around this time period, so even in actually history around this time people were actively looking towards inviting flying machines, so the attempt isn't so unrealistic, but I understand that gowia is afraid everyone will start trying to make airplanes, and zeppelins realistically two hundred years early if we are comparing our current technology to that of the 1700s. Other than commercial use flight is kind of a lost hope.
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Of course, airplanes are simply impossible with 1700's technology (Well, there were steam planes, and steam power was actually invented in the late 1700's, but those planes were absolutely worthless). Hot air blimps do exist, and their propulsion is actually possible using technology of the era (references at the end of post). However, they would likely be incredibly slow. Dirigibles are most likely too heavy to be carried by hot air, and Zeppelins refer exclusively to blimps and dirigibles produced by the German Zeppelin company. Aside from commercial use, intimidation is also valid. When Sputnik as launched, the American populace was afraid the Soviets would nuke them from space. Although nuking someone from space would have little effect on the actual outcome of the attack, and Sputnik was definitely too small to carry a nuke, people were still intimidated. And now, over fifty years later, we still haven't put anything beyond emergency pistols into space. Sure, it may have no practical use, but people will still be scared of it.

In fact, the first record of powered flight going any significant distance is in 1785, when Jean-Pierre Blanchard used a hot air balloon equipped with hand-powered wings (Think oars, but in the air) and birdlike tail to cross the English Channel. There's even a painting, well, drawing.
[img=http://upload.wikimedia.org/wikipedia/commons/thumb/5/56/BlanchardChannelFlight.jpg/220px-BlanchardChannelFlight.jpg]
So with a hot air balloon flight is completely and totally possible.

References:
Plausibility:
http://en.wikipedia.org/wiki/Dirigible#Early_pioneers
Differences between the terms:
http://en.wikipedia.org/wiki/Dirigible#Dirigible
http://en.wikipedia.org/wiki/Dirigible#Blimp
http://en.wikipedia.org/wiki/Dirigible#Zeppelin
(It says Dirigible in all of them because I was looking for a Dirigible example)
Hot-air balloon airships:
http://en.wikipedia.org/wiki/Thermal_airship