the tnt block will not act normally and project the player forward when i use tnt cannons (properly)

What I expected to happen was...:
I expected the tnt to launch me forward

What actually happened was...:
I stayed in the same place

Steps to Reproduce:
1. Make a tnt cannon in minecraft 1.8.3
2. set it off like you normally would (whilst standing in the right position)
3. Nothing happenes