clearly we've had a very busy few days in the at Bristol office but it's been time well spent I promise you because we've been investigating what turns a piece of paper into a piece of aeronautical engineering and today we're going to be sharing with you the science behind making a perfect paper plane here I have the classic paper plane design known as a dart to get this in the air we need to be concerned with four primary forces gravity drag thrust and lift so to get our paper plane to fly we need to generate lift so how does a wind do this you might have seen something called an aerofoil which is that classic plane wing design with an aerofoil that relies on something called the Bernoulli effect with the air traveling over the top of the wing going faster than the air underneath this creates a difference in pressure because the air on the top of the wing has a lower pressure than the air underneath this higher pressure then pushes up on the wing creating left but the wings of our paper plane aren't shaped like an aerofoil they're flat so how do they generate lift well it's all down to Newton's third law of motion that every action has an equal and opposite reaction your paper plane doesn't fly like this it flies like this so as the air comes in and hits the wing it's deflected downwards the force of this air traveling down creates an equal and opposite force pushing up and that's lift so what you may have noticed is that the dart tends to nosedive and the reason for this is because of its center of gravity which is around about here so as the dart flies through the air it starts dipping down we lose that angle of attack and stop generating lift so what we need to do is to shift that center of gravity further back we've refined this design and folded in the nose shifting that center of gravity back and this should hopefully keep that angle of attack for longer generating more lift let's see how this does okay so this generated so much lift that eventually the drag overcame the thrust and we crashed but we still need to think about shifting that center of gravity so we've replaced the dart now with a mark 3 which again has a similar design folding that nose back to shift the center of gravity but isn't quite as Extreme as this so hopefully this should have the right balance okay not too bad but what are the problems you might be encountering is your plane rolling which is caused by your wings being angled down any uneven airflow passing over the top of the wings is going to push it so that's flying upside down you can overcome this by increasing something called the dihedral angle and pushing your wings up this increases the stability because any airflow passing over the top and pushing it this way is going to be counter balanced by the opposing wing leveling it back out so there are loads of different ways to make a paper airplane but through our scientific experimentation we quite like the mark 3 so maybe you've got your own designs tweet us and let us know but in the meantime stick around and we'll show you how to make this one you for more on the science of things going up watch how to make a hot air balloon and for things going down check out the physics of for and for more science every week click subscribe thanks for watching