The Unkindness of Ravens were inspired by figures from Norse and Celtic mythology such as the Valkyries and The Morrígan. Filming took place during 2014 in Fife, Edinburgh, and Perthshire, and moved into post-production in 2015. To help with costs, Brewster opened a crowdfunding campaign through Kickstarter, with the goal to raise £40,000. The campaign was successful and marked the first Scottish crowdfunding campaign to raise such a large amount of money and the highest funded British horror film on Kickstarter. Horror film critic Kim Newman reviewed "The Unkindness of Ravens", writing that it was "a demanding, complicated film which might well require repeat
Specific impulse to impulse provided by external air that has been used for combustion and is exhausted with the spent propellant. Jet engines use outside air, and therefore have a much higher specific impulse than rocket engines. The specific impulse in terms of propellant mass spent has units of distance per time, which is an artificial velocity called the "effective exhaust velocity". This is higher than the "actual" exhaust velocity because the mass of the combustion air is not being accounted for. Actual and effective exhaust velocity are the same in rocket engines not utilizing air or other intake propellant such as