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True hypermiling for naturally aspirated piston-powered aircraft would require flying in ground effect. Imagine skimming across a lake with the lowest part of your fuselage maybe 1 to 5 meters above the water depending on visibility, responsiveness of the aircraft, marine traffic and your own bravery / stupidity level. You’re brave if it works out for you, stupid if it doesn’t.
Aircraft manufacturers don’t publish consumption specs for this but pilots are trained how to take advantage of this when doing short field take-offs. The idea of a short field take-off is to get the wheels off the ground as soon as possible since the amount of drag once airborne is greatly reduced. Then the key thing is to keep the nose as close to the ground as possible. Firstly because an airplane can so easily get into ground effect – think of Bernoulli’ principle and that piece of paper being blown across a table – and secondly because an airplane that gets off the ground quickly can easily lose lift and stall a wing. You effectively lift off too soon and then force it to stay close to the ground.
Once off the ground flying in ground effect, the aircraft accelerates at its fastest rate so that you can use the speed to pull up and clear taller obstacles, or just get clear of a short or rough runway quickly. The toughest part is trying to stay close enough to the ground because as you accelerate the aircraft goes more and more out of trim and it takes a serious effort just to keep the nose down – the aircraft is fighting you to climb and you are pushing the yoke very hard towards the ground. Fun stuff… but I sure wouldn’t have wanted to be a bomber transport pilot in WWII flying 50’ above the Atlantic doing deliveries to England… no wait, that would sure be more fun than sitting at my desk job.
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