It took Diemer 87 minutes to reach 9,760 meters.
In June of 1919 a BMW engine powering a Deutsche Flugzeugwerke F 37/III climbed to 9,760 meters or a little more than 32,000 feet, setting the company’s first world record, according to BMW.
The pilot, one Franz Zeno Diemer took off from Munich’s Oberwiesenfeld airfield and put his fate in the trust of a BMW IV airplane engine. Based on the existing BMW IIIa, the IV engine had its bore and stroke increased by 10 mm to boost output from 185 horsepower to 230.
On the Sunday he set the record, the weather was fair. It took Diemer 87 minutes to reach the record-setting height, for an average climb of 368 feet per minute, a rate that some light aircraft today can’t sustain on in hot weather after only a couple of thousand feet.
After the flight Diemer claimed that the engine still had the ability to climb, but that he himself had reached the limits of his capacity.
In his open pilot’s seat he experienced temperatures as low as -50° Celsius, but also the low oxygen levels in the air altitude, which took their toll on him physically. He was lucky he didn’t suffer from hypoxia and didn’t pass out. In fact, some skeptics say that without supplemental oxygen, it wouldn’t have been possible for him to remain conscious at that height.
Franz Zeno Diemer took off from Munich's Oberwiesenfeld airfield and put his fate in the trust of a BMW IV airplane engine.
The challenge Diemer faced was caused by the same underlying problem that all engines have struggled with since their invention, the loss of power at altitude. Normally an airplane produces its maximum output on the ground, which allows it to get enough airflow over the wings and control surfaces to produce lift and allow it to take off. But, as always, military needs pushed development into new areas, and the ability to out climb an enemy was one of the keys to survival that emerged during the War to end all Wars.
Since air density steadily decreases with altitude, unless you have a way of forcing more air into an engine than ambient pressure, power diminishes as well. Two different approaches were and still are pursued in an attempt to counteract the loss of output in the thinning air. Some manufacturers, such as rival Daimler, turned their attention to supercharging, whereby air was forced into the carburetor by means of a compressor. But this technology complex and only established itself in the 1930s. Friz opted for an “over-square” high-compression engine for the first BMW aircraft engine, the forerunner of the IV world record engine.