The fascinating Napier Dagger air-cooled aero engine was an interesting device featuring a vertical H layout with 24 cylinders.
Obviously two crankshafts would be better than one. Wouldn’t it?
Article by Doug Switzer Moto/ology publisher
Continuing our examination of wild and wonderful engine configurations, we bring you the “H” engine. Two layers of “flat” opposing cylinders with two crankshafts and an amazing degree of complexity… what could possibly go wrong?
We’ve all heard the old adage that “There’s no substitute for cubic inches” and it’s no doubt that the pursuit of this philosophy led to the idea that “we probably should add more cylinders to get more power.” Of course, the reason for more cylinders was the size of the humungous pistons flying up and down (or back and forth) was getting so large that there was a danger of this incredible mass self-destructing at any useable speed. It was therefore decided that smaller pistons would be the order of the day, we’d just have more of them in the engine. This had the added advantage of smoothing out the power impulses and creating an engine that didn’t “thump” as much as it “purred”.
“This is great!”, said the proponents and they started adding cylinders. Inline fours became sixes and even eights, but then there arose another problem. The crankshaft was getting very long and with all these pistons and con-rods zipping around, it was noticed that the crankshafts were starting to twist and wind up. Adding pistons and cylinders in a linear fashion wasn’t going to be the best solution.
What to do? Well, designers figured they could arrange the cylinders and pistons in a “V” configuration and that led to the arrival of the V4, V6, V8 and even V12-style engines. Once again, however, it became apparent that with a V12, that old crankshaft wind-up issue was coming back again because the danged thing was just too long.
Designers pondered what could they do now to address this situation once and for all? They had experimented with a “flat-Vee” engine, also referred to as a “horizontally opposed” layout. Someone somewhere came up with the idea of combining two of these flat opposed-cylinder engines and stack them on top of each other with two crankshafts running through a common output gear. They must have said, “Wow! that’ll be great” … and so the “H-engine” layout came to be.
As designs developed and experiments continued, H-engines in both vertical and horizontal configurations were designed.
These complex and intricate piston aero-engine designs came at an inopportune time in aircraft development, however. With the advent of the gas turbine or “jet” engines arriving on the scene, the high–powered piston-engine spinning a propeller was falling out of favour. Piston aero engines were relegated to smaller, less powerful applications like the personal aircraft used by the private operators in the general aviation industry.
Meanwhile, back on solid ground…
The development of advanced piston engines, including those in the H-configurations may have been superseded by alternative means of power in the aero industry, but this was not the case for the automotive sector, especially those involved in motorsports.
Those working on racing engine development in automobiles had run into the same issues as the aero-engine designers when the ever-increasing number of cylinders and corresponding crankshaft lengths came to be. A solution had to be found and at one point in the early-to-mid 1960s, the Owen Racing Organization, makers sf the cutting-edge BRM Formula One Grand Prix racing cars figured they had the solution. They’d take a page from the aero-engine designers and build a 16-cylinder “H-engine” that would fit in the back of a Formula One racing car.
Other competitors had worked on V8 and V12 designs for the 2.5 litre class in the 1950s and Ferrari had even worked on a V6 layout in their shark-nosed “Dino”-based 156 Formula One championship-winning cars, but these were made for the diminutive 1.5-litre Formula of the early 1960s. When the new 3-litre specification came into being in the mid-1960s, a rethink had to be applied. The V8 and V12 layouts once again came to the fore, but BRM was always looking at novel ways to gain an upper hand and a 16-cylinder engine promised smooth, powerful performance. The hitch was, BRM had built a V16 engine previously and knew all too well the problems with that configuration. As we said, they took a page from the aero-engine designers and settled on an H-configuration.
The BRM H-16 sounded wonderful and looked the part, but alas it was again, too complex too heavy and proved to be too unreliable. It was used unsuccessfully in the BRM P83 Formula One car and also had a brief stint in the Lotus 43, and it was with this car Jim Clark scored the engine’s only victory at the 1966 US Grand Prix. The H-16 is considered a glorious failure as it was quickly overshadowed and overtaken by the magnificent Cosworth V8 that went on to dominate the sport for the next 2-plus decades.
To see an interesting video on the 24-cylinder Napier Sabre “H” aero engine watch the video below: