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Interesting Engines:
The Pratt & Whitney R-4360

August 20, 2012 by Matt

Pratt & Whitney R-4360 Wasp Major on stand

I’ll admit it. I’m an engine junkie. Despite not being an engineer by degree or trade, I’m fascinated by the myriad methods pioneers have devised to produce motive power for vehicles. So then, this post will kick off a new series aimed at discussing engines I find particularly interesting.

Let’s go for the gold in the first post: The Pratt & Whitney R-4360 Wasp Major, the largest mass-produced aircraft piston engine ever made. A 28-cylinder, 71-liter, air-cooled radial monster, the ultimate incarnation—the “51VDT”—could deliver a staggering 4,300 hp. Even the first versions of the R-4360 could crank out north of 2,500 hp. Initially “just” supercharged, the final evolution of the Wasp Major incorporated a turbocharger as well.

Pratt & Whitney R-4360 Wasp Major case assembly crankcase pistons

As illustrated above by a view of the engine’s crankcase, the four rows of seven cylinders were offset radially to allow cooling air to reach the rear rows; even so, there were teething problems getting temps under control in the rearmost cylinders. The mixture powering each piston was ignited by two spark plugs per cylinder, meaning a full 56-plug change was a full-day job for a mechanic. Fuel injection was in its infancy during the R-4360’s gestation, so a pressure carburetor (with a concept similar to single-point injection) metered fuel to the engine.

Applications? The Wasp Major powered some of the largest and most potent aircraft of its time, including six for the Convair B-36 Peacemaker, and four for both the Boeing B-50 Superfortress and Northrop’s pioneering B-35 flying wing. More recently, the R-4360 has found success in pylon-based air racing, the re-engined Hawker Sea Fury Dreadnought clinching gold in the Unlimited class at the Reno Air Races in 1983 and 1986.

Perhaps one of the most amazing aspects of the Wasp Major arises not from the engine itself, but from the turboprops and jet engines that replaced it. Consider, for example, that eight R-4360s were necessary to lift Howard Hughes’ admittedly gargantuan Spruce Goose just 70 feet off the water for a mile. And nowadays, a jetliner of roughly the same size and gross weight like the Boeing 777-300 is accelerated to speeds and altitudes unheard of during the Wasp Major’s heyday with just two General Electric GE90 turbofans. It says a lot for the quantum leap in efficiency and reliability that the 777’s engines are arguably less complex than the R-4360 even as they develop an order of magnitude more power. We’ve made amazing technological progress in the past 60 years, but that doesn’t dampen a bit of the Wasp Major’s fascination.

Editor’s note: This post is part of an ongoing series examining unique and significant powerplants. Read the other installments here:

Filed under: Interesting Engines, Technical

11 Comments

  1. John D says:

    The short block itself is very impressive. I have never known much about engines used for airplanes. Fascinating.

  2. dragon xp says:

    scary engine too much capacity but quit a lot of power this engine is on my list of what the hell were they thinking list. it is big it is crazy looking and these pistons need a diet. this thing is a a lot more complicated than jet engines i believe. your post is amazing keep up the work and maybe make a crazy patent engine ideas series too

  3. Gary says:

    Tilly-Steven’s Diesel.. (next)?

  4. Lincoln Gable Riley says:

    Can anyone explain to me why a three row 27 cylinder radial engine of the same displacement would not be simpler and just as powerful? Does the number of rows have to be an even number? There has to be a simple reason why not. Maybe it’s just not mechanically viable. Scratching my head trying to remember what they told me in A&P school — maybe it’s because the firing order doesn’t compute —

    • Matt says:

      Frontal area. A three row of the same displacement would cluster 9 cylinders per row, and would increase the diameter of the engine and thus the drag produced by the nacelle containing the engine.

      That’s my best guess at least. :)

  5. Brian Milne says:

    If you write of the Tilling Stevens engine, you also need to write of the Junkers engine that it is derived from.

  6. BERGE JERMAKIAN says:

    There are many problems with multiple row radial spark ignition engines. Most can be over come such as cooling, fuel & exhaust manifold routing. The main difficulty is balancing the crankshaft which is almost if not impossible.

  7. Automan says:

    I worked for the Douglas aircraft plant in long Beach, I started on the burr bench in building 4, and worked my way to flight test in building 41. What most of the reply’s forget is these piston powered engines were made to produce the big power at low RPM, like 2,500 to 2,800 RPM, and on gasoline. The Germans had direct cylinder fuel injection in 1936, and had 50/50 water/alcohol injection. They also had 3 stages of nitros oxide in the BA/ME 109 Daimler Benz 605 inverted engine. The Wasp Major was produced from 1944 to 1956……

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