The Westland Whirlwind Reassessed

July 30, 2021

The very first aircraft article I ever did on Military Matters, before Forgotten Aircraft was actually a thing, was on the Westland Whirlwind. In that, I said:

“The story of the Westland Whirlwind is one of an aircraft of great potential, but which was let down by inadequate engines and bad timing.”

The wonderful thing about history is that pretty much every conclusion is open to debate and, when new evidence comes to light, reassessment. And that it seems is exactly what we need to do with the Whirlwind.

Aviation historian John Dell has written an excellent article on the latest research on this aircraft and I thought it would be of interest to go through the new conclusions on the Whirlwind, plus some other exciting developments.

First, a bit of background to this aircraft.


The Whirlwind was developed to a British 1935 specification for a fighter carrying four 20mm cannon. This was an unparalleled amount of firepower at the time, and the aircraft featured a number of other cutting edge design ideas.

The Whirlwind was a twin-engine fighter with a thin and sleek fuselage housing both the heavy armament and a single pilot under a teardrop canopy – one of the first production aircraft to have this feature. This configuration means that it is generally considered today a “heavy fighter”, but as John Dell has pointed out, that isn’t really accurate and certainly not what was the proposed intention. Instead, it was to act as an interceptor and zone defence fighter.

The Whirlwind seemed to have huge promise, but that didn’t really pan out. It was slow to develop, and construction proved tricky, with the first production aircraft flying in May 1940. But in fact, these first aircraft were not serviceable, and it wasn’t until December 1940 that the type deployed for combat use.

In service the Whirlwind proved disappointing at altitude, rendering it largely useless for its intended roles, but did ultimately find a niche as a low-level attack aircraft. But, with a limited production run of only 114 aircraft, it only performed this role from the beginning of 1941 through to mid-1943. After that, the aircraft was replaced by later designs and vanished into the history books.

But its solid performance as an attack aircraft, advanced features and popularity with the pilots who flew it have also caused the Whirlwind to be a subject of continuing speculation. What could it have been capable of had it had the same development cycle as its contemporaries -the Supermarine Spitfire and Hawker Hurricane?

The consensus opinion is generally that it could have been a truly great aircraft.

But is that accurate, and what did go wrong with the Whirlwind?

The standard view is that the problem, and the cause of its failures, was its engine – the Rolls Royce Peregrine. This was the ultimate development of the pre-war Kestrel, a very successful liquid cooled design that in fact was used on several fighters in the early-1930s, including the prototype Messerschmitt Bf 109.

But the Peregrine, despite its solid roots, proved unreliable, hence dooming the Whirlwind. And this opinion has led to the view, including in myself previously, that if the Whirlwind had been designed for the Merlin engine it might have been a truly exceptional aircraft.

After all, allying the sleek, cutting edge and massively armed fighter with an engine that would prove a stalwart throughout the war surely represents a lost opportunity? This means that the Whirlwind gets ranked as one of those great “what-if” aircraft.

Of course, hindsight is a wonderful thing. But in this case, it is probably in error.

Because new research indicates that firstly, the Peregrine may not have been the problem at all.

And secondly, the Whirlwind really may not have been all it has been imagined to be, and its fate more complicated than “new engines = good plane.”

Let’s look at these issues in order.

Firstly, the Peregrine did play a part in the failure of the Whirlwind. But this is largely due to the delays in developing the engine, and more specifically, the management of the program.

The Peregrine was, as stated, an improvement of the Kestrel. Rated as delivering 880hp, the new engine saw the addition of an improved supercharger and a glycol cooling system. As far as the Air Ministry were concerned, as a development of the well-proven Kestrel, the Peregrine should be no problem.

What they were concerned about was ironing out the issues with the new Merlin engine, which in 1937 was suffering with a host of problems and which was coming into service in large numbers with many of the RAFs newest aircraft. Obviously, failure of the Merlin was the thing of nightmares and, under pressure from the authorities, Rolls Royce threw itself into resolving the problems in the new engine.

This meant the Peregrine was neglected and the first production engine didn’t get delivered until February 1940. This in turn led to substantial delays for the Whirlwind.

Ultimately, with only the Whirlwind using the engine in service, a limited run of Peregrines was permitted and then the line was shut down so Rolls Royce could focus on Merlin production.

The performance of the engine was far below what was expected of it, especially at altitude, and it seemed to have reliability issues – generally attributed to the low development attention paid to it.

But, in the light of new research, this doesn’t seem to be an accurate assessment.

The first issue for the Peregrines problems on the Whirlwind was the cooling system. These were a result of the Whirlwind’s designer, Teddy Petter, making significant compromises in the aircrafts design. Circular radiators had to be used, because they were all that was available at the time, and these proved inefficient.

On top of that, the radiator intakes shut automatically when the landing flaps engaged. This meant pilots had to be precise with their use of their flaps in landing and takeoff, or else the engines could either overheat or cool too quickly, stressing them excessively.

But what about the problem of failure to perform at altitude?

This is perplexing because the second Whirlwind prototype demonstrated great performance when it flew for the first time in 1939, achieving an altitude of 31,000ft and a top speed of 354mph.

This was excellent for an aircraft of that time, but when the production aircraft entered service the engines performance dropped dramatically above 20,000 ft and would rapidly begin to show signs of complete failure.

This has long been written off as an issue with the Peregrine, a product of its low development priority. But now research by Matt Bearman of the Whirlwind Fighter Project has apparently found the answer.

The issue wasn’t with the engine – it was with the propellor.

The second prototype used Rotol propellors, while the production aircraft used deHavilland ones. These were thicker and this seems to have caused a problem that wasn’t well understood at the time.

Basically, a rotating propellor pushes the air out the way of the blade. The thicker a blade, the more air it needs to push aside. Pushing more air out of the way means that the air has to move faster.

At a certain point the air will need to move aside faster than the speed of sound. At this point, you get shock waves, that create massive drag.

Propellors need to be especially designed to compensate for this effect. But on the deHavilland propellors, the constant speed mechanism would try to compensate for the slowdown caused by the increase in drag by altering the pitch of the blade.

This would cause a sort of feedback loop in the Peregrine’s, causing erratic performance and putting massive strain on the engine, leading to parts failure. And the higher the altitude, the lower the speed of sound – hence the issues with the Whirlwinds at altitude.

I am giving an incredible simplistic explanation here, and I strongly advise you to go to John Dell’s article on the Whirlwind for a fuller explanation. But for anyone asking why this wasn’t an issue with other aircraft engines – it seems it may well have been.

This factor probably played a major role in the problems of several high-power engines that were in development during the war.

But in relation to the Whirlwind, it seems entirely possible that the problems could well have been solved with a different propellor. Of course, this still would have doomed the aircraft to becoming obsolete in short order as the Peregrine never had a future, even if it could have been made to work well.

So why was no attempt made to build the Whirlwind with the Merlin?

There is another modern opinion that is widely held on this, and that is that the Whirlwind could never have been converted for the Merlin – the engine was fundamentally incompatible with the Whirlwind airframe, far too powerful, etc.

Things is, there was a plan for a Merlin-powered variant.

In January 1941 Westland wrote to the Commander of Fighter Command stating that they could build a Whirlwind powered by two Merlin XXs, the same engine as used on the Hurricane Mk.II. This Whirlwind would have had nearly 3,000hp and, according to Westland, a top speed of 410mph and a ceiling of 37,000 feet.

But the RAF at that time was still recovering from the Battle of Britain and rebuilding its strength. A German invasion was still very much considered the priority threat, and the emphasis was on getting numbers of available aircraft into the air.

One Merlin Whirlwind would’ve meant two less Hurricanes, and despite its theoretical performance, the Whirlwind, just coming into service, was proving both disappointing and, quite frankly, a bit of a pain.

In fact, and here is the ultimate irony, if the Whirlwind had been designed to use the Merlin from the start, it may never have seen service at all. The complexities of the aircraft, its heavy use of strategic materials and the complex and difficult to produce design meant that it might well have been dropped from production in even shorter order than it actually was.

It seems, bizarrely, that the fact that the Whirlwind uniquely used the Peregrine engine, long thought the bane of the aircraft, was a major factor in the aircraft being built at all.

And there is another factor to consider on the “Merlin Whirlwind”.

Because though this aircraft never existed, the Westland Welkin did.

This was a single-seat high altitude fighter, with four 20mm cannon and powered by two Merlin engines.

Sound familiar?

While it might not have been the “what-if” Whirlwind that has been subject of discussion for decades, this is very much an aircraft that learnt from its predecessor. And if you’ve seen my article on the Folland Gnat, you’ll know that the Whirlwind’s designer, Teddy Petter, very much took the lessons to heart on the need for simplicity in wartime fighter aircraft.


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