A 12-gun fighter with 2 RR Kestrel engines for the RAF?

[tomo pauk]

Westland won the '4 cannon' spec with the entry that was to be powered by two of these engines, later to became Peregrine-powered Whirlwind. So let's stipulate that RAF issues a spec for a fighter armed with 12 .303s in 1934 (a year earlier than the F.37/35 specification that materialized as Whilry), and that is won by a project that looks very much like Whirlwind, has two then-current Kestrels (talk Mk. VI with 640 HP for prototype flying by mid-1937, and the Mk.XVI - 745 HP at 14500 ft - by the series production is under way by early 1939).
Is there any merit in the proposal? Growth potential, bar the upgrade with Peregrines and cannon installation by time these can be had? Go with a tailor-made airframe for the least drag and weight, or go with a bigger airframe so it is better suited for substantial upgrades?

 

[GTX]

Well there was this real-world 12 x 0.303 MG armament trial for the Westland Whirlwind:

So that provides a starting point for appearance potentially.

 

[Howard Gibson]

A serious upgrade would have to be to Merlin engines. The power of two souped up Kestrels is less than that of a two-stage supercharger Merlin. How were the Kestrels at altitude?

Specification F.37.35 actually was for armament of four 20mm Hispano cannons. Twin engines was Westland's way to get all the armament concentrated in the nose.

 

[tomo pauk]

A serious upgrade would have to be to Merlin engines. The power of two souped up Kestrels is less than that of a two-stage supercharger Merlin. How were the Kestrels at altitude?

745 HP at 14500 ft for the best, down to zero at ~55000 ft.
A 2 stage Merlin for late 1930s??

 

[Shortround6]

A serious upgrade would have to be to Merlin engines. The power of two souped up Kestrels is less than that of a two-stage supercharger Merlin. How were the Kestrels at altitude?

A two stage engine running on 87 octane gas????

A 2 stage Merlin for late 1930s??

The idea of using even two Kestrels was to achieve performance higher than what one engine (that would be available in the time frame) would give.

If you want to to use two Merlin's in 1937-39 then you need a larger, heavier more expensive airplane than the Whirlwind wound up being.

Yes you can make a higher performance plane that the two Kestrel machine or two Peregrine machine but you have a higher cost machine.

 

[Howard Gibson]

My point is that the Whirlwind was an excellent airframe. When it turned out that the Peregrine engine would not be developed, and that the Merlins did not fit, the aircraft was declared obsolete. By late 1942, a twin-Kestrel powered fighter has more frontal area and less power than a Spitfire_IX. Which do we go with?

 

[tomo pauk]

My point is that the Whirlwind was an excellent airframe. When it turned out that the Peregrine engine would not be developed, and that the Merlins did not fit, the aircraft was declared obsolete. By late 1942, a twin-Kestrel powered fighter has more frontal area and less power than a Spitfire_IX. Which do we go with?

Late 1942, when it is about a fighter for 1939??
Is that such a great chore to read the 1st post?

 

[Howard Gibson]

Late 1942, when it is about a fighter for 1939??
Is that such a great chore to read the 1st post?

I am trying to understand how long the thing remains effective. Spitfires were front-line aircraft to the end of the war.

 

[tomo pauk]

I am trying to understand how long the thing remains effective.

That will depend on upgrades it is capable to receive. See this:

Go with a tailor-made airframe for the least drag and weight, or go with a bigger airframe so it is better suited for substantial upgrades?

 

[Shortround6]

Shades of the bf 110.
If you size the airframe to be more capable with later upgrades you run the risk of going to war with the early crap engines installed in some airframes.
1/4 to 1/3 of 110s in Poland were powered by Jumo 210s instead of DB 601s.
Germans lucked out and few, if any, Jumo powered 110s were engaged by Polish forces.

Some aircraft were upgraded easily, but designing upgrades in ahead of time is a bit like designing multi role aircraft. A lot of nice to have things get installed and the plane winds up overweight.

 

[wuzak]

F.18/37 was a specification for a 12 gun fighter.

Proposals include:
Hawker Tornado - 1 x Rolls-Royce Vulture (no, does not count as 2 Peregrines)
Hawker Typhoon - 1 x Napier Sabre
Bristol F.18/37 - seems to be a family of fighters with 1 x Bristol Centaurus
Supermarine Type 324 - 2 x Rolls-Royce Merlin with tractor props
Supermarine Type 325 - 2 x Rolls-Royce Merlin with pusher props

This is a few years later than Tomo's project.

I would say that by 1934 it is unlikely that the airframe manufacturers would chose to use Kestrels instead of Merlins. The Merlin was the latest and greatest thing from Rolls-Royce, promising 30-40% more power without that amount of extra weight.

We do know that the specifications F.36/34 and F.37/34 were written around the Hawker Hurricane and Supermarine Spitfire respectively, each with a single Merlin and an 8 0.303" gun armament. (F.36/34 was based on Hawker's submission to the earlier F.5/34.)

I'm not sure that the Peregrine was at a stage that it could have been considered at that time.

The Napier Dagger ran on the bench about that time, so it may have been considered a viable engine (as it was for the Martin-Baker MB.2 for F.5/34).

Note: the Supermarine Type 324 proposal was reworked into the Type 327 to be considered as a back-up to the Whirlwind. Its primary armament was 6 x 20mm cannon, but the outer wing sections could be changed with ones fitted with 6 x 0.303" each for strafing roles.

 

[don4331]

1st of all, an upgraded Kestrel is going to happen whether you rename it the Peregrine or just change to Arabic numbering or bigger Roman numeral - in '34, there are enough planes using/planned for it. So, an 885hp engine on 87 octane is in the cards, a 1,200 to 1,350hp one on 100 octane would depend on the success of your plane.

Merlin of '34 is an evaporative cooled disaster; a small, independent company like Westland gambling heavily on their advanced air frame can't afford game on both power plant and air frame. And in any case, 2 x 650hp Kestrel VIs makes more power than a 950hp Merlin C. So WEW Petter, like Kelly Johnson, surmises that the armament requirement is too heavy for a single and designs a twin.

Aside: It almost feels like spec Specification F.37/35 required Fowler flaps as both Supermarine and Westland entries had them (or they were the solution of the day and everyone was installing them as a result). A spec without or a little earlier so they aren't the fad would result in a slightly larger wing - I'll going to spitball and say the Fowlers were worth 20%. So, we are looking at ~300 ft^2 wing area. Slats keep the ailerons working at higher angles of attack (i.e. when landing), so the temptation will be there to include them initially (we can strengthen or replace with fuel tanks for thirstier engines later). And we need some of the latest research from NACA and Germany - to use newer airfoils and keep the thickness <15%. We note Lockheed was having issues getting the USA wind tunnels to test at speeds they were expecting from P-38, so RAE not testing in those regimes isn't a surprise (and give the issues F1 teams have 90 years later with their porpoises, I'm not faulting them).

The next challenge is that a twin, you expect it to go further, so temptation is add fuel and increase the aspect ratio of the wing to make it more efficient. Then you add a navigator to get you back home, and weight/size spiral up, you add a rear gunner and you're >400 ft^2 of wing and performance is mediocre. Whirlwind/Fw.187 do OK on limiting fuel increase, but terrible on aspect ratio - we're designing Falcons, not Condors. Aspect ratio needs to be <6 ideally. (Supermarine 324 was close, XF5F Skyrocket is bang on).

So, we know we will be getting more powerful Kestrels, and they will probably be heavier. Therefore, our design needs to have any easy strengthening path ala Spitfire - built up longerons and spars that can be added to. And we need to balance the plane with the Kestrel VI at 980lbs, and plan for Kestrel ??? at 1,140lbs. The easiest balance solution is to put the radiator under the engine ala Bf.109C&D/Bf.110B, then move it to wing trailing edge (cleaning up the install at the time) ala Bf.109E/Bf.110C.

The hypothetical Whirlwind would be in position to supplant the Hurricane as the bomber destroyer during BoB. That leads to future upgrades - either 2 speeds, possibly 2 stage Kestrels or swap to Merlins/cannons. etc.

With 2 place cockpit and folding of outer wings (maybe swap Kestrels for Taurus's to eliminate glycol on the carrier), it can supplant the Fulmar.

 

[tomo pauk]

This is a few years later than Tomo's project.

I would say that by 1934 it is unlikely that the airframe manufacturers would chose to use Kestrels instead of Merlins. The Merlin was the latest and greatest thing from Rolls-Royce, promising 30-40% more power without that amount of extra weight.

Westland won the later (1935) specification with Kestrel-powered proposal. Thus the thread about a fighter powered by Kestrels. Not Merlins. Not Daggers. Not any other engine.

We do know that the specifications F.36/34 and F.37/34 were written around the Hawker Hurricane and Supermarine Spitfire respectively, each with a single Merlin and an 8 0.303" gun armament. (F.36/34 was based on Hawker's submission to the earlier F.5/34.)

Hurricane and Spitfire have like 1000-2000 threads on this forum? They don't need another one, especially not to clog a thread about something completely different.

Merlin of '34 is an evaporative cooled disaster; a small, independent company like Westland gambling heavily on their advanced air frame can't afford game on both power plant and air frame. And in any case, 2 x 650hp Kestrel VIs makes more power than a 950hp Merlin C. So WEW Petter, like Kelly Johnson, surmises that the armament requirement is too heavy for a single and designs a twin.

Aside: It almost feels like spec Specification F.37/35 required Fowler flaps as both Supermarine and Westland entries had them (or they were the solution of the day and everyone was installing them as a result). A spec without or a little earlier so they aren't the fad would result in a slightly larger wing - I'll going to spitball and say the Fowlers were worth 20%. So, we are looking at ~300 ft^2 wing area.

Good so far, with caveat that Merlin was not the one with evaporative cooling, that would be the Goshawk.

The next challenge is that a twin, you expect it to go further, so temptation is add fuel and increase the aspect ratio of the wing to make it more efficient. Then you add a navigator to get you back home, and weight/size spiral up, you add a rear gunner and you're >400 ft^2 of wing and performance is mediocre.

This is RAF, not Luftwaffe, and certainly not any of the Japanese air services. Thus, there is no such thing as long-range fighter - fighters are supposed to defend the UK against enemy bombers.

The hypothetical Whirlwind would be in position to supplant the Hurricane as the bomber destroyer during BoB.

Bingo.

 

[Shortround6]

A lot going in the mid 30s.
The Kestrel was designed with water cooling. The Goshawk was an attempt to go to evaporative cooling. After that bombed they tried ethylene glycol cooling. And increased pressure in the cooling system/s. Each system requires different sized radiators and air flow for the same size engines.

The Fowler flap was designed in the 1920s but the first commercial use was on the Lockheed 14 airliner. First flown in the summer of 1937. Not much experience by anybody on how they worked in practice.
Slats on the other hand were common practice in many countries, but the fictitious advantage claimed by the 109 boys didn't exist. Slats were used to keep the the outer wing from stalling and keep aileron control near stall. They only affected the area of the wing right behind the slats, not several feet sideways. If the slats only affect around 1/3 of the wing area (or less) and you have 2/3rds of the wing area stalled both maneuverability and landing performance are going right in the toilet. The slats allowed the pilot to retain lateral control and keep the plane level as it stalled instead of having one wing descend faster than the other and throwing the plane into a spin or hitting a wingtip on the ground. Slats were such a standard feature that the first 50 Handley Page Halifax's built had them. There were other ways to get the same effect. Some of them caused increase drag. A number of planes used fixed slots but that came with the increased drag and was not used by many fighters although it was popular on bombers, transports and such.

The British navy had no problem with putting glycol on carriers. Their problem was several fold. Small decks and some less than speedy carriers meant low landing speed was even more important that the Americans. Throw in the fact that the Taurus was strictly a low altitude engine (several thousand feet below the low attitude engines used in the Fulmar) and while the torpedo bombers could use it it would have been a disaster for carrier fighter. Granted in was in the 1930s and everybody was looking at the Taurus with rose colored glasses.

 

[Shortround6]

This is RAF, not Luftwaffe, and certainly not any of the Japanese air services. Thus, there is no such thing as long-range fighter - fighters are supposed to defend the UK against enemy bombers.

The Whirlwind was credited with slightly longer operational range over water than the single engine planes. In part due to it's supposed safety of having two engines to get back to land.
Of course many twin engine planes had no such safety margin, except in the minds of the paper pushers, due to lack of redundant systems (dual pumps or generators), fuel systems not interconnected to the working engine and lack of feathering propellers to cut drag in single engine operation.

Thus the thread about a fighter powered by Kestrels. Not Merlins. Not Daggers. Not any other engine.

Merlins are not an easy swap out, you need a whole new plane so you are quite correct on this.

The Dagger also turned out to be a non-starter, the punters (race track gamblers?) who bet on the Dagger were sorely disappointed. going into it any further doesn't do much to advance Tomo's idea.

Now maybe Tomo's idea gives them time to sort out some of the Problems the Whirlwind had before the summer of 1940 but considering the slapdash effort put into the Bristol Blenheim fighter it does require more changes than was done historically.

 

[wuzak]

Westland won the later (1935) specification with Kestrel-powered proposal. Thus the thread about a fighter powered by Kestrels. Not Merlins. Not Daggers. Not any other engine.

Production Kestrels or projected Kestrels that didn't yet exist (ie Peregrines)?

Hurricane and Spitfire have like 1000-2000 threads on this forum? They don't need another one, especially not to clog a thread about something completely different.

Just pointing out the way the Air Ministry and airframe manufacturers were thinking.

 

[wuzak]

Merlins are not an easy swap out, you need a whole new plane so you are quite correct on this.

We are talking of proposing an aircraft with twin engine to carry 12 rifle calibre machine guns in 1934. If the Merlin was chosen it would have been part of the design from day 1, not swapped in at a later date.

The Dagger also turned out to be a non-starter, the punters (race track gamblers?) who bet on the Dagger were sorely disappointed. going into it any further doesn't do much to advance Tomo's idea.\

Aren't we applying hindsight in this?

In 1934 we do not know that the Dagger would be a failure. We do not know if the Merlin was going to be a success, yet in 1934 the Air Ministry bet on two Merlin powered fighters for future defence requirements.

In 1934 what engines do we have?
We have the Rolls-Royce Merlin (in development), the Rolls-Royce Kestrel (don't think the XXX was around, maybe the XVI was, in any case, best was ~600-650hp), Rolls-Royce Buzzard (~800hp, but also out of production), Bristol Mercury (~600hp) and Napier Dagger (~700hp).

Was the Peregrine even a projected engine at that stage?

What else was there? Just some low(ish) powered radials?

Now maybe Tomo's idea gives them time to sort out some of the Problems the Whirlwind had before the summer of 1940 but considering the slapdash effort put into the Bristol Blenheim fighter it does require more changes than was done historically.

Having a Whirlwind type fighter proposed in 1934 will likely not alter the availability of the fighter too much because (a) Rolls-Royce are devoting much of their resources to the Merlin, trying to sort, and then the Vulture. The timeline for the Peregrine would not be advanced much compared to the historical time line, so your 1939 Whirlwind will likely be stuck with Kestrel XXXs of ~700hp, at best. The airframe would be lacking 350-400hp.

 

[tomo pauk]

Production Kestrels or projected Kestrels that didn't yet exist (ie Peregrines)?

This is what Tony Butler says, via Wikipedia:
... the Westland P.9 had two Rolls-Royce Kestrel K.26 engines and a twin tail.
I can't get any help from Lunmsden's book on what specifically is the K.26 engine.

Peregrine is much more than a Kestrel that does not yet exist.
In early 1937, when P.9 won the contract, the newest Kestrels were the sub-types of the Mk. XIV and Mk.XVI, eg, XVI VP (variable prop) capable for 773 HP at 12250 ft, or the 'base' XIV and XVI good for 745 HP at 14500 ft.

Just pointing out the way the Air Ministry and airframe manufacturers were thinking.

Roger that.
Trying to do the same

Having a Whirlwind type fighter proposed in 1934 will likely not alter the availability of the fighter too much because (a) Rolls-Royce are devoting much of their resources to the Merlin, trying to sort, and then the Vulture. The timeline for the Peregrine would not be advanced much compared to the historical time line, so your 1939 Whirlwind will likely be stuck with Kestrel XXXs of ~700hp, at best. The airframe would be lacking 350-400hp.

Kestrel XXX is a wrong engine for a fighter, being the 'MS' (ie. supercharger drive set for low altitudes), and capped to 2750 rpm vs. 3000 rpm for the 'fighter' types that were 'FS' (fully supercharged, ie. S/C drive set for high altitudes).

 

[ThomasP]

In my notes I have the Kestrel Mk XXVI listed as the original designation for the Peregrine engine.

 

[don4331]

Throw in the fact that the Taurus was strictly a low altitude engine (several thousand feet below the low attitude engines used in the Fulmar) and while the torpedo bombers could use it it would have been a disaster for carrier fighter.

Fulmar I used Merlin VIII with critical altitude of 7,500'; while Taurus's critical altitude is 4,000' so I suppose you are correct in saying that its is making its power lower, but each Bristol engine makes 1,110hp at critical altitude, while the RR engine only makes 1,080 at its critical altitude. Yes, the Merlin VIII power is increased to 1,275hp with 100 octane, but I don't have figures on how much that reduced critical altitude For reference, Merlin III lost 3,500' in critical altitude when boost increased to take full advantage of 100 octane; Merlin 30 in Fulmar II has critical altitude of 6000'.

In either case, the advantage of nearly double the power of radials would allow the twin to trade a lot of altitude in a carrier fighter.