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

[don4331]

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

Someone should tell Messerschmitt that you can't swap Jumo 210s for DB601s in Bf.109/110s. And tell Supermarine that they can't replace a Merlin with a Griffon - Griffon being over 1/3 larger than Merlin while Merlin is only 1/4 larger than Kestrel.

If the plane was designed for the growth, both power and balance, swapping Kestrels for Merlins would have been a planned swap.

 

[don4331]

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

That was point I was trying to make: Whether you call it Kestrel Mk. XXVI, Mk. 26 or Peregrine (all of which are same engine), the engine was the logical extension of the Kestrel XVI-P, beefed up to take full advantage of 87 octane fuel.

And if you follow the Kestrel to Peregrine naming and consider them different engines, the Merlin X (1st with 2 speed supercharger) should be different name as the crankcase has changed, the Merlin XX yet a different name, the Merlin 60 series with 2nd stage another, and the Merlin 100s yet another.

Right up there with Gen I small block Chevrolet. Very little from a 400 will bolt into an original 265, but they are all referred to as the same family.

 

[wuzak]

And tell Supermarine that they can't replace a Merlin with a Griffon - Griffon being over 1/3 larger than Merlin while Merlin is only 1/4 larger than Kestrel.

The Griffon was 1/3 greater in capacity, but not 1/3 bigger physically.

I'm not exactly what the problem was, but it was considered impossible or too much work to convert the Whirlwind to Merlins. The Spitfire had to be strengthened to take the Griffon, such as the longerons being changed from aluminium to steel.

 

[ThomasP]

From what I have read, the main reason for cancelling the Merlin-Whirlwind was due to the rationalization of aircraft production - there being too much work involved to up-engine the airframe with little or no gain in performance over the next-generation Spitfire Mk IX. The studies said that the climb rate would be the only major performance gain vs what could be done with the Spitfire.

The last major hold-up to the Merlin possibly being fitted to the Whirlwind was maintaining CoG while accommodating the Merlin and the main landing gear in the nacelles. Somewhere on the internet there is a February 1941 memo from Westland informing the Air Ministry that the issue had been resolved, but the basic decision had already been made not to proceed with the improved Whirlwind program, and the decision was finalized in March 1941.

Found the letter(s):

and

 

[Geoffrey Sinclair]

Using the wartime Ministry of Aircraft Production Figures, the Napier Dagger was being produced in numbers in the first half of 1939 at the latest, the Rolls Royce Peregrine came into production in the first quarter of 1940. Rolls Royce Kestrel, no production in the June to December 1939 period, then 228 built Q2 and Q3/1940.

 

[Shortround6]

Someone should tell Messerschmitt that you can't swap Jumo 210s for DB601s in Bf.109/110s. And tell Supermarine that they can't replace a Merlin with a Griffon - Griffon being over 1/3 larger than Merlin while Merlin is only 1/4 larger than Kestrel.

Actually the Merlin was over 30% larger than the Kestrel and went to 40% larger (heavier) very quickly even for single stage single speed engines. Likewise the radiators and oil coolers go up in proportion to the power, not the displacement.

Very little from a 400 will bolt into an original 265, but they are all referred to as the same family.

True but then the 400 version didn't show up until the big block 396-427-454 had been around for a while. In fact the 327-350 used a different height engine block to accommodate the longer stroke cylinders compared to the 265-283. Sticking a "big block" in might fit under the hood but called for a lot of changes to accommodate it as suspensions, and brakes didn't work properly with the heavier engine.

 

[Admiral Beez]

A serious upgrade would have to be to Merlin engines.

Or to Napier Sabres or RR Nenes. There's no way an aircraft designed to optimize the 960 lb. Kestrel can fit a 1,600+ lb Merlin. You might as well try to sit a P&W R-2800 Double Wasp into a Curtiss P-36.

 

[Admiral Beez]

a project that looks very much like Whirlwind, has two then-current Kestrels. Is there any merit in the proposal?

To be competitive with two Kestrels I suggest the fighter would need to be smaller and lighter than the Whirlwind, perhaps the size of the de Havilland DH.88 Comet or Grigorovich E-2.

Replace the Comet's de Havilland Gipsy Six R engines and two-bladed props for liquid cooled Kestrels running three-bladed props, remove the second seat, add armament, radiator and some armour and we have something. But it will be too small for later upgrading to the Merlin, etc. You can see how small the Comet is below.

 

[Admiral Beez]

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

It won't look like a mini-Whirlwind, but how about two Kestrels in something like the Fokker D.XXIII?

 

[don4331]

Actually the Merlin was over 30% larger than the Kestrel and went to 40% larger (heavier) very quickly even for single stage single speed engines. Likewise the radiators and oil coolers go up in proportion to the power, not the displacement.

True but then the 400 version didn't show up until the big block 396-427-454 had been around for a while. In fact the 327-350 used a different height engine block to accommodate the longer stroke cylinders compared to the 265-283. Sticking a "big block" in might fit under the hood but called for a lot of changes to accommodate it as suspensions, and brakes didn't work properly with the heavier engine.

4.000" bore blocks have the exact same block height (9.025) as the previous 265-283 blocks, they just have larger bearing journals (2.45 mains/2.10 rods) versus previous (2.30 mains/2.00 rods). 400 blocks (4.125" bore) have same block height, but still larger 2.65" mains. I've built dozens of them, often mixing parts - there were adapters to put older cranks in newer blocks for less bearing friction (in theory).

Yes, the cooling (oil and liquid) increase with power, but if increase in engine weight is balanced with increased radiator weight and/or lead, the plane still balances. Its just heavier - so, it plane needs more speed to take off, doesn't turn as well, and lands faster. But, it flies faster and that is what is critical.

On the Cobra we built, while we didn't get the ability to re-balance the car, the fenders were bulged to allow bigger tires and larger brakes, and the big block version stopped just as well as the small block one.

 

[don4331]

There's no way an aircraft designed to optimize the 960 lb. Kestrel can fit a 1,600+ lb Merlin.

I repeat - then how did Messerschmitt do it for the Bf.109/110? Ju.210 was 974lbs, while DB.601 was 1,300+ lbs.

And how did Supermarine replace a 1,230lb Merlin II with a >1 ton Griffon 83?

Until you get into 2 stage Merlins, the Merlin is a sub 1,400lb engine.

p.s. DH Comet and Grigorovich E-2 have even worse aspect ratio than the historic Whirlwind. Great for long distance racer that never turns, terrible for a fighter that needs to turn. Think Grumman Skyrocket, Fairey Firefly or DH Hornet for correct wing (both area and aspect ratio) for your ideal twin.

 

[wuzak]

To be competitive with two Kestrels I suggest the fighter would need to be smaller and lighter than the Whirlwind, perhaps the size of the de Havilland DH.88 Comet or Grigorovich E-2.

View attachment 660444 View attachment 660451

Replace the Comet's de Havilland Gipsy Six R engines and two-bladed props for liquid cooled Kestrels running three-bladed props, remove the second seat, add armament, radiator and some armour and we have something. But it will be too small for later upgrading to the Merlin, etc. You can see how small the Comet is below.

So replace the Gipsy Six's, weighing about 470lb and making 230hp, with a Kestrel, weighing about 960lb, not including cooling systems, and making 650-700hp?

 

[Jabberwocky]

I repeat - then how did Messerschmitt do it for the Bf.109/110? Ju.210 was 974lbs, while DB.601 was 1,300+ lbs.

Because the 109 was designed with an eye towards larger engines from the first place. The DB600, which is a ~1230 lb (dry) engine, was already running on the bench by 1932 and was ready for aircraft by 1935. The V13 and V14 prototype 109s were fitted with DB 600As and some racing/world record attempt aircraft were fitted with DB 601 prototypes.

And how did Supermarine replace a 1,230lb Merlin II with a >1 ton Griffon 83?

With a near total redesign (new wing, new tailplane, new landing gear, new radiator arrangements, revised control arrangements). Along with an absolute shed-load of ad hoc engineering and trails work over the course of nearly four years.

If you look at what Supermarine, Rolls-Royce, the A&AEE and AFDU did to get the late Griffon powered Spitfires/Spitfuls/Seafangs into an acceptable state (particularly in terms of directional stability and stall behavior), its clear the aircraft were fundamentally different from the early Merlin powered marks.

 

[tomo pauk]

Because the 109 was designed with an eye towards larger engines from the first place. The DB600, which is a ~1230 lb (dry) engine, was already running on the bench by 1932 and was ready for aircraft by 1935. The V13 and V14 prototype 109s were fitted with DB 600As and some racing/world record attempt aircraft were fitted with DB 601 prototypes.

(my bold)
Do we know for sure that Bf 109 was designed with an eye towards the later engines?

With a near total redesign (new wing, new tailplane, new landing gear, new radiator arrangements, revised control arrangements). Along with an absolute shed-load of ad hoc engineering and trails work over the course of nearly four years.

How much of a total redesign was the Spitfire XII vs. the Spitfire V, apart from obvious engine and cowling change, as well as installation of a bigger cooling system?
Italians were pretty expedient in redesigning the radial-engined fighters into the V12 powered fighters, too (yes, their ability to actually mass produce stuff was awful). The V12s being heavier, longer, and requiring addition of liquid cooling system.

 

[Shortround6]

I repeat - then how did Messerschmitt do it for the Bf.109/110? Ju.210 was 974lbs, while DB.601 was 1,300+ lbs.

Messerschmitt did a lot for the 109. The 109 with the DB 601 didn't fly until Dec 1937 not counting the two race planes.
Mock up was inspected May 11th 1934. The favored engine at the time was the BMW 116 and an installation mock up arrived in July 1934. First metal was cut in Dec of 1934.
The Jumo 210 was now favored over the BMW 116 but the Jumo wasn't ready either.
May of 1935 sees the Bf 109V1 fly with the Kestrel. The 109V1 was repowered after a crash and both it and the V2 flew within a day or two of each other in Dec 1935.
Now I am sure that Messerschmitt had heard of the DB 600 engine. Especially since the Bf 110V1 and several more 110V series planes flew with starting in May of 1936. The 110 didn't switch to the Jumo 210 until 3-4 (?) planes with DB 600s were built due to problems both with the DB 600 engine itself and with the delivery of sufficient numbers of DB 600 engines.

The 110 was never intended to use the Jumo 210 so the question of how they fit the DB 600 into the 110 doesn't apply.

Because the 109 was designed with an eye towards larger engines from the first place. The DB600, which is a ~1230 lb (dry) engine, was already running on the bench by 1932 and was ready for aircraft by 1935.

The DB 600 was far from "ready for aircraft by 1935" and it wasn't really ready for much of 1936. It was flown in those years but while the Germans considered suitable for bombers in the early years it was not considered suitable for fighters. How fast it could be sorted out was questionable, and lead to a lot of planes using Jumo 210 and Jumo 211 engines. DB couldn't reach production deadlines either.

Now for all of the engine swappers here, it could be done, but the change over for many planes was a more than just comparing the weight of the "dry" engine.
The 109E (with four machine guns) had a take-off weight 450kg more than the Jumo 210 powered aircraft. The fuselage structure as well as the undercarriage were both beefed up.
In addition to all the visible changes. Which did include going to the 400 liter tank (with little or no protection)

Messerschmitt may have been dreaming of a DB powered version of the 109 in 1935-36 but the DB 600-601 engine was not a viable product at that time and Messerschmitt was turning out scores if not hundreds of Jumo powered 109s while DB was getting their act together.

How much of a total redesign was the Spitfire XII vs. the Spitfire V, apart from obvious engine and cowling change, as well as installation of a bigger cooling system?

Doesn't look like a Spitfire V rudder to me

They got lucky with the Spitfire.
I get taken to task when ever I say that but and the "luck" was accompanied for by a lot long hours and sweat and hard thinking.
However the Spitfire happened to have enough wing and a long enough fuselage and other attributes of size that some of the needed modifications weren't too disruptive.
Want to try to imagine a Buffalo with enough rudder and fin to control a 1600-1700hp engine on it's short, pudgy fuselage
The Spitfire's largish wing kept take-off and landing speeds more manageable as the weight and power increased than planes with about 3/4s the wing size.

 

[tomo pauk]

However the Spitfire happened to have enough wing and a long enough fuselage and other attributes of size that some of the needed modifications weren't too disruptive.

This is why I've left the two options for the twin Kestrel fighter:
- tailor-made for the Kestrel; ~ 250 sq ft wing, or a 'Whirlwind minus'
- a more 'comfortable' airframe; talk 300-320 sq ft wing, a bit longer than the Whirly; or, an '1-seater British Fw-187' - greater drag, but a better platform for the engine upgrade

Comparison vs. Fw 187 gets us to the 2 x 745 HP at 14500 ft vs. 660 HP at 12140 ft (670 PS at 3700m). Not bad.

 

[Shortround6]

For Tomo's original question figure out the difference in engine weight of the Kestrels, figure out the weigh of twelve .303 guns (about 300lbs) and the weight of the required ammo, (280lb pounds? for 350rpg), figure out if you can lose 15-20 gallons of fuel and keep the same endurance.

Now figure out some of the unknowns. Will the Air Ministry sign a pact with Devil and use variable pitch propellers one of more years early?
Will the early KW (Kestrel Whirlwind) be allowed to land and take-off at similar speeds/distances to the later Whirlwind or will a larger wing be needed?
Will an early KW be allowed to use the Fowler flap or will an older flap and larger wing be needed?

Can a tight design give enough performance with the Kestrel engine?
Please remember that the Whirlwind had a wing almost exactly between the Spitfire and the Hurricane and this is one of the sticking points about trying to modify it to take two Merlin's.
The amount of modifications needed were never spelled out in the letter and the changes to low speed flight performance never addressed.

In another book we have a weight breakdown of the Spitfire I with wooden propeller. the power plant went 2,035lbs including fuel and oil tanks, but not the cowling.
airscrew hub was 36lbs and wooden airscrew and spinner were 96lbs. Bare engine was 1410lbs.

Trying to fit over 4000lbs of power plant weight into an 8300lb tare weight airplane (with Peregrines and DH variable pitch propellers) is the trick.

 

[Jabberwocky]

(my bold)
Do we know for sure that Bf 109 was designed with an eye towards the later engines?

Yep, we do.

The internet just ate my very detailed reply, so broadly:

The DB 600 was already in consideration as a potential powerplant for German fighters by very early 1934. The RLM's fighter development contracts issued in February 1934 specified the Jumo 210 as the powerplant, but there was a provision made for use of the DB 600.

BFW considered not only the Jumo 210, but the (similarly sized) BMW116 and the DB 600 as potential engines during the design stages of the 109 in 1934-1935. At least five of the pre-production prototypes (V 8, V 9 V 10, V 11, V 12 and V 13) all had DB 600s originally fitted or Jumo 210s replaced with DB 600s.

Bowlderising the history, but the 109 was designed to be capable of handling DB 600 series engines from the outset, but had to use the Jumo 210 for a number of years because the engine A) wasn't fully reliable yet, and B) the bombers got more priority for engines than the fighters did.

 

[tomo pauk]

Yep, we do.

The internet just ate my very detailed reply, so broadly:

The DB 600 was already in consideration as a potential powerplant for German fighters by very early 1934. The RLM's fighter development contracts issued in February 1934 specified the Jumo 210 as the powerplant, but there was a provision made for use of the DB 600.

I was hoping for a source to back up the claim that "Bf 109 was designed with an eye towards the later engines", I still do.

BFW considered not only the Jumo 210, but the (similarly sized) BMW116 and the DB 600 as potential engines during the design stages of the 109 in 1934-1935. At least five of the pre-production prototypes (V 8, V 9 V 10, V 11, V 12 and V 13) all had DB 600s originally fitted or Jumo 210s replaced with DB 600s.

Radinger and Shick in their book 'Bf 109; von 109A bis 109E' disagree with that. They note this, for the V8 (I've replaced the umlauts and double S with English characters):
"Es besteht die moeglichkeit, dass in die V8 der einzige fuer die Bf 109 bestimmte DB 600 in Rechlin 1937 eingebaut wuerde."
that google-translates into (my bold):
"It is possible that the only DB 600 intended for the Bf 109 would be installed in the V8 in Rechlin 1937."

Bowlderising the history, but the 109 was designed to be capable of handling DB 600 series engines from the outset, but had to use the Jumo 210 for a number of years because the engine A) wasn't fully reliable yet, and B) the bombers got more priority for engines than the fighters did.

The Bf 110 was the type designed with DB 600 in mind, not the Bf 109.

 

[wuzak]

View attachment 660584
Doesn't look like a Spitfire V rudder to me

But it is a Spitfire V fin, wing, tail plane, and most of the fuselage.