Full-radial engine FAA?

[tomo pauk]

The problem with the Hercules is that is was not ready for service use until 39/40 (Hercules I didn't enter production until 1939) whereas the Merlin II/III is in service use from ~1937. This means that for the FAA to have a Hercules power fighter, it must be designed around an engine that existed only as a prototype (so the spec was always changing)

The Hercules was indeed in prototype form in second half of 1937 (Flight article). Fairey (or other airframe maker) can try to cover it's bets, engine wise. Like it was done with Battle, that was flown on several engines, at least 3 radials among them.

and was giving rather unimpressive output compared to the much lighter Merlin and the R-1830. According to Lumsden, the Hercules II dry weight was 1929lb (wikipedia via Lumsden 2003 and it also gives much lower output) and gave only 1375hp at TO and 1375hp at 5000ft. Compare that to an R-1830 with a dry weight of 1250lb which gave 1200hp at TO and at ~2000ft. The Hercules III only gained 25hp by using 100 octane fuel, according to Lumsden.

For Merlin - I'd reiterate that 1st some 300 lbs worth of cooling system need to be added, and then we can make comparison.
The R-1830 that weighted 1295 lbs (and not 1250 lbs) was the -9, for P-35, and that one gave 950 HP for take off, and have had no military rating, max continuous being the next best at 840 HP. The -13 was making 1050 HP for TO, still no military rating, and 900 HP at 10000 ft. Weight - 1370 lbs. For 1200 HP for take off, and still no military rating, we have -17, that weights 1403 lbs. The 1st engine giving military power of 1200 HP (at 3700 ft), we wait until -51, that weights 1473 lbs. By then, Bristol has the Herc VI in offering? Conceiving the next gen FAA 2-seat fighter, around a foreign engine that gives 950 HP for TO in 1937 does not make much sense.

About Hercules weights - do we know how heavy were the later marks? Lumsden, at least in earlier issue, lumps all the weights at 1845 lbs, from Herc I to 103.

The Merlin VIII with 100 oct fuel was still 100 HP down vs. Hercules IV on 87 oct fuel in TO power.

 

[Glider]

Janes has the Hercules as follows

TO power
XI 1870lb 1590hp
VI and XVI 1930Ib 1615hp
VII and XVII 1,915lb 1725hp
XVIII 1,930lb 1725hp

 

[RCAFson]

Janes has the Hercules as follows

TO power
XI 1870lb 1590hp
VI and XVI 1930Ib 1615hp
VII and XVII 1,915lb 1725hp
XVIII 1,930lb 1725hp

XI 1870lb 1590hp (available late 1940 probably with lower output) = service use by early 1941
VI and XVI 1930Ib 1615hp (available late 1941) = service use by early 1942

Trying to put together a Hercules engine history is a bit trying, but it seems that there were problems with engine production and HP output which, for example, led to the development of the Beaufighter II which changed over to the Merlin XX to improve performance.

 

[RCAFson]

For Merlin - I'd reiterate that 1st some 300 lbs worth of cooling system need to be added, and then we can make comparison.
The R-1830 that weighted 1295 lbs (and not 1250 lbs) was the -9, for P-35, and that one gave 950 HP for take off, and have had no military rating, max continuous being the next best at 840 HP. The -13 was making 1050 HP for TO, still no military rating, and 900 HP at 10000 ft. Weight - 1370 lbs. For 1200 HP for take off, and still no military rating, we have -17, that weights 1403 lbs. The 1st engine giving military power of 1200 HP (at 3700 ft), we wait until -51, that weights 1473 lbs. By then, Bristol has the Herc VI in offering? Conceiving the next gen FAA 2-seat fighter, around a foreign engine that gives 950 HP for TO in 1937 does not make much sense.

A radial engine also adds weight for the cooling system but probably not to the same extent as a liquid cooled engine, and the heavier bulkier radial engine means added weight to fit it into the airframe. The radiator for the liquid cooled engine can also be fitted closer to the aircraft's CG.

But the R-1830 was in production so you could design an aircraft around it, and as you can see above, the Hercules took some time to achieve higher output. I'm not suggesting that they should have used the R-1830 but rather it was an example of current engine technology.

About Hercules weights - do we know how heavy were the later marks? Lumsden, at least in earlier issue, lumps all the weights at 1845 lbs, from Herc I to 103.

The Merlin VIII with 100 oct fuel was still 100 HP down vs. Hercules IV on 87 oct fuel in TO power.

To design an aircraft around a Hercules means starting from a fresh design that won't be available until sometime after the Fulmar enters service. Initial production of sleeve valve engines were plagued with reliability problems as well. The test bed version of the Hercules II, in the Fairey Battle, didn't start flying until Feb 1939.

 

[RCAFson]

This one, down, was captioned as Centaurus-powered Hurricane project, though that engine would've been quite a beast to be grafted to the Hurri. The one with Hercules should've looked similar?

View attachment 263959

added: if you think I'm a what-if wacko, check out this:

Hurricane MkII Hercules

Hercules Hurricane:

from:
http://www.k5083.mistral.co.uk/PROJECTS.HTM

The view over the nose would be somewhat worse than in the Merlin Hurricane, and it's carier landing characteristics would suffer accordingly.

 

[wuzak]

Hercules Hurricane

Radial engined HAWKER HURRICANE!

I think this is not a whatif...(Bristol Hurricane)

 

[Shortround6]

I am still trying to figure out the benefit.

Step 1. add some propeller horsepower
Step 2. subtract exhaust thrust ( Hercules doesn't get rearward exhaust until the 100 series).
Step 3. Add a crap load of drag ( British 1939-41 radial engine installations were a bit less than stellar).

equals???????? for performance.

 

[FLYBOYJ]

A radial engine also adds weight for the cooling system.

Aside from cowl flaps, the only other cooling system on a radial is baffling around the cylinder heads which is nothing more than thin sheet metal.

 

[tomo pauk]

XI 1870lb 1590hp (available late 1940 probably with lower output) = service use by early 1941
VI and XVI 1930Ib 1615hp (available late 1941) = service use by early 1942

Trying to put together a Hercules engine history is a bit trying,

Indeed; many thanks for members here trying to decipher the exact dates power levels. Bristol (and, for example, DB ) engines do reserve a well researched book on them.

but it seems that there were problems with engine production and HP output which, for example, led to the development of the Beaufighter II which changed over to the Merlin XX to improve performance.

The Merlin XX installation was an attempt to avoid the perceived shortage of Hercules engines, that were either used or earmarked for Wellington, Stirling and Halifax bombers, among other aircraft. There was no improvement in performance with Merlin in Beaufighters.

A radial engine also adds weight for the cooling system but probably not to the same extent as a liquid cooled engine, and the heavier bulkier radial engine means added weight to fit it into the airframe. The radiator for the liquid cooled engine can also be fitted closer to the aircraft's CG.

Installation of the radiators too close to the CoG is not such a god idea, since it is either sticking out too much in the airflow (like Hurricane) or eats too much of the CoG-neutral volume (like in P-39) that is better used for consumables, like fuel and ammo.

But the R-1830 was in production so you could design an aircraft around it, and as you can see above, the Hercules took some time to achieve higher output. I'm not suggesting that they should have used the R-1830 but rather it was an example of current engine technology.

The R-1830 was not better than Perseus in the time FAA was making the decisions about the two-seater that will replace Skua. It was about as good as the Fiat A.74, found in Fiat CR.42, G.50 and MC.200.

To design an aircraft around a Hercules means starting from a fresh design that won't be available until sometime after the Fulmar enters service. Initial production of sleeve valve engines were plagued with reliability problems as well. The test bed version of the Hercules II, in the Fairey Battle, didn't start flying until Feb 1939.

I'd disagree that it would've taken a fresh design to take Hercules aloft for the FAA. We can recall that many aircraft were successfully re-engined from V-12 engines into radials (La-5, Ki-100), and vice versa (P-40, many Italian fighters, Fw-190), that was even a tougher job. Most of the conversions were done while countries of origin were under intense pressure from their enemies. Fairey Battles with radial engines (two Bristols, and Wright Cyclone):

 

[tomo pauk]

I am still trying to figure out the benefit.

Step 1. add some propeller horsepower
Step 2. subtract exhaust thrust ( Hercules doesn't get rearward exhaust until the 100 series).

Technically, the Beaufighter installation have had the rear facing exhaust. Sure enough, the individual stacks were a better bet, yet we should still get some amount of exhaust thrust.
The current (1940-41) Merlin exhaust stack layout was also a bit behind what the German and US V-12 used, ie. 2-in-1 (or, 4-in-2-in-1?, when counting exhaust valves) instead of individual (per cylinder) stacks. Cost was eg. 6 mph for the Spit V.

Step 3. Add a crap load of drag ( British 1939-41 radial engine installations were a bit less than stellar).

How good were the British V-12 installation? Hurricane - sorta speed brake, also a hazard when ditching? Spitfire should do much better, but also not as good as practically possible? Maybe Fulmar's was the best?

equals???????? for performance.

Equals the performance good enough to take off with decent payload, even from not so fast cruisers on no-wind situation in Mediterranean?
Other than performance: the Barracuda can be a safe aircraft from day one? Increased resilience against bomber's return fire? One less system to cater for? Safer ditching, without belly or low wing radiator? Fine performance even without two-stage engine, once Mk.XI and VI are available? Less worrying about the hi-oct fuel availability in the next several years?

 

[parsifal]

Make it a twin, then. Tomo, you're gonna like this, being into leftfield ideas. How about a naval Beaufighter? Folding wings, strengthened rear fuse to take a hook, but reduced armament in the wings for weight saving?

There are some immediate problems to consider, quite apart from the aircraft development. First is that a twin engined carrier bird takes up space and this reduces CAG sizes even further, which was already a problem for the RN.

Second problem are the low headroom of the British prewar carriers. Would make wing folding for a twin aircraft fairly difficult. It would mean all prep work would need to be done on the deck and this would slow prep and take off times considerably.

Melbourne operated Trackers postwar, but when we embarked them, our nominal aircraft capacity dropped from 24 to 14 a/c and the carriers spot rate (the speed an aircraft could be prepped and launched) was halved. We accepted it, and compensated for it by some really intensive training, and using the angled deck to full advantage. Melbourne was built with a somewhat higher hangar clearance which probably would make a difference.

Last problem was the elevator sizes on the older carriers. Glorious, Courageous, etc all had tiny lifts, these carriers would not be able to operate such a big aircraft, again might be able to resort to prep on the deck, but these carriers already were slow in aircraft turn around and were limited deck spaces as well.

Big, big problems with operating a twin engine aircraft from a Brit carrier of this era. .

 

[Shortround6]

Technically, the Beaufighter installation have had the rear facing exhaust. Sure enough, the individual stacks were a better bet, yet we should still get some amount of exhaust thrust.
The current (1940-41) Merlin exhaust stack layout was also a bit behind what the German and US V-12 used, ie. 2-in-1 (or, 4-in-2-in-1?, when counting exhaust valves) instead of individual (per cylinder) stacks. Cost was eg. 6 mph for the Spit V.

Just because the final outlet was pointed backwards instead of sideways doesn't mean you get a whole lot of benefit. Since thrust is mass (of gas) times velocity of escaping gas, long, convoluted exhaust systems slow down the escaping gas and the Bristol system which uses the forward part of the cowling as a exhaust collector works as both a expansion chamber (untuned) and exhaust cooler, cooler gas has less pressure/velocity in the exhaust gas system.

V-12s (some) and short stacked radials have blasts of high velocity gases leaving the pipes, not a constant flow.
Exhaust gas velocity of a Merlin XX was supposed to be anywhere from 1395fps at 15,000ft/48.24in manifold pressure to 1901fps at 30,000ft/34.30in manifold pressure. The difference in atmospheric pressure affecting the back pressure on the exhaust. Running some of your cylinder's exhaust through 4-6 feet of cowling leading edge before routing through several feet of rearward facing large pipe is going to kill a fair amount of exhaust gas velocity.

How good were the British V-12 installation? Hurricane - sorta speed brake, also a hazard when ditching? Spitfire should do much better, but also not as good as practically possible? Maybe Fulmar's was the best?

A little harsh on the old Hurricane? Granted it did like to play submarine when ditched if not flip over but claiming the Hurricanes radiator equaled the drag of an Early Hercules installation? The entire radiator housing was thinner that the center section of the Hurricane wing and was just a few inches wider than the Merlin engine. Perhaps around 4 sq ft? and the front of the radiator housing/fairing was smaller than the middle. Add 4 sq ft to the under 6 sq ft of the Merlin (well faired) ant the 14/7 sq ft of a Hercules still looks pretty bulky. May want to do something about the air intake on the Hercules too

Photo of later model Hercules on Australian Beaufighter;

Also please note exhaust pipes going forward to collector and and collector protective leading edge.

Equals the performance good enough to take off with decent payload, even from not so fast cruisers on no-wind situation in Mediterranean?
Other than performance: the Barracuda can be a safe aircraft from day one? Increased resilience against bomber's return fire? One less system to cater for? Safer ditching, without belly or low wing radiator? Fine performance even without two-stage engine, once Mk.XI and VI are available? Less worrying about the hi-oct fuel availability in the next several years?

Which planes?
There were only 30 Barracuda MK Is built with Merlin 30s. Was the delay because they were waiting for the Merlin 32 or for other reasons. 1590-1600hp Hercules doesn't seem to offer any greater safety than 1625hp Merlin. Barracuda shouldn't be trying to shoot down enemy bombers

Granted the one less system to cater for.

Fine performance compared to what without a two stage engine? 2 Speed Hercules vs single speed Merlin? 2 speed Hercules had FTH of around 12,000ft. And you only get the Hercules to give much over 1300-1400hp with 100/130 octane fuel. Since you need a few hundred extra HP to fight the increase in drag I am not sure what you are gaining.

 

[FLYBOYJ]

WHAT THE HELL IS THAT GUY WITH THE SPANNER DOING TO THE PROP!!! GET HIM AWAY FROM THE AIRCRAFT NOW!!!

 

[tyrodtom]

WHAT THE HELL IS THAT GUY WITH THE SPANNER DOING TO THE PROP!!! GET HIM AWAY FROM THE AIRCRAFT NOW!!!

He might have been caught in the act of repositioning the wrench for use somewhere else.

Or the photographer told them he wanted them all to look like they were doing something.

 

[wuzak]

The current (1940-41) Merlin exhaust stack layout was also a bit behind what the German and US V-12 used, ie. 2-in-1 (or, 4-in-2-in-1?, when counting exhaust valves) instead of individual (per cylinder) stacks. Cost was eg. 6 mph for the Spit V.

Were the British (ie Rolls-Royce) really behind the Germans and the Americans?

After all, the Americans only had the P-40 at that time, and IIRC Vees for Victory states that Allison didn't develop the exhaust stacks - that was down to the airframe manufacturer! The fact that cylinders were paired doesn;t automatically make them worse.

 

[nuuumannn]

There are some immediate problems to consider, quite apart from the aircraft development.

Yes, you are probably right, Parsifal; the Beaufighter was a rather large beastie and this is not even taking into consideration the difficulties its crews had on handling the thing on the ground. I've spoken to a number of pilots and read a number of accounts that talk of how difficult the Beau could be on the ground. Ground loops were common and when night fighter crews went to the Mk.II with its Merlins, already awkward handling got worse.

I suggested it to whet Tomo's appetite to see what he might come up with in terms of a proposal. He's very good at that sort of thing.

 

[FLYBOYJ]

He might have been caught in the act of repositioning the wrench for use somewhere else.

Or the photographer told them he wanted them all to look like they were doing something.

I'm hoping it's the latter of the two, and I would bet dollars to donuts there's nothing close to that size within 10 feet of him.

 

[fastmongrel]

He's adjusting the left handed inflatable waffle grommets on the Widget valve they always came loose on Hercules.

 

[tyrodtom]

He's probably the go-getter. He gets up and down his ladder to get tools for the other two guys. He's just trying to look busy.

 

[tomo pauk]

Just because the final outlet was pointed backwards instead of sideways doesn't mean you get a whole lot of benefit. Since thrust is mass (of gas) times velocity of escaping gas, long, convoluted exhaust systems slow down the escaping gas and the Bristol system which uses the forward part of the cowling as a exhaust collector works as both a expansion chamber (untuned) and exhaust cooler, cooler gas has less pressure/velocity in the exhaust gas system.

V-12s (some) and short stacked radials have blasts of high velocity gases leaving the pipes, not a constant flow.
Exhaust gas velocity of a Merlin XX was supposed to be anywhere from 1395fps at 15,000ft/48.24in manifold pressure to 1901fps at 30,000ft/34.30in manifold pressure. The difference in atmospheric pressure affecting the back pressure on the exhaust. Running some of your cylinder's exhaust through 4-6 feet of cowling leading edge before routing through several feet of rearward facing large pipe is going to kill a fair amount of exhaust gas velocity.

Thanks for the overview.
The day fighter/bomber exhaust(s) do not need to be several feet long, like in the night bombers' installation (needed for the flame suppressor). Bristol can also try and come out with another set-up, with at least one 'collective' exhaust pipe, so 7 cylinders share one pipe, so the losses are further lowered.

A little harsh on the old Hurricane? Granted it did like to play submarine when ditched if not flip over but claiming the Hurricanes radiator equaled the drag of an Early Hercules installation? The entire radiator housing was thinner that the center section of the Hurricane wing and was just a few inches wider than the Merlin engine. Perhaps around 4 sq ft? and the front of the radiator housing/fairing was smaller than the middle. Add 4 sq ft to the under 6 sq ft of the Merlin (well faired) ant the 14/7 sq ft of a Hercules still looks pretty bulky. May want to do something about the air intake on the Hercules too

Fair enough Granted, it would take two-stage Merlin for the Hurricane to cross 350 mph line. Hercules aboard would've given some other benefits, apart from extra speed.

Photo of later model Hercules on Australian Beaufighter;
Also please note exhaust pipes going forward to collector and and collector protective leading edge.

Thanks for the photo.

Which planes?
There were only 30 Barracuda MK Is built with Merlin 30s. Was the delay because they were waiting for the Merlin 32 or for other reasons. 1590-1600hp Hercules doesn't seem to offer any greater safety than 1625hp Merlin. Barracuda shouldn't be trying to shoot down enemy bombers

Granted, having 30 'safer' Barracudas don't change anything for the ww2. Might save a few of them (and their crews) from a splinter damage to the cooling system, along with some other that would be with 1500-1600 HP engine instead of 1300 HP one? A tidbit from Wikipedia:
The Barracuda's primary problem in the Pacific was the need to fly over Indonesian mountain ranges to strike at targets on the eastern side of Java, which necessitated a high-altitude performance which the Barracuda's low-altitude-rated Merlin 32 engine with single stage supercharger could not provide.

Fine performance compared to what without a two stage engine? 2 Speed Hercules vs single speed Merlin? 2 speed Hercules had FTH of around 12,000ft. And you only get the Hercules to give much over 1300-1400hp with 100/130 octane fuel. Since you need a few hundred extra HP to fight the increase in drag I am not sure what you are gaining.

Hercules VI and subsequent models (those with 13 in impeller) have had 2nd FTH at 15000 ft, making there 1500 HP an more (the Mk.XI preceded the Mk.VI). Plenty of HP will be saved via non-use of underslung radiators.
Hopefully, our (my?) new fighter will be much better performer than the Re.2000, that was sporting a 1000 HP radial and still making almost 330 mph. Without resorting in a tiny and/or 'trick' wing, and without any great shakes in streamlining of a radial engine and exhaust stacks layout.

Were the British (ie Rolls-Royce) really behind the Germans and the Americans?

After all, the Americans only had the P-40 at that time, and IIRC Vees for Victory states that Allison didn't develop the exhaust stacks - that was down to the airframe manufacturer! The fact that cylinders were paired doesn;t automatically make them worse.

Guess you're right re. V-1710 exhaust stacks. At any rate, one of improvements for a single Spitfire V, that saw the fighter making some 380 mph after modifications, was installation of 6 exhaust stacks per side, and that change earned 6 mph on top speed.