35 replies to this topic

[Wuzak]

I was reading the book Development of Piston Aero Engines by Bill Gunston when I came across this statement in reference to the Rolls Royce Merlin:

During the war Packardintroduced their own features, apart from American accessories, one being th euse of water injection in th V-1650-11 of 1944, to give a war emergency power of 2,270hp at 90 in manifold pressure, or about 29.5 lb/sq in boost. Even thiswas eclipsed by the RM.17SM, which in 1944 was un at Derby on 150-PN fuel, plus water injection, at a boost pressure of 36 lb/sq in (103.2 in), the brake horsepower being 2,640. The BMEP was 404 lb/sq in, and in IMEP (Indicated MEP) 535 lb/sq in. I have never heard of this being exceeded.

The test engine was able to sustain this for maybe 15 minutes.

My question is, how does the BMEP compare with modern racing engines, turbocharged, supercharged or otherwise?

I am guessing that their aren't many categories in the world today which have such high octane fuels to use.

The boost pressure of 36psi (just under 2.5 bar) is less than some F1 engines were using in the mid '80s prior to the FIA's imposition of boost limits. How did the turbo F1 engines compare?

[McGuire]

Any of the decent F1 turbo-era engines could best that Packard Merlin BMEP figure, as could some some Indy car engines as well.

In boosted applications BMEP is mainly a function of how much charge pressure you are willing (or allowed) to screw into the engine, so the number doesn't mean much in comparison to NA engines. For example, at 500 CID, 8500 rpm and upwards of 8000 hp, an NHRA Top Fuel engine develops nearly 1500 PSI BMEP. ( ! )

Speaking to the room, BMEP is a calculated value of the useful pressure produced in the cylinders, extrapolated from the engine's measured output... for example, one lb ft of brake torque per cubic inch of displacement equals 150.8 PSI BMEP. Or, BMEP = (BHP x 792,000) / (CID x RPM)

[Wuzak]

Thanks McGuire.

I guess the author's claim that he has "never heard of this being exceeded" must be confined to aero engines, as the book was first published in 1993.

[McGuire]

In unlimited air racing (Reno and all that) the Merlins have been producing 3000+ hp for years so that must be another arena Gunston is not familiar with.

[Wuzak]

Originally posted by McGuire
In unlimited air racing (Reno and all that) the Merlins have been producing 3000+ hp for years so that must be another arena Gunston is not familiar with.

Do they do that through extra boost or do they increase the RPM?

I have read that with racing Merlins the rods need replacing in order to be able to increase the rpms.

[McGuire]

Both. RPM can be increased but is limited by propeller tip speed. The hot dogs are running up to 140 inches of manifold pressure at 3400 rpm. Jack Roush makes many of the parts. Pretty interesting stuff, there are several decent web sites you can google up.

[dosco]

Originally posted by McGuire
In unlimited air racing (Reno and all that) the Merlins have been producing 3000+ hp for years so that must be another arena Gunston is not familiar with.

Probably. Gunston is the same guy who thinks the B-2 flies by virtue of "levitation," since its 'puny engines cannot possibly make enough thrust to fly the jet.'

Yeah.

Right.

[Wuzak]

This is what happens if you push your Merlin too far.....

http://blogs.sun.com...e/Reno 554.jpg

http://blogs.sun.com...e/Reno 555.jpg

[desmo]

I'd expect the hydroplane guys should have been able to push the boost/tuning envelope further than the airplane guys by simple dint of the consequences of an engine failure being comparatively trivial for them.

[Bill Sherwood]

Hope this will all fit in ....
---------------------------------------------

Reno for Gearheads, Tweaking Fighters for Racing


By Graham White

WATCHING THE INCREDIBLE racers hurtle around the circuit at Reno, Nevada, few people give regard for the incredible engineering - as well as flying - that makes for success. Those looking for a "usual Reno report had best avert their gaze now. This concentrates on the go-faster features and state-of-the-art engineering that makes Unlimited air racing the world's fastest motor sport.
I wish I could also give race results. Alas, owing to the despotic acts of terrorists on September 11,2001, no races occurred - therefore, no race results. Twenty-nine Unlimiteds had entered for 2001, ranging from balls-to-the-wall, out-and-out racers to "stock" warbirds.

Pete Law has been involved with Unlimited teams since the 1960s.He started his racing career by designing systems - cooling, carburation, anti-detonation injection (ADI) and hydraulic - for Darryl Greenamayer's F8f Bearcat. This aircraft re-wrote the rules for the Unlimiteds. Not surprising really, considering that until his recent retirement, Pete was a high-level executive working at the Lockheed "Skunk Works". I recently got to know Pete and he kindly took three hours out of his busy schedule to introduce me to every Unlimited team. Additionally, Pete is a fountain of knowledge on just about every aircraft, mainly because he probably rebuilt and set up the carburettor, designed the spray bar system and ADI system.

Unlimited racers compete around an 8 mile (13km) course marked off with pylons. The pylons are 55 US gallon (208 litre) oil drums placed high up on a pole. Although no restrictions exist for the type of aircraft flown, the vast majority of racers are former World War Two fighters. This is simply because these aircraft represented the fastest piston-driven aircraft ever manufactured. Of course, the top racers are highly modified - as we shall see. An argument that has raged almost from the days of the Wright brothers' first flight is; Which is better- air-cooled radial or liquid-cooled in-line? That argument has still not been settled, and perhaps this is the way it should be. The see-saw battle of liquid-cooled in-line versus air-cooled radial will, apparently, never abate.

Let's take a more detailed look at some of the 2001would-be racers.
No.4 'Dago Red TP-51D Dago Red is right at the top of Unlimited racing. It has held the Federation Aeronautique Intematiotiale 9-mile (15km) straight line record at 517.06mph (832. 1Okm/h) since 1983 and Us presently the one of the fastest qualifiers ever at Reno, 490.825mph (789.88km/h). Dago Red is owned by Terry Bland and flown by Skip Holm. What makes this aircraft such a phenomenal performer?
N5410V has been on the race circuit for many years. It started out as a P-51D Mustang that was wrecked and rebuilt in its current highly-modified form, and has now been a leading race campaigner since 1982. It's hard to say what percentage of the original aircraft remains, but it isn't much.

P-51Ds are normally powered by a Packard-built Rolls-Royce Merlin V-1650-7 rated at l,450hp (l,081kW). Dago Red's engine puts out an estimated 3,500 to 3,800hp (2,611 to 2,835kW). In order for a Merlin to survive at such remarkable powers, first order of business is to beef up the basic structure and strengthen it. As is typical with most V-12s, the Merlin features seven main bearings to support the crankshaft. In the Merlin's case, the main bearing caps have additional support provided by cross bolts that go right through the engine's crankcase and through the main bearing caps - one either side of the main bearing hold-down studs. Rigidity of the crankcase and crankshaft is essential to make the engine survive under high-power operation. Therefore, one of the first modifications is to increase the size of the cross bolts.

With seven main bearings and two cross bolts per main, a total of 14 main bearing cross bolts are utilised. As an additional aid to stiffening, the entire power section structure, the 14 cross bolts go through massive external steel plates that run the entire length of the power section. So far so good. But all this additional power introduces another problem not envisioned by Rolls-Royce. The massive four-blade Hamilton Standard propeller is driven through a spur reduction gear that is housed in a nose case. Of course, all this additional power is translated into more propeller thrust. In order for the nose case to stay on the engine, a steel strap attached to the nose case, bolts to the crankcase inside the intake valley. Interestingly, this modification may have been inspired from a repair scheme of World War Two. It was quite common for aircraft to make emergency gear-up landings. With a Merlin this would inevitably result in a damaged nose case and/or crankcase.

Another key item that needs improving over 'stock' is the lubrication system. A 'stock' Merlin has a conventional dry sump system and runs 60-80psi hot oil pressure. Under racing conditions, this is not sufficient. First off, the 'stock' pump gears are replaced with longer ones to increase the pump's displacement. However, even this is not sufficient, so an additional pump is installed in parallel with the original pump. Merlins have two accessory drive pads on the rear of each cylinder head - four in all. Normally, these pads are used for driving an air compressor, tach generator, etc. One of these drive pads is used for the additional oil pump. A V-1710 pump does the trick. Oil pressure, with the these modifications, now runs over lOOpsi hot. With all this additional oil being pumped into the engine, scavenging becomes more critical. Normally, a Merlin has a windage tray to catch oil slung off the crankshaft. An additional windage tray is installed to improve scavenging. To further improve scavenging, the vacuum pump is now pressed into service as an additional scavenge pump.
OK, now we have taken care of the oil supply and scavenging chores, however, the oil has now picked up a tremendous amount of rejected heat. A 'stock' P-51D uses an air-to-oil honeycomb cooler mounted in the so-called dog-house. For Dago Red, this oil cooling system is totally inadequate. So Dago Red utilises the P-51H oil cooling system. In other words, a water/glycol to oil cooler is mounted in front of the firewall. Coolant is pumped through the oil cooler then to a radiator mounted in the dog house. This offers a far more effective heat rejection route. To further condition the oil, a sophisticated deaerator is installed to purge the entrapped air. However, it's not just the oil that needs to be cooled, the engine coolant, a 50/50 mix of water and ethylene glycol, is circulated through the engine.

Running at elevated power settings, a 'stock' cooling system would simply be overwhelmed. It seems that a power setting of 80in of mercury manifold pressure is about all the 'stock' cooling system can scarecly handle. To combat overheating, a highly modified radiator, manufactured by Dave Griswold, is used. It has more tubes, more fins and more rows. To further augment cooling, water is sprayed on the radiator core. Water is introduced via a spray bar system designed by Pete Law. Bill Kirchenfaut, Dago Red's crew chief, eloquently stated; at race speeds, "it's like Niagara Falls spraying on that radiator core." The fact that no after-cooler is employed (see explanation later) allows a larger engine radiator to be used. The area normally occupied by the aftercooler radiator is used for engine cooling chores. If one looks carefully at TV images of top Reno Unlimited racers, a distinctive trail of steam can be seen issuing from behind. This steam is generated by spray bar water that flashes off as it makes contact with the high-temperature radiator core. Dago Red will consume approximately 60 US gallons (227 litres) of spray bar water in a race, which lasts about 15 minutes. With all these cooling system modifications, coolant temperature runs at 100 degree C and oil runs at 85 degrees C.
From the foregoing, it can be ascertained that raising the power of the Merlin is a question of chasing down all the potential weak points.

One component in a high horsepower engine that undergoes incredible stress is the connecting rod, possibly one of the most critical of all internal parts. 'Stock' Merlin connecting rods are typical of their ilk, they are blade-and-fork, although Rolls-Royce took the more difficult manufacturing route of using the 'marine block' variation on this concept. Although exquisitely made, Rolls-Royce connecting rods were only designed to tolerate the loads of a 'normal' engine. When manifold pressures exceed lOOin, they become fragile. One of the Merlin's main competitor's during World War Two was the General Motors-built Allison V-1710. Conceptually it was very similar to the Merlin; ie liquid-cooled V-12 and similar displacement. Although much-maligned, the Allison was another superb example of aircraft engine design. One feature in particular that distinguished the Allison was the stoutness of its connecting rods. As with the Merlin they were of blade-and-fork design but considerably stronger. This hands the 'hot-rodders' a golden opportunity. Although the centre distances from the journal to the wrist pin are slightly different, this can be compensated for by forging special pistons with a higher compression ratio. The ultimate Allison series built were the 'Gs', specifically the G6. These G6 rods are the ones installed in Dago Red's Merlin. One normally thinks of Allisons being built in the tens of thousands, which is true, however, only 750 G6s were built. Their only application was the North American F-82 Twin Mustang. The available supply has been further depleted by 50-plus years of unlimited hydroplane racing and as tractor pullers where they were the favoured Allison. For this reason, G6 Allison rods are a much sought-after component.
Now that the engine has received structural rigidity, an oil system and cooling system that can handle the additional requirements with Now that the engine has received structural rigidity, an oil system and cooling system that can handle the additional requirements with beefed up internal and external components, it's time to get serious about making more power. With a highly supercharged engine such as the Merlin, the easy and obvious route is to simply crank up the manifold pressure. And that's exactly what Dago Red does - among other things.

It is almost a waste of time trying to improve upon the intake port design or finish. In 'stock' configuration, Merlins' were ported and polished. In service, Merlins' were usually limited, depending on dash number, to 60in. This pressure was preset via the automatic boost control. In other words, a pilot could push the throttle to the firewall but the engine would not be overboosted, but it would not operate at full throttle at sea level either. So of course the first thing the racers do is get rid of the automatic boost control. One undesirable by-product of supercharging is increased charge temperature, due to compression heating. Rolls-Royce took care of this by having an intercooler and aftercooler incorporated into the supercharger. This simply means two supercharger impellers run in series to boost manifold pressure.
A coolant jacket in the supercharger housing acts as the intercooler between the two stages, but it really does not accomplish much. Most of the heat from compression is rejected via the after cooler. This is a rectangular, boxy-looking heat exchanger that sits on top of the engine towards the rear. It is a radiator core with compressed fuel/air mixture on the outside of the radiator tubes and coolant flowing though the tubes. Works great for reducing charge temperatures, however, it creates a restriction that reduces manifold pressure by about lin. For a conventional Merlin, it's not significant, but for Dago Red's race engine, running at an astronomical manifold pressure, it's a problem to the tune of costing approximately Sin. To get by this problem, a simple pipe replaces the aftercooler.
This introduces the problem of how to get the charge temperature down. This is accomplished by introducing massive amounts of ADI fluid. This serves two primary purposes; firstly it reduces the charge temperature, via evaporation, as it is sprayed into the intake system. A lower charge temperature increases the density of the charge and reduces the onset of detonation. Secondly, once ADI enters the combustion chamber, it reduces the flame front temperature, again delaying the onset of detonation. ADI fluid is introduced at the intake elbow, colloquially referred to as the 'Horse's Ass' because that's what it looks like! ADI fluid is made up of a 50/50 mix of distilled water and ethanol or methanol. Engines with the aftercooler removed are referred to as 'tube engines.' by the racers.

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[Bill Sherwood]

As noted above, P-51Ds were typically powered by a Packard-built V-1650-7. However, that was not the ultimate Merlin. After World War Two, Rolls-Royce developed a civilian version of the Merlin for the more demanding environment of civilian airliner operation, (long-range cruise at high power). Rolls-Royce foiled long and hard to get some semblance of reliability and longevity out of the engine. The outcome was the so-called 'transport engine' or more correctly, the Merlin 500 and 600 series. These had all heavily stressed parts beefed up, improved cooling jacket design, heavy duty valves, etc. Dago Red uses a Merlin 622 power section with a Packard-built V-1650-9 supercharger. The -9 has optimal supercharger ratios for increased boost.

This brings up the next question; how much boost does Dago Red run in a race? The quick and easy answer is; it all depends. During qualifying, only sufficient power is used to move up to the next
round. However, when it gets down to the final Gold Race, everything is allowed to hang out. Maximum boost is primarily determined by engine rpm and secondly by ambient temperature and air pressure. In this engine it can run in the 135-140in of mercury range when at 3,400rpm.

Assisting boost is a carefully-designed ram air scoop. For Dago Red it is made from fibreglass with an ideal convergent/divergent design. This design picks up approximately 3-5in of manifold pressure at race speeds. Theoretically, it is possible to run an even higher manifold pressure than 140in. At 140in, the point of diminishing returns has been reached. In other words, so much power is consumed driving the supercharger, very little, if any, additional power is fed to the propeller. At 140in, the Merlin two-stage supercharger is consuming in excess of l,000hp (746kW) to drive. It has even been argued that anything in excess of lOOin does not produce any additional power to the propeller, however the aircraft will fly faster when running in excess of lOOin. The argument presented is the fact jet thrust from the exhaust stacks is increased at the higher manifold pressure resulting in a higher air speed.

With all these radical modifications, the engine now has to spin up faster. A Merlin is red-lined at 3,000rpm. This may not sound like much but remember, this engine has a 6in stroke. By modifying the
'speeder' spring in the propeller governor, Dago Red runs at 3,400rpm. It would be nice if the engine could be spun faster, however, engine speed is limited by several factors; lowest reduction gear ratio for a Merlin is 0.420:1 and secondly, propeller tip speed. When tip speeds approach or exceed 1,000 feet per second (304m/sec), propeller efficiency goes down hill. In the past folks have tried to make their own reduction gears with lower ratios than 0.420:1, however, this means using a smaller pinion and a larger gear. The smaller pinion introduces unacceptably high gear tooth loadings so at the present, this is not an option. Two massive oil jets squirt oil into the reduction gears at the point of engagement, so it's not a question of too little lubrication.

All external airframe skins are smoothed out. The so-called radiator "Dog-House' (the device which is responsible for the P-51D being able to develop positive 'jet thrust' sufficient to offset cooing drag, sometimes referred to as the "Meredith Effect' (named after the RAE engineer who is generally credited with the concept) is totally redesigned with reduced frontal area. Interestingly, Dago Red's dog-house does not feature a laminar flow splitter as one would normally expect to see. A tiny bubble canopy replaces the "stock' P-5 ID'S. Wing area is reduced by clipping the wings. The propeller is "stock', albeit highly polished on the front and flat black on the rear. While the prop could be polished both sides, but this would introduce severe glare, resulting in a serious safety concern for the pilot.

After Monday's qualifying, it was noticed that an exhaust stack on Dago Red's "B' bank was smoking. After further investigation, coolant was found on the centre spark plug - a bad sign. The crew set to and removed the head and bank assembly. Sure enough, a large crack was found in the centre of the cylinder head that had migrated into the intake port. That head is now an expensive paper weight, it is unrepairable. A spare head and bank assembly was installed. For those who have not worked on a Merlin, this is a major operation, particularly for a race version.
During a 15-minute race, it is not unusual for Dago Red to consume an astounding 2,2001bs of liquid in the form of fuel, ADI fluid and spray bar water broken down as follows: 9001bs of spray bar water, 3001bs of ADI fluid and l,0001bs of fuel.

Voodoo a Modified P-51D intended to race but suffered a catastrophic engine failure just prior to the races. Owned by Button Transportation and flown by Matt Jackson, Voodoo has always been a top contender but to date has only ever been a bridesmaid. For 2001, Jack Hovey built up a special race engine. Time was flown on the newly rebuilt engine and everything was looking good. The power was brought up in increments to 90in of mercury. At this point the engine backfired.
Normally, an engine backfiring is no big deal. But with a highly supercharged engine it is serious stuff. Backfiring can be caused by a number of factors, the primary ones being; lean mixture and
leaky intake valves. With Voodoo it is thought that the carburettor (a Bendix PD-18) was set up too lean. When an ignition source is introduced into the intake system, such as a backfire, this lights off a highly-explosive, compressed fuel/air mixture. The pressures generated from this uncontrolled combustion are so great that it wreaks havoc through the entire engine. Serious damage is incurred by the supercharger and intake ducting. More seriously, this high pressure momentarily blows open all the intake valves. Allowing high pressure gasses into the cylinder at the wrong time produces what is in effect an "hydraulic lock' resulting in bent connecting rods.

Jack had built this engine with Merlin 622 connecting rods, the ultimate Rolls-Royce built rods. Voodoo's backfire and its consequent unacceptably high loading on the power section resulted in bent rods. Afterthe backfire, Matt Jackson, the pilot, kept the engine running but when he pulled the power back for landing, a connecting rod failed, resulting in a destroyed engine. As an aside. Jack Hovey is one of the more.experienced rebuilders of Merlins. He built the race-winning engine for the 1972 Gold Champion, the Roto Finish Special. A unique feature of Voodoo is its use of a carbon-fibre cowl. This represents a weight saving and makes it easier to remove the cowl.
A P-51D cowl is a real chore to take off due to the gazillion Dzus fasteners that have to be removed!

'Strega' a Mdified P-5 ID Flown and owIjed by Tiger' Destafani, Strega is right up there with Dago Red for being at the top of the heap for Unlimited racing. Its engine features all the modifications incorporated into Dago Red, in fact both aircraft share a lot of race technology and even look very similar. One interesting deviation from Dago Red is the placement of the coolant header tank. P-SIDs have a coolant header tank that is horseshoe-shaped, wrapped around the engine nose case. In the case of Strega, it is repositioned behind the pilot. This probably does not enhance performance but it makes for additional room to work on the engine, consequently making maintenance chores simpler to perform.
Critical Mass' a Modified Sea Fury is One of the last great piston-powered fighters developed was the British Hawker Sea Fury. Developed for the British Fleet Air Arm, it incorporated Hawker's experience from developing a number of high-performance fighters in World War Two. Originally, it was powered by the massive and impressive Bristol Centaurus XVIII sleeve valve engine rated at 2,470hp (1.843kW). Although this engine was a superb example of aircraft piston engine development, its scarcity, particularly in the US, has dissuaded folks from overhauling them or modifying
them for racing. This has resulted in the majority of Sea Furies flying in the US being converted to Wright R-3350 power.

Over the years, a considerable amount of experience has been gained on how to make R-3350s perform. Perhaps most, if not all the credit, should go to Lyie Shelton who has campaigned a Grumman
F8F Bearcat Rare Bear powered by the R-3350. With this experience in mind, Critical Mass has what is essentially the same type of engine with the same modifications as Shelton's. Owned and flown
by Tom Dwelle, Critical Mass is clearly a top contender and in the same class as Dago Red or Strega.

Like many other aircraft engines that remained in production for a long time, R-3350s went through a lengthy evolutionary development phase. Starting out with the under developed and problematic
Boeing B-29 Superfortress engines, R-3350s evolved into possibly the most advanced piston engine in the form of the R-3350 turbo compound, powering such aircraft as the Douglas DC-7 and later version of the Lockheed 1049 Super Constellation.

Turbo-compounding was experimented with by all the major piston engine manufacturers but Wright was the only one who managed to get one into production. Turbo-compounding simply mean
that the exhaust gasses are utilised to power a blow-down turbine which feeds power back to the crankshaft. Or, as Wright referred to them power recovery turbines (PRTs).

Although the concept sounds great and it was for large transport due to the considerable fuel savings it generated, for racing, the PRTs three per engine, represent too much weight for too little power gain However, the PRT engines also represented the strongest and best components. Critical Mass employs a PRT engine but with the PRT removed. An adapter plate between the power section and blower section accomplishes this with a weight savings and reduced engine length Unlike in-line V-12s, radial engines do not tolerate over revving. Several factors account for this, one being the extreme loads imposed upon the master rod bearings. Remember, with a blade-and-fork rod set up in most V-12s, only two cylinders are acting on each connecting rod bearing big end bearing. A radial, on the other hand, needs a master rod bearing that can withstand the loading of nine cylinders. With this in mind, Critical Mass races at 3,100rpm - still a very high number for such a massive engine. By comparison a R-3350-26W is rated at 2,700hp (2,014kW) at 2,900rpm.


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[Bill Sherwood]

One of the best propellers developed for the R-3350 was the one installed on the Douglas AD Skyraider. As with all the other racers, the holy grail of power and efficiency is a low(er) revving propeller. Critical Mass accomplished this via a rare and hard to find nose case. At the end of the piston engine era, Lockheed developed the ultimate airliner, the magnificent L.1649Starliner. Although it superficially looks It like a Constellation, it was really an entirely different aircraft. Wright developed a special engine for this aircraft called the EA2. It had a very low reduction gear ratio
of 0.355:1, ideal for driving the Skyraider prop. In all, 287 of these engines were built, most of which have been scrapped, however Critical Mass uses one of these nose cases. Again, by comparison, the popular R-3350-26WD uses a less desirable 0.4375:1 ratio.

The exhaust system is fabricated from scratch utilising North American T-28 Trojan parts. A total of ten pipes are used - five per side. The outlets are arranged to promote 'air pumping' through the
cowl and residual jet thrust. Critical Mass team members admitted to 4,100hp (3,058kW) - reality may be considerably higher. Of course, with this amount of potential power on tap, massive amounts of ADI is used to keep detonation under control, as well as contribute to lower head temperatures. A 'stock' (Sea Fury) sized spinner is used, although made from carbon fibre. The engine cowl is modified from a Douglas DC-7 component.

Sea Furies use a single rectangular oil cooler housed in a wing leading edge. For the power generated by Critical Mass, this would be totally inadequate. To keep oil temperatures under control, two
'stock'-sized oil coolers are used - one in each wing. To further control oil temperatures, spray bars are used. Although the basic airframe is a Sea Fury, little remains of the original configuration with clipped wings, a new and larger vertical tail and a small bubble canopy.
Furias - is another highly modified Sea Fury, flown by Bill Rogers and owned by Bill Rogers and Dale Stolzer. Interestingly, this aircraft is powered by a Pratt & Whitney R-4360-63A. This highly complex 28-cylinder engine represented the largest piston engine to enter series production. Its 28 cylinders, arranged in four rows of seven, displaced a total of 4,363 cubic inches. Because relatively little racing experience has been developed with this engine, modifications are quite few.
The modifications seem to be restricted to changing the -63A nose case for a -59 nose case. The reason for this is that the -63A nose cases use an unusual SAE 70 spline propeller shaft. Consequently, the only propeller available is the three-blade Douglas C-124 Globemaster II; the aircraft originally powered by the -63A. So a -59 nose case, used on the Boeing KC-97 Stratofreighter, replaces the -63A. With an SAE 60 spline, the -59 propeller shaft offers a far better choice of propellers even though the reduction ratio remains the same at 0.375:1. Like the R-3350 powered Sea Fury brigade, Furias uses a Douglas Skyraider prop. The R-4360 propeller shaft rides in three bearings; a massive rolling element bearing installed at the front of the nose case. This bearing handles thrust loads and radial loads. In the middle and at the rear are two copper/lead plain bearing that run inside the hollow crankshaft. At race speeds, up to 6g can be generated on the airframe.
These tremendous loads are also imposed upon the propeller. Exacerbating the situation is the fact that the prop acts as a huge and powerful gyroscope. Of course all these loads are transmitted through the propeller shaft and consequently into the crankshaft via the two rear propeller shaft bearings.
These additional loads require the front main crankshaft bearing to be beefed up, otherwise it would suffer undue stress. Fourteen ejector exhaust stacks are used. This set-up siameses appropriate pairs of cylinders for maximum exhaust scavenging. In a similar fashion to Critical Mass, Furias uses two 'stock' oil coolers, one in each wing. Again, spray bars are used to augment the oil coolers. Spray bar fluid is sprayed at the rate of one gallon per minute at 25psi. Being air cooled, the R-4360 needs all the help it can get. As with all the top radial engined racers, a beautifully-designed convergent/divergent duct is designed from the spinner and inner cowl.

To further augment cooling, a controversial method is used. But before going into that, the basic cooling system of the R-4360 needs to be understood. Unlike single row or double row radials which simply deflect cooling air from front to rear, the R-4360 is made up of seven plenums. Each plenum is formed by the space between each row of cylinders. Cooling air enters the cowl and is forced into the seven plenums where it is then directed through the cylinders, almost cross-flow fashion. On the leading edge of the inside diameter of the inner cowl, seven spray nozzles are incorporated. At race speeds and powers, these nozzles spray water into each plenum, thus getting atomised water directly on the cylinders. A R-4360-63A is rated at 3,800hp (2,835kW). It would be safe to say that Furias has in excess of 4,000hp (2,984kW) on tap.

Race 21 - This 'stock'-looking Sea Fury is one of the few race aircraft to sport military markings. It is painted up to represent an Royal Canadian Navy example. It is powered by a Wright R-3350-26WD, a Douglas Skyraider, non PRT engine. As with some other Sea Furies, it uses a carbon-fibre copy of a Blackburn Beverley spinner. 'Race 21' is owned and flown by Joseph Thibodeau. Probably a good contender for the Bronze Race. Even though this leaves the remarkably narrow annular gap of l~in (3.8cm) for air entry into the cowl, cooling is not a problem. This is accounted for by the excellent design of the R-3350-26WD cylinder. It incorporates a forged cylinder head with all cooling fins machined in. The forging process offers a more structurally sound design without any of the limitations of a casting. The fins are closely spaced and deep, thus offering a large cooling fin area. The cylinder barrel has Wright's patented 'W' finning which, again, offers considerable cooling area and efficiency.

Merlin's Magic' - Modified P-51 D
This aircraft - owned by Stu and Marilyn Eberhardt, flown by Bill Eberhardt- can truly be called a wolf in sheep's clothing. Belying its 'stock' appearance, except for clipped wings, it sports a Dwight Thorn, balls-to-the-wall race engine. Even though the racers were just warming up on the last day of flying, Monday, September 10, it achieved fastest qualifying speed at 432mph (695km/h). However, it may have been pushed just a little too hard. After landing, a maintenance check revealed metal in the oil screen - a bad sign. Rather than risk a $150,000 race engine, it was wisely decided to remove the race engine and replace it with a 'stock' Merlin.

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[Bill Sherwood]

Yaks are now becoming increasingly popular among warbird owners. This is due to their availability and relatively low cost, compared to, say, a P-51D. The original Soviet powerplant is all but impossible to find, so most are powered by US-built engines. Owned by Sam Davis it is flown by Tom Camp, 'Race 27', it powered by a Pratt &: Whitney R-2000.
Normally, one does not think of an R-2000 as a race engine but when paired with the Yak-11, it makes for a good combination. R-2000s only powered a handful of aircraft, the most numerous being the Douglas DC-4 followed by the DHC Caribou. Pete Law designed an ADI system for this racer, which allows a manifold pressure of 52in. Further helping power output are ejector exhaust stacks.

Predous Metal - Modified P-51D
We normally think of P-51Ds being powered by Packard-built Rolls-Royce Merlins. However, the last piston engine mass-produced by Rolls-Royce was an even larger engine than the Merlin. Displacing 2,239 cubic inches, the V-12 Griffon entered service in the early 1940s. As good as the Merlin was, it still had some fundamental problems that would have been difficult to fix once the engine was in production. The Griffon recognised these problems and benefited from previous experience. Except for the pair of oil lines that feed the contra-rotating propellers, no external oil lines are to be seen on the Griffon.

The profusion of external oil lines on Merlins have proved to be a maintenance headache over the years. Another key change made to the Griffon was to drive the camshafts from the front of the engine. Likewise, the single magneto is also driven from the front of the engine. This reduced the torsional vibration the cam drive and magneto drive gear trains are exposed to, particularly when driven from the rear of the crankshaft like the Merlin.

The Whittington brothers in Fort Lauderdale, Florida, originally modified this aircraft for Griffon power. Engine modifications follow the same concept as the race Merlins. Precious Metal uses a mix of components from different Griffon variants. The power section and contra-rotating nose case is from a Griffon 58. The two-stage supercharger is from a Griffon 74 which would normally power a British Fleet Air Arm Fairey Firefly IV. An adapter plate is required to mate the 74 blowers to the 58's power section. Like the full race Merlins, the aftercooler is removed and replaced with a tube. All charge temperature issues are dealt with by massive doses of ADI.
Griffon 58s were normally used to power the Avro Shackleton maritime patrol bomber. The engine drove a pair of contra-rotating propellers. Precious Metal retains this propeller and nose case, albeit in modified form. First off, the propeller diameter is dramatically reduced and at the same time more pitch is used. The engine runs at 3,200rpm, conventional redline is 2,7500. A modified speeder spring in the propeller governor allows the higher engine speed. All Griffons used up-draft carburation. Precious Metal uses a downdraft Bendix PRIOO carburettor originally used on Pratt & Whitney R-4360s.

For the Griffon application, a PRIOO is overkill to the point of being over carbutated. However, this may be due to its prior life as a powerplant for an Unlimited hydroplane boat racer. The boat racers used to turn their engines up to much higher engine speeds. In the future, I would not be surprised to see a PR58 carburettor replace the present set-up. A ram air scoop on top of the cowl feeds air to the PRIOO. Converting to the PRIOO requires the use of an adapter plate that rotates the intake elbow 180 degrees in order to accommodate the downdraft set-up. An additional adapter plate is required to mate the PRIOO to the Rolls-Royce intake elbow. A modified radiator is augmented by spray bars.

As with full race Merlins, lubrication is enhanced via an additional pump driven off one of the accessory pads. The Griffon, like late-model Merlins, used what is known as an end-to-end crankshaft lubrication system. This means the oil is fed in at both ends of the hollow crankshaft rather than the more conventional method of feeding oil to the crank via each main bearing. The advantage with end-to-end lubrication is that it eliminates the necessity for oil distribution grooves in the main bearings in order to feed the connecting rod journals. Precious Metal's Griffon utilises the additional oil pump to feed extra oil into each main bearing. Not only does this provide enhanced lubrication, it also carries away heat thus preserving the life of the grossly over loaded bearings.

Of course, modifications are not restricted to the engine and propeller, Precious Metal also has a radically modified airframe. A small bubble canopy replaces the 'Stock' one, wings are clipped and overall aerodynamic clean-up has been done. Precious Metal is flown by Ron Buccarelli and is owned by Lake Air Inc.
A modified Hawker Sea Fury Flown by Howard Pardue and owned by the Breckenridge Aviation Museum, this 'stock'-looking Sea Fury has potential as a fast racer. Its exhaust system features 18 equal length exhaust stacks. The exhausts exit through what appears to be a very modified cowl. Judging by the design; it is optimised to take maximum advantage of jet thrust and pumping effect to get additional cooling air through the cowl. It is powered by a Wright R-3350-26WD with race power settings of 57-58in of mercury at 2,900rpm. The engine picks up induction air via a pair of wing root mounted scoops. This arrangement is a throw-back to the days when it was powered by the Bristol Centaurus. The Centaurus featured a pair of intakes to the supercharger located
at mid-height of the engine. Of course, the R-3350 has downdraft carburation so this wing root location is not ideal for good ram induction.
For the future it is planned to have a ram scoop mounted on top of the cowl. It's estimated that this simple modification will pick up another 3in of manifold pressure. A carbon fibre copy of a Blackburn Beverley spinner is used. The resulting annular gap of 1 in is still sufficient to keep cylinder head temperatures down to a remarkably low 180 degrees at race speed and power.

'Czech Mate' - Modified Yak-1 I
In the 1960s and into the early 1970s, Unlimited aircraft racing was dominated by Darryl Greenamayer flying a highly-modified Grumman F8F Bearcat powered by a Pratt & Whitney R-2800. This aircraft went on to gain the world's air speed record for piston driven aircraft. This record has subsequently been beaten. With the foregoing in mind, it is surprising that more racers don't take advantage of this formidable powerplant. The small and light Yak-11 airframe is ideal for it. Czech Mate is owned by John & Marcia Moore and is flown by Sherman Smoot.
Little is known about the engine except that it was built up by Ray Anderson, owner of Day Air, a P&W overhaul facility. The engine is A commercial version of the R-2800, a CB3. It is thought that Czech Mate may be using some of the 'go fast' modifications used by Darryl Greenamayer all those years ago.
What is known is that it features ADI and a pair of Grumman S2 oil coolers, which are situated behind the pilot. Air for the coolers comes in from scoops on the side of the fuselage under the cockpit canopy. A reduced diameter Skyraider propeller is used. No cowl flaps are used - cooling air is augmented by the pumping effect of the ejector exhaust stacks. Induction air comes in from ram air scoops in the wing roots which is then ducted to the top of the engine into the Bendix PR58 carburettor - again set up by Pete Law.
No. 104 'Russian Roulette' - Yak-9
In the 1990s a number of newly-built Yak-9s were made. It's hard to say what category these aircraft would fall into - they were not restorations and yet it would be difficult to call them reproductions. Made in the former Soviet Union, they used the same tooling and manufacturing techniques used to make the originals in World War Two. Even aircraft serial numbers continued on from the last one built during the war. The main deviation from the original aircraft is the installation of an Allison V-1710 in place of the original M-107 - a Russian development of the pre-war French Hispano Suiza Y series. Original engines are now all but unobtainable.

This immaculate aircraft is powered by a Bud Wheeler-built and maintained Allison. To date it is not highly modified, however plans for the future may include an engine with a G6 power section and various other modifications such as changing blower gears to boost manifold pressure. Russian Roulette is owned by Shawn Carrol and flown by famous test pilot Dave Morss.

'Spirit of Texas' -Hawker Sea Fury
This conventional-looking aircraft, except for the Wright R-3350-26WD engine, has a few modifications worth looking at. Owned and flown by Stewart Dawson, it is another immaculate restoration to come out of Nelson Ezells shop in Texas. At race speeds, the engine is run at 57in and 2,900rpm.
It retains the single oil cooler. However, the oil cooler installed in this Sea Fury uses a fin-and-tube radiator matrix instead of the honeycomb matrix installed on the original aircraft Honeycomb radiators and oil coolers were very common in the early day of cars; and aircraft continued to use honeycomb oil radiators right up to the end. The honeycomb radiator is simply a bundle of tubes sweated together. Oil flows around the outside diameter of the tubes and cooling air flows through the centre of the tubes. The big advantage with this type of cooler is the fact it can withstand extreme pressures, unlike fin and tube radiators. Although installed on the scavenge side of the oil system, one would think that the oil cooler would not be exposed to high-pressure. Under most circumstances, that would be a correct assumption, however, under cold conditions, oil can congeal to the consistency of gel. This can generate undesirably high-pressures which, on occasion, can burst a cooler. Nevertheless, Spirit of Texas has opted to use a fin and tube radiator with its enhanced cooling capability.

'September Fury* - Modified Hawker Sea Fury
This is another balls-to-the-wall racer. Powered by a Wright R-3350 PRT engine, it has tremendous potential. Unlike Critical Mass, the other Sea Fury powered by a PRT engine, September Fury simply installed a PRT engine and removed the PRTs. Whilst this will work for producing a prodigious amount of powet, there is a size and weigh penalty by not incorporating an adapter plate between the power section and the blower section. This engine also retains the direct fuel injection used on most PRT engins. Two massive 9-cylinder fuel injection pumps are mounted on the "master control" unit, a mass air flow device that replaces the carburettor. Fuel is injected right into the combustion chamber. Pete Law designed the ADI system, as well as the unique oil cooling system on this aircraft. Rather than use a conventional air-to-oil system, Pete designed a so-called 'boiler system'. Using a massive Douglas DC-7 oil cooler with 7,000 tubes, it is mounted in the fuselage, under the
pilot. The cooler is immersed in ADI fluid. As the temperature of the oil increases, heat is rejected through the ADI fluid and as the fluid boils, steam and gasses are dumped overboard. ADI fluid is used because of its low boiling point of 170 degrees F.
Although the writer did not get definitive power settings, it is safe to say that under race conditions, the engine is operating in excess of 60in manifold pressure and over 3,000rpm. Clearly, this aircraft is another top contender in the Gold battle. September Fury is owned and flown by Michael Brown.

A question that often arises is; why don't the top racers use nitrous oxide. As Bill Kerchenfaut jokingly put it II are already good at blowing up engines, why would we want get better at it..!!?" With
the stresses already imposed upon these engines, it simply would not be practical to use nitrous - but it has been tried. Nevertheless, when running at 140in manifold pressure, even injecting all the ADI the engine can stand, will not quell detonation. The next recourse is to use a high-performance number fuel. The top racers are burning 160PN fuel. Even more exotic fuels, such as Triptane, would work even better, but this much desired fuel is no longer available.
One has to admire the professionalism demonstrated by the owners and crews that work on these ultimate "hot-rods'. Running an aircraft on the ragged edge of destruction, as many do, is what Unlimited racing is all about.

[McGuire]

There were/are only a handful of people in the world with expertise on hot-rodding the Merlin... Dwight Thorn, Jack Hovey, the late Dave Zeuschel and a few others. It's a small club and they all know each other from hydoplanes and air racing. Hovey used to work for Thorn I think.

Couple of interesting things about the Merlin... in air racing circles it is known as the "mouse motor" because it is actually smaller than most of the engines (big radials) it races against. An interesting perspective: 1650 CID as "small." Also, it seems the Merlin has never taken well to turbocharging. Apparently when that big supercharger is removed from the engine a lot of vibration issues arise.

[Wuzak]

Thankyou for that Bill...a great read.

About turbocharging the Merlin, Rolls Royce were reluctant to use turbocharging because they would lose exhaust thrust . This was significant - eg the original Mosquitos had an exhaust manifold system where all the exhaust from one bank was directed through one outlet. Later this was changed to individual stacks (except on the inside of the neacelles where the rear two were joined) with a resulting increase of top speed of around 15mph!

One version of the experimental Crecy had the exhaust going through a turbine which helped to drive the engine mounted compressor. If they did this it could potentially release 1000hp! Question is, would the weight be worth it?

Pity that there doesn't seem to be any Napier Sabres about. In late war stock form they were already delivering 3500hp from 2239cid!

[Bill Sherwood]

Originally posted by Wuzak
One version of the experimental Crecy had the exhaust going through a turbine which helped to drive the engine mounted compressor. If they did this it could potentially release 1000hp! Question is, would the weight be worth it?

That's similar to the Wright turbo-compound engines - They had three turbines in the exhaust, and they were fluid coupled to the crankshaft to extract energy from the exhaust gasses and help power the engine. It had a large but otherwise conventional supercharger on the front though.

[Wuzak]

I know Allison had a turbo compound engine under development late in the war for the V-1710. It was capable of just under 3000hp, apparently.

[Powersteer]

Holy cow Bill, that has to be a record. Copy and paste record nice.

[Bill Sherwood]

I can't remember where I scavenged it from, but it's a ripper read so I kept it.
It's excellent for occasions such as this.

[ray b]

Originally posted by desmo
I'd expect the hydroplane guys should have been able to push the boost/tuning envelope further than the airplane guys by simple dint of the consequences of an engine failure being comparatively trivial for them.

hydroplane guys have all moved on to chopper turbines AKA jets in the unlimited class
years ago but the neat sounds are lost no more thunder boats just jet whine
more power and far far less rebuilding with rare long out of production parts
the days of cheap surpluss stacks of motors are long over

saddly we lost out local unlimited class hydroplane race when hurricane ANDREW trashed the stands on Virgina Key
and the local city commission would not repair them

[ray b]

BTW I wonder if 150 octane was real or just a rating gimmic of the time
have we really lost the high test or is that rom/ron/??? = to modern race gas

[McGuire]

Yep, when the boats went to turbines it freed up a hoard of parts for air racing, but that stuff is now pretty much used up. Rutan's Pond Racer (powered by Nissan GTP engines) was going to fix all the supply problems but the plane was a flop.

[Rosemayer]

Here is one with a great record of wins.


www.rarebear.com/page1.html

[sblick]

Come to Jack Roush's museum in Livonia, MI and see an engine on display and a couple of propellers. He also has an interesting "dyno" in back to do break-in of the motors. He has an old early 70's flat bed truck that he puts chocks in front of the wheels, locks the brakes, and fires up the engine. It is a very effective parking lot sweeper. The techs will run it to full power. The one demonstrtion I saw was amazing. Good size trees 150 yards away were being bent over from prop wash. The rumor is he owns all the rigths to produce the parts for P-51 engines.

[desmo]

Originally posted by sblick
The rumor is he owns all the rigths to produce the parts for P-51 engines.

At this point in time, surely any exclusive rights, patents etc. associated with those parts has long since passed into the public domain?

[McGuire]

I believe Roush is the only fully certified FAA repair facility for Merlins and Mustangs.

[desmo]

Of course. I'd forgot about FAA certification.

[sblick]

That makes sense. On both accounts.

[Powersteer]

Rolls-Royce Meteor ?

[Wuzak]

The Meteor was an unsupercharged version of the Merlin used in tanks nd PT boats.....

[LS 1]

Originally posted by desmo
I'd expect the hydroplane guys should have been able to push the boost/tuning envelope further than the airplane guys by simple dint of the consequences of an engine failure being comparatively trivial for them.

I seem to remember a time in the late 80's when the all-dominant Miss Budweiser was running a "Rolls Royce Griffin" engine, which I was under the impression was an upgraded Merlin. The pecking order at the time was "Bud(Griffin)--a few others (Merlin)--and the back markers (Allison)." Anyway, the Griffin supposedly produced about 3500 hp, was ridiculously rare and absurdly expensive, and the Bud crew apparently had every single one in existence. Which led to endless complaints by the others and was one more reason why everyone moved to turbines.

[crono33]

i guess you mean Griffon

http://en.wikipedia....s-Royce_Griffon

Originally posted by LS 1


I seem to remember a time in the late 80's when the all-dominant Miss Budweiser was running a "Rolls Royce Griffin" engine, which I was under the impression was an upgraded Merlin. The pecking order at the time was "Bud(Griffin)--a few others (Merlin)--and the back markers (Allison)." Anyway, the Griffin supposedly produced about 3500 hp, was ridiculously rare and absurdly expensive, and the Bud crew apparently had every single one in existence. Which led to endless complaints by the others and was one more reason why everyone moved to turbines.

[LS 1]

Yep, well that's what 20 years and an aging memory will do to you. Looks like I also was wrong on the two being related. Looking at the stats in that article, there must have been extensive racing development of the Griffon to take advantage of its larger displacement.

[desmo]

Yeah I remember when the Miss Bud with the Griffon was the team to beat. The Griffon sounded a little throatier than the Merlins and the turbocharged Allisons of course lacked in the exhaust note department. I used to go to the races but honestly was more into the bikinied babes and beer than the boats

[Rosemayer]

yarchive.net/car/octane.html

[Canuck]

Originally posted by desmo
Yeah I remember when the Miss Bud with the Griffon was the team to beat. The Griffon sounded a little throatier than the Merlins and the turbocharged Allisons of course lacked in the exhaust note department. I used to go to the races but honestly was more into the bikinied babes and beer than the boats

There were boats there?