Rolls-Royce Crecy engine which was to be installed in Spitfire

[Nicknick]

Taking advantage of the stratified fuel charge in the engine.

The sprint part was running the engine with lots of fuel to make lots of power (at high power settings, the fuel helps cool the cylinders), call it 8:1 air:fuel ratio.

But remember that stratified charge setup? That lets you run the engine with very little fuel per stroke. Call it 18:1 air:fuel ratio or even leaner, since they talked about running the engine at an overall mixture ratio that wouldn't ignite at all. At any rate, using less than half the fuel per stroke, and maybe as little as 1/3 the fuel.



The stratified charge system did need sleeve valves to work at the time. Poppet valves would have taken the space needed for the combustion bowl at the time.

That said, modern F1 engines use a similar stratified charge pre-combustion chamber and have poppet valves in the head so it could be made to work with what we know now.




Honestly, had the engines been reliable enough to install in planes in 1940, it might have been a very different war. Hearing the Crecy engines roaring as the Spits and Hurricanes take off to intercept the Blitz...

But when it wasn't ready till 1944, the jets just took over.

-the Crecy was a uniflow design.

-the Formula one has prechambers, but they work differently. The injection has to be outside of the prechmber and just one spray hole is targetet to spray fuel in the chamber from outside to inside. In the Crecy it is the other way.

The pre chamber volume of the Crecy is hughe whereas tthe Formular 1 prechambers are tiny. They also have multible small holes to produce turbulence. The Crecy is differen with just one big opening to the cylinder. The use of different spray pattern for part load and wot is quite unique (Pinteaux nozzels have something like that too). The crecy could run at idle without throtteling, do the Lambda was propably around 6-8 (AFR about 100:1)

 

[Foo Fighter]

Can they make new Merlin/Griffon motors these day? Possibly 3D printing etc?

You could still put them in a new/bespoke airframe and save those warbirds that remain.

 

[TomcatViP]

Honestly, fans are focusing on the alleged performance forgetting that there was other thousands HP engines allegedly ready for production that, similarly, never were. When you see the money spent on those Ricardo design and how few much of it managed to produce anything valuable enough to be put in the hands of the British Fighter and Bomber Command pilots, this only should give a hint of the viability of the overall design. Last but not least, suffice to say that probably the best mass produced sleeved engine went through a torturous development (Taurus to Centaurus to make it short) in a much more simpler architecture (radial 4 stroke) with the benefits of thousand airframe flying to gain experience (Wellington, Beaufighter, Tempest to name only the most famous).

Just like German engine development can not be rationally seen through the lack of available material, British Sleeved engine achievement should only be seen through the scrutiny of non-pedantic engineering.
Just like you can´t see through WWII French fighter design without the lens of reliability and military usage.

Engineering is full of people advocating intricated complexity and the abuse* of technical linguicism, only akin to a venue of psychologist or Michelin stared Chefs. Layman (and public officials) should keep themselves away from such.

*I vividly remember a recent (paid) conference on Battery stochastic analysis where AI and other neologisms were abusively used when all the equations for solving the problem at hand this particular day were solved, discretized and tested 20 years ago.

 

[Scott Kenny]

OK, what would a 'reasonably' powerful engine and airframe combination look like? Is it not possible to come up with a sensible combination that would be entertaining while remaining affordable (Reasonably)?

It must be possible, they have done it before.

Assume for racing at Reno/Roswell?

Initial assumptions:

1. The airframe needs to weigh a minimum of 4500lbs, so we can do large displacement engines.
2. Any such engine will be dry sump due to g-forces.
3. electronic fuel injection is available, but would require using at least two completely separate computers, injectors, etc for safety.

I would start with the mega-displacement drag racing engine blocks. I've seen an 872ci V8 out there, running in a Naturally-Aspirated class. Then bump it to a 90deg V12, ~1300ci. You're basically buying a billet block anyway, might as well make it a V12. Make sure it'll happily spin at ~6000rpm for long periods of time (tens of minutes). Gear it down 3:1 so your prop spins at 2000rpm or so. Turbocharge to ~30psi boost. Don't blow the engine up.

The P-51 is a good shape generally, but the Papa Five One "Thunder Mustang" is too light to compete in the Unlimiteds. Gross weight is only 3200lbs with a Falconer V12, and rules require 4500. The new engine may well be heavier, but you can't add ~1300lbs without screwing things up.

I wish we had more data on the Bugatti Model 100 air racer. Twin engines amidships, driving counter-rotating props at the nose. A replica got built but fatally crashed before we saw any good performance data. The Model 100 used a pair of 4.5L Bugatti straight-8s, back in the 1990s I'd thought about using a pair of the Ford Modular v8s, 4.6L DOHC. These days I'd use a Coyote 5.0L DOHC instead.

Something like an Fw190D could be an option (vee engine under the cowling).


==============
I still want to fly the Pond Racer airframe.

• Airframe seemed adequate, it was let down by the need for engines that would fit within the 24" diameter circle of the nacelles. What was available at the time was those Nissan VG30s, which suffered from overheating in the very tight cowling. Wankel rotaries are 16" wide and ~20" tall, so they'd have more air space under the cowling.
• The other major issue in the Pond Racer was running on methanol, not Avgas or ethanol. You want to use ethanol because even at 35psi boost the fuel evaporating in the intake ports will suck enough heat out of the air to make the outside of the intake sweat like a glass of ice water! Methanol would also cause that much cooling, but burns with an invisible flame. I'd like to see the fire before it burns my wings off, thanks.
• Run a long-tube exhaust header back to the monster turbo installed aft of the engine, ceramic-line the inside of it to preserve as much heat as possible for the turbo. Add a major heatshield between exhaust manifold and intake manifold.
• Expect to need about 35psi of boost, size the turbo to make that much boost at 10,000ft.
• Intake can be a simple Log and runners, but you will want relatively long runners to tune for ~7700rpm. So you might be placing that log at ~1 oclock on the engine, looking forward to the prop. Packaging may require a flattened oval versus a simple round tube.
• 3.5:1 prop speed reduction.

 

[Scott Kenny]

You need to keep the frontal area small, so 90 deg bank angle is not ideal.

No, it's not. but it's convenient from an adapting-an-existing-design perspective.

Long intake runners are not usefull for turbocharged engines, the turbo can fill the cylinders more efficient.

You should still have runners long enough to allow the E85 to evaporate completely downstream of the injector.

Long exhaust runners are difficult for packaging and heating up the surrounding.

That is specifically to keep the exhaust runners within that 24" circle of the Pond Race cowlings. Might go to a 26" circle if the prop hub is large enough to argue for it.

I would prefer 4 small turbos on a V12, they could provide enough boost at the given altitude.

You might be able to get away with a hot V layout, turbos inside the V and intake ports on the bottom of the V.

Same setup as the Ferrari 296 engine.

The Bugatti layout is way to complex

Probably, but it does have minimal frontal area.

 

[Scott Kenny]

I know the guy who designed the 296 engine and I know that a high power V-6 with a 120 deg bank angle is quite tricky because of the main bearing loads. A 60 deg design would be lighter, less design effort and have a smaller frontal area.

Oh, yeah, I'd just meant exhaust ports and turbo(s) on the inside of the V, not the 120deg bank angle. A large-enough engine would have plenty of space between the banks for one turbo per 3 cylinders.

I have no expieriences with ethanol, but I guess with high boost pressures and small CAC it could work with direct injection.

In this case you specifically do NOT want direct injection, because you're using the evaporation of the fuel to cool the intake charge and it takes time/distance for the fuel to evaporate.

 

[Scott Kenny]

Can they make new Merlin/Griffon motors these day? Possibly 3D printing etc?

You could still put them in a new/bespoke airframe and save those warbirds that remain.

You could definitely 3d print the cores and then cast the parts as normal (Jay Leno bought an early 3d printer to do that for his classic cars). That's probably the best way to deal with old blocks. You'd still need to machine the steel parts as normal, I don't think you can get enough strength out of laser-sintered metal parts.

 

[Scott Kenny]

A hot-V could work with90 deg (has been done by BMW, Ford, Cadillac) but than the engine height will be increased. The exhaust piping is still quite long compared to outside turbos, because you dont want to expell the exhaus gases right on the canopy.

Yes, you'd need to roll the turbo exhaust over the tops of the cylinder heads.

And routing the intake pipes would be interesting with 4 turbos in the V.

In a Di engine, the evaporation heat adsorbed during intake and compression, thus making them more knock resistant. It could be, that wall wetting will be a problem with Ethanol/Methanol.

Not sure about the wetting, though that's definitely an issue with alcohol fuels in general.

I know I'd rather deal with port injectors than direct. Much lower working pressures, you can get away with ~100psi instead of 3500psi. Which means all the other parts are able to be lighter. And you have more time for the alcohol to evaporate when it's injected into the intake manifold instead of into the cylinder (or rotor, in my case).

 

[Scott Kenny]

Yeh... A new sport class racer or some such ?

Regards,
357Mag

Has my vote

 

[Scott Kenny]

The obvious solution would be an inverted V with the turbos in the valley (hot-V) and the exhaust pipe running below the fuselage for an exhaust behind the cockpit.
That way you could also turbo-compound to the prop shaft via a turbo-generator and an e-motor that will also act as a starter-motor (don´t know if that has been ever attempted but the rotating mass of the prop might ease the starting process).

I think you're better off with a mechanical turbo-compound rather than an electrical one. Fewer losses going through a gearbox. Electical transmission is ~80% efficient (~90% generator, times 90% motor).

A mechanical turbo-compound should be able to recover around 20% of the engine's rated power. Kicking an 850hp engine up to 1000hp.

Regarding the question with supersonic props, Reno are open air races meant to attract the public. It depends of the venue to generate a profit. If 80% of them become deaf the first year*, you might have some difficulties further on.

*but, hey, what a blast, as they say

Even with people doubled up on ear protection (plugs and muffs), I suspect that the shockwaves off the prop would be nausea-inducing based on reports from the XF-84H.

 

[Scott Kenny]

What would be the intended ultimate application for this imagined propeller-driven aircraft, whose engine is a turbo-prop, or turbo compound, or electric or electric/ hybrid; etc ?
In other words... if the postulated aircraft has an engine in it other than a " reciprocating" one ?

With regards,
357Mag

Unlimited air racing, where the aircraft must be piston engine and propeller driven. (very short list of rules that the unlimiteds run under)

 

[Scott Kenny]

Scott -

Yeh…. That’s what I thought was being intimated.

Barring some major change(s) in the purse or race organization, it is doubtful the
“ big iron “ will be back. Before things went South, there had been restrictions put in-place to suppress any wide scale participation of new-wave airframe designs.
If memory serves… they had made a point to keep allowed airframe & power plant restrictions open enough to not disclude the FM….and R-2800 powered Yak, but something like a suped-up Glasair would be out.

Well, the other major rule is an empty weight in excess of 4500lbs, which does keep out things like an LS-powered Glasair.

But that does allow twin engine planes, like the Pond Racer or Dornier Do335 Arrow. Or probably the Bugatti Model 100. You need a very creative engineer to come up with a low frontal area design for any twins, or you put both engines on centerline.

 

[Scott Kenny]

I think the Bugatti 100 would be excluded under the current wt limit, as it weighs 3,086lb empty.

Even w/ a notional 200lb pilot, I doubt the plane would hold 1,200lb of fuel.

Yes, the existing Bugatti 100 would be too light by far. Scale it up 10-15% in all dimensions. And, frankly, I'd want bigger engines inside anyways, like a pair of turbo LSs. Saves you from having to spin them as fast to make power.

Change the rules, night whar ?

I think that'd take a lot of convincing of the warbird owners. They're using up engines and airframes, of course, but metal planes can pretty much be rebuilt from raw aluminum sheets as long as you have the original data plate to rivet on. (not much original left of a lot of flying "restorations")

The 4500lb limit is to make it so that you don't have the equivalent of a Glasair or one of the Formula planes with a 1000+hp twin-turbo LS engine that only weights 2000lbs empty competing with a 7500lb Mustang.

Which is why I'd want to mess with the Pond Racer design. It's 3500lbs empty, so would need to be enlarged anyways, but I have a wicked idea involving loading dry ice onboard to chill the fuel before the intercooler and then dumping it into the engine. Ethanol cooled by dry ice will be just above its freezing point, -125degF.

 

[Jemiba]

Those 40+ last posts not about RR engines, not to mention the Crecy, were moved to a new thread here
https://www.secretprojects.co.uk/threads/modern-racing-engines.44100/

 

[Scott Kenny]

Those 40+ last posts not about RR engines, not to mention the Crecy, were moved to a new thread here
https://www.secretprojects.co.uk/threads/modern-racing-engines.44100/

Need to move most of mine over there as well, please.

 

[Jemiba]

Sorry, moved back !

 

[TomcatViP]

Sorry, moved back !

Thanks! (also deleted my post with the request)