Large Radial Engines Were About As Good As Can Be?

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A bit off-topic, but there is an interesting, modern twist to radials. A civil company, Zoche Aero Diesels from Germany, has developed diesel radials with an even number of cylinders. At present, their offerings ranges from 70 to 150 to 300 HP.

The thing that is interesting to me is the 8-cylinder, 300 HP Zoche Aero Diesel is 271 pounds or 123 kg for 220 kW power. That seem impressive to me considering the weight includes the starter/generator, the hydraulic [prop governor, the turbo and supercharger, and oil & fuel filters.

Not WWII, but impressive for the weight and an even-cylinder radial with advertised perfect rotational balance.
 

Not aviation related, but Nordberg's specialty was its two-stroke, radial diesels with vertical crankshafts. They were sold in 11 and 12 cylinder versions. They also didn't use the same sort of master rod system as do all aircraft radials except Salmsons.

Zoche's engines are very interesting (they ostensibly make a V-2 and 4-cylinder radials as well as the 2-row 8 cylinder model) and are, at least on paper, a good engine to build a light airplane around. Their engines have also been in development for about 20 years with no deliveries in sight.
 
Immediately after WWII came the turbo-compound radials, the most successful of which was the Wright R-3350 Duplex Cyclone. These engines used waste heat to turn a turbine to add power to the engine (as opposed to compressing the intake air in a traditional turbo-charged engine.) Turbo-compound engines were more fuel-efficient than regular radials, but at a significant cost in added complexity and maintenance issues. Turbo-compound engines had only the slightest headstart on turboprops, and it didn't take long for turboprops to put turbocompound engines into the wastebin of technology.
 

Are they 2 stroke Diesels? That would make sense for the even number of banks.
 


Any idea if these engines are more fuel efficient that a modern turboprop?
 
kitplane01 said:
Any idea if these engines are more fuel efficient that a modern turboprop?
Click to expand...

They were, by quite a lot. The sfc of the turbo-compound R3350 was around 0.35, vs about 0.45 for the best of the turboprops. Of course, the cost of operation of the turboprop is a lot lower.
 
swampyankee said:
They were, by quite a lot. The sfc of the turbo-compound R3350 was around 0.35, vs about 0.45 for the best of the turboprops. Of course, the cost of operation of the turboprop is a lot lower.
Click to expand...

With turbo props its often customary to quote the fuel consumption in lbs of fuel per ehp, with ehp being "equivalent horse power" which is the thrust at some specific speed converted to horsepower using the P=F.v relationship. I think the speed used is often 550 feet per second as 550 foot pounds is a horsepower and its also about realistic 360mph but beware it can be quoted with any speed.

I think the Rolls Royce Tyne had a sfc of about 0.48lbs/hp/hr but when at cruise and taking into account jet thrust as ehp its about 0.39/ehp/hr. (Im not sure google and bing are crap and I cant find the data anymore, its probably in janes). Of course the turbo compounded engines would also have significant jet thrust but just not as much.

The TP400 used on the A400M has (from Wikipedia)
  • Specific fuel consumption: In cruise: 10.7 g/kN/s (0.38 lb/lbf/h)
  • Power specific fuel consumption: At takeoff: 0.228 kg/kW/h (0.170 kg/hp/h; 0.37 lb/hp/h)+ (2003 estimate); In cruise: 0.21 kg/kW/h (0.16 kg/hp/h; 0.35 lb/hp/h)
  • Power-to-weight ratio: 4.41 kW/kg (5.9 hp/kg; 2.68 hp/lb)

I don't know if this is sloppy data but that is quoted as hp not ehp or shp. Its an interesting engine, I think a A320neo/B737-8 sized aircraft with this engine would be about 20% more efficient.
 
wuzak said:
Are they 2 stroke Diesels? That would make sense for the even number of banks.
Click to expand...

Two Stroke Diesels were of course used by the Germans from about 1933 mainly on flying boats but also the Ju 86: the supercharged Junkers Jumo 205 and the turbo-supercharged variant of it the Jumo 207 (which retained the mechanical supercharger). They had extremely good fuel economy, as good as the post war Napier Nomad, which was also a two stroke diesel using sleeve valves though the Nomad was lighter. The Jumo's had two crankshafts and punched inwards. A 10:1 stroke can produce 20:1 compression.

The interesting thing about this is that the American Company Archates power has begun to develop these engines for Truck use. Brake thermal efficiencies of 55% seem possible.
This is a video of Archates power founder, Dr James Lemke, talking about how the Jumo 205 in part inspired his endeavour. What's interesting is that he mentions why the modern engines are more efficient. Lemke specifically refers to CFD "Computational Fluid Dynamics"

Lemke

Engineering Explained has nice animations:


Modern engine designers have the following advantages
1 3D CAD systems
2 The 3D CAD can input directly into simulations using CFD Computaion Fluid Dynamics to model inlet and exhaust airflow and combustion as well as thermal load as well as bearing lubrication.
3 The above also allow Finite Element Analysis allows the vibration and stress to be analysed.
The above really speeds development.
In addition modern alloys are much better allowing smaller engines.

Spark Ignition Engines seem to have a upper bound is cylinder displacement, not quite sure why, something to do with flamefront propagation whereas Diesels are independent of this and I think this would have kept cylinder count down.

Sandia National Laboratories has developed a very simple modification to injector nozzles that completely eliminates particulates, by a Bunsen like shroud which now allows an uncompromising focus on NOX:
Sandia National Laboratories: Diesel engine revolution

If it had not have been for the Jet engines I think we would be winging our way around the world on turbo compounded diesels.

Interestingly the Fischer-Tropsch fuels the Germans (and Japanese) used in their diesels eliminated most particulates anyway on both jets and diesels (86% in a CFM56 and 10% NOX). Then there is the synthetic fuel OME which produces essentially zero pollution in a diesel.
 
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BiffF15 said:
Because I couldn't afford a 1966 Shelby Cobra 427SC...
Click to expand...
I'd take any of those three cars in a heartbeat. What a beautiful SS396 Chevelle. That 396 is great engine. Engine technology improvements have been amazing. A 1966 2500 lb 427 Cobra would go from 0-60 in 4.5 seconds. Incredible for the time. But, it is same time my 201 cubic inch dual turbo, fuel injected 3800 lb G70 four door sedan will go to 60.
 
I wonder if, as an analogy, we could ask the same question of the air-cooled in-line engines of the period.
Compare them to the air-cooled engines offered today.
 
The biggest changes that improve modern engine power are due to electronics. First through improved efficiencies and exacting tolerances when the parts are designed and produced. Second, with the addition of the engine management systems that totally control all aspects of the combustion process.

While a Chevy LS more or less looks something like the old small-block Chevy it makes far more horsepower far more reliably. The LS was designed using about a cabillion hours of computer time dedicated to figuring out combustion, airflow, harmonics, metallurgy, and every other thing known to engineering.

Then they straped a very sophisticated computer to it to monitor and control every aspect of the power making process. After all that you have a huge difference in performance, reliability, and longevity.

If you were able to apply the same engineering process to a clean sheet 28 cylinder radial, I expect you would have a very similar outcome, and that result would be a far superior product than the wonderful but ancient P&W R2800 or Wright R3350.
 

When are they going to fly? How much will they cost? 271 lb all up for 300 hp is close to incredible. Angle valve TIO-360 Lyc is closer to 375-400, with accessories & turbo, and gives only 200-210 hp. Zoche website gives zero info about how close to flight testing they are, let alone certification. You know anything they're not saying? If they're as good as they say they are Cont & Lyc ought to be ought of business within a year or two.
 
Good topic!

I'd say the biggest change would be in the electronics available today.

If had the money, I'd love to do a diesel conversion to a P&W R2800

Not really a good option for aero usage back in the day. Purely mechanical diesels were limited to about 1/3rd hp per CU. You could add boost and fuel, but at the expense of longevity, and very heavy rotating mass.


Not so with modern common rail injection. Electronics allow for staged injection events eliminating the slamming effect on pistons, rods, cranks. Makes for a much smoother, quieter, lighter engine. But also, allows outputs near 1hp per CU. Compression ignition also eliminates: Mixture issues, detonation issues, eliminates ignition system and simplifies boost control, not to mention 20% better bsfc.

We do have some non-aviation examples that prove this out.

The AVDS 1790 tank engine:
  • This engine started out as an 850hp 1790cid gasoline air cooled V12 engine.
  • It was converted to a turbocharged diesel with mechanical injection and controls: 780hp with half the bsfc of the gas version and twice the TBO.
  • Since the 90's this engine has been upgraded with modern electronics and is now pushing 1500hp and has better bsfc than it's mechanical predecessor. Not quite, 1hp per cubic inch, but the duty cycle in a tank is even more extreme than an aircraft.
Another is the Ukrainian 6TD tank engine. (This is the evolution of the Junkers 205)
  • Opposed piston, 2 stroke diesel, 995cid, liquid cooled opposed 6 cyl engine.
  • This 6 cyl engine was derived from an earlier 5 cyl in the 80's. Started out and a mechanically injected engine of 1000hp and has since been pushed to 1800hp in the -4 version, using electronic engine management.

Point is: Modern diesels can give excellent hp ratios and the tech could be applied to WWII type piston engines, but you'll never get the TBO of a turbo-prop out of one.
 
m37b1 said:
Not really a good option for aero usage back in the day. Purely mechanical diesels were limited to about 1/3rd hp per CU. You could add boost and fuel, but at the expense of longevity, and very heavy rotating mass.
Click to expand...

not a real good idea today.

" Weight: lbs. dry (with accessories)........5,100"

from: AVDS-1790 1050HP Engine

This includes cooling fans and a 650 Ampere alternator but DOES NOT include transmission.

or see: Continental AV1790 - Wikipedia

around 5000lbs for even a 1500hp engine is simply pathetic for an aircraft engine. Even if you could get it down to 4000lbs it is still pathetic.

the Ukrainian 6TD tank engine.
6TD | www.malyshevplant.com
weight is about 1200kg give or take depending on the model. Liquid cooling system not included.

In aircraft nobody really cares what the cubic inches/displacement of the engine is, it is somewhat useful for comparing engines of a given time/technology but the aircraft designers of the day did not pick engines based on their displacement or power per cu in. They picked them on the power, weight, and compactness of the installation.
 
Okay - I think we can all agree with Shortround6, that you can't pull engines out of tanks and bolt them on aircraft wings.

So . . . Back to the point -

We've established the reliable HP per cubic inch capacity of modern diesels is in the area of 1 hp/cu.

So, can that tech be applied to radial aircraft engines that reached their zenith of design in the 50's.

While I stated, I'd like to try dieselization of an R2800, (Due to one sitting in one of my shops). A better path would be the Wright R-1820. Why? Because its already been done in the form of the RD-1820. This was done by Caterpillar during WWII as a alternative engine for the Sherman tank (M4A6).

They were rated at:
450HP @ 2000 RPMs
1470 lb-ft Torque @ 1200 RPMs

Pretty bad, at 1/4th hp per cu.

Now - I don't know this as fact, but I don't think Cat changed the basic engine structure during this modification. The combustion chamber and valve angles look the same as the gasser heads. Crank and rods look the same as well. So it may have been a piston change to achieve 15:1 compression ratio. Not sure, as I've never seen one of these engines, only have the manual for reference.

So the question is - Can we take modern diesel tech and apply it to an aircraft radial engine to achieve the desired hp to weight ratio?
 
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