What if the WANKEL engine had been invented in WW II?

[Burmese Bandit]

The Wankel rotary engine was the answer to the fighter designer's dream in the 30s and 40s ... a simple, reliable engine, highly economical to produce, with tiny frontal area and excellent power to weight ratio, limited only in its high fuel consumption.

What if the Wankel had been ready in 1940 or even 41? Your thoughts, gentlemen.

 

[Parmigiano]

I don't think it was the answer:the issues are fuel and oil consumption, plus need of maintenance probably comparable with early jets.

The wankel is not more reliable than a Otto engine, it has less parts but the rotor is much more delicate than a cylinder block

The added weight of fuel to achieve the same range would have jeopardized the advantage in engine weight.

Look at the Mazda mx-7: even with today metallurgy know-how and materials the wankel uses more oil and fuel than a comparable Otto engine.

 

[wilbur1]

The other probb with a rotary is torque, they wont build the necessary torque to pull aprop through till 4000 rpm then your only 3000 rpm from the end of the power curve

 

[Burmese Bandit]

Parmigiano, I really, really think you need to check the maintenance data. The data I have (admittedly imperfect, but unless someone else shows me better, I think I am right) shows the Wankel to have much more reliability than piston engines - in fact, the Wankel aircraft engine community contemptuously calls piston engines "repricorsaurs".

The only two legitimate issues I see with the Wankel are fuel consumption and torque.

Fuel consumption is bad, but still far, far better than even today's jet engines, not to mention the jets of the 40s!

And if you look at the Mazda website, you will see that the decrease in today's generation of Wankel engines are not due to metallurgy, but more due to port design - which is a design feature that could plausibly be held to have existed sixty years ago.

 

[Burmese Bandit]

From the Wiki "Wankel" -

"...A further advantage of the Wankel engine for use in aircraft is the fact that a Wankel engine can have a smaller frontal area than a piston engine of equivalent power. The simplicity of design and smaller size of the Wankel engine also allows for savings in construction costs, compared to piston engines of comparable power output.

Of perhaps the most importance is that Wankel engines are almost immune to catastrophic failure. A Wankel that loses compression, cooling or oil pressure will lose a large amount of power, and will die over a short period of time; however, it will usually continue to produce some power during that time. Piston engines under the same circumstances are prone to seizing or breaking parts that almost certainly results in complete internal destruction of the engine and instant loss of power. For this reason Wankel engines are very well suited to aircraft. However, a Wankel is extremely susceptible to damage from pre-ignition, also known as detonation or "knocking"..."

Furthermore...

"...Wankel engines have several major advantages over reciprocating piston designs, in addition to having higher output for similar displacement and physical size.

Wankel engines are considerably simpler and contain far fewer moving parts. For instance, because valving is accomplished by simple ports cut into the walls of the rotor housing, they have no valves or complex valve trains; in addition, since the rotor is geared directly to the output shaft, there is no need for connecting rods, a conventional crankshaft, crankshaft balance weights, etc. The elimination of these parts not only makes a Wankel engine much lighter (typically half that of a conventional engine of equivalent power), but it also completely eliminates the reciprocating mass of a piston engine with its internal strain and inherent vibration due to repeated acceleration and deceleration, producing not only a smoother flow of power but also the ability to produce more power by running at higher rpm.

Because of the quasi-overlap of the power strokes that cause the smoothness of the engine, and the avoidance of the 4-stroke cycle in a reciprocating engine, the wankel engine is very quick to react to throttle changes and is able to deliver a near-instantaneous surge of power when the demand arises, especially at higher rpms counts. This is more true when compared to 4 cylinder reciprocating engines and less true when compared to higher cylinder counts..."

 

[Burmese Bandit]

Thus we have a lighter engine, which has a higher fuel consumption penalty. In the case of interceptors which are designed to be short range aircraft anyway, one cancels out the other, and indeed as the aircraft burns off fuel with time it becomes far lighter and therefore much more maneuverable.

It seems to me that it is only for longer range planes that the higher fuel consumption of the Wankel becomes a negative factor.

And let's not forget this part, Wilbur...

"...the wankel engine is very quick to react to throttle changes and is able to deliver a near-instantaneous surge of power when the demand arises, especially at higher rpms counts.

 

[ccheese]

You guys can rant and rave all you want about the Wankel rotory engine. To
the best of my knowledge, Mazda is the only auto maker that uses the rotory
engine in their cars, at present the Mazda RX-8. I work for Mazda, and right
now we are replacing '04 and '05 RX-8 engines at about three a week.
Mazda has extended the engine warranty on the RX-8 to 100,000 miles
or 96 months from original delivery date because of it's failure rate.

Evenrude tried a two rotor outboard. They dumped that after less than a
year because it was unreliable. An outboard motor, above all else, needs to
be reliable.

I don't know of any home built airplane that has a rotory engine in it. The
builder would have to be crasy.

Charles

 

[Burmese Bandit]

And, later in the same Wiki article, some interesting points...

"...The first Wankel rotary-engine aircraft was the experimental Lockheed Q-Star civilian version of the United States Army's reconnaissance QT-2, basically a powered Schweizer sailplane, in 1968 or 1969. It was powered by a 185 hp (138 kW) Curtiss-Wright RC2-60 Wankel rotary engine.

Aircraft Wankels have made something of a comeback in recent years. None of their advantages have been lost in comparison to other engines. They are increasingly being found in roles where their compact size and quiet operation is important, notably in drones, or UAVs. Many companies and hobbyists adapt Mazda rotary engines (taken from automobiles) to aircraft use; others, including Wankel GmbH itself, manufacture Wankel rotary engines dedicated for the purpose.One such use are the "Rotapower" engines in the Moller Skycar M400.

Wankel engines are also becoming increasingly popular in homebuilt experimental aircraft, due to a number of factors. Most are Mazda 12A and 13B automobile engines, converted to aviation use. This is a very cost-effective alternative to certified aircraft engines, providing engines ranging from 100 to 300 horsepower at a fraction of the cost of traditional engines. These conversions first took place in the early 1970s. With a number of these engines mounted on aircraft, as of 10 December 2006 the National Transportation Safety Board has only seven reports of incidents involving aircraft with Mazda engines, and none of these is of a failure due to design or manufacturing flaws. During the same period they have issued several thousand reports of broken crankshafts and connecting rods, failed pistons and incidents caused by other components which are not found in the Wankel engines. Rotary engine enthusiasts derisively refer to piston aircraft engines as "reciprosaurs", and point out that their designs have remained essentially unchanged since the 1930s, with only minor differences in manufacturing processes and variation in engine displacement.

Peter Garrison, Contributing Editor for Flying magazine, has said that "the most promising engine for aviation use is the Mazda rotary." Mazdas have indeed worked well when converted for use in homebuilt aircraft. However, the real challenge in aviation is producing FAA-certified alternatives to the standard reciprocating engines that power most small general aviation aircraft. Mistral Engines, based in Switzerland, is busy certifying its purpose-built rotaries for factory and retro-fit installations on certified production aircraft. With the G-190 and G-230-TS rotary engines already flying in the experimental market, Mistral Engines hopes for FAA and JAA certification in 2007 or early 2008. Mistral claims to have overcome the challenges of fuel consumption inherent in the rotary, at least to the extent that the engines are demonstrating specific fuel consumption within a few points of reciprocating engines of similar displacement. While fuel burn is still marginally higher than traditional engines, it is outweighed by other beneficial factors.

Since Wankel engines operate at a relatively high rotational speed with relatively low torque, propeller aircraft must use a Propeller Speed Reduction Unit (PSRU) to keep conventional propellers within the proper speed range. There are many experimental aircraft flying with this arrangement...."

 

[Burmese Bandit]

I think the above post is in contradiction of your view, Charles. And was the United States Army crazy to use the Wankel in its Q-star? And Thailand uses Wankel aircraft as primary trainers....and I haven't heard of the Thais losing a single pilot yet.

Ah, yes, found it: The RFB Fantrainer. Used by Thailand for primary training.

ANOTHER APOLOGY: Same as below. That aircraft was initially offered to the Thais with Wankels, but they chose to use the turbo engine alternative instead.

 

[Burmese Bandit]

A quick google search found two FAA certified Wankel Aircraft now flying: The Diamond DA 20 and the ARV super 2. Am continuing to find new examples...

APOLOGY: Both Aircraft have indeed flown with Wankels, but have not been certified. My apologies to the entire forum if I have mislead them!

 

[Mstcnc]

From 1963 NSU start making cars with wankel motors and result was disaster as materials available at that time didn´t handle wear and loads.
NSU cars were joke with wankel motor, even with need of more gas and lubrication oil could be ok if sealing would be lasting more than couple thousans kilometers.
It was similar case as it was with Jumo 004 engines at time of war end when materials good enough was not available.

M

 

[Burmese Bandit]

We seem to have a disagreement here, centering on whether it was materials not available in the 1940s that were the cause of the nonreliability of the early wankels, or whether it was engine design.

Who here can give us both sides of the story, and has the hands on experience to prove it?

 

[Mstcnc]

If one compare early NSU and late Mazda designs there is no big differensies in design itself.
Most differensies are caused of manufacturing abilities available now.
I do not know if sealing in latest desingns could ever be made with technology available back then.
One thing more with the quality of materials is quality and knowledge of lubricats now.
Performance of modern lubricants give a lot of reliability to even traditional engines.

As development and design of wankel at war time I personaly do not believe it could be ever made then.
Wankel history show it was not easy task, actualy NSU went bankruptcy as all they money went to development of wankel motor.
Whole desingn base of wankel was so promising they beleved too much of it, they sold patent rights at unbeleavable price of one us dollar (!),
(patens were sold to eg. Mazda,Curtiss-Wright and MB).
Mazda is only one who is made something commercialy bearable result with wankel.

M

 

[KrazyKraut]

The main benefit of the wankel is it's quietness and relatively little vibrations. But then it needs delicate tolerances. I don't think it would've made a big impression in WW2 aircraft except maybe in some isolated cases like trainers.

 

[Clay_Allison]

The Wankel is probably ready with modern knowledge and materials to become a real player in the aircraft world. That said we still do not have all of the bugs worked out and I really can't see it doing much with 1940s materials.

 

[Parmigiano]

I think is just a matter of investments: if there is a market for modern non-jet small airplane engines the current technology can provide many alternatives.

Just take the example of a modern turbo-diesel, like the small Fiat 1,2 litre (but you could take also the 1.4 Peugeot or VW, with a warning that the latter is 3 cylinder and more prone to vibrations)

weight: 130 kg complete with all accessories for car installation (means that you can reduce it a lot for aircraft installation)

common-rail with multi-injection
4 valves per cylinder
variable blade turbo

power : released in 90 or 105 HP version
torque : 20,4 KgM @ 1.750 rpm
Noteower and torque in modern diesel are mainly managed by electronics: without the heavy pollution restrictions and for aircraft use (where the engine works 90% of time at ideal temperature and constant rpm) you can easily and safely set the mapping at 150 HP

Major maintenance scheduled at 250.000 km (time belt), oil change at 30.000 km ( as gross estimate, considering an average speed of 50kmh this translates in 5.000 and 600 hours of use)

An engine like this comes with self-built electronics that manage almost everything (injection cycles phased with temperature, adjustment for air density etc.) and is available at cheap price because is built in millions.
Plus, being turbocharged you have automatically solved the altitude problems.

It goes by itself that the fuel efficiency would be unattainable for any other engine.

So, couldn't it be a good solution for small airplanes if somebody would see the business and invest a couple of millions for 'avionization' and certification?

 

[ccheese]

I twisted a wrench [yea... hands on] on VW's and Mazda's for the better part
of 25 years. However, I never worked on an RX-8. I tore into plenty of
RX-7's tho... Two major problems. The apex seals wear much too quickly,
which causes loss of compression. I don't have to explain that, everyone
knows for an engine to run you need fuel, spark and compression. Problem
number two is the oil consumption. Mazda will tell you the rotory engine does
not "burn" oil, it consumes it. Sometimes at an alarming rate !!

So lets go back to this rotory aircraft engine. How many rotors ? Two
rotors give the RX-8 235 HP at 8,500 rpm. Not many horses compared to
a Pratt Whitney. P&W's will keep going with one or two jugs shot off.
The rotory ? Take a hit in any rotor and compression is gone.

I still maintain that a rotory aircraft engine in a military aircraft is asking for
trouble. In a private [read: sport] aircraft you're still playing with fire.

Charles

 

[Clay_Allison]

Mistral Engines of Switzerland is making wankel aircraft engines and working on FAA type certification for 200-360 hp engines.

 

[Burmese Bandit]

Here is a suggestion.

Very well. Let us say that the rotary WAS theoretically possible to design and build cheaply during WWII. Let us also accept, as Charles has said, that it was an oil and gas guzzler and the tips wore out quickly.

WHY NOT USE IT AS AN AUXILIARY ENGINE???

Let's look at the G model of the Me 109.

It had a Nitrous Oxide pack behind the pilot that could boost engine power by 20% for 5-10 minutes at a time. And said pack could work well only above 20,000 feet. And said pack, with gas, tank, and insulation, weighed 300 kg - 660 lbs.

So...why not replace said pack with a wankel?

The wankel would power the new 109 like the 335: through a propeller in the tail like the Do 335. It would easily fit in the rear fuselage. It would give at least 600 hp (wankels inherently have 150% the power to weight ratio of pistons).

And it would be used only twice in a sortie: for five minutes at take off and climb, and for 5-20 minutes in combat. Total, 25 minutes per sortie. All other times it would be switched off.

Result: a 109 with 1400 hp in normal mode and 2000 hp for emergencies. And unlike the NO2 system, it works at any altitude. It also doesn't strain the main engine. And we know that the wankel has a very fast throttle response.

What do you think?

 

[Clay_Allison]

Here is a suggestion.

Very well. Let us say that the rotary WAS theoretically possible to design and build cheaply during WWII. Let us also accept, as Charles has said, that it was an oil and gas guzzler and the tips wore out quickly.

WHY NOT USE IT AS AN AUXILIARY ENGINE???

Let's look at the G model of the Me 109.

It had a Nitrous Oxide pack behind the pilot that could boost engine power by 20% for 5-10 minutes at a time. And said pack could work well only above 20,000 feet. And said pack, with gas, tank, and insulation, weighed 300 kg - 660 lbs.

So...why not replace said pack with a wankel?

The wankel would power the new 109 like the 335: through a propeller in the tail like the Do 335. It would easily fit in the rear fuselage. It would give at least 600 hp (wankels inherently have 150% the power to weight ratio of pistons).

And it would be used only twice in a sortie: for five minutes at take off and climb, and for 5-20 minutes in combat. Total, 25 minutes per sortie. All other times it would be switched off.

Result: a 109 with 1400 hp in normal mode and 2000 hp for emergencies. And unlike the NO2 system, it works at any altitude. It also doesn't strain the main engine. And we know that the wankel has a very fast throttle response.

What do you think?

It would be like a poor man's Turbo-Compound engine. The Russians tried some late war planes with auxilliary jet engines as well. http://en.wikipedia.org/wiki/Mikoyan-Gurevich_I-250_(N)