The motor we've all been waiting for!
Posted: Mon Aug 01, 2011 10:51 am
I saw the flat-four side-valve D-motor displayed at Sywell in 2010 and was immediately fascinated by its dinky size and low weight.
http://d-motor1.vpweb.be/Product---Produit.html
Since then, I have become even more impressed: I think that it shows a brilliance of approach and real "thinking outside the box".
Today, people regard side-valves as an archaic pre-war device fit only for lawn-mowers. This is because, to produce more power, engines need to turn faster; and since the volumetric efficiency (or "breathing") of a side-valve engine is poor at high revs, designers of modern engines turned to OHV & OHC valve-gear. However, since a direct-drive aero-engine produces its power at very low revs, it has no need for overhead valves. The boffins at D-Motor are to be praised for ignoring convention and reviving the "humble" side-valve.
In addition to its obvious simplicity, cheapness, compactness and lightness, the side-valve has other benefits for an aero-engine. The combustion chamber design precludes valve-overlap; and the D-Motor makes a virtue of this necessity by providing efficient combustion at low rpm as fresh fuel cannot disappear unburnt down the exhaust. Also, while a side-valve engine becomes inefficient at high rpm, the valve gear (with its stubby tappets and lack of pushrods & rocker arms) can cope easily with high engine speeds. And whereas a dropped valve is catastrophic in an ohv engine (because the valve will almost certainly hit the piston and perhaps cause seizure), valve failure is of minor consequence in a side-valve engine, which could still chug along on its remaining cylinders back to the safety of an airfield.
The flat-four D-motor will be ideal for microlights and VLAs; but I see that D-Motor are also working (with the help of government funding) on a flat-six version.
http://d-motor1.vpweb.be/Recent-information.html
As with the modular Jabiru range, it is very easy to make a 6 out of a 4, since almost all that is needed is a longer crankshaft and crankcase.
It seems to me that the proposed flat-six D-motor may well be the engine that sweeps the board.
The Jabiru 2200 weighs 60kg and produces 85bhp; and its big brother, the 3300 weighs 81kg, and produces 120bhp, 107 continuous.
Clearly then, a flat-six need weigh only 33% more than a flat-four.
(And the Rotax 912 weighs 60kg and produces 80bhp; and its big brother, the turbo 914 weighs 78kg, and produces 115bhp, 100 continuous).
The liquid-cooled D-motor 4-cyl weighs 47kg and produces 80bhp; so (by analogy to the above figures) its big brother, the 6-cyl might weigh only 63kg and yet produce, say, 115bhp or more. In other words, a 6-cylinder D-Motor might weigh barely more than an R912 or J2200; yet would produce nearly 50% more power.
And this is with fuel injection, making carb-heat a thing of the past. If the price is right, it could be the motor we've all been waiting for!
Finally, I remain a fan of reduction gear, to enable the prop to operate slowly and efficiently. If the D-motor (and the Jabiru units too, come to that) were to have a simple 3:2 reduction gear, the prop could be full-size and could extract maximum power while turning less than 2,000 rpm. As it is, both the D-motor and the Jabiru engines must inevitably use small inefficient fast-spinning props; and even so, these engines will probably never be able to reach maximum output, which is 3,300 rpm in the Jabiru's case.
http://d-motor1.vpweb.be/Product---Produit.html
Since then, I have become even more impressed: I think that it shows a brilliance of approach and real "thinking outside the box".
Today, people regard side-valves as an archaic pre-war device fit only for lawn-mowers. This is because, to produce more power, engines need to turn faster; and since the volumetric efficiency (or "breathing") of a side-valve engine is poor at high revs, designers of modern engines turned to OHV & OHC valve-gear. However, since a direct-drive aero-engine produces its power at very low revs, it has no need for overhead valves. The boffins at D-Motor are to be praised for ignoring convention and reviving the "humble" side-valve.
In addition to its obvious simplicity, cheapness, compactness and lightness, the side-valve has other benefits for an aero-engine. The combustion chamber design precludes valve-overlap; and the D-Motor makes a virtue of this necessity by providing efficient combustion at low rpm as fresh fuel cannot disappear unburnt down the exhaust. Also, while a side-valve engine becomes inefficient at high rpm, the valve gear (with its stubby tappets and lack of pushrods & rocker arms) can cope easily with high engine speeds. And whereas a dropped valve is catastrophic in an ohv engine (because the valve will almost certainly hit the piston and perhaps cause seizure), valve failure is of minor consequence in a side-valve engine, which could still chug along on its remaining cylinders back to the safety of an airfield.
The flat-four D-motor will be ideal for microlights and VLAs; but I see that D-Motor are also working (with the help of government funding) on a flat-six version.
http://d-motor1.vpweb.be/Recent-information.html
As with the modular Jabiru range, it is very easy to make a 6 out of a 4, since almost all that is needed is a longer crankshaft and crankcase.
It seems to me that the proposed flat-six D-motor may well be the engine that sweeps the board.
The Jabiru 2200 weighs 60kg and produces 85bhp; and its big brother, the 3300 weighs 81kg, and produces 120bhp, 107 continuous.
Clearly then, a flat-six need weigh only 33% more than a flat-four.
(And the Rotax 912 weighs 60kg and produces 80bhp; and its big brother, the turbo 914 weighs 78kg, and produces 115bhp, 100 continuous).
The liquid-cooled D-motor 4-cyl weighs 47kg and produces 80bhp; so (by analogy to the above figures) its big brother, the 6-cyl might weigh only 63kg and yet produce, say, 115bhp or more. In other words, a 6-cylinder D-Motor might weigh barely more than an R912 or J2200; yet would produce nearly 50% more power.
And this is with fuel injection, making carb-heat a thing of the past. If the price is right, it could be the motor we've all been waiting for!
Finally, I remain a fan of reduction gear, to enable the prop to operate slowly and efficiently. If the D-motor (and the Jabiru units too, come to that) were to have a simple 3:2 reduction gear, the prop could be full-size and could extract maximum power while turning less than 2,000 rpm. As it is, both the D-motor and the Jabiru engines must inevitably use small inefficient fast-spinning props; and even so, these engines will probably never be able to reach maximum output, which is 3,300 rpm in the Jabiru's case.