Interesting post from LAA forum -- D-Motor Aircraft Engine Users Forum

[ Show ]

Support VoyForums

[ Shrink ]

VoyForums Announcement: Programming and providing support for this service has been a labor of love since 1997. We are one of the few services online who values our users' privacy, and have never sold your information. We have even fought hard to defend your privacy in legal cases; however, we've done it with almost no financial support -- paying out of pocket to continue providing the service. Due to the issues imposed on us by advertisers, we also stopped hosting most ads on the forums many years ago. We hope you appreciate our efforts.

Show your support by donating any amount. (Note: We are still technically a for-profit company, so your contribution is not tax-deductible.) PayPal Acct: Feedback:

Donate to VoyForums (PayPal):

[ Login ] [ Contact Forum Admin ] [ Main index ] [ Post a new message ] [ Search | Check update time ]

[ Next Thread | Previous Thread | Next Message | Previous Message ]

Date Posted: 11:33:41 08/07/11 Sun
Author: Nick
Subject: Interesting post from LAA forum

Trevor Lyons

Joined: 12 Jan 2008
Posts: 87
Location: Staffordshire

Posted: Mon Aug 01, 2011 9:51 am

Post subject: The motor we've all been waiting for!
I first saw the flat-four side-valve D-motor displayed at Sywell in 2010 and was immediately fascinated by its dinky size and low weight.
<a rel=nofollow target=_blank href="http://d-motor1.vpweb.be/Product---Produit.html">http://d-motor1.vpweb.be/Product---Produit.html</a>
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.
<a rel=nofollow target=_blank href="http://d-motor1.vpweb.be/Recent-information.html">http://d-motor1.vpweb.be/Recent-information.html</a>
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.
_________________

Trevor Lyons

PostPosted: Thu Aug 04, 2011 1:02 pm
Post subject:
A side-valve motor has poor breathing at high rpm, but the simple valve gear offers no mechanical obstacle to high revs; so (in theory at least), provided the D-Motor's crankcase & internals are up to it, there seems no reason why it might not benefit in future from an induction boost via a turbocharger or supercharger. After, all the engine is so light to begin with, the extra weight of a charger would not signify much.

Just imagine: a flat-six turbocharged D-motor weighing perhaps 75kg and producing 140bhp!
_________________

[ Next Thread | Previous Thread | Next Message | Previous Message ]