A New Engine

[Piers Bowlan]

Wondered if anyone had come across this. Sounds interesting. It is basically a Wankel engine turned inside out, so now it has an oval rotor and a triangular chamber with the seals on the inside of the chamber instead of on the outside of the rotor. The result is that lubricating the seals is easier and heat distribution in the engine is not so much of an issue. They have built a 'gas' as well as a heavy fuel version apparently, kerosene and diesel, and claim two to three times better fuel economy than the gas version. Apart from the smoothness and low parts count the power to weight radio is amazing.

Now they have funding from DARPA to build a 40hp prototype which will weigh just 30kg and is destined for UAV use. I don't know if the 70cc version would be any good for a model aircraft but I suspect it will cost a bit more than a Laser!

[Jon H]

I know hp is not everything, but only 3hp at 10k rpm from 70cc? that is not exactly high. Our 40cc 240v kicks out more than that at 10k

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Edited By Jon Harper - Laser Engines on 15/12/2016 11:52:17

[Piers Bowlan]

Yes I looked at that bit Jon but it is an early version so who knows what might be possible. I was right, it is a bit more pricy than a Laser, here - you can buy a development engine if you have $30,000 burning a hole in your pocket. Not for everyone then! I thought it might have potential if DARPA are investing in it.

[Nigel R]

Posted by Jon Harper - Laser Engines on 15/12/2016 11:49:34:

I know hp is not everything, but only 3hp at 10k rpm from 70cc? that is not exactly high. Our 40cc 240v kicks out more than that at 10k

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Edited By Jon Harper - Laser Engines on 15/12/2016 11:52:17

Aren't Wankel's a bit odd when it comes to displacement measurement?

(and clearly a Laser is better )

[Frank Skilbeck]

Also need to look at the specific fuel consumption, if it consumes less for 3HP then the cc isn't relevant.

Years ago a friend had a Kawasaki 400 triple which he claimed was more efficient than another mates 850 Norton as it generated more HP per cc, the Kwack did around 30mpg and the Norton around 60mpg.

[Colin Leighfield]

Have you got the same problem as you have with the Wankel in determining what the true capacity is? That was always a debate with the brilliant (and much missed) Norton rotary racing bikes, that lead to arguments about whether they're 600 or 1200cc. Really you can have the same kind of argument about two strokes or four strokes, although at least in both those cases there is a clearly defined cylinder dimension. Probably the best comparison is about the total physical size and weight of the motor as related to its power output.

This design might be better than the traditional Wankel in terms of rotor tip sealing, although I thought that had been pretty much resolved anyway, but it doesn't seem to answer the main deficiency of the design in terms of exhaust losses, high emissions and poor thermal efficiency. As I understand it, that was the final nail in the coffin that caused Mazda to finally abandon the RX8. However, they are talking about bringing the rotary back in 2019 in a new improved form in a fantastic looking car called the RX9. Watch this space. I must confess that I've always been fascinated by this technology.

ARV engines in Shenstone, who inherited the rotary engine manufacturing activity from Norton Motorcycles, is still in business and its main market is making engines for drones. (Proper aeroplanes I mean, not these irritating rotary wing things that seem to be the rage at the moment). Some of those are probably small enough to be of interest for bigger models, I don't know if anyone has ever asked the question,

 

Edited By Colin Leighfield on 15/12/2016 12:46:22

[Jon H]

Posted by Frank Skilbeck on 15/12/2016 12:38:12:

Also need to look at the specific fuel consumption, if it consumes less for 3HP then the cc isn't relevant.

Thats fair enough, and in my haste i did forget all about the vague nature of rotary displacement calculations.

[Geoff S]

Posted by Colin Leighfield on 15/12/2016 12:45:02:

Have you got the same problem as you have with the Wankel in determining what the true capacity is?

I remember Wankel engines were always quoted as having the capacity of one swept side until petrol rationing vouchers were based on engine capacity (ie bigger engines got more fuel vouchers) and the capacity tripled.

Geoff

[Colin Leighfield]

Yes Geoff, odd that wasn't it!

[Martin Whybrow]

The Wankels are indeed used on flying platforms that are not expected to come back, if you get my drift; in these cases, the high wear rate on the rotor seals isn't an issue!

[Frank Skilbeck]

Posted by Colin Leighfield on 15/12/2016 12:45:02:

This design might be better than the traditional Wankel in terms of rotor tip sealing, although I thought that had been pretty much resolved anyway, but it doesn't seem to answer the main deficiency of the design in terms of exhaust losses, high emissions and poor thermal efficiency. As I understand it, that was the final nail in the coffin that caused Mazda to finally abandon the RX8. However, they are talking about bringing the rotary back in 2019 in a new improved form in a fantastic looking car called the RX9. Watch this space. I must confess that I've always been fascinated by this technology.

Edited By Colin Leighfield on 15/12/2016 12:46:22

Colin, that maybe, but another fundamental difference with this engine is that the inlet and exhaust are via ports in the piston not in the housing, also the combustion chamber is significantly different, with maybe much better thermal expansion and less exhaust losses, added to which it feeds cooling air through the rotor which also mixes with the exhaust gases which may in turn help emissions. Be interesting to see some comparisons, but they aren't marketing it at the automotive sector more the hand tools sector where a rotary engine without the vibration may be better. Would be great to see a model engine version.

[Colin Leighfield]

Fascinating stuff Frank. One of the early breakthroughs with the Norton twin-rotor engine was separating the incoming air and passing it through the rotors before it got to the carburettors. It cooled the rotors and gave a big boost in power. Although tip seal wear was an early problem I know that they solved it. Twice in the last three years I've met a chap in the Isle of Man at Manx Festival Week riding a Norton Commander in excellent condition, it sounds wonderful. Last time he had done 130,000 miles on it, many of those touring on the continent.

Martin, not all of these UAVs are one-shot wonders, many are used over and over again. It's worth a look at the ARV engines web-site, fascinating to see the range of engines and complete assembled motor units complete with propellers. It says they are making 150/200 per week! Fascinating stuff. They have developed one that will run on heavy oil and is suitable for very long range duration flights.

Jon, ever thought of making one? I know that machining the chamber shape (epitrochoid)? Isn't straightforward.

[Frank Skilbeck]

Wasn't it the earlier race and road versions that fed the air through the rotors and then the carbs for cooling, but the later race versions had a special exhaust which pulled air through the rotors so that the carbs were fed with fresh cold air, increasing the charge density and hence power.

[Colin Leighfield]

I think you're right Frank. I was referring to the earlier days when David Garside found that bringing the air through the rotors in the way described resolved a low power problem with the prototype twin rotor engines.

There was no question that the later racers were well sorted and fast. I was in the island in September 2015 when they brought over a number of the factory racers for demonstration. John McGuiness did a lap on no.19, the bike that Steve Hislop won on in 1992 at over 120 mph. Michael Dunlop rode one of the JPS specials in the Classic TT and he was really shifting. Sadly he stopped on the first lap, it turned out they'd used the wrong oil and messed the engine up. Great to see and particularly hear them again, one of the memorable episodes in bike racing since I started riding in 1963. Made you feel proud to be British again for a few years!

The OS Wankels seem to fetch a good price when they come up on EBay. We need to see a new one fitted with a turbocharger, that's the way to do it, whether using the conventional rotor approach or this new idea.

[Jon H]

Posted by Colin Leighfield on 15/12/2016 20:05:23:

Jon, ever thought of making one? I know that machining the chamber shape (epitrochoid)? Isn't straightforward.

The short answer is no. We were also asked for some rotary valve parts years ago but what they asked for wasnt worth doing.

Given our use case, the reliability and self sealing nature of a poppet valve cannot be beaten. Just imagine the nightmare that would be a tiny bit of dirt ingress into an engine like that. In a poppet valve engine you could regrind the valve seat, or replace the ring, or the bore etc as required to fix the damage. With this the whole thing would need replacement as the parts are more multi function.

its a cool idea, but rotary engines have been around in one form or another for many years and have never displaced poppet valve engines. Sleeve valve engines are the same.

Personally, i love the old sleeve valve WWII era engines but the advantages dont really come into play at our scale of engine. I do really hope the Canadian Typhoon restoration effort succeeds and they get some Napier Sabre's running and flying. The sound will be awesome!

[Colin Leighfield]

I'm sure you're right Jon. There are good reasons why the conventional piston engine with poppet valves remains supreme. Also agree with the prospect of hearing the ripping sound of a Napier Sabre before I snuff it. Mind you I've agreed with my mate that we are going to celebrate our second seventieth birthdays in 2086, so there's a chance if WW3 doesn't annihilate us in the meantime. Put it in your diary, we'll get the beer in and you are invited.

[Jon H]

Top job, count me in

[Colin Leighfield]