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By: - 1st October 2002 at 18:27 Permalink - Edited 1st January 1970 at 01:00
RE: Centaurus
[updated:LAST EDITED ON 01-10-02 AT 06:31 PM (GMT)]Hi Keithmac
I have always been interested in engines, and I, like others have found your posts very interesting and informative, I think the most interesting type of engine is the type used in the early years of flying, cant think of the proper name for them, but the type that the crank shaft is held still and the cylinder heads rotate around it with the prop bolted to them rather than the crankshaft, I think the idea being to help cooling, its a wonder they worked at all!!…..anyway may be you can do a bit about them.
Thanks and keep up the good work
Dezz
BTW the Centaurus is a cool looking bit of kit
:-)
By: - 1st October 2002 at 19:19 Permalink - Edited 1st January 1970 at 01:00
RE: Centaurus
Hello Dezz. The early engines you're talking about are rotary engines. I have to say they were even before my time, and I was never trained on them. I've a basic idea how they work, but I've no diagrams or drawings. So for the moment I'll have to admit defeat. I'll try and dig out some info and when I have I'll try and put something together.
KeithMac.
By: - 1st October 2002 at 19:25 Permalink - Edited 1st January 1970 at 01:00
RE: Centaurus
hi keithmac
i had a feeling they were called that, but whene i hear the words rotary engine i think of the Mazda RX7!! different type of rotary engine
Thanks again
Dezz
:-)
By: - 1st October 2002 at 19:54 Permalink - Edited 1st January 1970 at 01:00
RE: Centaurus
I think of the Wankel Rotary engine. Not quite in the same league methinks!
By: - 1st October 2002 at 22:51 Permalink - Edited 1st January 1970 at 01:00
RE: Centaurus
Cheers Kieth,that Centaurus is a mean looking piece of kit.I was just wondering if you could explain the term 'Brake Horsepower'.Is it different to straightforward horsepower and if so in what way?
When I think of rotary engines I think of Norton motorbikes from the 1980's.A friend of mine has a pair of these machines,one an ex-police, air cooled Interpol,and a liquid cooled Commander.I've had the honour(!) of helping him strip and rebuild both machines,and boy they're pretty complex!Having said that,they run smooth as a baby's bum.I've stood a 50p piece on it's edge on top of the fuel tank with the engine running,and it stays there throughout the rev range. Quite a number of microlights also use Wankel rotary engines and they have always given a very good account of themselves.
By: - 2nd October 2002 at 09:22 Permalink - Edited 1st January 1970 at 01:00
RE: Centaurus
Hi Keith!
I´ve seen pictures of sleeves and the intricate design of the ports to fit the holes in the cylinder when rotating/oscillating. In the sleeve there were two inlet ports, one exhaust port and one port that was alternatingly inlet/exhaust.
I´ve tried to figure out if valve overlap was possible for a sleeve valve engine? It seems to me as it wasn´t possible!?
If I´m correct, wasn´t this a drawback in the design which gave a lower volumetric efficiency?
For those who might not know, valve overlap in a poppet valve engine means that the inlet valves open before the exhaust valves close. In a suction engine, valve overlap is short whereas in a supercharged engine it´s longer.
On the exhaust stroke, it seems to me that at the top of its motion the piston covers the ports. Are the exhaust ports designed, elongated towards the top, to allow gas to sneak down beside the piston?
Thanks for the new "series"!
Christer ;-)
(Who didn´t understand the comment about getting out more in the other thread! Maybe I should too and all other people with a teccie interest?)
By: - 2nd October 2002 at 09:49 Permalink - Edited 1st January 1970 at 01:00
Rotary engines
[updated:LAST EDITED ON 02-10-02 AT 09:51 AM (GMT)]I was borne in the swedish town where Enoch Thulin had his aeroplane factory in the early twentieth century. It so happens that, in our club house at the flying club, we have a LeRhône rotary engine and this is what I know about it.
First of all, engines are stupid. They don´t know if the crankshaft or the crankcase is supposed to turn. It really doesn´t matter and if you start any engine and let it loose on the floor the crankcase will rotate in the opposite direction of the crankshaft.
So if you fix the crankshaft to the airframe the crankcase will rotate.
The crankshaft was hollow to allow the air/fuel/lubricant mixture into the crankcase.
The principle was four stroke with two valves. The exhaust valve is in the top of the cylinder with an outside actuating rod. The inlet valve is an automatic valve in the top of the piston. At the top of the exhaust stroke the exhaust valve closes, when the piston travel down the cylinder an underpressure is created which opens the automatic inlet valve and the mixture is sucked into the cylinder.
This wasn´t very efficient so, soon the inlet valve was moved to the top of the cylinder as well and it too was controlled by an actuating rod. On these engines there were tubes running along the cylinders connecting the crank case with the inlet valve becuse the mixture was still ingested through the crankshaft.
Neither this arrangement was efficient and to allow further developement in terms of HP the rotary design was abandoned.
I hope this helps,
Christer :)
(who seems to be older than Keith)
By: - 2nd October 2002 at 11:01 Permalink - Edited 1st January 1970 at 01:00
Horse Power
Ant,
Break Horse Power (BHP) is a unit used in the non metric countries.
One BHP = 745,400 W.
It originates from how much work a horse could do in a mine. It´s a convention that a person just decided to use, albeit after some study of the working animals.
The term was Horse Power, the Break was added when engines were tested by breaking them on a test stand.
The Metric Horse Power (MHP), also called Cheval Vapeur (CV), is different. Is this what You mean by straightforward horsepower?
One MHP = 735,499 W.
I´m not 100 % sure but I think that it is connected with converting a certain measure of steam into boiling water in a steam engine.
What is measured on the test stand is the torque over the operating range of rpm. A formula is used to convert torque to BHP. Maximum torque is alwas at a lower rpm than maximum BHP which means that rpm is in there somewhere in the formula.
I found these links:
http://www.howstuffworks.com/horsepower2.htm
http://www.howstuffworks.com/question622.htm
Hope this helps,
Christer :-)
By: - 2nd October 2002 at 11:46 Permalink - Edited 1st January 1970 at 01:00
RE: Horse Power
Christer
The proper spelling is "brake horsepower". As you stated, it was measured by applying load to an engine, or "braking" it.
As you can imagine, there is a considerable difference between "braking" and engine, and "breaking" it.
On the subject of the LeRhone rotary engines, I seem to remember that another characteristic of them was that they flung castor oil all over the aircraft and the pilot and this was one easy way to tell if the pilot had been flying a rotary engined aircraft - his face and flying jacket were covered in oil at the end of the flight. After a while, the jacket was totally stained with oil where it was exposed above the cockpit coaming.
Regards
The Wombat
By: - 2nd October 2002 at 11:50 Permalink - Edited 1st January 1970 at 01:00
RE: Horse Power
Christer
The proper term is "brake horsepower" and as you stated, it was measured by applying a load, or "brake", to the engine.
You will appreciate that there is a considerable difference between "braking" an engine, and "breaking" it.
Another point I seem to remember concerning the LeRhone rotary engine is that it flung copious quantities of castor oil out as it rotated, coating the aircraft and the pilot liberally whilst in flight. It was easy to tell the rotary engined fighter pilots from other engines during World War 1, because of the oil all over their faces and jackets. After a while, their flying jackets became so oil-sodden that they changed to a darker colour, particularly where they were exposed to the slip-stream above the cockpit coaming.
Regards
Wombat
By: - 2nd October 2002 at 12:34 Permalink - Edited 1st January 1970 at 01:00
Breaking the brake ......
Well, I sat there thinking that something is wrong but couldn´t find out what.
Thanks for pointing it out but, did You have to rub it in twice? ;-)
Christer :D
By: - 2nd October 2002 at 22:16 Permalink - Edited 1st January 1970 at 01:00
RE: Rotary engines
Thanks for the info Christer and Wombat
If I remember correctly, the movies of rotary engines, that ive seen, did look pretty Smokey, so its no wonder the pilot got covered in oil, as an aside, I never even dreamed that castor oil was ever used in engines!! Just goes to show “you learn something every day”
Thanks again
Dezz
:-)
By: - 3rd October 2002 at 09:15 Permalink - Edited 1st January 1970 at 01:00
RE: Rotary engines
Christer
Sorry - I don't know what happened there. Been having some probs. with my pc lately, keeps dropping out and telling me I've performed an illegal operation. If it keeps it up, it'll find out that flying is a whole new sensation for a computer!!!
Regards
Wombat
By: - 3rd October 2002 at 11:22 Permalink - Edited 1st January 1970 at 01:00
RE: Rotary engines
Wombat!
I know these things can happen and I said it with a wink and a lol.
It has never happened to me though but, the following has:
I type a message and while doing this I hit "back" to check the post I´m referring to and then "forward" again to continue typing. From time to time a gremlin is there and nicks what I´ve typed and that´s irritating since I´ve got a low hitrate on the keys.
Now I always highlight what I´ve written so far and hit "ctrl-c" before stepping back.
Christer :+
Posts: 341
By: keithmac - 1st October 2002 at 17:28
Just look at this for a piece of wonderful engineering - The Bristol Centaurus. 18 Cylinders with a bore of 5.75 inches and a stroke of 7 inches, a magnificent 53.6 Ltrs. This beauty is a Centaurus 661 and produced 2,625 brake horsepower at take off boost.
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