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Old 05-26-2005, 09:46 PM
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why not radial engines?

Why don't people use radial engines in cars?

I've read about them and radial engines don't seem to have any disadvantages whort of there low RPMs and there size


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Old 05-26-2005, 09:50 PM
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Cooling might be the largest hurdle to overcome from the engineering point of view. The complexity and cost associated with it would be another.

Larry
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Old 05-27-2005, 12:45 AM
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space and oiling is tough-

K
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Old 05-27-2005, 02:19 AM
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Lets do the Wankle

Chubby Checker could have made a record like that as a dance to go along with "The Twist" and really mopped up with it. lol

I don't remember how reliable they were. They were only used for a short time so that may be the answer. I went to Rotary engine and got this info.

Al

The Basics
Like a piston engine, the rotary engine uses the pressure created when a combination of air and fuel is burned. In a piston engine, that pressure is contained in the cylinders and forces pistons to move back and forth. The connecting rods and crankshaft convert the reciprocating motion of the pistons into rotational motion that can be used to power a car.
In a rotary engine, the pressure of combustion is contained in a chamber formed by part of the housing and sealed in by one face of the triangular rotor, which is what the engine uses instead of pistons.


The rotor and housing of a rotary engine from a Mazda RX-7: These parts replace the pistons, cylinders, valves, connecting rods and camshafts found in piston engines.



The rotor follows a path that looks like something you'd create with a Spirograph. This path keeps each of the three peaks of the rotor in contact with the housing, creating three separate volumes of gas. As the rotor moves around the chamber, each of the three volumes of gas alternately expands and contracts. It is this expansion and contraction that draws air and fuel into the engine, compresses it and makes useful power as the gases expand, and then expels the exhaust.
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Old 05-27-2005, 03:46 AM
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I remember pullng one of those apart when I was doing my aerospace engineering degree, never did get it back together again right, I had all kinds of pieces left over. I can't remember the capacity but it was huge and had two banks of cylinders, air cooled, was as big as my house and probably weighed as much as it too (okay... slight exaggeration there).

They aren't all that great really, at least if you're talking aircraft powerplants, gas turbines took over at those kind of power levels as they were smaller, lighter, easier to maintain and gave way better fuel economy.

If a modern version were to be built it could be a different story because materials and technology has progressed so much. I would imagine a small capacity radial could be built (would still be a large engine) that was water cooled, overhead cam (actually scrap that, just think about dealing with like 16 camshafts! or 32 for DOHC!... timing would be a nightmare).

Actually the more I think about what this would entail, the more I love the good old V8, give it some thought and I think you will answer your own question... large, heavy, pain in the *** to maintain, lots of moving parts, expensive. It would be kind of a backwards step if you ask me as far as automotive technology is concerned.

It would sound amazing though and would have great torque!

Rich
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Old 05-27-2005, 03:50 AM
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Quote:
Originally Posted by Gr8 '48 bow tie
Chubby Checker could have made a record like that as a dance to go along with "The Twist" and really mopped up with it. lol

I don't remember how reliable they were. They were only used for a short time so that may be the answer. I went to Rotary engine and got this info.

Al

The Basics
Like a piston engine, the rotary engine uses the pressure created when a combination of air and fuel is burned. In a piston engine, that pressure is contained in the cylinders and forces pistons to move back and forth. The connecting rods and crankshaft convert the reciprocating motion of the pistons into rotational motion that can be used to power a car.
In a rotary engine, the pressure of combustion is contained in a chamber formed by part of the housing and sealed in by one face of the triangular rotor, which is what the engine uses instead of pistons.


The rotor and housing of a rotary engine from a Mazda RX-7: These parts replace the pistons, cylinders, valves, connecting rods and camshafts found in piston engines.



The rotor follows a path that looks like something you'd create with a Spirograph. This path keeps each of the three peaks of the rotor in contact with the housing, creating three separate volumes of gas. As the rotor moves around the chamber, each of the three volumes of gas alternately expands and contracts. It is this expansion and contraction that draws air and fuel into the engine, compresses it and makes useful power as the gases expand, and then expels the exhaust.
Umm, I think we are talking about two different beasts here.

You're talking about a rotary engine which is the wankel, but I think the rest of us are talking about a radial piston engine exactly as in the original drawing posted.

Rich
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Old 05-27-2005, 04:32 AM
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Perhaps the strangest radial engine ever built was the 30 cylinder tank engine provided by Chrysler early in the last "official" war. This was used only until GM was able to tool up for the engine most tank veterans encountered. The Chrysler engine was essentially 5 of the Chrysler flatheads on a common crank.

(I found a picture of this engine while going through a file cabinet in the Research Department at Chrysler Engineering in Highland Park in the late fifties. Another interesting picture was of a double overhead cam for the old straight six. This was the "other choice" if they hadn't gone with the hemi. I wonder how automotive history might have been changed if they had opted for the six.)
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Old 05-27-2005, 06:36 AM
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Many radial engines are still pugging away in duty. The 950 that the Dehaviland Beaver and other planes use is still quite popular, but getting harder to find parts for.
I think one problem with using a radial in a car would be the crank centerline. Some sort of drop box would be needed between the crank and the differential.
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Old 05-27-2005, 07:31 AM
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While not a true radial. there is a 8 cylinder opposed engine in the Dayton air museum. It has the cylinders in a circle. Four on each end. The rods and pistons are one piece. There is no crankshaft but rather a swashplate like a a6 a/c compressor. The cam is a flat bumpy plate that rotates with the swashplate. A.very compact unit with good performance for it's weight. As I remember it put out 1hp per ci at about 1lb per ci engine weight. It was an experimental in 1945 that was dropped at the end of the war because there was no more need. I would like to see someone ressurect this motor with modern metalurgy and technology.
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Old 05-27-2005, 07:49 AM
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Quote:
Originally Posted by willowbilly3
I think one problem with using a radial in a car would be the crank centerline. Some sort of drop box would be needed between the crank and the differential.
Yes, this is the big problem. Might be more practical to have a vertical crankshaft and right angle drive, but driveline efficiency would suffer.

How about a small radial engine at each drive wheel? With computerized control, multiple engines would not now be impossible. Naah, unsprung weight would be excessive.

In the early sixties, the future was supposed to be "hydrostatic drive." The engine would power a hydraulic pump and there would be hydraulic motors at each drive wheel. This was also a time when everybody was trying to avoid front wheel drive by bending the driveshaft to achieve more foot room. I believe Pontiac even produced a Tempest with such a driveshaft for a year or two. Seemed crazy at the time, but Chrysler had cars running around with the same setup and I heard Ford was doing the same.

Maybe we'd better stick with what we've got.
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Old 05-27-2005, 08:13 AM
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Quote:
Originally Posted by 61bone
While not a true radial. there is a 8 cylinder opposed engine in the Dayton air museum. It has the cylinders in a circle. Four on each end. The rods and pistons are one piece. There is no crankshaft but rather a swashplate like a a6 a/c compressor. The cam is a flat bumpy plate that rotates with the swashplate. A.very compact unit with good performance for it's weight. As I remember it put out 1hp per ci at about 1lb per ci engine weight. It was an experimental in 1945 that was dropped at the end of the war because there was no more need. I would like to see someone ressurect this motor with modern metalurgy and technology.
This is the same principle used in most aircraft hydraulic pumps although the swashplate is driven and the pistons are pumping hydraulic fluid. I still think any major improvement to power output and efficiency is going to involve moving away from the reciprocating piston engine entirely. This is why I have always loved turbines, and I still get a shiver down my spine every time I fly.

I remember during my studies that one day our whole class was taken outside our college hangar (the college was at a local airfield) and a APS turbine (auxilliary power supply) was tractored outside, it's basically a small trailer mounted turboshaft engine tied directly to a generator that is used to generate electrical power and start air for aircraft that don't have a built in APS (most have them built in to the tail). This was the first time I had come within an arms length of a gas turbine.

We were all given ear protection, and the thing was fired up. At first it was just the starter motor winding up, but then at a certain RPM the thing fired and the bass vibrating through the ground was unbelieveable, I've never been near a blast furnace, but that's the only thing my mind can make a comparison to, the heat ripping through the cold morning air. Then this thing just wound up, I've never heard something spin so fast, must have been close to 30,000RPM at full throttle.

Unbelieveable, I was awestruck by this thing, scared out of my wits to be standing so close to it opened up like that. I've been somewhat obsessed with them ever since.

Anyway, sorry to go off topic like that, yep, I think we should go simpler, less moving components, higher efficiency... turbines are the way to go. Most piston engines manage a 20% efficiency in terms of converting energy from fuel to useable kinetic energy. The latest ultra high bypass turbofan engines are upwards of 70 - 80% efficient.

Rich
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Old 05-27-2005, 09:44 AM
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They were fairly common on cropdusters were I used to live. They would dust the sugarcane fields once or twice a week. Nearly all the planes were biplanes that would fly low enough and slow enough. I always loved watching them fly only about 5ft above the sugarcane then land at the refueling station. The pilots were some cool people too. sorry to get off subject.
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Old 05-27-2005, 12:11 PM
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Quote:
Originally Posted by rlackey

Anyway, sorry to go off topic like that, yep, I think we should go simpler, less moving components, higher efficiency... turbines are the way to go. Most piston engines manage a 20% efficiency in terms of converting energy from fuel to useable kinetic energy. The latest ultra high bypass turbofan engines are upwards of 70 - 80% efficient.
Rich
That 20% might be a pretty good average, for the entire operating range, but the maximum would be closer to 30%. The rule of thumb is a third into the water, a third into the exhaust, and the rest to power the car.

Rich, you'd have enjoyed being at Chrysler Central Engineering during the fifties and sixties for the sight of a turbine car was very common. We called them "vacuum cleaners" at the time. Well, that's what they sounded like. Everybody thought they were "cool," but the most pessimistic people (regarding their eventual production) you could talk to were the engineers responsible for their development. The auto magazines seldom touched upon the big...and apparently insurmountable...problem of compressor inertia. The guys who drove them said the trick to getting through an intersection without holding up traffic was to hit the throttle when the cross traffic's light went amber. And, they all had experienced terrifying moments when attempting to pass on 2 lane roads. Yes, they're great when operating at constant speed...as in an APU or in a race car at Indy..., but not very practical when powering the family sedan.

The compromise might be the free piston engine, as developed by GM. Don't know what happened to that, but it certainly solved the compressor inertia problem.
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Old 05-27-2005, 03:27 PM
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well hey thanks for all the input!

and the things about the rotery engiens and the turbine engines were also good stuff to know!

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Old 05-27-2005, 04:04 PM
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rlackey
Rich Lackey
Umm, I think we are talking about two different beasts here.

You're talking about a rotary engine which is the wankel, but I think the rest of us are talking about a radial piston engine exactly as in the original drawing posted.

Rich


Yes Rich, I know what we are talking about are two different engines. The Wankle has already been used to power automobiles whereas the radial would be very difficult or impossible to use in the automotive industry. With improved technology such as we have today I think the Wankle could be upgraded to use Hydrogen as a fuel easier than a piston driven engine. Kinda sorta almost maybe but not quiet the same as the Radial, but I believe it just might work. On the other hand, I am not an engineer or even close to being one, I like to dream and sometimes dreams do come true.

Al
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