Simviation Forum - Are Wankel engines piston engines?

May 25^th, 2009 at 6:30am

chornedsnorkack Offline
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See
http://www.flightglobal.com/articles/2009/05/24/326897/mistral-prepares-piston-e...

The engines are repeatedly described as "piston" engines. But are wankel engines piston engines?

Also, what exactly is a "rotary" engine? Surely a rotary engine is a reciprocating engine where crankshaft is fixed and pistons move?

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Reply #1 - May 25^th, 2009 at 6:39am

machineman9 Offline
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Just got this off the Google machine:

"An engine which uses no pistons. In place of pistons, triangular-shaped rotors revolve in specially shaped housings."

Nice article on Wankel engines

Diagram to show what it does

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Reply #2 - May 25^th, 2009 at 7:01am

ShaneG Offline
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After owning 2 RX7's, I can say with much assurance, that a Wankel is nothing like a piston engine.

Same results as a piston engine, just different means of achieving them.

I just wish they had solved the oil consumption problem on the old 12B motor. Nothing like having to detail your engine bay once a week. Sad

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Reply #3 - May 25^th, 2009 at 8:17am

chornedsnorkack Offline
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And Wankel engines are certainly not reciprocating engines.

Thus, they are neither reciprocating nor turbine engines.

What are the relevant performance requirements?

From
http://www.flightsimaviation.com/data/FARS/part_121-183.html
planes with 4 or more reciprocating engines must sustain a certain rate of climb at a certain height with 2 engines out.

But for planes with 2 inoperative out of 4 or more turbine engines have different requirements:
http://www.flightsimaviation.com/data/FARS/part_121-193.html

the climb rate must merely be positive, or indeed less.

What precisely are the performance requirements for a plane with 4 or more Wankel engines, with 2 engines out? Seeing how neither reciprocating nor turbine engines apply?

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Reply #4 - May 25^th, 2009 at 9:15am

Brett_Henderson Offline
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I think, as far as aviation goes, I'd call them reciprocating engines.

They use a version of "suck, squeeze, bang, blow"; it's just different geometry.

I always thought they'd be ideal aircraft powerplants. Their service life, and dependability in automobiles never could keep up with piston engines... BUT remember that scooting a car around requires regular ventures into RPM ranges WELL above 3,000.

With the proper prop (and/or gear-reduction).. and considereing that useful airplane engin life-spans are only 2000 hours. They'd be just fine.

Considering that the engine in say a C172, never exceeds 3000 rpm.. and that it pretty much HAS to be yanked and rebuilt at 2,000 hours. Airplane engines get rebuilt, just about the time they're getting broken in; by automobile engine standards.

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Reply #5 - May 25^th, 2009 at 12:29pm

DaveSims Offline
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Brett_Henderson wrote on May 25^th, 2009 at 9:15am:

I think, as far as aviation goes, I'd call them reciprocating engines.

They use a version of "suck, squeeze, bang, blow"; it's just different geometry.

I always thought they'd be ideal aircraft powerplants. Their service life, and dependability in automobiles never could keep up with piston engines... BUT remember that scooting a car around requires regular ventures into RPM ranges WELL above 3,000.

With the proper prop (and/or gear-reduction).. and considereing that useful airplane engin life-spans are only 2000 hours. They'd be just fine.

Considering that the engine in say a C172, never exceeds 3000 rpm.. and that it pretty much HAS to be yanked and rebuilt at 2,000 hours. Airplane engines get rebuilt, just about the time they're getting broken in; by automobile engine standards.

Actually, what is reciprocating in a wankel engine. Using the term suck, squeeze, bang, blow doesn't make it one, even jet engines work on that same priniciple Wink

. From my experience with Wankels and other rotary engines, lifespan has been a problem. The tips of the rotor get worn causing compression loss and oil consumption. Newer technology and metallurgy has helped, but is still an issue. However, pound for pound versus a "reciprocating" piston engine, Wankels are much more powerful and efficient.

As a note, TBO time for an aircraft engine isn't neccessarily a requirement, but a recommendation. As long as the aircraft is not for hire, compressions stay good, and it isn't consuming oil, you can fly that engine as long as you like. I've seen some engines go 1000 hours over TBO before having a problem (although I have seen engines blow up with less than 100 hours too).

Dave

www.flymcw.com

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Reply #6 - May 25^th, 2009 at 12:56pm

Fozzer Offline
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DaveSims wrote on May 25^th, 2009 at 12:29pm:

......As a note, TBO time for an aircraft engine isn't neccessarily a requirement, but a recommendation. As long as the aircraft is not for hire, compressions stay good, and it isn't consuming oil, you can fly that engine as long as you like. I've seen some engines go 1000 hours over TBO before having a problem (although I have seen engines blow up with less than 100 hours too).

Well....

...that's interesting... Shocked

...!

I've always assumed it the been an FAA/CAA requirement that an aircraft (piston) engine has to be stripped, examined, and rebuilt by the Factory or qualified Mechanic, after a certain number of operating hours!

Paul...G-BPLF.... Cool

...!

BTW....before this Thread gets removed as "unsuitable for small Children"... Shocked

...!

...the German word "Wankel" is pronounced "Vankel"... Wink

....

...!

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Reply #7 - May 25^th, 2009 at 1:12pm

Brett_Henderson Offline
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Quote:

Actually, what is reciprocating in a wankel engine. Using the term suck, squeeze, bang, blow doesn't make it one, even jet engines work on that same priniciple . From my experience with Wankels and other rotary engines, lifespan has been a problem. The tips of the rotor get worn causing compression loss and oil consumption. Newer technology and metallurgy has helped, but is still an issue. However, pound for pound versus a "reciprocating" piston engine, Wankels are much more powerful and efficient.

Turbines do it constantly.. the sucking, squeezing, banging and blowing do not have begining and ending points.. and they have specific parts that to do only one thing.

Take a look at the "rotor" in a Wankel.. it most certainly reciprocates**, and that rotor does all those steps, in a piston-like manner.

I agreed that Wankels cant' rival piston life in cars, where duty-cycles and RPM ranges are much greater.. but they'd do fine in a TBO window.

As for taking your soul up into the air on an engine past TBO ? I guess people do all kinda stupid things, when they're allowed. If the standard is good enough for planes for hire, I'll abide by it. You might have a tough time making an insurance claim too.. if you start your takeoff roll on an expired engine Wink

** If you stand in front of a Wankel, and observe the rotor's center of mass, it goes from one side of the center of rotation, to the other side of the center of rotation.. over and over..

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Reply #8 - May 26^th, 2009 at 4:41am

chornedsnorkack Offline
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How does the reliability of a car engine first produced in 1955 compare against the reliability of a car engine designed from scratch and first produced in 2008?

How would the in-flight shutdown rate of a plane engine designed from scratch in 2008 compare against the in-flight shutdown rate of a plane engine first produced in 1955 (Lycoming O-360)?

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Reply #9 - May 26^th, 2009 at 10:33am

The Ruptured Duck Offline
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Brett_Henderson wrote on May 25^th, 2009 at 9:15am:

I think, as far as aviation goes, I'd call them reciprocating engines.

They use a version of "suck, squeeze, bang, blow"; it's just different geometry.

I always thought they'd be ideal aircraft powerplants. Their service life, and dependability in automobiles never could keep up with piston engines... BUT remember that scooting a car around requires regular ventures into RPM ranges WELL above 3,000.

With the proper prop (and/or gear-reduction).. and considereing that useful airplane engin life-spans are only 2000 hours. They'd be just fine.

Considering that the engine in say a C172, never exceeds 3000 rpm.. and that it pretty much HAS to be yanked and rebuilt at 2,000 hours. Airplane engines get rebuilt, just about the time they're getting broken in; by automobile engine standards.

Just say NO to geared engines! Reduces the TBO big time.

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Reply #10 - May 26^th, 2009 at 10:44am

DaveSims Offline
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chornedsnorkack wrote on May 26^th, 2009 at 4:41am:

How does the reliability of a car engine first produced in 1955 compare against the reliability of a car engine designed from scratch and first produced in 2008?

How would the in-flight shutdown rate of a plane engine designed from scratch in 2008 compare against the in-flight shutdown rate of a plane engine first produced in 1955 (Lycoming O-360)?

With the exception of a few new engine types, aircraft engines have remained relatively unchanged over the years.

As for flying past TBO, I'm not advocating just flying til it dies. If you decide to fly past TBO, engine monitoring becomes important. But if you have an engine with all 75+ compression and little to no oil consumption or other problems, why tear it apart. It may never run that good afterwards.

Dave

www.flymcw.com

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