Can the engine start in the opposite direction?

Hippike

Hippike

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Hippike
I'm still a student pilot, so excuse my lack of knowledge or the silliness of the question, but I was wondering:
Props spin clockwise (when viewed from the cockpit) and they do so because they are designed that way and because the starter motor starts spinning it clockwise (and because somebody at the beginning of time decided so... But would it be possible to hand-prop an aircraft in the opposite direction? Ignore the fact that the prop blade is designed so it generates forward thrust when spinning clockwise, but would the engine actually start if I kept propping it counterclockwise?
What determines the rotation of the crankshaft? Pistons have no idea what phase of cycle they are in, all they see is up and down, in their view "up" is either compression or exhaust.
"Who" decides if the crankshaft turns left or right?
 
Absolutely not.. for several reasons
the fuel can not be introduced by the exhaust system.
The Mag can not produce a spark when rotated backwards.
Valve timing would be backward.
 
Hippike said:
"Who" decides if the crankshaft turns left or right?
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The engine designer.

Some diesel engines can be started in reverse, but no gas can. its all about induction and the gas engine must breath in one direction.
 
If you are flying an ultralight or something with a 2 stroke engine I believe that they can actually run in either direction. Some 2 stroke snowmobiles actually achieve reverse by stopping the engine and restarting it in the opposite direction. All with the push of a button.
This website has some cool engine animations.
 
Hippike said:
I'm still a student pilot, so excuse my lack of knowledge or the silliness of the question, but I was wondering:
Props spin clockwise (when viewed from the cockpit) and they do so because they are designed that way and because the starter motor starts spinning it clockwise (and because somebody at the beginning of time decided so... But would it be possible to hand-prop an aircraft in the opposite direction? Ignore the fact that the prop blade is designed so it generates forward thrust when spinning clockwise, but would the engine actually start if I kept propping it counterclockwise?
What determines the rotation of the crankshaft? Pistons have no idea what phase of cycle they are in, all they see is up and down, in their view "up" is either compression or exhaust.
"Who" decides if the crankshaft turns left or right?
Click to expand...
A four stroke engine has inlet, compression, power and exhaust (suck. Squeeze, pop, blewy) and they need to be in that order so it can’t start backwards. In my opinion the cam shaft controls which way the engine runs.

A two stroke will run both directions because the events are controlled by ports in the cylinder and they don’t know which way the engine is turning.

Some aviation engines are set up to run the opposite direction so they can have opposite turning propellers on a twin. It is primarily a change of camshaft although there are other subtle differences.
 
GlennAB1 said:
I believe, on those twins, it's just the propeller turning the other direction through opposite gearing.
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Direct drive on most of the spam can twins so no gearing.
 
Vance Breese said:
A four stroke engine has inlet, compression, power and exhaust (suck. Squeeze, pop, blewy) and they need to be in that order so it can’t start backwards. In my opinion the cam shaft controls which way the engine runs.

A two stroke will run both directions because the events are controlled by ports in the cylinder and they don’t know which way the engine is turning.

Some aviation engines are set up to run the opposite direction so they can have opposite turning propellers on a twin. It is primarily a change of camshaft although there are other subtle differences.
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Yep, ever wonder why they place a R or L in the mag P/N ? and different p/ns for alternators, starters.
 
Clark1961 said:
Direct drive on most of the spam can twins so no gearing.
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And it might be more accurate to say "most spam can twins are 'conventional'" not "counter-rotating" propeller driven. The two best selling small twins, the PA-23 and Cessna 310 are both conventional.
 
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As said above 4-stroke engines won't run backwards due to the cam and valves only working in one direction. Some 2-stroke engines can run in reverse, but poorly as the ignition timing would be way off. Only model airplane engines with glow plug and reed valves truly don't care which way they're running.

Re twins with counterrotating props, some WWII aircraft were originally done that way, but most were were retrofitted with two engines turning the same way... the spare parts nightmare trumped any theoretical advantages of the opposite rotations.
 
There are plenty of piston twins that are direct drive LEFT turning engines. Continental makes L- versions of the 360. I think even the geared lycomings acheive left turning by turning the entire engine the opposite direction rather than a reversing gear in the gear box.
 
Dana said:
A Only model airplane engines with glow plug and reed valves truly don't care which way they're running.
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Yuo, I used to fly the little Testers on a string planes, and sometimes the engine would start backwards. I normally stopped it by putting a heel into the prop. Never seemed to hurt anything.
 
Tom-D said:
Pretty much shows you where Glen is with GA engines>
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Tom, I like you, and I like Glenn. You both have lots of knowledge to give. But what I don't like[1] is when the two of you go at it like rabid dogs. Guys, please don't ruin another thread.

[1] And I'm sure I'm not the only one.
 
GlennAB1 said:
And it might be more accurate to say "most spam can twins are 'conventional'" not "counter-rotating" propeller driven. The two best selling small twins, the PA-23 and Cessna 310 are both conventional.
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Except for the piper Seminole, one of the most widely use twin trainers, the senica, the pa39 twin commanche, and I believe the beech duchess. They are all counter rotating.

Bob
 
Dana said:
Some 2-stroke engines can run in reverse, but poorly as the ignition timing would be way off
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A buddy had a Bultaco that liked to kick back and end and up running backwards - you couldn't really tell until you let the clutch out. Pretty funny when it happened at the start of a race when he would dump the clutch while revved up.

4 strokes typically one changes the cam around (boats, many aircraft engines) - things like starters and distributors/mag change as well. I my experience, the crank will have some changes, but a right hand crank can work in a left hand engine - long story.
 
I'll just leave this here...http://www.mejor.com/356/maestro/stories/912crank.html

What are the odds lol? How many manufactures make engines with interchangeable starters that run in opposite directions?

And then there's this:


Of course that still won't make the engine run in reverse, but it's interesting.
 
Dana said:
As said above 4-stroke engines won't run backwards due to the cam and valves only working in one direction. Some 2-stroke engines can run in reverse, but poorly as the ignition timing would be way off. Only model airplane engines with glow plug and reed valves truly don't care which way they're running.

Re twins with counterrotating props, some WWII aircraft were originally done that way, but most were were retrofitted with two engines turning the same way... the spare parts nightmare trumped any theoretical advantages of the opposite rotations.
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I have probably posted it before, but this reminded of he 1st FIRC I attended where the presenter asked the group “which way do the propellers turn on the P38”, the old instructor in the back of the room answered “After Maintenance got a hold of them they might turn any direction”
 
Tom-D said:
Yep, ever wonder why they place a R or L in the mag P/N ? and different p/ns for alternators, starters.
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Alternators don't care which way they turn. The only difference would be the fan, if it has tangential vanes instead of straight radial vanes.
 
The engine only starts in the direction its made to go whether diesel, gas, propane, hydrogen or milk. The key is in construction as many have noted. The camshaft controls that direction and any four stroke with a cam will only turn one way. The rest of the fixtures, accessories and ancillaries are made to work in that direction. That means mags, airpumps etc. Many twins have engines turning opposite directions and that is how they do it. The cams are different.
In 2 stroke engines it depends on the ignition system. Some will run equally well in either direction and others won't run at all in the opposite of intended. It has to do with whether the ignition system is electronic and limited to one direction.
Some engines will kick back and appear to be running in reverse but it is only temporary and due to excess fuel and bad timing.
The good news for the original poster is that you can't inadvertently hand prop an engine and have it start backwards.

Frank
 
My hi-school friend had a 2 stroke Saab, that he would "pop" the clutch in a forward gear while backing down a hill. He then had 4 reverse gears and one forward.

And, by far, the most famous 2 stroke, the MK-75, MK-78, Merc-800 Mercury outboard had no gears. To go into reverse, you'd stop the engine and restart it in reverse. It was nicknamed "The Dockbuster," but worked VERY good and fast if you had a good battery.

T5nrJj.jpg
 
GlennAB1 said:
And it might be more accurate to say "most spam can twins are 'conventional'" not "counter-rotating" propeller driven. The two best selling small twins, the PA-23 and Cessna 310 are both conventional.
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I would not say that as both the PA-23 and the 310 are direct drive. Both statements are equally accurate.

Look Glenn, I know you are competitive and strongly driven to be "right." That's fine. No need to try to recover from this foo-paw <---I'm not French.
 
you don't need to be French to know it is faux pas. Not being French is your cross to bear.
 
Ravioli said:
you don't need to be French to know it is faux pas. Not being French is your cross to bear.
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Not being French is one of my joys thankyewverymuch.
 
Vance Breese said:
Some aviation engines are set up to run the opposite direction so they can have opposite turning propellers on a twin. It is primarily a change of camshaft although there are other subtle differences.
Click to expand...

Yabut the engine will run in one direction only without being modified to run in the reverse direction. It is not as simple as cranking it in the other direction.

-Skip
 
BiffJ said:
Some engines will kick back and appear to be running in reverse but it is only temporary and due to excess fuel and bad timing.
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Some old cars and trucks would do that. Shut the ignition off while the engine was hot, and it would diesel on a bit, knocking and lurching, and then suddenly it would run backward for a second or so, quite smoothly. The hot carbon in the cylinder heads get small, glowing points that act as igniters, and during the initial stumbling stage some cylinders aren't firing, so the exhaust system gets full of fuel/air mix. Then one cylinder diesels just a bit too soon, the engine is kicked backward, and those little glowing points ignite the fuel/air mix as it's drawn backward through the engine and out the carb. The worst vehicle I ever owned--a '78 Dodge half-ton with the Slant Six--did that reliably almost every time I shut it off. I got used to letting the clutch out, in gear, as I turned the ignition off.
 
Dana said:
As said above 4-stroke engines won't run backwards due to the cam and valves only working in one direction. Some 2-stroke engines can run in reverse, but poorly as the ignition timing would be way off.
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Not true. I had a Harley Davison golf cart with a 250cc 2-stroke designed to run in one direction for forward, and the other for reverse. Ran very well both directions. Matter of fact that thing could back up like a scalded cat. Like others have said, which way it ran depended on which direction the starter motor was turning.

Oh, and it had standard breaker points, not electronic ignition.
 
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eman1200 said:
French toast got me banned once so I’m not very tolerant.
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A French kiss got me more than banned once, by another who wasn't tolerant.
 
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