Engine Running Backwards

[SixPapaCharlie]

So a senior pilot with whom I'm friends gave me some advice.
If you are turning the engine off but are going to start it right back up again like for refueling, don't use the mixture, just turn the mags off. Then when you get back in, there is fuel in the cylinders ready to go.

I did this and the plane went cough cough cough and then it began spinning the opposite direction. The engine was running in reverse.

I don't even know what question to ask...

 

[oldShar]

I assume that you NOW pulled the mixture and killed it ...
(it's not still running)

How is it running?
Carburetted? Electric fuel pump?

 

[jesse]

So a senior pilot with whom I'm friends gave me some advice.
If you are turning the engine off but are going to start it right back up again like for refueling, don't use the mixture, just turn the mags off. Then when you get back in, there is fuel in the cylinders ready to go.

I did this and the plane went cough cough cough and then it began spinning the opposite direction. The engine was running in reverse.

I don't even know what question to ask...

I would suggest you not do that. You're leaving your airplane in a state similar to a loaded gun with a hair trigger that is easy to bump. One of the primary reasons we use the mixture to shutoff aircraft engines is to make them less likely to start incredibly easily. It'll really ruin your day if by some chance you have a p lead malfunction after you shut it down via the mags (which I know sounds unlikely but **** happens) and you bump the prop and the engine starts up.

As to it starting in the "opposite" direction...what airframe/engine do you have? If you are starting on both magnetos and you have an impulse coupling on only one magneto that can happen and is probably more likely if you shut down w/ some fuel still in the system.

As a point of reference I own a Flybaby which is an experimental homebuilt single seater low wing wood and fabric airplane. I have a Continental A75 and no electrical system. The only way to start it is by prop starting it.

I also have an old Stromberg carburetor and although I do have the mixture hooked up and working properly (many people just wire them full rich) the mixture at full lean is not lean enough to stop the engine from running. I shut it down by turning the fuel off and then I wait a solid two to three minutes or so before it shuts down. I could just turn it off with the mag switch which would make it much easier to start again and wouldn't require the wait but the safety risk of it being a "loaded gun with a hair trigger" in that condition isn't acceptable to me.

 

[SixPapaCharlie]

Lycoming 320
Carburated
Yes killed it with mixture.

Started normally and ran fine after

 

[N747JB]

I have never heard of one running backwards, except the old Cox .049's we used to run on our string controlled models. I use the term controlled very loosely.
He may have been referencing a hot start procedure that a guy showed me for GITSO's leave the throttle in place, kill engine with mixture. Then when you start it, push the mixture up and only prime after the engine fires and keep it going with primer. It worked OK, but there is 100 ways to start a hot, injected Continental and very few of them work on every plane, every time.

 

[Capt. Geoffrey Thorpe]

It ran backwards for a sustained time (I doubt it) or it kicked back and spun for a few revs (not at all surprising and no big deal)?

 

[Norman]

What Jesse said. You don't want to discover you have a hot mag by getting hit by the prop. They make good people processors.

 

[Graueradler]

You can get a gasoline engine to start and run backwards momentarily if you load up the exhaust with fuel. I used to do it as a bet with a 50 Chevy. Head up a hill. Kill the ignition and floor the gas will leaving it in gear and let it coast to a stop. Coast backwards down the hill and pop the clutch in second gear.

If your engine fired off of the non impulse coupled mag (check the P lead and/or switch), it could have kicked backwards enough to start it backwards.

 

[Sac Arrow]

Yeah until it was fixed, the engine in the Arrow (Lyc IO360) was difficult to shut off completely and would diesel backwards on shutdown sometimes.

 

[Captain]

It can happen. Both engines will run backwards (sustained) on my airplane.

Gotcha

 

[Sac Arrow]

Well no wonder, the wings are pointing backwards as well.

Is the Piaggio a true canard, or are those canard winglets?

 

[flyingriki]

It can happen. Both engines will run backwards (sustained) on my airplane.

Gotcha

Man those are beautiful! They sound nice too! !

 

[Dan Thomas]

Four-stroke engines can run backwards briefly if the ignition is shut off AND if there are glowing bits of carbon in some cylinders. The exhaust system loads up with air/fuel mixture, the RPM gets low, the glowing carbon ignites an incoming charge early enough that it stops the engine and starts it turning backward, and it will diesel like that until it's used up the mixture in the exhaust system. The mags aren't involved at all.

I had a '78 Dodge pickup that was famous for doing that. I would just shut it down as I let the clutch out, in gear, to prevent it.

I used to fly an Auster with the deHavilland Gipsy Major engine. The throttle lever pulled the mixture lever back to full rich when throttle to idle (I know, that's backwards, to have the mixture rich with lever aft, but the Brits drive on the wrong side of the road, too, and the prop on that engine turned the wrong way), so it was impossible to kill it with mixture. You either shut the fuel off and waited, or used the ignition. If it was hot, it would just keep running on the glowing carbon in the cylinders even with the ignition off, so full throttle and mixture lean would usually stop it. Usually.

Dan

 

[gismo]

You can get a gasoline engine to start and run backwards momentarily if you load up the exhaust with fuel. I used to do it as a bet with a 50 Chevy. Head up a hill. Kill the ignition and floor the gas will leaving it in gear and let it coast to a stop. Coast backwards down the hill and pop the clutch in second gear.

If your engine fired off of the non impulse coupled mag (check the P lead and/or switch), it could have kicked backwards enough to start it backwards.

BTW, killing the engine with the magnetos, especially if the throttle wasn't closed all the way will indeed leave fuel in the exhaust, ready to be sucked into the engine if it kicks backwards during the subsequent start attempt. And there is a chance of damaging the starter when this happens as it's unlikely to disengage. If the starter remains engaged with the engine running backwards the starter motor will likely spin much faster that it was intended to.

 

[Captain]

Well no wonder, the wings are pointing backwards as well.

Is the Piaggio a true canard, or are those canard winglets?

Piaggio is very sensitive on the subject of canards. They loudly tell you they are NOT canards. They are the 'Forward Wings'.

Supposedly a true canard has to have pitch authority and the Piaggio's forward wing does not. Pitch is controlled with a conventional elevator on the tail. The forward wings do have a flap each that moves in sequence with the inboard and outboard flaps on the main wing.

Trivia: the fuselage provides 20% of the airplanes total lift. This extra lift accounts for a 34% reduction in main wing length and the whole thing is laminar. If you look at the photo you can clearly see the fuselage is shaped like an airfoil.

 

[mikea]

....Supposedly a true canard has to have pitch authority and the Piaggio's forward wing does not. Pitch is controlled with a conventional elevator on the tail. The forward wings do have a flap each that moves in sequence with the inboard and outboard flaps on the main wing.
...

Nope. If "pitch authority" mans control surfaces than that's wrong. The canards on the Rutan designs provide 40% of the lift and have no controls, the pitch is controlled with the elevator on the tail.

If you mean you can stall the forward wing and still have pitch control than that is different.

The whole reason you can't stall a Long-EZ is that the canard is set at a higher angle of attack so it stalls first, loses that 40% of lift, and lowers the nose to break the stall.

 

[Captain]

Not my fight. Just passing on what Piaggio says. The forward wing does stall first on a P180 too. I'd think it'd have to as if the main stalled first you'd die on every stall.

Also, those big delta fins on the tail make stalls a non-event. If fact, the only way to hard stall it is to zoom up to some crazy AoA and hold that. If you just kill the power and hold altitude the yoke hits the stops and you float down without ever really stalling...nose drop and all.

 

[Capt. Geoffrey Thorpe]

I also have an old Stromberg carburetor and although I do have the mixture hooked up and working properly (many people just wire them full rich) the mixture at full lean is not lean enough to stop the engine from running. I shut it down by turning the fuel off and then I wait a solid two to three minutes or so before it shuts down. I could just turn it off with the mag switch which would make it much easier to start again and wouldn't require the wait but the safety risk of it being a "loaded gun with a hair trigger" in that condition isn't acceptable to me.

The mixture on the Stromberg only effects the main circuit - not the idle. So, yes, you can not shut it down with mixture.

Call me lazy, but I always used to shut it down with the mags (same as my Rotax which has no mixture) which is probably how many people do it. (The Rotax manual specifically says to use the mags.)

Shutting off with the mags lets you know that the P leads are probably working OK, but intermittent faults do happen, switches get bumped, etc. And if the prop is in the right position only a couple of degrees of prop movement is needed to trip the impulse.

You can't get complacent around propellers.

 

[kyleb]

Nope. If "pitch authority" mans control surfaces than that's wrong. The canards on the Rutan designs provide 40% of the lift and have no controls, the pitch is controlled with the elevator on the tail..

The only pitch authority on Rutan and similar canards is from the canard mounted elevators. The main wing has the ailerons.

 

[redtail]

Not my fight. Just passing on what Piaggio says. The forward wing does stall first on a P180 too. I'd think it'd have to as if the main stalled first you'd die on every stall.

Also, those big delta fins on the tail make stalls a non-event. If fact, the only way to hard stall it is to zoom up to some crazy AoA and hold that. If you just kill the power and hold altitude the yoke hits the stops and you float down without ever really stalling...nose drop and all.

I read that the lift provided by the forward wing allows the main wings(and engines) to be placed further aft, which in turn reduces the overall cabin noise. Is it really that much quieter than other twin turboprops?

I see them flying into JFK sometimes. I never fully understood the unique sound of the engines/props. I think I read something about them producing a Square Wave waveform

This is one of my favorite planes to fly in X-Plane!

 

[jesse]

The mixture on the Stromberg only effects the main circuit - not the idle. So, yes, you can not shut it down with mixture.

Call me lazy, but I always used to shut it down with the mags (same as my Rotax which has no mixture) which is probably how many people do it. (The Rotax manual specifically says to use the mags.)

Shutting off with the mags lets you know that the P leads are probably working OK, but intermittent faults do happen, switches get bumped, etc. And if the prop is in the right position only a couple of degrees of prop movement is needed to trip the impulse.

You can't get complacent around propellers.

I always test the p leads after I shut the fuel off to make sure they work. Since I have to prop start it and almost always have to do some ground handling to get it somewhere where I can tie the tail I don't want the engine on a state where it'll start incredibly easy.

I actually don't have impulse couplings at all which I don't mind since it makes it less likely it'll be accidentally started and still isn't that bad to prop start.

 

[Sac Arrow]

Not my fight. Just passing on what Piaggio says. The forward wing does stall first on a P180 too. I'd think it'd have to as if the main stalled first you'd die on every stall.

Also, those big delta fins on the tail make stalls a non-event. If fact, the only way to hard stall it is to zoom up to some crazy AoA and hold that. If you just kill the power and hold altitude the yoke hits the stops and you float down without ever really stalling...nose drop and all.

So basically, the main wing and the forward wing will stall before the tail then. Is the tail loaded negatively like a conventional tail?

 

[jhausch]

If you have a dry vacuum pump, the reverse running may have damaged it (or so I have heard)

 

[Dan Thomas]

If you have a dry vacuum pump, the reverse running may have damaged it (or so I have heard)

Only if it was worn out anyway. The vanes get too short, and the angle of the vane slots will make them jam if the pump is turned backward. A good pump will withstand being run backward briefly.

Dan

 

[Captain]

I read that the lift provided by the forward wing allows the main wings(and engines) to be placed further aft, which in turn reduces the overall cabin noise. Is it really that much quieter than other twin turboprops?

I see them flying into JFK sometimes. I never fully understood the unique sound of the engines/props. I think I read something about them producing a Square Wave waveform

This is one of my favorite planes to fly in X-Plane!

Close. You have the cart before the horse though.

Piaggio is built around efficiency. That's why the fuselage airfoil for example. Along those lines the most efficient place for a wing is in the middle of a fuselage. Low wing and high wing configuration create extra drag at the roots. Many jets encorporate farings in an effort to 'trick' the air into believing the wing is really in the middle. But true middle is best.

But you don't want a wing spar in the middle of your cabin...so...the wing got moved aft. With the main wing so far aft they needed a small wing to hold up the nose.

The design allows all three lifting surfaces to be positive lift. The elevator just modulates positive lift to keep the plane in trim. The only time the elevator provides negative lift is to rotate on takeoff and flare to land. All other times it's some level of positive lift.

 

[redtail]

Close. You have the cart before the horse though.

Piaggio is built around efficiency. That's why the fuselage airfoil for example. Along those lines the most efficient place for a wing is in the middle of a fuselage. Low wing and high wing configuration create extra drag at the roots. Many jets encorporate farings in an effort to 'trick' the air into believing the wing is really in the middle. But true middle is best.

But you don't want a wing spar in the middle of your cabin...so...the wing got moved aft. With the main wing so far aft they needed a small wing to hold up the nose.

The design allows all three lifting surfaces to be positive lift. The elevator just modulates positive lift to keep the plane in trim. The only time the elevator provides negative lift is to rotate on takeoff and flare to land. All other times it's some level of positive lift.

Had to read that twice and take another look at the picture. I never gave it much thought that this is a 'middle fusalage' wing design or why. Makes a lot of sense now though. Thanks for explaining that.

 

[Captain]

The wing going back does quiet thing up. Keeps the people ahead of the noise...

I've never been in a King Air to compare, but I use a Telex 5x5 pro headset (single ear piece) and find the noise levels comfortable. I wouldn't call it 'whisper quiet' but a normal level conversation can be had, even in the back of the plane.

I'm really sorry this has hijacked this thread. Every post I think I'm making 'just one more' but then more questions roll is. I'll start a new thread for the next post if needed.

 

[Bill]

The engine was running in reverse.

I don't even know what question to ask...

Did you back into the hangar?

 

[TriGear28]

Aren't a lot of lycoming oil pumps gear driven? If so, my primary concern of a "sustained" backward run would be loss of oil pressure during the run. Or an avionics power spike of some kind. Either way, no use leaving fuel there, ready to ignite. My marlin 30/30 has three safeties. Half-cock, lever lock, and safety. The only safety you'd have left on a primed engine is a p lead, either of which can become accidentally ungrounded.


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[gismo]

Aren't a lot of lycoming oil pumps gear driven? If so, my primary concern of a "sustained" backward run would be loss of oil pressure during the run. Or an avionics power spike of some kind. Either way, no use leaving fuel there, ready to ignite. My marlin 30/30 has three safeties. Half-cock, lever lock, and safety. The only safety you'd have left on a primed engine is a p lead, either of which can become accidentally ungrounded.

AFaIK all engine oil pumps are "gear driven" but since a 4 stroke engine won't run backwards after the small amount of fuel in the exhaust runs out combined with the fact that said engine is neither running at high RPM or producing significant power the lack of oil pressure isn't likely to cause any distress. As to the "avionics power spike" there's nothing about running backwards that could possibly cause that.

Even if you stop an engine with the mixture control it's quite possible that it could fire if you move the prop by hand with the mags on. IME that's only a little more likely if you stop the prop with the mags. And generally once the engine cools off it won't fire easily because the fuel isn't vaporized or atomized.

 

[Jimmy cooper]

I always test the p leads after I shut the fuel off to make sure they work. Since I have to prop start it and almost always have to do some ground handling to get it somewhere where I can tie the tail I don't want the engine on a state where it'll start incredibly easy.

I actually don't have impulse couplings at all which I don't mind since it makes it less likely it'll be accidentally started and still isn't that bad to prop start.

In the last 10 years I've had three taildraggers, all prop starts. One always treats a prop as a potential killer , never touching it, including never leaning on one when posing for a photo. If you learned in an older taildragger( I did) you were taught to never trust a prop, always treat it as hot. All three of mine had impulse starters as they make it so much easier to start when hot or very cold. I always turn mine off with the mag switch as the Strombergs are usually wired. You run it rich up to 5000 feet anyway and most fly them lower including me. I always tie it down before starting it. Always.

 

[comanchepilot]

omg immediate teardown required. .. running backwards?

Does that mean the hobbs goes backward too?

I'm seeing a choice here - mount the prop backwards and off we go.