Swinging it
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Swinging it
Flying out of North Weald yesterday I saw a few Yak's starting up for formation training. I was just wondering why the pilots were manually rotating the prop before starting? I would have asked one of them but the other 10 or so Yak's were making a lot of noise.
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Pilots of radial engine powered aircraft turn the prop through a few revs before starting (either manually, or on the starter) so as to check for or clear hydraulic lock. If not cleared, hydraulic lock, caused by oil in the lower cylinders, could hold the valves closed, and cause valve train damage when it starts.
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It is to prevent hydraulic lock due to oil getting in the cylinder.
This can cause a bent con rod as the oil prevents the piston from getting to TDC.
This then allows the bottom rings to exit the bottom of the cylinder and then they break off on their way back up. So you end up with a bent conrod, a damaged piston and cylinder and the engine full of bits of piston ring.
This is a lot more expensive than pulling the prop through.
This can cause a bent con rod as the oil prevents the piston from getting to TDC.
This then allows the bottom rings to exit the bottom of the cylinder and then they break off on their way back up. So you end up with a bent conrod, a damaged piston and cylinder and the engine full of bits of piston ring.
This is a lot more expensive than pulling the prop through.
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Having pulled the prop through to clear potential hydraulic locks, it is also usual to pull the prop through when priming a cold engine, one blade per shot on the primer pump.
The colour illustrated translation of the original Russian Yak-52 manual shows that once your enlisted ground crew have finished doing this for you, the head of the ground crew delivers a crisp salute to the sky-god in the cockpit, who then proceeds to start the engine (and everything disappears in a cloud of smoke, although the manual doesn't show this).
I've repeatedly shown this diagram to the Waltham donglers, but the only salute I've been delivered with thus far was of a cheerfully un-military variety.
The colour illustrated translation of the original Russian Yak-52 manual shows that once your enlisted ground crew have finished doing this for you, the head of the ground crew delivers a crisp salute to the sky-god in the cockpit, who then proceeds to start the engine (and everything disappears in a cloud of smoke, although the manual doesn't show this).
I've repeatedly shown this diagram to the Waltham donglers, but the only salute I've been delivered with thus far was of a cheerfully un-military variety.
Fairly common on some other old technology engines, not just radials. I have a share in something with a flat 6 Franklin where we do the same. If you forget, and the aeroplane's been sat there for a while, the prop will move about 5 degrees and just sit there.
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Not sure I would be happy "pulling through" with the starter - you need to feel if you have a "lock" as you will need to remove lower plugs to drain out the oil if it is that bad.
We work on a blade for every cylinder plus one as a minimum.
We work on a blade for every cylinder plus one as a minimum.
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Hand-turned radials.
Hi Guys,
Forgive me, but I'm not sure some of what has been said on this subject is correct.
If it really was necessary to hand-turn radials to clear hydraulic lock, then just imagine trying to do it on a Short Stirling or a Blackburn Beverley! You'd have to be twelve feet tall, or else erect a scaffoling platform first! Anyway, you probably couldn't physically hand turn an engine that size.
Whenever I have seen film footage of airmen hand-turning a big radial, it has always looked to me more like they were 'blowing-out' an engine that had perhaps been flooded during a botched start-up and from which the plugs had been removed to facilitate the 'blowing-out' process.
If hydraulic lock was indeed the issue, then it would also be true of inverted engines, like the Gypsy Major and the Cirrus Minor and not just radials. Yes, you do hand turn them, but not to clear hydraulic lock. It's for 'sucking-in' fuel into your cylinders prior either, to throwing the left magneto and hand swinging the prop, (or firing the cartridge starter if it's something like a military spec Chipmunk).
Furthermore, if hydraulic lock really was present, then you would be physically unable to turn even a small engine; you'd have to call the mechanics to it to remove the ignition plug(s) and drain off the oil first.
Anyway, you would only get hydraulic lock if your lower cylinders had very badly worn rings and/or bores. And long before they reached that state, you would have oily plugs and a high oil consumption. You would have constant bad starting and misfiring and vibration on startup, which would warn you about the state of your engine long before hydraulic lock became a possibility.
I would submit that since a radial requires two whole revolutions in order for every cylinder to complete its cycle of suck-squeeze-bang-blow, the prime purpose of hand-turning the engine is purely for 'sucking-in' and nothing else.
With a big aeroplane, however, like a Beverley, either the batteries would be big enough to do the sucking in before the engine started, or perhaps a trolley-acc would be used to take the strain off the batteries at start-up.
Well that's my view anyway.
Broomstick.
Forgive me, but I'm not sure some of what has been said on this subject is correct.
If it really was necessary to hand-turn radials to clear hydraulic lock, then just imagine trying to do it on a Short Stirling or a Blackburn Beverley! You'd have to be twelve feet tall, or else erect a scaffoling platform first! Anyway, you probably couldn't physically hand turn an engine that size.
Whenever I have seen film footage of airmen hand-turning a big radial, it has always looked to me more like they were 'blowing-out' an engine that had perhaps been flooded during a botched start-up and from which the plugs had been removed to facilitate the 'blowing-out' process.
If hydraulic lock was indeed the issue, then it would also be true of inverted engines, like the Gypsy Major and the Cirrus Minor and not just radials. Yes, you do hand turn them, but not to clear hydraulic lock. It's for 'sucking-in' fuel into your cylinders prior either, to throwing the left magneto and hand swinging the prop, (or firing the cartridge starter if it's something like a military spec Chipmunk).
Furthermore, if hydraulic lock really was present, then you would be physically unable to turn even a small engine; you'd have to call the mechanics to it to remove the ignition plug(s) and drain off the oil first.
Anyway, you would only get hydraulic lock if your lower cylinders had very badly worn rings and/or bores. And long before they reached that state, you would have oily plugs and a high oil consumption. You would have constant bad starting and misfiring and vibration on startup, which would warn you about the state of your engine long before hydraulic lock became a possibility.
I would submit that since a radial requires two whole revolutions in order for every cylinder to complete its cycle of suck-squeeze-bang-blow, the prime purpose of hand-turning the engine is purely for 'sucking-in' and nothing else.
With a big aeroplane, however, like a Beverley, either the batteries would be big enough to do the sucking in before the engine started, or perhaps a trolley-acc would be used to take the strain off the batteries at start-up.
Well that's my view anyway.
Broomstick.
Many years ago when I was flying Aunty Betty's Beavers. I forgot to pull the prop through the required number of times. my excuse was there was a flap on. Anyway I had to take the spare a/c and I did pull that one through!
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You're entitled to your view - just don't try joining any Yak syndicates though - if you want to destroy an Ivchenko, make sure you own the whole thing and not just a share of it!
You're correct in that if you do have a significant hydraulic lock, the resistance to pulling the prop through increases to the point that you can inflict damage on the engine if you insist on trying to force it round - at which point it is certainly time to pull some plugs (and if you don't pull it through, you won't know about it).
Leaving even small amounts of oil pooling in the lower cylinders can lead to small hydraulic effects which have been blamed for the propensity of the Russian spark plugs - invariably in the lower cylinders - to blow out the ceramic cores. The cylinder may well continue to fire after a fashion on the other plug, and make a god awful noise in the process - as well as leaving the shattered end of an HT lead in the engine compartment, and if you're really unlucky, the gasses escaping via the blown-out plug can be drawn back in and choke the engine - at least one example has ended up in a field that way.
Your engine need not be be worn for oil to start pooling in the lower cylinders - it might just have been designed that way.
You're correct in that if you do have a significant hydraulic lock, the resistance to pulling the prop through increases to the point that you can inflict damage on the engine if you insist on trying to force it round - at which point it is certainly time to pull some plugs (and if you don't pull it through, you won't know about it).
Leaving even small amounts of oil pooling in the lower cylinders can lead to small hydraulic effects which have been blamed for the propensity of the Russian spark plugs - invariably in the lower cylinders - to blow out the ceramic cores. The cylinder may well continue to fire after a fashion on the other plug, and make a god awful noise in the process - as well as leaving the shattered end of an HT lead in the engine compartment, and if you're really unlucky, the gasses escaping via the blown-out plug can be drawn back in and choke the engine - at least one example has ended up in a field that way.
Your engine need not be be worn for oil to start pooling in the lower cylinders - it might just have been designed that way.
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Well that's my view anyway.
Your comments suggest that pulling an engine through before starting has nothing to do with hydraulic or liquid lock. It has everything to do with hydraulic lock.
Yes, you do hand turn them, but not to clear hydraulic lock. It's for 'sucking-in' fuel into your cylinders prior either, to throwing the left magneto and hand swinging the prop, (or firing the cartridge starter if it's something like a military spec Chipmunk).
Yes, you do hand turn them, and yes, it's to check for, and sometimes to clear a hydraulic lock. If hydraulic lock is discovered, one generally doesn't clear it by pulling the prop through, as this can damage the engine and is a good way to bend a rod. One generally removes a spark plug to drain oil when a hydraulic lock is discovered.
Furthermore, if hydraulic lock really was present, then you would be physically unable to turn even a small engine; you'd have to call the mechanics to it to remove the ignition plug(s) and drain off the oil first.
Anyway, you would only get hydraulic lock if your lower cylinders had very badly worn rings and/or bores. And long before they reached that state, you would have oily plugs and a high oil consumption. You would have constant bad starting and misfiring and vibration on startup, which would warn you about the state of your engine long before hydraulic lock became a possibility.
Hydraulic lock is often the result of worn valve guides, as the oil entering the cylinder doesn't drain from above the piston, but from beneath, through the cylinder head. Oil consumption has nothing to do with hydraulic lock, and has nothing to do with a worn engine. Neither vibration, misfiring, or hard starting has anything to do with liquid lock, and these do not warn of impending liquid lock. One can hydraulic a cylinder after it's been sitting for only a few minutes after shutdown, or it can go months without becoming hydraulically locked. All with having perfectly run the last hundred flights, and on a new or freshly overhauled engine.
I would submit that since a radial requires two whole revolutions in order for every cylinder to complete its cycle of suck-squeeze-bang-blow, the prime purpose of hand-turning the engine is purely for 'sucking-in' and nothing else.
Running the engine through on the starter motor is advised with some engines, but not others, largely because some starter motors utilize a slipping clutch which will protect the engine as it's pulled through on the starter. In this event, pulling the engine through on the starter is safer than pulling it through using propeller blades, because there's a lot more damage to be done by the long arm of the prop blade than there is from the starter. The propeller is a big lever.
In cold weather, flooding the supercharger while cranking (after having pulled the engine through, usually two separate operations) is part of the start procedure, usually done with the mixture in cutoff. Various techniques apply...in this particular case, one is drawing fuel into the cylinder, but not at all the same as the concept you're thinking about. You're envisioning priming the engine and turning it through to better "prime" it, and all this does is wash protective oil off cylinder walls...it doesn't enhance the start.
A cold weather start on a big radial is a raw affair that's part technique and part brute application of fuel, and generally involves the use of a rosary bead of prayer stick.
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I was taught that one pulls the engine 'backwards' first if hydraulic locking is the reason (and yes blowing out too)
Turning an engine over on the starter would seem ill advised if the above is correct.
BTW I was told not that long ago the Lycomings shouldn't be pre-start turned either way as the oil pump won't deliver and dry metal to metal contact will cause wear if prolonged hand turning occurs.
Sir George [old hand cranker] Cayley
Turning an engine over on the starter would seem ill advised if the above is correct.
BTW I was told not that long ago the Lycomings shouldn't be pre-start turned either way as the oil pump won't deliver and dry metal to metal contact will cause wear if prolonged hand turning occurs.
Sir George [old hand cranker] Cayley
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Radials
Hi Guppy,
No, I have never operated a radial, but radials were covered in the ATPL groundschool course I did. Although admittedly that was donkeys years ago.
I was taught (by an ex-RAF instructor who had flown in WWII) that it was for 'sucking in' and to call out 'sucking in' before swinging the prop (with the fuel turned on but the mags off). Once this was done, the swinger called out 'switches on', the person in the cockpit threw the left mag and replied 'contact'. The prop was then swung again to start the engine. I was flying Austers and Tiger Moths at the time and they didn't have starter motors, they were all hand swung.
Point taken.
I was sure it could't be a requirement for all radials, which seemed to be what was being suggested here; the impossibility of doing this on Beverleys and Stirlings being cases in point.
Yes, but that is what was current in the UK in the 60s. It was actually in the POH for the aircraft in use at the time. I always assumed that the designers had made some kind of balance judgement that it was better to pay the penalty of fast wearing cylinder walls than repeated poor starting.
Regards,
Broomstick.
Sounds like the view of someone who has never operated a radial engine, and who has no training in operating a radial engine.
No, it's not, and if you're hand-turning the propeller to "suck in" fuel, then you're doing something stupid. Don't do that. This is why you have a starter motor.
Hydraulic lock is often the result of worn valve guides, as the oil entering the cylinder doesn't drain from above the piston, but from beneath, through the cylinder head. Oil consumption has nothing to do with hydraulic lock, and has nothing to do with a worn engine.
Running the engine through on the starter motor is advised with some engines, but not others...
You're envisioning priming the engine and turning it through to better "prime" it, and all this does is wash protective oil off cylinder walls...it doesn't enhance the start.
Regards,
Broomstick.
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Lycomings shouldn't be pre-start turned either way as the oil pump won't deliver and dry metal to metal contact will cause wear if prolonged hand turning occurs
I agree that an engine which has not run for many months probably would have a delay picking up oil through the pump, and this would result in some dry running. If this is the case, the rather loose fit oil pump is well down the list of components about which I would worry. Crankshaft bearings, and for Lycomings, the high camshaft bearings running dry would worry me more.
An excellent reason for regular operation of engines! Let's all fly more!
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I was taught (by an ex-RAF instructor who had flown in WWII) that it was for 'sucking in' and to call out 'sucking in' before swinging the prop (with the fuel turned on but the mags off).
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I was taught (by an ex-RAF instructor who had flown in WWII) that it was for 'sucking in' and to call out 'sucking in' before swinging the prop (with the fuel turned on but the mags off). Once this was done, the swinger called out 'switches on', the person in the cockpit threw the left mag and replied 'contact'. The prop was then swung again to start the engine. I was flying Austers and Tiger Moths at the time and they didn't have starter motors, they were all hand swung.
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No, it's not, and if you're hand-turning the propeller to "suck in" fuel, then you're doing something stupid. Don't do that. This is why you have a starter motor.