Swinging it

[The500man]

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.

[Pilot DAR]

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.

[Zulu Alpha]

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.

[eharding]

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.

[Genghis the Engineer]

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.

G

[rocco16]

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.

[BroomstickPilot]

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.

[wrecker]

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!

[eharding]

Well that's my view anyway.


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.

[SNS3Guppy]

Well that's my view anyway.

Sounds like the view of someone who has never operated a radial engine, and who has no training in operating a radial engine. You're wrong.

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).

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.

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.

That's the whole point of pulling the engine through in the first place; one is checking for hydraulic lock. If one finds resistance, then one stops pulling, and starts removing spark plugs.

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.

Not at all true.

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.

Completing the four-cycle evolution is irrelevant, as one isn't firing the engine. One only needs the piston to move.

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.

[Sir George Cayley]

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

[BroomstickPilot]

Hi Guppy,

Sounds like the view of someone who has never operated a radial engine, and who has no training in operating a radial engine.

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.

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.

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.

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.

Point taken.

Running the engine through on the starter motor is advised with some engines, but not others...

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.

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.

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.

[Pilot DAR]

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

Though equally possible with any engine, I would not be the least worried about this effect for the amount of horse power I can personally produce. The engine does not know what force is turning it over, just that it is. A dozen revolutions on the starter motor would have the same result as hand swinging the prop.

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!

[Sir George Cayley]

Seconded :ok: SGC

[SNS3Guppy]

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).

With all due respect to your instructor, whom I've likely never met, I flew radial powered airplanes utilizing R-1340's, R-2600's, R-2800's, R-3350's, and R-4360's, and have a little bit of an idea of radial engine operation...not from listening to someone else, but from having done it as a professional pilot in the cockpit, as well as years of working on that equipment as a mechanic. The information I previously relayed to you is correct.

[SA Brit]

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.

Why was just the left mag used when starting?

[stevelup]

Probably because only the left mag was an impulse magneto?

[waldopepper42]

So how did they check / clear hydraulic locks on Stirlings, Sunderlands et al? Just interested.....

[mad_jock]

So how did they check / clear hydraulic locks on Stirlings, Sunderlands et al? Just interested.....

A big spanner, some minor swearing and a bit of sweat.

[Malcom]

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.

My Tiger Moth & my Chipmunk are a little prone to hydraulic locks having an inverted engine, but I also must be "doing something stupid" to prime and start them too. Being fitted with Armstrong Starters, I really cant avoid it.

[Rod1]

"Fairly common on some other old technology engines, not just radials."

And some newish tec no radials.

Rod1

[Lister Noble]

Silvaire,thanks for the info,didn't know that.
We have an L4 Cub,Continental A 65,always prime 1.5 to 2 pushes,6 blades on no throttle,start no throttle.
Always fires up first swing.
Lister:)

[Jan Olieslagers]

FWIW: before cold starting a Rotax 4-stroker, I was taught to check the oil level by opening the reservoir, then rotating the prop by hand until hearing from the reservoir a noise like flushing the loo, then apply the dipstick. But other pupils started the engine for a minute, then stopped it to check. Not sure which is best, likely it is the most troublesome...
When hand-turning the prop, it has to be done counterclockwise (as one looks at it) otherwise air might be sucked into the oil circuit. That's to say, if my dusty memory is to be trusted.

[Big Pistons Forever]

As was stated above, unless the engine has a starter with a slipping clutch all radials must be pulled through to ensure that there is no oil in the lower cylinders which would cause a hydraulic lock. When doing this by hand one should always go gently and stop at the first sign of resistance. On the smaller radials like the YAK's MP14, you can exert enough force to damage a hydraulically locked engine, especially if you are pulling on the end of the blade and therefore have lots of leverage.

Another occasion for pulling through an engine is if the starter is very weak. Pulling through will limber the engine making the starter's job a bit easier especially if its cold. You can also hasten the start by prestart priming. For example on a simple carburated 4 cylinder (cold), give it a 1/2 shot of prime turn the prop 1/2 a rev, and repeat 3 more times add one last 1/2 shot and hit the starter, the engine will immediately start everytime. Obviously you will have the mags off when pulling through, but you still consider the prop hot and take appropariate precautions.

[Noah Zark.]

So how did they check / clear hydraulic locks on Stirlings, Sunderlands et al?

They got an 'erk' on a stick! :)

[Pilot DAR]

Obviously you will have the mags off when pulling through, but you still consider the prop hot and take appropariate precautions.

Yes...

With all of the chatter here about the need, or at least benefit, of pulling the engine through proir to start, lets not overlook a very real hazard. The only time I have ever damaged an aircraft was during an unexpected start during pulling through. Unsafe and embarrassing!

On another occaion (different plane) I was hand starting for a trusted friend. I called "mags off", he called "mags off". I pulled the prop through. The engine started, and ran. I glared at him through the running propeller, so as to convey my unhappiness about his error in ignition selection. To convince me he had not made an error, he held up the keys, which I saw through the windshield, and turning propeller. Failed key switch.

EVERY time you put your hand on the prop, you should be ready for the engine to start, both in propeller clearance, and aircraft restraint. If you have ANY doubt about swinging a prop safely, don't do it!

That said, during winter starts, and particularly when a preheat is not possible, I very certainly "limber up" and prime an engine by hand - as long as the aircraft is restrained, and I have satisfied myself with a prior live mag check.

[troddenmasses]

So how did they check / clear hydraulic locks on Stirlings, Sunderlands et al? Just interested.....

I used to belong to Cardiff Wales Flying Club, which had at one point been the HQ for Cambrian Airways - which amongst other aircraft used DC-3's. One of the PPL's at the club had been an engineer at Cambrian, and told me about 'rope starting' on really cold days when the batteries weren't up to much, and explained the procedure. I wasn't sure whether he was winding me up or not, so had a look on the internet and found this:

http://www.douglasdc3.com/prop/proprope.gif


IN CASES OF EMERGENCY, DC3 ENGINES CAN BE ‘ROPE STARTED’, SHOULD THE
STARTER MOTOR BE INOPERATIVE. IN CARRYING OUT THIS OPERATION, IT IS
ESSENTIAL TO PAY PARTICULAR ATTENTION TO SAFETY AND PROCEDURE AND ALWAYS
START THE ENGINE TO BE ROPE STARTED, FIRST. IN ADDITION, A CHECK SHOULD
BE MADE THROUGH THE OPERATIONS OFFICE TO ENSURE THAT NO OPERATIONAL
ALTERNATIVE IS POSSIBLE.

PROCEDURE:- WITH THE APPROVED ROPE SLING ON HAND, PROCEED AS FOLLOWS:--

A) CHECK THAT IGNITION SWITCHES ARE 'OFF' AND MIXTURE CONTROL IN IDLE
CUT-OFF,
B) THE ENGINE TO BE STARTED SHOULD BE TURNED OVER BY HAND, FOR FOUR AND
A HALF COMPLETE TURNS (14 BLADES), TO CHECK FOR HYDRAULICING
C) PRIME ENGINE.
1) IGNITION OFF (2) MIXTURE IDLE CUT-OFF
3) THROTTLE SET (1/2 INCH ON GATE) (4) BOOSTER PUMP ON
5) WHILE THE ENGINE IS BEING TURNED BY HAND, GIVE PRIMING IN ONE SECOND
BURSTS (FOUR FOR HOT AND UP TO, PERHAPS, FOURTEEN FOR COLD ENGINE)
6) BOOSTER PUMP OFF.
D) FIT ROPE SLING. PLACE END BOOT OVER ONE BLADE TIP AND ROTATE ENGINE
BACK WARDS UNTIL THE FOLLOWING BLADE IS AT THE EIGHT O'CLOCK POSITION
AND THEN PLACE SECOND BOOT OVER THE TIP ENSURING THAT :-
A) BOOTS CENTRALLY POSITIONED AROUND BLADE TIPS.
B) ROPES PARALLELED (NO TWISTS)
c) RUBBER SLEEVE (1) LOCATED FIRMLY AGAINST TRAILING EDGE
OF BLADE (B)
D) RUBBER SLEEVE (2) LOCATED ABOUT 2 FT. FROM LEADING EDGE
OF BLADE (B)

LAY OUT REST OF ROPE IN STRAIGHT LINE TOWARDS THE PORT OF THE AIRCRAFT.

YOU ARE NOW READY TO START, TO CHECK 'All CLEAR' DOOR SHUT, STEPS AWAY
ETC.

WITH THE PILOT IN THE COCKPIT, MAN THE ROPE WITH, PERHAPS, THREE PEOPLE
PLACED
COMFORTABLY HOLDING THE ROPE WITH A SLIGHT SAG IN THE MIDDLE,

THE PILOT NOW SWITCHES IGNITION 'ON', BOOSTER PUMP 'ON' AND, AT A GIVEN
SIGNAL THE ROPE 15 PULLED THROUGH WITH A JERK AND, IMMEDIATELY THE
ENGINE FIRES THE PILOT OPENS THE MIXTURE CONTROL AND FLICKS THE PRIMING
SWITCH IF NECESSARY.

SHOULD THE ENGINE NOT START ON FIRST PULL, REPEAT PROCEDURES FROM D)
ENSURING THE IGNITION SWITCHES ARE 'OFF' WHILE THE PROPELLER IS BEING
HANDLED.

CAUTION:- To AVOID POSSIBLE FLOODING ETC.; RETURN MIXTURE CONTROL TO
‘IDLE CUT-OFF’ AND SWITCH OFF BOOSTER, AS SOON AS IT IS REALIZED THAT
THE ENGINE HAS NOT STARTED.

[BackPacker]

FWIW: before cold starting a Rotax 4-stroker, I was taught to check the oil level by opening the reservoir, then rotating the prop by hand until hearing from the reservoir a noise like flushing the loo, then apply the dipstick. But other pupils started the engine for a minute, then stopped it to check. Not sure which is best, likely it is the most troublesome...
When hand-turning the prop, it has to be done counterclockwise (as one looks at it) otherwise air might be sucked into the oil circuit. That's to say, if my dusty memory is to be trusted.

This is true but has nothing to do with the original thread.

On the Rotax 4-stroke (912/914) there's a separate oil reservoir but there's no pump between the sump and this reservoir. Instead, blow-by from the cylinder gases past the piston rings provide pressure in the crankcase to push the oil into the reservoir.

To ensure that all oil has returned to the reservoir, so that you can take an accurate measurement of the oil level in there, you hand-turn the prop slowly (with the ignition off, obviously). The hissing sound is the piston blow-by, and the burbling sound means that all oil has been pushed back. What you're hearing is the crankcase air burbling in the oil reservoir.

Starting the engine for a few seconds would work too, but only if you are absolutely sure that there's oil in the engine/reservoir to begin with. And that was the purpose of the pre-flight wasn't it?

[easy307]

More info on Hydraulic lock..

Air Accidents Investigation: Hunting Percival P56 Provost T1, G-AWVF (http://www.aaib.gov.uk/publications/bulletins/october_2010/hunting_percival_p56_provost_t1__g_awvf.cfm)

[austerwobbler]

As well as checking for hydraulic lock and then for sucking in fuel it has the added benifit of priming the engine with oil if it has not been run for a while, also it give's you the chance to manually asess what the compression's feel like and if they are fairly even.

Austerwobbler
" no starter, suck in fuel by hand every time by hand" :ok: