Hydrolocking

[GyvAir]

I'm curious why an entire thread about a broken R985, hydraulicking and how to prevent and deal with it would have disappeared?

[Colonel Sanders]

Sigh. It doesn't really matter. What pilots need to
do is download and read the frikken P&W radial engine
operating manual.

Here it is: https://dl.dropbox.com/u/16541550/PWRadial.pdf

[Beefitarian]

Some things just magically happen here. Often there's no explaination so you have to guess what the reason might have been.

[GyvAir]

Sigh. It doesn't really matter. What pilots need to
do is download and read the frikken P&W radial engine
operating manual.

Here it is: https://dl.dropbox.com/u/16541550/PWRadial.pdf

Thanks for the link, CS. I'm all for reading the manual rather than relying on AvCanada pop quiz answers for operational or maintenance information. However, this particular manual didn't answer my question about whether there is any way for one to know they've over-primed a cylinder before they've bent a rod in the subsequent attempt to start the engine.

[Chuck Ellsworth]

However, this particular manual didn't answer my question about whether there is any way for one to know they've over-primed a cylinder before they've bent a rod in the subsequent attempt to start the engine.

Let me take a stab at figuring out this issue.

How long would it take the primer line to fill the cylinder with fuel to the point it hydraulic locks?

Assuming of course it is not a throat prime system.

[Sulako]

I'm curious why an entire thread about a broken R985, hydraulicking and how to prevent and deal with it would have disappeared?

OP wanted it gone, so it went away.

[GyvAir]

OP wanted it gone, so it went away.

Fair enough.

As for my question of how you would know if a cylinder was over primed... I can well imagine how it gets that way; I've watched people valiantly trying to prime an already flooded engine to life all too often.
I guess what I'm asking is whether there is a warning sign or indication that you've managed to fill a cylinder with fuel, other than the engine coming to a sudden stop or near stop as the laws of physics regarding the compression of fluids takes over?
Also curious, if you have bent a rod, is there a way of knowing it's happened before it separates and starts punching its way out through the side of the case?

[Chuck Ellsworth]

O.K. Lets look at this again.

If the engine is being over primed during the starting process it means the engine is being turned over.

There are four strokes during this process.

One of which is exhaust.

How can a cylinder hydraulic lock if the exhaust valve opens in its normal sequence?

So now back to priming and not engaging the starter.

How long would it take to fill the cylinder with that little primer line?

[Chuck Ellsworth]

The only way you might know there is a bent rod would be the noise it might make before it let go....you may have time to shut it down before it really comes apart.

It is really exciting if you have a supercharger fly apart.....really exciting.

[GyvAir]

Agreed, it should not be possible to hydraulic lock an engine with fuel if you start priming after the engine is already turning.

As for priming before engaging the starter, the amount of fuel required, if I've done the math correctly, would be about 22 cubic inches (that's a cup and a half) of liquid in An R-985 cylinder for the piston to run out of room to travel. That's assuming that to do damage the entire space remaining at TDC has to be filled with liquid.
In any case, that is a LOT of fuel, which is what I presume you are implying in asking how long you'd have to lean on the primer button or stroke the pump to achieve that.
Even having marvelled at the small lake of fuel I've seen some people dump on the ramp under a flat engine through over-priming, it doesn't seem likely that they'd pump the amount required to lock a cylinder (about a cup per cylinder for a 520 with a 7.5:1 CR), even with a blocked sniffle valve.

So, is hydrolocking an engine with fuel on start up a real thing?

[Beefitarian]

Do some of the very large radial engine aircraft have electic primer pumps? Leave that switch on for a while and you should be able to get your giant puddle.

I think you should wait a few seconds after priming an engine to let the fuel evaporate into a much faster burning state than a pool of liquid also.

[Colonel Sanders]

Even having marvelled at the small lake of fuel I've seen some people dump on the ramp under a flat engine through over-priming

Heh. Because 100LL evaporates so slowly -
and this is true in spades in the cold - you would
be amazed at the number of engines that like
to have fuel running out the bottom of them,
to get a successful start.

You would laugh as to how I cold start the flat
TCM IO-360 in the Maule. 8 seconds of prime
with the knobs forwards, check. Pool of gas
under the cowling, check. Knobs back, mags
off, pull the prop through 6 times to check the
compression and avoid locking. Push the
aircraft back to get the pool of gas ahead
of the engine. Climb back in, and it will start
on the first blade.

The continental starters are really cheesy, a
real maintenance problem - check the AD's -
and as such must be babied unless you like
to waste time and money on them.

I have had the puddle of fuel on the ground
underneath the cowling on fire more times
than you could imagine. Line boys run all
around frantically waving their arms in the
air, grabbing fire extinguishers, which is silly
because it will blow right out.

I now push the aircraft back after priming
to avoid people getting upset and hurting
themselves when the puddle lights off.

[Blakey]

Colonel,

There must be something wrong with your cold weather technique because it's almost exactly the same as mine for the 0-470!

I have three, slight, differences. I prime twice, once before the pull through of the blades and then again before engaging the starter. I also leave the primer out so I can feed her a bit more if she leans out after right after she starts. I always like to leave the prop just at the top of the compression stroke to give the starter a running start at the next cylinder.

Works well and I've never had to replace a starter.

Blakey

[2550]

I was always taught cold starting was about the worst thing you could do to a piston engine. A good preheat only takes a few hours of planning ahead....

[Beefitarian]

Yes 100LL is very volitile yet somehow can still hydrolock a cylinder.

I was always taught cold starting was about the worst thing you could do to a piston engine. A good preheat only takes a few hours of planning ahead....

I think he's talking about a 15 C cold start not a -20 C.

[Colonel Sanders]

cold starting

Yup! Down south here in eastern ontario, a
"cold start" is +10C

[Blakey]

Yes 100LL is very volitile yet somehow can still hydrolock a cylinder.

I was always taught cold starting was about the worst thing you could do to a piston engine. A good preheat only takes a few hours of planning ahead....

I think he's talking about a 15 C cold start not a -20 C.

I'm actually talking about starting, after pre-heating, in cold weather. I HAVE had to overhaul an engine so I'm a big fan of pre-heating. Lots!

[Beefitarian]

Ah, sorry.

I suspect when it's very cold there is more risk of a fuel hydrolic lock, since the cylinders may get to the point that the air in there gets saturated by fuel fumes and then it would be more likely for the liquid to start to gather. It used to be somewhat common in older cars and we called it "flooding".

[Rowdy]

It is really exciting if you have a supercharger fly apart.....really exciting.

I had the blower eat itself on a 985.. and can attest to that!

I always gingerly pull the prop through on cold starts with the 985 now. So generally, every morning.

If you know the feeling, You can certainly tell when a cylinder has some oil in it.. Have only once had to have the ame pull a bottom plug and drain it (engine near its TBO, eating lots of oil) and the machine had been sitting for about a week.

I havent heard of one of the rounds here locking with fuel, but I've seen it happen on one of the boosted auto engines...

[Chuck Ellsworth]

Do some of the very large radial engine aircraft have electic primer pumps? Leave that switch on for a while and you should be able to get your giant puddle.

They have fuel boost pumps that must be turned on to operate the primers.

You prime with the prime switch, and you determine how much prime you want by how long you hold the prime switch down.

Normal start for the P&W 1830 is fuel boost pumps on.

Engage starter and count twelve blades to check for hydraulic lock.

Mags on.

Hold down primer switch for about four seconds.....the engine usually starts using that method.

Once the engines are running you turn the fuel boost pumps off, and the engines will now run on the gear driven fuel pump.

[Siddley Hawker]

Voice from the back of the room...
Leave the primer unlocked and blip the boost pump a few times if you need a bit of extra prime to keep a cold Otter running.

[Mr. North]

Same works for the manual primer, although probably not recommended. On cold days after the initial prime I would have the primer handle out, full of juice, just to give an extra little squirt here and there to keep her rumbling. Once she's purring along I would very slowly push the primer down and lock it.

I sure miss flying radials. A lot more finesse involved compared to turbines and they sound better too!!

[GyvAir]

I used to prime more before cranking, but have found I have much better success cranking and priming at same time. Much less chance of flooding. Adding fuel when you already have airflow and compression, the fuel/air ratio should cross the sweet spot at some point as you start dumping it in with the primer.
Yes I do prime a bit before cranking when it's colder, but I never go for the puddle on the pavement anymore.

[pelmet]

Even having marvelled at the small lake of fuel I've seen some people dump on the ramp under a flat engine through over-priming

Heh. Because 100LL evaporates so slowly -
and this is true in spades in the cold - you would
be amazed at the number of engines that like
to have fuel running out the bottom of them,
to get a successful start.

You would laugh as to how I cold start the flat
TCM IO-360 in the Maule. 8 seconds of prime
with the knobs forwards, check. Pool of gas
under the cowling, check. Knobs back, mags
off, pull the prop through 6 times to check the
compression and avoid locking. Push the
aircraft back to get the pool of gas ahead
of the engine. Climb back in, and it will start
on the first blade.

The continental starters are really cheesy, a
real maintenance problem - check the AD's -
and as such must be babied unless you like
to waste time and money on them.

I have had the puddle of fuel on the ground
underneath the cowling on fire more times
than you could imagine. Line boys run all
around frantically waving their arms in the
air, grabbing fire extinguishers, which is silly
because it will blow right out.

I now push the aircraft back after priming
to avoid people getting upset and hurting
themselves when the puddle lights off.

Hmmm...thats interesting. I found the IO-360 usually really easy to start with the occasional difficult to start. In the end, I put the boost pump on high and opened the throttle until I got 60 lbs/ hour fuel flow and then it would usually start(I think that was the procedure from the manual. Frequently I left the boost pump on while cranking it over.

If I had a problem, I would intentionally overprime and then turn it over with the mixture in idle cutoff until it leaned out to the right fuel air ratio and cought and then put the mixture to rich. But I was surprised one time to see a bunch of fuel pouring out.

One worry was that I have read that overpriming leads to increased engine wear because oil is washed off the cylinder walls. Do you have an opinion on that Mr. Colonel?

Interestingly, I never seemed to have difficulty with vapour lock preventing a star as I have read can happen in hot fuel injected engines. Lycoming fuel injected on the Arrow....different story. What a pain sometimes.

[Colonel Sanders]

I have never found the Continental IO-360/520/550
difficult to start - though I should mention, some
people have. I still like to baby the starters on these
engines. Heck, I was just talking yesterday to a guy
with a TCM O-200 in a buck 50 and he had to rebuild
the bottom end after starter problems. Ouch.

The Lycoming IO-360/540 are a completely different
story. The starters are external to the engine and
have four bolts holding them on. Cheap and easy
to change. The very worst thing you can do to it
if you are a complete idiot is strip the teeth off the
ring gear and you can even change that by simply
pulling the prop. No need to tear down the engine,
like a continental.

And yes, I have had plenty of fun hot starting Lyc
IO-360/540. All worries of hydraulic locking and
babying the starter go out the window with these
engines on a hot day. If you let the engine heat
soak after landing - you can hear it hissing angrily
at you, like bacon frying under the cowling - it's
going to be a hot start. What I prefer to do is
point the cowlings into wind, open up the oil
access hatch, and go have lunch and let them
cool off. It's probably my age, but on a hot day,
I would prefer to hot start a fuel-injected Lyc
either within 2 minutes or after 30 minutes after
shutdown.