Why are Radial Engines so Hard to Start.
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Why are Radial Engines so Hard to Start.
R3350's both turbocompound, and otherwise.
A few R4360's (Boeing Stratocruiser)
Many R2800's (DC-6B's)
R1830's (DC-3's)
Of course, I didnt start them in -40C, either.
Liquid locks (hydraulicing) in radials... you can never be too careful. Nine blades by hand in the normal direction of rotation on a DC3 to make sure it was OK to start. Only ever encountered a liquid lock when an engine hadn't been turned for a few days or more. No problem - remove lower plugs and move the prop until all the oil was out.
However... used to maintain an Antonov An2 (ASz 621R engine, a metricated version of the Cyclone) - turned the engine by hand as per normal for the first start of the day and attended to some other issue for ten or fifteen minutes. Jumped in, started up (inertia starter), engine fired and a couple of seconds later stopped dead with such force that I felt a wing lift (a lot of stored energy in that huge four-blade prop).
Sick feeling - took lower plugs out and watched a small stream of oil run from one cylinder. Never did find out the reason. Blown supercharger seal maybe... Replacement engines from Poland only cost about $2,500 then so it wasn't that great a tragedy.
Re starting techniques, I knew a very experienced DC3 pilot who started in rich as a matter of course (as opposed to ICO in the book) and there was always a smooth result.
Can't beat that lovely clanking, burbling radial idle.
However... used to maintain an Antonov An2 (ASz 621R engine, a metricated version of the Cyclone) - turned the engine by hand as per normal for the first start of the day and attended to some other issue for ten or fifteen minutes. Jumped in, started up (inertia starter), engine fired and a couple of seconds later stopped dead with such force that I felt a wing lift (a lot of stored energy in that huge four-blade prop).
Sick feeling - took lower plugs out and watched a small stream of oil run from one cylinder. Never did find out the reason. Blown supercharger seal maybe... Replacement engines from Poland only cost about $2,500 then so it wasn't that great a tragedy.
Re starting techniques, I knew a very experienced DC3 pilot who started in rich as a matter of course (as opposed to ICO in the book) and there was always a smooth result.
Can't beat that lovely clanking, burbling radial idle.
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Some radial installations had an oil dilution switch to reduce cold weather starting torque and a boil-off procedure to restore oil viscosity after start.
How do you preheat a Merlin, or for that matter, any water cooled aircraft engine? Is there such a thing as a block heater for these engines?
Hey..Old Fella...I think the number was 9, wasn't it!
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Blade count
Hi EW73. It is more than 40 years since I was starting R1830's, R985's or Bristol Hercules engines, so I will have to take your word for the number of blades counted before introducing ignition, however I suspect you are spot on. As has been written by others it was always a bit of a juggling act getting the cranking, counting, priming and ignition all "in step" to get a smooth start. I don't recall any particularly dramatic events such as exhaust fires etc being a regular occurrence.
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I'm surprised some here say crank with ignition off to clear any oil.
I used to part own a Yak52 (Vendeneyef M14P 9-cylinder radial) and it was drummed into us to pull it though 10 blades by hand before starting. The M14P uses air start with an air distributer which turns the engine very slowly, but even that can damage the engine if it locks hydraulically.
Also, with those engines, if it's not run for more than a few days it's cowlings off and take out the drain plugs in the inlet pipes of the lower 3 cylinders. Oil can collect there and it won't come out by hand-pulling it through as the 'elbow' in those inlet pipes is below the level of the exhaust valves. So any oil stays there 'till start up, wherupon it gets sucked into the cylinder where it can cause a lock. If you are lucky, the engine breaks there and then and you get you wallet out. If you are unlucky you bend a con rod and the engine fails some time later, and somewhat dramtically, as the rod breaks in the air one day.
There was a recent tragic case of a Piston Provost engine failure in UK. One thing that was discovered in the investigation was that some Provots pilots had waggled the prop back and forth to get oil to run out of the exhaust before start. Problem with that was that it allowed some oil to drain into the intake pipes as the inlet valve opened, with catastrophic results on start up or later due a bent rod.
Starting the Yak was definately an art. A friend once described it as 'biblical'; lots of noise, lots of smoke, and the smiting of lesser aeroplanes that might be parked in the propwash! (OK, we did ensure there were none of the latter!).
I used to part own a Yak52 (Vendeneyef M14P 9-cylinder radial) and it was drummed into us to pull it though 10 blades by hand before starting. The M14P uses air start with an air distributer which turns the engine very slowly, but even that can damage the engine if it locks hydraulically.
Also, with those engines, if it's not run for more than a few days it's cowlings off and take out the drain plugs in the inlet pipes of the lower 3 cylinders. Oil can collect there and it won't come out by hand-pulling it through as the 'elbow' in those inlet pipes is below the level of the exhaust valves. So any oil stays there 'till start up, wherupon it gets sucked into the cylinder where it can cause a lock. If you are lucky, the engine breaks there and then and you get you wallet out. If you are unlucky you bend a con rod and the engine fails some time later, and somewhat dramtically, as the rod breaks in the air one day.
There was a recent tragic case of a Piston Provost engine failure in UK. One thing that was discovered in the investigation was that some Provots pilots had waggled the prop back and forth to get oil to run out of the exhaust before start. Problem with that was that it allowed some oil to drain into the intake pipes as the inlet valve opened, with catastrophic results on start up or later due a bent rod.
Starting the Yak was definately an art. A friend once described it as 'biblical'; lots of noise, lots of smoke, and the smiting of lesser aeroplanes that might be parked in the propwash! (OK, we did ensure there were none of the latter!).
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"Biblical" Start on the CAF's B23
Wiil it? Won't it?
Crank it! Crank it!
Even after pulling through 9 blades there's gallons of the stuff still swilling around.
Last edited by Agaricus bisporus; 30th Jan 2011 at 15:25.
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I'm surprised some here say crank with ignition off to clear any oil.
I used to part own a Yak52 (Vendeneyef M14P 9-cylinder radial) and it was drummed into us to pull it though 10 blades by hand before starting. The M14P uses air start with an air distributer which turns the engine very slowly, but even that can damage the engine if it locks hydraulically.
I used to part own a Yak52 (Vendeneyef M14P 9-cylinder radial) and it was drummed into us to pull it though 10 blades by hand before starting. The M14P uses air start with an air distributer which turns the engine very slowly, but even that can damage the engine if it locks hydraulically.
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Shaggy Sheep Driver (re the M14P):
That's what I'd call (in software terms) a bad bug. (Microsoft would call it a "feature").
But I guess that's what you expect in a monopolistic design environment - The good ol' USSR. Market forces would have starved this "feature" out of the system.
Also, with those engines, if it's not run for more than a few days it's cowlings off and take out the drain plugs in the inlet pipes of the lower 3 cylinders. Oil can collect there and it won't come out by hand-pulling it through as the 'elbow' in those inlet pipes is below the level of the exhaust valves. So any oil stays there 'till start up, wherupon it gets sucked into the cylinder where it can cause a lock.
But I guess that's what you expect in a monopolistic design environment - The good ol' USSR. Market forces would have starved this "feature" out of the system.
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In fact, one wonders why any multi-row radial in a taildragger doesn't also have the same oil-in-the-intake-pipe problem. Think about the pipes for the front row cylinders - they'd be able to collect a substantial amount of oil with the engine oriented a few degrees nose-up. 
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I'm amazed that any big engine is pulled through on the starter. The oil comes out of the big Pratts and Wrights so slowly that you'll pull through a couple of blades fairly easily and then it suddenly comes to a stop, and then you're heaving, or rather leaning on the blade as it moves ever so slowly as the oil pours out, then frees up for another few blades until it comes to the oiled pot again which pulls through with less resistnce than before and produces another run of oil, and the third time around (by blade 9 (or 12 on the '29) the resistance is pretty even. Then you can try a start, but its going to be a while running on 8 or 16 before the fuel washes the plugs on the bottom pot(s) clean enough for to fire and its hitting on all cylinders. Music!
That old B23 covered visitors fifty yards away with oil spots on the start pictured, and they didn't half holler. In true Texan fashion they were informed that if they chose to walk behind an aircraft that was starting up what did they expect.
That old B23 covered visitors fifty yards away with oil spots on the start pictured, and they didn't half holler. In true Texan fashion they were informed that if they chose to walk behind an aircraft that was starting up what did they expect.
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I'm amazed that any big engine is pulled through on the starter.
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I'm amazed that any big engine is pulled through on the starter.
Standard ops, at the airlines where I worked...long ago.
Sudden thought...
Maybe...they just knew how.
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In day to day airline operations they would hardly have a chance to drain down to the lower cylinders, if the engines were in reasonable shape. After a week or so standing a pull though by hand was always the accepted way. When you meet resistance pull the lower plugs on that engine and drain it out. I don't recall having to drain any of them, but maybe ours were good engines.
We also seem to have forgotten the experience of the pilots on the P-47's etc. as at the begining of this thread. Not much!! You will also see on some WW2 films that the mechanic/fitter started the engine as the pilot ran to get in. The mechanic/fitter knew a lot more about starting the things than the pilots.
Speedbird 48.
We also seem to have forgotten the experience of the pilots on the P-47's etc. as at the begining of this thread. Not much!! You will also see on some WW2 films that the mechanic/fitter started the engine as the pilot ran to get in. The mechanic/fitter knew a lot more about starting the things than the pilots.
Speedbird 48.
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Barit1...I was trying to come up with a tongue-and-cheek answer having to do with how far up I could reach during the walk-around, but you have completely captured the thought... 
First lesson as a new copilot: it's fine to stick your head out the window when counting the blades, but before responding to the command from your left of "Switch on!", be sure to fully withdraw your head from the window frame...it is pretty hard to suppress the startle reaction to the backfire, and the window frame hurts...
First lesson as a new copilot: it's fine to stick your head out the window when counting the blades, but before responding to the command from your left of "Switch on!", be sure to fully withdraw your head from the window frame...it is pretty hard to suppress the startle reaction to the backfire, and the window frame hurts...
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But I guess that's what you expect in a monopolistic design environment - The good ol' USSR. Market forces would have starved this "feature" out of the system.
Also, what market forces give with one hand, they can take away with the other - such as discarding a cargo door failure in testing as irrelevant in order to beat competitors to market. We all know how that one ended up.
All this reminds me of an old Datsun I had once, a blown head gasket was allowing a cylinder to accumulate coolant during the day while I was at work. It would lock when cranked but the starter would push coolant out and back to...well somewhere and it would run fine for the drive home.
Got by with it like that for 3 weeks before getting a reman engine.
Got by with it like that for 3 weeks before getting a reman engine.
Speaking as a current DC-6 Flight Engineer, I would say most of the info here is true. I just have 2 small corrections.
Someone mentioned that radials would be easier to start with magneto impulse couplings. There are a variety of ignition systems used on the round engines, some work better than others. Eg, the R-2800s on the DC-6 will frequently start on the mag alone before I even touch the ignition boost. (That's why you leave the mags off while checking for hydraulic lock on the starter.) By contrast, our C-46s also run R-2800s, but with slightly different ignition systems, and they will not start without boost. In any case, the boost works just fine.
Second, the statement was made that the big radials have poor induction distribution compared to horizontally opposed engines. I believe it's the other way around. The proof is that the radials are regularly run lean of peak from the factory, even though they are carburated. A Lycoming or Continental carburated engine will run very poorly lean of peak. Even the injected flat engines require after-market balanced injectors to run lean.
Re # of blades, on an R-2800 with a 3 bladed prop, it takes 6 blades to complete 2 full revolutions of the engine and check each cylinder for hydraulic lock. Anything after that is for pre-oiling, particularly of the prop reduction gears. We use 15 blades for a cold start, 9 for a hot start within 1 hour at cold ambient temps, and 6 for a hot start within 1 hour in the summer. We never pull through the prop by hand, just use the starter. Don't seem to have many problems. The C-46s have a starter clutch to protect the engine, I don't think the -6s do.
As for whether or not a radial is hard to start, I guess it would depend on what you're comparing it to. Obviously, on a modern car with numerous sensors, and computers tweaking the fuel, air and ignition timing several times a second, you'll have more problems maintaining the electronics than you will getting it started.
On the old radials, there are numerous actions which must be taken by multiple people; when those actions are done correctly, the engine usually starts easily and reliably. When there are problems, you just have to guess whether it's too lean or too rich; that's where experience comes in handy.
Someone mentioned that radials would be easier to start with magneto impulse couplings. There are a variety of ignition systems used on the round engines, some work better than others. Eg, the R-2800s on the DC-6 will frequently start on the mag alone before I even touch the ignition boost. (That's why you leave the mags off while checking for hydraulic lock on the starter.) By contrast, our C-46s also run R-2800s, but with slightly different ignition systems, and they will not start without boost. In any case, the boost works just fine.
Second, the statement was made that the big radials have poor induction distribution compared to horizontally opposed engines. I believe it's the other way around. The proof is that the radials are regularly run lean of peak from the factory, even though they are carburated. A Lycoming or Continental carburated engine will run very poorly lean of peak. Even the injected flat engines require after-market balanced injectors to run lean.
Re # of blades, on an R-2800 with a 3 bladed prop, it takes 6 blades to complete 2 full revolutions of the engine and check each cylinder for hydraulic lock. Anything after that is for pre-oiling, particularly of the prop reduction gears. We use 15 blades for a cold start, 9 for a hot start within 1 hour at cold ambient temps, and 6 for a hot start within 1 hour in the summer. We never pull through the prop by hand, just use the starter. Don't seem to have many problems. The C-46s have a starter clutch to protect the engine, I don't think the -6s do.
As for whether or not a radial is hard to start, I guess it would depend on what you're comparing it to. Obviously, on a modern car with numerous sensors, and computers tweaking the fuel, air and ignition timing several times a second, you'll have more problems maintaining the electronics than you will getting it started.
On the old radials, there are numerous actions which must be taken by multiple people; when those actions are done correctly, the engine usually starts easily and reliably. When there are problems, you just have to guess whether it's too lean or too rich; that's where experience comes in handy.