Why are Radial Engines so Hard to Start.
 

In this video of some P-47 Thunderbolts starting up, they pilots seem to have a devil of a time getting them started, and even after thay start the have a propensity to quit.

As well, they often admited puff of smoke after about 30 seconds. I know radials are smokey after on startup, oil pooling in the lower cylinders etc. But why the puffs?

It also seems that the Merlins on the Mustangs start up and go much like a modern engine.

Thoughts anyone?

YouTube - P-47 Start-up

Radials hard to start
 

It is a long time since I had anything to do with a Radial, however it is not so much a problem starting the engine but rather that they are rotated through several revolutions before introducing ignition to ensure that any remaining oil in the lower cylinders is purged before actually firing up. We used to count off the blades before selecting the ignition switches to ON. The puffs of smoke are simply small pockets of oil getting past the rings while the engine is cold and clearances greater than when normal operating temperature is reached.

My experience is with old pratts and curtiss wrights.
Cranking the thing thru so many blades to clear the oil and lower the risk of blowing the heads off then tickling the primer balancing the throttles and the ignition.Been many many years but it was an art form to get them started without stalling it, over priming, under priming ignition to early blam fart bang crash ...The risk of fire was pretty high too!

I guess it is mainly the oil issue with dirty plugs.They sound a bit clunky until the boost kicks in too. cant beat the sound of big piston engines when going full noise.

The oil problem was hydraulic locking, and therefore not an ignition issue ne'st pas?

Radials tend to be technology 60 years old and more.

What you are maybe overlooking is that at that time and before, almost ALL reciprocating engines were hard to start. On road vehicles the first diesels were such a nightmare that truck and bus operators (the early advocates of them) would tend to leave them running all night if they could. Early railway diesel locomotives were likewise.

I you've ever tried to start a petrol lawnmower after winter storage, or to get an old car going with a crank handle, you'll regard radials as a cinch to start !

Even a newly built IO-360 can be difficult to start (might be because the design is decades old... ;) )...

Part of the starting issue is that to get a reciprocating aircraft engine to start, you have to get the mixture into a runnable range without the benefit of modern digital technology. ;)
To get a reliable start, normal procedure is to start either too lean or too rich and transition to the opposite condition and if the ignition system is working, you will get a start somewhere in the middle. With big radials, a start near the lean condition will often cause a damaging backfire, so it is usually better to start from the too rich condition and transition towards lean. At least that is what we did in the T-28 and C-1A if I remember correctly. On the R-1820 we were supposed to turn the engine over by hand first before attempting to use the starter to avoid the oil hydraulic lock problem and resultant blowing off the cylinder head.

Because starting a radial (or most any other reciprocating engine) required the operator to have some "feel" for the machinery, something severely lacking amongst most of those those weaned on Nintendos.

Nope, it's because people don't know how to start them.

I agree. However, my old Hughes 269B with an IO-360 had a throttle that a bit more resistance just after you opened it. When you twisted the throttle you could feel a slight bit of resistance at which point you pushed the starter button. It never failed to start if you followed this procedure.

If someone had put an impulse magneto on a radial it would be a pussycat to start. Actually the R-985 is not bad to hand-prop - I have a treasured video of my Dad (age 70+) propping one.

Starting large radials
 

In the dim past I flew a 4 engine a/c which had Wright R3350 engines, which are similar to those on the P47. The R3350 had oil seals in the supercharger which did not seal properly until there was significant oil pressure. Consequently, there was always a large puff of smoke on start.

It's also true that large radials, due to the less controlled cylinder/head temperatures (compared to liquid cooled engines) had larger tolerances between moving parts, and this led to more oil getting past the valves and cylinder rings. For the R3350, acceptable oil consumption in flight was 3 gallons per hour, although we would not normally see more than 1. Our aircraft had 80 gallon oil tanks per engine.

As for being hard to start, I don't have any recollection of that, at least in summer temperatures. Arctic conditions are a different story, and starts were always sporty there, even when we had taken precautions. There is a reality show running called "Ice Pilots NWT" which features a Yellowknife based airline operating WWII transports. The frequent starting issues shown on that show seem realistic.

Merlins, BTW, were no easier to start in the Arctic. They do at least have the advantage of a wonderful sound when running.

Postscript:

Winter starting required huge amounts of prime, which led to exhaust flames up to 20 feet long. This led to some complacency about flame on start up. One pilot of my acquaintance had an event during which the intercom equipped ground crew monitoring start was saying, for some time "torching.. torching.." upon which the captain looked at the engine and replied "Torching my a**, that engine's on fire" - at which point the ground crew dropped his fire extinguisher and left the scene! Crew had to use the on board engine fire extinguisher.

Just this week a student had trouble starting the 985 in a Beaver. He tried twice but it would not catch. It was pretty cold so I told him to prime again and give it another go. He primed, turned on the starter but still no joy. The prop came to a complete stop, he looked at me as if to say "what do I try next?", when the engine started, all by itself, no starter engaged.
Great old engine.

Hey..Old Fella...I think the number was 9, wasn't it!

Cheers,
EW73

I've operated mostly R985's, R1340's, R2600's, R3350's, and R4360's. Smoking on start is due to oil, primarily in the lower cylinders, but also due to excessively rich mixtures and a lot of unburned fuel initially passing through the engine.

Unlike a turbine engine in which one or several burner cans can typically be lit at the same time and easily, the radial engine may have 9 to 28 cylinders to individually light off.

During the start process as prime is applied, it's dumped into the supercharger as raw fuel, slung around the supercharger, and dumped into cylinders. Even in a small piston engine, mixture isn't consistent from cylinder to cylinder, and the mixture needs to be within an easily ignitable range for the cylinder to fire. Too rich or too lean, and it wont' fire. During start when airflow is low through the carburetor, establishing a consistent mixture is compounded a lot more for each of the cylinders on the engine.

The spark plug in each cylinder needs to be able to fire, and plugs that are fouled with lead or oil tend to fire weakly or not at all. The end result is that some cylinders will fire while others won't.

You may have noted that some radials tend to catch fire on start more than others. This is partially due to starting techniques, and partially due to the construction of the engine itself. Particularly in the case of cold weather starts, large amounts of prime are sometimes used, and improper starting techniques can result in a lot of gasoline and fires. On some motors, we would have five gallon buckets under the engine during the start to catch fuel pouring out of the supercharger drain, as the technique involved flooding the engine then starting it off the mixture.

Unlike "modern" horizontally opposed recip engines, the radial offers a fairly poor induction distribution system with respect to establishing a consistent mixture at each cylinder. This is more pronounced at start. The first few blades (counted as blades passing a given point, by whomever is turning the starter on a particular airplane) are done with ignition off to clear the engine, ensure no hydraulic or liquid lock (particularly in the bottom cylinders), and to begin drawing fuel into cylinders (eventually); the initial part of the start looks slow to an observer because the engine is being turned through a number of revolutions before the start actually begins. In some cases, this is done by hand to protect the engine, but in most cases it's done with the starter to protect the engine (because the starter clutch will slip before bending a connecting rod in the event of a hydraulic lock). The particulars depend on the engine and the operator practice.

Once fuel and ignition is introduced, each cylinder must be individually awakened. This isn't necessarily a fast process. Whereas there's a lot of mass for the starter to turn over, it doesn't happen quickly, the mags aren't turned rapidly, and mag points don't open rapidly at first, and spark isn't necessarily as hot. Plug fouling and inconsistent mixture mean that each cylinder will "wake up" at a different moment, and enough cylinders need to be firing (and firing consistently) enough to keep the engine turning. The result is that the engine tends to lope and cough on start, belching smoke, often banging and after firing (and in some cases, undesirably, backfiring (the difference between burning through the exhaust or through the induction; a backfire can separate induction tubes and cause an engine fire, whereas an after fire does not).

Starting some radial engines is part science, part art. The start can vary, depending on how much oil is in the cylinders. Some engines can be dry consistently, and then one start be locked or wet ("wet," with a radial, can be expressed in terms of both excess fuel, and oil) on the next. Some engines can sit for months and never liquid lock, while others can sit for five minutes and have hydraulic lock problems, or oil pooling in the lower cylinders. For some radial engines, especially in cold weather, starts can be more art than science.

There's a series of Youtube videos about starting a R-985 after storage - see:
YouTube - Starting a Pratt & Whitney 985 Part 1 (Intro)

...then look for others in the series.

I don't know, I think the sound of a big radial waking up one cylinder at a time is way better than a merlin.

And of course sometimes they'll just start right up fine.

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?

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.

After an excellent landing you can use the airplane again!

Hmmm, I never thought they were so hard to start, and I've started plenty of 'em over the years.
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. :)

Oil dilution doesn't "reduce starting torque," but reduces oil viscosity by thinning with avgas. This allows for easier oil flow in the absence of preheating, during the initial start. Most dilution systems are deactivated or removed. Preheating and preoiling is always a better choice.

The same way one preheats any aircraft engine.

We did 9 for a warm motor and 15 for a cold one on 2800s. Thinking about it that doesn't much sense because it you will have gone through all the cylinders by 9 blades. Started the primer at 12, can't remember the number when they were warm. It's been a while.

http://img413.imageshack.us/img413/7...spitfirevb.jpg

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.

Gup

I sure does reduce the torque needed to turn the engine which was what I meant.

After an excellent landing etc...

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!).

"Biblical" Start on the CAF's B23
 

http://i213.photobucket.com/albums/c...Fslides-04.jpg

Wiil it? Won't it?

http://i213.photobucket.com/albums/c...Fslides-10.jpg

Crank it! Crank it!

http://i213.photobucket.com/albums/c...Fslides-03.jpg

Even after pulling through 9 blades there's gallons of the stuff still swilling around.

That's where knowing your aircraft becomes important. In some aircraft, use of the starter motor is ill advised, while in others, it protects the engine. Where the starter motor is used to pull the engine through, it protects the motor because if liquid lock is present the starter clutch will slip. This will not work with all starter installations or systems.

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.

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. :eek:

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.

What's the alternative on this ship?

Odd, I never had any problems, using the starter.
Standard ops, at the airlines where I worked...long ago.
Sudden thought...
Maybe...they just knew how.;)

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.

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... :D

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...

Er, that would be "undocumented feature" to be precise. Of course, Apple will simply tell you that there are no bugs in their software and you must be doing it wrong. ;)

Now now, Russian warbirds could be a bit "agricultural", but bearing in mind the whole country was effectively agrarian in nature as late as the 1920s I think they picked things up pretty well - in later years they certainly developed some interesting solutions to rocketry problems that the West relied on brute force to solve.

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.

:E

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. :ugh: 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.