Why are Radial Engines so Hard to Start.

[nomorecatering]

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 (http://www.youtube.com/watch?v=kmFJ08E0l1k&feature=related)

[Old Fella]

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.

[ampclamp]

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.

[Yamagata ken]

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

[WHBM]

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 !

[STBYRUD]

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

[Machinbird]

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.

[twochai]

Why are Radial Engines so Hard to Start.


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.

[Peter Fanelli]

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


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

[rotornut]

Even a newly built IO-360 can be difficult to start

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.

[barit1]

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.

[plt_aeroeng]

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.

[plt_aeroeng]

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.

[boofhead]

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.

[EW73]

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

Cheers,
EW73

[SNS3Guppy]

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.

[barit1]

There's a series of Youtube videos about starting a R-985 after storage - see:
YouTube - Starting a Pratt & Whitney 985 Part 1 (Intro) (http://www.youtube.com/watch?v=YV-J_t0khLQ&playnext=1&list=PL8C17C82DE8A93880)

...then look for others in the series.

[Peter Fanelli]

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

2d4HQ8ZM_2k&feature=related

[rotornut]

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?

[Flash2001]

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!

[411A]

Why are Radial Engines so Hard to Start.

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.:}

[stevef]

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. :)

[SNS3Guppy]

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.

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.

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?

The same way one preheats any aircraft engine.

[MarkerInbound]

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



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.

[Yamagata ken]

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? http://img413.imageshack.us/img413/7391/fa18386sspitfirevb.jpg

[Old Fella]

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.

[Flash2001]

Gup

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

After an excellent landing etc...

[Shaggy Sheep Driver]

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!).

[Agaricus bisporus]

http://i213.photobucket.com/albums/cc189/agaricusbisporus/Confederate%20Air%20Force/CAFslides-04.jpg

Wiil it? Won't it?

http://i213.photobucket.com/albums/cc189/agaricusbisporus/Confederate%20Air%20Force/CAFslides-10.jpg

Crank it! Crank it!

http://i213.photobucket.com/albums/cc189/agaricusbisporus/Confederate%20Air%20Force/CAFslides-03.jpg

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

[SNS3Guppy]

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.

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.

[barit1]

Shaggy Sheep Driver (re the M14P):
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.

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.

[barit1]

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:

[Agaricus bisporus]

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.

[barit1]

I'm amazed that any big engine is pulled through on the starter.

What's the alternative on this ship? (http://www.youtube.com/watch?v=s7t3KK_ywBA&feature=related)

[411A]

I'm amazed that any big engine is pulled through on the starter.

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.;)

[Speedbird48]

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.

[Mansfield]

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...

[DozyWannabe]

That's what I'd call (in software terms) a bad bug. (Microsoft would call it a "feature").

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. ;)

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.

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.

[Peter Fanelli]

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

[Caboclo]

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.

[Shaggy Sheep Driver]

Russian warbirds could be a bit "agricultural",

Part-owning the Yak taught me a lot about Russian aeroplanes. They are not 'agricultural', just 'different'. The Yak was superbly and very cleverly engineered, designed with a different but not inferior mind-set to western equivalents. I had a great deal of respect for it as an aeroplane; the more I flew it and got iinvolved in maintaining it, the greater my respect for Russian aircraft design and engineering.

And one has to bear in mind the operating environment it was designed for. Not the UK flying club scene, but the Russian Air Force. Mechanics would do all the preparation for the pilots, and mechnaics would be standing by with fire extinguishers during start.

The U/C didn't fully retract, and the prop was wood, so if young student Ivan forgot the gear on final, the prop snapped and saved the engine, and the aeroplane still ran along the ground on the main gear and the tail skid. Jack it up, change the prop, and go flying again! In Russia. Not in the west, where a shock-load strip would be insisted upon.

[Old Fella]

I think most of us posting here understand that the engine is "pulled through" by hand before any attempt to start an engine which has stood for any time. Counting off the blades before introducing ignition is simply a means of clearing residual oil.

[SNS3Guppy]

A Lycoming or Continental carburated engine will run very poorly lean of peak.

Not if you know what you're doing. A horizontally opposed continental or lycoming runs very well lean of peak.

In fact, one wonders why any multi-row radial in a taildragger doesn't also have the same oil-in-the-intake-pipe problem.

They do, just like any radial. Various run-arounds have been devised address the problem, but the bottom line is that in a radial, oil bleeds past the valve guides and eventually floods lower cylinders.

[osmosis]

What about the use of some of these smaller radials in military vehicles? I can remember my father telling us his tank had to be towed around prior to starting, an inconvenience he did not enjoy as I remember. At least some of these engines were mounted upright (horizontal crankshaft) and would suffer the same problems, correct? Also, if memory serves me, I remember seeing at least one laid flat (vertical crankshaft) in the engine compartment. If so, did IT lock too?

[SNS3Guppy]

Radial engines have been used in cars, helicopters and tanks, as well as other applications. Even on motorcycles, albeit for novelty. I've never flown or driven or worked on any of those installations, so I have no idea how they fare.

http://www.motorcycle-usa.com/PhotoGallerys/xlarge/JRL_Cycles_Radial_Chopper.jpg

I suppose the utility is limited only by the imagination.

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.

I flew ag for a number of years, including eastern block aircraft (PZL M18 Dromader). Eastern equipment is very utilitarian. They came with very spartan tool kits, and were largely very simple designs. On the M18, for example, lubrication of all hinge points was external; squirt oil from outside the hinge on flaps, ailerons, etc, and do it as part of the daily walk-around. If the bolt and hinge were dripping, they were lubed.

Their ASz-62IR motor was very tough. We mostly flew turbine conversions, but we also had a number of the radial powered airplanes.

In the ag world, radials have largely fallen out of favor; the weight is replaced by lighter, ore reliable, more powerful turbines, allowing ag airplanes to carry more, go faster to and from the field, and single airplanes to do the work of multiple airplanes. The Bull Thrush, with it's 1820, carried 500 gallons. The current Thrush 660, with it's Pratt PT6A-65 installed, carries nearly eight hundred without the spray booms.

Radial engines were the staple and maintstay of the ag industry for many years, and a lot are still in use on AgCats, Thrush's, etc. By and large, however, few of us truly miss having to sit up all night doing cylinder changes, constantly chasing oil leaks, burned and cut fingers from safetying bolts after replacing cam follower gaskets, or the deafness that came from flying round motors.

Operating round motors takes significantly more skill, attention, and effort than operating turbine engines. A lot of romance is tied to round engines, and they do have their charm. Set aside the glossy magazine shots and the excitement of the airshow, and they were loud, dirty, hot, tempermental engines that required a lot of love, support, and parts. Radials can be a lot of fun, they're neat to watch, and they're still very viable powerplants, but until one has spent the night covered in oil changing out a power recovery turbine or struggling alone on a cold ramp in the dark to get past the kidney sump to a bottom cylinder for a change, or fought 40 knot freezing winds on top of a rickety ladder that's lashed to the engine, in a snowstorm, while swapping jugs, one doesn't really appreciate the realities behind operating those motors.

[mike-wsm]

Here are some vids of the JRL radial bike being started and run on the Sturgis dragstrip:
YouTube - Cold-Starting The Radial Engine Motorcycle JRL Cycles Prototype (http://www.youtube.com/watch?v=fU_HYXOgbRw)
YouTube - JRL cycles at sturgis dragstrip radial engine powered motorcycle (http://www.youtube.com/watch?v=CXRic0X8aA0)
and here are some warbird radials being started:
YouTube - B-17, B-24, B-25 Startup and takeoff (http://www.youtube.com/watch?v=k_elvlp6yV8)
Enjoy!
.

[CISTRS]

Bit surprised that nobody has mentioned cartridge starters , trolley accs.....

[SNS3Guppy]

Cartridge starters get the engine turning, but don't keep it turning. Starting technique does that.

The rope trick might also be included, along with hand propping as methods of turning the engine over during the start (yes, it is possible to hand prop a radial), but none of these address the process of actually getting it started. Just turning it over.

There's far more to the start than simply rotating the engine.

[nevw]

Because of the technical knowledge required to start radial Engines, on some Aircraft poilots were not allowed to start them.:ok:

[Mannrice46]

Back in the 70s, i hauled auto parts around the eastern u.s. in a beech 18. I never had any trouble starting an r-985 ONCE I GOT THE HANG OF IT. heck, I didn't even know how a radial engine worked. I would look at it and wonder how those cylinders could work together to make the prop turn. I had no clue until one day I looked it up. For me starting was a matter of feel more than anything. As best as I can recall, the printed matter said Don't pump the throttles, but I always pumped the throttles and I believe most everyone else did too. Nothing scientific. You just had to get the hang of it. That's my two cents worth. Mannrice46

[Centaurus]

Because of the technical knowledge required to start radial Engines, on some Aircraft pilots were not allowed to start them

The Convair 440 had P&W R2800 engines. They could be difficult to start especially in cold weather. I saw one catch fire after two Royal Australian Air Force maintenance engineers with almost no experience on starting the R2800 tried to start the engines. Here is the story, suitably edited for length:-

Quite unrelated to the preceding events was another incident involving a Convair fire on start-up; this time at Canberra where I was scheduled to conduct a period of dual instruction on a new pilot to the squadron. As explained earlier, the R2800 engine was difficult to start particularly in cold weather.

The pre-start throttle setting was critical and if too much throttle was set, extremely loud back-firing occurred and would continue until the offending throttle lever was pulled back. The starting technique included running the engine on prime fuel alone until reaching a certain RPM, when the mixture control was slowly moved out of the cut-off position. Once the mixture cut in the engine would momentarily lose RPM and it was important to release the primer switch at that instant. Failure to do so would result in an over-rich mixture with a guarantee of an exhaust fire.

Because of the complicated and quite critical starting procedure, pilots were given at least twenty practice starts before being signed off as competent to operate the engines. Not so the RAAF ground staff, who were lucky to be shown two starts before being cleared for solo engine runs.

Arriving at the Convair on the tarmac I was surprised to see three airmen boarding prior to an engine run. One of the airmen was “Taffy” an electrical fitter whose job today was to adjust the generator output of the engines. The other two were engine fitters with one being given his first dual exercise on engine starting. I watched with interest and then some alarm as the starboard propeller turned slowly and the engine caught with a huge backfire that reverberated between the hangars.

Hands could be seen in the cockpit as switches were selected and the port engine started. It died – started again with a series of backfires then died. To my consternation a long flame shot out of the open cowl flaps at the top of the engine and then it was on for young and old. On the ground a fire-guard quickly moved his wheeled fire extinguisher towards the now slowly rotating propeller while at the same time another airman warned him to stay well clear while the prop was turning.

In the cockpit the supervising engine fitter directed his student to keep the propeller turning in the hope of blowing out the fire. He failed to notice his student was still actuating the primer switch and feeding the fire. ATC saw the fire and sounded the emergency siren and fire engines set forth from the other side of the airfield.

With the fire still erupting from the cowl flaps, the supervising engineer called for Taffy the electrician to open the hydraulically operated door. I could see Taffy’s white face pressed against various windows as he ran up and down the cabin in fear. With Taffy having panicked at the sight of the flames, the engineer was forced to leave the cockpit to open the door himself. Meanwhile the student engineer kept his fingers on the starter switch and the primer.

As the air-stairs touched the tarmac I raced up the stairs only to be knocked flat by a gibbering Taffy bounding down the stairs to safety. Having managed to regain lost dignity I again headed for the cockpit and saw that the mixture control was in the forward or rich position and the student was still toggling the primer switch. I told him to stop priming and cut the mixture control – which he did. The fire went out almost immediately and apart from scorching of the cowl flaps there was no damage. The fire crew were quite disappointed that they weren’t needed.

Hearing the commotion Squadron Charlie "X", the squadron engineering officer, arrived puffing on to the scene and immediately laid charges on both engineers for dereliction of duty or whatever the official term was. I thought that was unfair since it was clear that neither airman had received proper dual instruction on starting Convair engines. Certainly they were qualified to start the engines of the squadron Dakotas, but no way were those engines comparable to the big R2800’s of the Convair 440.

Later over a beer I suggested he drop the charges against his airmen but he stubbornly refused. I tried another tack and asked if he himself had started a Convair engine and he hadn’t. I then suggested he should at least be qualified before hearing the charges which he himself had initiated otherwise how could he prove dereliction of duty when he did not know that duty himself?

I suggested he should carry out a couple of engine starts under my supervision and he went along with that. The following day I was due to fly the same Convair, so Charlie and I took our seats and I showed him the multi-fingered switching technique. Looking out of the cockpit window I noticed the fire-guard in position near the wing was the supervising airman under charge. Charlie tried to start the first engine and rocked the hangars with a series of loud back fires. He had set the throttle just a bit too wide At each backfire I could hear the sound of cheering and glancing outside there I saw a crowd of airmen clapping their hands and cheering at each explosion. The fire-guard winked at me from his safe position under the wing.

Charlie had the same problem with his next attempted start and this time he saw his men cheering. After I manage to convince him that his men had never been given a course of dual instruction on engine starting and had been learning on the job, he realized it was his own lack of supervision of his ground staff that had led to the current situation. The next day, all charges against the two airmen were dropped. It was a happy ending, more so when a six pack of beer from the airmen was left at my locker in the crew room

[North Shore]

R2800 on a CL215(as best as I can remember) Cold: Mags off, throttle closed, mixture ico. 12+ blades on the starter, mags on, 'tickle' (on-off-on-off etc..) the primer while advancing the throttle, and holding the starter engaged ( a third hand helps here!) Once she catches, primer on full, adjust the throttle to a decent idle (~7-800 rpm? IIRC) once that is settled, mixture rich, and primer off. lean out the mix a little to reduce plug fouling.

Hot: mags off, throttle open to the control lock gate, mixture ico. 6 blades, mags, tickle while closing the throttle, etc...

[Uplinker]

But in answer to the question "why are radial engines so hard to start", well that is because most old aircraft piston engines are essentially very crude machines. The conditions of mixture and timing etc of a piston engine have to be guessed at by the person starting them, or using their experience as to what is about right. There are no measurements to give direct feedback as to whether the person is getting this right, and only backfiring, exhaust fires and lack of ignition to indicate when they are getting it wrong! Also the carburettors, valve clearances and piston ring sealing are less than optimum until the engine has reached operating temperature and run for several minutes. So the cold, crude aircraft piston engine is a right difficult bugger.

Modern car engines have very sophisticated engine management, ignition and fuel control systems which analyse, adjust and optimise engine settings hundreds of times each second. They have fuel injection and knock sensors and exhaust analyser probes to optimise the mixture and ignition timing and they have hydraulic tappets to give near perfect valve clearance. All of this makes them extrememly reliable and dependable. I am old enough to remember the 'dawn chorus' of people in the street trying to start their crude, low tech cars in the winter in the 1970's. You had to know the knack of jiggling the throttle, and the choke (and in some cases the timing) to get the damn things going. I mean, they had a physical mechanical switch to operate the coil circuit to produce the ignition sparks, and the timing was adjusted with a vacuum device that physically moved the switch to advance or retard the ignition!! You had to be sat in the car so that you could operate all the variables just to get the engine started. Nowadays, You don't even have to be in the car - just turn the key to start the engine and the ECU does everything for us and to a much higher accuracy than we can. Modern electronics has made this possible.

[riff_raff]

That's it in a nutshell. The old air-cooled radial aircraft piston engines were hard to start because they had low compression ratios, and crude fuel and ignition systems.

Ever notice how the engine in your new car immediately starts and idles smoothly just after turning the ignition key?