Why are Radial Engines so Hard to Start.

[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]

Pulling through

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.



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]

Starting radials

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
YouTube - JRL cycles at sturgis dragstrip radial engine powered motorcycle
and here are some warbird radials being started:
YouTube - B-17, B-24, B-25 Startup and takeoff
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.

[Mannrice46]

Radial engines hard to start

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?