radial engines

[Desdamona]

What are the advantages and disadvantages of radial engines?

 

[flywithastick]

advantage - sound better

disadvantage - leak a lot of oil

seriously...

advantage - dynamically they probably have an advantage (vibration, mounting issues, etc) since the length of the engine is short as compared to the number of cylinders. Shorter crank handles operating loads better & will be lighter. Multi bank radials cram a lot of cylinders in a fairly short distance (reduced bending moments at the eng mount - similar to first item).

disadvantage - lot of profile drag, oil collects in the bottom cylinders causing possible damage if not cleared when starting, a little more difficult to route exhaust manifold, plug leads, etc around the engine, round profile not quite as suited to the generally oval profile of most planes (getting weak).

 

[00Dog]

They don't have the reliability of turbines and they aren't as aerodynamic as flat engines.

 

[pilotyip]

Run better when damaged

I believe because they have more cylinders, they can take more internal damge and continue pumping out power, I have had to shut 4 radials in about 1000 hours of radial flying. Only one was a complete failure, in the rest the engine was still running and I made precautionary shutdowns

 

[avbug]

The last season I spent in the 4Y, in four months I shut down five engines...over about a 50 hour period. Typical.

Then again, I've gone almost a hundred hours without shutting one down...once.

Radial engines have their place, but do not match turbines for power, reliability, maintenance frequency, vibration, etc.

The origional idea of the radial was to increase power in a piston engine with a minimal increase in weight, while retaining adequate cooling. The engine is short compared to an inline engine. Harmonic vibration issues created along longer crankshafts are not nearly the issue.

Someone mentioned vibration being a benifit of the radial...if you consider an increase in vibration to be a benifit, then yes, it is. Otherwise, you're stuck with a lot more airframe stress when running a radial engine. This is especially true if everything isn't running perfectly. Foul a plug, you have vibration. And so on. I've seen 3350's break their mounts, and 2600's crack of their prop governor housing assembly. I had two runaway props due to vibration breaking and shorting wires in the cannon plug to the prop governor.

Radials like to catch fire, some more than others. The 4360 seemed to like it a lot. So did the 1820, and 3350.

Radial engines are loud, and burn a lot of oil. I typically serviced each engine with 3-6 gallons of oil per flight hour.

I have lots of late-night experience changing cylinders from a ladder in the rain, being consumed by mosquitoes, and eating pizza that is wet and tastes like 60 weight oil and avgas. I also have a lot of clothing that has stains from 60 weight oil all over it.

You haven't lived until you've oiled your airplane in high winds using a 5 gallon bucket with a funnel and a ladder, and end up wearing half the bucket, and drinking the other half when you get blown off the ladder. Or burned your hands on hot exhaust stacks changing out gaskets and seals during a working day.

Radial engines are large, and heavy. With one only a couple of exceptions, they're old, and parts are no longer manufactured, but reconditioned.

With respect to piston engines, they're quite efficient in terms of what they can do for their size.

Folks will talk about how one could blow a jug and keep on flying, but those folks never owned one, or had to work on one. I've certainly never continued to operate one after it started banging; I shut them down right now. I've had jugs come off, pistons burn through, sucked valves, disintegrated superchargers and supercharger clutches, failed inductions, carburetor failures, propeller failures and governor failures, fires, etc. In each case, I shut them down, except one. In that case, I had a governor base rupture on #4 and a supercharger die on #1. I shut down the governor rupture due to excessive oil loss and a fire hazard, and kept #1. I flew to the next stop, replaced the governor base and assembly, and then departed on all four, shutting down #1 for the remainder of the flight.

The advantages are that you may be flying an airplane with radial engines, and those are what you've got. They keep you aloft.

That, and a radial engine certainly sounds better...unless you happen to live at the airport and need to get some sleep.

Radial engines do NOT take abuse well.

Radial engines are geared engines in most all cases, and demand a lot more respect. Cooling issues may be more critical in many cases, as well. Radials are not as tolerant of abusive power or operating techniques. A great deal more backlash is found in them, and these engines should be operated most all the time at power settings adequate to keep the slipstream from driving the prop. Radial engines are prone to hydraulic lock, something far less common in other types of engines, and rarely heard of in turbines .

 

[Tri-holer]

Avbug

While certainly not first-person experience, my Dad flew Skyraiders for the Air Force during the Vietnam war. He has related many stories of guys coming home with jugs of their 3350's blown off.

I am sure the thought of shutting it down while it was still running and deep in indian country never entered their minds.

He also talked of the reliability of those engines - such as punching through a thunderstorm with rain so heavy that there was a whirlpool on the floor draining into the stick well. Never skipped a beat.

Admittedly, the modern turbine engine can't be beat but those old engines certainly did the job.

 

[avbug]

Triholer,

Single engine ops are a little bit different ballgame. So are military ops. If I were somewhere I didn't care to build a summer home, and blew a jug, I'd be for running it until it wouldn't run any more, too.

The heaviest rain I ever saw was in a radial powered airplane, and it didn't miss a beat (did have to adjust the carb heat, however). The rain was in Florida, and was heavy enough I couldn't see my inboard engines. I've never seen rain that bad before, or since. I do recall thinking about the thermal effect on the engine, at the time. That much water running over the cylinders, cooling them unevenly, and no cracking, no apparent adverse affects. I never did understand that. The R-2600 was a tough engine, when it was running.

It was a really tough engine, when it wasn't.

 

[Desdamona]

Thanks for all the info. I get the impression that sounding really cool might be outweighed by maintainance issues and operating costs? Guess I'll have to look for something more practical

 

[tdvalve]

I've got about 5000 hours of being pulled thru the air by radial engines. Everything from 985's on Twin Beeches to 3350's on Connies. Had two engine shutdowns during that time. One was due to a broken crankshaft on an 1820. That one quit without warning and the prop wouldn't feather. The other shutdown was on a 3350 that had swallowed a valve. It was still producing power, but we elected to shut it down before it started making metal.

 

[avbug]

Desdamona,

TDValve touched on something important, indirectly. The way in which the engines are operated makes a very big difference. Two engine shutdowns in five thousand hours is quite remarkable for radial engines, but it makes a point. Engines which are being operated consistantly and held at constant power settings for long periods of time will surely (as a rule) outlast engines that are constantly being jockeyed with big power changes and flying at extremes.

My summer boss flies behind radials in single engine airplanes, as do many friends, and hasn't had hardly a lick of trouble. His father has spent a lifetime behind them, mostly on singles, and the same holds true.

An airplane being operated in a point to point type condition, flying from A to B with reasonably constant power settings and small changes, will most always last a whole lot longer.

Is the sound worth it? I dunno...My bike is a ricemobile because while I appreciate the "Americanness" of Harley, I can't stand the noise (can't afford the noise, either... ). The experience certainly is. You need to have an attraction to that sort of thing. If you're the sort who sees a beaver on floats and suddenly finds himself or herself short of breath with a quickened heartbeat, then certainly flying behind a radial engine is worth it. If you're wanting to push on to a job in a 737, it's probably worth it for the entertainment value...but may not necessarily be your cup of tea.

I was sitting on the ramp one morning with a senior captain, with a few moments of quiet. It was early, the sun just beginning to rise. Across the ramp I spotted a DC-3; tired, but sitting hopeful with nose in the air. I commented that I'd trade spots in a heartbeat. He looked in the general direction and commented that the Citation X there would be okay. No, I said. The Doug. The what? The Douglas. The DC-3.

Oh, he said. Hadn't even noticed it. Wouldn't have even seen it if I hadn't pointed it out. Different strokes to different folks; he saw what he wanted to see, and so did I. If you want to fly a radial powered airplane, then do so; in my opinion, you won't regret it. I love everything about a radial engine, including the times it makes you sit up and open our eyes wide, and the greasy burns from safety wire cuts and avgas while working on them. Even the oil stained clothes have a certain familiarity about which I cannot complain.

TD, I didn't get to fly the Connie. I would love to have done so, however. Some airplanes just stand out as being shapes that draw you, like the sillouette of a woman, it turns your head. The GV is that way, as is the Beech Staggerwing. Every bit as much, the Connie to me is a timeless airplane...one of these days I'd sure like to fly one.