Large Radial Engines reliability.

[Guptar]

There are still a reasonable number of large radial engines being operated around the world, mostly on warbirds from DC-3 to B-29. It seems that most suffer from poor reliability of the engines even with them being looked after well and overhauled by some pretty good shops so it seems the engines are a little better maintained that during WW2.

So why the problems, of course if they were being operated at 3500Hp, however most are running at maybe 60% for takeoff etc. No power recovery systems in use and so on.

Are the overhauls using "new" parts that may have been made 50 years ago. I read recently that they tries a hybrid development on the last B-29 flying, mixing cylinders and crank cases from deferent versions of the engine in the search for reliability but with no luck.

Is there something I have missed or is it just engines of that size are so mechanically complex that something approaching reliability cannot be attained. I always thought that radials were inherently well balanced.

[SOPS]

I'm only guessing, as I am no expert in radial engines. But could it be that the things were developed to within an inch of their lives, and as such were inherently unreliable ?

[5th officer]

Good question Guptar, from my experience in Beavers and other radial engined aircraft, I suggest it may have a bit to do with the Pilot.
Radials require very careful engine management right from the pre flight (Oil in the lower cylinders) through to the shut down. I do not believe that current training methods teach the correct disciplines that we were taught when I first flew in the 60's.
I have always felt that a radial is a very robust power plant in the right hands or they would not have built as many as they did?

[LeadSled]

Guptar,

Engines like the P&W R-1830 and the Wright R-1820, overhauled to a high standard, and operated by competent pilots, are very reliable beasts, and, I would suggest, just as reliable as most blown flat engines.

As with all such engines, the engine handling is absolutely critical, and there are now lots of pilots around who, sadly, wouldn't have a clue and don't seem much interested in leaning.

No blown engine is just like another 0-200 or O/IO-320 or the like.

Tootle pip!!

[Walter Atkinson]

I have found radials to be quite reliable when operated properly. For example, the R-3350-TC-18 when operated ROP had a TBO of 600 hours. When operated LOP like American Airlines operated it, it had a TBO of 3600 hours.

The R-985, R-1340, R-1820, R-1830, R-2600, R-2800 (all of which I have operated) all had and still have excellent service records.

As a general rule, military operation resulted in poor service histories; commercial operation has been quite reliable. The reason seems to be mission profile.

[Big Pistons Forever]

I have personally operated the R1820, R 1830, and R 2800

The biggest issue now IMO, is getting good overhauls. It is a declining business and as the old timers with all the institutional knowledge have retired there are is not a lot of new blood with the knowledge and motivation to take over.

The second issue is money. A R2800 overhaul can range from USD 60,000 to 250,000. The difference is how many parts are replaced with new. Many big round engines are operated by non profit groups or individuals that are reluctant to spend the big dollars for a top end overhaul.

Finally as was pointed out there are fewer pilots with extensive radial engine operating experience and so the tricks of the trade are being lost.

[Exaviator]

Logged over 2000 hours on a pair of 1830s in conditions of extremes from ISA +15 down to -30. They never let me down once :ok:

Definately a case of good maintenance and correct handling procedures.

[VH-XXX]

Watching the Ice Pilots series you could be led to believe that they are terribly unreliable, but it's hard to know how much they have dramatized their small issues.

[Andy_RR]

As a general rule, military operation resulted in poor service histories; commercial operation has been quite reliable. The reason seems to be mission profile.

I'll bet the real reason is the commercial imperative...

[T28D]

I operate 2 Pratt 985 and one R1820 Wright all are remarkably reliable, the 985 are a bit of a trick to start with Bendix throttle bodies but once going nothing much will stop them, and yes operate them LOP, the R 1820 is a delight, easy to start, always delivers full power auto mixture is LOP and the exhausts tell a good story nice soft grey colour.


They will always get you home, the rotational nature of operation and the way the master rod carries the link rods (Con Rods to the un initiated ) is much kinder on torsional motion than the horizontally opposed general aviation engines and despite their frontal area the radial is very efficient with really even cylinder cooling without the need for complex baffling.


The like good pilot skills in engine handling, if you can see you hand moving you are feeding power in too quickly, slow and gentle and they will reward you with long life and smooth power delivery on the numbers.

[Andy_RR]

The radial engine configuration offers a host of advantages, frontal area unfortunately not being one of them. The crankshaft, always being the heaviest part of an engine, is short and stiff, as is also the crankcase. This offers the potential of very high power densities. Also, theoretically, they are perfectly balanced with a single counterweight to the n-1 order (n = no. of cylinders). Unfortunately, the master-link rod arrangement that T28D talks of makes n-1 cylinders operate with an effectively ellipsoidal crankshaft rather than circular, adding a bunch of harmonics to the vibration characteristics that shouldn't really be there.

I found an interesting series of papers once on t'interweb which described the torsional problems that Wright (I think) had to solve on the Cyclone (was it?) because of this very ellipsoidal problem.

Lovely engines though.

[Guptar]

Forgive my indulgence;

B-29 "FIFI" A Story of New Engines - YouTube

Best watched when you have the house to yourself, grab a comfy chair and a beverage of choice....and turn the sound up...........way up!

B-29 FiFi flying with B-25's & TBM's at Oshkosh 2013 Friday - YouTube

B-29 SuperFortress Engine Start / Maintenance Check Flight - YouTube

B-29 Superfortress FiFi Start up - YouTube

[Metro man]

Is there something I have missed or is it just engines of that size are so mechanically complex that something approaching reliability cannot be attained.

Basically, yes. The turbo compound engines fitted to the Lockheed Super Constellation were about as far as the technology could go. More power output would result in a bigger, heavier engine with greater frontal area and therefore more drag, resulting in higher fuel consumption and reduced payload.

Fortunately, by this time the jet engine was ready for commercial use and it took over from then on. Smaller, lighter, less complex, using cheaper paraffin instead of petrol, and far more reliable it brought in a new age of air travel.

Even in other areas radials find it difficult to compete with turbines, the Pratt & Whitney PT6 can be found in crop spraying aircraft and converted DC3s

[T28D]

http://media-cdn.tripadvisor.com/media/photo-s/02/f5/14/67/national-museum-of-the.jpg (http://www.tripadvisor.in/LocationPhotoDirectLink-g60785-d603950-i49615975-National_Museum_of_the_U_S_Air_Force-Dayton_Ohio.html)

[Big Pistons Forever]

Fortunately, by this time the jet engine was ready for commercial use and it took over from then on. Smaller, lighter, less complex, using cheaper paraffin instead of petrol, and far more reliable it brought in a new age of air travel.



Personal Number of large Radial Engines shut down in flight = 3

Personal Number of Turbine Engines shut down in flight = 3

:hmm:

[tail wheel]

T28D mentioned corn cobs...........

http://i526.photobucket.com/albums/cc347/garberc/Reno%202013/100_4754_zps95841011.jpg

Another use for radials?

http://i246.photobucket.com/albums/gg107/lippy055/8939.jpg http://farm9.static.flickr.com/8103/8618684940_a087b42867_m.jpg

[T28D]

Round engines ROCK, there was never an attempt in an inline engine to achieve the same power density that the corn cob made.


The engine was designed for the B 36 Peacemaker bomber which had 6 of them on pusher propellers, the last big piston bomber and If I am not mistaken the biggest bomber built I think it is bigger than a B 52.


Cooling the engine was an issue.


The torsional issues in the radials also stems from the firing order 1,3,5,7,9,2,4,6,8 in the Wright 1820 and all are same with odd number od cylinders.


The inline engines were all even numbers until Audi solved the crankshaft geometry and the inline 5 cyl was born in production cars then the V10 I had a V10 in an Audi R8 beast of a car but a really sweet engine.


Torsional issues are a common problem the flat engines have an array of floating weights in differing designs to solve the problem.


In motor bikes the crank design is a definite art, my Ducati 1198 engine has really unique design to help solve the problem and uses 11degree valve angle in the head to increase the power without compromising vibration as it is a 90 degree twin.


Other brands use 60 degrees or similar, motor bike engines I am lead to believe are the closest to radials in power density.

[nomorecatering]

Tailwheel, what engine is that, looks like it has too many cylinders to be a 4360.

[Two_dogs]

Post 16 engine.
I think I have a fouled spark plug.
Can you please have a quick look at it for me?

[Big Pistons Forever]

Post 16 engine.
I think I have a fouled spark plug.
Can you please have a quick look at it for me?

Don't laugh the Airlines operating the Stratocruiser would QEC the engine to do a plug change:ouch:

[onetrack]

NMC - The 56 cylinder radial is two P&W R4360's bolted together and put on display at Reno. I doubt whether the engine is a runner.
The owner called it a "P&W 5600 XBSAP" and stated it produced 7000HP. I think the whole effort was some pranksters finest effort.
He apparently had a couple of viewers who "remembered flying an aircraft with that engine". :)
The rear-cylinder cooling problems with the R-4360 were well known, I'd hate to think what temperature the rear cylinders on that 56 cylinder monster would run at.
Four rows of cylinders in a radial were deemed by P&W as the maximum practical number of rows, due to cooling issues.

[Old Akro]

I doubt whether the engine is a runner.

I think I have seen video of it running - albeit at idle.

[Centaurus]

As a general rule, military operation resulted in poor service histories; commercial operation has been quite reliable

Having flown the Dakota and the Convair 440 Metropolitan in RAAF service, I must say that we were given precious little documentation on radial engine handling. When I flew those types, all that was available to gen up on, were Air Ministry (RAF) Pilot's Notes for Dakota that gave us the essentials on to fly the aircraft. Nothing in-depth about engine handling. For the Convair 440 we had a US publication called the Dash-One for the type. The Dash One was far better than the RAF or RAAF Pilot's Notes series, but still lacked the more detailed information on engine handling that has appeared in relatively recent times.

[T28D]

The USAF manual on the T28 is quite detailed on engine handling but lacks that essential piece of radial advice. "If you can see you hand moving the throttle" you are moving it too fast, radials don't like sudden power changes, all is a delicate symphony of gentle movement.


The Beech 18 manual is also quite good, lots in there re icing, shows its heritage and the original 985 carby's were prone to icing, as well the B 18 was a favourite freight hauler, it will out lift anything in its class. Winter in northern U.S. was a bitch.

[Walter Atkinson]

BUT, if you operated the R-985 in accordance with the fine print footnote in the 1935 P&W manual about running the manifold heat to assure proper F:A ratios, the coldest temp in the carb was slightly above freezing. In over 1000 hours operating a twin beech in this manner I never once had carb ice. Not once. Of course, I doubt many pilots have ever read that footnote!!

[Caboclo]

I engineered on the DC-6 with Everts in Alaska not long ago. Reliability was not good. Don't know where they were getting their overhauls done. The R-2800 is one of the better round engines, but in my 14-month career, I had 1 catastrophic failure (gearbox), and numerous precautionary shutdowns for cracked jugs. Also a precautionary shutdown because the wire fell off the oil cooler door motor, left it stuck full open. Oil temp was OK during T/O and climb, but as soon as we leveled off and reduced power it dropped below the bottom limit. By comparison, in 3K hours of running flat engines, I had 1 failure. Also 1 failure in 3K hours in T-props.