Large Radial Engines reliability.
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Large Radial Engines reliability.
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.
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.
short flights long nights
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 ?
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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?
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?
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!!
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!!
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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.
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.
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.
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.
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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 
Definately a case of good maintenance and correct handling procedures.
Definately a case of good maintenance and correct handling procedures.
Last edited by Exaviator; 6th Feb 2014 at 22:08.
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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.
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.
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.
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.
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.
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
Personal Number of Turbine Engines shut down in flight = 3
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T28D mentioned corn cobs...........
Another use for radials?
Another use for radials?
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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.
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.
