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#1
September 18th 04, 04:50 PM
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"Mike Rapoport" wrote:
A diesel doesn't cost any more that a piston engine. A STC'd conversion costs more but, in a new airplane the cost should be the same. Right. Some people seem to think that diesels are somehow magic. The basic construction of a diesel and a gasoline engine are almost identical. The only differences I can think of a 1) Higher compression ratio. This could be done with a longer-throw crankshaft, a taller piston, a lower head, or some combination of all three. 2) A fancier (higher-pressure) injector pump. 3) No spark plugs. Which means no ignition system (be it electronic or magnetos). 4) Possibly the addition of some kind of starting assist such as glow plugs. The biggest problem I can see with a diesel is cold-weather operation. I used to have a diesel car (1980's era VW Rabbit). It was a bitch to start in really cold weather. If the glow plugs were in good shape, you were fine down to about 20 F. Once you got down below about 10 F, you probably weren't going to get it started without a preheat. Somewhere down around 15 F, normal diesel fuel starts to gel. These are temperatures commonly experienced aloft even at the altitudes spam cans fly at in the winter in temperate climates. It would be real bad news to get the engine going, only to have the fuel gel up in the tanks when you reached cruising altitude. But, I suppose the Jet-A folks have figured out the right additives to solve that problem. 
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#2
September 18th 04, 05:06 PM
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In rec.aviation.owning Roy Smith wrote:
"Mike Rapoport" wrote: A diesel doesn't cost any more that a piston engine. A STC'd conversion costs more but, in a new airplane the cost should be the same. Right. Some people seem to think that diesels are somehow magic. The basic construction of a diesel and a gasoline engine are almost identical. The only differences I can think of a 1) Higher compression ratio. This could be done with a longer-throw crankshaft, a taller piston, a lower head, or some combination of all three. 2) A fancier (higher-pressure) injector pump. 3) No spark plugs. Which means no ignition system (be it electronic or magnetos). 4) Possibly the addition of some kind of starting assist such as glow plugs. The biggest problem I can see with a diesel is cold-weather operation. I used to have a diesel car (1980's era VW Rabbit). It was a bitch to start in really cold weather. If the glow plugs were in good shape, you were fine down to about 20 F. Once you got down below about 10 F, you probably weren't going to get it started without a preheat. Somewhere down around 15 F, normal diesel fuel starts to gel. These are temperatures commonly experienced aloft even at the altitudes spam cans fly at in the winter in temperate climates. It would be real bad news to get the engine going, only to have the fuel gel up in the tanks when you reached cruising altitude. But, I suppose the Jet-A folks have figured out the right additives to solve that problem. Because of the higher compression ratio, a diesel has to be built "beefier" than a gas engine to last as the automakers found out when they tried a direct conversion on their gas engines in the 80's. All the aircraft diesels have a constant speed prop and FADEC. If gelling of Jet-A were a problem, airliners would be falling out of the sky on a regular basis. -- Jim Pennino Remove -spam-sux to reply.
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#3
September 18th 04, 05:43 PM
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#4
September 18th 04, 06:06 PM
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In rec.aviation.owning Roy Smith wrote:
wrote: Because of the higher compression ratio, a diesel has to be built "beefier" than a gas engine to last as the automakers found out when they tried a direct conversion on their gas engines in the 80's. Well, the Rabbit I had was built with exactly the same block, pistons, crank, etc, as the gas version. The basicly just slapped a shallower head on the thing to increase the compression ratio. We drove the car into the ground at about 160k miles. We replaced pretty much all of the accessories (starter, water pump, alternator, radiator, etc) at least once, and the clutch wore out at about 110k, and the body was more rust than steel, and the electrical system was a mess, but the core engine was just fine. The only thing that ever happened to the engine core was a blown head gasket, but that was really my fault. We had chronic overheating problems due to a leak in the cooling system that we didn't fix for a while. Eventually, the gasket said, "OK, if you want to keep abusing me like that, I'm outta here". The debacle I'm talking about was Chevey's (?) attempt to power pickups with a gas engine converted to diesel by basically the same method. You can get away with this if the basic engine is strong to start with and you're not trying to pull too many horses out of it. -- Jim Pennino Remove -spam-sux to reply.
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#5
September 19th 04, 12:37 AM
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Well, the Rabbit I had was built with exactly the same block, pistons, crank, etc, as the gas version. The basicly just slapped a shallower head on the thing to increase the compression ratio. I could have sworn the Rabbit Diesel had a way different engine, but I could be wrong. The debacle I'm talking about was Chevey's (?) attempt to power pickups with a gas engine converted to diesel by basically the same method. Not pickups AFAIK; station wagons and maybe sedans. This was Roger Smith at his finest. A friend bought one with a dead@55000 mile engine. It was an stock gas block; no where NEAR beefy enough. The blowby was so bad, the engine soiled itself at every seal; he'd get 250 miles to the quart; all leakage. At least it didn't rust! It had a one-of-kind starter and flywheel. The distributor was replaced with a vacuum pump to drive the HVAC door flaps. It had dual batteries, designed wrong. The brakes were run off the PS pump, so when the engine stalled, stop NOW. He put in a gas 350 and drove it for 10 years more. -- A host is a host from coast to & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433
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#6
September 19th 04, 01:12 AM
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In rec.aviation.owning David Lesher wrote:
Well, the Rabbit I had was built with exactly the same block, pistons, crank, etc, as the gas version. The basicly just slapped a shallower head on the thing to increase the compression ratio. I could have sworn the Rabbit Diesel had a way different engine, but I could be wrong. The debacle I'm talking about was Chevey's (?) attempt to power pickups with a gas engine converted to diesel by basically the same method. Not pickups AFAIK; station wagons and maybe sedans. This was Roger Smith at his finest. A friend bought one with a dead@55000 mile engine. It was an stock gas block; no where NEAR beefy enough. The blowby was so bad, the engine soiled itself at every seal; he'd get 250 miles to the quart; all leakage. At least it didn't rust! It had a one-of-kind starter and flywheel. The distributor was replaced with a vacuum pump to drive the HVAC door flaps. It had dual batteries, designed wrong. The brakes were run off the PS pump, so when the engine stalled, stop NOW. He put in a gas 350 and drove it for 10 years more. -- A host is a host from coast to & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 There were pickups. A friend bought one new and had the engine blow at about 40k miles. Thanks to California smog laws, he found his choices were replace it with another new diesel (big bucks) or get an old gas engine and convert it to propane and try to recover some of the investment. This was way before 50k warranties. -- Jim Pennino Remove -spam-sux to reply.
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#7
September 19th 04, 05:49 AM
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#8
September 19th 04, 04:12 AM
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#9
September 19th 04, 02:07 PM
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"Newps" wrote in message ... wrote: If gelling of Jet-A were a problem, airliners would be falling out of the sky on a regular basis. It is a problem. It is solved by heating the fuel. .... and since hydraulic fluid needs cooling they locate the hyd.cooling coils inside the fuel tank(s). That helps solve two problems.
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#10
September 19th 04, 02:54 PM
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Excerpted from other posts.......
Any talk about Jet-A jelling sounds....bogus.. If gelling of Jet-A were a problem, airliners would be falling out of the sky on a regular basis. It is a problem. It is solved by heating the fuel. It is a problem on long flights at high altitudes and high latitudes. The fuel filters on the Boeings that I flew were heated to prevent the screens from "waxing" over. The fuel itself was not heated. The filters were heated with hot engine bleed air and heated for one minute every thirty minutes when the fuel temperature dropped below zero degrees celsius. At PanAm, we had three procedures for dealing with extremely low temperatures across the North Atlantic. 1. Re-route to a more southernly (warmer) route. 2. Reduce altitude to a warmer OAT. 3. Increase speed for a greater friction effect on the tanks. At around M.80, the Ram Air Temperature is about thirty degrees higher than the True Air Temperature. All of these required extra fuel of course and we depended on the Dispatcher providing a good Temp Aloft forecast. Bob Moore ATP B-707 B-727 PanAm (retired)
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