Three power eggs....

[Lucky13]

Just curious here, as to why, the Italians fascination (right word?), with three engined aircraft, why was that?

 

[GrauGeist]

Because..."Three shall be the number thou shalt count, and the number of the counting shall be three. Four shalt thou not count, neither count thou two, excepting that thou then proceed to three. Five is right out"

That's why.

 

[pattle]

Because they had weak engines, either the SM79 or Cant Z1007 or possibly both were supposed to have been twins but were built as tri-motors because the Italians did not have powerful enough engines.

 

[davebender]

Until a couple decades ago there was an aviation rule that passenger flights over water must have at least three engines. That was for safety purposes as most early model twin engine aircraft lacked the power to fly well (if at all) with one engine out.

Sm.79 and Ju-52 were passenger aircraft before conversion to military purposes. So was Ju-252.

Some jet passenger aircraft had three engines for same reason.

 

[FLYBOYJ]

Until a couple decades ago there was an aviation rule that passenger flights over water must have at least three engines. That was for safety purposes as most early model twin engine aircraft lacked the power to fly well (if at all) with one engine out.

"Over water" Over the Atlantic or over the Caribbean ?

The Boeing 247, Douglas DC-2 and DC-3 continually operated over water. I'd like to know what that "rule" is/ was considering that in the 1930s there were no "joint" aviation authorities and little or none joint certification agreements.

 

[Glider]

I have no idea if the rule I am thinking about applied to the 247/DC2/3 but I think I am right in saying that there was a rule that limited the time that a twin engine aircraft should be from an airfield in case an engine failed and they had to fly on one engine. This in turn made the routes they would have to use on transatlantic/pacific flights impractical, which is one reason why the DC10 and Tristar were designed with three engines. They had the same engine out restrictions as the four engine aircraft and were cheaper to operate.

 

[yulzari]

Yes, the lack of available engines powerful enough for twins. Just like the Ju52 was single engined but had to go to three for mass production with German not Rolls Royce power.

 

[FLYBOYJ]

I have no idea if the rule I am thinking about applied to the 247/DC2/3 but I think I am right in saying that there was a rule that limited the time that a twin engine aircraft should be from an airfield in case an engine failed and they had to fly on one engine. This in turn made the routes they would have to use on transatlantic/pacific flights impractical, which is one reason why the DC10 and Tristar were designed with three engines. They had the same engine out restrictions as the four engine aircraft and were cheaper to operate.

I believe that was part of FAR 23 which required commercial aircraft over 12,000 pounds overflying the Atlantic or Pacific to have "4" engines. I believe the DC-10 and Tri-Star circumvented that because of the third engine and if I'm not mistaken were able to maintain controllable flight on one engine depending on weight.

 

[rinkol]

A further issue that adversely affected early twin-engined aircraft was the use of fixed pitch propellers that could not feather. The asymmetric drag introduced by a dead engine with such a propeller was a serious problem in a twin engined aircraft, particularly on take-off. Variable pitch propellers were an important, but often overlooked, refinement that was introduced with the DC-2 and Boeing 247. Nevertheless, even some later twin engined aircraft could be a handful in single engined flight.

In the case of the Italian aircraft, there were also reliability issues with the more powerful two row radial engines.

 

[FLYBOYJ]

Variable pitch propellers were an important, but often overlooked, refinement that was introduced with the DC-2 and Boeing 247.

Perfect point!

 

[GregP]

In the case of an engine failure, variable pitch wasn't nearly as important as the ability to feather. Constant-speed propellers made the planes of the day climb better, but full-feathering props made engine-out operation MUCH safer.

I believe early variable pitch props were more of a cruise-or-climb thing, and the ability to feather was a bit later. Certaily the ability to feather was there by the mid-1930's. The biggest boon to safety were props that would feather automatically in the event of an engine failure.

If I am not mistaken the first auto-feather propellers were fitted to the Martin 404 twin and then to the Convair 240 - 340 Metroliner twins just a bit later. They made the recips a LOT for go-around.