Why wasn't three-engined bomber more popular?

[Mad Dog]

Is this restricted to pre-jets? Because there almost was a tri-engine bomber that the USAF had considered, the Martin XB-51, and it was even in a movie(forget the title)
View attachment 593629

A more practical version - Lockheed Tristar airliner.

 

[GrauGeist]

There's scores of civil "trijets" that have been, or are, in service:
Dassault 900
McDonnel-Douglas DC-10, MD-11
Hawker-Siddley Trident
Boeing 727
Tupolev Tu-154
Etc...

It's more the norm than the exception.

 

[pbehn]

There's scores of civil "trijets" that have been, or are, in service:
Dassault 900
McDonnel-Douglas DC-10, MD-11
Hawker-Siddley Trident
Boeing 727
Tupolev Tu-154
Etc...

It's more the norm than the exception.

In the 1980s I flew to the middle east on Tristars and DC-10s Maybe as S/R explained about the early days of aviation a three engine plane was easier to approve for some routes.

 

[Shortround6]

A jet in the tail is a whole lot easier for the passengers to put up with than a piston engine and prop in the nose

Stinson Model A

240hp Lycomings. 8 passengers?

 

[Gen. MacArthur]

I think 2 or four engined bombers have the best performance and best bombardier stations. On a tri motor bomber the engine and fuel are someware near the nose. I would want that to explode on my face!

 

[Denniss]

Trimotor was a quick and dirty fix if your engines lacked sufficient power for a twin-engine configuration.
For the later Trimotor Jets (Tri-Star, DC-10 family) it was probably easier to implement than to invest in larger/heavier wings with 4 engines.

 

[SaparotRob]

Trimotor was a quick and dirty fix if your engines lacked sufficient power for a twin-engine configuration.
For the later Trimotor Jets (Tri-Star, DC-10 family) it was probably easier to implement than to invest in larger/heavier wings with 4 engines.

Lost in the mists of time, I read that the two tri-jets (DC-10 and L-1011) had a third engine because the Federal Aviation Administration wanted it. The FAA wanted more than just two engines on passenger planes on trans-oceanic flights at the time of their introduction. I didn't really believe that. Since we're talking tri-motors I'd like to get to the bottom of that.

 

[Denniss]

ETOPS - twin engine airliners were required to stay in a (2 hour?) distance to an airport during transatlantic flights thus they couldn't fly the shortest possible route. Trimotors were not affected by such strict ETOPS regulations

 

[SaparotRob]

And now I know. Thanks!

 

[Shortround6]

Once the twins had enough power to stay in the air for hours using one engine the requirement for the third engine was dropped.

 

[swampyankee]

Once the twins had enough power to stay in the air for hours using one engine the requirement for the third engine was dropped.

It wasn't so much power, but reliability.

One of the other factors pushing airliners to two engines is noise abatement. Since the airliners need to maintain a sufficient rate of climb with one engine inoperative, a twin will have relatively more surplus thrust with both engines operating than with an aircraft with three or four engines.

 

[fastmongrel]

For civilian work there is also going to be initial cost. 3 x 600hp engines vs 2 x 900hp engines if the 600hp engines cost £10,000 each and the 900hp engines £15,000 each that looks good but when both types of engine need 1 hour of servicing per flight then paying a highly skilled and well paid man to do an extra hour of servicing every time the plane takes off the wages soon add up.
3 x 7 cylinder 600hp engines at 2 x spark plugs per cylinder needs 42 plugs
2 x 9 cylinder 900hp engines at 2 x spark plugs per cylinder needs 36 plugs

I have made the figures up because I have no idea of 1930s engine costs or wages but I bet I am not too far off. The accountants killed off the Tri-Motor.

 

[swampyankee]

One other issue is that the likelihood of an engine failure increases with the number of engines, simply because there are more engines to fail. Also, since the most likely time for a commercial engine to fail is around takeoff (frequently when power is reduced from takeoff power to continuous power), many engine failures will result in a quick return to the starting airport.

 

[fastmongrel]

many engine failures will result in a quick return to the starting airport.

Many engine failures in the 1930s resulted in a very quick return. Often vertically.