There is a civilian aircraft section in this forum. Maybe it is more appropriate to send this question there.

But to answer your question, prior to the eighties and below, it is generally believed for large passenger liners you need more than 2 engines to provide that safety redudancy. If you lose one engine, and left with the remaining engine, the plane would be imbalanced and difficult to fly. As four engined planes might be too expensive, wallah, the three engined configuration meets those requirements. Please note that the most common trijet are not what you just mentioned, but the Boeing 727.

Quality and safety has improved to the point however, that this requirement is abandoned, and with considerations towards economy, dual jets became the norm.

Another factor was the power of the jet engines. Early, two engines were not powerful enough to move a medium sized jetliner, but when more powerful engines were introduced, two became enough.

I only used the L-1011 and DC-10 as examples; I was specifically asking about the apparent aversion of the military to build 3 engined planes. I appreciate your comments and they are what I more or less expected. maybe I’m wrong but I look at the automobile industry and see niches for 4-cylinder, 6-cylinder and 8-cylinder cars, etc.. why not the same for military aircraft? You can design an aircraft optimized for performance with 2 state-of-the-art engines but if you need a aircraft that’s say 30% larger, shouldn’t you consider adding a 3rd engine instead of making the jump to 4 engines?

[QUOTE=Adrian_44]The answer is YES, to the NCTR capability for the Sidewinder-9X. One reason the “-9X” is so effective is due to it having infra-red imaging I²R. This system does not detect a hot spot like prior IR missiles did. It detects an image which looks like a negative of a black and white photograph. Like the JDAM, this image is compared to images stored in the memory. The processor rotates the image detected versus the memory’s image. The rotation continues until an match is made. Once the match is made, the missile guidance then knows its direct angular relationship to the actually aspect angle to the target. Now the intercept algorithm can determine the most direct path to the target.

Thanks for the info Adrian.. that settles it for me.

Don’t think that NCTR (what an word!) can be used as IFF. It sees things in the longer IR spectrum, so as long as one doesn’t give the own aircraft some special IR-paint scheme that can be ID’d, it can only tell the type (provided your database is good – talking about external stores, etc), not the nationality.

That was the intent of my original query, that the AIM-9x could differentiate between the shapes of different airframes.. so far there’s no conclusive answer based on the responses received. there’s some conjecture thatthe missile can actually target specific parts of an aircraft such as the cockpit, for example.. if true, then identifying a aircraft’s shape shouldn’t be a problem.. Obviously, it can’t discriminate nationality but neither can radar..