1+1=2?

[Jia Hsing Fu]

I was thinking if aircraft installed more engine will obtain same thrust? For example,777 always have two engine then installed more two engine will get 4x thrust? Or will be 3.8 or 3.5. Like GE90 have 77000 lbf thrust,will be 77000 x 4 =308000?
BTW,assume structure allow.

 

[Szymon Kurzacz]

Static thrust - yes, but 2 more engines weight more, so all 4 engines need to push harder to get same performance... And 4 engines is also MORE fuel burn, and that may not count in total. Because adding 2 engines may increase weight and decrease range, so it will not be very economic.

We have now powerfull engines that can provide enought thrust for heaviest planes. Lets say RR Trent-1000 can provide enough power for 777 to fly signle engine over atlantic. Do not mention that old 744 engines have around 20% of Trent-1000 power, so YES, single Trent-1000 can fly 744

 

[Jia Hsing Fu]

Thanks for reply Szymon

Of course installed more engine could be not necessary,but i just thinking if do that will be gain same amount thrust,or gain less thrust with installed more engine. I not have any related background for aircraft,so .

Cheers .

 

[Szymon Kurzacz]

Ok.

Lets have an airplane. For start with 1 engine. It will have 10klbs of thrust. And cruise speed will be maintained with 100% power.
Now lets add another engine of same type. It will have 20klbs of thrust. Cruise speed will be maintained with MORE than 50% of power (probably around 80-90%), because of bigger weight and airdrag from second engine. It will be little better because it will not work at 100%, and will have some power in reserves for emergency, or flying higher, also if engine is good enough it will maintain aircraft in air after one engine failure.
Second engine will add almost nothing to top speed, but will slightly increase acceleration and top vertical speed for climb.


Something like that overall..