Agrajag wrote:

The point would be to design an aircraft for, say, 500 passengers in 3 comfortable classes, but with much better economics than an A380. The small engines will essentially be used for providing the additional thrust when required, such as at takeoff, but provide much less drag and fuel consumption when the extra thrust is not required. I also like the idea that the smaller engines could retract up into the with when not required, or into a more aerodynamic fairing/pod. Just a thought exercise.

Agrajag wrote:

:roll: Pikachu
Im sure such comments are your way of making yourself feel superior (perhaps making up for shortcomings elsewhere) but its unnecessary. And, as it turns out, after a bit of research, the 'thought' has been deemed good enough to make it into production on several aircraft.

Agrajag wrote:

Pikachu, you continue to embarrass yourself. Why the frustration? Things not going well.? Retractable engines will happen in commercial flight, youll see.

Agrajag wrote:

I have no need to prove anything, the purpose of the thread is quite clear. You seem to be an 'angry' chap who is quite vulnerable.
Anyway, back to my chosen topic. In the future i am certain that 'deployed as needed' engines will be in use.

Agrajag wrote:

Fine, jog on!
I am thinking, in this thought exercise, about a clean sheet design concept, where optimal cruise engines are supplemented by retractable thrust to be deployed when needed i.e at takeoff. I dont see that as such an outlandish concept for the future despite what that silly sausage Pikachu says above.

Agrajag wrote:

And yet you are still here... Says a lot.
Making predictions is difficult, especially about the future. Thats why its a thought exercise.

I wonder what happened to you to make you behave like this?

Agrajag wrote:

The advantage is obvious, reduce drag. I am sure that is the very reason the jet engines are retractable on gliders. Not such an amazing leap of imagination to see that concept being applied on larger aircraft IN THE FUTURE! Could even be centre-line thrust, not wing based.

I am interested to know some of the potential technical difficulties. Is that not what this Forum is for? If you dont like my thread, i give you my permission to scroll past.

Agrajag wrote:

The advantage is obvious, reduce drag. I am sure that is the very reason the jet engines are retractable on gliders. Not such an amazing leap of imagination to see that concept being applied on larger aircraft IN THE FUTURE! Could even be centre-line thrust, not wing based.

I am interested to know some of the potential technical difficulties. Is that not what this Forum is for? If you dont like my thread, i give you my permission to scroll past.

Agrajag wrote:

Galaxyflyer, at least i got some sense from you. My questions are not necessarily about what has gone before or even the state of the art now, its a concept for the future.

Agrajag wrote:

Galaxyflyer, at least i got some sense from you. My questions are not necessarily about what has gone before or even the state of the art now, its a concept for the future. The notion that it wont ever happen because it hasnt happened already is clearly false.

Agrajag wrote:

I am thinking, in this thought exercise, about a clean sheet design concept, where optimal cruise engines are supplemented by retractable thrust to be deployed when needed i.e at takeoff.

PerVG wrote:

Agrajag wrote:

I am thinking, in this thought exercise, about a clean sheet design concept, where optimal cruise engines are supplemented by retractable thrust to be deployed when needed i.e at takeoff.

That concept already exists as a possibility for future hybrid aircraft, were electric fans augment a cruise gas turbine during take-off/climb and recharge the batteries during descent.
It *might* became viable in the future.

As for your, 2 big + 2 small/retractable conventional, fuel-burning turbofans, I think you can forget it. It would be a maintenance nightmare, take-off engine out certification nightmare and the fact the "booster"engines would just be ballast for most of the flight would just negate any possible efficiency gains.

GalaxyFlyer wrote:

You’d never get JATO certified under today’s Part 25, not to mention get an airline to buy it.

GalaxyFlyer wrote:

It’s dead crazy, even the military hasn’t used it for decades.

kalvado wrote:

PerVG wrote:

Agrajag wrote:

I am thinking, in this thought exercise, about a clean sheet design concept, where optimal cruise engines are supplemented by retractable thrust to be deployed when needed i.e at takeoff.

That concept already exists as a possibility for future hybrid aircraft, were electric fans augment a cruise gas turbine during take-off/climb and recharge the batteries during descent.
It *might* became viable in the future.

As for your, 2 big + 2 small/retractable conventional, fuel-burning turbofans, I think you can forget it. It would be a maintenance nightmare, take-off engine out certification nightmare and the fact the "booster"engines would just be ballast for most of the flight would just negate any possible efficiency gains.

And again.... C-130 JATO comes to mind. Not exactly retractable turbofan, though, but takeoff assistance nontheless... I just saw a mention JATO was considered for 727 hot-and-high.
Advantage here is much smaller weight and smaller drag footprint.