B200, just to re-iterate. Putting your post in bold is the equivalent of shouting and it really doesn't help get your point across.
What you quote from the Gulfstream manual is all in accordance with part 25.115, the conditions of which are (amongst others) are for a failure of the most critical powerplant at V1.
In the extraordinary event that the powerplant doesn't fail a number of interesting things happen. One is that you rotate earlier in terms of distance along the take off roll. Another is that you overcome the initial drag of flap and gear more easily. If you get rid of the gear promptly and continue to accelerate to V2 you can then pitch for your initial climb and achieve a much better gradient than if you lose an engine at V1. Crucially you can also keep accelerating. Once you achieve the point (in terms of speed) where you can retract the flap you will further increase your rate of climb. Your gradient will depend on what speed you choose to accelerate to. However, if you choose to argue that raising the flap will somehow degrade either your rate of climb or gradient, why would you raise the flap at all? Why raise it at 1500 feet? Why not continue to climb in the flapped condition and benefit from the increased performance?
You only degrade the gradient if your forward speed becomes high - remember we are still all engines operating here so the gradient will only become an issue at the point where your forward speed is so high that you degrade the climb such that it impinges on the original required gradient.
Hopefully we are all on the same page so far - now what happens if you lose an engine?
If we lose an engine from V1 up to V2+20 I think we are all on the same page.
If I have started to retract the flaps - ie the flaps have just started to travel at the point where the engine fails - I am STILL in an improving situation and here is the reason. All the time the flaps are travelling, the drag is decreasing. Thats why we retract the flaps at 1500 feet as explained above. All thats happened is that I have used the extra energy of having two engines operating to retract the flaps and attain my final segment configuration at an earlier stage. The climb rate clean at my flap retract speed has to be as good or better than in the flapped condition at V2 because thats why I retract the flap at 1500 feet. All the time the flaps are travelling from the take off position to the up position the trend is towards this better configuration.
Next case. Lets say I'm now clean and climbing at 4 or 500 feet, speed is now above V2+20, more like V2+40 or 50 and increasing. I'm now quite a long way above the required gradient because both engines have been operating but I agree completely that I have no way of proving how much and I haven't factored that into my calculations because its an unknown. Now the engine fails. I need to reduce speed to V2+20 which will give me back the known gradient that I need. I'm in the final segment configuration and climbing with max thrust because I still have time available (I've got up to 5 minutes). After that I will reduce thrust to max continuous for the one engine I have left and now that things have settled down I'll deal with the problem.
At all times, I'm above the gradient. If you (or anyone else) believes that the climb is degraded by raising the flap and flying clean what is your justification for doing it at 1500 feet? Because if its "they told me to" you haven't thought through the problem. When we learn about this stuff we focus heavily on the most critical condition - the whole thrust of this from me is that I dont think we work through this correctly and at every stage. I think we should. I think the manufacturers do and thats why, for a substantial number of aeroplanes, the manuals are written the way they are.
There are advantages to doing what the AFM says. In the event of a failure of a powerplant higher up the initial climb, you are likely to be in a better configuration for the climb and have an aeroplane which is substantially easier to fly. Because you are faster the fin is more effective so the initial rudder correction will need to be less - if you don't recognise it immediately (and the majority of engine failures are not like the events in the sim - there's a high level of shock, stress, vibration, possibly noise, probably horrible smells etc) I believe that what I'm talking about gives you a better chance to deal with it.
I don't fly noise abatement departures at all in Africa because off the very high chance of birdstrike. I don't want to hit birds when I am 20 degrees nose high with all my focus on the artificial horizon, the ASI, and generally scanning in the cockpit. I want the aircraft in a sensible climbing attitude, accelerating sensibly, and I want to see the monitor birds, the herons, and the clouds of swifts etc so that I stand a chance of avoiding them. At 200 kts and climbing the way I do I have seen and been able to miss large birds on a number of occasions and when you are climbing out of Kinshasa and all thats beneath you is jungle and the Congo river you think carefully about how you are going to climb the plane.
I'm not really enjoying the thread any more because I feel that some of you are so entrenched in one way of thinking that you don't even read the posts properly and simply sign on to have a gang mentality rant. Thats not why I started this - it was actually to discuss why some operators go blasting through the flap up speed and only retract flaps because they achieve a certain height and I don't understand that mentality.
I wanted to provoke a discussion and perhaps uncover something interesting and I have other things I'd like to discuss with regard to noise abatement (my first job was as an Acoustic Engineer for a company called Bruel and Kjaer) and I think with some cohesive discussion and effort we can present sensible noise solutions for business jets which are much easier for us to fly.
but I'll only get shot down so whats the point!