Managing Takeoffs Fenix A320 CFM vs. IAE Engines

[G550flyer 1,015]

I'm not sure about the EFB calculations, but from a real world aircraft performance stand point, I will say this. Aircraft takeoff performance and configurations follow a curve so to speak. There are two items that will impact this. Runway available and required climb gradients. These two items may drive where you will fall in that curve. Some manufacturers allow you to take full advantage of the curve and some allow you to take certain sections of the curve. For example, the DC10 and G550 that I have experience with. The DC10 took full advantage of the curve allowing 200 flap configurations from 5 to 25. The compromise between runway available/conditions and climb gradients will lead to the optimum flap setting/max weight for that takeoff. In the G550, you only have 10 and 20 for takeoff. You get two stabs at the curve, but that jet can takeoff at max weight on 5000FT of dry runway, so do you need the full optimized solution? no. 10 for high climb requirements and 20 for short runways. 

On the typical curve, the front end usually gives you good climb performance because of less flap drag, but may limit weight capability. The middle of the curve will give you a good compromise of climb and weight capability if it's possible. The aft end of the curve will get you off the runway quicker with all of the flaps, but again, may limit your weight and hurt your climb because of the drag.

Now, in regard to the Airbus, flaps 1, 2 and 3 fall on the curve and will be based on conditions in an optimized solution. What I'm saying is that flaps 3 should not "kill" you or cause issues because it's on the performance curve. With flaps 3, the calculated Vr, Vmu and V2 should work. Yes, you will have more drag and less climb capability than 1 or 2 for a given weight and power setting. But, the aircraft won't fall out of the sky and get into stick shaker because of flap 3. Flaps 1, 2 and 3 should all have the same percentage of Vstall, which creates the curve.    

[Maxis 1,878]

I've received a few flap three recommendations and for me as long as i am carefully following the flight director in this very critical phase and not blowing past it pulling back on the stick looking for 757 performance the aircraft flies as it should.  You will lose airspeed and drop into into a prot mode if you ignore the recommended climb profile trying to gain altitude or retract flaps too early. the airspeed will increase to the flap retraction speeds and move right on up to the clean wing configuration as long as you accept and fly the guidance given as shown in the video @Aamir just posted.

Another factor is the weight. Simbrief seems to like to make sure almost all seats are filled each flight. So i suspect its not the engines being weak but the high drag of the flap selection and your packed to the gills flight resulting in sluggish initial phase climb performance.

[Fiorentoni 4,266]

17 minutes ago, Maxis said:

I've received a few flap three recommendations and for me as long as i am carefully following the flight director in this very critical phase and not blowing past it pulling back on the stick looking for 757 performance the aircraft flies as it should.  You will lose airspeed and drop into into a prot mode if you ignore the recommended climb profile trying to gain altitude or retract flaps too early. the airspeed will increase to the flap retraction speeds and move right on up to the clean wing configuration as long as you accept and fly the guidance given as shown in the video @Aamir just posted.

Another factor is the weight. Simbrief seems to like to make sure almost all seats are filled each flight. So i suspect its not the engines being weak but the high drag of the flap selection and your packed to the gills flight resulting in sluggish initial phase climb performance.

I've done two config 3 takeoffs on the IAEs and each time I was only able to pass the ILS antennas by only 5 feet, and this only by pulling full up at the last second. Almost like this (except for the fact that I did not take the wrong intersection...): https://www.tiktok.com/@drtruuth/video/7339396335054916906

 

[Cpt_Piett 4,750]

31 minutes ago, Maxis said:

I've received a few flap three recommendations and for me as long as i am carefully following the flight director in this very critical phase and not blowing past it pulling back on the stick looking for 757 performance the aircraft flies as it should.  You will lose airspeed and drop into into a prot mode if you ignore the recommended climb profile trying to gain altitude or retract flaps too early. the airspeed will increase to the flap retraction speeds and move right on up to the clean wing configuration as long as you accept and fly the guidance given as shown in the video @Aamir just posted.

Well said, and a very instructional video, emphasizing the importance of carefully following the SRS. 

Edited April 9 by Cpt_Piett

[G550flyer 1,015]

1 hour ago, Fiorentoni said:

I've done two config 3 takeoffs on the IAEs and each time I was only able to pass the ILS antennas by only 5 feet, and this only by pulling full up at the last second. Almost like this (except for the fact that I did not take the wrong intersection...)

This, when flying per the procedures, leads me to believe that there may be some issues in performance calculations for flaps 3. As I mentioned in an earlier post, aircraft performance will follow a curve in regard to flap settings. Another part of the curve that I didn't mention is the accel go portion of certification requirements. There is part for accel stop too😝. For example, FAA certified aircraft will be at 35FT at the end of the accel go distance. All depends on the certification requirements. What this means is that regardless of the flap setting used, the aircraft has to meet no less than that requirement ENGINE OUT. Now in a sense, for the same weight, flaps 3 should easily meet that requirement because more flaps get you off the ground quicker/easier. But regardless, if a higher weight is calculated for flaps 3, it still has to be no less than certified height by the end of it's respective accel go/balanced field length engine out.

Based on my experience, if I am rotating in the last 500FT and I am not engine out, something is wrong. You do have the responsibility of ensuring you are not runway limited for a specific weight, but I'm unsure of what the EFB is doing in the back ground. At least in the real world, you are comparing runway limiting weight wet/dry and climb requirement weight to calculate the optimum/max weight. If your actual weight is less than those, you can flex to a point. These days, computers will spit that out in seconds once the conditions are entered.   

[Bobsk8 12,792]

I recently stopped flying the Fenix, but when I was flying it with the IAE engines, I noticed that the aircraft seemed to use a great deal of runway, much more than the 737 usually does on the same runways, with about the same weight load. I always use Flaps 1, and usually runway in the 8,000 + ft range. Just seemed a bit underpowered. 

[Fiorentoni 4,266]

55 minutes ago, G550flyer said:

Based on my experience, if I am rotating in the last 500FT and I am not engine out, something is wrong.

I think the Vr was alright, it was at a plausible point on the runway. The problem appears after rotating: It just won't climb for a couple of seconds. Maybe it's a too high flex number calculated or an issue with drag, I don't know.

[G550flyer 1,015]

1 hour ago, Fiorentoni said:

I think the Vr was alright, it was at a plausible point on the runway. The problem appears after rotating: It just won't climb for a couple of seconds. Maybe it's a too high flex number calculated or an issue with drag, I don't know.

Reminds me of flexing in the Gulfstream. Before you flex, you better make sure you are still making the min climb gradients and not exceeding runway available lol. Run your scenario again and see what it does at full rated takeoff thrust. Take notes on lift off point and climb rate after lift off. This is interesting.

Edited April 9 by G550flyer
Forgot