Flap Selection
James Albright (a former G450 driver)
Updated: 2017-10-23
It isn't written anywhere, but most G450 pilots use the following flap schedule:
Clean configuration until 200 knots, then extend 10° of flaps,
10° of flaps until 180 knots, then 20° of flaps,
20° of flaps until 160 knots, then 39° of flaps.
As it turns out, that flap schedule works pretty well. You just have to understand the limits to the technique. My advice: as long as you weigh less than 58,500 lbs the technique is rock solid. If you get much heavier than this, keep an eye on your display controller's VREF indicator and stay at least 15% higher if you intend to maneuver.
Keep in mind this is technique. You could also just keep an eye on the VREF indication on your display controller and decide how much of a pad you want on top of that. If you keep the airplane 15% higher than that number, you will be protected against turbulence. How do I know that? See: G450 Turbulence Penetration Speed.
The 200/180/160 technique is much easier. But is it valid?
Everything here is from the references shown below, with a few comments in an alternate color.
G450 Maneuvering Speed Versus the Technique
The AFM tells you maneuvering speed is 206 knots but that is only for one specific condition. 206 KCAS it is an absolutely meaningless number in the world of flying a Gulfstream G450. But VA is a critical number. If the 200/180/160 technique kept you close to VA, it would be validated.
Figure: Example V-G Diagram, from author’s notes
Gulfstream does not give you anything more than this when it comes to maneuvering speed: VA = 206 knots. That works for some conditions, such as the one shown for a GIII at 65,000 lbs grossweight, 8,000' pressure altitude, gear up, and flaps up. But the real number changes with weight, altitude, and configuration.
But we also know that if you limit yourself to positive G forces, your maneuvering speed is equal to your stall speed times the square root of your acceleration (G) limit. How do I know this? See: VA - Maneuvering Speed.
We know that with the flaps up we have a 2.5G limit and our VA will be 1.58 VS and that with the flaps extended we have a 2.0G limit and a VA of 1.41 VS. How do you know all this? See: G450 Maneuvering Speed.
Figure: G450 Stall Speed, Flaps 0°, from G450 AFM, §5.1.
Figure: G450 Stall Speed, Flaps 10°, from G450 AFM, §5.1.
Figure: G450 Stall Speed, Flaps 20°, from G450 AFM, §5.1.
So our task is to find the limits of the 200/180/160 technique. You can slice this in many ways, I've chosen to limit the airplane to its maximum landing weight (66,000 lbs), 15,000' altitude, and no more than 2.0 Gs. I could have used 2.5Gs at Flaps 0° but that would exceed the 200 knots. So if you promise to keep within 2Gs you get this:
So you are okay until you are at Flaps 20° and starting to slow down. Flying at 160 KCAS with Flaps 20° doesn't really work at this weight or altitude. You may want to come up with a different maximum altitude and/or weight to make the numbers work for you. Since we keep our aircraft within ASC 007 (maximum landing weight 58,500 lbs) I can adjust the numbers this way:
Therefore I know I can fly up to my ASC 007 maximum weight of 58,500 lbs and up to 15,000 feet while in the clean configuration down to 200 knots, with Flaps 10° down to 180 knots, and with Flaps 20° down to 160 knots and be close to my aircraft's maneuvering speed.
Note that this keeps you within the auto speed profile defaults in the FMS:
Climb
V2 on takeoff
At 400' with flaps up and FLC: 200 knots
At 1,500': V1, VR, and V2 disappear
At 2,500' / 4 nm: 250 knots
At 10,000': 300 knots
Descent
TOD to 10,000': Mach / 300 knots
At 10,000': 250 knots
IAF or 15 nm: 200 knots
Flaps 10: 180 knots
Flaps 20: 160 knots
Flaps 39: VREF + 5 knots
References:
Gulfstream G450 Airplane Flight Manual, Revision 35, April 18, 2013