Vy and Vx make sense to me. They are used for fastest height gain at a given time and biggest angle of climb. But what is the purpose of that speed (it’s from DA20 POH)? It’s only 3 kts faster than Vx.
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I just can’t understand the purpose of this speed. I can use Vx and I will be well over any obstacles ahead. Maybe this speed is used as some kind of benchmark for calculation of ground roll & takeoff distance that will place me exactly at 50ft height over end of a runway?
it is also should to be maintained during engine failure after takeoff.
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It’s just a compromise speed for ease of use and balance of climb rate and angle between Vy and Vx that the aircraft has been tested at I think – they have also done similar for the EFATO case where in the training environment it can be taught tommaintain the same, single airspeed as you were selecting during the climb out
The speed for climbing through 50 ft is a reference speed for the AFM/POH take-off performance. The take-off distance to 50ft is a required number in the AFM, as is the corresponding speed, which has to be at least 1,2 x stall speed in take-off configuration. Without it the given take-off distance would simply not be adequately defined. You need to use that speed for the initial climb to get the AFM performance, but if obstacle clearance is not a concern, it is not necessarily a recommended speed.
What is “50 ft obstacle climbing speed”
For this type of aircraft from a certification perspective it is the end of the take-off… (flaps at take off and wheel down) which from a practical perspective isn’t really all that helpful, unless you plan on levelling off…
If the manufacturer wanted to demonstrate the absolute shortest number to get to 50ft, you would have a speed at 50ft a little lower than Vx and probably with some flap, but rather than leave you hanging they have sensibly chosen to demonstrate a take-off that is ‘completed’ (the 50ft) at 60knots. I have never flown a Da-20, perhaps they give some guidance on speed for initial climb out I would have guessed 65 knots, lifting off around 55 or maybe they just are suggesting 60knots in the initial climb is the one to aim for which would be reasonable as well. Keep in my they have made no adjustment for weight, which is pretty sensible too.
For my Bonanza, Vx (83 Kt) and Vy (96 Kt) are published only for the clean configuration. With the gear down and the Flaps down, Vx (61 Kt) and Vy (68 Kt) are dramatically lower. This information used to be published. If one uses the published speeds with the gear and flaps down for Vy, the Bonanza will barely climb if at all. The balked landing speed is 70 Kts. Note how close the balked landing speed is to Vy in the gear and flaps down configuration, which is the reason it was chosen in the first place. For short field takeoff, I begin the rotation about 3 Kts before the book speed so that liftoff occurs at the book speed and set a pitch angle of +12 degrees. The aircraft continues to accelerate and will reach the proper speed at 50 feet.
