What is "50 ft obstacle climbing speed"?

[super jet 100]

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.

pic: www.i.stack.imgur.com/A2QVy.png

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.
pic: sketch 1501933501463 ? imgbb.com

[Flyingmac]

Optimum climb angle for a no-flaps departure. Nothing to do with 50ft over the end of the runway. Sometimes runways are different lengths. The reference to 50ft is meaningless without a distance.


The others are-


Angle of climb for obstacle clearance= shortest distance covered to 50ft. Flaps down.


Rate of climb for optimum height gain= longer distance covered to 50ft. Flaps down.

[Genghis the Engineer]

It's the figure that was used in flight testing to obtain the take-off distances in the manual.

G

[westhawk]

I'll use a Piper Archer as an example:

From the POH
Vx is 64 KIAS. (flaps up)
Recommended short field takeoff procedure is to use flaps 25, rotate at 55 KIAS and climb at 60 KIAS until clearing obstacle. Then pitch down to accelerate. Flaps 10 passing 64 KIAS then flaps 0 and maintain 76 KIAS (Vy)

This procedure provided the shortest total distance from brake release to a 50' height above the runway during flight testing.

[tmmorris]

What date is that POH? The POH for ours (PA28-180 1972) specifically states the only takeoff procedure is to accelerate to the "takeoff safety speed" 68KIAS and initiate the liftoff. "This speed applies to all weights and altitudes."

I've heard the technique you describe recommended but it's not in our POH.

[Flyingmac]

Hit 50kts. Drop 2 stages of flap. Lift off. nod the nose to 60kts and climb. Works a treat.


I avoided the term 'Rotate'. It's more of a skip and level off.

[fireflybob]

What date is that POH? The POH for ours (PA28-180 1972) specifically states the only takeoff procedure is to accelerate to the "takeoff safety speed" 68KIAS and initiate the liftoff. "This speed applies to all weights and altitudes."

I've heard the technique you describe recommended but it's not in our POH.

tmmorris I think that was the only technique scheduled performance in the original (CAA) Flight Manuals and is still included as a CAA annexe to the later (FAA) POHs. One point to note is that FAA figures are not factored whereas CAA usually are (i.e. X 1.33 for take off, 1.43 for landing and HWC 50%, TWC 150%).