"Dave Butler" wrote in message
...
Mike Rapoport wrote:
The problem with this logic is that the 50' obstical distance is
genarally greater with the short field flap setting. Only the ground run
is shorter.

I don't have any documentary evidence, but this is counterintuitive and
contrary to my unquantified experience. The Cherokees feel like they go up
at a much steeper angle with the flaps. Is it an illusion?


I think so. The Helio Courier flight manual gives different flap settings
for minimium ground run vs. minimiunm 50' obstacle clearance with a lower
flap setting for the obstacle clearance distance. These airplanes have more
sophisticated flaps than a Cherokee (single slotted fowler flaps on the
Helio) so I assume that the Cherokee is even more disadvantaged as the flaps
are deployed since they are creating relatively more drag for each increment
of increased lift. Of course, if the runway is not hard and dry, anything
that reduces ground roll will likely reduce the obstacle distance.

Also, the maximium performance takeoff in a Super Cub is to accelerate with
the flaps retracted and then deploy full flaps to break ground, then to
reduce flaps while accerating in ground effect to Vx and then to climb at
Vx. It is impressive to see someone do this well.

You will need more pitch with the lower flap setting.

Perhaps someone with a newer Cherokee could look in the manual and see if
there are obstacle clearance charts for the different takeoff
configurations?

Mike
MU-2