On 07/29/2013 11:25 AM, GRAHAM SINGLETON wrote:
> don't use 30 degree flap, Europa tested it and found you are starting to
> lose aileron control at the low speeds achieved in ground effect.
I have some trouble believing this (and even when it is true it is
questionable whether this is still a valid reason for the XS with the
increased aileron span and with more powerfull engines).
With higher flap settings you are getting more drag than additional
lift. With 10% more flap (30 degree instead of 27) you will get maybe
just 5% more lift. If the ailerons are inadequate for this tiny bit of
extra lift I think they would have difficulties handling 27 degrees as
well. Furthermore, in the XS the ailerons are substantially increased in
lenght, significantly more than 5%, and should have much more control
power at low speeds! Even if control problems were the limiting factor,
than it is questionable whether the same limit would still be needed for
the XS.
I thought that the limitation in flap was because of the 80hp engine
used for the certification, which might have lacked sufficient power to
exercise a go around with full flaps under full load (which is, if I
remember correctly, a certification requirement. For the same reason the
older Cessna's have 40 degree flaps, where the newer ones have 30 degree
which was instantly rewarded with a 30Kg higher MTOW without any
structural changes).
Furthermore, in the tri gear the fact that you have the option to use 30
degree flaps doesn't mean that you will have to use this all the time.
There are situations where more flap would be welcome, and there might
be situations where using less flap would be better. I can't see the
benefit of the 26 degree limit. Of course for the mono you have no other
option than to land with full flaps, so maybe in this case the
limitation is justified.
I know folks having drilled a new hole in the lugs on the flap control
tube, so that the actuator can drive the flap further (and faster). No
control difficulties are observed even in quite a few nasty situations
with 30 knots wind and lots of turbulence. Instead the short field
capabilities are somewhat improved.
Regards,
Frans
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