In response to my enquiry about stall strips, I received the following
helpful advice from Andy Draper. It explains exactly why we fit stall strips
and what you should be looking out for when there is a wing dropping
problem.
I have added my comments at the end.
ORIGINAL MESSAGE
-- Europa-List message posted by: "Andy Draper" <andy@europa-aircraft.com
Dear Carl,
The fitting of stall strips was originally devised as a means of complying
with the requirement that it is necessary to provide a stall warning of at
least 5kts. The wing alone provided only 2 -3 3 kts. The stall strips were
also found useful in enabling the 'tuning out' any adverse behaviour at the
stall, as some Classic wing owners do find, however if fitted or adjusted
incorrectly you could also adversely affect the take off and landing
performace. Correctly fitted, they will not do so. The template provides
a good starting position for the stall strips which should not make much
affect at all, except perhaps increase pre stall buffet. Only subsequent
flight tests will enable the fine tuning for eliminating any wing drop at
the stall.
You probably know all this anyway as it's all described in Chapter 9 of the
Owners Handbook, but your question to the Forum indicated that you may have
thought that it may no longer be valid with the introduction of the audible
stall warner. My philosophy now is to suggest the fitting of the audible
stall warner for stall warning and only fit stall strips to tune out bad
behaviour at the stall.
One thing to check before you go to far is to check the flap extension
angles. As the wing drop only occurs in the landing configuration, is
perhaps one flap extending slightly further than the other? A more extended
flap will enable the wing to stall at a slightly higher CL.
Also to confirm is that the aircfaft is in fact in balance at the stall
rather than the 'ball' being in the middle. I have seen Turn Coordinators
set so they are level with the panel but the panel itself is not quite level
with the aircraft.
I hope that this is of some help.
Best Regards
Andy Draper
Dear Andy,
Thanks for the info which I found most useful.
I think the way forward (weather permitting) is to first check the symmetry
of the flaps etc (whether one is extending further than the other) and also
check . Then if everything is ok start playing around with the stall strips.
Mike Dolphin did the original flight test and he felt that the wing drop
was not uncommon on the Europas he had flown. The stall warner goes off a
good 5kts before anything adverse happens so there is a level of protection
there.
As one dosent normally stall an AC deliberately this isnt a pressing issue
at the moment but if for any reason the stall warner failed to operate and
the wing dropped close to the ground we would be in an unrecoverable
situation (as opposed to both wings stalling simultaneously). There is of
course always the pre stall buffett but I know from past experience that
when things are going wrong in the air ones brains are often on a different
planet and even the most obvious warning signals can be ignored.
I think until the wing drop issue is resolved we need to be sure the stall
warner is checked prior to each flight (it is now part of the pre flight
checks).
Many thanks again for your help.
Regards,
Carl
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