Re: Flight characteristics questions
David J. Gall
They look likeBINGO! Well, not quite. Airfoil choices are a compromise and sometimes a
band-aid is needed to make a particular choice work in a particular
application. The LS(1) airfoil wasn't the only choice at the time, but it
had a goodly amount of marketing hype propelling it along in the early
'80's. We've since learned that its not such a hot GA airfoil after all, but
for a high wing loading (like on a Q200 canard) it is one of the "good"
choices. Unfortunately, its trailing edge is curved just the wrong way for a
Strainers are one possible solution to fix such a problem, but not the best
for the hangar-rash issues you mention, among others. The advantage of the
strainers is that they have a long leverage arm behind the elevator hinge
line. You could use a fixed trim tab instead, but it would have to be pretty
large since it would be closer to the hinge line. See the Long-EZ "new"
canard with the Roncz 1145MS airfoil for the correct way to do it. Roncz
essentially designed a fixed trim tab into the airfoil along the entire span
of the elevator. Most people don't even notice that it is there, but it is.
It is "tweaked" so that the elevator's natural "floating" angle of
deflection is appropriate for a low cruise speed for the airplane without
any trim system or control system forces being applied. Your strainers
should be adjusted similarly, if the designers and builders did their jobs
Meanwhile, since no one has adapted the Roncz airfoil to the Q-birds, I
recommend that you keep the strainers and follow the advice offered on this
list, especially the advice to have some experienced sets of eyes look over
your plane. I suspect you've got a problem with your strainers or maybe even
with the construction of your elevators.
David J. Gall
P.S. an anti-servo tab could be adapted, but it would only be flush at one
elevator deflection, likely close to full "up" elevator (trailing edge
down). Tabs, by their very nature, are not "flush."