(From CP43, Page 1, January, 1985)
The standard Long-EZ
canard, if built according to the plans, is identical to the VariEze plans-built canard.
On the Long-EZ however, there has been a history of what has become known as the
"rain trim change’. This trim change is usually a nose down trim change when
flying into rain requiring a small aft force on the stick to maintain altitude, which is
easily trimmed out, using the bungee trim system. According to feedback we have received
from builder/flyers, this is what most pilots notice. For the average Long-EZ pilot, this
is of course no problem, rather more of a minor annoyance and once you have experienced it
a few times, you simply trim for the condition and press on. A few builder/pilots however,
report that their Long-EZ’s exhibit a more pronounced nose down trim change,
requiring most of the available bungee trim force to fly "hands off" and in a
couple of cases, pilots report not having enough trim authority to trim "hands
off’. During the last two years we have spent a lot of time and effort to try to
understand what causes this trim change.
Thanks to John Roncz (airfoil designer par excellence) we now do
understand it and have the analytical tools to predict and to overcome this phenomenon. We
have built and tested five completely different canards with different airfoils. Many
flight hours have been flown and a considerable data base has been generated. Also, a
video camera was used to document tuft behavior on each airfoil . The lift and hinge
moments with and without rain were documented. A method to simulate the rain effect was
developed. Surprisingly one airfoil had no rain trim change at approach or cruise speed
but had a considerable reduction in max lift, resulting in a nose drop if rain were
encountered in the flare. The result of this extensive testing was the data John needed to
model the rain trim change in his computer program. Soon he was able to duplicate the
flight test results on the computer and from there was able to produce a brand new
airfoil, the Roncz 1145MS, which we have recently tested on the prototype Long-EZ, N79RA.
This completely new and never flown before airfoil is by far the
best we have seen. It has a negligible rain trim and the rain only adds 2 knots to stall
speed. Of course some more flight testing remains to be done, however, we are confident
that we do indeed have what we have been looking for. The R1145MS produces considerably
more lift than the original GU—5(11)8 airfoil, and in fact more than any we have
tested so far. This enables us to reduce the span, reducing whetted area, and thus drag.
The basic airfoil is also very low drag. Its trailing edge shape provides the correct
stick forces without external devices.
At this time, the span from the outboard tip of the left elevator
to the outboard tip of the right elevator is 130". This compares to 140" on the
original GU canard. We have incorporated the John Roncz designed curled-up wing tips first
seen on Mike and Sally’s N26MS. These tips are specifically optimized to enhance the
vortex coming off the tip of the canard and position this vortex in the "sweet
spot" over each main wing. The remaining test and preparation/printing of the plans
should be completed by April 1.
The new Roncz 1145MS canard will not be recommended for
the VariEze. The airfoil used on the VariEze main wing, is working very hard to maintain
attached flow even with the GU canard. This new canard may ruin the stall characteristics
of a VariEze. Feedback from VariEze flyers indicates that while most VariEze's do have a
small rain trim change, it is just that, a small trim change that in most cases is not
significant enough to warrant the flight test program that would be required to qualify a
new canard for the VariEze.