About a month ago I emailed the group about our first flight with long
wings. We performed some glide tests which resulted in the following
data:
Minimum sink was 267 fpm (234 fpm normalized for altitude) at 50 kts
IAS and best L/D was 22.6 at 55 kts IAS.
These glide tests were without fairings on the fixed outriggers legs and
without a cowl flap.
We have since built and installed outrigger leg fairings and a cowl
flap. New glide tests were performed with following data:
Minimum sink was 254 fpm (229 fpm normalized for altitude) at 55 kts
IAS and best L/D was 25.8 at 60 kts IAS.
The outrigger fairings were copied from what Dave Anderson did on his
motor glider. We used a hot wire to cut aerodynamic shapes for the
nylon outrigger legs and kept the foam in place with 2 inch diameter
heat shrink tubing. This allows considerable flexing of the nylon leg
without damaging the fairing.
The cowl flap is located at the lower, rear of the XS cowl / cooling
duct, allowing us to close off the exit air from the coolant and oil
radiators. Air from the eyeball inlets in the upper cowl that exits on
the sides of the lower cowl is not closed off. This is the air that
cools the cylinders and muffler.
Besides the improvement in glide performance, we noticed a 2 knot
improvement in cruise speed with the cowl flap closed. At 75% cruise
(5.3 gph fuel flow) we got 114 kts IAS with the cowl flap open, and 116
kts with it closed. At 5500 feet altitude and 18 deg C OAT, this was
about 129 kts TAS. Our coolant and oil temps went from about 183 deg F
to about 195 deg F with the cowl flap almost completely closed. Our IAS
readings may not be all that accurate, so we need to check this data
with some GPS runs at a later date. We are looking forward to testing
cruise speed with cowl flap closed with our short wings installed,
hoping for a similar improvement.
Regards,
Terry Seaver
A135
Mono-wheel XS with Rotax 912S, Airmaster prop
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