Friday, 15 January 2016

Speedy V-Tail sloper

For the last 2 weeks the wind strength has rarely dropped below 20kn. To keep flying I needed to
design something that could handle strong winds. The obvious candidate was a speedy slope racer.

The balsa-pod version of my Ultralight Sloper was available because it was superseded by the mad-flipping Fusion. Here are the mods needed to transform it into a high wind speedster.

V-Tail 1

Many slope racers use a V-Tail, and I had never tried one, so that was my first mod. I used tape covered 3mm balsa, hot glue and guessed the dimensions. The tail servos are down on the tail, which is not ideal. Not so much for the extra tail weight but the added aero drag.

It flew OK but did not track well at all, drifting and wandering side to side. This prototype V-Tail did not provide enough vertical area.

V-Tail 2

Further reading here suggested that my V angle should be sharper, about 110ยบ and the area needed to be increased.

That improved the tracking heaps but I noticed my tail boom was twisting alarmingly when operating the rudder, as demonstrated in the video below.

Rudder function on a V-Tail is not as effective as a conventional vertical rudder because the control surfaces are acting at an angle to the airflow.  Most of the force goes into twisting the tail rather than moving it sideways, and the twist is in the wrong direction, a bit like adverse yaw from the ailerons.
Seems like V-Tails prefer more bank and yank style flying.

V-Tail 3

To increase the stiffness I shortened the tail boom by 150mm, cut 20cm off the 1.5m wing and 30mm off each tail section.

The shorter tail boom and smaller tail reduced the flex nicely resulting in much better speed and tracking.

In strong wind you can add ballast to give more momentum and penetration, which results in more speed. With a 2200mAH Lipo plus an extra 50g in metal washers it could handle 30kn flying crazy fast.

These photos show the final dimensions.

Flying weight with 1300mAH Lipo - 500g
Add ballast to taste
Wing - RG15 160mm chord
XPS foam hot wire cut
Covered with document laminating film
Servos - TGY9018 x 4

Strong wind V-Tail sloper overview and flights

Future design for more speed

For more speed I'll need to increase the tail stiffness further and reduce the drag.
My next high wind sloper design will have two tubes glued together for a stiffer tail boom and a conventional tail for less twisting. With a stiffer tail boom I should be able to place the servos in the fuselage for less drag, and run long push rods to the tail.

Weight is not a problem with these slopers, in fact more weight means more speed.

Stay tuned for updates.