CONFIRMING CG LOCATION
You can confirm the CG location via the
inverted flight test
below:
Inverted Flight Test:
A well balanced Alula-TREK should fly inverted with a little forward stick (down
elevator), assuming good lift and moderate airspeed. If it takes NO forward stick, then the glider is slightly
tail-heavy, and if it takes more than 1/3 forward stick the glider is a bit nose-heavy. How much this bothers
you should be dictated by the previous CG tests, and how much you like to fly inverted. Some prefer their
gliders to be a bit more nose-heavy, as they tend to be more stable and predictable. We like ours quite
neutral, as this gives the glider a smooth and precise feel and makes for the straightest launches to altitude,
although it will require a little more concentration to fly.
ADJUSTING ELEVATOR RATES
At the same time you are working on the CG, you'll probably find that your elevator rates need adjusting.
For a flying wing, having too much elevator movement is as bad as having poor balance. This is especially
so if you move the CG back a bit, as this will make your plane more sensitive to pitch, i.e. elevator inputs.
The easiest way to test elevator rates is the
Loop Test:
1.
In decent lift, an Alula-TREK with proper CG and elevator rates should be able to do a nice, reasonably
tight loop after building airspeed in a dive. If the plane has too much elevator throw, when attempting
a loop the glider will nose up quickly and then hesitate, perhaps not finishing the top of the loop. This is
a sign of excessive elevator throw, and the hesitation is a type of stall caused by too much control
surface movement. If you see this, you need to reduce your elevator rates.
2.
Likewise, if the loop is huge and it seems like the glider could be looping tighter, you can increase the
elevator rates. If the CG is close to right on, you won't need to do much. We recommend increasing the
rates a little at a time until you get a nice loop from a reasonable entry speed. We like our elevators
relatively insensitive, so we don't usually set our elevator rates as high as other people (We find it
makes the elevator too sensitive and thus makes the glider harder to fly smoothly and efficiently). Play
with it until you get it "dialed in" exactly the way you like. The elevator response should be nice and
smooth.
3.
A final note:
If, when flying, you pull back and the glider’s nose bobs up and down very rapidly in a
“hyper-stall,” then you've got way too much elevator deflection. If you have your control surface rates
set to the recommended amounts and you have your CG correct, YOU WILL NOT SEE THIS. However, if
you are seeing it, it's a sure sign your elevator rates are too high.
20.
