Sunday, January 27, 2008

Vintage "Old Timer" Chuck Glider

I've finished and flown the Bowers glider (see photo left). It ended up at 30g flying weight, which is not amazingly light, but not heavy either. The main aim was achieved though, which was to improve over the Wallerstein 22" that I built too heavy at 50g (see earlier blog, Wallerstein was the "wing donor").

Flying at dusk in cool, still air, I was getting "still air times" of 36 to 42s. I may be able to improve the launch by moving the decalage closer to 0-0 for a more direct up line, but it's working consistently at the moment so I'll leave it alone. CoG ended up at about 60%.

In the air it looks "retro-fabulous" and floats around flatly. In the park a bloke and his son wanted to know where to get one! I explained it was self-built from a 1930s design, but did give them a closer look, explained how the DT works, and let the son have a little chuck.

I reckon it could fly away, so I fitted a simple DT flap (shown in the other two photos). This type of DT is typically made with aluminium foil from a drinks can, but I find balsa easier to work with and keep flat to the fuselage. The orange paint on the inside is an aid to see the DT operate. I use 3M Blenderm(TM) tape for the hinge, a little "fingernail" from a drinking straw to push the flap out and a balsa triangle stop to keep the flap perpendicular to the fuselage side. The airflow does the rest. There is negligible weight penalty with such a DT as the timer and parts add up to little over 1g and it is all in the nose.

There is a small increase in profile drag of course, but that will mainly affect the high speed launch, which is one of the biggest variables in any case! After testing, the flap was cut down to about 2" in length, which was found to be enough to turn the glide from the left hand circle into a straight line, while just about avoiding a dangerous "lawn dart" dive.

That's one problem with drag flaps - too big and the plane can spiral dive hard to the right and die an ugly death on crash landing. If the flap is too small, it willl not bring the glider down from a thermal and it goes OOS.

Personally, I think it is important that the flap turns the glide into a straight line, not a turn to the right, so that the plane exits the thermal.

It's all in the lap of the thermal gods!

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