Thanks! I'd forgotten about venturis. I've flown a bunch of them.

On 10/29/2015 12:34 PM, wrote:
A non-icing turn and bank is one that is electrically driven or powered by a vacuum pump instead of an external venturi. Walk around a small airport and you're almost certain to see older light aircraft with large external venturis used to drive the gyros. Look at enough old pictures of gliders and you'll even see them there on occasion. The drawback of using a venturi to drive blind flying instruments in the clouds should be pretty obvious.

I've got an up to date correction card in my glider. Anyone ever try flying a compass course accurate to within 2 degrees in a sailplane? Good for a laugh.

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Dan, 5J