If it was good enough for the late Geoffrey de Havilland on the appropriate aircraft it's good enough for me:ban:Had I known I was going to start an Internet fight I would have just kept that pic to myself. I thought it was neat and I still think it's practical for where numbers don't matter. Obviously a pitot-static ASI is better otherwise they wouldn't be the most popular type now.
I can say with certainty however (with around 200 PIC hours spread between Johnson and DH types) that they're not as flawed as Dan thinks. On the Tiger Moth there's a pitot system as well and it matches the sprung ASI knot for knot between 40 and 90 but I've always been too busy to look at it outside that range. Likewise, in the E-2 and J-2 they always read about 40 at takeoff, 45 in the climb and 50-55 in cruise regardless of temperature or station pressure. In other words, density altitude doesn't affect it at any different rate than it affects the wing's ability to produce lift, which is really the only thing the ASI is for on a puddle jumper anyways.
Dan, if we're ever around the same airport at the same time and the weather permits let's go for a ride and I can show you.