Friday, September 30, 2011

Checking Airspeed

There's a great article in the September 2011 issue of Sport Aviation about how to rig up a homemade manometer for checking your airspeed indicator. Since I was a budding scientist (and haunted science fairs and other geeky events) before I became a theatre major , such things interest me and I had to make one of my own for my own amusement as much as anything.

Note the intriguing tangle of tubing, the symphony of scales, all the neat lines and squiggles and numbers. Ah, 'tis a veritable work of art.

Then come the usual caveats. Nothing can be accomplished in the world of science without caveats.

First and foremost, the scientist has to have a point of beginning for the experiment and rules to give him a stable platform on which to build his argument. No experiment can merit serious consideration without these essential ingredients.

Next, a convenient means of measurement must be provided in order for the scientist to gauge the success of his experiment. This is done by reference to numbers placed in very scientific fashion here and there so as to lend credence to the scientist's work. In this case, those numbers refer to air pressures converted to airspeeds and begin to mean something when the scientist adds colored water to the tubing (paying careful attention to the amount) and applies pressure to an open end by carefully blowing into the tubing (p.s. never do this. The proper method of applying pressure is to attach a length of flexible rubber or silicone tubing to the end and roll it up to provide the pressure you need, but I didn't pay attention to this part of the article). When enough pressure is applied, the open end of the tubing is sealed by either crimping the tubing or, more often, by plugging the end with the scientist's tongue. This hurts like blue blazes after awhile and leads to verbal exchanges with the second member of the scientific team that are right comical at times.

Every self-respecting scientist has an alternate means of compiling his data, so in the event a level, stable platform cannot be achieved in the beginning this blue scale shows the total difference between fluid levels in each tube and converts this differential to an airspeed. Since we are dealing with arguably the most commited scientists, to wit: pilots, every opportunity to achieve a result must be explored. Newton, Bernoulli, Boyle ... none of these guys could fly and we still remember their names. Go figure.

All in all, the manometer experiment was a success. My airspeed indicator is fairly accurate and the system leak rate is acceptable. For a much better explanation of how to build and use a simple manometer, you'd be smart to check Sport Aviation for September. Maybe this link will work: