Little X’air niggle

I’m pretty certain that the X’air’s airspeed indicator is under-reading. You notice it at all speed ranges – the aircraft unsticks when taking off at what looks to be a very low speed (indicated 40 mph, possibly a bit less) even with two on board and with 50 litres or so of fuel, when you lower the nose after take off, it takes some time to get an indicated 50mph for the initial climb and when climbing at an indicated 45mph, at what should be the best climb speed, you get get a climb rate of quite a bit less than 500 ft/min. But the time you really notice it is on landing when with 50mph showing, as you approach the runway, it’s obvious that you’re doing quite a bit more than that.

The pitot tube has been snapped off several times (the most recent was when the inspector backed onto it …. ahem :shock:) and the tube now fitted is a bit smaller in diameter than the original. I asked about this on the BMAA forum today but the news from those who know about these things is that pitot diameter is not critical and that if under-reading is happening, it’s more likely to be due to an air leak in the system. Or, I suppose, a faulty gauge although we hope that this isn’t the case of course. So it looks as though we need to track the reason down. I’ll start though by cleaning up and filing the end of the tube into a streamlined profile because apparently that can make a bit of a difference, and I’m pretty sure it’s just been left as a blunt end from when it was cut using a plumber’s cutting tool. If that doesn’t work, though, we’ll need to look at other parts of the system. It’s a pity we can’t fly the X’air alongside MYRO and compare airspeeds but unfortunately I can’t be flying both aircraft at the same time 😉