In my last post I wrote about cruising with a REP powered airplane. As I said, you may want to plan your cruise using the performance tables provided with the kneeboard.
That’s a good thing but you must remember that on the performance tables the speed is reported as TAS (True Air Speed) while the airspeed indicator reports it as IAS (Indicated Air Speed).
This means that you cannot directly compare the speed indicated by the instrument with the one reported on the performance tables!
If you don’t know the difference between IAS and TAS, you may want to read this article: https://en.m.wikipedia.org/wiki/True_airspeed
Basically, the point is that the IAS is usually lower than the TAS. So, if you read 150 knots TAS on the performance tables at 8000 feet, expect the IAS indicated on the instrument to be lower!
To calculate your TAS there is a simple rule of thumb. Just add to your IAS the 2% every thousand feet. For example, 150 knots IAS at 8000 feet are around 150 + 16% = 174 knots TAS.
On the other side, if you read 150 knots IAS on the airspeed indicator at 8000 feet, it means that you’re actually flying faster (your TAS is higher than your IAS).
This is quite a complex topic for a side note but I hope you simmers now know a little more how to work with the tools REP provides you. 🙂