Machmeter under reads

Hello all,

I startet the last couple of days some long range flights with the Lear 35 (standard, without the LR mod).

During long range flights it is very important to check the FF, Mach/TAS, etc. to meet the required values from the flight plan, because otherwise you will propably not get there where you want to 😉
I noticed the "underrreading" already at some prior flights I´ve done, so I deceided to write me some notes onto my nav log to show you what it´s about.

Here´s what I´ve written down and what the Mach number actually read and what it should read:

Read              Should     (OAT           /  TAS       )
.678                .707          (OAT -60°C / TAS 405)
.68                  .71            (OAT -60°C / TAS 407)
.649                .689          (OAT -55°C / TAS 399)
.63                  .667          (OAT -45°C / TAS 395)
.621                .659          (OAT -44°C / TAS 391)
.63                  .66            (OAT -45°C / TAS 391)
.621                .648          (OAT -51°C / TAS 379)
.641                .647          (OAT -55°C / TAS 375)

As you can see the biggest difference is at the beginning of the flight and the difference decreases while loosing weight.
This is of course nothing really seriuos, as I´m using the TAS and FF to compare my flight progress, but it would a "nice to have", you know!?

Cheers

Edited October 23, 20205 yr by JackJones