I recently read the POH for a M20V, the advertising for this aircraft states that the top speed is 242 KIAS. The POH gives the Vne at 196/195 KCAL/KIAS. I have found a similar discrepancy, the Vl3 (light sport aircraft) mentions the aircraft has a Vne of 165 KIAS, yet one of the engine choices gives the plane a max cruise speed of 195. I find these numbers confusing can anyone shed a light on this?
$\begingroup$
$\endgroup$
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
3
The reason is that cruise speeds are usually given in TAS (True AirSpeed) rather than IAS (Indicated AirSpeed) or CAS (Calibrated AirSpeed). See e.g. this answer for details on what these speeds are.
Have a look at the following plot showing TAS as a function of altitude for the two Vne speeds you gave (assuming ISA conditions):
You can see that the claimed cruise speeds are achievable above 14,000 ft for the M20 and above 11,000 ft for the VL3 without exceeding Vne.
You said that advertisement for the M20V claimed a top speed of 242 KIAS, but I think that is a mistake. It should be KTAS, not KIAS. Wikipedia also claims:
Cruise speed: 242 kn (278 mph, 448 km/h) (TAS)
answered Jul 3, 2020 at 7:18
-
$\begingroup$ So is VNE (at least on some A/C, maybe those where the VNE is dictated by flutter and not load factors), my A/C has a plaque reporting a decrease in IAS VNE with altitude. $\endgroup$ Jul 3, 2020 at 18:16
-
$\begingroup$ @Caterpillaraoz You are right that Vne can depend on altitude, but it is always given in IAS or CAS, not TAS. For the Mooney M20, it just says Vne is 196/195 KCAS/KIAS in the POH (see e.g. here). Even if Vne is lower at higher altitudes, the max. cruise speed will obviously be below that (after conversion from TAS to IAS/CAS) at that altitude. $\endgroup$ Jul 3, 2020 at 21:31
-
$\begingroup$ The more i dig into this more more complicated the thing becomes. $\endgroup$ Jul 5, 2020 at 17:16