The low VNE just doesn’t make sense to me.
I’ve seen 155kts quoted, but for a plane that will cruise between 140-150kts, that VNE seems dangerously low to me.
Maybe they got flutter at 156kt 
AF wrote:
The low VNE just doesn’t make sense to me.
I’ve seen 155kts quoted, but for a plane that will cruise between 140-150kts, that VNE seems dangerously low to me.
Those numbers would be crap in certified aircraft , you get continuous cruise as VCC(kts) = 33*sqrt(wingload lbs/ft^2)
Then you test for dives at VD = 1.4*VCC and VNE at 0.9*VD, but still subject to flutter limitations
I tried gliders in smooth air for aeros 2kts close to their VNE in clam air, in turbulent air with no parachute anyone will chicken way before that
Well if it’s anything like the 912 then it will be a great engine andI bet the fuel figures will be better than any comparable lyco or conti.
I’d really like to see this engine in a da42 or how about a new PA28-140?
It’s a 915.
Is VNE IAS or TAS ?
If IAS, it’s more than ok.
Jujupilote wrote:
Is VNE IAS or TAS ?
Flutter limits are in TAS, aerodynamic forces limits are in IAS, so not clear where the mix sits !
Manufacturers will rarely test flutter TAS limits they just show there is no flutter at 1.2*VD (IAS) and get you a VNE as (TAS) with 10% margins (5000ft-15000ft altitude?)
https://www.flyingmag.com/technique/proficiency/technicalities-are-you-feeling-lucky/
Ibra wrote:
Flutter limits are in TAS, aerodynamic forces limits are in IAS, so not clear where the mix sits !
All the speeds should be KIAS
Vne is specified in IAS – it is on the ASI so must be IAS.
The actual aerodynamic factors which determine Vne are based on IAS with some and TAS with others, AIUI. For example flutter is firmly based on the speed of the airflow i.e. TAS. Aerodynamic forces are based on IAS… for example the authority of control surfaces is IAS related. And Vne must be calculated backwards taking into account the achievable (or certified, if lower) ceiling, because you are much closer to flutter onset if you commence a -1000fpm dive at 15000ft and IAS=150 than at 2000ft and IAS=150 (because TAS is a lot higher in the former case). Some previous discussions on that.
Flutter is a specific frequency or harmonic range, it’s not linked to amount of aerdynamic forces which generally relate to IAS, but it is linked to TAS and mass-elasticity of structures
The distinction TAS/IAS is never an issue for say PA28 as it’s never found at 25kft or above it’s demonstrated ceiling but it’s something that appears regularly in gliders
I think no one will be able to answer what happens to C172 at VNE IAS in 35kft
VNE is IAS of course, although their 145 cruise speed are in TAS.
