Overspeed crash trigger speed

Presently you will crash as soon as you hit the limiting speed, Vne, Vno/Mmo.

IRL there a considerable margin until reaching the actual limiting speed Vdf/Mdf, ~20%.

Certification note: Each part of the airplane must be demonstrated in flight to be free from excessive vibration under any appropriate speed and power conditions up to Vdf/Mdf.

So there’s no need to add heavy buffeting etc. simply delaying the crash would be sufficient IMO.

2 Likes

I have the same issue too and it’s really annoying.

I mainly fly the C208 which has a Vmo of 175kts, currently if you go about 178kts you ‘crash’. This mostly happens when cruising at 160kts and hitting unexpected turbulence/gusts/windshear that push your airspeed up to 178kts, even momentarily.

(I am aware the turbulant air penetration speed is 148Kts in the C208, but speed increasing to 3Kts over Vmo due to unexpected weather wouldn’t break the plane, or any other certified plane for that matter)

As previously stated, in real life the margins are a much more generous before you reach Vdf. But even a conservative 10% margin above Vne/Vno/Vmo would be much more realistic and sufficient to stop this issue.

It should also be really easy to implement in the sim, Asobo simply need increase the ‘crash trigger’ (which currently uses the aircraft’s max speeds from flight_model.cfg) to be 1.1x or 1.2x the value in that file.

The margins for certified aircraft are stated in JAR/FAR Part 23, Rule 23.335.

Which generically states:

  • Design Cruising Speed (Vc) = 33 * Sqrt (wing loading)
  • Design Dive Speed (Vd) = 1.4 * Vc
  • Never Exceed Speed (Vne) = 0.9 * Vd

And those are MINIMUM requirements!


So Vd for the C208 should be at least 175 / 0.9 = 194kts! Meaning the aircraft shouldn’t ‘crash’ until you, at the very least, exceed 194kts (assuming you stay within the G limits of course).

2 Likes

A video with some good context around certification requirements and generally Vmo/Mmo/Vd/Md https://www.youtube.com/watch?v=UcpPQcvBHJ8
The opening lines make exactly the same point as this thread :smiley:

When reaching the red limit zone at high speed, the aircraft is far from being in a danger zone. Above Vmo, or Mmo, there is still a huge flight domain that is free of flutter. The aircraft can fly up to Vd or Md, which are design dive speeds, used for the structural sizing. Limit loads are only reached with severe manoeuvres, and these loads are not achieved with a simple overshoot of Vmo or Mmo.

1 Like