# Why are there restrictions on speed above 10000 ft still

Hello,
I was just wandering why speeds are restricted in this flight sim. In real life planes cruise at like 800km/h groud speed above 10000 ft but we arent allowed to go over certain speeds in this sim. Is there a specific reason for this?

1 Like

The speed limits above 10,000 feet are restrictions bounded to the airframe. If you tried going above the speed limit in planes in the real world, the forces acting on the plane may cause some pretty serious damage.

7 Likes

Itâ€™s totally achievable in IF. The speed youâ€™re reading in HUD is KIAS or Knot Indicated Airspeed, and 800 is the ground speed (GS) measured in kilometers per hour. Generally, with the same KIAS, the higher you fly, the faster your GS will be.

The 4 Types Of Airspeed, And What Each One Means For You | Boldmethod

FAR 91.117. This talks about the restrictions on airspeed in the US.

As others have said, GS is not the limiting speed. IAS is directly related to pressure force the airframe experiences from moving through the air. As @LordWizrak indicated, the airframe has design limits on how much pressure force it can take.

Mach speed measures how close your TAS is to the speed of sound. If the aircraft is flying with TAS too close to the speed of sound, some airflows over the aircraft become transonic before the aircraft itself, so you need a speed gap below M1.0 (for subsonic aircraft obviously), due to some nasty effects near the speed of sound (unless specifically designed for).

You can get a very high GS as long as you are high enough to keep the IAS down (thinner air; less pressure in the relative wind).

Hereâ€™s a visual shorthand I once wrote about speeds:
1)Wind Speed: how fast the cloud is moving toward the mountain
2)TAS: how fast you are moving toward the cloud
3)GS: how fast you are moving toward the mountain
4)IAS: how much dynamic pressure (â€śwind biteâ€ť) for the wing (and flaps etc.)
due to the speed of the relative wind (TAS) adjusted for how â€śthickâ€ť is that
moving air (density due to altitude adjusted for temperature)
5)Mach: how fast you are moving toward the cloud as a fraction of the speed of sound (again TAS)

2 Likes

This topic was automatically closed 90 days after the last reply. New replies are no longer allowed.