Behaviour at high altitude?

[TurboHog]

There seems to be something wrong with it. Try flying 250kts IAS at 40000ft in neutral (default) weather conditions.

 

It behaves much like when you are flying too fast at low altitude (unintentional rolls). Try pulling a 2g turn and you will tumble out of the sky. I suppose that's not what it should do? Or is it really that uncomfortable to fly at high altitudes?

[jocko417]

What's the machmeter say at 250KIAS at 40,000'?

[effte]

250 KCAS should equal M.82.

[IvanK]

I guess its debatable that 2G could be sustained at .82/40K .... certainly no where near transonic buffet boundary's.

[jocko417]

250 KCAS should equal M.82.

 

Had your whiz wheel handy? :)

[effte]

Had your whiz wheel handy? :)

Always. Never leave home without a CR-3! ;)

[RagnarDa]

Behaviour at high altitude?

 

I guess its debatable that 2G could be sustained at .82/40K .... certainly no where near transonic buffet boundary's.

 

 

What is the critical mach of the Sabre?

Edited August 3, 2014 by RagnarDa
typo

[TurboHog]

Aren't the adverse high speed aerodynamic effects based on (absolute) airspeed.

 

Suppose I try to prevent these effects from happening I must be flying 200kts indicated at 40000ft. You can not even a do very simple manoeuvre.

 

Surely that can't be right?

[RagnarDa]

Behaviour at high altitude?

 

IAS is the relative dynamic pressure, not the airspeed. The best measure of airspeed at height is your Mach meter which uses calculated TAS. The adverse effects are because of the high airspeed around the airplane body. Hope that helps.

 

Edit: Think of it like this: You need IAS to not stall, but it will decrease as you climb. On the other hand you shouldn't fly too fast because of sound barrier effects. Look up http://en.m.wikipedia.org/wiki/Coffin_corner_(aerodynamics)

Edited August 3, 2014 by RagnarDa
more explanation

[TurboHog]

IAS is the relative dynamic pressure, not the airspeed. The best measure of airspeed at height is your Mach meter which uses calculated TAS. The adverse effects are because of the high airspeed around the airplane body. Hope that helps.

 

And how does stall speed change in IAS? It remains the same or becomes lower?

[RagnarDa]

The stall speed remains the same but the IAS-readout will decrease as the air get thinner. Again, IAS is dynamic pressure which is what you need for the wings to generate lift. Flying at or above the critical Mach could cause stall-like behaviors like Mach-tuck but it's not the same thing. As you get higher you will have a progressively smaller window between too fast (Mach-effects) and too slow (stall). Apparently the U2 had a window of 5kts when at its operating height...

[RagnarDa]

Dynamic pressure is the force acting on the airplane.

[Knubinator]

What is the critical mach of the Sabre?

Mach .92 I believe, since that's at the point that the wings so providing lift and you begin to lose control.

[krazybiskit]

I thought there was a post about how sabre had a compressability issue between mach .8 and mach .9

[26-J39]

There seems to be something wrong with it. Try flying 250kts IAS at 40000ft in neutral (default) weather conditions.

 

It behaves much like when you are flying too fast at low altitude (unintentional rolls). Try pulling a 2g turn and you will tumble out of the sky. I suppose that's not what it should do? Or is it really that uncomfortable to fly at high altitudes?

 

I have no problems holding a 210-220kt sustained 2.5g turn at 40,000. I was actually suprised how well she held energy. Major buffeting if I hunt for 3g.

[Sabredog]

The Sabre seems pretty response to me at altitude. Quite pleased with how she handles. With less air to bite into up there it's difficult to put on the G's without the wing exceeding the critical angle of attack.

[whartsell]

the second half of this video explains it well....

 

yes I know its the FJ2 (Navy F-86) but the flying qualities are similar