Creating an Excel chart for V-G Diagrams

[hawker111 1]

Hello to all,

 

Would anyone be interested in helping me with a project I am working on?

 

I have V-G diagrams for the F-101, F-104 and F-105. I'm working on creating flight envelope charts in Excel, but I have a couple of questions regarding the stall line.

 

If anyone would be interested in taking a look at one of the flight envelopes, and could tell if I did it correctly, please send me a PM.

 

Thanks a lot,

 

Hawker111

[Fubar512 1,350]

Stall line at what weight (full or partial internal fuel, external stores, etc)?  At what indicated airspeed (the most obvious)? At what level of thrust?  At what air temperature (affects air density at all altitudes)? 

 

Most of the charts you'll find in a pilot's manual are meant to be used as guidelines, and as such, do not necessarily represent real-world conditions. 

[hawker111 1]

Here's a question regarding the stall line.

 

The F-105D Thunderchief, according to the V-G diagram, will stall below 160 knots.

 

My question is, will the F-105 stall just below 160 KIAS at 40,000 feet as well? Or, at 40,000 feet, such a high altitude, will the stall speed be greater that 160 KIAS?

[Fubar512 1,350]

160 knots indicated, in clean configuration on a "standard" day, with probably noting more than 1/2 internal fuel. 160 knots indicated at 40,000 feet is still  "160 knots :indicated", understand?

 

The F-105 has a very capable flap system, and it enables laden stall speeds to just below 160 knots when fully extended, but at too high an angle of attack for safe landing. Laden, safe landing speeds are in excess of 180 knots indicated,

[hawker111 1]

So even if the F-105 was at 55,000 feet, it would stall once airspeed dropped below 160 KIAS. I understand.

[Fubar512 1,350]

[hawker111 1]

What do the broken lines at 10,000 ft., 20,000 ft., 30,000 ft., and 40,000 ft. mean? That at those altitudes the stall speed (indicated) is higher than at sea level?

[Fubar512 1,350]

What do the broken lines at 10,000 ft., 20,000 ft., 30,000 ft., and 40,000 ft. mean? That at those altitudes the stall speed (indicated) is higher than at sea level?

That chart is using Calibrated Air Speed (CAS), and not Indicated Air Speed (IAS).  https://en.wikipedia.org/wiki/Calibrated_airspeed

 

The broken lines denote various altitudes, and nothing more.  Where they intersect the horizontal and vertical lines is what is of importance. The lines running horizontally represent (G) loading.  The lines running vertically represent calibrated air speed. 

 

For example look at the solid line, which represents 4,000 feet ASL. Note where the 1-G line intersects the airspeed line.  That represents your aircraft's stall speed in level flight, Also, take notice of the text in the center of the diagram, regarding clean configuration and stores.

[Constellation1710 4]

An airplane with a stall speed of 160 KIAS at sea-level one would think would theoretically stall at 160 KIAS at 60,000 feet: However it doesn't exactly work that way.  The reason has to do with mach-numbers and that plays a role in shockwave formation: 160 KIAS, sea-level is around Mach 0.24; at 60,000 feet is between Mach 0.81 and 0.82.  The shockwaves and the pressure gradient makes stalls easier so the critical alpha will lower as you go up.

 

Technically it might be more practical to think in terms of mach number first; then think of airspeed as the amount of air you are plowing through.

[Fubar512 1,350]

Precisely, though for the purposes of the series in question (SF2), we are usually addressing sea level to 40,000 feet, though of course, 160 kias at 40K would still result in a somewhat higher mach level than at SL.

 

My favorite was the narrow flight envelope for the U2 at 70K feet. The difference between a stall and critical Mach at that altitude was about 4 knots!

[Constellation1710 4]

Fubar512,

 

And a higher mach number has different airflow traits...

 

What you're describing with the U-2 is coffin corner: It even happens 747's where you have a 10-20 kt window at heavy weights.