CAS vs IAS

[tgrayson]

Maybe my wording here is funky or partially incorrect but do you see where I am going with that tgray?

Not even slightly. Thrust isn't flat in a propeller aircraft (it slopes downward), but it essentially is flat in a turbojet. Power = Thrust * velocity, so the power available curve does depend on the thrust available curve. Power in a propeller aircraft is relatively flat, assuming a constant speed prop, but power increases with airspeed in a turbojet.

Regardless, I used the flat thrust curve to demonstrate the reasoning process.

Drunken, the resultant change in Vx and Vy has to do with the clockwise rotation and upward shift of the power required curve.

No, it doesn't. That rotation only happens when graphed in true airspeeds, but Vx/Vy are indicated airspeeds.

 

[shdw]

No, it doesn't. That rotation only happens when graphed in true airspeeds, but Vx/Vy are indicated airspeeds.

Than remove clockwise from the statement, upward shift would be the reason or at least that explains Vy. Remind me how Vx is determined on the PaPr curve, I was pretty sure it could be but am failing to remember how. Here is an easier picture for Vy:

 

[tgrayson]

upward shift would be the reason or at least that explains Vy. Remind me how Vx is determined on the PaPr curve, I was pretty sure it could be but am failing to remember how. Here is an easier picture for Vy:

You're quoting my own chart to me? You're missing the significance of the red and light blue arrows. They show the direction of movement of the power required curves and power available curves with increasing altitude. The important points:

1. When plotted in indicated airspeed, the power required curve only shifts upwards with increasing altitude, and
2. When plotted in indicated airspeed, the power available curve shift down and to the left.

The point is that the velocity of minimum power required does not change, but the point of maximum power available shifts towards lower airspeed. Hence, the change in airspeed for Vy at higher altitudes is due to the shifting of the power available curve, not the power required curve.

You really can't determine Vx from a power chart, although you can find the point of minimum drag by drawing a line from the origin tangent to the power required curve. That doesn't tell you, however, where the maximum excess thrust occurs. If you were to derive a thrust/drag curve from the power curves, you'd see that decreasing power makes the thrust available curve (which slopes downward to the right) decrease more slowly with velocity, meaning a flatter curve. This moves the point of maximum excess thrust to the right.

 

[shdw]

You're quoting my own chart to me?

That wasn't intended as to you but in general since I figured you knew it anyways, funny though that it is your creation I didn't notice that on the site. Thanks for clearing that up for me bud.

PS Your first post I quoted earlier still baffles me, seems too unexplained compared to your usual replies.