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#21
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Vx and Vy get a little more complicate with altitude change.
Vx increases with altitude, Vy decreases with altitude. Robert M. Gary wrote: BTW: There is a formula to get Vy, Vx, and Vso (and probably best glide) for each weight. I don't have it in front of me right now. That formula is on the Flight Engineer FAA written exam. -Robert, CFI |
#22
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George wrote:
d&tm wrote: Wont the best glide speed also keep you in the air the longest? if not what speed will? No, best glide doesn't do that. The best loiter speed is a bit lower than that for the best angle of climb. It's usually not published, but you can determine it pretty well by empirical experimentation. Vms really has nothing to do with Vx. Vms minimizes power-off power loss, Vx maximizes power-on excess thrust. Vms is easy to calculate. It's just 76% of Vbg (make sure you do IAS-CAS-*0.76-IAS; i.e. multiple CAS, not IAS). Hilton |
#23
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Robert M. Gary wrote:
BTW: There is a formula to get Vy, Vx, and Vso (and probably best glide) for each weight. I don't have it in front of me right now. That formula is on the Flight Engineer FAA written exam. Vs is easy, but modifying Vx and Vy for weight would be a very complex equation if done correctly since it would have to compensate for propellor efficiency, engine efficiency, etc as the airspeed changes. Hilton |
#24
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On Tue, 14 Dec 2004 at 06:50:15 in message
, d&tm wrote: Wont the best glide speed also keep you in the air the longest? if not what speed will? Nope. Minimum sink rate is close to maximum lift AoA. Strictly, for simple math, it is at max (CL^(3/2))/CD. Best glide angle is at Maximum CL/CD which is usually at a lower AoA than minimum sink. -- David CL Francis |
#25
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In article , David CL Francis wrote:
On Tue, 14 Dec 2004 at 06:50:15 in message , d&tm wrote: Wont the best glide speed also keep you in the air the longest? if not what speed will? Nope. Minimum sink rate is close to maximum lift AoA. Strictly, for simple math, it is at max (CL^(3/2))/CD. If you had a way to measure TAS instead of CAS, it would be at almost exactly 2/3 of best glide speed for any reasonable aircraft. This is only academically interesting, since airspeed indicators are notoriously inaccurate at the low end of their range. It's significantly slower, though. If you really want to know what it is, you can determine it (roughly) by experiment. You won't get an exact number without shutting down the engine, but I don't recommend that. Mike Beede |
#26
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On Fri, 17 Dec 2004 09:15:40 -0600, Mike Beede wrote:
In article , David CL Francis wrote: On Tue, 14 Dec 2004 at 06:50:15 in message , d&tm wrote: Wont the best glide speed also keep you in the air the longest? if not what speed will? Nope. Minimum sink rate is close to maximum lift AoA. Strictly, for simple math, it is at max (CL^(3/2))/CD. If you had a way to measure TAS instead of CAS, it would be at almost exactly 2/3 of best glide speed for any reasonable aircraft. This is only academically interesting, since airspeed indicators are notoriously inaccurate at the low end of their range. It's significantly slower, though. If you really want to know what it is, you can determine it (roughly) by experiment. You won't get an exact number without shutting down the engine, but I don't recommend that. Mike Beede Actually, its much closer to 3/4 Vbg (not 2/3) 76% to be more precise. This is also very close to stall AOA in most light GA aircraft, so you will amoost certainly have the stall warning blaring at you if you try and fly at Vmin-sink. |
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