Vx/Vy as Altitude increases.....
- Thread starter CaptChris
- Start date
mtsu_av8er
Well-Known Member
Just peep the POH...it's pretty obvious!!!
casey
Well-Known Member
[ QUOTE ]
Okay... I want to hear as much info on this as possible. I got in an argument with a few fellow pilots the other day at the local FBO regarding Vx/Vy as altitude increases.
Any and all people throw their findings at me...... Much appreciated.
[/ QUOTE ]
Go out and pick a density altitude and climb through it every 5 kts from stall up to cruise or so. ie, pick 5000 ft da, figure out what altitude that is today and start 500 ft low, climb at a constant airspeed and note the VSI as you pass through your altitude. Repate for as many speeds as you want.
What you have now are points to make a graph of airspeed vs climb performance. Draw 2 lines to it, a horizontal tangent (a horizontal line that touches the curve in only 1 place), that place is Vy for that altitude. Now draw an ordinate tangent (a line that passes through the point 0,0 and touches the curve in only 1 place), this place is Vx for this altitude.
Now make a couple of these curves at increasing altitudes, and watch for yourself what Vx and Vy do as altitude increases.
You'll note that climb rates are not always positive, but take the data points anyway, just note a negative VSI. When you finally hit your absolute ceiling there will only be 1 airspeed that maintains altitude (0 climb) and all others yield a descent. This is the only condition where a horizontal and ordinate tangent can touch the curve at the same point, and hence be equal, which is why Vx=Vy at absolute ceiling.
Okay... I want to hear as much info on this as possible. I got in an argument with a few fellow pilots the other day at the local FBO regarding Vx/Vy as altitude increases.
Any and all people throw their findings at me...... Much appreciated.
[/ QUOTE ]
Go out and pick a density altitude and climb through it every 5 kts from stall up to cruise or so. ie, pick 5000 ft da, figure out what altitude that is today and start 500 ft low, climb at a constant airspeed and note the VSI as you pass through your altitude. Repate for as many speeds as you want.
What you have now are points to make a graph of airspeed vs climb performance. Draw 2 lines to it, a horizontal tangent (a horizontal line that touches the curve in only 1 place), that place is Vy for that altitude. Now draw an ordinate tangent (a line that passes through the point 0,0 and touches the curve in only 1 place), this place is Vx for this altitude.
Now make a couple of these curves at increasing altitudes, and watch for yourself what Vx and Vy do as altitude increases.
You'll note that climb rates are not always positive, but take the data points anyway, just note a negative VSI. When you finally hit your absolute ceiling there will only be 1 airspeed that maintains altitude (0 climb) and all others yield a descent. This is the only condition where a horizontal and ordinate tangent can touch the curve at the same point, and hence be equal, which is why Vx=Vy at absolute ceiling.
[ QUOTE ]
[ QUOTE ]
Okay... I want to hear as much info on this as possible. I got in an argument with a few fellow pilots the other day at the local FBO regarding Vx/Vy as altitude increases.
Any and all people throw their findings at me...... Much appreciated.
[/ QUOTE ]
Go out and pick a density altitude and climb through it every 5 kts from stall up to cruise or so. ie, pick 5000 ft da, figure out what altitude that is today and start 500 ft low, climb at a constant airspeed and note the VSI as you pass through your altitude. Repate for as many speeds as you want.
What you have now are points to make a graph of airspeed vs climb performance. Draw 2 lines to it, a horizontal tangent (a horizontal line that touches the curve in only 1 place), that place is Vy for that altitude. Now draw an ordinate tangent (a line that passes through the point 0,0 and touches the curve in only 1 place), this place is Vx for this altitude.
Now make a couple of these curves at increasing altitudes, and watch for yourself what Vx and Vy do as altitude increases.
You'll note that climb rates are not always positive, but take the data points anyway, just note a negative VSI. When you finally hit your absolute ceiling there will only be 1 airspeed that maintains altitude (0 climb) and all others yield a descent. This is the only condition where a horizontal and ordinate tangent can touch the curve at the same point, and hence be equal, which is why Vx=Vy at absolute ceiling.
[/ QUOTE ]
And I thought that moi could get techy. That just pegged the geek-o-meter.
/ubbthreads/images/graemlins/grin.gif
[ QUOTE ]
Okay... I want to hear as much info on this as possible. I got in an argument with a few fellow pilots the other day at the local FBO regarding Vx/Vy as altitude increases.
Any and all people throw their findings at me...... Much appreciated.
[/ QUOTE ]
Go out and pick a density altitude and climb through it every 5 kts from stall up to cruise or so. ie, pick 5000 ft da, figure out what altitude that is today and start 500 ft low, climb at a constant airspeed and note the VSI as you pass through your altitude. Repate for as many speeds as you want.
What you have now are points to make a graph of airspeed vs climb performance. Draw 2 lines to it, a horizontal tangent (a horizontal line that touches the curve in only 1 place), that place is Vy for that altitude. Now draw an ordinate tangent (a line that passes through the point 0,0 and touches the curve in only 1 place), this place is Vx for this altitude.
Now make a couple of these curves at increasing altitudes, and watch for yourself what Vx and Vy do as altitude increases.
You'll note that climb rates are not always positive, but take the data points anyway, just note a negative VSI. When you finally hit your absolute ceiling there will only be 1 airspeed that maintains altitude (0 climb) and all others yield a descent. This is the only condition where a horizontal and ordinate tangent can touch the curve at the same point, and hence be equal, which is why Vx=Vy at absolute ceiling.
[/ QUOTE ]
And I thought that moi could get techy. That just pegged the geek-o-meter.
/ubbthreads/images/graemlins/grin.gif
MidlifeFlyer
Well-Known Member
[ QUOTE ]
Haha, this is almost COMICAL. EXACT same argument we had! Can anyone elaborate on this topic?
[/ QUOTE ]What's the argument? Pull out any POH and look at the numbers for Vx and Vy. The POH (every) will show a smaller IAS number for Vy at altitude than at sea level, but a higher number for Vx.
Of course, the trick twist is that we're talking about IAS here. TAS in both cases increases since the 2%/1000 ft approximate increase in TAS over IAS usually more than compensates for the Vy decrease.
Haha, this is almost COMICAL. EXACT same argument we had! Can anyone elaborate on this topic?
[/ QUOTE ]What's the argument? Pull out any POH and look at the numbers for Vx and Vy. The POH (every) will show a smaller IAS number for Vy at altitude than at sea level, but a higher number for Vx.
Of course, the trick twist is that we're talking about IAS here. TAS in both cases increases since the 2%/1000 ft approximate increase in TAS over IAS usually more than compensates for the Vy decrease.
Grabo172
Well-Known Member
We had this discussion a little while ago... here's what went down...
http://jetcareers.com/ubbthreads/showflat.php?Cat=&Number=182378&page=1&view=collapsed&sb=5&o=&fpart=1
http://jetcareers.com/ubbthreads/showflat.php?Cat=&Number=182378&page=1&view=collapsed&sb=5&o=&fpart=1