controls speed & power controls descent rate
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controls speed & power controls descent rate
Why when we train for the PPL are we taught pitch controls speed & power controls descent rate, yet when we start Instrument training it is the reverse, power controls speed and pitch controls descent rate ? it confusing to me why we are taught one way to have it then reversed. Does anybody know why ?
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Generally the former is when the path of descent is not important, you just want to descend. When you need to acheive a particular path e.g. ILS then you steer the aircraft along that path using aileron/rudder/elevator and are left with power to control speed.
Join Date: Apr 2001
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I suppose when we teach descending, we start with the glide and the Elevator does control the attitude and the speed. We build from there. Add some flap, maintain speed = rate of descent increases. Add some power, maintain speed = rate of descent decreases. The Military train pilots to fly fast heavy things with lots of inertia. They tend to teach the other way. In reallity we are doing a bit of both. Either way is correct.
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Attitude+Performance=Performance
I was taught to pitch for airspeed myself, but have later found that that shouldnt be done (unless your doing carrier landings. Aerodynamics for Naval Aviators mentions this)
When flying light trainer aircrafts pitching or adjusting power for altitude wont really make a big difference since the airspeed is very slow.
But consider:
1 degree of pitch change equals a change in vertical speed of aprox. 2% of the airspeed. Since 1 knot is aprox 100 FPM (feet per minute) you can see that 2% of 100knots=200 FPM, 2% of 250 knots=500 FPM. This relationship holds true in any airplane as long as the speed is held constant and is accurate to about 10%.
So you can see from this that pitching for airspeed or altitude doesnt matter much in a C172 with approachspeed around 80-90 knots, but its quite significant when your flying heavy aircrafts approaching at 15-180knots, or flying enroute at several hundred knots.
When flying light trainer aircrafts pitching or adjusting power for altitude wont really make a big difference since the airspeed is very slow.
But consider:
1 degree of pitch change equals a change in vertical speed of aprox. 2% of the airspeed. Since 1 knot is aprox 100 FPM (feet per minute) you can see that 2% of 100knots=200 FPM, 2% of 250 knots=500 FPM. This relationship holds true in any airplane as long as the speed is held constant and is accurate to about 10%.
So you can see from this that pitching for airspeed or altitude doesnt matter much in a C172 with approachspeed around 80-90 knots, but its quite significant when your flying heavy aircrafts approaching at 15-180knots, or flying enroute at several hundred knots.
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High on approach:
A) Reduce Power to increase ROD
Lower Nose to retain airspeed
or
B) Lower nose to maintain flight path
Decrease power to maintain airspeed
either equate to the same thing, however A tends to take a little longer than B, which when combined with increased inertia, leaves B as the better alternative.
PPL teaching generally assumes low inertia aeroplanes where under some circumstances you may not have sufficient power to maintain the desired airspeed. As a result, PPL teaching traditionally involves using attitude to control airspeed on an approach.
In contrast the teaching for turning, involves using attitude or pitch to maintain height/ altitude whilst power controls speed. Possibly, because it is normal to accept a loss of 5 Kts in a medium turn the power/speed relationship is overlooked.
The next time you fly a visual approach, try method B, you'll probably never go back to method A again unles you fly TMGs.
A) Reduce Power to increase ROD
Lower Nose to retain airspeed
or
B) Lower nose to maintain flight path
Decrease power to maintain airspeed
either equate to the same thing, however A tends to take a little longer than B, which when combined with increased inertia, leaves B as the better alternative.
PPL teaching generally assumes low inertia aeroplanes where under some circumstances you may not have sufficient power to maintain the desired airspeed. As a result, PPL teaching traditionally involves using attitude to control airspeed on an approach.
In contrast the teaching for turning, involves using attitude or pitch to maintain height/ altitude whilst power controls speed. Possibly, because it is normal to accept a loss of 5 Kts in a medium turn the power/speed relationship is overlooked.
The next time you fly a visual approach, try method B, you'll probably never go back to method A again unles you fly TMGs.
