Gyro theory Slow Flight

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t-bird
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Gyro theory Slow Flight

Postby t-bird » Sat Jun 22, 2013 2:36 pm

Hi Pieter
This is only the theory of slow flight, don’t try this on your own, practise it with your INSTRUCTOR and let him/her explain all the pitfalls.
Your question about safe height and power settings should be answered by your instructor not me.

This is how I understand slow flight and PLEASE FEEL FREE TO ADD COMMENTS.

The first thing you would do is to reduce your power to fly slower.
A reduction in power will lead to a reduction in airspeed and will effect your lift.
The lift formula is:
Lift L=CL ½R S V²
We can only influence CL – angle of attack and V² which is velocity of airflow.
You have adjusted your velocity down that means that if you want to achieve the same lift you can either change the angle of attack – back pressure on your stick or reapply power. In this case you will apply back pressure.

This will result in a high nose attitude at a reduced airflow.

Induced drag will now increase due to the slow airspeed.
You will see from the diagram that induced drag will shoot up at slower speed. The yellow line.
Lift drag.jpg
Lift drag.jpg (27.81 KiB) Viewed 4479 times
Some of Gyros have a rudder to the right in normal flight due to the propeller vortex generated by the prop. The gyro will tend to turn right if you reduce the power and flying slower. I don’t know how applicable this is to the Xenon with two rudders.

Your next step would be add power/thrust to overcome this drag.
You can end up using all the power available at slow speed with a high nose attitude to compensate for the increase in drag.

This bring us to the power curve
P curve.jpg
P curve.jpg (30.69 KiB) Viewed 4479 times
You will notice that your power required at low speed increase exponentially.
You will also notice that below 20 mph per the graph you would not have enough power available. This area of the graph is where you are flying behind the power curve.
Let say that your power available is equal to power require – where the two lines cross on the graph.

You can then hover at this point until the power required is increased due to sink or engine power is reduced due to turbo exceeding engage time.
Your only method of recovery now is to reduce the power lower the nose and apply power. Whereby airflow will increase and increasing lift and angle of attack reduce reducing induced drag.

Why reduce power for recovery if you are already behind the power curve ? The reason is that you can experience a Power Push over by reducing the attitude dramatically at WOT “wide open throttle.
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PieterKotze
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Re: Gyro theory Slow Flight

Postby PieterKotze » Sat Jun 22, 2013 3:29 pm

Wonderful summary!!!! Had to study all this for the exams, and got this from the Rotorcraft Flying Handbook, but this is a great summary.

Thanks!!! Keep up the teaching its really keeping me glued.

Pieter
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Re: Gyro theory Slow Flight

Postby ZE-Bud » Tue Jul 16, 2013 10:47 am

Hi Pieter and T-bird.

I Thought this video sums up the situation of "behind the power curve" very well ! :shock:

"Dons Calidus autogyro first flight at SCCMAS" on youtube

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