Best margin above a take-off obstacle

WaspAir

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In a glider, with just a little practice, you easily can tell airspeed accurately by sound alone, but gyros have too much extra noise for that to work as well.

Glider pilots often use an audio variometer (VSI) so that they can fly continuous low speed turns with lots of bank, close to stall, to rise in turbulent thermals, avoiding other gliders circling just above and/or just below them, without looking at the panel. It makes a tone that varies with your rate of climb or descent. After a while you don't exactly hear it -- it becomes more of a subliminal thing so that you're aware of what's happening but not consciously checking or actively listening, while adjusting your turn shape and position to optimize climb rate.
 

ventana7

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In a glider, with just a little practice, you easily can tell airspeed accurately by sound alone, but gyros have too much extra noise for that to work as well.

Glider pilots often use an audio variometer (VSI) so that they can fly continuous low speed turns with lots of bank, close to stall, to rise in turbulent thermals, avoiding other gliders circling just above and/or just below them, without looking at the panel. It makes a tone that varies with your rate of climb or descent. After a while you don't exactly hear it -- it becomes more of a subliminal thing so that you're aware of what's happening but not consciously checking or actively listening, while adjusting your turn shape and position to optimize climb rate.
Audio variometers are also nearly instantaneous unlike a vsi in an airplane or gyro which has considerable lag. in an earlier post I mentioned using a dot on the windshield lined up with the horizon to maintain precise altitude during steep turns. The dot will have far less lag than your VSI, altimeter or the G feeling in the seat of your pants.
Rob
 

PW_Plack

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Behind the power curve is defined by a drag greater than the propeller thrust due to a too low forward speed. So it's a downhill flight despite full power.
JC, please do not perpetuate this false definition.

Your gyro has a minimum power-required speed, the speed at which it can fly straight and level with the lowest power and thrust. It is the point at which increasing parasitic drag and declining induced drag from the rotor meet on a graph. If you are flying at this speed, flying any slower will require more power. It is then you are on the "backside of the power curve," or "behind the power curve."

You can be behind the power curve and still be climbing. Getting so slow that full power will not maintain altitude is an extreme case.
 

Jean Claude

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I agree, your definition is correct. In France, aerodynamicists say for that: "second fligt mode" because "first flight mode" is the normal mode of airplanes.
But the gyroplanes is often flying in this second mode, even when cruising. It is not a dangerous criterion for them. The danger comes only when the maximum power can no longer give an ascending flight.
Hence their different definition .
 
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Philbennett

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This is an interesting topic and one I’ve debated here in the UK and I’m not entirely sure that its something widely taught or even talked about over here - to the degree that should a pilot elect to take off using Vx or Vy as their datum I don’t think it would correlate that well with the POH.

First of all the referenced airspeed is quite a bit lower than what is widely taught in the UK - where typically 65-70mph is used certainly to the first 300ft as a guard against issues should the engine fail. Of course the immediacy in the need to climb away and the deck angle would be a surprise (certainly if Vx is referenced) to many in the UK.

Next is the process in getting airborne. We have talked many times about the wheel balance phase and how long that should be and that will have a large influence on the ability to achieve POH Vx/Vy take off distances. The other huge factor is the time taken to achieve 100% throttle and lately in the UK some advice is that 100% throttle isn’t even required.

The point being if your usual take off process is <100% throttle (at any point), a focus on wheel balance and a higher than usual climb out airspeed then trying to reference Vy and certainly Vx will be a big variation and I doubt the ability of many to achieve POH data.
 

Jean Claude

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My purpose is not to change the good takeoff practices on a clean deck.
I'm just saying that to pass a near obstacle with the best margin, it's not by waiting Vx in the ground effect before climbing at this speed. It is better to do it as soon as a little slower speed is reached. And of course, with full throttle!
 

Philbennett

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Sorry JC i maybe causing some thread drift and I was really thinking aloud.

I guess the point I was making JC is that at some point operation of the aircraft with reference to Vx or Vy and the POH may well be because of potential limitations found during flight planning - I.e my runway is 500m grass and it’s 30C at MTOW.

Sure you can always say no but that’s not really proper flight planning - that’s just giving yourself a big margin to the actual limitations of the aircraft. For some sensible but not all that intelligent nor really a great reflection upon pilot training.

So what I’m saying is if you get taught to climb out at 70mph having pre-rotated to 200rrpm, wheel balanced for an indeterminant length of time and on part throttle then the performance data in your POH will be night and day away from what you’re achieving.

Indeed if you use our virus self isolation to look at some YouTube clips of take offs for Gyroplanes and time things then use fairly basic acceleration/ time / distance maths to work out the take off distance you’ll see that pretty much 100% of pilots you see are using far more distance relatively lightly loaded than the POH gives at MAUW.
 
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