Vx vs VY

Vance

Gyroplane CFI
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A friend of mine posted this on another thread and as a gyroplane flight instructor it set off alarm bells for three reasons. English is not his first language and I left in the errors so it would feel more like you were listening to him. He is writing about the gyroplane training he received in France.

“in many small airfield I had to accelerate a lot and then pull hard the stick at the last moment to pass above a row off trees , of curse I was trained to zero g situations and I did reduce engine thrust and carefully pushed the stick ahead, but with no doubt my ass was not pressing the seat anymore.”

  • If I want to climb over an obstacle after takeoff the best angle of climb speed (Vx) is what I use. In my experience anything more or less won’t work as well.
On a cool day solo The Predator (the two place tandem gyroplane I train in) will climb out at around 1,000 feet per minute at Vx (43kts). At Vy (46kts) best rate of climb she will climb out closer to 1,100 feet per minute but I will likely hit the object I would have just missed at Vx.

I have done zoom climbs at air shows and seen 2,200 feet per minute climb in The Predator. I typically used over a mile of descent to get up to a speed that allows this sort of zoom climb and it is not a particularly safe maneuver because the rotor tends to unload at the top of the zoom as my airspeed gets low and my horizontal stabilizer becomes less effective.

  • Flying out of an airfield with trees near the departure end of the runway may be problematic because if I am taking off into the wind there may be significantly descending air on the leeward side of an obstacle.
The air had to go up to clear the tree line on the windward side and will descend on the leeward side. As the wind speed increases the sink becomes more pronounced.

If I am flying a marginally powered gyroplane this may be enough to create a collision hazard and is exacerbated by using anything other than Vx.

  • In my opinion there is no way to train for zero gs in a gyroplane.
I feel any low g event should be avoided in a gyroplane.

Most modern gyroplanes use a two blade semi rigid teeter-head system that in my opinion needs gravity to work properly.

In my experience in The Predator I could not get below .6gs or above 2.2gs even with very aggressive maneuvers. At .6gs the rotor is slowing down and will soon reach an RPM below the minimum recommended for Sport Rotors (275 rotor rpm).

In a high thrust line gyroplane in relation to the center of gravity I recommend a reduction in power in a low G event for any reason. Most modern gyroplanes have a high thrust line.
 

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WaspAir

Supreme Allied Gyro CFI
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Standard airworthiness aircraft have POH performance charts from which one can get a pretty good idea of distance necessary to clear a standard obstacle, producing numbers from which one can make adjustments for wind, load, density altitude, and the like (at the cost of doing a little arithmetic). Those charts are prepared after extensive testing and rigorous data collection. Homebuilders of gyroplanes don't often have comparable quality data. If I found that a particular field frequently made this a problematic issue, as suggested in the quotations provided above, I might choose to trailer out and fly elsewhere. One thing common to many gyroplanes is the ability to land in places from which getting out is seriously difficult or impossible, and the wiser choice might be not to try it.
 

XXavier

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The mere fact that you have to clear trees, powerlines, etc. climbing at Vx, Vy or Vz, doesn't mean that you'll be forced to decelerate sharply after the climb, unloading the rotor. Killing that vertical speed softly, thus minimizing the negative acceleration at the end of the climb, is a matter of elementary gyro airmanship...
 

jm-urbani

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Hi Vance ,

you did well starting this thread, I could be misunderstood

I did not say that I was trained to accelerate on ground effect and pull the stick at the last moment ( this is something that I am doing to make sure an engine failure won't gets me in the trees is some of the small field I sometimes take off from)

the french training consist of accelerating on ground effet but not to pull the stick at the last moment of course !

I said that I was trained to handle Zero G Situations , it was just an example of zero situations one can meet ( engine failure)

that said as I told on the other thread I usually take off accelerating on ground effect as much as I can and then I pull the stick and ascent at 80 KM/h (certainly my Vx) , this the way I was trained to take off, not to manage to overtake the obstacles higher ( the vx method leads you higher I agree) , but only to prevent engine failure consequences , the " jump" gets me fastly above the dead zone "

if the engine stops, I will have passes the obstacle.

I did not invent all of this of course, it is part of the french training ( and of other countries training .. the fact it is france is just an example, we are not better then the others)
 
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thomasant

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It's energy management. Trading kinetic energy at a high forward speed in ground effect and doing a "cyclic climb" to trade off the speed to gain potential energy with height. Speed will keep dropping during the climb, as the climb rate cannot be sustained. In helicopters we used to do the "cyclic climb" often to clear obstacles. The downside to this is that if the obstacle has not been cleared with a safe margin, one is not left with much options if the engine quits while forward speed drops. Hence we always were taught to clear obstacles like trees, power lines, etc at a 45 deg angle so that one could turn back if the engine quit.
In the gyroplane, it is easy to see the effect of "balooning" during the flare. Similar thing, except that here one is coming in for landing. In this case too, there will not be enough RRPM for a soft landing if the engine quits, and the aircraft will descend rapidly if speed drops below approach speed.
Just my thoughts.
 
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