Maoraigh wrote:
There are 2 airfields which I use where I start a gentle turn once I cannot land on the runway remaining. Both because If I don’t turn, height will not increase as I climb due to rising ground. Both turning over the sea.
Yup, I know a few!
Ibra wrote:
How they get to plot such H-V graph? I don’t think the same way as exploring/expanding V-G flight envelopes
Pretty well, it’s rather scary stuff. I’ve done the low altitude side of the testing, but not the high altitude side. You get to a point where you decide that any more into the “curve” (on the chart), and a safe cushioned landing is not assured.
Ibra wrote:
Any reasons (apart from those that apply to aeroplanes) why a helicopter can’t cope with V=120kt at H=20ft ?
The helicopter pilot must purposefully enter autorotation. Some helicopters also have a maximum speed for entry into autorotation. In an airplane, the pilot just keeps doing what they’re doing, other than to know that they’re about to land somewhere in front!
Airborne_Again wrote:
Pilot reaction time if something bad happens.
That is no different than low flying in aeroplanes then, I was thinking of something specific to helicopters (e.g. aerodynamic flutter near the ground?)
Ibra wrote:
Any reasons (apart from those that apply to aeroplanes) why a helicopter can’t cope with V=120kt at H=20ft ?
Pilot reaction time if something bad happens.
Pilot_DAR wrote:
I do recognize that sailplane techniques may be different, I’m not a sailplane pilot. This discussion did originate on power plane techniques, and that is what I have commented….Is true for airplanes as it is for helicopters, just airplanes do not have a very slow speed side of the chart
Fixed-wings all fly the same: jets, aeroplanes and gliders it is just matter of time scale, range of hight, speeds and g-forces and how tight those corners…
How they get to plot such H-V graph? I don’t think the same way as exploring/expanding V-G flight envelopes 
Any reasons (apart from those that apply to aeroplanes) why a helicopter can’t cope with V=120kt at H=20ft ?
“I do hope, that for the vast majority of takeoffs, the departure is planned to be along the runway heading, or very nearly so.”
Agree for almost all takeoffs.
There are 2 airfields which I use where I start a gentle turn once I cannot land on the runway remaining. Both because If I don’t turn, height will not increase as I climb due to rising ground. Both turning over the sea.
The theme of my expression of concern is a situation where a pilot has deliberately climbed the first few hundred feet after takeoff, at a speed slower than Vy. I do hope, that for the vast majority of takeoffs, the departure is planned to be along the runway heading, or very nearly so. Therefore bank angles, and turns do not really factor into this discussion. If the engine stops during a climbout at around 200 feet or so (meaning not as high as 500 feet), then according to fixed wing training, and good practice, the resulting forced landing should be straight ahead, only altering heading to avoid obstacles. Once the engine stops, it’s an approach to a landing, and a critical one at that. You certainly want that landing to be the result of a stabilized approach! Thus, abrupt maneuvers, and particularly large bank angles should certainly be avoided! Similarly, pitch changes should be no more aggressive than needed to assure speed management. Negative G? No, not at a couple of hundred feet! I agree that pushing to zero G prevents a stall, but the whole point of this whole thing is to assure that there is enough speed in reserve to assure an approach to stall is not required at any point during the approach! Worse would be pulling G at any point (like compensating for just going to zero G), as pulling G will cause a drag increase, which is the very last thing you want close to the ground, during an obviously stabilized approach!
I do recognize that sailplane techniques may be different, I’m not a sailplane pilot. This discussion did originate on power plane techniques, and that is what I have commented.
This:
https://en.wikipedia.org/wiki/Helicopter_height%E2%80%93velocity_diagram
Is true for airplanes as it is for helicopters, just airplanes do not have a very slow speed side of the chart, and thus would have a smaller curve, but it’s a reality none the less. If I had my way, these values would be determined and published for all airplanes, so they would form a part of instruction. It’s sad that some pilots are entirely unaware of this risk, and operate in the range while toying with STOL operations. It’s worth noting that commercial and military STOL operations are more commonly in multi engined aircraft, where asymmetric thrust and Vmca are also factors. Therefore, STOL operations focus more on getting the aircraft safely off the ground, and then accelerating before climbing – eliminating this risk. At the end of the day, “STO” stands for short take off, not stupid steep climb out!
As Pilot_DAR, if you are in that “ugly corner” I don’t think the outcome will be any better if slow & hight & angle (not sure how you would sum them up) are bellow some energy whatever you do with the stick, but there are other conrners for which this is the quickest way to recover: turn in valleys, negative g-lock…
Once you go there it all depends on how fast you change rate of rate on some X quantity delta (you lose concious quickly if you take a quick increase in Gs, too late to notice an engine failure, how quickly your engine loose power and how quickly you push the stick…), but you should not be there in the first place if it is game over (hanging on the prop while on steep climb at Vs is a literal expression not just a figure)
“to recover from that attitude without taking zero or too much negative Gs (as far as I remember from some unorthodox instructors I had in the past) was to bank the wing while unloading the stick, let the nose drop and opposite bank before the nose crosses the horizon,”
Done with no thrust, and low speed? Not letting the nose drop below the horizon? Would there be much negative G at low speed?
Bank and let nose drop after climb to reduce speed, and levelling wings after a low G,180 turn, with height loss is good for a tight turn in a valley.
But after power loss in a steep, slow, climb with little height?
Pilot_DAR wrote:
a sudden propulsion loss will not catch you out with insufficient energy to safely flare at the bottom of your glide.
I would not qualify what happens when the engine quits as “glide”, one is flying because he is continuously unloading the wing and taking a huge Rate of Rate of Decent (basically -2000ft/min for each second), once you pull the stick you will stall
I guess, this is completely different from flaring after PFL practices or recovering winch cable breaks but can be simulated high in the air, the fastest way to recover from that attitude without taking zero or too much negative Gs (as far as I remember from some unorthodox instructors I had in the past) was to bank the wing while unloading the stick, let the nose drop and opposite bank before the nose crosses the horizon, not sure how much of that applies to an EFATO or a winch cable breaks close to the ground on glider/aeroplane with their typical roll rates, you need probably 90deg/sec to get that manoeuvre right and you don’t get that easily on a aircraft with slow stall speeds…
BackPacker wrote:
That’s why the winch launch procedure is carefully designed so that wherever, whenever the cable breaks (and it will, eventually), you always have either the kinetic energy or the potential energy to recover.
Which is why sailplanes don’t count! Sailplane pilots are smart enough to avoid a Vx climb! If you aren’t in that ugly corner of the avoid curve, a sudden propulsion loss will not catch you out with insufficient energy to safely flare at the bottom of your glide. Some foolish power plane pilots think that because they practiced forced approaches umpteen years ago under very agreeable circumstances, and never had to actually land, now they can hang the plane off the prop without considering the very different conditions they have created for themselves. Hence the discussion….
