But it's not that simple, is it?

A helicopter "Avoid curve" tells you when you can autorotate down and land on flat ground below you - it assumes that there will always be flat ground below you and you can haul a handful of collective to flare it to a stop before touchdown if the ground ain't that smooth.

The equivalent for a fixed wing aeroplane would need to also account for current heading, available runway headings and distance to that runway (even if the runway is a field it needs a piece that is long enough to accomodate a landing from that heading). It would essentially be a set of 3-dimensional maps overlaid on the terrain with one for every few degrees of heading. The map would have riges over every tree, house and rough-ground feature.

I can see this as a potential (very complex) database add-on for a navigation system, but it's not really something you could get in a simple 2-dimensional graph in a flight manual AFAICS.

€0.03 supplied,

PDR

With synchronised stall turns, if one aircraft goes in marginally slow, is there pressure not to yaw and descend until the other chap does? i.e. Does that explain the slight tailslide?

Not that I know if the Twister is approved for tailslides, mind you, which it may be.

The helicopter avoid [height/velocity] curve is not so much about the landing surface, but rather making it to the point where a flare should be begun, with enough stored energy to arrest the rate of descent to that at which you're comfortable hitting. If you're low and slow, engine quits and you're on your way down without enough height to accumulate the energy you'd like to have to fully flare with - so flare, but descent continues unarrested - until the surface.

Every airplane I have flown has the same characteristic, but the data is not published, and thus usually not trained. If you find yourself at 50 to 100 feet AGL either slow, or pulling some G, and the engine stops, you'll have to lower the nose to enter a glide. By the time you lower the nose, the ground is right there - If/when you pull the flare, you stall, and continue down.

This is of particular concern with STOL modified Cessna's particularly heavy amphibians with lots of drag. You can fly power on at 40 - 45 KIAS, but a suitable glide speed for an approach to a power off landing is nearly twice that speed. If it quits at 100 feet, and 45 KIAS, you will be at the ground before having reached 80 KIAS from which you could effectively flare.

Happily, unlike helicopters, airplanes have little reason to be flown for more than a few moments within their "avoid curve", so it's a low risk - except for low altitude maneuvering....

In the F-16 community we use the avoid curve.

in the aircraft manual there is a chart that indicates the minimum airspeed vs altitude low level, from which you can do a 3 G pull up to 30 degrees climb, bunt at 300 KTS, achieve best glide/engine start speed of 250 KTS, and have time for 1 air-start attempt before reaching min recommended ejection altitude. Below 2000 ft AGL you will need at least 420 KTS to have a chance. Hence, we never fly slower then 420 low level (usually 480) unless we are in the pattern.

Admitted, following this curve will most likely not put you in a position from which you can land in an F-16 in case the engine doesn't relight (unless there is 6000 ft of RWY directly in front of you), but what it will do in any type of fixed wing aircraft, is buy you altitude and time, which translates directly to better options regarding where to put it down.

OK, got that, Teach. See above for vid.

Ref continuing the display, most air shows crash plan involves immediately continuing the display to avoid crowd fixation and surge towards the accident site. Big displays have two crash "columns" of emergency vehicles, situated at opposite ends of the airfield to avoid the possibility of all emergency vehicles becoming casualties. Each is fully capable of dealing with an incident, allowing the other to continue to provide cover.

LD

Given that the pilot is going to be ok, is it ok to have a little smile at the aircraft reg? :)

During my time in flight testing I learnt to avoid tempting the fates, so no sorties on 1st April or Friday 13th and I would have run away screaming from an aircraft with such a registration. Must have worked, I'm still here.

My phobia in flight testing is priests. Every time the station padre came along to see what we were doing, something went wrong. I would still land an aeroplane immediately if I thought that there was a priest watching a flight trial.

G

I guess you've never flown a Vickers, then? :)

Excellent post.

Despite our correspondence over the last year plus I never was aware you flew rotary Step Turn. Me too for the last 28 years. We are of course talking about what we in the UK call the avoid curve.
https://en.m.wikipedia.org/wiki/Heli...locity_diagram


Of course in my fixed wing training 37 years ago we were just taught to pick a field or area straight ahead as we climbed out to 500 ft in a C152 or PA38.

I am not sure how much risk assessment goes in flying these days.

Perhaps reliability of modern engines has removed the thought that the power plant could stop:ok: