Qui sotto un'interessante articolo (in inglese) sull'anello di McCready.
L'autore, Benjamin Néglais, ripercorre l'evoluzione di questo semplice (ma rivoluzionario) strumento fino ai giorni nostri suggerendone l'impiego attuale vis-à-vis del Netto.
(Fonte, Benjamin Néglais - team coach/pilota della squadra francese e resp. vendite c/o Schempp-Hirth)
Netto what ?! And story about the "Ring"
We all know the Variometer is a great tool for optimisation and exploitation of lifts, it is probably the best friend of any sailplane pilot. But when time comes to fly between two lifts, a lot of us rely on the McCready ring and your eyes need to check every few seconds that your-speed-fit-to-yoursink to adapt (in fact react).
So why with modern gliders it is “so yesterday” to do that and what Mr Netto has to do with this topic?
When Dr McCready invented his ring, he was flying a good old Breguet 901, 18m wingspan Open class glider from the 50s and he won St-Yan 1956 World Gliding Championship… with his McCready ring (among other innovations like a... string on the canopy!). It is a great tool!
This tool made the performance polar of the glider directly “visible” on the vario to adapt the speed! A practical and analogical approach of what we, the pilots, must do, to optimise flight speed depending on current sink rate and the next thermal strength! Just brilliant!
The “dolphin style” became the trend and this ring is still famous in the cockpits and among the pilots. Even if there could be something wrong on today's standard to this ring, it has a great advantage : it invites all sailplane pilots to understand background theory and make you better in real life in the cockpit.
Practically, this ring had one immediate shortback pilots noticed immediately:
- if the sink rate is worse than the natural sink rate of the glider (airmass is sinking around you),
- then the ring tells "you need to fly faster!".
Good, but by doing that, your sink rate becomes even worse, so the "ring" tells you to fly even faster, so you push again... and so on and so on.
It was called, at least in France "Racing the McCready". But after having few flighthts, pilots handled that easily by "polishing" their style, no big deal.
The 70s and 80s saw another step coming with electronic inside cockpits, and the polar of gliders became possible to implement inside the e-vario, even basically, to be able to compare the actual sink to the predicted sink related to indicated speed (the one of your glider's polar). This opened up a new world in what you can display to pilots.
The popular “speed to fly” indicator was born.
Basically, an arrow (like the one of your variometer) telling you to push or to pull, “dolphin style” became even greater king, along the fact that higher wingloading with ballast system became reality too. And there is no better satisfaction than transforming speed in altitude and altitude into speed, a great comfortable feedback for the pilots, with the famous “Gs” coming with this sensation of power "under the foot".
But, if you were studying more closely the different styles of pilots, 2 clear groups were popping out the:
- “hardcore push pull” and
- “steady speed”.
The first group was not always winning even if, on the paper, they should have, as they applied stricto senso the McCready theory to make optimal speed fit to sink rate. But the energy evaporated during this many changes of angles of attack, and the fact that any e-vario is still showing you the past (around 2 seconds lag) made the theory-to-reality not that easy. Also, 2 seconds in the 50s was no more than 40 to 50 meters you made in a glide, in the late 70s and 80s it was more 60 to 80 meters so a past much further away behind you!
Currently manufacturers of e-varios are working on this lag, they add G meter and other clever features to find a way to make varios faster, but still usable in real life (yes you need to damp the vario signal or it would be difficult to read them with constant instantaneous changes).
We can see in modern championhsips that the style of the pilots is also evolving to:
- more and more steady speed and
- less and less hard push-pull.
But how do they chose this "steady speed"?
Well, it is still related to Mr McCready theory, but in a more complex manner. McCready used to make an assumption: that between two lifts you would always be in a stable airmass (which is not the case, we all know that some areas are "lifts" and some others are "sinks"), so his theory was "you will fly your glider as its polar of performance".
But, if you check some flights, you can see best pilots are able to get much more from the gliders in the glide than the raw data from the polar of performance would suggest!
It is basically as if, instead of a glider able to make 30:1 at 140 kph on the raw data (polar performance of the glider) you get a, let's say 36: 1 at 140 kph, a bump of 20% more on performance!
Simply because there is a human inside the cockpit, using all her/his strength and experience to optimise the path in this clear thin air between 2 thermals to "use the lifting area and avoid the sinking one". This turns you Std class glider in a 15m one, your 15m one into an 18m one, and so on.
So then comes the "what speed to use?".
If the glider is better compared to expected on the paper, then we will have to use faster speed than the typical one out of the McCready ring... This speed will still be also in accordance to the "what will be next vario strength", so again McCreadwy roots are there, even if, also, today's trend is to average the vario of the day and not too much focus if the next one is 0,5m/s better than the former one (lucky you) or 0,5m/s worse... Perhaps skip this one if possible ;-)
So this "mixture" of "I am able to turn my glider better than what it is" (are you?) and "today's average climb is a rough x.xm/s (or kts for my imperial friends)" gives you: A GLIDING SPEED ! You could use "all day long" (don't be dumb and silly reading that, you will still have to adapt during the day, especially to keep good altitude, this is gliding sport!).
So, pilots choose an average speed to glide and work around this speed, a bit higher if sink is greater currently, a bit slower if there is a kinda lift around and that’s it.
But how to figure out this better/worse sink rate in the cockpit?
Looking at the vario?
Comparing vario to McCready ring speeds?
But, we just said few lines above that, this ring was assuming you don't fly - you + the glider - better than the glider itself... And frankly, checking the vario and knowing the polar performance of your glider, set with wingloading (you use ballast right?) and bugs, and whatever, and then comparing this data to the current data (sink rate) you fly know?...
Am I dumb or it is just not possible for a brain?
And if it was, you have no better to do like checking for next hint of where is this next best thermal to get this next turnpoint (and where is Mr Kawa)?!
This is where Mr or Mrs Netto make your life easier.
Basically, the Netto function on a e-vario uses the polar of your glider and implement it in the vario. Right? What for?
Simple: to not display your actual sink rate but the one of the air mass around you.
This makes a big difference in the cockpit indeed, on your eyes, on your retina in fact.
There is one single information it is super-that-easy for your brain to process in a 10th of a second : the "zero" hoizontal reference on the vario! It is this needle on the "horizon". And your brain knows very deep that reference from ages to just keep walking straight. it is also one of the greater tool you use and watch avidly in thermals from your first flight in the air (and 30% of your flying time is about thermalling, so do the maths…).
What this horizon is telling you?
Also a very basic thing. Your brain tells you:
- needle above zero is full of happiness, i.e. you gain energy (and climb),
- needle below zero and you are sad and angry, losing more energy than expected.
The loop in your brain is so super fast to process this info and to make you act. Every other way to display an information means way more energy (and time) consuming. In our case, comparing the little speed indication on McCready ring to actual ASI speed, processing how much I have to push or pull on the stick and then wait for adaptation of speed, checking again the sink rate and the speed on the ring… STOOOOOP! The raw data speed of this Netto is unbeatable for your retina and what is hidden behind (your grey matter)!
How to act now in the cockpit?
Simple… You have determined today’s glide speed with your glider is around 165km/h:
- netto needle unhappy => fly a bit faster to skip this sinking area,
- netto needle happy => fly a bit slower, et voila.
Even better, an unhappy needle but with a “going up” trend to happy zone means you were in a sink area and enter a less sink area (or perhaps a lift area) so you know already that you need to potentially apply a slowing speed trend, and perhaps will find a lift not so far away (perfect help to find thermals in blue conditions). And vice versa. To get the best data of your Netto, you will have very likely to reduce the damping time below 2 seconds (and stick to above 2 seconds for vario data), to avoid using data from 100m behind you...
Some will argue “hey Benj a vario shows me same thing” and I say again: yes but no!
A normal vario will show you that: at 165km/h, you fly with -2.0m/s sink rate, but you have no idea if it is the normal sink rate of the glider at this speed or if you are in a sinking area! And how to determine difference between -2.1m/s and -2.6m/s with your eyes, horizontal reference with clear treshold between happiness and sadness is gone! Between -2.1 and -2.6 your brain is sad for the exact same amount ! But needle at +0.1 or at -0.3 is super easy to spot on the Netto as Zero is the reference, below, you sad, above, you happy …
So, one device, the Vario, tells you that you sink, the other, the Netto, tells you that you sink but also what to do straight on and for how much. This in just the time of impact on the retina and then all about your own style to act. You like hard push-pull, do it, you are more subtle, do it. Netto is raw data with super high speed processing. Use it if you think it is worth it!