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isoaritfirst

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Stands for ‘energy management’. Since this thread was current it’s become more than one style, but they share the common feature that the plane is turned away from the slope on an upwards trajectory before the turn, then after the turn flies back towards the pilot at the centre. The path is a kind of bent figure of eight. There are several ways of achieving this, which is why it’s no longer a single style.

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Expanding on what John said with a couple of videos, the first would be 'classic' EM (and is in a massive thermal!) on a big slope

This one in Rugen is on a low cliff causing a narrow band of vertical lift fairly local to the slope. There is much less lift (dramatically so) out in front of the slope, so the turns have a vertical emphasis to stay in the lift band and get back in the 'compression' on the edge ASAP. It could also be described as EM.

So the turn style is adapted to suit the slope. There are some slopes, big vertical cliffs like the Crest, Wrecker and back of Wrecker in Wales where 'old fashioned' reversals are still arguably the quickest way round the course.

 

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Phil.Taylor
1 hour ago, MikeE said:

Do you think there might be a DS element behind the trees in David Status flight?

Quite possibly - David Stary is good at that sort of thing !

 

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As a relative newcomer to f3f, I’ve found the EM turn a bit confusing. I’ve been led to believe that it’s rudder and elevator around the turn, but looking at the video’s it seems there is slight ailerons being used as well? 

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Given that a key part of f3f is maximising efficiency and extracting the most energy possible from any slope, every turn is about managing energy.

However, what's known as em works on any slope where the wind gradient changes within the turn radius. Small cliffs go from mostly vertical lift right on the edge, to mostly horizontal just above the edge. Pierre described a 'belly to the wind' principle some years ago, and this is effectively what you're doing when using em turns (maintaining upward thrust under the wing allows forward thrust to be maintained (or built when done correctly)).

Slopes with wide lift bands of constant gradient can work with an em style turn, but without giving much advantage over other turn types.

Wales (wrecker slopes) is generally suited to reversals because the vertical lift component goes some way above the edge and there is room to use the compression with the dive in after a reversal. Having said that, I flew 50/50 em/reversal at the last Welsh open and was within 1% of the lead, so an adapted em may still yield more benefit. The most effective turn style at the typhoon race appears to be a dip into the compression before pulling out into a rapid em/banking turn. (Similar edges to wrecker)

Reversals don't work at all (comparatively) on low edges because you go straight into horizontal air as you go up for the reversal, killing lift under the wing. Doing reversals at Rugen in strong wind will almost certainly end up in a trashed model.

The other benefit of em (done properly on the right hill) is that you should be able to fly heavier and get the benefit of gravity combined with maintained upward air under the wing.

Flying an effective em turn is as much about being set properly for the turn as flying the turn itself. The belly-to-wind idea is good to have in mind at all parts of the flight.

There are numerous Web posts about elevator-snap settings, and the extent to which snap flap should be used to reduce drag with increasing angle of attack (rather than using it to try to sharpen the turn), so you have to experiment to find the optimum settings for any given model. Ideally though, no ailerons through the turn, and no sharp pulling at the apex.

Flying em well probably means stepping backwards temporarily as far as results are concerned as it takes a while to get out of reversal/tight-pull habits to start to make progress. 

 

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5 hours ago, Mikeb52 said:

As a relative newcomer to f3f, I’ve found the EM turn a bit confusing. I’ve been led to believe that it’s rudder and elevator around the turn, but looking at the video’s it seems there is slight ailerons being used as well? 

I don't use alot of rudder in an EM turn (others do). Its about setting the model right as you approach the turn, for me you are diving into the turn, not dramatically so but a downward trajectory, roll to between 45 and 60 degrees then its all elevator until the model is coming back towards the slope. If you get it pointing back towards the other base initially as it takes a bit of getting used to having the model heading back towards you in the middle at speed (scary!). So the ailerons are used to set the model up before the turn and then to flip it in the middle to set up for the next turn.

Maybe start without rudder and then you can experiment with the effects of rudder as you get the hang of creating nice smooth figure of eight type patterns across the slope and maintaining speed.

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oipigface

I drafted this when Mike’s post was only a few minutes old, but I’ve come back fromIceland with a nasty cold and didn’t manage my energy well enough to actually post it:

 

Like so many things in F3F, pilots do what they find best for them, and it’s practise - lots of it - rather than discussion that will help you figure that out.
The manoeuvre is called an energy management turn, because relative to other turn styles it is supposed to i) increase the energy gathered from the compression zone by keeping the wings with their undersides facing the airflow as much as possible; ii) reduce the drag from control surfaces by using them as little as possible. I was told when I started practising EM turns to roll away from the centre of the slope using aileron (maybe 1/8 roll). Then initiate the turn with elevator, and complete it with rudder only. This can be done but is tricky. Some pilots have rudder differential programmed so that (in an extreme version) only one side of the V-tail works. (A different side depending on whether you are doing a left or right turn.)

Some pilots have recently been advocating ‘elevator first EM turns’, but I’ve not been able to figure out a good way for this to work for me.

Incidentally one big advantage of the EM turn is that makes timing the turn a little bit easier. (I think)

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Phil.Taylor
1 hour ago, oipigface said:

Incidentally one big advantage of the EM turn is that makes timing the turn a little bit easier. (I think)

I have found this too - the plane is up & away from the slope - already going around the turn - easier to judge when to finalise the turn on the beep.

Rudder - seems strange to me - why would you want to deliberately yaw the plane & add sideslip drag? (but then - I've just flown full-size - with the yaw string on the canopy that you have to keep straight 🙂)

Phil.

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oipigface
16 minutes ago, Phil.Taylor said:

why would you want to deliberately yaw the plane & add sideslip drag?

I suppose (but can’t claim to know) that the reduction in drag from using rudder instead of ailerons is greater than the increase in drag from the yaw.

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