Ok, as promised, here are some thoughts on this thing about flaring and holding off with and without power on. It's a bit of an essay, sorry. As ever, I'm just some guy on the internet, your instructor is the one in charge, blah blah.
BTW, when I say 'with power on', I mean
a little power on in the flare and hold-off. There is one situation where you might keep quite a lot of power on, but I'll come back to that. I'm talking about normal landings for now. I'm also talking about normal training aeroplanes, not exotic types that need different techniques. I don't know anything about those.
There are advantages and disadvantages of keeping power on in the flare and hold-off. Advantages first:
Because you still have some thrust, the airspeed will decay more slowly. This gives a more gradual loss of lift, so you can afford a more gradual application of back pressure (and hence increased angle of attack) to compensate. So you have more time to see what's going on as the aeroplane descends through those final few feet. For low-hours students, this can be very helpful, as until you've had a reasonable amount of practice, it can all happen in a bit of a blur. And as we've discussed, you only get about 10 seconds of actual landing per circuit.
Actually, this is the only advantage I can think of.
With power, you also get a flatter approach, requiring a smaller pitch change in the transition to the hold-off, but I don't think that's an advantage.
Disadvantages:
- It doesn't help you learn glide approaches, which are essential to practise in case you get an engine failure one day.
- It doesn't help you land if the runway is short. Taking longer to slow down means you will touch down further down the runway.
- Touching down further along increases the temptation to land flat just to 'get it down'.
- If you're having to coordinate gradual power reduction during the flare and hold-off, as well as gradually increasing the back pressure as the speed decays, that is more work than you need. In the last few seconds before touchdown, especially if it's gusty, the last thing you want is more stuff to do, and have to do it for longer than you need.
Much better IMO is to close the throttle completely once you know that you can make the runway. Keep your hand on it (you might need to add power promptly if you get some unexpected sink), but unless you need it, leave it shut.
Then, concentrate on the flare and hold-off. It will happen quicker, but you'll still get used to it.
Early on, because things are happening faster, there will be the temptation to panic a tiny bit, and subconsciously add larger control inputs. That's one thing that might account for ballooning when you closed the throttle on very short final. You just hadn't expected it all to happen quite so quickly, and overcompensated. That's all a balloon is - too much back pressure.
Without power, the last bit of the approach will be a bit steeper, so you'll need a bigger pitch change in the transition from the flare to the hold-off. If you're not used to it, it's easy to overcook it, especially if you're slightly stressed.
With practice, it'll become easier this way than when you were fiddling about with the power as well.
Why is it harder when the wind is calm?.
Suppose your approach speed is 60kt, and you're used to headwinds of, say, 10kt. You'll be used to approaching the threshold with a ground speed of 50kt. Then one day there's no wind, so your ground speed will be the full 60kt.
This has a number of effects. First, even if you stick to exactly the same airspeeds, you'll get to the threshold sooner (because you're going faster over the ground), and the flare and hold off will likewise use up more runway. If you're subconsciously used to increasing the back pressure when you have a particular visual picture, you'll be too early. If the aeroplane hasn't had time to slow down properly to approach speed, you could also be too fast.
With runway going past faster than you're used to, a few knots too much airspeed because you got to the threshold sooner than you're used to, it's easy to apply the back pressure too early and/or too much, and balloon upwards.
Solution:
- More practice with the throttle closed on short final, and staying closed all the way through the flare and the hold off. Unless you need power of course - you always need to be alert to unexpected sink. But having a trickle of power on doesn't protect you against that.
- More patience in the hold-off, even though the runway is going past faster than you're used to. If the hold-off is taking more time (as opposed to more distance), your airspeed is too high. Go around if you're running out of runway.
Does headwind affect airspeed at all?Short answer:
no. You're flying through a big parcel of air. The aeroplane doesn't know whether that parcel of air is itself moving relative to the ground, which it doesn't care about, even a little bit.
Longer answer: there are wind gradients, and usually the headwind close to the ground is less than the headwind 50' up in the air. So as you descend through a decreasing headwind, your airspeed will decrease. However, this doesn't affect the most important part of the landing, namely the hold-off. This is all at more or less constant height. The thing that the headwind affects is the ground speed, not the airspeed. When the ground goes past faster than usual, it looks weird, so if you're not expecting it, it can fool you.
Very short field landingsSo, why would you ever want to have quite a lot of power on in the later stages of the approach? If you haven't got the hang of normal landings yet, you probably won't have encountered this. It's where you want to land absolutely as short and as slow as you possibly can.
For this, the last part of the approach will be quite a lot slower than usual. So the angle of attack will be quite a bit higher than usual, which will cause quite a lot more drag than usual. To counter this you'll need significant power, which, if removed, will result in a rapid deceleration (due to all that drag), and hence loss of lift and increased sink. The idea is to remove all that power just before touchdown, which means that you'll touch down almost immediately with virtually no float, with the nose well off the ground for maximum drag once down.
As you can imagine, this technique requires a deft touch, especially when it's gusty, and it absolutely isn't a gradual power reduction during the hold-off - it can require many power changes, some quite large, to maintain the airspeed at a margin above the stall that's much less than you're used to. And you absolutely have to be very awake indeed. If your airspeed control isn't good enough for this, don't blame me if you smack it into the ground.
This technique allows you to cheat at spot landing competitions, as the removal of the power means a more or less instantaneous landing (if you're at the right height. It's a crash if you're too high). Personally I think all spot landing competitions should be off a glide approach from no closer than the downwind/base corner