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The importance of speed on final

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The importance of speed on final

Old 20th Jul 2015, 14:02
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The importance of speed on final

Really enjoying all these stories. And the Sea Fury one just goes to show that speed is everything on final. This example isn't as dramatic but is just an example of an experience I had that helped solidify the learning I did on my NPPL course last year.

During my training my instructors hammered home to me how important speed is and I've actually seen why when a few months ago I was landing into a gusty headwind, pretty much straight down the runway. I approached at 65 which is the recommended approach speed for a crosswind/gusty wind (60 on a calm day or light wind day) and I was really glad of those extra few MPH. The headwind limit on the Eurostar is 23knts and the wind was blowing between 8 and 15knts so well within the aircrafts limits. BUT this pilot (i.e. me) has not really landed in such a gusty headwind before. As I float down final at around 100ft the wind just stops blowing.... Oh dear!

I'm set up with 2 notches of flap (Again recommended crosswind setup) so I go from 65mph IAS to around 50mph. In this configuration the aircraft stalls at about 40mph so I still had plenty in hand, but obviously I noticed the increased sink rate and it felt more dramatic than actually was. So, I lowered the nose (I hate doing that on final, it always feels wrong, especially when that close to the edge of the air) and applied power and went around for another go, this time landing no problem.

But the point is this. If I had not been approaching at 65mph, i.e. if I'd approached at 60mph (like a normal day) which is the figure in the POH for a calm day, then all of a sudden I would have found myself at 45mph, much closer to the stall and dangerously low on height with not much potential to recover it if I did stall.

Like I said, not a very dramatic story but one which helped to reinforce the learning I'd done on my course, and I think its these kinds of incidents that really help you to become a pilot, i.e. after you have gained the license to learn, so to speak.

When I do my downwind checks now, I'm consciously thinking, "Wind - ok, so whats my approach configuration going to be, what speed am I going for and what flap setting am I going to use". Whereas I think if I'm honest, when I was doing my circuit bashing last year it was more a case of chanting the checks and ensuring I didn't forget them, rather than having the mental capacity to think about the consequences of each item and have a plan of what it means for me and the approach.

Anyway, just thought I'd share that for any new pilots who want to understand why their instructor takes control if they drop below approach speed on final. Yes you might have a safe margin still, but consider what would happen if something (in this case the wind) takes away 90% of that margin.

Always fly on or above recommended approach speed for the conditions, NEVER below.
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Old 20th Jul 2015, 14:11
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The importance of speed on final

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Last edited by Radix; 18th Mar 2016 at 02:54.
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Old 20th Jul 2015, 14:54
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Yes, you are correct, it was 75% not 90%, but my point I think is still a valid one. Also, for clarity, I deliberately used mph when referring to the speed of the aircraft and knots for the wind speed as the ASI is calibrated in MPH on the Eurostar that I fly.
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Old 22nd Jul 2015, 09:10
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I always taught my students to watch their speed...... so many instructors taught them to watch the rpm's, which I think is silly. Speed is much more important! anyone disagree?
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Old 22nd Jul 2015, 15:58
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Attitude first, adjusted by reference to speed. Power set to achieve the right approach angle - which generally doesn't require you to look at the RPM guage.

G
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Old 22nd Jul 2015, 18:10
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What Genghis said, and none of that need require looking at an instrument...
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Old 23rd Jul 2015, 04:32
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What Genghis said, but also trim out the stick load.
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Old 23rd Jul 2015, 10:28
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I am sorry folks I disagree with Genghis’s post and all those since.

In 1961 I was being trained as an instructor by the RAF at CFS. My instructor wanted me to patter Genghis’s technique. I tried to explain why I thought it was wrong. He would not listen. So the next time I was flying an approach I put us 10kt slow at 200ft and said “Sir will you please show me how to get the speed back by lowering the nose?" He opened the throttle and I was given an instructor change.

Why teach a technique for flying the beginning of an approach that cannot be used in the final stages of an approach? Please tell me!

Incidentally back in the 1960s when the Blind Landing Experimental Unit was trying to develop autoland they programmed both techniques into a Varsity trials autopilot. Surprise surprise, they found the approach was more accurate when the throttle controlled speed.

Last edited by John Farley; 23rd Jul 2015 at 10:29. Reason: typo
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Old 23rd Jul 2015, 16:37
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John, I enjoyed that tale when I read it in "A view from the hover", and I enjoyed being reminded of it again!
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Old 23rd Jul 2015, 20:35
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Fully agree with JF's statement, in fact the RAF changed their teaching method to attitude controls glide path and power controls speed works on every type of aircraft, try flying a constant aspect approach and see which method works best.
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Old 25th Jul 2015, 01:35
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CFS ("trappers" as we used to call them) also standardised their methods of instruction - obviously post 1961 though, which was well before my time.

In gliders you only got one tool. In airplanes you got two - power for airspeed and pitch for angle works best in my book, but don't pi$$ about with both of them at the same time would be a good bit of advise for a new PPL.
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Old 25th Jul 2015, 11:40
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Do a Hover - it avoids G
 
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My modern glider mates say most gliders today have airbrakes and that they set up an approach with them half out and thereafter use them like a throttle to control speed. Seems sensible.
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Old 25th Jul 2015, 21:40
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No John, No! The airbrakes on a glider control RATE OF DESCENT. THEY DO NOT CONTROL THE AIRSPEED.

The speed is controlled by the attitude of the glider. Nose down, goes faster. Nose up goes slower.

The effect of the airbrakes, which on most gliders look like slices of toast sticking out of a toaster, when fully deployed will dramatically increase the rate of descent....in short, you are no longer flying a craft with a 27 to one glide ratio, but one more like a Cessna with a 10 to one glide ratio. Delightfully confirmed by the demonstration of trying to land with no airbrakes deployed at all, on a best glide speed of say 50 knots, and the glider will carry on floating into the next county!
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Old 26th Jul 2015, 00:34
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Yes John, yes!!

Sorry Mary, but airbrakes are different to spoilers. When you pull the airbrakes on a glider the first thing that happens is a drastic reduction in airspeed due to the immense drag. (Sure, they diminish the lift, but that is a secondary effect). To regain the speed one lowers the nose and achieves the desired objective of steepening the glide.

Spoilers on the other hand make little or no difference to the airspeed, and mainly serve to reduce the lift, which again serves to steepen the glide angle but without changing the pitch.
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Old 26th Jul 2015, 11:59
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Do a Hover - it avoids G
 
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Mary and deefer

I will leave you two experts to it!

J
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Old 26th Jul 2015, 15:19
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I am feeling nostalgic for a time when I used to have tremendously enjoyable technical arguments with John in meetings, usually finishing with the chairman saying mildly "G and J, could you tell us what we just decided."

The reality of this is that both methods work, and both have their problems. Increasing power without changing pitch input will, in the vast majority of aeroplanes, reduce speed, also requiring forward movement on the stick to maintain airspeed. Simply using the stick will upset the flightpath, so you need to use throttle as well.

So in the full analysis, you generally need both.


I have learned and used both methods - and both work. But, in good visual conditions, I still prefer to emphasise attitude, and use stick as the first point of input to correct attitude. Does that make me right and John wrong? Not really - there is room for opinion here.

G
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Old 26th Jul 2015, 17:26
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John/Genghis:

I hesitate to jump in between two of my favorite contributors here, but, in a way, you are both right.

In reality, most experienced pilots control the speed and angle of descent on the approach with a combination of throttle and pitch, subconsciously balancing kinetic and potential energy with the stick, whilst adding, and subtracting energy with the throttle.

Unfortunately, in it's pure form, this skill is very difficult to teach, and so most instructors use one of the standard 'devices' of splitting the functions of throttle and stick to make it easier for their students to find somewhere to 'hang their hat' whilst they 'get the hang of it'.

It shouldn't matter which of the two methods they use, because they are just a means to an end. The end being to develop the student's appreciation of energy mananement to a point where he/she can dispense with the device the instructor has used, and use the controls instinctively to manage the energy as required.

Having said that, some types of aircraft lend themselves to one method or the other, and the instructor should use the method best suited to the type being used for the training. For instance, high wing Cessnas lend themselves to 'power for angle of descent/pitch for speed'. This is at least partly because an increase in power to arrest a 'too steep' descent will by the nature of the aircraft configuration, pitch the nose up.

I find that lighter, low wing loading aircraft tend to favour this method, whilst heavier, higher wing loading aircraft tend towards the 'point and squirt' method.

Unfortunately, many students, mainly due to lazy instructors, never progress beyond the device their instructor used, and try to apply this to all the aircraft they fly, thus finding it difficult to fly approaches in aircraft that don't favour the particular device they are still using.


MJ

Last edited by Mach Jump; 26th Jul 2015 at 19:48. Reason: Grammar
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Old 26th Jul 2015, 19:04
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I think that your point about type specificity is a particularly strong one.

The AA5 I use for trundling around the UK to meetings in is pretty content with either power-and-pitch or pitch-for-speed, and particularly on an IFR approach I'll usually tend to fly to use power-and-pitch as much as anything because it's how I was taught when I learned instrument flying in the type.

I'm in the middle of a test programme on an SLMG at the moment, which is the complete opposite. Whilst it's not particularly lacking in power, the airspeed response to speed is pretty small and sluggish. On the other hand, it is very slippery and incredibly responsive in speed to changes in pitch attitude, and as I develop an optimal landing technique, I'm gravitating towards throttle closed / stick for speed (but by the way, if I'm too fast, it flattens the approach angle out, as best glide is above 1.3Vs), then fine-tuning the approach angle with airbrake.

G
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Old 26th Jul 2015, 19:39
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In an SLMG simply close the throttle completely when you're abeam the numbers. Do not touch it again, just use the airbrakes.
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Old 26th Jul 2015, 20:11
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Many SLMG pilots select full airbrake early, then control the approach on throttle.

I'm going for the approach of "understand and test" the specific (and as yet uncertified) aircraft which in this case is also influenced by a significant pitch trim change with airbrake selection.

G
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