The importance of speed on final

[chillindan]

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. :ok:

[Radix]

............

[chillindan]

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.

[WestWind1950]

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? :confused:

[Genghis the Engineer]

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

[Pilot DAR]

What Genghis said, and none of that need require looking at an instrument...

[CISTRS]

What Genghis said, but also trim out the stick load.

[John Farley]

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.

[flybymike]

John, I enjoyed that tale when I read it in "A view from the hover", and I enjoyed being reminded of it again!

[Above The Clouds]

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.

[deefer dog]

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.

[John Farley]

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.

[mary meagher]

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!

[deefer dog]

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.

[John Farley]

Mary and deefer

I will leave you two experts to it!

J

[Genghis the Engineer]

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

[Mach Jump]

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:ok:

[Genghis the Engineer]

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

[DaveUnwin]

In an SLMG simply close the throttle completely when you're abeam the numbers. Do not touch it again, just use the airbrakes.

[Genghis the Engineer]

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

[DaveUnwin]

" Many SLMG pilots select full airbrake early, then control the approach on throttle."
Really? Well, every day's a school day. I never knew that. And in my own limited experience (only about a dozen different types of SLMG, ranging in performance from T-61 to S-10) Its throttle to idle and airbrakes only.

[Genghis the Engineer]

That's how I was taught to fly them too, but appears to not be universal when I've been preparing for the flight testing.

Won't work with this aircraft - the airbrake won't stay out without continuous pull, which would scupper anything but the technique you've just described, but ultimately, you test the aeroplane that's there, and need to be open to the conclusion that the aeroplane is safe but requires non-standard handling techniques.

G

[mary meagher]

John, Deefer, Genghis and Mack, I believe you chaps do most of your flying in power? correct me if not the case.

I think best to simply quote Ken Stewart, from his book The Glider Pilot's Manual, he discusses the use and effect of the airbrake.

Says Ken, page78, "Due to the low drag of the glider and the resulting low rate at which it uses energy, it would be very difficult to land, requiring a very large landing area. ....When extended, ....airbrakes increase the drag dramatically and disrupt the airflow over part of the wing, thus reducing the lift produced....steepening the angle of approach and making the glider easier to land in smaller areas. The amount of airbrake can be varied over the complete range, between fully closed and fully open, giving an infinite number of settings and allowing the glide angle to be adjusted to match the approach path required....
Apart from their use as an approach aid, some airbrakes have another, less used purpose, that of "speed limiting" or DIVE BRAKES. ....and can be used to limit the airspeed of the glider should control be lost while cloud flying or carrying out aereobatic maneuvers."

Certainly beginners may end up "rowing" down the approach, with airbrakes rising up and down, but the airspeed is controlled by the attitude of the glider. The term airbrake does lead to confusion.

[Genghis the Engineer]

You're quite right only a small portion of my flying is on sailplanes, although I've certainly had adequate reason over the years to understand unpowered flight, and powered sailplanes, and your quote matches my normal understanding.

The approach of full A/B, partial throttle surprised me also, but it does appear to be how some pilots operate SLMG / SSS on approach and was something that came into my pre-trials research.


Being able to use the A/B as speedbrakes is a further issue, and relies upon a degree of drag which may not exist on every design (present aircraft again, etc. etc).

G

[Piltdown Man]

I'm afraid I've too often heard that 65 is the magic number used by PPL holders for an approach, unless it's windy when they add a few more knots. But very few will tell you their stall speed for their actual landing weight. It's a shame really because as the OP suggested, getting the speed right for an approach is critical. But right in this context means getting it "Goldilocks" right; not too fast and not too slow, just right.

As to how you get there, I'm in the Farley camp. Yes, I do adjust the pitch when I change speed, but the speed is controlled by use power or adjusting the airbrakes. The pitch adjustment is required to maintain or correct the approach angle. And as John pointed out, how do you correct an under-speed close to the ground? Lastly, what happens when you side slip? If you are too slow do you lower the nose or stop the slip?

PM

[RatherBeFlying]

Once you have full air brake out, you can let the nose down to increase speed and drag (by the square of the speed).

Once you level out the speed drops rapidly with full air brake – same applies to Cessnas with 40 flap.

Not to be done until you reliably flare at the correct height lest something get bent.

[chevvron]

My Monnet Moni had a ventral airbrake and opening it caused a marked nose up pitch, so on final I used to set airbrake open and rpm 4,500, which gave me about 60mph. I would shut the throttle over the hedge and fly it on ie no flare; I did this a couple of times and it dropped like a stone and I heard that several US designed homebuilts eg Quickie Q2 needed to be landed this way.

[blind pew]

Too slow with side slip!
The gliders (sailplanes) that I have side slipped loose the ASI once the side slip has developed due to the airflow around the pitot.
I have also tried to stall a glider whilst in full side slip...never achieved it. I presumed because of partial blanking of the elevator.

As to airbrakes or speed brakes;
I used the latter term when I returned to gliders after years of big jets...had no end of criticism and wasn't allowed solo until I used them like airbrakes to control the rate if descent rather than speed brakes to control the speed.

The reason the BGA is so strict is because the number of undershoot accidents with pilots putting the nose on where they want to land and in a progressive undershoot case they can end up stalling trying to reach the threshold.

When I stopped instructing the current philosophy was to teach a half to two thirds airbrake approach...any less close them completely until you reached the "slot" ...any more pick another aiming point.

[boofhead]

One thing I emphasize with new students is to never ever let the nose come up to the point where they cannot see the runway touchdown point. If the nose remains down below the horizon the airplane cannot stall (unless the airplane has a very high bank angle, not likely while on final).

I also tell them that if the stall warning comes on during approach they are too slow. If it does not come on during the flare to land they are too fast.

Don't need no steenkin airspeed! (joke)

[OpenCirrus619]

If the nose remains down below the horizon the airplane cannot stall

I think this statement needs to be qualified, in much the same way as "the stall speed is XXXkts" - it's only correct under certain conditions.

Q: What happens in a stall recovery if the pilot is too aggressive pulling out of the ensuing dive?
A: A (secondary) stall - with the nose below the horizon.

Q: What happens if the stick is held fully back in some gliders?
A: A rapid, fully stalled, descent with the nose WELL below the horizon.

OC619