An extra ten knots for mum and the kids

[PilotDAR]

I'm not a believer in the extra ten knots for mum and the kids. I believe that a normal approach in a powered aircraft should be flown at the published speed for the condition and configuration. Personally, I tend toward higher steeper, lower power approaches, but I accept that there are variations on this, and within a band there's more than one "right way" to fly an approach.

However, when it comes to power off forced approaches, I am tending more toward the extra ten knots for mum and the kids, and away from the book "best glide speed". This has been inspired by the writings of a famous test pilot (John Farley, Hawker Harrier, whom I had the delight of meeting). John says that the only time you want to be at a slow "best glide speed" following an engine failure, is when you are trying to achieve the least sink rate or greatest time or distance aloft - to reach shore, or get beyond the mountains, perhaps. But, if you do not need to "reach" a distant suitable landing area, the extra ten knots will make the final moments of arrival to earth much easier to get right.

Flaring an aircraft to touchdown is, by necessity, an exercise in acceleration above your glide path. The acceleration is to change your path from "forward and down" to just "forward", and very nearly parallel to the landing surface. Remember: Chance of survival is inversely proportional to angle of arrival. We want a very, very acute arrival angle at touchdown!

To accelerate the aircraft (with no power available) will require a momentary increase in lift, which will result in an increase in drag too. The increase in drag is going to cost you airspeed, do you have it to spend? Have you arrived to the point of the flare with enough extra airspeed to accomplish the flare, and then leave you the margin to still make a decent landing out of it? If you were gliding down at the "best glide speed", perhaps not.

A helicopter autorotates with a rotor RPM faster than normal, a reserve of energy, stored for when you are going to need it - the flare, to arrest the rate of descent, or accelerate away from the approach path. And airplane can only store energy as speed, so why not?

I would rather have to slip or flap off too much energy at the last moment, than wish I had more. I would rather overshoot and hit the obstacle at the far end of the forced landing area, at a slower speed, than to undershoot it, and hit the near end obstacle at near flying speed.

I have been training this to pilots during type training recently, with great success, and indeed, never anything other than an ideal touchdown. They are always from inside a "normal" circuit position, and often near resemble an autorotation entry, but they work.

The ultra 182 amphibian will glide at 55 KIAS, but crossing the fence even as slowly as 75 KIAS is un nerving. I have found that 85 to 90 KIAS results in a comfortable flare, and perfect touchdown. Similarly y Teal will glide at 60 MPH, but if you don't want to slam on, you;d better be gliding at at least 80MPH as you enter the flare.

I hope that while conscientious pilots out there are doing their regular forced approach practice, they'll try this out for themselves, just to see the difference in ease of precision power off landing when you have that extra stored energy in speed.

If that practice results in some acceptance of the concept I present, next consider where you are in the "opportunity to glide to a safe landing" box, if you are climbing away after takeoff at those silly slow speed, steep angle departures we see from pilots enthusiastic to "get the most" from their aircraft. You're climbing out at 60 KIAS, 'cause it will, and..... the engine quits, now you need to push over, and accelerate to 80 to be able to get that nice flare opportunity you have found will work nicely. How much altitude will it take to enter a glide and accelerate 20 KIAS at the same time? Do you have enough altitude for that yet? Turnback landings are very hard to accomplish for these reasons.....

[ahramin]

I would never add 10 knots for mom and the kids, but will add it for many other reasons. In the case of an engine failure to an unknown landing site, it is a very good practice. In mountainous terrain you don't add 10 knots, you add as much as you can right to Va.

Unless the forced landing site is definitely flat and smooth and short, keep extra speed.

[Illya Kuryakin]

It's not 10 knots for mom and the kids.....it's an extra half hour of fuel for mom and the kids!
Illya

[ahramin]

I don't carry that either.

[Pop n Fresh]

I'm with you on the extra height, I can alway lose too much without power.

[Colonel Sanders]

How many knots do you subtract
for each ex-wife?

PF, we need a formula! Something
non-linear would be nice.

[photofly]

I'll work on it.

If you're really trying to stretch that final approach it seems to me you're likely to have a headwind, and therefore would want to fly faster than the "book" best glide speed, anyway.

I'm sticking with aiming for a full-flap landing to minimize my ground speed (and therefore metal-bending and bone-breaking energy) at touchdown, and maximize the braking thereafter; once the flaps come down, my target is a regular-ish approach speed the rest of the way down, which has enough margin built in for a very nice flare.




Someone is going to have to explain to me why going faster is a good idea if the surface isn't smooth.

[+RA]

Vmkglide = Vglide+(4.11√(X+9)-3)

X = Number of wives / ex-wives

Doesn't work if you have more than 8.46 ex-wives

[Colonel Sanders]

Thank you - that feels much better.

[Illya Kuryakin]

I don't carry that either.

Not as important these days, but back in the day, it saved our bacon more than once. Bare minimum fuel is for far braver souls than I!
I remember having a beer (or 7, or 8?) with a BOAC 707 crew....what's their alternate? 23R!
Illya

[pdw]

I would never add 10 knots for mom and the kids, but will add it for many other reasons.

For M.T.O.W. ( "mum and the kids" )

[donnybrook]

FYI a helicopter does not automatically carry a higher rotor RPM during autorotation, unless it has been improperly rigged. During powered flight it has a relatively narrow range due to fuel governing, and a wider range power off. If you do not lower the collective quickly enough to maintain sufficient RRPM you are in trouble, and too high of an RRPM will result in higher than desired rates of descent.

[PilotDAR]

my target is a regular-ish approach speed the rest of the way down, which has enough margin built in for a very nice flare.

And of course that is an answer which conforms to the flight manual, so it can't be wrong. However, I opine, and have proven to myself many times, that this is one of those cases where more is better. Energy in my back pocket should I need it at the last minute, and I can dump it off if I don't.

On the other hand, if my aiming point turns out to be not so suitable, and I have used everything, while overflying another landing zone, I'm now stuck. I would have been better to point it down into the closer spot faster, than stretch into the farther one, and maybe not make it.

If I forced approach onto a "rough" surface, I might light to have the extra energy, so that when I arrive to the point where I can actually recognize texture and small, but meaningful hazards, I have a little left to get around/past them. I can make a better landing, if I have more to work with.

Using helicopter autorotation as the similar model of the technique, if you arrive to the flare entry at the minimum rotor RPM, you don't have much to work with to cushion the touchdown - you've got no stored energy. Yes, the rotor RPM range for autorotation is wider than powered flight. From powered flight, you have one or two seconds to lower the collective upon engine failure, and you will surrender distance for the higher RRPM, but it's desirable to carry that higher RRPM if you can. It's really not that different for airplanes, it's just stored in KTS rather than RPM.

[photofly]

my target is a regular-ish approach speed the rest of the way down, which has enough margin built in for a very nice flare.

And of course that is an answer which conforms to the flight manual, so it can't be wrong.

Tactfully put.

And interesting thoughts.

[trey kule]

PilotDar..

The OP refers only to a forced approach...right?

If I understood that correctly, i am not disputing the wisdom of your post, but the practability.
In a forced approach you may or may not be dealing with a head wind for most of the approach.

But the main issue is when it happens in real life the human factors. The difference between say, 65 kts and 75 kts on a high lift wind is substantial. In training and practice dealing with that extra speed is easy peasy. Not so much in a real situation when that extra speed could cause you problems at the end. In general it is best to have a speed burned into our little brain that when panic steps in we will resort to it. If there is time afterwards, we can do some plotting.

Many years ago, many pilots, me included , would fly a high approach for single engine landings... Then someone did some studies and determined that your chances of having a problem were less if you just did a normal approach...

So while the theory you purpose is sound, I am not certain it is practical for the average pilot.

Just a though

[PilotDAR]

Not so much in a real situation when that extra speed could cause you problems at the end. In general it is best to have a speed burned into our little brain that when panic steps in we will resort to it.

If I were going to attempt to burn two things into pilot's brains, they would be these:

The "best glide speed" in the Flight Manual is a minimum speed, if you can find a suitable landing area closer, and fly a faster speed, you should do that. This equates to don't aim far for a forced landing, aim close. And,

Arriving to the point of the intended flare at a minimum glide speed will result in a minimum opportunity to flare to arrest the descent, and the maximum likelihood, that an imperfect flare will result in hard ground contact.

Each plane I fly gets a glide landing, and more, if I'm not happy about it. I need to prove to myself that it is possible. This lesson has passed by my, poorly absorbed for decades of flying, I always did get the plane down. But once I started test flying planes with very draggy modifications, this became much more an issue. The Grand Caravan with the very draggy survey bird tucked up to the belly was the most dramatic. I was required by TC to demonstrate engine failures from 50 feet, with a glide landing, and then at a speed slower than the "best climb" speed. Doing that was very un nerving. Scarier than the dozen plus spins I did on that plane.

I realized that with all that drag, it slowed down so fast that I could not enter a glide which enabled me to maintain the energy I would need to flare. So, I perfected gliding that plane, and then trained that to other company pilots. Glide faster. The extra speed over the fence gives you better control and precision of placement crossing the threshold. Bleeding off those extra knots was not a problem.

So what about slippery planes? I was training power off landings in the 182RG, with full flaps, same thing, a glide approach at best glide speed required a precisely timed flare, right the first time. 20 flaps was easier, but not much, and resulted in alarmingly tail low touchdown, during which a feared a tailstrike. Steeper, faster was better, with full flap applied in the flare, once the runway was made.

For a power off approach, extra speed, at worst, results in landing longer, if not bled off. But I would rather cross the fence exactly as I intend, get down, and over run slowly, than to hit the fence, 'cause I could not make it over.

[trey kule]

The "best glide speed" in the Flight Manual is a minimum speed,

Perhaps I am misinterpreting this, but it does not make sense to me. The best glide speed in the POH is just that. I dont see where it is a minimum speed. Go slower or faster and you will not glide as far(subject, of course to wind, temp, aircraft weight and loading which will all have a effect on it). But it is a good reference number to have in your memory.

I think the old saying we used to have was it was better to hit the fence at the far end of the field at taxi speed than to hit the near end fence at flying speed,and there is truth to that.
But at the risk of sounding flippant, the idea is to cross above the near fence at the correct speed.

To be clear I am not disputing your claim, but for the average pilot it is better to have a number in their head and then fly that number with precision. If they can relax in this type of real situation, then they have the time to adjust things. They also need to do some faster approaches to land in general to get the control feel when in ground effect at the higher arrival speed to avoid any ballooning. For experienced pilots this comes naturally.

[Colonel Sanders]

People obsess about best glide speed,
but unless you're trying to reach a
distant field, it probably doesn't matter
as much as

1) maintaining control of the aircraft
(no stall or spin)

2) making the chosen field
(remember to aim 1/3 of the way down)

I ask people, if you're 5000 feet directly
above the airport and your engine fails,
does it really matter what speed you fly
in the descent?

If you happened to be Bob Hoover or
Sean Tucker, you could do some nice
aerobatics on the way down, out of
boredom.

https://www.youtube.com/watch?v=zl5TIR1 ... page#t=338

[PilotDAR]

for the average pilot it is better to have a number in their head and then fly that number with precision. If they can relax in this type of real situation, then they have the time to adjust things. They also need to do some faster approaches to land in general to get the control feel when in ground effect at the higher arrival speed to avoid any ballooning. For experienced pilots this comes naturally

I wonder how many experienced pilots actually can put their aircraft on neatly power off.... It is my hope that this thread will cause a few to review their skills, and try a variation of glide speeds to the the flare.

Yes, if you need to make the best distance over the ground, you need to glide at the best glide speed. But, planning your forced landing to actually use that greater distance before you land, when there is no other benefit to doing so, is lessening your reserve of energy, and thus safety.

Experienced pilots should also be able to manage speed and drag control to a good flare position. This would include use of flaps if the aircraft is equipped, and slipping, if that is appropriate for the type. For sue, you'll have at least on of those two options. I agree that some pilots struggle with ballooning, which is a result of poor speed and attitude co-ordination at the flare. That has to be trained and practiced out of those pilots. Learning to land power off is a really good way to do this, ans you're not falling back on opening the throttle to make up for a botched flare. If Cat Driver were contributing here, he'd be jumping in to say that when he was training PBY Catalina pilots (no flaps) to land, they only got to use power on final after they had demonstrated they could land it well power off. Harsh, but I agree with him.... (and I hope he is well, and pops back in to AvCanada).

I'm not trying to conflict with, or rewrite any flight manuals here, but I do hope to make pilots reconsider their techniques for power off landings, and practice more.....

[Colonel Sanders]

I wonder how many experienced pilots actually can put their aircraft on neatly power off

That's actually an item on the CPL
flight test now - 180 degree power
off landing from downwind. I
understand that many candidates
are unable to perform it.

A neat skill to develop, is to set a
power setting on approach, and not
touch the throttles again until just
before touchdown.

That power setting might be idle.

Note that is how I land the

1) Pitts - power off on downwind
2) C421 - 21 inches MP and 1800 RPM
3) L39: 85% N1 heavy, 83% N1 light

I am not a big fan of throttle jockeys,
for a number of reasons.

https://www.youtube.com/watch?feature=p ... RzueM#t=22

The helmet cam shows where I was looking
during that power-off approach - hear the
engine afterfiring at idle the entire time.
Did I ever bother looking at the airspeed?

[pdw]

Looks/sounds fairly fast (youtube).

Is familiar surroundings also helping your recognition here, or the customary whistling / audible noises from memory that align themselves for recognizing an airspeed range ?

[Colonel Sanders]

Like catching a ball, what you look at is
the runway.

You don't need an airspeed indicator after
a while - the pitch attitude is a good proxy.

[Shiny Side Up]

Looks/sounds fairly fast (youtube).

Is familiar surroundings also helping your recognition here, or the customary whistling / audible noises from memory that align themselves for recognizing an airspeed range ?

He doesn't need any of those things, he's fibbing in the post above above, he's not telling you that he lands by sense of smell. Hence why he's immune to the effects of variable tailwinds on final.

[pdw]

Oh yeah ... the smoke oil in the nostrils.

[photofly]

I was thinking about PilotDAR's point here:

The Grand Caravan with the very draggy survey bird tucked up to the belly was the most dramatic. I was required by TC to demonstrate engine failures from 50 feet, with a glide landing, and then at a speed slower than the "best climb" speed. Doing that was very un nerving. ...
I realized that with all that drag, it slowed down so fast that I could not enter a glide which enabled me to maintain the energy I would need to flare.about how gliding an aircraft with a whole load of excess drag leaves you a lot closer to the stall than gliding an aircraft without the extra drag

Best glide (and approximately, best rate of climb) is achieved at the AoA that gives you best lift/drag ratio.

An aircraft with a whole lot of extra drag achieves its best glide (distance) speed at an AoA much closer to its critical AoA than the same aircraft without the extra drag. That means that with the extra drag you have a much smaller lift "reserve" in terms of how much you can increase the AoA - and therefore how much you can afford to slow down, which backs up his experience. It's not (just) that you lose airspeed faster, it's that you're closer to the stall in the first place. You can show that with a couple of graphs; I'll sketch them out and post them in a day or so when I have time.