Powered vs. Power at idle landings.

[photofly]

Why do we train like marching soldiers to fly forced approaches only at best glide speed? From which, any deviation of airspeed - up or down - results in a steeper glide.

To increase controllability with no power all one needs is higher airspeed...

.'s right, of course. If you have a field in close enough range, wouldn't it make more sense to fly a forced approach at, say, best glide+10? Then you've got some controllability by pitching up, or down.

Heresy, I know - but why not?

[Beefitarian]

The one issue being you need to get rid of that +10 preferably before touch down.

[photofly]

Not a problem. You have to transition from best glide into the flare, anyway, and we're already accomplished at increasing the descent rate and losing energy with extra drag by lowering flaps and/or side slipping.

[Chuck Ellsworth]

Lets not skew this subject to far.

Generally speaking using the airspeed recommended for the airplane is the best method to use during the approach.

Controllability at that airspeed should not be a concern whether or not you are using power on the approach, the power off approach will be steeper than when using power.

With some high drag airplanes you can get rid of excess airspeed very quickly.

[Beefitarian]

True but you can slow down even more quickly if you are already going the slowest safe speed.

The next thing is, "Well, 10 knot faster worked pretty good. Next time I'm going to try 25." Some nice test pilot guys already found the best glide speed. Should be ok to go a little faster but I prefer to have a reason for decisions like that.

If it's pretty bumpy and gusty out you probably want to add a few knots.

[BTyyj]

Lets not skew this subject too far.

Hasn't it been already?

Like . has pointed out, controllability is based on airspeed; the aircraft doesn't know if the engine is full or idle, just its velocity.

But, what if you've gone below the angle at which the best glide speed will get you to the field, at power idle and zero flaps?

[photofly]

Some nice test pilot guys already found the best glide speed.

Best glide speed doesn't get its name because it's the best one to use; it gets its name because it takes you the furthest from a given altitude. "Best" is not to be taken as value judgement on its suitability in all circumstances.

Which is what I'm asking about: from the point of view of making it without power to a nearby field, best glide is thoroughly suboptimal from the point of view of controllability; however you deviate from it, you're coming down more steeply.

The only case when best glide is actually "best" is when the field you've picked is at the outer limit of reachability, in which case the choice of field itself is probably suboptimal, and you'd be better off to pick another one that's closer, glide a little faster, and have more control.

Wouldn't you?

[Colonel Sanders]

You have to transition from best glide into the flare

Actually, the United States Navy doesn't bother
flaring to land, even when they aren't landing on
an aircraft carrier!

With the right landing gear, flaring is optional.

[photofly]

I believe their motto, having a dig at the USAF, is "flare to land, squat to pee"

[Colonel Sanders]

Their unusual landing technique involves full
throttle at touchdown. When landing on a
runway with no wires - and two afterburners -
this can lead to interesting results.

[Beefitarian]

Now you have gone beyond my knowledge.

We need to ask someone else.
Do you have anymore control at 10 knots over best glide speed?

My answer is no. I await being corrected.

[photofly]

I'm sure I haven't gone past your knowledge at all!

At 10 knots faster than best glide, you can shallow your descent angle by pitching nose-up slightly and slowing (moving towards best glide speed), and you can steepen your descent by pitching nose down slightly and flying slightly faster. I'm not claiming this is instantly going to turn you into a spot landing champion, but it's an improvement over maintaining best glide speed precisely, where any pitch change - up or down - means coming down more steeply.

[trey kule]

Photofly?

Or Colonal Saunders V 2.0? I know he posted a terrible thing about you awhile back but I thought it was just a passing comment.

I agree with what you posted in general, but I thought this was about power off or power on landings?
Not approaches.. So many types of aircraft (single engine) that is a bit hard to generalize, but,
if you are talking power on approach at best glide speed plus 10, then you can simply reduce or add a bit of power just as easily as pitching the nose up or down a bit.. If you mean power off, or on a forced approach you have to temper your genralization a bit I think. At best flide speed plus 10, partidularily in a small single , you might actually get a bit better range if you are flying into a headwind.. And if no headwind, you will not be getting the range you could at best glide speed.
So...if you hold best glide speed (no head wind) and you come up short, you go to plan B.
If you are going to land long, then you can raise the nose a bit (not really my choice in a forced landing situation), use flaps, or, if the aircraft can be sideslipped, do that..
There is also the human factor if we are drifting into the forced approach..When it happens for real, all that silly FTU drills, secures, restarts etc, tend to go out the window...the object is to fly the plane and get it safely into a field..Dont fancy it up. That is OK for pilots who do these types of things every day, but they are not the typcial single engine pilot.. My thoughts are KISS...Nail your best glide speed, see how things look and progress and then make any speed change decisions if they will work.

In any event, this thread was not about that, but as there are so many types of airplanes with different landing characteristics, Cat's original question does not welcome vast generalizations.
One of the difficulties we have with new CPL's is trying to get them to stop attempting to fly a new type like they did the last type they flew. It is important for pilots to understand that there are differences that they must adjust their flying technique to..
So power at idle, vs. power at touchdown...Depends...and that is the best answer anyone will give.

[Chuck Ellsworth]

Cat's original question does not welcome vast generalizations.
One of the difficulties we have with new CPL's is trying to get them to stop attempting to fly a new type like they did the last type they flew. It is important for pilots to understand that there are differences that they must adjust their flying technique to..
So power at idle, vs. power at touchdown...Depends...and that is the best answer anyone will give.

Exactly.

When I started this discussion I used the PBY as an example.

I had hoped that the discussion would evolve around piston engine airplanes for the simple reason that is what most pilots here would be flying.

Jets are a completely different animal.....however they can be landed from a great height with no power.

So back to my reason for posting this.

I feel that pilots should be equally proficient with landing power off or using power for their landings......because some day you may need to be proficient landing without the power crutch.

By the way the jet pilots did have a bit of resetting their thought process to get comfortable with the power off from 200 feet to touch down....

Once they got the picture they had no problem.

The last six pilots I gave PBY type ratings to were doing it because they really wanted to fly that type of airplane enough to pay for their ratings, 10,000 Euro which included at least fifty water take offs and landings in line training carrying passengers for insurance purposes after they had the type rating.

[Chuck Ellsworth]

Or Colonal Saunders V 2.0?

Looks like I'm not the only one who sees a similarity in the delivery.

[Colonel Sanders]

I guess now would be a bad time to mention
that Dr. Aero is what I post as when I'm drunk?

PS I ain't half as smart as PF. He has 3 degrees,
I only have one! I'm the moron of my family. My
father has 2 degrees, my sister has 2, and my mom
skipped 3 grades and got her undergrad when she
was 19. I'm a bit like Sheldon Cooper's sister, except
she's taller and has slightly bigger boobs.

[Chuck Ellsworth]

Hey Colonel.

I don't have any degrees.

I'm just plain smart.

[photofly]

I agree with what you posted in general, but I thought this was about power off or power on landings?

I was just too scared of . to start a new thread.




Sorry.

[Colonel Sanders]

Sobered up a bit and thought about this.

My observation: it doesn't matter what throttle
position you choose - just don't be a throttle jockey.

In the C421B, I set 21 inches MP on downwind and
don't touch the throttles again until power reduction
over the runway threshold. I control the glidepath
and speed with drag increases (gear, flaps).

Pretty much the same thing in the L39. 83% N1 if
I am light, 85% if I am heavy with fuel on downwind,
gear at 180 knots, first stage flaps 160 knots, then
full flap turning final. If I fly it right, I do not need to
touch the throttle.

In the Pitts, it's throttle to idle on downwind abeam
the runway numbers. Turn 45 degrees of bank, and
put the nose down about the same. On the ground
in 20 seconds, and if I do it right, I don't need to touch
the throttle until I am taxiing after the rollout.

Same thing in the Taylorcraft BC12D - power to idle
abeam the numbers - except with all the wing, it's
almost a glider. Takes a long time to come down
1000 feet. But again, if I do it right, I don't need
to touch the throttle - just a little sideslip. No flaps,
of course.

As TK observes, pilots these days take pride in flying
as few types as possible, and this cripples them at
first.

IMHO an experienced, skilled, competent pilot
ought to be able to fly almost anything, if you
toss the POH at him so he can figure out the
fuel and landing gear systems, and review the
emergency procedures.

Nosewheel or tailwheel, wheels or floats or skis,
fixed gear or retractable, stick or control column,
right seat or left seat, day or night, VFR or IFR,
single or multi, prop or jet, boxer or radial piston,
turbo-prop or turbo-fan, certified or homebuilt,
straight and level or upside down.

I know this is heresy to people who like to fly only
plastic nosewheel trainers with a square yard of glass
in the panel.

[dr.aero]

Being the drunk version of CS, I feel obligated to reply to one, Mr. Photofly.

Mr. Photofly, what sort of controllability are you looking for while flying a forced approach? If I may suggest that you keep the aerobatics to a minimum while descending to your doom?/landing on the soft earth. Flying at best glide + wind correction, as you pointed out, will get the airplane the furthest distance which actually corresponds to the shallowest approach angle. Considering that the angle of descent is usually steeper than 3 degrees, plus or minus a pinch, at the best glide speed, it would be good for the purposes of judging the landing and flare to approach at an angle roughly approximate to 3 degrees.

Mr. Photofly, picking one speed for a pilot to aim for when in a distress situation (you agree the pilot would be distressed? at least a little perturbed...) will provide for the best outcome from a human factors standpoint. As someone else pointed out, KISS.

Mr. Photofly, one last thing - have you ever flown an airplane in a power-off glide while on a forced approach exercise (or real) where you didn't have, what you would call, the "required maneuverability"? If so, please explain.

Cheers!
CS

[dr.aero]

As TK observes, pilots these days take pride in flying
as few types as possible, and this cripples them at
first.

IMHO an experienced, skilled, competent pilot
ought to be able to fly almost anything, if you
toss the POH at him so he can figure out the
fuel and landing gear systems, and review the
emergency procedures.

Your drunk-you approves!

[photofly]

Controllability is a bit like chocolate. I can't think of a time when more isn't better.

Someone else posted this quote, earlier:

Hawker Harrier Test Pilot John Farley makes excellent remarks about forced approaches in his book "A View From the Hover". He suggests that the forced approach is sometimes better carried out as a faster than normal glide, while controlling (adding) drag at the bottom to enable the landing as desired. Retaining this excess energy until you no longer need it, could compare to carrying power into the approach. Just another thing to practice....

That sounds very sensible to me. I wondered if there were any good arguments against it, and why we don't teach that ab initio.

[Colonel Sanders]

why we don't teach that ab initio

PFL's are very poorly performed during ab initio flight
training. They are historically one of the very worst
items on the PPL (and even CPL) flight tests. Heck, I
think I can remember a class 2 flight instructor that
flunked his instructor renewal flight test, because he
didn't make the field!

Against this backdrop ...

The PPL flight test guide specifies +/- 10k airspeed
from best distance in the POH. It's one of the few
quantitative measurements in the flight test guide
for the PFL, and most students have very poor
control of their airspeed, which (avert your eyes)
is mostly ok with me, as long as they make the
field.

Not making the field in a PFL is a major error. Poor
airspeed control is a minor error - as long as he
doesn't stall it. That would be a major error.

I worry that if we hoist the jolly roger and tell
students that airspeed doesn't matter (which is
sort of the truth) then they will arrive over the
runway threshold with 100 knots indicated and
be unable to land the runway on the chosen
field, and end up running off the end into the
trees/fence/whatever obstacle.

This is probably heresy, but the big advantage
to being close to the best distance glide on final
is that you have a hope of getting down to your
proper approach speed over the threshold!


Of course, sometimes you just don't have a choice.
Many years ago, I flew a 172 into Pearson to pick up
a friend's 182 which had some work done on it.

ATC was hollering at me the whole way down on
final, to keep my speed up. It was night, I couldn't
see squat, but I set power for top of the green arc
until I was over the runway threshold, ATC moaning
and bitching and pissing and whining the whole time.

Power off, but that didn't really matter. It was a
good thing the runway was a gazillion feet long.
Couldn't lower the flaps - I wasn't anywhere near
the white arc. Somehow got it down. Maybe I
sideslipped it. Can't remember. Eventually saw
white arc, full flap, got it stopped and off the
runway ASAP.

Anyways, my long-winded point is that a high-speed
approach is not always the best, if your runway isn't
several miles long!

[photofly]

The PPL flight test guide specifies +/- 10k airspeed
from best distance in the POH. It's one of the few
quantitative measurements in the flight test guide
for the PFL, and most students have very poor
control of their airspeed, which (avert your eyes)
is mostly ok with me, as long as they make the
field.

The Flight Test Guide for the PPL is a bit more nuanced than this.
For the forced approach, it says (my emphasis):

- control the aeroplane and initially establish the recommended best glide speed (+10/-5 knots);

Then it goes on to say (again, my emphasis):

Note 1: After initially establishing the recommended glide speed, the candidate may vary the airspeed and flight profile, as required to achieve a successful and safe approach, without exceeding any aircraft limitations.

I might be reading it wrong, but there's nothing there to say using a faster speed than "best glide" for better controllability is frowned upon.

why we don't teach that ab initio

PFL's are very poorly performed during ab initio flight
training. They are historically one of the very worst
items on the PPL (and even CPL) flight tests. Heck, I
think I can remember a class 2 flight instructor that
flunked his instructor renewal flight test, because he
didn't make the field!

Against this backdrop ...

I think the point you're making is that the forced approach exercise should be kept simple because the pass rate is already low enough and to make it more complicated would lower the pass rate even more.

A clever guy once said, "you should make things as simple as possible, but no simpler." (Who was that?) Perhaps the pass rate for the exercise is so low because we've made it too simple?

Suppose I teach someone to play chess. It's a complicated game and it takes a while even to pick up the way the pieces move. "Don't worry about the horse-shaped pieces," we say, "just concentrate on the others." Our student loses a whole string of matches. The wrong conclusion to draw is that we will improve the scores of future students by simplifying further and leaving out the bishops and rooks too.

Remember "as simple as possible, but no simpler." Maybe - just maybe - teaching people that it's "best glide speed, all the way down" is making things simpler than possible?

[Steve Pomroy]

A clever guy once said, "you should make things as simple as possible, but no simpler." (Who was that?) Perhaps the pass rate for the exercise is so low because we've made it too simple?
... <snip> ...
Remember "as simple as possible, but no simpler." Maybe - just maybe - teaching people that it's "best glide speed, all the way down" is making things simpler than possible?

Was this rhetorical? If not, it was Einstein, although the quote is probably not what he actually said:

http://www.flightwriter.com/2011/02/ein ... razor.html

I'm inclined to agree that we shouldn't be simplifying things as far as we do. But I don't think that's the problem with the PFL. The techniques usually taught for the PFL require a great deal of judgement. On the face of it, judgement is great, but it takes experience to develop. Expecting someone with 40-60 hours to complete a PFL method based so heavily on judgement is IMHO unrealistic -- especially when we account for the average quality of instruction provided.

The circling PFL technique taught to Air Force candidates is bulletproof and requires almost no judgement, just an ability to control your airspeed, use ground references, and fly a procedure. This technique is accepted by TC (and is included these days in the FTM), but it doesn't seem to have made much headway into the training community.

Cheers,
Steve
http://www.skywriters.aero
http://www.flightwriter.com