Needless steep climbouts

[AuxBatOn]

Drag, whether the aircraft is in a 5 degrees or 45 degrees climb is roughly the same for a given speed (in fact, it will be less in a 45 deg climb but let’s consider them to be roughly the same). What slows you down faster is gravity.

AuxBatOn, let’s say an aircraft is in a STEADY STATE climb that produces a 45 degree climb angle. (6,000’/nm a 100% climb gradient which is far beyond the capabilities of any airplane most of us have flown) Is it correct to assume that the total drag is reduced in this situation because engine thrust is producing a very large share of the lift required thereby reducing the amount of lift needed from the wing? This, in turn will reduce the amount of induced drag produced. In other words, thrust is taking the load off of the wing. Carried to the extreme your CF-18 in a steady state vertical climb, induced drag would be negligible.

Yes, induced drag will be reduced. For a given power setting, form drag will also be reduced since the aircraft will most likely be faster at lower angles of climb (assuming the aircraft is on the front side of the power curve.) I did say it was reduced in my opening statement and I stated an assumption, for the sake of simplicity, I considered the same. A further reduced drag only strengthens the argument that drag has no bearing on how quickly an airplane decelerate after the engine fails, when compared to an the same aircraft that is straight and level when the engine fails.

[photofly]

resulted in a stable glide before the altitude had descended even back to 3000'.

Which is half the objective. Did the airplane, as flown to establish that glide, have enough reserve energy (speed) to be flared prior to 3000 feet, to arrest the rate of descent at 3000 feet momentarily?

It's getting a bit theoretical at that point: you're asking if an aircraft can have an engine failure at zero altitude, climb using its airspeed to a hundred feet or so, and then land successfully. In practice if you've already been climbing at Vx, then you don't need to arrest the descent at the same height as the power failed - you have some altitude in hand. But in this case yes, best glide speed is more than adequate for a power-off roundout and fllare.

But there are two questions to answer: what's an appropriate technique to recover best gliding performance with minimum loss of altitude, and secondly, what's the best speed to have at the end of the glide in order to land successfully.

This is why I have never been satisfied with a practice forced approach, when the instructor calls for addition of power, and an overshoot at 100 feet up on final, the candidate would not really know if a successful forced landing could have been accomplished. Yes, the plane is gliding, but if you were slow, you might have pulled, or flared early, and run out of energy before landing.

It's not particularly unusual to complete a forced landing to the ground if the runway is in the right place and it's not unusual to make a "regular" gliding approach to a full stop that matches the end of a successful forced approach. You and I have discussed some draggy types or modifications where landing power-off needs more airspeed than best glide speed, but I've never seen it in a stock small airplane on wheels.

A part of this is how precise your flare is. If you do it really well, you can do it later and lower, and thus not need so much speed reserve. But the configuration of the plane (different from others) could really affect how it slows and can be flared. Even changing from a thin blade two blade prop, to a wide blade three blade can make a vital difference! Following my change to a three blade MT, my amphibian glided very differently, and I had to develop new techniques and skills - in the plane I knew well from having 500 hours in it on the two blade Hartzell.

I absolutely agree that there's no substitute for knowing the airplane you're in.

[PilotDAR]

A further reduced drag only strengthens the argument that drag has no bearing on how quickly an airplane decelerate after the engine fails, when compared to an the same aircraft that is straight and level when the engine fails.

I'm certainly not a jet pilot, but I don't think this applies to a GA airplane, particularly a draggy one. Memorable to me was in my early days, front seat in a Tiger Moth on skis, I pulled the power well back to begin an approach to land. The next thing I found myself doing, was recovering a stall, to lots of laughter in from the back. I had not pushed the nose down, as I removed power, and the plane more or less stopped in the sky, and stalled, before I realized what was happening. A J-3/PA-11 Cub would have started a slow deceleration, and given me time to notice that I was not paying attention (well, maybe!).

This can be easily noticed in a Cessna Caravan: following a power reduction to idle, and setting up a glide, then feather the prop (the engine still runs fine), and you feel like there's been a big push from behind. Now you're retrimming for a much nicer glide.

The point being, and my reason for a glide PFL to an actual landing, is that depending how draggy the plane, it may slow down a lot more than you expect between the time to initiate a flare, and the time you arrest the rate of descent, and you may not get the descent arrested - if it stalls first. Where a really slippery plane may float longer than you expect, and should not have been glided too fast. The difference between a Cessna 18x on wheels or amphib floats in this regard is very important.

The candidate pilot will know that they got the PFL right, when they land from it. If you went around with power, you cannot be so certain it was set up well. Sure, in a wheelplane factory configuration trainer, you're going to be close. In a draggy plane, actual practice is a good idea - very certainly, if the plane is not accompanied by a flight manual supplement with a recommended glide speed for that configuration!

[rxl]

Yes, induced drag will be reduced. For a given power setting, form drag will also be reduced since the aircraft will most likely be faster at lower angles of climb (assuming the aircraft is on the front side of the power curve.) I did say it was reduced in my opening statement and I stated an assumption, for the sake of simplicity, I considered the same. A further reduced drag only strengthens the argument that drag has no bearing on how quickly an airplane decelerate after the engine fails, when compared to an the same aircraft that is straight and level when the engine fails.

Thanks. Makes sense. I asked the question because of your first statement that drag is actually less at the steeper climb angle. I just wanted to make sure my understanding of the situation is correct.
I think the assumption being made in the thread is that a draggier version of exactly the same aircraft given exactly the same flight state (same all up weight, Vx climb etc.) will lose airspeed more quickly if thrust is reduced to zero.
ie. A C-172 floatplane in this situation will lose airspeed more quickly than a C-172 wheel plane. They are actually very different aircraft in this respect.

[trey kule]

I think we have strayed a bit from the intent of the OP.(simply an observation , not a criticism)

But at Vx, and an engine failure, without getting into all the aerodynamic issues, the plane is going to slow down faster than it would at Vy, and, more importantly, needs a bigger pitching movement down, as well as the danger of a delay in reaction and slowing down into the back side of the lift/drag curve.

Altitude may be your friend, but speed can be converted To altitude, or give you more time to react.

Besides that, in small piston planes Vx provides poorer engine cooling, and in many VFR aircraft less view for traffic.

Ignoring all the arguments, I believe Vx climbs should only be used for clearing an obstacle, and only as long As required to accomplish that task.

Doing them for shits and giggles when not necessary, IMO, displays a lack of good airmanship.
Practice them at altitude if you think you need practice.

So, I agree with PilotDar here. Steep climb outs below Vy That are not necessary are really not a great idea.

Lastly, I thought that comment about the snowbirds was in extremely poor taste, and off the mark.

[AuxBatOn]

A further reduced drag only strengthens the argument that drag has no bearing on how quickly an airplane decelerate after the engine fails, when compared to an the same aircraft that is straight and level when the engine fails.

I'm certainly not a jet pilot, but I don't think this applies to a GA airplane, particularly a draggy one. Memorable to me was in my early days, front seat in a Tiger Moth on skis, I pulled the power well back to begin an approach to land. The next thing I found myself doing, was recovering a stall, to lots of laughter in from the back. I had not pushed the nose down, as I removed power, and the plane more or less stopped in the sky, and stalled, before I realized what was happening. A J-3/PA-11 Cub would have started a slow deceleration, and given me time to notice that I was not paying attention (well, maybe!).

This can be easily noticed in a Cessna Caravan: following a power reduction to idle, and setting up a glide, then feather the prop (the engine still runs fine), and you feel like there's been a big push from behind. Now you're retrimming for a much nicer glide.

The point being, and my reason for a glide PFL to an actual landing, is that depending how draggy the plane, it may slow down a lot more than you expect between the time to initiate a flare, and the time you arrest the rate of descent, and you may not get the descent arrested - if it stalls first. Where a really slippery plane may float longer than you expect, and should not have been glided too fast. The difference between a Cessna 18x on wheels or amphib floats in this regard is very important.

The candidate pilot will know that they got the PFL right, when they land from it. If you went around with power, you cannot be so certain it was set up well. Sure, in a wheelplane factory configuration trainer, you're going to be close. In a draggy plane, actual practice is a good idea - very certainly, if the plane is not accompanied by a flight manual supplement with a recommended glide speed for that configuration!

The physics is the same for jets or GA aircraft. The difference is the effect (difference between Vy and Vx, and the stall speed for GA aircraft is generally smaller) of gravity. Gravity has a much more pronounced effect if the nose is up (the same true with the nose down). For a given configuration (including prop position and RPM), the drag polar is the same. As discussed earlier, induced drag is, in straight flight, maximal in a level attitude and reduced as soon as the aircraft is in a steady climb or descent and 0 at 90 degrees climb angle. Incidentally, the g required to maintain a 45 deg climb or descent is 0.7g, which also reduces the stall speed. Given that GA aircraft can’t climb too steeply normally, those concepts are not taught (perhaps rightfully).

[PilotDAR]

The physics is the same for jets or GA aircraft.

Hmmm.... Then something is different, as there can be a noticeable difference for the power off characteristics, between a 172 wheel plane, and a 172 floatplane. From my limited understanding of jets, some possess the ability to climb on inertia ("zooming" I believe?), where you'll have a hard time zooming a 172 floatplane anywhere, even if the engine is developing power! If the jet pilot were flying power off, knowing that his/her gear were down and aerodynamic dive brakes were stuck out, they'd perhaps do things differently. The floatplane is like that all the time...

[JasonE]

Interesting conversation folks!

I have simulated this several times when I had my Cherokee 140 with similar results as photofly. Mind you I was prepared mentally for what i was about to do and had recently practiced rope breaks in a glider. Boy does that get your attention when your instructor releases it without warning at 300 feet !! We landed on the cross runway, as was his plan.

[rxl]

The physics is the same for jets or GA aircraft.

Hmmm.... Then something is different, as there can be a noticeable difference for the power off characteristics, between a 172 wheel plane, and a 172 floatplane. From my limited understanding of jets, some possess the ability to climb on inertia ("zooming" I believe?), where you'll have a hard time zooming a 172 floatplane anywhere, even if the engine is developing power! If the jet pilot were flying power off, knowing that his/her gear were down and aerodynamic dive brakes were stuck out, they'd perhaps do things differently. The floatplane is like that all the time...

I think you can “zoom” climb any airplane. Even a draggy, low (under?) powered 172 floatplane descending at Va has some excess inertia that is available to trade for altitude. The CF-18 pilot at 400KTS obviously has an awful lot more excess inertia available for that same trade off. There’s no magic to it. The only “magic” that most jet powered airplanes have that most propeller driven airplanes do not have is a large amount of excess thrust available, but even that is limited by physics.
A less draggy 172 wheel plane in the same conditions will “zoom” just a little longer than the float version and gain a little more altitude in the process. Don’t do it at low altitude and to be clear, by “zoom” I mean a smooth, well coordinated increase in pitch attitude allowing the airspeed to bleed off to no less than Vx or Vy.
Won’t be quite as impressive as a CF-18 pulling from 400KTS or even a Challenger from 320KTS, but I think the physics is the same.

[PilotDAR]

well coordinated increase in pitch attitude allowing the airspeed to bleed off to no less than Vx or Vy

What I'm talking about is not that, it's a pilot who has chosen to climb more slowly than Vy to begin with. Anything to do with Va, or hundreds of knots is outside the scope of the discussion, as would be pitching up at all following an engine failure in the climb in a GA plane. It's more a matter of how quickly and how far you'll have to pitch down to glide accelerate to a speed from which you can safely flare and land, and how much altitude you're going to loose while you do that.

[AuxBatOn]

well coordinated increase in pitch attitude allowing the airspeed to bleed off to no less than Vx or Vy

What I'm talking about is not that, it's a pilot who has chosen to climb more slowly than Vy to begin with. Anything to do with Va, or hundreds of knots is outside the scope of the discussion, as would be pitching up at all following an engine failure in the climb in a GA plane. It's more a matter of how quickly and how far you'll have to pitch down to glide accelerate to a speed from which you can safely flare and land, and how much altitude you're going to loose while you do that.

The difference is the delta between Vx/Vy and Vs. In a jet, you have more speed (greater delta between Vy/Vy and Vs) to trade for altitude when compared to a small GA aircraft. That is the difference, not physics behind drag. Also, given that kinetic energy is proportional to the square of the speed, at higher speed, for the same delta, you can gain more potential energy for the same delta in airspeed.

Assuming that KCAS is roughly equal to KTAS (low altitude, ISA), a Cessna 150 (Vx=55 kts; Vs=40 kts) have a zoom capability of 67 ft. A Tutor (Vx=120 kts; Vs=90 kts) has a zoom capability of 280 ft. It's not necessarily about zooming per se but more about demonstrating the excess energy above stall speed (which buys you time).

[PilotDAR]

demonstrating the excess energy above stall speed (which buys you time).

Yes, and the key is that if you're near or at stall speed descending, you'll not have enough reserve to arrest the descent before you hit. Pilots must be certain that they consider maintaining a reserve of energy to arrest a descent before hitting the ground. That reserve is not assured at low altitudes slower than Vy. So the pilot must understand that they could be flying at a speed and altitude combination from which a safe gliding landing is not possible.

Sadly, unlike a helicopter, there is no requirement to present this important information to the pilot of an airplane. The manufacturer would rather not talk about it. The STC holders for all the mods perhaps have not considered it, and certainly not in combination with other mods, and instructors seem to not teach it. Helicopter manufacturer's publish this information, because it's a requirement.

We know that a twin will fly slower than Vmca, but it you loose an engine doing it, you'd better have some altitude. This is the same danger, just the elephant in the room for GA singles...

[rigpiggy]

had a guy who insisted on a v2 climb to 1500 30degree deck angle. the book said v2 till clear obstacles, then 8-10 degrees as commanded by the Vbars........you just can't tell some people

[photofly]

For a given airframe, the more drag you have, the closer your best glide is to the stalling speed. I’ll post some diagrams later to explain why. In the case of unlimited (or at least overwhelming) drag, best glide is at the stalling speed (stalling AoA).

(By best glide I mean maximum lift to drag ratio, the speed that gets you the furthest distance. It may not be best by other criteria.)

It’s not hard to add enough drag that best glide is a lot slower than 1.3Vs1. That would mean you’d have to dive for airspeed at the end of the glide, in order to flare safely.

[digits_]

For a given airframe, the more drag you have, the closer your best glide is to the stalling speed. I’ll post some diagrams later to explain why. In the case of unlimited (or at least overwhelming) drag, best glide is at the stalling speed (stalling AoA).

(By best glide I mean maximum lift to drag ratio, the speed that gets you the furthest distance. It may not be best by other criteria.)

It’s not hard to add enough drag that best glide is a lot slower than 1.3Vs1. That would mean you’d have to dive for airspeed at the end of the glide, in order to flare safely.

Looking forward to the diagrams!

Are you aware of any airplane types where the manufacturer defined best glide speed is close to the stall speed? I've never encountered that, but haven't really flown super draggy amphib planes either.

[Blakey]

The American Champion Aircraft 8GCBC (Bellanca Scout) has a clean stall of 53 mph and a best glide of 55 mph. The POH states "While 55 mph IAS will give the maximum glide range, due to this speed being close to the stall speed, when conducting a forced landing or Practice Forced Landing the speed shall be increased to 70 mph.

[photofly]

The American Champion Aircraft 8GCBC (Bellanca Scout) has a clean stall of 53 mph and a best glide of 55 mph. The POH states "While 55 mph IAS will give the maximum glide range, due to this speed being close to the stall speed, when conducting a forced landing or Practice Forced Landing the speed shall be increased to 70 mph.

Do you have a link to a manufacturer POH that says that? The details I can find online don’t match those.

[PilotDAR]

My collection of flight manuals does not include the Scout, but I do have the Decathelon, similar but different. Interestingly, it does say for an obstacle takeoff to maintain 58 MPH IAS, with a warning: " The aircraft must be pitched forward to a safe power off speed should a power failure occur during climb-out; failure to respond immediately may result in a stall at low altitude". And, under soft field: "Warning, the aircraft will lift off at a very low IAS, however, continued climb-out below takeoff obstacle speed is not recommended". And for forced landing: " 80 On Final Approach - Airspeed 75 MPH (70 MPH minimum).". So for the Decathelon, to comply, were you climbing out at Vx of 58, and suffered and engine failure, there is an expectation that you would accelerate in the glide to 75 MPH to execute a forced landing. It'll take quite a pitch down, and some altitude loss to gain that speed in the glide.

[digits_]

What do they list as best glide for that decathlon?

[photofly]

Looking forward to the diagrams!

Here's the polar diagram (Cd vs Cl) for the representative NACA2409 airfoil, from Von Mises:

1.png (196.45 KiB) Viewed 2921 times

The horizontal scale is stretched by a factor of 5 relative to the vertical scale, because Cd is quite small compared to Cl (it's an efficient airfoil) and otherwise the data is all a bit squished up. The annotated dots represent different angles of attack.

Here's how it applies to a representative airplane:

2.png (213.08 KiB) Viewed 2921 times

Adding the airframe to the wing results in an increase Cd, (equivalently, the vertical axis is moved to the left) and the blue line represents the steepest value of Cl/Cd available, because it's the steepest tangent. The blue dot is the operating point at (for example) 9° AoA. This represents best glide - and the actual glide ratio is the gradient of the blue line.

If you add more drag to the same airframe the vertical axis moves further to the left. For example:

3.png (235.79 KiB) Viewed 2921 times

The best lift/drag ratio that you can get (green line) is considerably worse (shallower) of course, but the AoA at which you get it (green dot) is much close to Cl_max - which is the AoA at which the wing stalls.

So by adding floats, you have:

• decreased your glide range
• and increased the AoA at which you achieve that best range

If you add enough drag, your best glide will be *at* the stalling angle of attack, which gives you nothing in reserve to flare with.

[digits_]

Nice, thanks!

You are basically adding all airframe drag to this one airfoil, right?
In the case of a floatplane, the floats also generate a small but significant amount of lift. Using the same reasoning, you would then lower the red axis, in turn increasing the L/D and decreasing the angle at which it happens, no? But since the drag is usually bigger than the added lift, you still end up with a higher AoA and lower glide speed than the clean airplane. Is that correct?

[AuxBatOn]

There is another, easier way (in my mind) to see the issue (if you are a tiny bit math inclined).

Starting from the drag equation:

D=0.5*r*V^2*S*Cd

Where

D is the drag
r is the density
V is the true airspeed
S is the surface area of the aircraft
Cd is the drag coefficient

Assuming a second order drag polar, Cd=Cd0 + Cl^2 / (Pi * e * AR)

Where

Cd0 is the form drag coefficient
e is the Oswald efficiency factor
AR is the Aspect Ratio

Plugging the drag polar into the Drag equation

D=0.5*r*V^2*S*(Cd0 + Cl^2 / (Pi * e * AR))

Using the lift equation:

Cl = 2*L/(r*V^2*S)

Where

L is the lift

Assuming level flight (it is an assumption using small angles but in any case, the point will remain the same), we can substitute Weight for Lift

Cl = 2*W/(r*V^2*S)

Going back to the drag equation and doing some manipulations

D=0.5*r*V^2*S*Cd0 + 4*W^2/(r*V^2*S*Pi*e*AR)

Max L/D happens when D is minimal therefore we need to derive D over V (dD/dV) and find where the tangent is 0.

In this case, dD/dV = r*V*S*Cd0 - 8*W^2/(r*V^3*S*Pi*e*AR)

dD/dV = 0 therefore r*V*S*Cd0 - 8*W^2/(r*V^3*S*Pi*e*AR)

Solving for V

V^4 = 8*W^2/(Cdo*r^2*S^2*Pi*e*AR)

As you see, as you increase Cdo (form drag), the speed at which max L/D happens decreases.

[AuxBatOn]

Looking forward to the diagrams!

Here's the polar diagram (Cd vs Cl) for the representative NACA2409 airfoil, from Von Mises:

You are using the same drag polar throughout all the examples or am I missing something?

[PilotDAR]

There is another, easier way (in my mind) to see the issue

Hmmm, I feel inadequate! My "easy way to see the issue" is to have my candidate fly at 3200 feet, at Vx, pull the power off, and tell them to arrest the descent momentarily at 3000 feet, and watch what happens. But then, I'm not so inclined to math, I'm sure it works too!

[Blakey]

The American Champion Aircraft 8GCBC (Bellanca Scout) has a clean stall of 53 mph and a best glide of 55 mph. The POH states "While 55 mph IAS will give the maximum glide range, due to this speed being close to the stall speed, when conducting a forced landing or Practice Forced Landing the speed shall be increased to 70 mph.

Do you have a link to a manufacturer POH that says that? The details I can find online don’t match those.

Best I can do is quote from the page in the POH as I've never found any of the manuals online. It is contained within the note at the bottom of the "Maximum Glide Range" chart. Interestingly, there is no glide ratio published for the airplane, you have to do the math from the chart.