Needless steep climbouts

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AuxBatOn
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Re: Needless steep climbouts

Post by AuxBatOn »

PilotDAR wrote: Thu Oct 29, 2020 8:02 am
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).
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Re: Needless steep climbouts

Post by 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...
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Re: Needless steep climbouts

Post by 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
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Re: Needless steep climbouts

Post by 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.
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Re: Needless steep climbouts

Post by digits_ »

photofly wrote: Thu Oct 29, 2020 10:24 am 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.
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Re: Needless steep climbouts

Post by 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.
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Re: Needless steep climbouts

Post by photofly »

Blakey wrote: Thu Oct 29, 2020 12:42 pm 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.
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Re: Needless steep climbouts

Post by 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.
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Re: Needless steep climbouts

Post by digits_ »

What do they list as best glide for that decathlon?
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Re: Needless steep climbouts

Post by photofly »

digits_ wrote: Thu Oct 29, 2020 11:29 am Looking forward to the diagrams!
Here's the polar diagram (Cd vs Cl) for the representative NACA2409 airfoil, from Von Mises:
1.png
1.png (196.45 KiB) Viewed 1746 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
2.png (213.08 KiB) Viewed 1746 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
3.png (235.79 KiB) Viewed 1746 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.
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Re: Needless steep climbouts

Post by 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?
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AuxBatOn
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Re: Needless steep climbouts

Post by 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.
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Re: Needless steep climbouts

Post by AuxBatOn »

photofly wrote: Fri Oct 30, 2020 5:26 am
digits_ wrote: Thu Oct 29, 2020 11:29 am 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?
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Re: Needless steep climbouts

Post by 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!
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Re: Needless steep climbouts

Post by Blakey »

photofly wrote: Thu Oct 29, 2020 4:33 pm
Blakey wrote: Thu Oct 29, 2020 12:42 pm 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.
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Re: Needless steep climbouts

Post by photofly »

I was thinking about some numbers in the shower this morning. Suppose you have an airplane that needs a steady 70Kts in the descent to make a successful power-off landing. Suppose further that in this plane you climb after takeoff at 50Kts.

To accelerate from 50kts to 70kts power-off will take a minimum of 130 feet of altitude. More, depending on how quickly you react, and what you do, if the fan up front goes quiet. If you have a power failure in that first 130 feet you're 100% going to bend something, break something, or hurt someone, depending.

If you climb out at 60kts, it will take you a minimum of 70 feet of altitude to accelerate from 60 to 70.
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Re: Needless steep climbouts

Post by shaynemarshallporath »

Steep climb-outs after a simulated TO can be practised at 2000 feet AAE and why not throw in a failed engine at anytime during the practice ( obviously, IAW the appropriate conditions and in a progressive manner ) Lake A/C owners may be the best ones to learn at altitude.
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Re: Needless steep climbouts

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There it was again yesterday, as I held short to cross 04-22, a 172 doing touch and goes on 04. Landing okay, then peeling it off, and climbing away at a needlessly steep angle/slow speed I would be surprised to find they were flying as fast as Vx! The pilot did a couple o these while I taxied in and secured the plane. Then later, while we met in the board room to discuss our flying, overlooking the runway, the 172 pilot was at it again for many more. The other pilots in the board room were as unimpressed as I, while watching. The super steep climb for the first 100-200 feet up put the occupants at a huge risk, had the engine quit. Risk with zero benefit - there was no obstacle to clear - it's a runway at a certified airport!

I worry that this was one instructor, with two different students, (a), putting them both at needless risk during training, and (b), teaching the student(s) that this is an acceptable thing to do, even when not necessary. Okay, teach ONE, to demonstrate how it is done, and why, accompanied by an explanation of the training risk, then do normal climbouts, at least Vy. Slow flight, and Vx flying can also (well, only) be practiced safely at altitude.

The last few days, I've been flying someone else's plane, and I fly it as though I own it. If the Chief Pilot saw me doing in the company plane, what I saw that 172 doing, I would be banished, and sent down the road unpaid! This student(s) will have some unlearning to do, I hope they get the more safe instruction!
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Re: Needless steep climbouts

Post by digits_ »

PilotDAR wrote: Thu Dec 17, 2020 7:54 pm There it was again yesterday, as I held short to cross 04-22, a 172 doing touch and goes on 04. Landing okay, then peeling it off, and climbing away at a needlessly steep angle/slow speed I would be surprised to find they were flying as fast as Vx! The pilot did a couple o these while I taxied in and secured the plane. Then later, while we met in the board room to discuss our flying, overlooking the runway, the 172 pilot was at it again for many more. The other pilots in the board room were as unimpressed as I, while watching. The super steep climb for the first 100-200 feet up put the occupants at a huge risk, had the engine quit. Risk with zero benefit - there was no obstacle to clear - it's a runway at a certified airport!

I worry that this was one instructor, with two different students, (a), putting them both at needless risk during training, and (b), teaching the student(s) that this is an acceptable thing to do, even when not necessary. Okay, teach ONE, to demonstrate how it is done, and why, accompanied by an explanation of the training risk, then do normal climbouts, at least Vy. Slow flight, and Vx flying can also (well, only) be practiced safely at altitude.

The last few days, I've been flying someone else's plane, and I fly it as though I own it. If the Chief Pilot saw me doing in the company plane, what I saw that 172 doing, I would be banished, and sent down the road unpaid! This student(s) will have some unlearning to do, I hope they get the more safe instruction!
Sounds like the instructor was doing simulated soft field short field takeoffs with simulated obstacles according to POH procedures. Can you fault him for that?

I've been asked to demonstrate that procedure during an FI renewal, I've been asked to perform the procedure during my CPL checkride, and at least some of my students have been asked to fly it on their checkrides.

A random 172 POH online: https://wayman.edu/files/Cessna-172N-POH.pdf
Page labelled 4-15, top of the page.
Climb with flaps 10 at 55kts IAS. Well below the suggested 60 or 65kts IAS engine out airspeed. Vx at sea level is 59 KIAS. The POH tells you to fly at a speed below Vx for this particular procedure.

I understand the point you are trying to make, but if examiners are asking students and instructors to demonstrate the procedure, what can an instructor do? Say no and have the student fail the checkride?
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Re: Needless steep climbouts

Post by photofly »

There’s no flight test requirement in Canada for a field that is both soft, and obstructed and/or short. Obstructed fields benefitting from a steep climb: no flaps, in an old 172.

As a data point, the aircraft should accelerate to a more normal climb speed as soon as the (simulated) obstacle is cleared. Flight test standards are to use a 50’ obstacle, which is about a wingspan and a half. So if preparing for flight test you don’t need to remain slow for very long at all.

PilotDAR didn’t report if the flaps were extended at takeoff, or whether the aircraft appeared to level off around 50’ while the flaps were retracted and the airplane accelerated to a normal climb profile. Were they, and did it?
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