Cessna's recommendation on flaps

[Star Keeper]

Full flaps at 10 miles out is the best procedure in the 172.

So you are the Buckee student doing the 6 mile patterns at 65 knots every monday morning during my training.

 

[MauleSkinner]

So you are the Buckee student doing the 6 mile patterns at 65 knots every monday morning during my training.

Or the guy I watched shoot an instrument approach for 23 minutes from my perch in a hood over the FAF.

I didn’t beat him to the ramp, but I did beat him into the FBO.

 

[Ryan F.]

True. He shouldn’t have used the term “typical single engine piston airplane”. One could possibly not realize that it applies to all airplanes.

Been friendly-jousting on the message boards for a long time! Had I said that, someone would have brought up a scenario involving a Harrier Jump Jet or something of that ilk. I find it a little easier to keep things in context, avoid those unproductive tangents and keep the discussion on track.

 

[dmspilot]

But your climb angle IS decreased when you add flaps.

That is not universally true.

Climb angle is a function of thrust available minus thrust required.

In propeller driven aircraft, thrust available is higher at slower speeds.

Some Cessna 182 models, for example, specify a Flaps 20° climb to clear an obstacle, at a speed approximately equal to the flaps-up stall speed. And the climb angle will be zero (or negative) at the flaps up at stall speed.

So that is a case of a "typical" aircraft that has a steeper climb angle with flaps than without. Ryan F's statement and your follow up statements are incorrect.

 

[455 Bravo Uniform]

One thing I don’t think anyone has touched on is the greater cushion between climb speed and stall speed when taking off with flaps. Not sure if it’s a primary reason, but at minimum it’s a side benefit. Yes, folks have had take-off stalls, and that’s why the PPL cert requires their practice, so it’s plausible that flaps on takeoffs become a safety SOP.

Besides, if “engine loss on takeoff with no runway left, land ahead”, your face smashing into stuff will be at lower velocity, without having one more thing to forget in an oh s**t moment. Also less chance of stall-spin in that scenario.

Me: 182 (but with canards), 95% of my takeoffs are flaps 20, and 95% of my takeoffs are simulated soft and/or short-field. They’re just more fun that way. Exception to the rule? I don’t know any different.

 

[Stewartb]

Cessna flaps lower the power-on deck angle at any given speed. If you've got obstacles in front of you flaps improve the view. The bigger point of leaving them on is not to upset the climb configuration until obstacles are cleared. The old retract full flaps to 20* after a balked landing may be safer in low powered airplanes but if the plane has enough power, leave the flaps alone until clear of obstacles. Training in the plane you fly helps you understand what it can or can't do much better than reading the POH can.

 

[MauleSkinner]

That is not universally true.

Climb angle is a function of thrust available minus thrust required.

In propeller driven aircraft, thrust available is higher at slower speeds.

Some Cessna 182 models, for example, specify a Flaps 20° climb to clear an obstacle, at a speed approximately equal to the flaps-up stall speed. And the climb angle will be zero (or negative) at the flaps up at stall speed.

But if you exercise one or two brain cells and climb at an appropriate speed for flaps up instead of at stall speed, the climb will, universally, be steeper.

 

[nauga]

But if you exercise one or two brain cells and climb at an appropriate speed for flaps up instead of at stall speed, the climb will, universally, be steeper.

Yes, if you climb at a speed where climb angle is steeper with flaps up then the climb angle will be steeper with flaps up. That's hardly "universal" in anything other than semantics, and your total distance to altitude including ground roll *may* be longer in that example. Know your airplane, fly your airplane.

Nauga,
and the difference between local and global optima

 

[dmspilot]

But if you exercise one or two brain cells and climb at an appropriate speed for flaps up instead of at stall speed, the climb will, universally, be steeper.

If the Delta been Tr and Ta is higher at the flaps 20 climb speed it will not be universally stepper with the flaps up even at the optimum speed for flaps up

 

[MauleSkinner]

Yes, if you climb at a speed where climb angle is steeper with flaps up then the climb angle will be steeper with flaps up. That's hardly "universal" in anything other than semantics, and your total distance to altitude including ground roll *may* be longer in that example. Know your airplane, fly your airplane.

Nauga,
and the difference between local and global optima

And part of knowing your airplane is knowing that crossover point exists and having an idea of where it is for the height above the runway you’re dealing with. In the case of the older 172s, it appears to be below 50 feet. In the case of the newer ones, it appears to be above 50 feet. Those heights seem kind of relevant to a takeoff.

 

[MauleSkinner]

If the Delta been Tr and Ta is higher at the flaps 20 climb speed it will not be universally stepper with the flaps up even at the optimum speed for flaps up

How do you know the delta is higher?

 

[dmspilot]

How do you know the delta is higher?

How do you know it isn't?

Thrust available is higher at slower speeds.

The climb angle will be steeper with flaps if the drag added by the flaps is less than the increase in thrust available.

Without the necessary data there is no way you and Ryan F. can say flaps always hurt climb angle. It's just not true.

 

[MauleSkinner]

How do you know it isn't?

Thrust available is higher at slower speeds.

The climb angle will be steeper with flaps if the drag added by the flaps is less than the increase in thrust available.

Without the necessary data there is no way you and Ryan F. can say flaps always hurt climb angle. It's just not true.

Ok…how about “flaps always hurt climb angle in every airplane with flaps that I’ve ever dealt with, including the ones this thread is discussing.”

 

[dmspilot]

Ok…how about “flaps always hurt climb angle in every airplane with flaps that I’ve ever dealt with, including the ones this thread is discussing.”

Where is your data?

 

[MauleSkinner]

Same place as yours.

 

[Roger Wilco]

It seems that a clearer differentiation between climb rate and climb angle would be helpful, and we can add climb gradient (height gained per unit of distance) as it is what we really want to maximize when obstacle clearance is a concern.

As dmspilot stated, the relationship between thrust and drag affects rate of climb. In order to understand the effect on angle of climb, it is necessary to take groundspeed into account. Flaps-up Vx is faster than Vx for flaps extended. Using the configuration-appropriate Vx, a climb with the flaps extended will result in a decrease in climb rate, but also a decrease in groundspeed, and those effects on climb angle tend to offset. If Vx is significantly lowered due to flap extension, then climb angle may be improved by the use of flaps. Even if climb angle were equal or slightly less using flaps, the shorter ground run may result in better obstacle clearance performance, as mauleskinner pointed out. In any case, if the objective is to clear an obstacle, maximizing climb gradient is what matters regardless of obstacle height and distance from the takeoff point, and best climb gradient directly coincides with best climb angle.

But the above is merely academic. With specific regard to the OP, examining the manufacturer’s published takeoff recommendations for a single aircraft type (C172) as this thread has done reveals that merely making a design alteration to an aircraft type can produce a meaningful difference in the configuration and speed under which optimum takeoff performance is achieved. It therefore seems ill-advised to over-generalize or make absolute statements because there are just too many variables that come into play when comparing different aircraft types, and even different models of a single type. A good working knowledge of basic aerodynamics is important, but most important is, as nauga succinctly advised, “know your airplane, fly your airplane.”

 

[dmspilot]

Same place as yours.

You stated your conclusion is universally true, it's your responsibility to provide evidence. I provided evidence, in the form of an explanation, that it's not universally true.

 

[Dan Thomas]

At some point Cessna realized the additional thrust from the more powerful engine outweighed the extra drag.

I think that's the key. Lower power means flap drag can become intolerable on takeoff. Lots more power, and the flaps enhance takeoff. 182,s 180s and 185s all perform takeoffs better with flap.

And that's just for Cessnas and their airfoil and wing planform. Others may vary considerably.

My old Auster did not want to take off expeditiously at all with flaps up. Flaps down 20° and it jumped eagerly into the air and climbed well. Junkers-style flaps, they were.



Like others have said: know your airplane and fly it the way it should be flown.

 

[Albany Tom]

That makes sense. I haven't jumped in because my experience is all Piper. But from experimentation, the PA-28-150s may take off and clear obstacles better at 10 than 25, where the poh recommendation is 25 short field. Light and with a good engine and low DA, they will climb at 40, at a weird angle and with quite a bit of forward pressure, but suffice to say that's not a recommended procedure at all. I think it's safe to say that although there are similarities, experience between 172/182 and PA-28 is not directly transferable. For one, the flap movement speed on a Piper can be quite a bit quicker...which could be a good or bad thing, depending on circumstances. (Retract the flaps on a PA-28, and they're retracted *right now* as an example.)

 

[Palmpilot]

So you are the Buckee student doing the 6 mile patterns at 65 knots every monday morning during my training.

I think he's the experienced pilot who doesn't put a or some such in his posts when he's being sarcastic.

 

[WDD]

Seem to be discussing Vx vs Vy. 10% flaps on a Skyhawk will decrease Vy but help Vx.