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Ed Cesnalis

The best rate-of-climb and angle-of-climb is always reached with flaps up.

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Lets take it to the next level :)

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The best rate-of-climb and angle-of-climb is always reached with flaps up.

The argument over zero vs neg six for best rate of climb is old, already settled and therefore boring.

The next level is about achieving best angle and the same logic applies, you get that clean as well.  I have always flown from 7,100' elevation and I have always used take-off flaps but until now I didn't realize that they only get me off the ground sooner at the expense of a poorer climb rate, hmmmm.

https://www.experimentalaircraft.info/flight-planning/aircraft-climb-performance.php

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7,000' runway at home so I can play with this.  In recent years I have accelerated in ground effect for Vy + and then climbed with good insurance against tailwind gusts.

Now I'm going to try cleaning up to negative flaps before I initiate my climb and see how I like that.  

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JLang   

Related to this, I’ve previously expressed frustration at the lack of detail in the POH, especially for my CTSW.  It only calls out Vx and Vy for 0 deg.  For the SW, what do others use for -6?  I have assumed about 84kts for Vy, mainly since it seems about right logically and the Dynon VSI bar seems to like that speed.  Of course, most times I cruise climb at 95-105 kts, depending on oil temps.  The CTLS POH specifies a Vx of 70 kts for -6, with Vy at 78.

Best Vy seems fairly straightforward, but I have to say I’m skeptical that for all aircraft the best climb angle is always at least flaps, simply due to the much higher ground speed.  This could be crudely tested by a few repeated take offs and climbs at different flaps, climbing until you are directly over a predefined point over land.  Highest altitude wins.  Or calculate the hypotenuse with the average VSI number at each flap setting and the ground speed.  Homework!

Also, in general, best glide should be close to L/D max and Vy, right?  I find it interesting that the SW POH says to use 63 kts at 15 deg.  The LS POH says to use 78 kts with 0 deg.  That’s well above the defined 0 deg Vy of 73 kts.  Anybody know why…?  Personally I plan to use -6 and 84 kts (or less, depending on weight).

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9 minutes ago, JLang said:

Best Vy seems fairly straightforward, but I have to say I’m skeptical that for all aircraft the best climb angle is always at least flaps, simply due to the much higher ground speed.  This could be crudely tested by a few repeated take offs ...

You are right, when you factor in ground roll.  There is disagreement about the aerodynamics and the wisdom behind the advice to climb with flaps (zero setting).

Best rate and best angle call for a clean configuration while starting from zero you are merging a zero degree angle (take-off roll) with your climb angle and you might need to minimize the zero degree portion to clear the obstacle, meaning use take-off flaps to get off the ground sooner even if climb is worse in both angle and rate.

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Anticept   

Be careful about broad statements like this. When flaps on aircraft go a true negative (above chord line), they begin to act like spoilers, increasing drag AND destroying lift.

I imagine designs could still be made where this is favorable, but still an important point to consider.

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55 minutes ago, Anticept said:

Be careful about broad statements like this. When flaps on aircraft go a true negative (above chord line), they begin to act like spoilers, increasing drag AND destroying lift.

I imagine designs could still be made where this is favorable, but still an important point to consider.

That's logical and fair warning but doesn't seem to be true and if true the purpose of the negative setting would be negated.

A spoiler's intent is to spoil lift where the intent on the reflex flap setting is to reduce drag not lift.  

I assume our buffer is more than six degrees because negative 12 works therefore negative 6 will work as a reflex flap and not as a spoiler.

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Anticept   

I avoided making assumptions about the CTs because I am not certain of the wing geometry. I was simply bringing up a point to consider :)

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1 minute ago, Anticept said:

I avoided making assumptions about the CTs because I am not certain of the wing geometry. I was simply bringing up a point to consider :)

I appreciate it and I thought long and hard about it because its a 'spoiler' (pardon the pun)

I find with CTs its good to get things down to a basic thought:

  • the fuel follows the ball
  • flaps are drag and can't aid climb rate or angle

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WmInce   
4 minutes ago, Anticept said:

I avoided making assumptions about the CTs because I am not certain of the wing geometry. I was simply bringing up a point to consider :)

And your point was absolutely valid.

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1 hour ago, Anticept said:

Be careful about broad statements like this. When flaps on aircraft go a true negative (above chord line), they begin to act like spoilers, increasing drag AND destroying lift.

I imagine designs could still be made where this is favorable, but still an important point to consider.

 

17 minutes ago, WmInce said:

And your point was absolutely valid.

 

Think about piloting such a plane where the reflex flap setting did not function correctly and you got spoilers when trying to clean up flaps :(

Because the reflex flap is intended to retract out of the airflow as a drag reduction device it cannot extend up into the airflow and act as a lift spoiler, the result would be both unintended and wrong.  And again we have at least a six degree buffer.

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My CT instructor used to set flaps to -6 as soon as he had a positive rate of climb, 70kts airspeed, and about 100ft altitude.  I usually stay at 15 until 500ft AGL, but I'm not wedded to that if there is a better technique.  

The only issue I see is that you have to have sufficient airspeed to get the climb benefit.  I start my climb out at 60kt, and I'm guessing at that speed I am going to climb nowhere fast at -6 flaps.  My airplane seems to get best rate of climb at about 78kt at -6; as long as you let the speed get near that speed I'm guessing you will get better climb than at lower flap settings and their respectives best climb speeds.

I will do some experiments with shallower initial climb and going to 0 and then -6 ASAP to try to maximize the climb.

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Climbing towards distant mountains is best done at reflex flaps.

Visibility in a CT comes from the huge doors and its surprising that some might cruise or cruise climb at zero for a better view.

cruise climb.jpg

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36 minutes ago, Ed Cesnalis said:

Zero climbs steeper yet you still might need 15 for obstacles on take off.

15 vs zero.jpg

That makes sense, and honestly I don't like the longer ground roll at 0 flaps.  I wonder if you might split the difference by taking off at 15 to break ground quickly, and then climbing very shallowly until you get to a higher speed, switching to 0 ASAP.  Almost like a soft field takeoff.

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Just now, FlyingMonkey said:

That makes sense, and honestly I don't like the longer ground roll at 0 flaps.  I wonder if you might split the difference by taking off at 15 to break ground quickly, and then climbing very shallowly until you get to a higher speed, switching to 0 ASAP.  Almost like a soft field takeoff.

You can't beat 15 for the take off roll but the settling when you retract to zero might be a concern for some.

15 can be a life saver in wind shear even if it is counter intuitive.  Its the same as my landing fast argument, at 15 you can be off the ground in 5 seconds so you don't have longer exposure to getting gusted with mains on the runway.

At Mammoth with high altitude, long runway and wind shear I do this:

  1. 15* flaps for 4 1/2 second take off roll (350')
  2. accelerate and clean up in ground effect or at least close to the runway to deal with tail wind gusts
  3.  climb away clean indicating 85kts

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1 hour ago, Ed Cesnalis said:

Zero climbs steeper yet you still might need 15 for obstacles on take off.

15 vs zero.jpg

Ed, your graphic is wrong. Zero flaps does not provide a steeper climb angle when compared to 15° on take off! What it does is provide a better rate of climb. You will reach your target altitude in less time, but cover a greater distance doing so. This equates to a shallower angle not steeper.

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2 hours ago, Tom Baker said:

Ed, your graphic is wrong. Zero flaps does not provide a steeper climb angle when compared to 15° on take off! What it does is provide a better rate of climb. You will reach your target altitude in less time, but cover a greater distance doing so. This equates to a shallower angle not steeper.

Tom,

My graphic is in agreement with these sources as well as any others i can find.  It also agrees with common sense in that you can achieve the best angle when configured to minimize the amount you must use on lift. (this might not be intuitive, zero is only steeper if you use a similar speed, at a higher speed zero may not be steeper but it does have more reserve power so it can be steeper if you set the pitch for it)

 

Sources: 

"Extending the flaps will decrease the climb performance as L/D ratio is reduced and the power required increased. The best rate-of-climb and angle-of-climb is always reached with flaps up. Hence the need to retract flaps after a go-around if there are obstacles in the climb out path."  http://www.experimentalaircraft.info/flight-planning/aircraft-climb-performance.php

"Flaps reduce aircraft stalling speed by increasing lift and it enables you to lift-off at a lower airspeed. Resulting in a shorter ground run. It also reduces the rate of climb (and angle) due to a somewhat higher drag."  http://www.experimentalaircraft.info/flight-planning/aircraft-performance-5.php

"The flap setting also affects the climb gradient. Increasing the flap angle increases the drag, and so reduces the climb gradient for a given aircraft mass. If there are obstacles to be considered in the takeoff flight path, the flap setting that gives the shortest takeoff distance may not give the required climb gradient for obstacle clearance."  http://www.skybrary.aero/index.php/AP4ATCO_-_Factors_Affecting_Aircraft_Performance_During_Takeoff_and_Climb

"No conventional airplane will climb more rapidly with the flaps extended than it does with them retracted."  http://commons.erau.edu/cgi/viewcontent.cgi?article=1026&context=jaaer

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2 hours ago, Tom Baker said:

Ed, your graphic is wrong. Zero flaps does not provide a steeper climb angle when compared to 15° on take off! What it does is provide a better rate of climb. You will reach your target altitude in less time, but cover a greater distance doing so. This equates to a shallower angle not steeper.

Tom,

Graphic seems correct.  Our old thinking is wrong, the better way to say it it is at zero the resulting angle is less steep because the take-off roll is longer. The flightpath portion alone is steeper.

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First are we talking about conventional airplanes or are we talking about the CT?

I have done some testing with the CT comparing take off and climb to 500 AGL with 0° and 15° flaps.  My findings didn't agree with what you are saying. Now granted my testing did not have fancy test equipment, nor controlled procedures.

here is what I found, from a standing stop to 500 AGL it took the same amount of time from brake release to 500 feet with both flap settings. The amount of time from ground break to 500 feet was less with 0° flaps. The distance from brake release was greater with 0° flaps. The difference between the two was greater than the difference between take off distances. There for the distance from ground break to 500 AGL was greater for 0° flaps compared to 15° flaps. This would seem to indicate that the angle is slightly less, but at a greater rate for 0° flaps

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21 minutes ago, Tom Baker said:

First are we talking about conventional airplanes or are we talking about the CT?

I have done some testing with the CT comparing take off and climb to 500 AGL with 0° and 15° flaps.  My findings didn't agree with what you are saying. Now granted my testing did not have fancy test equipment, nor controlled procedures.

here is what I found, from a standing stop to 500 AGL it took the same amount of time from brake release to 500 feet with both flap settings. The amount of time from ground break to 500 feet was less with 0° flaps. The distance from brake release was greater with 0° flaps. The difference between the two was greater than the difference between take off distances. There for the distance from ground break to 500 AGL was greater for 0° flaps compared to 15° flaps. This would seem to indicate that the angle is slightly less, but at a greater rate for 0° flaps

CTs and conventional both work the same here.  spend less of your power on lift with zero flaps and you can climb steeper

from a standing start the comparison isn't valid.  

From a standing start you have 2 angles of climb that get averaged 1) zero degrees for the roll and x degrees for the climb.  the average really suffers when zero is one leg.

Look at my graphic again and notice the hair and the tortoise result, 15 degrees isn't as steep gets more time between rotation and target to make the result (average) steep.

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WmInce   
7 hours ago, Ed Cesnalis said:

Zero climbs steeper yet you still might need 15 for obstacles on take off.

15 vs zero.jpg

There is an error there.

Given an identical wind condition:

Best rate of climb is Vy.

Best angle of climb (steeper) is Vx.

  • Upvote 1

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29 minutes ago, WmInce said:

There is an error there.

Given an identical wind condition:

Best rate of climb is Vy.

Best angle of climb (steeper) is Vx.

The graphic is correct I think.

You are correct that best rate is Vy and best climb is Vx.

The graphic does not compare Vy to Vx but rather zero flaps @ Vy to 15* flaps at Vy.  There is no Vx in the diagram to be made wrong by your statement.

 

 

 

 

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WmInce   
57 minutes ago, Ed Cesnalis said:

. . . "You are correct that best rate is Vy and best climb is Vx." . . . 

No.

Best angle is Vx.

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15 minutes ago, WmInce said:

No.

Best angle is Vx.

Bill,

Yes that's what I meant.

Vx doesn't enter into this discussion though, the diagram is correct.

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