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Ed Cesnalis

-6 has best ANGLE of climb - debate resolved IMO

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16 minutes ago, Ed Cesnalis said:

No that doesn't stand to reason.  The fact the Vx is slower than Vy for either flap setting doesn't change the fact that improving Vx requires either more thrust or less thrust required.

Steep climb performance means a high rate of velocity that includes a large vertical component.  Obviously that vertical component is very power dependent.

 

Do you agree that you have more drag when climbing at Vx compared to climbing at Vy?

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38 minutes ago, Tom Baker said:

So when you have more drag climbing at Vx doesn't that seem to imply that climbing at Vx is not dependent on having the least amount of drag?

No. Its more the opposite.

We  now have to agree that at either flap setting the amount of lift produced remains equal to the weight.

Variable list:

  • thrust from the prop - equal at both flap settings
  • weight of aircraft - equal at both flap settings
  • angle of attack selected -  Vx is different at both settings, AoA is likely different and not known to us. AoA for Vx must be found by pilot for current weight.
  • drag - much greater at 15

With these 4 variables the only one that is useful for predicting which setting can produce the steepest climb is drag so we have to rely on it not discard it.

Granted we are not looking for highest L/D, that would correspond to Vy but we are looking for the best L/D for Vx.  L is constant and D has a big Delta, we have to look to D. 

 

 

 

 

 

 

 

 

 

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26 minutes ago, Ed Cesnalis said:

No. Its more the opposite.

We  now have to agree that at either flap setting the amount of lift produced remains equal to the weight.

Variable list:

  • thrust from the prop - equal at both flap settings
  • weight of aircraft - equal at both flap settings
  • angle of attack selected -  Vx is different at both settings, AoA is likely different and not known to us. AoA for Vx must be found by pilot for current weight.
  • drag - much greater at 15

 

I agree in level flight lift must be equal to weight.

Thrust from the prop is dependent on speed. Copy and pasted from the internet: "The faster the aircraft speed, the less acceleration is being created on the intake air. Therefore thrust decreases with increasing airspeed.". If you are flying slower with 15° flaps then you have more thrust available. Because of this you are likely able to climb steeper. As I have always said how steep you climb is not about maximum climb rate, but rather climb rate compared to forward speed.

I agree weight is equal.

Angle of attack will be determined by the speed chosen, and is likely different between flap settings, because the cord line is changed.

Induced drag is greater, but parasite drag is less. Because you are flying slower, the overall increase in drag may not be as much as you think.

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1 hour ago, Ed Cesnalis said:

@Tom Baker

What does Piper know that you don't :)

The Tomahawk.

Flight Design says the best rate of climb for the CTLS is better at 0° flaps than -6° flaps. What do they know that you don't?:P

  • Upvote 1

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1 hour ago, Tom Baker said:

The Tomahawk.

Flight Design says the best rate of climb for the CTLS is better at 0° flaps than -6° flaps. What do they know that you don't?:P

That's the question at hand.

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On 9/27/2017 at 5:35 PM, Ed Cesnalis said:

Perhaps you didn't read me correctly?

I have been doing that routinely, obstacles haven't been an issue and I use absurdly long runways.

 

I was contending that others seldom use it, I believe I am an exception because I am looking for best angle to clear terrain at -6 frequently.  I was shooting Mt Whitney and the southern Sierra this morning and used steepest angle at negative six several times.  I don't know Vx for any flap setting, my old CT provides few numbers.  I take my best guess at -6 just like I do at 15.

Actually it is.  Lift is precisely equal to current weight, changing flaps doesn't change weight and it doesn't change quantity of lift except momentarily before you are stabilized.

Its due to the lower stall speed.

I see no point in gliding at 0, or 15 because -6 out performs every time.  

I fly at a lot of different weights so I find best glide visually and minimum sink by watching my VSI.

So by stating that "I seldom use Vx" you meant "everybody else but me seldom uses Vx." So yes, I guess I didn't read you correctly.

Lift is precisely equal to weight with different flaps ONLY at steady state, and then only at very different speeds. Climbing is not steady state.

How do you explain lower stall speed and lower liftoff speed with flaps if lift is the same as with -6?

You still have not answered what speeds you assume or have determined for Vx and Vy.

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1 minute ago, JLang said:

So by stating that "I seldom use Vx" you meant "everybody else but me seldom uses Vx." So yes, I guess I didn't read you correctly.

Lift is precisely equal to weight with different flaps ONLY at steady state, and then only at very different speeds. Climbing is not steady state.

How do you explain lower stall speed and lower liftoff speed with flaps if lift is the same as with -6?

You still have not answered what speeds you assume or have determined for Vx and Vy.

Climbing is  steady state once momentary stabilization occurs.

My field is 7,100' elevation.  At 15 I take off in 375'.  At -6 it takes a multiple of that.

I have answered.  I fly at varying weights so I determine real time based on current weight.

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To my thinking, the longest glide distance is not the relevant matter in the case you are trying to make, the longest glide time is, so yes, you may not make the airfield.

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On 9/29/2017 at 4:56 PM, Ed Cesnalis said:

Climbing is  steady state once momentary stabilization occurs.

 

Is climbing steady state?  I'd say "yes and no".

As you said, it is once stabilized.  BUT that is a short term performance condition.  You can't stabilize at 500fpm climb and keep it there indefinitely.  As you get higher you'll lose climb performance and will have to either raise AoA/lower speed or you'll have to accept a slower climb rate.  So from the longer term perspective, you can't really have a stabilized climb.  

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14 minutes ago, FlyingMonkey said:

Is climbing steady state?  I'd say "yes and no".

As you said, it is once stabilized.  BUT that is a short term performance condition.  You can't stabilize at 500fpm climb and keep it there indefinitely.  As you get higher you'll lose climb performance and will have to either raise AoA/lower speed or you'll have to accept a slower climb rate.  So from the longer term perspective, you can't really have a stabilized climb.  

The FAA considers there is such a thing as a steady state climb. I agree that as you go up climb performance decreases, and in theory they should be constantly changing. However the change rate is very slow, and in our airplanes you will have a fairly long period of time where the numbers are steady.

BTW if your speed is at best rate or slower raising the nose/increasing the angle of attack will cause a reduction in climb rate. The one exception would be an initial zoom if the change was abrupt.

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Ed, I have been thinking about the numbers for the CTLS and best rate of climb being less at -6 flaps. I am theorizing that while -6 has less parasitic drag than 0, but more induced drag. 

-6 might require a higher angle of attack to produce the lift required to support the weight at its minimum drag configuration, than 0 flaps at its minimum drag configuration. This would mean -6 has more induced drag, and less parasitic drag when it is producing its least drag, but its total drag is more than 0° flaps at its minimum drag. As speed increases the parasitic drag transfers the advantage to -6 flaps for better speed.

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12 minutes ago, Tom Baker said:

BTW if your speed is at best rate or slower raising the nose/increasing the angle of attack will cause a reduction in climb rate. The one exception would be an initial zoom if the change was abrupt.

Agreed, that's why I chose 500fpm as an example climb, it's well below max performance for our airplanes at most altitudes.  "You can't get blood from a stone" as they say, and once you are at best climb rate for conditions raising AoA is not going to help.

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17 minutes ago, Tom Baker said:

Ed, I have been thinking about the numbers for the CTLS and best rate of climb being less at -6 flaps. I am theorizing that while -6 has less parasitic drag than 0, but more induced drag. 

-6 might require a higher angle of attack to produce the lift required to support the weight at its minimum drag configuration, than 0 flaps at its minimum drag configuration. This would mean -6 has more induced drag, and less parasitic drag when it is producing its least drag, but its total drag is more than 0° flaps at its minimum drag. As speed increases the parasitic drag transfers the advantage to -6 flaps for better speed.

Tom,

Andy's confirmation shows I was on to the right answer from the get go but confused too.  It isn't simply a TA TR Comparison but a Comparison of the 2 curves for each configuration.

Clean should win for speed and rate but it could go either way on angle.  Once the comparrisons are made, similar to the graphic the speed is the point on the X Axis and amount of thrust is on the Y as the height between the curves.

Above you are listing factors why the result could be either.

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1 hour ago, FlyingMonkey said:

Is climbing steady state?  I'd say "yes and no".

As you said, it is once stabilized.  BUT that is a short term performance condition.  You can't stabilize at 500fpm climb and keep it there indefinitely.  As you get higher you'll lose climb performance and will have to either raise AoA/lower speed or you'll have to accept a slower climb rate.  So from the longer term perspective, you can't really have a stabilized climb.  

To the topic at hand, the important point I was trying to make is that lift is not the same with all flap settings, steady state or not.

The way I work through it, if you are flying at steady state, either in level flight at constant speed, or in a stabilized climb (or descent), and you change flaps, then three things happen, all of which momentarily deviate from steady state: change in lift, change in drag, and change in angle of attack.  Depending on how/if we adjust control input, we'll end up back to steady state, but only with a different combination of climb, attitude, and airspeed.

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36 minutes ago, JLang said:

end up back to steady state, but only with a different combination of climb, attitude, and airspeed.

true but lift goes back to where it was, equal to weight.

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1 hour ago, Ed Cesnalis said:

true but lift goes back to where it was, equal to weight.

At the same speed or angle of attack, lift is greater with flaps.  Adding flaps adds lift.  After adding flaps, steady state will return ("goes back to where it was"), but only at a different attitude/power/airspeed configuration.  Yes, at steady state lift = weight, but that is not saying the same thing.

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1 hour ago, JLang said:

At the same speed or angle of attack, lift is greater with flaps.  Adding flaps adds lift.  After adding flaps, steady state will return ("goes back to where it was"), but only at a different attitude/power/airspeed configuration.  Yes, at steady state lift = weight, but that is not saying the same thing.

The end result of adding flaps is no lift is added because no weight is added.

The thrust curve will change  and the drag curves will change, the speed will change angle of attack will change about the only thing that doesn't change is lift.

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31 minutes ago, Ed Cesnalis said:

The end result of adding flaps is no lift is added because no weight is added.

The thrust curve will change  and the drag curves will change, the speed will change angle of attack will change about the only thing that doesn't change is lift.

The end result is that AFTER the additional lift and drag and change in angle of attack is combined, you get back to steady state.  Weight does not change.  Lift does, and if nothing else changed other than adding flaps, then you would start a climb.  However, usually airspeed decreases, with additional drag, and then the lower lift with the lower airspeed goes back to balancing the weight.

This is from your own post:

"Clean configuration does give best speed, obviously, due to reduced drag, and should also give best rate for the same reason... but not necessarily best angle, because the extra lift the flaps provide may add more vertical speed than you lose from the additional drag, especially at lower speed (drag increases with the square of airspeed, remember)"

 

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If you add flaps and want to maintain your speed you will have to change your angle of attack.  I can maintain 62 kts in level flight with any flap setting from -6° to 35° or 40°, depending on the airplane, and lift will always be equal to weight.

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So much to talk about.....bottom line the CT(LS) glides best at around 80 zero flaps. Takeoff  0 flaps and climb 0 flaps at 70-80 kts, ( very little advantage of  15 flaps takeoff portion of the climb)  and ALWAYS assume the engine may quit. With 15 flaps and no engine you loose considerable altitude transitioning to best glide. Try it. I'm still alive from the addiction of flying for 60 years....

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