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Ed Cesnalis

-6 has best RATE of climb - argument resolved IMO

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The concensus was argued for 15degrees being steepest like this:

  • zero degrees has best rate - zero degrees has the most excess power at its Vy speed and excess power is used to achieve climb including best rate.

The -6 argument:

  • -6degrees has best rate --6degrees has the most thrust available due to it being the lowest drag setting and available thrust is used to achieve climb including best rate.

 

The Aerodynamic lesson below illuminated the correct terms, definitions and theory.

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I agree that excess thrust beyond what is needed for steady state flight can be used for either acceleration or climb.  But how does that resolve the -6° vs. 15° for best Vx debate?

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1 minute ago, FlyingMonkey said:

I agree that excess thrust beyond what is needed for steady state flight can be used for either acceleration or climb.  But how does that resolve the -6° vs. 15° for best Vx debate?

When you use the correct terms (TA, TR) definitions and theory -6 ends up with thrust available to use for climb or speed that the other settings lack.

When you use ambiguous terms (excess power) and the definition argued then the settings with more drag end up with more 'excess power' to use for climb (but not speed)

The former wins, it is the theory that is used and taught and gives the best performance to the low drag setting where it belongs.

The latter is  flawed and sees hides available thrust arguing that the available thrust is consumed as thrust required but using the wrong definition for thrust required.

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8 minutes ago, FlyingMonkey said:

I agree that excess thrust beyond what is needed for steady state flight can be used for either acceleration or climb.  But how does that resolve the -6° vs. 15° for best Vx debate?

Your agreement is agreeing with the losing argument.  I would say it like this:  'excess thrust beyond what is needed for lift and to offset drag can be used for either acceleration or climb'

See the difference?  You are saying it like Tom 'for steady state' but some of that is TA because it is beyond what is needed for lift and drag and it is now providing more speed  (increasing kinetic energy)

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Thrust required to maintain speed (in overcoming drag) cannot me used for acceleration.  By "excess thrust" I simply mean what force remains in pounds, kilograms, newtons, or whatever, beyond what is required to maintain current speed.  I don't know what else "excess thrust" could mean...  

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52 minutes ago, FlyingMonkey said:

Thrust required to maintain speed (in overcoming drag) cannot me used for acceleration.  By "excess thrust" I simply mean what force remains in pounds, kilograms, newtons, or whatever, beyond what is required to maintain current speed.  I don't know what else "excess thrust" could mean...  

Notice in the lesson I posted and elsewhere in aerodynamics the terms TA and TR thrust available and thrust required?

The lesson I posted shows how -6 has more TA than other flap settings and this is useful for showing that -6 has best climb and best speed.

The 'Tom' argument based on 'excess power' or now 'excess thrust' has a completely different meaning that doesn't permit best performance comparisons like TA does because its based on a moving scale where TA is based on TR which is fixed and permits comparison of the resulting TA.

The different terms and the different ways they budget energy are the reasons I see Available power to be used at the pilots discretion for speed or climb where Tom sees it as available for climb only and not the pilot's tool.

Ultimately the difference is why I see Fast Eddie was right, best climb (angle or rate) come from no flaps and its also why the 'excess power' group sees flaps as having an advantage.

Thing is only one side is correct.

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5 hours ago, FlyingMonkey said:

It seems if we call excess thrust TE and state [ TE = (TA - TR) ] in your jargon, can't we just all accept that definition and move on from there? 

That's wrong TE >< (TA - TR).  That would usually result in a negative number.

I think your trying to say TE = TA.  Closer but still wrong.

TA is useful for seeing that Vx is results in a speed with a steeper climb angle.  TE is not a fixed number and not useful for this comparison.

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15 hours ago, Ed Cesnalis said:

That's wrong TE >< (TA - TR).  That would usually result in a negative number.

I think your trying to say TE = TA.  Closer but still wrong.

TA is useful for seeing that Vx is results in a speed with a steeper climb angle.  TE is not a fixed number and not useful for this comparison.

No, I'm saying excess thrust (TE) is Available Thrust (TA, thrust the engine can produce), minus Thrust Required (TR) to maintain flight at the current speed and AoA.  In other words, the thrust leftover to increase speed or climb is whatever remains of total thrust after you subtract what you need just to maintain your current flight condition.  Hard to see how that could be wrong.  TE *will* be negative if the amount of thrust required to maintain the flight condition exceeds available thrust (engine out, pitched into a very steep climb, etc)

Sorry if that misused any of your terms and confused you.   

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I understand your term and definition.  Its the same as Tom's and can't be compared to TA because its basis is the current speed which could be any of a range of numbers.

TA and TR are useful, thing of it this way, (not 1,000% true but close enough for our purposes):

  • TR has to do with the airframe
  • TA has to do with the powerplant

These are useful metrics to see how one flap setting can outperform another.  

Flaps, that's airframe, thats TR.  We know more drag more TR

We also know more TR then less TA

The conclusion is less TA = less performance, less speed if trimmed for best speed, less angle if trimmed for best angle and less rate if trimmed for best rate.

With this simple formula we can show that -6 with its lowest drag out performs the other settings and we show why.

Using available power we cannot compare at all.

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Perhaps so, but it seems like you'd need special equipment and wind tunnels to measure TR.  After all, you can't set a throttle setting, even in smooth air, and say "oh, I'm using 53.7hp right now"...

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2 hours ago, FlyingMonkey said:

Perhaps so, but it seems like you'd need special equipment and wind tunnels to measure TR.  After all, you can't set a throttle setting, even in smooth air, and say "oh, I'm using 53.7hp right now"...

When can you do this and what purpose does it serve? Giving up something you don't already have has no downside.

We can use Rotax tables to see how many horsepower we are producing at WOT at the right altitude for current pitch.  From this I know I'm generally using ~55 hp at altitude.

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