Climbing at -6 degrees vs 0 degrees?

[Ed Cesnalis]

16 minutes ago, Doug G. said:

Yes, lift, drag, speed (or rather thrust), and AOA are all related, but your argument is semantic. You can use the lower drag to create more speed, or more lift, or both. There are, of course catalogs of wing designs that have different L/D ratios that have no relationship to weight at all. In fact the formula for calculating L/D does not involve weight. Once you add relative wind (by whatever method) you generate lift which is not related to weight.

Oh, and I did not say lift remained the same at 0° as at -6°.

How do you define the chord of a wing. Does it change when the flaps are lowered? 

It is not semantic it is a black and white argument.

I am saying lift remains the same at both flap settings. Lift necessarily = weight so lift is the same at both settings.

For the 2nd time wing chord change is irrelevant, if it changes or not lift still = weight and only drag changes.

[Mike Koerner]

Ed, Doug,

I think there's a simpler way of looking at this (I certainly hope there is):

For every indicated airspeed there is an optimum flap setting. If you flying around 90 knots or faster, you ought to have the flaps up. Slower than about 65, lower them a notch. In between, leave them faired at the zero setting. (These are just approximate speeds. The actual optimum flap position transition speeds vary a little with aircraft model and gross weight.)  

So, if your cruise climbing at high speed you should have the flaps up. If your're trying to climb steeper, at a lower speed, set the flaps accordingly.

Remember too, that drag goes up as the square of speed. Your engine has to work hard to make you go fast. At the limits of aircraft performance (high speed, high gross weight, high altitude, etc.) you will have to slow down to climb. When you do, set the flaps accordingly.

Mike Koerner

.

 

[Ed Cesnalis]

40 minutes ago, Doug G. said:

There are, of course catalogs of wing designs that have different L/D ratios that have no relationship to weight at all. In fact the formula for calculating L/D does not involve weight. Once you add relative wind (by whatever method) you generate lift which is not related to weight.

There is no formula to calculate L/D because it is a simple ratio.  L/D is determined for any particular airspeed by measuring the lift generated, then dividing by the drag at that speed. These vary with speed, so the results are typically plotted on a 2D graph.

Measuring lift means weighing the airplane so L/D is the same as W/D.

[Ed Cesnalis]

7 minutes ago, Mike Koerner said:

if your cruise climbing at high speed you should have the flaps up. If your're trying to climb steeper, at a lower speed, set the flaps accordingly.

Mike,

To climb steeper we should always use reflex not 'set flaps accordingly.'  The only need for flaps is when an obstacle is involved but for steepest climb least drag and reflex flaps are called for.

As I am pointing out to Doug you cannot change the lift by changing flap settings, lift will equal weight at any setting you are only changing drag and therefore L/D.  You have pointed out before that negative flaps change the wing chord but even if true it doesn't matter because lift remains = weight and all you are doing is adding drag and losing thrust available for climb.

[Mike Koerner]

Ed,

I never said flaps change the cord. Our flaps don't. Fowler flaps do.

If you leave the flaps up at low speed you are generating additional lift, so as to equal weight as you say, by increasing the angle of attack. That's not the optimum wing profile. Furthermore, the fuselage will not be faired optimally.

Mike Koerner

[Ed Cesnalis]

6 minutes ago, Mike Koerner said:

Ed,

I never said flaps change the cord. Our flaps don't. Fowler flaps do.

If you leave the flaps up at low speed you are generating additional lift, so as to equal weight as you say, by increasing the angle of attack. That's not the optimum wing profile. Furthermore, the fuselage will not be faired optimally.

Mike Koerner

Mike,

Cool, leaving the cord change out only simplifies things.

When I leave the flaps up, even at low speed I am generating precisely the same lift, as I say equal to the weight.

Beyond there being no additional lift there is no non-optimized wing profile. 

Slower/Steeper with reflex flaps means:

• No increase in lift, lift remains constant (there is momentary disruption as you change attitude then stabilization at the same lift as before disruption)
• Increase in drag - (results in slower speed and steeper angle just like more flaps)
• Increased angle of attack over prior climb angle but not non-optimal. Increase beyond prior angle is different than the increase in pitch attitude you see over the pitch attitude at the zero setting.  The reflex setting does result in a higher deck angle than the zero setting but at the higher angle of the relative wind it remains optimal.

[Tom Baker]

On ‎9‎/‎17‎/‎2017 at 2:51 PM, Doug G. said:

A couple of years ago I flew over the ND Badlands. I started out at 3500' on what was a 90 + degree day on the ground. I decided to climb to find the "air conditioning." That ended up being 7500'. I used the autopilot to set a climb and was almost immediately hit with the "more elevator" trim signal. I added trim until I began to lose significant airspeed. I then switched to 0 flaps and climbed well eventually leveling off at 7500 and returning to -6 in cooler air.

 I am sorry I cannot recall either the DA or my rate of climb at the time.

In un-accelerated level flight lift produced will always equal weight. By adding flaps you change the shape of the airfoil. This makes the wing capable of producing the lift required to support the weight at a slower speed without the big change in angle of attack required without the extra flaps. A good example of this is stalling speed. With flaps the wings will produce the lift required to support the weight of the aircraft at a slower speed, hence the difference between stall speed with flaps retracted and extended.

Ed, you keep saying that the airplane will climb at a steeper angle with -6 flaps. Again steeper is defined by altitude gained over distance covered. The greater speed required for the -6 climb does not produce a steeper angle because you are moving forward at a greater speed to produce the climb, it does however produce a greater rate of climb. The numbers from the CTLS AOI show this. Both configurations climb at nearly the same angle, but the angle is slightly steeper with 15° flaps. You go further to say the only time you need 15° flaps is when obstacle clearance is required. This statement contradictory to your statement that best angle is at -6 flaps. Clearing an obstacle is the only time when you need to climb at the best angle of climb. There are no positive benefits of climbing at best angle other than obstacle clearance.

[Buckaroo]

13 minutes ago, Tom Baker said:

In un-accelerated level flight lift produced will always equal weight. By adding flaps you change the shape of the airfoil. This makes the wing capable of producing the lift required to support the weight at a slower speed without the big change in angle of attack required without the extra flaps. A good example of this is stalling speed. With flaps the wings will produce the lift required to support the weight of the aircraft at a slower speed, hence the difference between stall speed with flaps retracted and extended.

Ed, you keep saying that the airplane will climb at a steeper angle with -6 flaps. Again steeper is defined by altitude gained over distance covered. The greater speed required for the -6 climb does not produce a steeper angle because you are moving forward at a greater speed to produce the climb, it does however produce a greater rate of climb. The numbers from the CTLS AOI show this. Both configurations climb at nearly the same angle, but the angle is slightly steeper with 15° flaps. You go further to say the only time you need 15° flaps is when obstacle clearance is required. This statement contradictory to your statement that best angle is at -6 flaps. Clearing an obstacle is the only time when you need to climb at the best angle of climb. There are no positive benefits of climbing at best angle other than obstacle clearance.

In my box canyon trap question I would think that immediately slowing and applying 15 flaps during the escape turn out would be the logical answer from Toms above post! More lift over shorter distance. Slower stall speed in the turn. 

Didn’t mean to bring that subject here but this discussion is in the same category of lift, distance, time etc.

[Ed Cesnalis]

3 minutes ago, Tom Baker said:

The greater speed required for the -6 climb does not produce a steeper angle because you are moving forward at a greater speed to produce the climb, it does however produce a greater rate of climb. The numbers from the CTLS AOI show this. Both configurations climb at nearly the same angle, but the angle is slightly steeper with 15° flaps.

Tom,

Thanks for the reply

Its true the book numbers do not imply that the reflex configuration produces best angle as well as best rate of climb. Its also  true that the book numbers are in conflict with what happens when I look for best glide.

You say: 'The greater speed required for the -6 climb does not produce a steeper angle because you are moving forward at a greater speed to produce the climb, it does however produce a greater rate of climb.'  and your are wrong on these points:

• The -6 climb does not require a greater speed and when the same speed is used the angle will be steeper.
• There is a range of steeper angles available at -6 over zero. Plotting on a 2-dim graph would allow comparison. The steeper range would begin at Vx for zero and go somewhere beyond Vx for -6 until the angle at -6 fell off to match the angle for  Vx for zero.

This concept is easy to visualize if you budget the power being used.  We are talking about climbs so WOT is the setting.  The major component of the energy budget is for lift and that takes the same at either flap setting because the lift require is equal to the weight.  The next thing in the budget is thrust to = drag and the zero configuration needs more thrust due to more drag. Now the balance of the budget is what we are discussing. It is always greater at -6 than at zero due to the lower drag.

Balance of the budget is available thrust and can be used as you like.  There are 3 maximum performance points you can set  your pitch attitude to achieve:

1. Best available speed - found at level flight
2. Best rate of climb - found at Vy
3. Best angle of climb - found at Vx

All 3 of these maximum performance rates are better at -6 than they are at zero due to less drag and more available thrust to achieve the targeted rate.  The only fly in the oinment is when you include ground roll and the combination of the 2 angles makes zero steeper to clear an obstacle.

[Ed Cesnalis]

8 minutes ago, Buckaroo said:

More lift over shorter distance.

Because lift is always equal to weight it is same lift not more lift. However you do have more drag and therefore less available thrust to use for your exit.

Again the slow tight turn is a logical choice but lacks protection from stall, drift and downdrafts that speed provides and it means you don't have energy in reserve in case you have to go to plan B.

[Buckaroo]

8 minutes ago, Ed Cesnalis said:

Because lift is always equal to weight it is same lift not more lift. However you do have more drag and therefore less available thrust to use for your exit.

Again the slow tight turn is a logical choice but lacks protection from stall, drift and downdrafts that speed provides and it means you don't have energy in reserve in case you have to go to plan B.

If lift is equal to weight your in level flight aren’t you??

[Ed Cesnalis]

6 minutes ago, Buckaroo said:

If lift is equal to weight your in level flight aren’t you??

Not necessarily, lift is also equal to weight in climbs and descents. This equilibrium is only momentarily disturbed when when you re-configure and or adjust angle of attack. 

https://aviation.stackexchange.com/questions/40921/does-lift-equal-weight-in-a-climb/40927

[Ed Cesnalis]

Simplified Thinking:

Zero flaps always has more drag than -6 and therefore always has less available thrust to use for best angle climb.

[Tom Baker]

53 minutes ago, Ed Cesnalis said:

Tom,

Thanks for the reply

Its true the book numbers do not imply that the reflex configuration produces best angle as well as best rate of climb. Its also  true that the book numbers are in conflict with what happens when I look for best glide.

You say: 'The greater speed required for the -6 climb does not produce a steeper angle because you are moving forward at a greater speed to produce the climb, it does however produce a greater rate of climb.'  and your are wrong on these points:

• The -6 climb does not require a greater speed and when the same speed is used the angle will be steeper.
• There is a range of steeper angles available at -6 over zero. Plotting on a 2-dim graph would allow comparison. The steeper range would begin at Vx for zero and go somewhere beyond Vx for -6 until the angle at -6 fell off to match the angle for  Vx for zero.

This concept is easy to visualize if you budget the power being used.  We are talking about climbs so WOT is the setting.  The major component of the energy budget is for lift and that takes the same at either flap setting because the lift require is equal to the weight.  The next thing in the budget is thrust to = drag and the zero configuration needs more thrust due to more drag. Now the balance of the budget is what we are discussing. It is always greater at -6 than at zero due to the lower drag.

Balance of the budget is available thrust and can be used as you like.  There are 3 maximum performance points you can set  your pitch attitude to achieve:

1. Best available speed - found at level flight
2. Best rate of climb - found at Vy
3. Best angle of climb - found at Vx

All 3 of these maximum performance rates are better at -6 than they are at zero due to less drag and more available thrust to achieve the targeted rate.  The only fly in the oinment is when you include ground roll and the combination of the 2 angles makes zero steeper to clear an obstacle.

You have 2 out of 3, so that isn't to bad. I agree with most of what you are saying. My only point of contention is angle of climb. With 15° flaps I agree you have more drag, and less available power for climb. This means you will have a lower rate of climb. You also have one other thing because of the 15° flaps, and that is a slower forward speed. Because of the slower forward speed you wind up with a steeper angle, even though you are climbing at a lower rate.

Yes you can climb at a slower speed with -6 flaps if you want, but your rate of climb will also go down with any decrease in speed below best rate of climb. It is this relationship between decrease in rate compared to forward speed that gives the advantage for best angle to climbing with 15° flaps.

[Ed Cesnalis]

9 minutes ago, Tom Baker said:

You have 2 out of 3, so that isn't to bad. I agree with most of what you are saying. My only point of contention is angle of climb. With 15° flaps I agree you have more drag, and less available power for climb. This means you will have a lower rate of climb. You also have one other thing because of the 15° flaps, and that is a slower forward speed. Because of the slower forward speed you wind up with a steeper angle, even though you are climbing at a lower rate.

Yes you can climb at a slower speed with -6 flaps if you want, but your rate of climb will also go down with any decrease in speed below best rate of climb. It is this relationship between decrease in rate compared to forward speed that gives the advantage for best angle to climbing with 15° flaps.

2 out of 3 we are getting close.  I was in your camp for decades but when Fast Eddie challenged my thinking I had to concede like you, I was wrong

You are only disagree  on angle not rate.  Once again your are your are changing speed and claiming the speed change dictates a steeper angle.

My first point above stands: The -6 climb does not require a greater speed and when the same speed is used the angle will be steeper.

You Conclude 'Because of the slower forward speed ...' but you can't base you conclusion on a slower speed!

You have to be clear on the argument here: Which is steeper Vx at zero or Vx at -6?  Angle is the result of both forward speed and vertical speed.  You are correct in that Vx at zero is slower than Vx is at -6 but you are ignoring that the vertical speed at -6 Vx  is greater than the vertical speed at zero Vx.  The resulting angle is steeper at -6 when you consider bother forward and vertical speeds.  Your argument continues to base on forward speed alone.

[FlyingMonkey]

2 hours ago, Ed Cesnalis said:

Because lift is always equal to weight it is same lift not more lift. However you do have more drag and therefore less available thrust to use for your exit.

Again the slow tight turn is a logical choice but lacks protection from stall, drift and downdrafts that speed provides and it means you don't have energy in reserve in case you have to go to plan B.

What exactly is the "plan B" from a wingover?  Just curious.

[Ed Cesnalis]

2 minutes ago, FlyingMonkey said:

What exactly is the "plan B" from a wingover?  Just curious.

• Chandelle
• Wingover without achieving the reciprocal heading to exit in the parallel canyon
• Up and over the end of the canyon
• Steep turn from the zoom climb

[Tom Baker]

1 hour ago, Ed Cesnalis said:

You have to be clear on the argument here: Which is steeper Vx at zero or Vx at -6?  Angle is the result of both forward speed and vertical speed.  You are correct in that Vx at zero is slower than Vx is at -6 but you are ignoring that the vertical speed at -6 Vx  is greater than the vertical speed at zero Vx.  The resulting angle is steeper at -6 when you consider bother forward and vertical speeds.  Your argument continues to base on forward speed alone.

I haven't been ignoring this fact. If you think I have, then you have been misreading my post. Vertical speed with -6 flaps at Vx can be greater than with zero, and it still be a shallower angle. If the reduction in speed is greater than the reduction in rate you will have a steeper angle. It is all about the ratio of forward speed compared to rate of climb.

Also as a point of contention I have always been comparing -6 to 15° flaps and claiming a steeper angle for 15°. I really haven't done any comparison between -6 and 0°.

[FlyingMonkey]

Just now, Ed Cesnalis said:

• Chandelle
• Wingover without achieving the reciprocal heading to exit in the parallel canyon
• Up and over the end of the canyon
• Steep turn from the zoom climb

Ah, you meant plan B *instead* of the wingover.  I thought you meant plan B *after* the wingover if it didn't achieve the desired result.  

 

[Ed Cesnalis]

5 minutes ago, Tom Baker said:

I haven't been ignoring this fact. If you think I have, then you have been misreading my post. Vertical speed with -6 flaps at Vx can be greater than with zero, and it still be a shallower angle. If the reduction in speed is greater than the reduction in rate you will have a steeper angle. It is all about the ratio of forward speed compared to rate of climb.

Also as a point of contention I have always been comparing -6 to 15° flaps and claiming a steeper angle for 15°. I really haven't done any comparison between -6 and 0°.

Yes your probably right that vertical speed with -6 can be greater than zero and still be shallower but that's not the point.  The point is that the cleaner the configuration, like -6 over zero or zero o over 15 or -6 over 15, the steeper Vx will be.  

Vx at -6 is steeper than Vx at zero or Vx  at 15 because in both cases less drag results in more available thrust to use seeking best angle.

[Ed Cesnalis]

10 minutes ago, FlyingMonkey said:

Ah, you meant plan B *instead* of the wingover.  I thought you meant plan B *after* the wingover if it didn't achieve the desired result.  

 

Right, I use the way up to evaluate what I'm going to do.  The last point of decision is when you are near stall and swapping ends and picking your exit target.  All of these options depend on speed and are not available using the min speed turn.

Canyons are skinny at the bottom and wider as they go up, most are v shaped few are u shaped.  My cruise / working altitude is tighter than the higher altitude I zoom to for an exit and since I zoomed up to it I have built in altitude to loose on my exit as long as I head the right way.

Low and slow can provide the tightest available coordinated turn, its just a shittty place to be.  The slow approach minimizes radius but uses horizontal space to do it.  The higher speed approach needs even more room but you can do your turn vertically instead of horizontally and there is no downside to the extra speed / safety.

[Buckaroo]

16 minutes ago, Ed Cesnalis said:

Yes your probably right that vertical speed with -6 can be greater than zero and still be shallower but that's not the point.  The point is that the cleaner the configuration, like -6 over zero or zero o over 15 or -6 over 15, the steeper Vx will be.  

Vx at -6 is steeper than Vx at zero or Vx  at 15 because in both cases less drag results in more available thrust to use seeking best angle.

I disagree with this last paragraph. With my big body at a7000 ft DA if I use -6 of flaps instead 15 flaps I’m going to eat a bunch of pine trees at the end of the runway. 15 is steeper than -6 anytime!

[WmInce]

48 minutes ago, Ed Cesnalis said:

Vx at -6 is steeper than Vx at zero or Vx  at 15 because in both cases less drag results in more available thrust to use seeking best angle.

I think you are dead wrong on that.

Otherwise, heavy aircraft would be taking off with little or no flaps. They don't. All of them accept more drag for steeper climb angle, reduced turn radius and stall protection.

I'm all in with Tom on this one.

In order to settle the debate, I think we need the help of an aeronautical engineer as a final authority.

Ant takers out there?

[Ed Cesnalis]

22 minutes ago, Buckaroo said:

I disagree with this last paragraph. With my big body at a7000 ft DA if I use -6 of flaps instead 15 flaps I’m going to eat a bunch of pine trees at the end of the runway. 15 is steeper than -6 anytime!

Both are true.  You need a dirty configuration to get off the ground sooner not because it climbs steeper.

[Ed Cesnalis]

2 minutes ago, WmInce said:

I think you are dead wrong on that.

Otherwise, heavy aircraft would be taking off with little or no flaps. They don't. All of them accept more drag for steeper climb angle, reduced ground coverage and stall protection.

I'm all in with Tom on this one.

In order to settle the debate, I think we need the help of an aeronautical engineer as a final authority.

Ant takers out there?

You are dead wrong. They are accepting more drag for a shorter take off roll, it doesn't produce a steeper angle once they are climbing nor does it produce extra stall protection it simply lowers stall speed.

Lift is a constant. They cannot accept more drag without using more power to equal the increased drag amount. With more power used to equal more drag less power is left to seek best climb angle, angle is reduced as a result of the take off flaps.  

You can't budget more power for the dirty configuration and somehow have more power left for a steeper climb instead you have less power left and a more limited climb angle.

No expert is needed on this one, logic alone is enough.