Flying with a pulse - oximeter

[Tom Baker]

The lift from the wings supports the weight of the airplane.

 

The speed of the airplane is controlled by the angle of attack.

 

In a steady constant airspeed climb it is the excess power that maintains the relative wind at a positve angle allowing the airplane to climb.

 

As for whether adding flaps will increase the climb, this will only happen if the increase in lift is greater than the increase in drag. For the CT 0 flaps is the normal shape of the airfoil, and -6 is considered clean. Switching from -6 to 0 will proved a greater increase of lift compared to drag, the switch to 15 may still provide more lift compared to drag. The lift to drag for 15 flaps would need to be tested to determine if 15 flaps would be advantageous thor climbing.

 

Roger, your example of climb after take off compared to runway length would be more an example of climbing at Vx compared to Vy. While you are higher at the end of the runway it takes you longer to get there because of a slower ground speed.

[FastEddieB]

Eddie, you're right. thanks

You're very welcome.

 

It's rewarding and one of the main reasons I bother to explain things. It also sends me in search of primary sources and exercises my reasoning and teaching skills.

 

And also gives me a chance to be proven wrong - which is the only way to learn and grow.

 

So thanks right back!

[FredG]

I think that Charlie Tango is correct regarding his opinion that at least some of the additional "lift" during climbing flight is coming from the wing in addition to the upward vector of force provided by the propeller.  This would be the case provided that the angle of attack of the wing in greater during climbing flight than during level flight.

 

If the angle of attack during climbing flight is equal to the angle of attack during level flight, then all of the force producing the climb is due to thrust.

 

In non-high performance airplanes, however, the AOA of the wing increases during climb, and that must increase lift.  

 

Thoughts?

[FastEddieB]

 

In non-high performance airplanes, however, the AOA of the wing increases during climb, and that must increase lift.  

 

Thoughts?

Yes, but only momentarily to begin the climb. As the airspeed slows in the climb, lift will again equal weight even at the higher AOA.

[FredG]

Eddie, point taken.

[Ed Cesnalis]

thoughts:

 

As I learned from the video above when you increase angle of attack there is a loss of lift from the new direction of lift from the wings.

[FastEddieB]

thoughts:

 

As I learned from the video above when you increase angle of attack there is a loss of lift from the new direction of lift from the wings.

And the rearward component of that "new direction of lift" is induced drag.

[Roger Lee]

Yes, but not enough to impede climb. Only if the flap is too much or you fail to have enough wing and power to overcome.

 

Just like prop pitch. It's all about balance.

[FastEddieB]

Yes, but not enough to impede climb. Only if the flap is too much or you fail to have enough wing and power to overcome.

Just like prop pitch. It's all about balance.

First, I have what I believe is zero experience with negative flaps.

 

But how about an experiment, and one which does not require struggling in the low teens.

 

Next time someone is out and about in their CT, or needs an excuse to fly, try this:

 

1) At a safe altitude, choose a power setting that results in about 50% to 60% power, or one that clearly results in a climb rate in excess of 100 fpm.

 

2) Pitch for Vy and begin a climb with 0° flaps.

 

3) Note the altitude where the climb rate touches 100 fpm and write it down.

 

4) Descend, then repeat for 10° of flaps.

 

5) Descend, then repeat for -6° of flaps (if available).

 

This will have to be done in pretty smooth air without a lot of thermals.

 

I'm still pretty sure that the service ceiling in this experiment will be lower with 10° of flaps, but I'm willing to be proven wrong.

 

Less certain of the effect of 0° flaps. That I'll have to think about/research and I'm curious as to the result.

 

If anyone has a CT in or near N GA and is willing, I'd be happy to help and record the experiment with my GoPro.

 

Let me know.

[Ed Cesnalis]

Eddie,

 

Anyone with much CT time instictively knows the results of this test.  In the next few days I will climb to 12,500 and then pitch for best climb at 3 flap settings and note climb rates.

 

The reason 15 will win is that the wings are producing more  lift with the better L/D freeing up more excess thrust.

[FastEddieB]

Eddie,

 

Anyone with much CT time instictively knows the results of this test.  In the next few days I will climb to 12,500 and then pitch for best climb at 3 flap settings and note climb rates.

 

The reason 15 will win is that the wings are producing more  lift with the better L/D freeing up more excess thrust.

Yay scientific method!

 

If your assertion is correct, is Flight Design leaving some performance on the table by not specifying flaps for all high altitude operations?

[FlyingMonkey]

Yes, but not enough to impede climb. Only if the flap is too much or you fail to have enough wing and power to overcome.

 

Just like prop pitch. It's all about balance.

 

That's what I was getting at.  If the increase in lift from flaps exceeds the loss of other forces, it will be a net positive for climb.

[Roger Lee]

Eddie,

 

You need new books.  

 

 Normal takeoff configuration for the CT can be zero flaps or 15. Many planes out there that use 10-15 flaps for takeoff. This isn't new.

 

 

 

That's exactly right Hank.

" If the increase in lift from flaps exceeds the loss of other forces, it will be a net positive for climb."

[FlyingMonkey]

As far as takeoff flaps, I think the difference is enormous.  At 15° flaps the airplane seems to leap off the runway in no time, at 0° it really takes a much longer roll and comes off with much less authority.  I took off with flaps -6° once and it seemed to take forever, almost scary how much runway it took.

 

I don't takeoff with anything other that 15° flaps unless the wind is howling right across the runway.

[Roger Lee]

"I don't takeoff with anything other that 15° flaps unless the wind is howling right across the runway."

 

Ditto for me.

I don't takeoff with anything other that 15° flaps unless the wind is howling right across the runway.

[Tom Baker]

 

 Normal takeoff configuration for the CT can be zero flaps or 15. Many planes out there that use 10-15 flaps for takeoff. This isn't new.

 

 

Many aircraft will get off the ground quicker and climb at a steeper angle with flaps, but the rate of climb will suffer. That is why the procedure for many airplanes is to retract the flaps after you have cleared your obstacle, so you can increase the rate of climb. 

[FastEddieB]

What Tom said.

 

I never questioned using flaps on takeoff when recommended. My Sky Arrow calls for 10°, and that's what I use. As an aside, my Cirrus called for takeoff flaps as well.

 

One of my prior links explained that the shorter ground roll can result in more clearance of obstacles because the plane has more time/distance to climb. This in spite of the fact that the climb rate will be lower with flaps - hence the recommendation to retract them as soon as clear of obstacles.

 

We still are not in agreement on the effect of flaps on climb rate and ceiling, but are in agreement that their use on takeoff can provide a short term benefit.

[gbigs]

Gliders do not ascend with excess thrust.  And powered aircraft can also get lift in the same way as a glider.  

 

Any flap config can be used on a takeoff, 0, thru -6...as the POH states.  Same with landing.  The best-rate-of-climb varies with each flap setting, -6 (71kts),  15 (61kts).  This is why 15 is the standard flap setting recommended.  Short field takeoff and the shortest runway length needed are also achieved using 15 say the POH.

 

There is a 10kt difference in stalling speed 30 (40kts) to -6 (50kts).  This is an indicator of lift delta between settings. 

[FlyingMonkey]

 

There is a 10kt difference in stalling speed 30 (40kts) to -6 (50kts).  This is an indicator of lift delta between settings. 

 

True, but what it doesn't tell us in the drag difference between them.  Climb performance will be based on airspeed, lift of the wing configuration, and drag of that configuration.  That last bit directly subtracts from Eddie's excess thrust.

[gbigs]

True, but what it doesn't tell us in the drag difference between them.  Climb performance will be based on airspeed, lift of the wing configuration, and drag of that configuration.  That last bit directly subtracts from Eddie's excess thrust.

 

Eddies 'excess thrust' theory is not stated quite correctly.   It is excess 'energy' that is required.  Uplift forces from ridge, wave and thermals can be a bigger factor is gaining altitude than thrust from the engine, and in the case of a glider it is the ENTIRE way a glider climbs.

 

To climb you need to get an increase in energy, not speed. This is normally done by increasing engine power output, or by trimming the airplane at a lower speed where drag is less, so more power remains for climbing.

 

If you use the airplane's kinetic energy as its source of thrust, the same mechanism can be applied to instationary climbs, where speed is traded for altitude, like in gliders.

The nose-up attitude is simply the result of a different flight path. Since the required aerodynamic lift will be almost the same, the angle of attack will also be almost the same and the whole aircraft needs to fly nose-up. This is similar to a car which has the same attitude towards the road, but when you drive uphill, both car and road will be tilted upwards.

This analogy breaks down when you change speed - flying at lower speed needs more angle of attack to still create the same lift, and this nose-up change will be added to your attitude angle.

[FredG]

Eddie, I have been thinking about the assertion that thrust is the sole force that results in an aircraft gaining altitude when the stick is pulled back and the AOA increases.  You mentioned in an earlier comment that the effect of increased AOA was transient and once a new steady state of climb occurred, lift again equalled weight and the fact that the airplane was climbing was all due to the upward component of the trust vector (since the propeller was "tipped" upward a bit during the climb and produced both a horizontal force component and a vertical force component).

 

Imagine the following hypothetical airplane - one on which the propeller is on a movable hub so that it is always perpendicular to the surface and its thrust vector is always horizontal, regardless of whether the airplane is pitched upward or downward.  Would such an airplane be unable to climb, even if the wing has a positive AOA?  I would expect this airplane to climb solely as a function of lift from the wings exceeding the weight of the airplane (although it would not climb as well as an airplane in which the plane of the propeller tipped upward as the airplane pitched up, as virtually all airplanes do).

 

What do you think? 

[Ed Cesnalis]

Great question Fred.  I was easily convinced and now I'm a skeptic again.

[FredG]

CT - glad it made sense!

[Doug G.]

It depends on the airplane. If it had a symmetrical wing like some aerobats the AoA (defined as into the relative wind) is all that creates lift. Even with symmetrical it is not all impact lift the shape is made to efficiently create lift at a range of AoA.

I have flown models that had slab wings with no airfoil shape at all, but with enough power to weight it doesn't matter - still impact and AoA.

A leaf falling in still air creates lift, just not enough to overcome weight.

[FredG]

Hi Doug,

 

I think you are answering a different question.  The question I am asking is whether an airplane with thrust that is always horizontal and therefore making no contribution to upward forces on the airplane (in opposition to the effects of weight) can still climb as a result of lift from the wings alone.  

 

My impression is that Eddie has stated that it would not and that the forces that differ between level flight and climbing flight are the result of thrust alone, but I am not convinced.  I wrote the above comment as a hypothetical to explore that statement.

 

fg