Flaps to aid climbing - truth or fiction

[Roger Lee]

"is very Zen Buddhist'

 

Nah, it's just self control. 

 

I can prove it. Have I ever yelled at you for starting an 18 page post on proper spark plug gaps?               

 

See just self control. Read the post and walk away.  

[FlyingMonkey]

SMH

[Ed Cesnalis]

CT, my point is that some topics don't belong here.  I have made this point before. 

 

It is not about safe-zones or about snowflakes or about "freedom of speech".  If this were the only place on the web to discuss gun control, presidential politics, climate change, etc, etc, that would be one thing.  It isn't.  This is a site about flying and CT airplanes.  I go elsewhere when I want to discuss other issues.

 

The "freedom of speech" issue is completely off point.  Sorry, but your right to free speech is in the public square, not on every forum and chat room on the internet.  My desire to not hear your opinions on climate change (or anybody else's regardless of whether I agree or disagree) here on CT Flier  is not any form of restriction on your constitutionally guaranteed right to free speech.  Frankly, I would appreciate not being accused of such.

 

My other and more central point has to do with ongoing tolerance of statements and information of dubious value.  Everybody gets the point.  Nothing ever happens about it.

 

Thanks. 

 

 

I do agree with you Fred. Some topics would be better served on forums meant for those specific ideas or personal preferences.

 

 

Just think if you started a no holds barred on religion, politics, guns or abortion.

Not a place i even care to go and read. If you can't hold it together on flaps then these may lead to contract killings.    

 

 

Here's the thing guys.  I posted a total of 3 words and they were not even on the subject of Climate Change.  They were merely and acknowledgement that the current issue (facts by consensus) did in fact exist elsewhere.  

 

I'm not capable of treading lighter than that and that seems a pretty trivial thing to me.

[Roger Lee]

Hi ED,

 

I don't see any issue with funny jabs and slapstick type comments in fun.

 

I see no issue with your three words (it's cool) unless Andy gets it and it goes 25 pages.     

 

Boy I can't wait to see Andy again in Oct. I'll get to give him a hard time in person. 

 

Are we done with Flaps? Maybe time for a new thread?

[Ed Cesnalis]

We never definitively answered the question.  Do zero and 15* flaps provide a better climb rate than cleaner configurations.  Clean gives the best rate of climb, is that valid in a CT with flaperons and reflex flaps?

 

After today I'm ready to say that the east side of the Sierra Nevada @ 12,000' is no place to be testing climb rates.  I can't feel the mild wave effects when they are smooth.    

 

I got to zero routinely but next time I go to 15 I'll ask myself if its improved rate or angle that I am using.

[FastEddieB]

We never definitively answered the question. Do zero and 15* flaps provide a better climb rate than cleaner configurations. Clean gives the best rate of climb, is that valid in a CT with flaperons and reflex flaps?

 

 

 

Let us know what you find. Make sure the speeds at each setting are actually Vy for that configuration, which may take some doing.

 

It's been intimated that sometimes "books" don't apply to the CT, weird animal that it is. Unicorn farts and fairy dust and all that.

 

But those hoary old books do seem to suggest:

 

1) Flaps - and flaperons - deflected downward increase lift.

 

2) Increasing lift, by necessity, increases induced drag.

 

3) That increased drag must be overcome by thrust in the climb.

 

4) That would leave less excess thrust available for the climb.

 

5) That would lead to lower climb performance with flaps - or flaperons - deflected downward.

 

If Ed's, and others, observations really do indicate better climb in a CT with flaps, rather than ridicule and toss out the books on aerodynamics, lets research how those results fit in with known aerodynamics. Identify which of those generally accepted tenets might be wrong, or not apply, due to some unusual design feature of the CT.

 

My pet theory is that somehow form drag is reduced my more than the increase in induced drag with drooping flaps and ailerons. If the effect is real, of course.

 

Don't forget, even with the CT...

 

[Tom Baker]

My pet theory is that somehow form drag is reduced my more than the increase in induced drag with drooping flaps and ailerons. If the effect is real, of course.

 

That may well be, because of the reduced speed required to maintain the lift needed to support the weight of the airplane.

[Ed Cesnalis]

...

 

1) Flaps - and flaperons - deflected downward increase lift.

 

2) Increasing lift, by necessity, increases induced drag.

 

...

 

 

Isn't there a big whole in your theory?  

 

How can there be an increase in lift?  You are comparing say zero flaps with 15* flaps both in steady state climb right?  Well then both according to your theory are providing lift = weight so there is no increase.  Actually according to your theory when you go from zero flaps to 15 flaps the amount of lift will be less by the weight of the fuel that you burned in the interim.

 

Decreasing lift, by necessity, decreases induced drag.

[FastEddieB]

"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."

Source: 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."

Source: 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."

Source: 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."

Source: http://commons.erau.edu/cgi/viewcontent.cgi?article=1026&context=jaaer

(That last one from Embry Riddle is especially worth a read)

The above represent the conventional wisdom concerning the effect of flaps on climb rate. I've already stipulated that the CT may be an outlier, which further flight data from you could prove*.

The overall lift may be the same, but the l/d ratio decreases, causing more drag for any given lift.

So I'll admit #1 & #2 were poorly stated, or at least overly simplistic.



*Does anyone have a line of communication to an actual Flight Design engineer or test pilot? I'd be interested in their take.

[Mike Koerner]

A few comments:

1) In response to the question about the CT2k - yes, it also has interconnected flaps and ailerons.

2) As a historical point of reference, the concept of interconnected flaps and ailerons is not new and certainly did not originate with Flight Design. All modern flapped sailplanes (dating back to at least the Glasflugel 301 Libelle in 1964) have a mechanism which provides the connection. In most cases the flaps move with the ailerons, though to a lesser degree, to improve roll rate without excessively increasing drag (recognizing that the inboard control surface is less effective in inducing roll due to it shorter moment arm). And of course, the ailerons deflect with the flaps so as to optimize the contour of the wing across the entire span for a given airspeed. However, this interconnection is usually limited to the range of flap positions used in flight. When landing flaps are deployed, the aileron droop is inhibited so as to retain sufficient aileron travel for roll control. In Ed's video clip you could see that the CT also has this limitation. From -6 to zero to +15 degrees the aileron movement is close to one-to one with the flap. Beyond 15 degrees, not so much.

By the way, the outboard flaps on commercial airlines are also often interconnected, to some degree, with the ailerons.

3) Negative flap settings are the norm on flapped sailplanes. The way I think of it is: Flaps increase the effective camber of the wing and thus its maximum coefficient of lift. In the process, they also increase drag. At lower speed you need the higher coefficient to maintain flight (lift equal to the weight), so you either need more flap or a higher angle of attack. But as Eddie pointed out, you need to keep the angle of attack within a limited range to minimize fuselage drag. Conversely, at high speed you'd like to minimize the camber. So, it makes sense to me that for every flight speed (and gross weight, and cg position) there is an optimum flap position.

4) As far as I know, for sailplanes the maximum L/D always occurs with the flaps set at zero. When you look at the way the flap on the CT fairs to the fuselage you would expect this to be the case on our planes as well. Yet, I agree with the other CT owners who point out that flaps increase your climb rate. I only bring them up during a climb if the engine is getting hot (which for me is anytime the oil is above 200 F by the way).

5) I think Ed's climb rate testing is flawed in that he is making measurements near his service ceiling. I have spent quite a bit of time in the 14 to 15,000 foot range, near max gross, taking pictures of mountain peaks (and here). Yes, you need flaps up there. But you end up flying so slow and at such a high angle of attack to climb at all, that I think this is more an aberration than a statement on the aircraft's flap trim settings. I would recommend instead comparing climb rates at a much lower altitude.

6) Again, referencing my sailplane experience, I don't think any testing that Ed can do in summer in the Sierra is meaningful unless it's conducted at dawn on an unusually still air day. He should spend his time taking pictures and sharing them with us instead .

Mike Koerner

[FastEddieB]

In browsing the internet for support for my position, I came across what appears to be a very concise compendium of practical aerodynamics from the Navy:

 

http://www.netc.navy.mil/nascweb/api/student_guides/Aero_student_guide_7_April_2008.pdf

 

It appears to sourced from a handful of respected sources:

 

1. Aerodynamics for Naval Aviators

2. Aerodynamics for Pilots

3. Introduction to the Aerodynamics of Flight

4. U.S. Standard Atmosphere, 1976

 

Looks like a good one to download for study and reference.

 

And, it also lends support to the proposition that flaps adversely affect climb rate:

 

"CLIMB PERFORMANCE FACTORS

Since weight, altitude, and configuration changes affect thrust and power excess, they will also affect climb performance. Climb performance is directly dependent upon the ability to produce either a thrust excess or a power excess. In the previous lesson, it was determined that an increase in weight, an increase in altitude, lowering the landing gear, or lowering the flaps will all decrease both maximum thrust excess and maximum power excess for all airplane. Therefore, maximum angle of climb and maximum rate of climb performance will decrease under any of these conditions."

 

BTW, I enjoyed and appreciated Mike's post above. Just need to reason through why the aerodynamics would change at lower air densities. Again, if they did, would not at least some planes publish a higher service ceiling with partial flaps? If such an animal exists, I'd like to be pointed to it, as it would certainly be evidence to consider. If not, that also seems evidentiary.

[FastEddieB]

As an aside, for Apple folks iBooks makes a nice repository for training materials.

 

Mine right now, with the latest addition on the upper left:

 

[Ed Cesnalis]

I enjoyed Mike's post as well.  I agree that testing climb rates in the lee of the Sierra or worse the lee of the Ritter Range does not give an accurate picture for comparing climb at different flap settings.  However the original purpose of my test was to demonstrate that flaps are used in a CT to extend its range to a higher ceiling.

 

For the above purpose my test was quite successful.  It showed these things:  One, the neg-six setting needs to be abandoned probably prior to 12,500'.  Two the 15* setting provides an initial balloon that is so meaningful that the balloon alone is likely to give you the immediate clearance you need when used.

 

For the purpose of showing extended range to a higher ceiling my test worked quite well.  For the purpose of comparing climb rates without conditions interfering I was too high and in the wrong place.

[FastEddieB]

I went ahead and focused on climb rate, which can also be a proxy for service ceiling since climb rate is how service ceiling is defined.

 

BTW, my new favorite aerodynamics book mentions some ceilings I was either never aware of or had forgotten:

 

"As an airplane climbs and PE decreases, the rate of climb will also decrease. The altitude where maximum power excess allows only 500 feet per minute rate of climb is called the combat ceiling. The cruise ceiling is the altitude at which an airplane can maintain a maximum climb rate of only 300 feet per minute. The service ceiling is the altitude at which an airplane can maintain a maximum rate of climb of only 100 feet per minute. Eventually, the airplane will reach an altitude where maximum power excess is zero. At this altitude, the airplane can no longer perform a steady climb, and its maximum rate of climb is zero. The altitude at which this occurs is called the absolute ceiling."

 

As an aside, single engine service ceiling in a twin is where it can no longer climb 50 fpm.

[Ed Cesnalis]

A number of piston powered airplanes are already at their combat and even their cruise ceilings while sitting on the ground here at Mammoth.

[FastEddieB]

No doubt!

[Ed Cesnalis]

...  I only bring them up during a climb if the engine is getting hot (which for me is anytime the oil is above 200 F by the way)...

 

MIke,

 

How is it that you can be based in SOCAL and have that opinion RE oil temps?  Do you thermal your way up and out of the LA basin?  Do your bigger wings make the difference?

 

Note/Question:  Does it make sense that short wing designs call for extra cooling capacity?

[FastEddieB]

Sorry if I'm a bit behind - camping with the kids and grandkids was a lot of fun!

 

 

In the thread about POH's and rate-of-climb data, John Vance confirmed that both rate-of-climb and ceiling info was included in his POH for each of three flap settings up to the absolute ceiling at various weights. I don't think I've ever seen such comprehensive Best Rate of Climb charts for a GA aircraft before, and I commend Flight Design for publishing them.

 

In order, from least to most flaps from the CTLS POH (each can be enlarged by clicking on it):

 

 

 

 

The charts for 0º and -6º look nearly identical as far as I can tell, though the footnote gives a slightly better rate of climb at SL for 0º over -6º.

 

But note the 15º chart has all the lines skewed to the left, indicating less rate of climb, across the board. And reaching the service and absolute ceilings at a lower level. All quite consistent with the various "old books" on aerodynamics, by the way!

 

Assuming this data was obtained by test pilots, I think its pretty strong evidence against the position that 15º flaps can make a CT climb consistently faster or reach a higher altitude.

 

I still encourage Ed to go ahead and experiment, but to be sure that all variable are taken into account - as I assume the Flight Design test pilots did.

 

As an aside, these charts make pretty clear that a CTLS can climb above, well above, 14,000' at lighter weights, in spite of the assertions of someone here.

[Ed Cesnalis]

If you can get a clear capture of the charts it would be great.  I can't read these.

[FastEddieB]

Try these at the highest Flickr resolution:

 

 

 

 

Remember to click on them for full size.

[Ed Cesnalis]

[Ed Cesnalis]

If the charts are correct and at least representative of what a CTSW does than I have to assume that when I use 15* to get over terrain that I otherwise wasn't going to make that the benifit I am seeing is a rapid deceleration to near Vx.  If Vx. at -6 is only 56kts  I'm not too interested.  A bit of shear and I would stall.

 

My POH shows  Vx at 66kts, how did they get to 56kts?  I'm not sure I believe it.  Its lower than 1.3 x Vso

[Ed Cesnalis]

These Vx numbers are too slow for me, in my wind shear prone environment  -6=56kts, 0=55kts, 15,=51kts.

 

This view does show at these Vx speeds 15 should climb steeper because its slower.  So per these charts 15 has a better/steeper Vx.

 

====================================================

 

Now compare Vy speeds.  -6=71kts, 0=69kts, 15,=61kts.

 

Notice the 20kt spread?  Here you have the same advantage for 15 over the faster settings.  When climbing at best rate or faster and terrain  is  blocking your way what happens with more flaps?  15* shows it best, when you go from cruise climbing at Vy or faster to 15* and Vy or faster, your rate will fall but your angle will get much steeper and you can clear what you otherwise wouldn't make.

 

My POH only gives 1 Vx and 1 Vy and if there is a 20kt spread from one setting to another than 1 set of number doesn't mean much.  I really only think Vx vs Vy on take-offs.  Otherwise I'm doing what works even if my understanding on why it is working is based on insufficient numbers and perhaps numbers that are out of range.

[FastEddieB]

The three Vx angles from the CTLS POH are:

  -6º - 7.3º

   0º - 7.8º

 15º - 7.8º

 

Usual stipulation that the CTSW may have different performance numbers for a variety of reasons.

 

BTW, I'm not sure where you're getting the 20 kt spread from. Only a 10 kt spread between Vy's at different flap settings, and between10 and 15 kts for the Vy/Vx spread. Unless you're talking about something else.

[Ed Cesnalis]

Your right, not 20kts but 10kts.  The point stands though, best rate at 15 is much steeper.

 

How many CT pilots use these low climb numbers?