{"id":4967,"date":"2018-09-06T16:49:42","date_gmt":"2018-09-06T23:49:42","guid":{"rendered":"http:\/\/tailwheelersjournal.mechadigital.net\/?p=4967"},"modified":"2021-08-26T20:37:52","modified_gmt":"2021-08-26T20:37:52","slug":"213-flap-usage","status":"publish","type":"post","link":"https:\/\/tailwheelersjournal.com\/213-flap-usage\/","title":{"rendered":"#213 “Flap Usage"},"content":{"rendered":"

<\/h2>\n

(I\u2019ve been sitting on this one, but probably started it in 2015)<\/p>\n

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I guess if I have a favorite aviation iconic phrase to \u201cclast\u201d, it would be that old wheeze, \u201cthe key to a good landing is a good approach\u201d.\u00a0 I feel that all too often that kind of thinking becomes a refuge for the undertrained.\u00a0 As all who have flown with me know, I think we all need to make good landings out of ANY kind of approach.<\/h3>\n

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\u00a0Julie Benson operates the flaps on a Polish Wilga.\u00a0 Flap handles vary widely and can be important considerations.<\/h3>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Incremental flap extension is, in my opinion, a method that encourages minimal training.\u00a0 (Here come the villagers with their torches and pitchforks!).\u00a0 Incremental flap extension is the popularly taught method calling for a few degrees on downwind, a few more on base and a few more on final.\u00a0 This technique requires little re-trimming or adjustment of pitch because the changes are relatively small.\u00a0 If you were to extend all your \u201cflappage\u201d at one time you would have a relatively large pitch and trim change (depending on the particular aircraft) in order to maintain the desired angle of attack and airspeed.\u00a0\u00a0 Such a technique would require greater skill and\/or practice on the part of the pilot.\u00a0 That\u2019s why I teach it.<\/h3>\n

Let\u2019s review the purpose of flaps (you know how I love fundamentals): \u00a0Flaps perform three basic functions:<\/h3>\n

When we extend them, they slow us down, which can be useful, considering that we are getting ready to land and every airplane should be landed just as slowly as it can go.<\/h3>\n

Flaps generate drag which decreases our glide efficiency, and this is one reason that I question the normal extension technique.\u00a0 That drag allows us to fly a steeper approach without increasing airspeed.\u00a0 This enables us to arrive on the runway with more of it in front of us if we have to clear an obstacle on the approach. The same drag which enables us to fly a steeper approach, clearing an obstacle, also makes it possible for us to vary our touchdown point. We could just shove the nose down to steepen that approach.\u00a0We would arrive at the same spot, but we\u2019d be flying faster and would have to wait for that speed to decay during the flare, thus resulting in a touchdown further down the runway. That would be particularly true in a nosewheel airplane which MUST be allowed to stall down on the runway.\u00a0 A tailwheel airplane can be \u201cwheel landed\u201d at a higher speed, then braked, if necessary.<\/h3>\n

Flaps also decrease the stall speed, enabling us to land at a slower speed.\u00a0This results in a shorter landing and perhaps less brake and tire wear.\u00a0 A reason for extending flaps on short final, which I prefer, is that we normally fly slower with flaps extended than we do with them retracted and I\u2019d like to see our speed higher as long as possible, thereby getting us to our destination a little faster (this is not a big issue, but more a matter of personal principle).<\/h3>\n

Flaps COULD serve to increase our spot landing accuracy if we used them like we use spoilers\/dive brakes in a glider.\u00a0 The normal technique for accuracy landing in a glider is to extend some of the spoilers on downwind.\u00a0 Many pilots like 1\/3 spoilers.\u00a0 Then the approach is flown as accurately as possible. Once at the \u201ckey\u201d position after the turn to base the pilot analyzes his glide. \u00a0If the approach looks short, the pilot closes some spoilers, thereby increasing lift and decreasing drag.\u00a0 The touchdown or flare points then move further away.\u00a0 If the target appears to be too far down the runway, the pilot simply applies more spoilers, thus steepening the approach course and moving the target closer.\u00a0 We could use flaps the same way, but most pilots are taught to never retract flaps except carefully on a go around with full power.\u00a0\u00a0\u00a0 The reason for this conventional wisdom is that flap retraction will result in increased sink because of the loss of lift.\u00a0\u00a0 It\u2019s worth it to do some experimentation on power-off flap retraction. The main difference between flaps and spoilers\/dive brakes is that flaps increase lift, while the combination found on gliders only increases drag while DECREASING lift.\u00a0 That\u2019s why students are discouraged from decreasing flaps while at low altitude\u2026such an action CAN decrease lift.\u00a0 However, some of the same techniques that are used with gliders can be used. \u00a0Obviously, all aircraft don\u2019t have the same flaps.\u00a0The cute little flaps on the Cessna 140 are more symbolic than effective.\u00a0 Retraction of those flaps on approach won\u2019t hurt much.\u00a0 The big ol\u2019 flaps on a newer Cessna are an entirely different story.\u00a0 For some thoughts on the use of flaps like that, I turned to one of my favorite consultants, Jerry Groendyke:<\/h3>\n

Jerry has played with retracting flaps on final in his 172, a technique that horrifies some who\u2019ve never experimented with it.\u00a0 The 172\u2019s 40-degree flaps are quite effective. Jerry\u2019s been known to have a bet riding on making a spot landing and intentionally putting in too much flap.\u00a0The other person is sure he\u2019s screwed up and is already counting his winnings. But then, when Jerry retracts some flaps, it feels like power has been added.\u00a0 His opponent will usually object with “that’s not fair, that’s cheating, that’s dangerous, bet’s off, etc, etc, etc…\u201d<\/h3>\n

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Jerry Groendyke<\/h3>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Jerry feels that, as a rule, in the small aircraft we fly, flaps should not be extended if the power is above idle. I couldn\u2019t agree more with just a few exceptions, like the power-off accuracy approach<\/strong>.\u00a0 The sequence should be: power to idle, speed controlled by pitch, then lastly flaps. Most of my students are familiar with my routine.\u00a0When they turn base I ask them if they are high or low.\u00a0 If they are really high, I\u2019ll advise them to put the flaps down right then and there.\u00a0In that case it\u2019s a coarse adjustment for a really high approach.\u00a0 But if they\u2019ve done a good job of designing an accurate approach and are in the middle of their glide range they won\u2019t need to add flaps until short final.<\/h3>\n

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There\u2019s more conventional \u201cwisdom\u201d to debunk when it comes to crosswind landings.\u00a0 The last-minute slip technique is used, as it should always be by competent pilots carrying passengers.\u00a0 Jerry likes to land in a crosswind with as much flappage as possible. Remember he\u2019s flying a tricycle gear airplane.\u00a0 We\u2019ll get to the tailwheel shortly.\u00a0 \u00a0He\u2019s still able to maintain runway alignment by crabbing. That\u2019s easy.\u00a0 The common thinking seems to be land fast with little to no flaps and fly the airplane onto the ground then try to keep it straight as it becomes a ground vehicle. But the problem is that area between fast enough to fly, and slow enough to be controllable with steering and brakes. Jerry and I both prefer as much flaps as possible.\u00a0 That allows us to go as slow as possible.\u00a0 We crab, which so far is no problem regardless of wind strength.\u00a0 It also keeps our passengers comfortable.\u00a0Then at the last second, and about a foot or so up, we side slip to put our upwind wheel on the ground (this is where you will find out if this speed and flap combination will work, sometimes you may need to try again with less flaps and more speed for rudder to be effective) while simultaneously raising flaps. Manual flaps are best of course, and for electric flaps you may need a third hand to raise the flaps when you say so (this is where I dearly love Cessna\u2019s \u201cset \u2018em and forget \u2018em\u201d electric flaps).<\/h3>\n

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The subject of crab-to-slip is possibly the most over-discussed subject in the airport bar.\u00a0I refuse to participate in that discussion.\u00a0 It\u2019s just too basic.\u00a0 Let\u2019s skip that old wheeze and discuss something that I think is really important and difficult.\u00a0 That\u2019s the proper retraction of flaps.<\/h3>\n

If you can be near flaps down stall speed, at a very slow ground speed due to a strong wind, as soon as you touch and raise the flaps you will quickly be below flaps up stall speed, weight is on gear, brakes work, and steering works<\/strong>.<\/h3>\n

As of this writing, one of my primaries is now practicing the fine art of raising her flaps in the middle of the flair.\u00a0 I love this technique, but it does require skill and practice.\u00a0 The benefits of it should be obvious.<\/h3>\n

In a tailwheel airplane crosswind technique can actually be easier.\u00a0 I guess it depends on what you\u2019re used to.\u00a0 Using the same general technique but perhaps carrying just a little more speed, you touch down in a wheel landing, planting the mains on the ground and raising the tail so that there is zero angle of attack.\u00a0 That accomplishes the same thing as Jerry\u2019s flap retraction and subsequent stall.\u00a0 You\u2019ll still be above stall speed but when you can no longer keep your tail up you should be below stall speed.\u00a0 You, too will have brake effectiveness which, combined with decreasing rudder but increasing tailwheel steering will more than equal the trike\u2019s nose wheel steering.\u00a0 I should point out that I still like Jerry\u2019s technique of flap retraction during the flare.\u00a0For one thing, if flaps increase the ship\u2019s weathervaning tendency, they only do so when the wheels are on the ground, so flap retraction will minimize that effect.\u00a0 Many pilots, especially those in high wings, land fast in a crosswind with no flaps, and spend a lot of distance swerving back and forth and sometimes run off the runway because they are just barely touching the ground.<\/h3>\n

Until modern flight training becomes more sensible (which is very unlikely), there will continue to be improper flap usage.\u00a0 Here\u2019s a great example:<\/h3>\n

There was once a pilot inbound to an airport in Florida from the Bahamas in a C172. \u00a0\u00a0He was very low on fuel and reported that fact to the tower. The wind was from the northwest at 30 or so knots, so he had a direct headwind. He was cleared to land straight in on 32. About two miles out, the pilot was observed lowering his flaps. \u00a0\u00a0That was probably how he was taught at Acme.\u00a0 To many of us, that would be like putting your car\u2019s parking brake on when you’re trying to make it to the gas station on fumes.<\/h3>\n

<\/h3>\n

And if you ever take one of my courses, ask me to demonstrate the only time that flaps can be used to actually extend the glide.\u00a0 It can be tricky, but with practice at the power- off approach, we can terminate that approach just short of the touchdown point. So, the objective must be to slightly extend the airplane\u2019s glide, so that it \u201cmakes it\u201d.\u00a0\u00a0 And we must do that without adding any power.\u00a0 How do we do it?\u00a0 By the very surprising use of flaps.\u00a0 But only if we\u2019ve resisted the temptation to extend them before reaching ground effect on short, short final<\/strong>.\u00a0 Because, you see, if you\u2019ve glided to that point and still have not extended your flaps, by extending them now, you will increase lift, and taken advantage of ground effect to extend that glide. It\u2019s a beautiful thing to behold and it is the most efficient use of flaps that I can imagine.\u00a0 It takes practice, just like every difficult maneuver we practice at Tailwheel Town.\u00a0 But it does prove the point that holding off on flap extension will avoid the drag they produce, thus extending your glide and also providing lift at the last possible moment, thereby extending the airplane\u2019s glide.\u00a0 This maneuver also proves that extension of flaps early in the approach, like on downwind or even base, is often wasteful and (with apologies to all those Acme instructors) \u2026 \u201cill- advised\u201d.\u00a0 (See how I adroitly avoided insulting a whole bunch of instructors by calling it \u201cstupid\u201d?)\u00a0 I should point out that I have NEVER met a pilot who uses this technique!\u00a0 Most \u201cAcme\u201d instructors have never heard of it and are slaves to the incremental flap extension that is taught at Acme.\u00a0I\u2019ve also found that virtually everyone I\u2019ve ever flown with wants to apply a bit of power if they are short.\u00a0They don\u2019t need to.\u00a0 They could simply extend flappage and thus extend the glide.\u00a0 But they won\u2019t, because they\u2019ve always done it that way!<\/h3>\n

Let\u2019s now talk about the device which we use to operate the flaps.\u00a0 It can be important.\u00a0 Many airplanes, especially older ones, use a \u201cJohnson Bar\u201d.\u00a0 I guess Johnson was an engineer or something.\u00a0 I love this one.\u00a0 You simply reach down and grab that bar, then pull it up and feel it click for each increment of flaps.\u00a0 To retract the flaps, you simply put a little tension on the bar, push the button on the end and lower it to the floor.\u00a0 Aerodynamics will be glad to help retract the flaps.\u00a0 I love this method of flap retraction, although you may be pretty busy using it if employing our crosswind, sudden-flap-retraction technique.\u00a0I should point out that the same system is used in our little Cessna 140 as is used in the larger Cessna 180 and 185.\u00a0Although they operate the same way, they are worlds apart in ease of operation.\u00a0 It takes some practice to smoothly or quickly use the larger Cessna\u2019s Johnson bar.\u00a0 One of my most talented fliers, who is very experienced, simply won\u2019t\u2019 deal with flaring flap retraction in his Cessna 180 because of the need to lean so far forward.\u00a0I trust his judgment.<\/h3>\n

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\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0The flap position indicator on an early Cessna<\/h3>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Early Cessna trikes started to be built with electric flaps.\u00a0 You could either look at the little indicator to see how many degrees of flaps were being extended as you held the flap switch down or you could just look out the window at the flaps and get the same information.\u00a0 This type of flap sucks because you have to hold that switch either up or down in order to extend or retract the flaps and you\u2019ve got better things to do with your right hand (like handling the throttle or holding your coffee cup).\u00a0 But if you have such an airplane, it\u2019s a \u201cRumsfeldian\u201d issue[1]<\/a>.\u00a0 That\u2019s what you\u2019ve got, so deal with it.\u00a0 Then Cessna came out with a device which was a pilot\u2019s dream and a mechanic\u2019s nightmare.\u00a0They got rid of that older flap switch and replaced it with a multi-position switch.\u00a0 You could reach over and flip the switch to a particular flap setting and the flaps would assume that degree of extension all by themselves while you added cream to your coffee.\u00a0 I call this the \u201cset-it-and-forget-it\u201d switch.\u00a0 I hate fixing it when it goes bad \u2018cause my little squirrel brain has trouble dealing with all those wires and micro-switches, but my Flying Squirrel paw absolutely loves it, especially in a sudden retraction, crosswind landing scenario.\u00a0 I love that I can flare the airplane and right before touchdown quickly reach over and flip that switch up, then go back to my throttle while the flaps are automatically retracting by themselves.\u00a0 I also love it in a touch-and-go scenario when I can flip it to ten degrees for the go.\u00a0I\u2019m adding power, removing carb heat, trimming and stirring my coffee while those flaps are going from 40 degrees to ten degrees all by themselves. I\u2019m even teaching this technique to some of my primary students (just make sure that they ARE retracting.\u00a0 I\u2019ve had the circuit breaker pop, rendering the flaps \u201cdown and stuck\u201d).<\/h3>\n

That\u2019s the rant on flap usage.\u00a0 Many thanks to Jerry for his input.<\/h3>\n

The article above is a great example of why I don\u2019t run a forum.\u00a0 If this were a forum the comments column would go for twenty or thirty pages and grow steadily!\u00a0 The \u201cCheeto-eating Trolls\u201d would be pounding their keyboards like crazy, with beads of sweat pouring off their brows as quickly as the insults flow from their computers.\u00a0 What you\u2019ve just read are the opinions of a couple of guys who think they know what they are doing.\u00a0 If you can find some useable info here, take it and run with it.\u00a0 If you are \u201cAcme-trained\u201d and disagree, keep doing what you\u2019re doing, start your own website\u2026 and try to keep the Cheeto-crumbs out of your keyboard.<\/em><\/h3>\n

Happy Swooping,<\/h3>\n

Brian<\/h3>\n

[1]<\/a>When that notorious \u201cOuchface\u201d, Donald Rumsfeld, was secretary of defense, he was asked if the U.S. Army was ready for an invasion of Iraq.\u00a0 Rumsfeld scowled at the questioner and replied, \u201cWell, you go to war with the Army you have, not the Army you WANT\u201d.\u00a0 Hence the term, \u201cRumsfeldian\u201d.<\/h3>\n","protected":false},"excerpt":{"rendered":"

“If this were a forum the comments column would go for twenty or thirty pages and grow steadily!\u00a0 The \u201cCheeto-eating Trolls\u201d would be pounding their keyboards like crazy, with beads of sweat pouring off their brows as quickly as the insults flow from their computers.\u00a0“<\/p>\n","protected":false},"author":3,"featured_media":4977,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_mi_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[3],"tags":[35,38,65,67,173],"_links":{"self":[{"href":"https:\/\/tailwheelersjournal.com\/wp-json\/wp\/v2\/posts\/4967"}],"collection":[{"href":"https:\/\/tailwheelersjournal.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/tailwheelersjournal.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/tailwheelersjournal.com\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/tailwheelersjournal.com\/wp-json\/wp\/v2\/comments?post=4967"}],"version-history":[{"count":0,"href":"https:\/\/tailwheelersjournal.com\/wp-json\/wp\/v2\/posts\/4967\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/tailwheelersjournal.com\/wp-json\/wp\/v2\/media\/4977"}],"wp:attachment":[{"href":"https:\/\/tailwheelersjournal.com\/wp-json\/wp\/v2\/media?parent=4967"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tailwheelersjournal.com\/wp-json\/wp\/v2\/categories?post=4967"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tailwheelersjournal.com\/wp-json\/wp\/v2\/tags?post=4967"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}