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Flaps and stalls


Roger Lee

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Food for thought,

 

I went out today and did a bunch of stalls. It was posted that you loose some of the stall speed advantage if you go from 30 to 40 flaps. In other words does the stall speed increase when you switch from 30 to 40 flaps. The answer for me was, Yes.

With 30 flaps my plane stalled around 36-38. When I used 40 flaps the stall speed went up4-5 knots. If you landed the same at 40 as you would at 30 and at full stall you could get in trouble quickly if something changed ever so slightly (i.e. wind change or human error, nobody's perfect ) and you were hanging on stall for 30 and was using 40. I never land near stall so it isn't an issue for me, but some of you do. One little miscalculation at 40 flaps at a full stall landing and it will be ouch time.

Some CFI's like to train using 30-40 flaps all the time and land at stall. For me this carries too many inherent risk and there really isn't a real need for it for the every day normal landing.

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Hi Roger,

 

I had the same experience in my SW. 30 flaps power off stall speed was around 36-38 and 40 flaps was 40-42. I would show my students this during slow flight. We would set up with 30 flap and maintain around 42 knots, the plane flew great, plenty of control and was just above the start of the pitch oscillations. I would have them add a little power and switch to 40 flap and the plane would immediately start the stall buffet and pitch oscillations. Easy recovery from both but 40 flaps resulted in a higher stall speed in my SW. Our new LS has the 35 flap setting and it seems to stall about as consistent with 30 flaps, it's very docile in all flap settings and full flap landings are not a problem as long as you don't flare to high and manage the energy just like in the SW, but it is a little more stable and easier to handle in all aspects of the approach. My students used to dread short field landings in the SW, but show much more confidence in doing them in the LS.

 

2 cents

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Absolutely verified by me. Flaps 40 stall is around 40-41, can do slow flight all day at flaps 30 and 36-37 knots. I also verified airspeed was correct by checking gps groundspeed in two directions. Instructors and examiner wants to know why POH is incorrect. I have no answer.

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As to flaps 40 landings, it's hard to imagine a situation where flaps 40 would be better than 30. Maybe an obstacle on approach that requires a steep decent? Otherwise I'd rather use flaps 30 and a 50 knot approach. There also seems to be a much greater tendency to drop a wing on landing at flaps 40.

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hmmm must check this. Seems to break a rule of good natured handling that implies winding on more of the same does not get you less good stuff so to speak. I mean why would you want to accept a worse stall behaviour - what advantage other than steeper L/D? And if more prone to wing dropping? Seems to me then the compromises are stacked negatively. I dont use 40 unless over the hedge a bit too fast, even then not always. Do I smell a FD SB on the way?

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Looks like 40 flaps is too large a wind brake and results in too much loss in lift in the rear of the wing. 40 flaps is still ok to use, but beware and don't do full stall landings here. One little mistake or issue and you may have a very unhappy landing. I believe 40 flaps is ok to land with just use common since and keep the speed up a little more. It also looks like 30 flaps for the SW is a better choice for the controlled short field landing, offering a little more forgiveness and a little slower speed.

Looks like I'm going to reduce my flap settings to 15, 25, 35

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  • 2 weeks later...

Hi All,

 

I just wanted to clarify some things on this post. It was never mine or anyone else's intension to make this post some kind of an alarmist thread. There is absolutely nothing wrong with a CT using 40 flaps. The whole intention here was to educate myself and anyone else that 40 flaps adds a lot more drag and increases your vertical decent for short field landings. With this increased drag you will loose speed more quickly and need to be managing your energy properly and be close to the ground at round out because speed bleeds quick. I like 40 flaps and have no issues with 40 flaps.

 

This all came about when I personally wanted to know if 40 flaps stalled at a higher speed than 30. I had seen this posted at other places. The whole purpose of this exercise was to file it into the back of my mind so when or if I had to land at next to stall I would truly know what I might expect at 30 verses40 flaps stall speed compared to each and to see if there was any stall speed change so I was mentally ready. I personally use 50 knots on approach and round out low and maintain a very steady hand (no pumping the stick) and all those 40 flap landings are a piece a cake. I know the 30 and 40 flaps can land slower, but this is my personal safety margin. This speed also gives better control with the rudder and stab. using 2600-2800 rpm all the way to the ground is another good technique to make that landing nice, controlled and soft. If you fly too close stall at 30 and 40 the controls are too mushy for my personal taste. Flying in at 45 or less with 30 or 40 flaps can be done, but you are hanging way way out on that proverbial limb if something changes or you make a slight miscalculation. For me I always prefer a way out or a safety margin. I guess this was ingrained in me as a firefighter and being in tight spots a lot or going to an emergency scene where another idiot played it too close and lost.

The one advantage to using 40 flaps for a short field is all the drag to help your vertical descent if necessary, slow you down just a few seconds before touch and on a roll out.

 

 

So bottom line go land and play at 40 flaps it isn't a big deal. Very much like 30 flaps, jut manage your energy and go practice at altitude so you have the facts and what's coming.

 

Sorry to shoot down any alarmist or SB's notices, but everything is good. Go fly.

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Roger, you and I have talked about 40 flap landings and you know that this is my normal landing mode. It has been my extreme good fortune to be able to fly with a "many thousand hour" professional pilot (fixed wing and rotary) who has shown me how 40 flaps can be done. Although I have not unraveled all of the mysteries of it and there are those "oh sh*t" times, this method is working well for me. Not to say 40 flaps 100% of the time because I practice using all flap settings on my CTSW. I'm not sure about the stall speed of 30 being lower than 40 and will have to look into this. Your comments about not flying near stall at any flap setting is a point well taken. A few knots extra margin is good advice. It is a fact if speeds are not maintained and if you aren't ready to actively work with the plane, you can get bitten. On the other hand, when I need to "make" a very short field or bleed off altitude when I've come in too high during final, 40 flaps becomes an asset. This is only one opinion and I realize that there are as many different methods to land as there are members of this forum! The low speed, high drag landing capability of our CT's can be fun and challenging and is a good "tool" to have for those times when one may not have a lot of runway to land on - or maybe no runway at all! For those of you who haven't experienced this, find a good CFI who is comfortable and knowledgeable and give it a try.

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I don't believe there is anything wrong with using 40 flaps, just a few people who do unwise things. Then we all hear about how bad they are because they got bit in the butt. Kind of like anything else in life if you take it to the edge often enough, you need to be able to take the bad as well as good because the odds may catch up.

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i remember when my aunt mary got a new 1963 corvair convertable, she drove with left foot on brake and right foot on gas and used them both at the same time. i was young but i was shocked!

 

30 degrees is normal for me because i glide in without power, it just seems normal.

 

now 40 is like aunt mary driving her corvair, i have the throttle open and those flaps hanging down at the same time. i use a pitch attitude that allows me to depend on engine instead of kinetic energy. the big benifit here is i can subtract the energy the moment i don't want it anymore (close the throttle) where the normal kinetic energy needs to bleed off.

 

FWIW i wonder if weight changes the behavior at 40 much? in england it seems 40 is normal but they do fly lighter as well.

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Charlie Tango, your comment, "the big benifit here is i can subtract the energy the moment i don't want it anymore" sums this up. Exactly. Cut the power when ready to touchdown and the flight stops. If in gusty conditions, just don't forget to keep flying the CT eventhough it's on the runway and get the -6 dialed in as soon as possible!

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I often use 40 on my decent changing back to 30 on the numbers this gives me the best of both ;)

 

Kenny d

 

If that works for you consistently, far be it from me to make you change, but...

 

...as an instructor, I like to see my students stabilized by about 100', if not well before. From that point, flaps should be where you want them, power at idle. Then you're just juggling three balls - height, alignment and lateral placement - as the speed bleeds off.

 

Landing an airplane properly is hard enough, and if one adds configuration changes and/or power changes into the mix, well, its often like that camel with the broken back.

 

Oh, and welcome, by the way!

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ED

 

Here in scotland 250m landings are common !! 40 deg of flaps switchin to 30 lets me clear the trees & get stoped before the fence

 

 

If i can get a strip long enough, 15 deg is great , almost lands it's self (but does take the fun out if it ) :blink:

 

Kenny d

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Kenny d, how about some pictures of those 250m strips? Landing on runways that short, you need the 40 flaps just to get the nose down so you have a good look at where you're going to land! :-) The CTSW and CTLS are capable short field planes yet can cruise at 120kts+ (with the 912 Rotax). That's impressive performance.

 

 

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FastEddie,

 

Your teaching technique, requiring or desiring students to be stabilized and gliding @ 100' makes a lot of sense to me.

 

The pilots in parts of Europe are taking full advantage of the CT's short field capability operating routinely on 300M strips or less.

 

The fact that Ken operates on 250M with approach obstacles shows he is capable of making adjustments closer in that are required for this kind of precession.

 

Stable @ 100' and gliding in would diminish my ability to land on the numbers, in fact many of us CT pilots have learned to approach as though we are playing chicken with the ground. At round out a CT with flaps can run out of energy instantly so we have learned to keep the nose down well under 100' and not round out until you seem to be close to a nose-wheel contact. If your speed is right your round-out and flare can be almost one event.

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At round out a CT with flaps can run out of energy instantly so we have learned to keep the nose down well under 100' and not round out until you seem to be close to a nose-wheel contact. If your speed is right your round-out and flare can be almost one event.

 

That's really the trick. I've estimated that at 50-55 knots, after roundout I have just about 5 seconds of energy. Time it just right and you get a good landing. Early, late or high, not so good. That's with flaps 15 or 30. Flaps 40 seems like only a couple of seconds.

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FastEddie,

 

Your teaching technique, requiring or desiring students to be stabilized and gliding @ 100' makes a lot of sense to me....If your speed is right your round-out and flare can be almost one event.

 

Cool.

 

I see three basic landing styles:

 

1) Fly it on. Good for jets, carrier landings, wheel landings in a tailwheel aircraft. Carry extra speed and just plant it. Not so good for a normal landing in small planes.

 

2) Round out and then flare - what I teach in all the small aircraft I've flown, and how I land, looking for a full stall/stick-all-the-way-back touchdown.

 

3) The "Stall Down" method - which is what I think you're describing. Round out begun early enough that you arrive at the ground stalled. That can result in a REALLY short landing, but can also result in damage (to ego or aircraft) if the timing is just a little off. Probably good for proficient bush pilots, but not so much for most of us most of the time.

 

For those of you who might not have seen it, here's a little video that includes a pretty good "Fast Eddie" landing (you can fast-forward to about 4:20 if you want to avoid a badly skidded turn to final!) :o

 

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...

 

3) The "Stall Down" method - which is what I think you're describing. Round out begun early enough that you arrive at the ground stalled. That can result in a REALLY short landing, but can also result in damage (to ego or aircraft) if the timing is just a little off. Probably good for proficient bush pilots, but not so much for most of us most of the time.

 

 

a fair description but consider the options and the reason.

 

option 1) open throttle - now dependent on engine

option 2) more speed - adds to the problem, the ct runs out of energy very quickly ( with flaps and closed throttle ) you still need your round out very close to the ground with the throttle closed

option 3) less flaps - more normal but less precise and longer landing roll out too.

option 4) fly it on - longer landing roll out, more energy to deal with.

 

better then "stall down" method, think; if flaps and closed throttle stall comes very soon after round out. with flaps i consider a level deck angle a stall attitude, you can't spend much time there at 1.3 Vso.

 

the above landing thinking is specific to the ct and a result of its big speed range, big flap range and big pitch attitude range.

 

my 2cents

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"Stall down" method. In 45 years of flying, never heard it called that. But, I use a version of it frequently. Not when I'm being turned every which way but loose. But, in good conditions, flaps 30 or 40, 50K, throttle closed, flare early and add 200-300 RPM at appropriate time, close throttle on touchdown. I'm not trying to arrive stalled but a little over. The result, for me, is a smooth landing on the mains and a run out of about 500 feet once the wheels touch. With the RPM added you leave yourself some margin for error and the bottom doesn't drop out. With the CTSW you have to concentrate on keeping the nose up after touchdown while keeping the plane on the ground. Too much speed or power or back pressure and you can easily come off the ground a little.

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But, in good conditions, flaps 30 or 40, 50K, throttle closed, flare early and add 200-300 RPM at appropriate time, close throttle on touchdown. I'm not trying to arrive stalled but a little over.

 

Bear in mind, I've never flown a CT*.

 

But as general advice, I would question routinely adding power on landing as SOP.

 

If you feel it helps, be sure to periodically practice some landings with NO power, just to be sure that if you ever had a real engine failure you'd be able to get a decent landing with no power available.

 

Practice that enough to become proficient at it, and you might even find the extra "shot" of power unnecessary. It sure is one less thing to focus on at what can be a very busy time.

 

And every bit of "a little over" the stall speed is extra energy to be dissipated somehow if something goes wrong.

 

But, again, whatever works for you! :)

 

 

*Open invitation and free lodging at our guest house if anyone want to fly into the beautiful N GA mountains (actually Copperhill, TN - 1A3) and treat me to a ride in a CT. I'd also offer to let you try my Sky Arrow for comparison. If those logistics don't work, I should be at Sebring for the Light Sport Expo with my wife, weather permitting.

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Ed,

 

With over 500 CTSW landings now I can do a pretty good job in any configuration. (Having said that my next landing might not be so pretty!!) However, in the configuration stated above I can consistently "squeak" it on almost every time. Whereas with many popular GA airplanes it is hard to screw up a landing, the CTSW requires a little more attention to detail. It's not difficult, maybe different, and unlike several that will practically land themselves, the CTSW requires that the pilot make it happen.

 

I don't understand your point about extra energy being a bad thing - unless you are doing an emergency off field landing. Even then I want the airplane flying, not stalled, until my wheels touch. If you flare early and arrive stalled then you had better be very good as there will be no margin for error. So, I like to float a few feet while I dissipate that energy very close to the runway. Since I can still stop in 500 feet (less with some wind) I am happy with the result.

 

I suspect that, in the end, we are ultimately saying the same or similar things. Just harder to get it out not being in real time.

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I don't understand your point about extra energy being a bad thing...

 

Among other hobbies I ride a BMW motorcycle. There's an acronym: ATGATT - All The Gear, All The Time. The question should always be, "What protective gear would you wear if you KNEW you were going down on today's ride?" IOW, since you never know when you may need gear, wear it all the time.

 

Similarly, "What speed would you like to touch down at if you KNEW that on this landing that the nose gear would collapse due to invisible corrosion?" Or if you KNEW a deer would run out right in front of you? Or if you KNEW a brake would fail on application? As a CFI, you know that inertia increases as the square of velocity increase. A difference of just a few knots can make the difference between grinding to a stop on the runway and cartwheeling, between stopping uneventfully and swerving off the runway.

 

I just try to aim for touchdown at the lowest possible speed, with the stick just hitting the rear stop as the mains touch. I have my student try to do the same. Over a lifetime of flying there just may come a time when one is VERY glad not to be carrying an extra 5 or 10k when things go awry.

 

Caveats:

 

This goes out the window if its really gusty, and I don't know if CT's have handling quirks that make this difficult or undesirable.

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