Flare and Touchdown

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Jim Hardin
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Flare and Touchdown

Postby Jim Hardin » Wed Jun 28, 2017 5:41 am

This is open to all.

At what altitude do you start to flare? - the transition from gliding to slowing to touchdown speed.

As you are slowing, close to runway, where do you look to judge altitude above the runway?

I teach to start flare at less than the height of a first floor window and about the height of a car. Now this is adjusted for airspeed and sink rate at that point.

Looking is divided between over the nose (around the cowling/glareshield as needed) for alignment/drift and the 11 or 1 o-clock position for height. More time spent looking over the nose.

What do you use or teach?

3Dreaming
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Re: Flare and Touchdown

Postby 3Dreaming » Wed Jun 28, 2017 7:52 am

I tend to break down what you are calling flare into round out and flare. Round out is the transition from the glide to flying parallel to the runway. Flare then becomes the gradual application of back pressure slowing the airplane to touch down. For the round out, especially with a new student I start much higher than you. I like to see a nice slow easy transition rather than an abrupt corner. This is how I do it, and it has seemed to work well for my students

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MrMorden
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Re: Flare and Touchdown

Postby MrMorden » Wed Jun 28, 2017 9:12 am

It took me a long time to get the flare height down in my CTSW. I would flare too high and drop it in for a carrier landing. Now I generally wait until after I feel the lift of ground effect, once through that I start to pull the stick back slightly to arrest the sink rate, then continue to work the stick back to minimize the sink rate until the mains touch. This process starts probably at 3-4ft or less. I have likened the round out in my CT to "playing chicken with the ground". YMMV with other aircraft types.

The problem with LSA in general is the low inertia means you need to round out lower than in most other airplanes. Otherwise the airplane runs out of energy at too high above the runway and you can drop in for a "carrier style" landing, which is hard on the gear. Ultralights have the same problem but even worse, watch them land and you'll see them round out just a foot or two above the ground.

Here's a video that might help, it shows a pretty typical landing in my CTSW, starting at about 2:30 in the video. You can see there is not really a "flare" per se, more like a level out and then just continuously increasing back pressure to minimize the sink rate:
Andy Walker
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA

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FastEddieB
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Re: Flare and Touchdown

Postby FastEddieB » Wed Jun 28, 2017 6:54 pm

I recall the rule of thumb was one wingspan above the ground.

Which, probably not coincidentally, is also about where ground effect begins.

That rule makes allowances for beginning the round out and flare higher in bigger planes.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
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Merlinspop
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Re: Flare and Touchdown

Postby Merlinspop » Thu Jun 29, 2017 8:26 am

Give this a quick watch. Maybe it'll help.

https://www.youtube.com/watch?v=Rv5HEJCyTuk
- Bruce

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MrMorden
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Re: Flare and Touchdown

Postby MrMorden » Thu Jun 29, 2017 9:40 am

FastEddieB wrote:I recall the rule of thumb was one wingspan above the ground.

Which, probably not coincidentally, is also about where ground effect begins.

That rule makes allowances for beginning the round out and flare higher in bigger planes.


Eddie, I think that is probably a good rule for most (heavier) airplanes, but in my experience it's a bit off for LSA. My CTSW has a wingspan of 28ft. If I come in to land power off and start a round out at 28ft above the ground, I will either have to add a lot of power, or buy new landing gear. :D I really need to wait until I'm past the little lift bump that marks ground effect to start the landing sequence, maybe half a wingspan or even less. The Tecnam I trained in was the same way. I'm not sure how it works in your Sky Arrow.
Andy Walker
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA

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dstclair
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Re: Flare and Touchdown

Postby dstclair » Thu Jun 29, 2017 10:01 am

Eddie -- I thought ground effect rule-of-thumb was within 1/2 the wingspan, although it is actually continuous from around 1 full wingspan down to the ground (http://www.faatest.com/books/flt/chapte ... effect.htm):
When the wing is at a height equal to its span, the reduction in induced drag is only 1.4 percent. However, when the wing is at a height equal to one-fourth its span, the reduction in induced drag is 23.5 percent and, when the wing is at a height equal to one-tenth its span, the reduction in induced drag is 47.6 percent. Thus, a large reduction in induced drag will take place only when the wing is very close to the ground. Because of this variation, ground effect is most usually recognized during the liftoff for takeoff or just prior to touchdown when landing.


I guess technically one wingspan would be correct but I don't think we'll notice a 1.4% decrease in drag.
dave

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Re: Flare and Touchdown

Postby 3Dreaming » Thu Jun 29, 2017 1:07 pm

MrMorden wrote:
FastEddieB wrote:I recall the rule of thumb was one wingspan above the ground.

Which, probably not coincidentally, is also about where ground effect begins.

That rule makes allowances for beginning the round out and flare higher in bigger planes.


Eddie, I think that is probably a good rule for most (heavier) airplanes, but in my experience it's a bit off for LSA. My CTSW has a wingspan of 28ft. If I come in to land power off and start a round out at 28ft above the ground, I will either have to add a lot of power, or buy new landing gear. :D I really need to wait until I'm past the little lift bump that marks ground effect to start the landing sequence, maybe half a wingspan or even less. The Tecnam I trained in was the same way. I'm not sure how it works in your Sky Arrow.


Andy, I start at least that high in my CT without problems. it is just a more gradual pull to arrive at the same spot where you are rounding out. As a side note I have been flying airplanes lighter than the CT for over 30 years, and have never felt a need to wait until 3 or 4 feet to round out.

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MrMorden
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Re: Flare and Touchdown

Postby MrMorden » Thu Jun 29, 2017 1:21 pm

3Dreaming wrote:Andy, I start at least that high in my CT without problems. it is just a more gradual pull to arrive at the same spot where you are rounding out. As a side note I have been flying airplanes lighter than the CT for over 30 years, and have never felt a need to wait until 3 or 4 feet to round out.


I'm not saying my way is the right way, and obviously if you start your back stick slowly enough, you can begin sooner. Everybody has their own technique. If you watch my nosewheel in the video I posted above, you can see it at a constant attitude in relation to the runway until pretty late in the sequence, it looks like no more than 5-10ft or so, and certainly not 28ft. The attitude change looks smooth and gradual to me, I can't see how you'd do it much slower than that.

Do you land with power on or power off? What type of airplane?
Andy Walker
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA

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Jim Hardin
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Re: Flare and Touchdown

Postby Jim Hardin » Thu Jun 29, 2017 1:44 pm

Interesting comments/examples, and no 'wrong answers' here.

I think local conditions are a factor as well. The lose of headwind due to wind gradient or flying into 'tailwind side of a runway thermal scrambles the best laid scheme of things...

One mentioned power. I prefer to have it at idle when we get there but if set higher, a smooth reduction to idle is used.

Anyone ever flare using the altimeter? ~ think night water landings :D

3Dreaming
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Re: Flare and Touchdown

Postby 3Dreaming » Thu Jun 29, 2017 4:19 pm

MrMorden wrote:
3Dreaming wrote:Andy, I start at least that high in my CT without problems. it is just a more gradual pull to arrive at the same spot where you are rounding out. As a side note I have been flying airplanes lighter than the CT for over 30 years, and have never felt a need to wait until 3 or 4 feet to round out.


I'm not saying my way is the right way, and obviously if you start your back stick slowly enough, you can begin sooner. Everybody has their own technique. If you watch my nosewheel in the video I posted above, you can see it at a constant attitude in relation to the runway until pretty late in the sequence, it looks like no more than 5-10ft or so, and certainly not 28ft. The attitude change looks smooth and gradual to me, I can't see how you'd do it much slower than that.

Do you land with power on or power off? What type of airplane?


Andy, it is really hard to tell anything from the video. From what I could tell the landing looked fine. What I didn't see was diving at the runway and playing chicken. I have seen people who fly at the runway and the make and abrupt pitch change a few feet above the runway. This is what I envisioned from your description. I would bet you start to add some back pressure to the stick higher above the ground than you think. When we are talking about one wingspan, that is when back pressure is started, not where you level off above the runway. If you are flying a slower approach speed the pitch change from the glide to parallel above the runway will have to happen much quicker, but I still start about the same time.

I mostly land power at idle. Flight Design CTSW, CTLS, MC, Tecnam P2008, Savanah, Taylorcraft, Piper Cub, Aeronca Champ, and Luscombe off the top of my head.

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FastEddieB
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Re: Flare and Touchdown

Postby FastEddieB » Thu Jun 29, 2017 5:46 pm

Good points raised by all.

Yes, ground effect is said to begin at one wingspan above the ground. And it increases at a nonlinear rate. Adding to the mix is the position of the wing - high or low - which will affect how soon ground effect becomes an issue from the pilot's perspective.

But I still think one wingspan is a good starting point, not a hard-and-fast rule. With experience, I don't think most pilots think about it a lot, it just comes naturally. But beginners and struggling pilots do need some guideline.

I looked at a couple videos to see if I could pin down where I begin the roundout. The only one taken from outside the plane made it look like I wait later, more in line with Andy's habit. But from an in-cockpit view, it appears my airspeed starts subtly decreasing from about the one-wingspan height as I ease down into ground effect.

Of course, the key is in a middle ground. Start the roundout too high, and you can end up with too little airspeed at the end if you don't manage the slowdown properly. But just as bad is to wait too long and "swooping" into ground effect with a lot of excess speed - and energy. This is especially a problem with low wings, which can seemingly float forever if too fast in ground effect. Which leads to all sorts of problems - overshoots and porpoising high on the list.
Fast Eddie B.

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foresterpoole
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Re: Flare and Touchdown

Postby foresterpoole » Tue Jul 11, 2017 1:04 pm

Given I have not been flying as long as most on this board and then only as a student, but I think it greatly depends on the aircraft. In the Technam I fly (P92 Super Echo) I round out 5-10 feet above the runway and let it come down slowly with a (seemingly based on sight picture) slight flare in to keep it on the mains, it almost flies onto the runway. Now the Cessna 172SP I an flying now is a whole other story I have learned. Round out is higher, the flair is more pronounced and the sight picture is extremely nose high in relationship to to the P92 (the instructor finally said just try a soft-field to get me to pick the nose up enough and not bounce it). I think this is due to where my head is in the aircraft, in the Tecnam I'm sitting much higher (in the wing root) than the Cessna (barely can see over the dash, yea I'm short). I also find that the gear on the Technam is more firm and does not like to bounce, than Cessna might as well feel like a bouncy house to me, it really wants to spring back up in the air. Just my 2 cents, I'm sure someone will disagree or have a different take on it...
Ed

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Re: Flare and Touchdown

Postby Merlinspop » Tue Jul 11, 2017 2:03 pm

I used to go out to a park off the departure end of the main runway at National (KDCA). Watching the airliners' wheels, they seemed to track a straight path all the way to what looked like inches before touchdown. It was the nose that rose (well, stopped descending as the mains 'passed' the nose on the horizontal plane) in the flare. Light GA planes seem to make more of a visual "swoop".
- Bruce

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Jim Hardin
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Re: Flare and Touchdown

Postby Jim Hardin » Mon Jul 17, 2017 6:35 am

Merlinspop wrote:I used to go out to a park off the departure end of the main runway at National (KDCA). Watching the airliners' wheels, they seemed to track a straight path all the way to what looked like inches before touchdown. It was the nose that rose (well, stopped descending as the mains 'passed' the nose on the horizontal plane) in the flare. Light GA planes seem to make more of a visual "swoop".


Completely different set of circumstances. The inertia of the weight as well as the speed vs runway length.

Heavy aircraft can have a landing weight of 274,000 lbs (747) to say 27,000 lbs (Cessna Citation). Those wights do not react to changes in pitch very quickly. In fact somewhere between 50 and 100 feet above touchdown elevation, an airliner cannot make a go around without hitting the runway.

Likewise brakes come into the picture. Not a wheel brake made that will work in the air. The drill is to get the brakes on the ground where they can be used, including nosewheel brakes. Interesting that the length of time spent in reverse thrust is far less on a long runway than a short one.

But your observations are interesting! As a kid we used to go to MKC (Kansas City Downtown) and watch the airliners take off and land. You could park and climb up the levees to be closer (no fences then). As the jets came into commercial service, the local paper would publish the takeoff and landing times for the 707's and DC 8's. Probably 100 or more people would be sitting on the levees at both ends of the runway.

Prior to 911, used to often land at DCA on the weekends and catch the subway over to the Mall. I miss those lunches on the Mall as well as Smithsonian visits...


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