A teachable moment

[FastEddieB]

Roger Lee just posted this YouTube video to a thread in another forum, which I've bookmarked as a "Favorite".

https://youtu.be/BUjLfjhZYZQ

We have hashed out appropriate landing speeds ad nauseum, so this is not meant to convince anybody of anything, but to point out to students what I think is an important lesson.

Every Sport Pilot and Private Pilot had to demonstrate a landing at approximately stall speed on his or her checkride. I was taught to use maximum flaps as consistent with conditions. That has held me in good stead for many decades, though I realize it makes some pilots uncomfortable, and may not be appropriate in all planes.

Which leads one to ponder, how did it come about that the pilot in the video came to land in the manner he did? It sure looks to me like minimal flaps were used, and to be generous the landing looked to be at least 10 kts fast.

How much energy is implied by an extra 10 kts? Step by step, assuming a full flap stall speed of 40 kts...

1) Divide the smaller number (40) into the larger number (50). The result is 1.25.

2) That means 50 is 1.25 times larger than 40, or 25%.

But kintic energy increases as the square of that increase, so...

3) Square 1.25, or just multiply it by itself. The result is 1.5625

4) Expressed as a percentage, the plane landing at 50 kts has just over 56% more energy to dissipate after touchdown. Has to go somewhere, and you can see how some of it got dissipated in the video.

As I said, I think assuming 50 kt touchdown speed in the above video is quite conservative. As an exercise, maybe compute the numbers as above for 55 or even 60 kts. Or at the other extreme, at just 45 kts. All assuming a full flap stall speed of 40 kts.

I am not going to go back and forth with the "fly it on" crowd - we're all adults and can land in any manner and at any speed we choose to. But as the thread title says, I just did not want a teachable moment to slip away.

[Merlinspop]

Too bad the other person was perfectly in the way and the person shooting the video moved the camera.

I agree with the point of your post. Land at the minimum controllable airspeed for the current conditions, is what I was taught.

[Half Fast]

Point well taken, Eddie.

You realize, of course, that the same kinetic energy argument applies to motorcycle cornering speeds...?

[HAPPYDAN]

Looks like he should have used a combination of soft field and short field landing techniques. Nose wheel dug in (heavy braking?) when he veered off the runway.

[FastEddieB]

Looks like he should have used a combination of soft field and short field landing techniques. Nose wheel dug in (heavy braking?) when he veered off the runway.

There's a thread on this over on CTFlier.com.

Apparently field was 2,500' long, albeit crowned and narrow.

Short field technique was hardly necessary in a Light Sport, but never a bad idea regardless.

[3Dreaming]

A normal, full flap landing would have been appropriate.

I really don't want to be contradictive, but that is not what Flight Design calls for. Per Flight Design a normal landing is made with 15° flaps, not full flaps.

I'm not sure what flap setting he used or the wind conditions, but he certainly carried to much energy into the landing.

[3Dreaming]

A normal, full flap landing would have been appropriate.

I really don't want to be contradictive, but that is not what Flight Design calls for. Per Flight Design a normal landing is made with 15° flaps, not full flaps.

I'm not sure what flap setting he used or the wind conditions, but he certainly carried to much energy into the landing.

On that runway, I would have probably used a full-flap landing. I've never flown a Flight Design, so I might change my mind if I had.

The runway was plenty long. According to the CTLS AOI the airplane will land as slow with 15° flaps as it does with full flaps. They also caution that full flaps should only be used for very short runways (less than 1,000 feet), and only under the best of conditions. The reason for this is that the ailerons are interconnected to the flaps via a mixer, so when you apply flaps the ailerons also droop. If there is any significant cross wind you should only use 15° flaps, because of the increased drag and increased AoA due to the lowered aileron on the downwind side of the airplane.

[CharlieTango]

A normal, full flap landing would have been appropriate.

I really don't want to be contradictive, but that is not what Flight Design calls for. Per Flight Design a normal landing is made with 15° flaps, not full flaps.

I'm not sure what flap setting he used or the wind conditions, but he certainly carried to much energy into the landing.

Not true. Full flaps were called for here, 30* for the less experienced, looks like he used zero.

Here's what his POH says on normal landings.

[CharlieTango]

The runway was plenty long. According to the CTLS AOI the airplane will land as slow with 15° flaps as it does with full flaps. They also caution that full flaps should only be used for very short runways (less than 1,000 feet), and only under the best of conditions. The reason for this is that the ailerons are interconnected to the flaps via a mixer, so when you apply flaps the ailerons also droop. If there is any significant cross wind you should only use 15° flaps, because of the increased drag and increased AoA due to the lowered aileron on the downwind side of the airplane.

The plane in the video was a CTSW. It too has flaperons. I have been landing mine for 10 years with full flaps.

If the CTLS can land as slow with 15* as full flaps you can't tell this by watching. What the plane can do and how pilots fly them are 2 different things. Pilots that land CTs with full flaps land slower than those that use 15*. Most CT pilots that use 15* don't come close to minimum speed landings.

[FastEddieB]

Of the 80+ airplanes I have flown, that would be full flaps, except the ones that had no flaps.

I actually pored through all my logbooks (7!), and only came up with about 50.

But I agree, in spite of my newbie status!

But I think we've established the CT is an odd duck, with effective flaps it seems like most avoid using most of the time.

[3Dreaming]

The runway was plenty long. According to the CTLS AOI the airplane will land as slow with 15° flaps as it does with full flaps. They also caution that full flaps should only be used for very short runways (less than 1,000 feet), and only under the best of conditions. The reason for this is that the ailerons are interconnected to the flaps via a mixer, so when you apply flaps the ailerons also droop. If there is any significant cross wind you should only use 15° flaps, because of the increased drag and increased AoA due to the lowered aileron on the downwind side of the airplane.

The plane in the video was a CTSW. It too has flaperons. I have been landing mine for 10 years with full flaps.

If the CTLS can land as slow with 15* as full flaps you can't tell this by watching. What the plane can do and how pilots fly them are 2 different things. Pilots that land CTs with full flaps land slower than those that use 15*. Most CT pilots that use 15* don't come close to minimum speed landings.

I know that it was a CTSW. I was part of the CT community when that happened. IMO it played a role in the split to the new forum. In my close to 10,000 hours flying time about 1,000 is in CT's, 400 in SW's, 600 in LS's, and even a little time in the MC. In 2008 when the CTLS was introduced, because I was CFI and Flight Design dealer I was part of the round table discussions during the dealer meetings at Sebring. This is the group that developed the training syllabus for transitioning to a CT. We also talked about the wind tunnel test for the CTSW that led to some of the changes on the LS. There was considerable talk about the use of flaps on landing, plus the flaperons. All of this led to the changes in the CTLS AOI. There was also a push to have the CTSW manual updated, but it did not happen.

The fact that a pilot doesn't land as slowly with 15° flaps as with full flaps doesn't mean the airplane can't do it. I teach my students to land nose high and close to stall speed with 15° flaps as the norm. Most of the pilots who use full flaps already are trying to land as slow as possible. and would do the same with 15°. The simple fact is you can't force the airplane on the ground like he tried to do. It doesn't work with 0° or 15° flaps, and it would be worse with full flaps.

[3Dreaming]

Not true. Full flaps were called for here, 30* for the less experienced, looks like he used zero.

Here's what his POH says on normal landings.

What the manual says is "Flaps as desired, 40° for short runways". I don't consider 2,500 to be a short runway. So per the manual any setting between 0° and 40° could be used. I will say that I wouldn't have used 0° flaps. I also wouldn't have tried to force the airplane on the ground like he did. IMO the landing could have been made with less than full flaps without any issue, and the use of flaps would not have helped if he tried to force the airplane onto the ground in the same manner.

[FastEddieB]

Interesting.

It does seem that from 30° to 40° would make little difference, with both recommending 62 kcas for the approach speed, indicating not much change in stall speed. Still, the extra drag from 40° would have to help at least a little.

But the difference from 15° to 30° is huge, with an 18 kcas difference in approach speed. That would make an equally huge difference in landing energy and, of course, distance.

I'm not a CT pilot, but my hunch is if I were, like Ed I'd perfect my full flap landings, and use them whenever conditions permitted, if only for practice for when they might be needed "in anger".

[MrMorden]

I have about 600 landings in my CTSW. I have very rarely used full flaps, which is 40°. But I very often use the 30° setting. It's easier to land that way, the speeds are within a knot or two in the two settings, and the flaperons give much better roll control at 30° than at 40°. At 30° I use a speed of 48-50kt on short final when solo, 55kt with a passenger.

Any setting above 15° is a bit of a handful in gusty winds over 8kt or crosswinds of the same amount. I prefer 30° in calm winds and 15° when the winds are up. The airplane is much easier to land at 15°, and likely a lot of pilots are a bit fearful of the higher flap settings. I know I was at first, and I really got my landings down before "graduating" to higher settings.

2500ft is not short for a CTSW (I have landed on 1500ft strips), but if you carry too much speed, you will float a long way, or you set it down with too much speed. The latter looks like the case here. On a soft sandy strip with an uneven surface, you really need to be using the higher flap settings to make a gentle, slow landing. The landing itself didn't bite the pilot here, the higher speed roll out on the soft, even ground got him. Panic braking and a lack of steering control played in too.

[3Dreaming]

Interesting.

It does seem that from 30° to 40° would make little difference, with both recommending 62 kcas for the approach speed, indicating not much change in stall speed. Still, the extra drag from 40° would have to help at least a little.

But the difference from 15° to 30° is huge, with an 18 kcas difference in approach speed. That would make an equally huge difference in landing energy and, of course, distance.

I'm not a CT pilot, but my hunch is if I were, like Ed I'd perfect my full flap landings, and use them whenever conditions permitted, if only for practice for when they might be needed "in anger".

Those are flap extended speeds. Stall speed with 40° flaps is listed as 39kts, and with 0° flaps at 42kts. They don't specifically list a number for 15°, but it is closer to the 39 than the 42.
In the CTLS adding full flaps pitches the airplane very nose down, and they do add drag. However the glide path does not seem to change significantly. With exception to the nose down pitching, it is more like full flaps in a Cherokee compared to full flaps in a old Cessna 172. One thing for certain is during the round out and flare the airplane will lose its energy more quickly. If you are not spot on you altitude above the runway you will drop it in. It doesn't provide that little bit of extra cushion for a mistake that 15° flaps provides.