Optimal landing speed

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LTek1
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Re: Optimal landing speed

Post by LTek1 »

I agree 100% with Colin on carrying some power and flying to the ground with a slight pitch up attitude. I'm 70 over the fence, start my pitch up a bit, then add a touch of power to slow the sink rate. Holding it off the runway and waiting for it to come down just never happens the way it does in a Cessna. The touch of power as the attitude changes really helps keep things docile. I'm working on stabilizing that earlier; while my landings are nice, I feel like I'm doing too much in the last moments to make them so.
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Keith M
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Re: Optimal landing speed

Post by Keith M »

I'm always concerned that if I get dependent on using power to help with the landing, I'll not be able to handle a glide approach should it become necessary. This caution paid off last November when I had an EFATO at 550 ft on runway 28 and was able to put it down on 13 without further incident. Having said that, I've had to rescue more than a few landings by applying a bit of power after the flare to reduce the sink rate, so I must have been concentrating really hard that time!

I'm going to try out Antoine's displaced touchdown point technique, to see if I can reduce my power dependence even more. Do you also do that in gusty conditions, Antoine?
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thefoxx
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Re: Optimal landing speed

Post by thefoxx »

How topical - I have been struggling with similar issues over the past 6 months in my DA20 - I'm sure similar issues between the two.

Thank you everyone for contributing - this is going to help me, and probably many others knowing we're not the only ones with this Diamond Landing Struggle!
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Re: Optimal landing speed

Post by Antoine »

Keith M wrote: I'm going to try out Antoine's displaced touchdown point technique, to see if I can reduce my power dependence even more. Do you also do that in gusty conditions, Antoine?
Funny I just posted this today!

https://youtu.be/Pq0e0REbAlo
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Re: Optimal landing speed

Post by BlueYonder »

Lots of really helpful stuff here. Thanks, all. And I'm glad I'm not the only one having these issues -- sometimes it takes a newbie to say the things a lot of people are already wondering about.

Based on your thoughts, it does sound like the failure point for me is the flare, and what happens after. I am indeed doing that Cessna thing of pulling all the power and waiting for it to settle down; and this may, in fact, be the core problem. I've been carefully instructed to keep the nose pulled way up in the flare, and I often get the stall horn -- and the times I've greased it (there have been a few), that's exactly what it looked and sounded like. But I still get at least some float probably 60% of the time -- and the hard bounce too often follows very soon after, because I lose enough energy in the float to then just fall straight down from a foot or two above the deck.

Next time I'm up (probably Saturday), I'll try two fixes recommended here. One is to keep just a little power in and the speed up over 65ktas all the way to touchdown -- breaking the Cessna habit of pulling power. Keeping the power in should reduce the float problem, and keep me from dropping out. The other is to focus less than I have been on keeping the landing short, and give myself more of the runway until I get the flare worked out perfectly, so it will have plenty of room to settle down under power. (Once I've got the long landing down, I can futz with shortening it back, but for now, I think I may be trying too hard to set it down too soon.)
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Re: Optimal landing speed

Post by Lou »

I found it really hard to transition from a C172 because the sight picture is so different. My instructor emphasized that the eyes are at the far end of the runway. That seemed to help me to start the flare lower. Then, if you have the energy, you can practically feel the cushion underneath, it slowly lets put and you settle nicely, stall horn blowing. If I dont have energy, I basically do a soft field landing on the back of the power curve. Which can also be fun.
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Re: Optimal landing speed

Post by Colin »

By the end I am pretty sure I didn't have a flare that looked like a classic trainer flare. As the plane came into ground effect I changed the angle of attack so that my sink rate slowed and my speed started bleeding off more quickly, but mostly I am pretty flat to the deck.

When I recently did a landing clinic with my multi-engine instructor down at Long Beach he was making the same correction, trying to convince me to push the nose down a little more between the numbers and the thousand foot markers, and trying to keep me from cutting the power completely.

I have a friend who was listening to a new student talk about landings who said, "The plane goes from being a truck, to being a bird, and at the end back to being a truck again. Managing those transitions is one of the hardest things a pilot faces."
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Re: Optimal landing speed

Post by Antoine »

Very curious to hear back from Sara.

I think that Sara did find the issue and it's a simple one. Coming from a high wing AC she probably needs to adjust her "landing picture".

When speed/weight is correct, I believe the DA40 offers a "landing corridor" that makes a perfect power-off gliding greaser. It is narrow, but it is real. The "aiming point" technique I learnt seeks to use this corridor:

1. In short final, aircraft is in landing configuration (flaps LDG, speed 75 max, pitch angle, trimmed, throttled back) and stabilized.
2. Aim for just before the runway (that's the aiming point). Do it as if you had machine guns and the bad guy was there. Keep him in your crosshairs.
3. Adjust pitch to keep the aiming point in place. This will produce an imaginary "glide path".
4. If dropping off path (aiming point slipping above crosshairs) add power bursts very moderately to compensate for wind effects. This has the potential to mess up everything so it has to be very very little. Each power burst will shift your glide path a small distance towards the runway.
5. Speed should have has bled to 65-70 when reaching the aiming point, us pitch to adjust.
At this point (in a DA40) the horn should be talking to you. My best landings were when music started just before crossing runway threshold.
6. Shift aiming point to far end of runway and start a smooth flare to the constant sound of the stall horn.
7. Pull gradually. As AOA increases, more lift and more drag are generated: the aircraft will want to climb and bleed speed. Therefore, the flare should be just enough to let it continue a very slow descent, not climb back, stall and "pancake in". This is the tricky bit. If you are close enough to the runway when you start the flare and manage this, it will settle down very smoothly.
The runway is a giant mattress: the closer you get, the less energy the aircraft bleeds - ground effect. That's why it will float if you have excess energy. Especially so in a low wing aircraft with very low wing loading.

Tips:

Use the wingtip-to-runway sides picture to set your desired image during the flare.
Flare as low as possible. The DA40's nose gear is VERY strong, so you're unlikely to break it if you touch nose first but if you ever do, GO AROUND first and think later.

When you pull on the DA40's stick, your arm's movement along your abdomen will naturally be slightly to the left, causing a bank and possibly a pilot-induced oscillation. Until this becomes a natural, you need to consciously pull straight back. More relevant when higher angles of pitch are reached.

If you flare too high or bounce, either go around or use the throttle to produce a second attempt - on a LONG runway obviously...
A big increase in AOA can help soften the touchdown, for example if you get caught by a gust just while flaring.
Have fun!
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Re: Optimal landing speed

Post by Chris »

BlueYonder wrote:Next time I'm up (probably Saturday), I'll try two fixes recommended here. One is to keep just a little power in and the speed up over 65ktas all the way to touchdown
I would never try to keep speed at 65 ktas all the way to touchdown unless I didn't have flaps down all the way.

I guess I use a some of the techniques already mentioned. Here's the mental model I use. YMMV.
  • 65 ktas over the fence if it's just me, up to 70 ktas if loaded, per Antoine.
  • Aiming point at the runway threshold.
  • Steeper approach angle than in the Cessna
  • Cut power completely well before the flare.
  • Flat and low flare, very different than the technique I would use in a Cessna. Just enough to keep the nose gear off the pavement until the mains hit.
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blsewardjr
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Re: Optimal landing speed

Post by blsewardjr »

My two cents re landings from flying the DA40 for five years after flying C172/182s for fifteen years.

-The sight picture is very different. You have to let the aircraft appear to get much closer to the runway before flaring than in Cessnas. Looking out at a 45 degree angle helps.

-The stick pressure is very different. Compared to a Cessna (except Cardinals), its very easy to over pull. Apply gentle but consistent pressure. That said, it takes some time to change your Cessna muscle memory so be patient with yourself.

-The flare picture is very different. Diamonds are much more like Cirri then Cessnas. It's not flat, but also not nose in the air like Cessnas.

-I prefer higher speeds -- 75 knots on approach, 65-70 over the fence. I find that in my aircraft this results in a better sight picture (nose is further down) and better control. Like you I find when I go slower, even at low weights, I sometimes drop the aircraft in. I know this runs counter to much of the experience of other DA40 drivers, but that is what works for my aircraft. What excess speed does do in all DA40s is create lots of float. Therefore, these are maximum as well as minimum limits. That said, you don't have to fly the aircraft at precisely those numbers, but the "slop" in the numbers is definitely smaller than in a C172.

-If I flare high and/or bounce AND I have lots of runway, I simply freeze or keep gently pulling back the stick AND add a small amount of power (depending on the sink rate) to (re) establish a gentle sink rate with the right flare sight picture. If I'm patient, the aircraft will easily settle down in a good touchdown.

-Finally, for a while an instructor had me add landing (full) flaps while on the BASE leg. While I don't do this as much any more as I've gained experience ,I found it helped stabilize my approaches, which in turn lead to better landings.
Bernie Seward, IR, AGI
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