Ground Effect Feeling

[Vas]

Silly question I was hoping y'all could help me with. I think I'm getting different feelings on the flight controls confused when trying to land. People talk about ground effect all the time, but what does it actually feel like? Can you feel it on the controls, do they get mushier like in a stall? Does the plane just feel lighter?

Also, any of your pro tips on stable approaches are appreciated, though that is more easily found by searching the board

Thank you!

 

[PaulS]

Can't feel it on the controls, but if you get into it going too fast when landing, you will float down the runway. It's important to understand what is going on, to make sure you have enough runway or you initiate a go around. And it's very important not to try to force the airplane on the ground as that is a big cause of bounces which turn into porpoises which turn into prop strikes in small planes..... very quickly.

It also can bite you if you don't pay attention to weight and balance and/or density altitude. If your airplane is being adversely affected by these things, ground effect will get your wheels off the ground just high enough to get yourself killed when you realize that the airplane can't climb any higher.

Also keep in mind that the controls feel different at different airspeeds, especially as you slow down in the flare to land. It is one of the things you should have experienced when practicing stalls and slow flight.

Good questions, others will chime in, but the last word on this stuff should be your instructor.

 

[Timbeck2]

It feels like “why isn’t it landing yet?”

 

[dmspilot]

Ground effect refers to reduced drag and increased lift that occurs due to interference of the ground with airflow around the wing. It is most apparent when the aircraft is at a height above the surface of less than half its wingspan.

 

[Domenick]

Accurate or not, I think of ground effect as a pressure wave building under the wings due to AOA and ground proximity. Similar to skimming your angled hand across the surface of water. I can't say I really feel it, though sometimes it seems the plane kind of round outs on its own. The controls are mushy during landing anyway due to flying close to stall speed.

The earlier comments speak to the major effect--floating.

 

[Jim K]

Not a silly question; with regards to "feeling it", it took me a while, too. Eventually you'll notice that without moving the controls, your descent rate slows when you're about 20-30 above the ground. I say it's like dropping something onto a pillow as opposed to dropping it onto the floor. It still hits the ground, but a little softer. With experience you'll be able to see it/ feel it "in the seat of your pants". The controls don't feel any different...that's dependent on airspeed, just the plane feels like it suddenly got much lighter and doesn't want to stop flying.

The thing that helped me most with learning landings is to set the correct airspeed using pitch and trim, then adjust the glideslope using power.

 

[Daleandee]

For me ground effect is where the thermals dissipate and the winds become a bit more predictable. Or so it seems!

 

[eman1200]

for both.........you'll know it when you see it and feel it. this will just come with practice and help from your CFI. for a stabilized approach, there are specific things needed to make it happen but you'll also just know it when it looks and feels right.

 

[Huckster79]

Yup just keep practicing landing at the right airspeed and the feel for using it will come. And the above folks are right you will really “feel” it when ya come in hot and the plane just floats and floats and floats…

 

[Dan Thomas]

Yup just keep practicing landing at the right airspeed and the feel for using it will come. And the above folks are right you will really “feel” it when ya come in hot and the plane just floats and floats and floats…

That's why proper landing technique involves getting the power back and raising the nose while still at 15 to 30 feet above the ground, to get rid of that extra speed. And that's if you're approaching at the right speed, usually 1.3 Vso. Too many pilots are approaching much faster than that, and then they don't flare until they get within three feet of the runway, and either float or they force it on and porpoise or wheelbarrow or something. Floating in ground effect is not a thing if things are done right.

 

[Tools]

Seems to create a pitching moment as well. I trimmed a plane hands off one night and let her ride all the way to the runway... As we entered ground effect, got a pronounced nose down pitch I may not have otherwise noticed if I were actually hanging on to the controls.

Don’t worry guys, it was a carrier jet perfectly suited for this type of experiment!

 

[Huckster79]

That's why proper landing technique involves getting the power back and raising the nose while still at 15 to 30 feet above the ground, to get rid of that extra speed. And that's if you're approaching at the right speed, usually 1.3 Vso. Too many pilots are approaching much faster than that, and then they don't flare until they get within three feet of the runway, and either float or they force it on and porpoise or wheelbarrow or something. Floating in ground effect is not a thing if things are done right.

absolutely! I know I was guilty of that in my early days. Tailwheel has taught me to fly be feel and my last airspeed check is probably about where you say to start that round out or a bit before- and so I have no doubt I’m likely decelerating a fair amount that last 10-20ft. I know since learning that she doesn’t float anymore!

it sure seems to be a very natural bad habit of pilots as many do and most have at some point in their learning.

 

[FastEddieB]

This is from Bill Kershner:

The upper has the plane maintaining approach speed into ground effect, where speed is then bled off in the flare. You can see how long the plane is “floating” in ground effect.

In the lower, the plane starts gradually bleeding off speed about one wingspan above the ground. I call this the “roundout” phase. As such, it arrives in ground effect with very little speed remaining and hence, little “float. It’s how I land and how I taught my students to land.

Here’s an example with two landings, one grass and one paved. My stall speed is about 39 kts IAS. 55 kts is my typical approach speed, but you can see I let it bleed off to maybe 45 kts as I enter ground effect, for very little float and touchdown right about at stall speed. You can watch the airspeed, panel upper left. I landed my Cirrus the same way, albeit at higher speeds.

 

[Clip4]

Silly question I was hoping y'all could help me with. I think I'm getting different feelings on the flight controls confused when trying to land. People talk about ground effect all the time, but what does it actually feel like? Can you feel it on the controls, do they get mushier like in a stall? Does the plane just feel lighter?

Also, any of your pro tips on stable approaches are appreciated, though that is more easily found by searching the board

Thank you!

Once you prefect your landings, you are going to be introduced to soft field takeoffs and landings where you will gain more understanding of ground effect.

For now just understand that you are getting a drag reduction close to the runway when the aircraft has to continue to slow to land. During this process your flight controls become less effective, especially the elevator, and you have to increase control inputs as the aircraft slows. The increased control inputs keep the plane at the same pitch attitude and properly aligned with the runway.

 

[Domenick]

1.3x times stall speed is slower than you think.

Practice your slow flight. If you are carrying too much airspeed into the flare, practice your slow speed in the landing configuration at altitude. If you experience and note how slow you can actually fly the plane, you will have more confidence close to the ground.

If your POH states a 63 kts approach speed, and you know the plane will fly well at 58 kts and stalls at 45 kts, you will feel comfortable passing over the fence at 58 kts.

 

[dmspilot]

This is from Bill Kershner:

The upper has the plane maintaining approach speed into ground effect, where speed is then bled off in the flare. You can see how long the plane is “floating” in ground effect.

In the lower, the plane starts gradually bleeding off speed about one wingspan above the ground. I call this the “roundout” phase. As such, it arrives in ground effect with very little speed remaining and hence, little “float. I

They both touch down at the same point and Kershner says they are different techniques for landing, not that one is proper and one is improper.

 

[Dan Thomas]

They both touch down at the same point and Kershner says they are different techniques for landing, not that one is proper and one is improper.

I was an instructor and can tell you that the float in the first picture will be much worse than shown, and more runway will be used up. If one wants to get proficient enough to go to shorter strips he had better get used to doing it as per the second picture.

The first technique usually ends in a flat, fast touchdown. That does the tires and brakes no good, and it beats up the expensive nosegear stuff. As an instructor I taught my students to do it right, since as a mechanic I got to fix all that damage. Spending time and money on that just results in increased costs for the student, and more downtime for the airplane, slowing the student progress.

Many GA airplanes don't float that much, especially high-wing aircraft and shorter-winged of any sort. You go get into an old Champ or Cub or 140 and find out what float really does with your carelessness. The Taylorcraft was a legendary floater. It could easily eat up three thousand feet on a warm day on pavement if you were too fast.

 

[David Megginson]

Silly question I was hoping y'all could help me with. I think I'm getting different feelings on the flight controls confused when trying to land. People talk about ground effect all the time, but what does it actually feel like? Can you feel it on the controls, do they get mushier like in a stall? Does the plane just feel lighter?

Also, any of your pro tips on stable approaches are appreciated, though that is more easily found by searching the board

Thank you!

You'll experience ground effect as an unwillingness of the wheels to settle down if you come in with too much airspeed. If you push the nosewheel down to try to force the airplane onto the runway, very bad things will happen, so don't do that.

 

[FastEddieB]

They both touch down at the same point and Kershner says they are different techniques for landing, not that one is proper and one is improper.

I did not mean to imply that one is proper and one is improper. Just that I prefer the bottom one, both for myself and my students. Zooming into ground effect at approach speed, prolonging the float, seems to lead to more problems with too fast landings, and porpoising, compared to beginning the flare at a speed just a few knots over stall speed.

But there’s no right or wrong, so do what works best for you.

 

[Daleandee]

You'll experience ground effect as an unwillingness of the wheels to settle down if you come in with too much airspeed.

If you want to watch a float fest then this is the video for you:

Hard not to continually yell at the screen, GO AROUND!!!

 

[saddletramp]

Forward stick would have stopped that circus. Too often pilots are afraid of forward stick fearing they'll hit the prop. Biplanes produce a lot of lift.

 

[Dan Thomas]

Forward stick would have stopped that circus. Too often pilots are afraid of forward stick fearing they'll hit the prop. Biplanes produce a lot of lift.

He probably never got any wheel-landing training. So he's trying to do a three-point with way too much speed and it ain't gonna work. Never does. Some people never got the teaching about angle of attack being related to attitude being related to airspeed. They somehow think the airplane should get to the proper landing attitude even if it's too fast.

And he was too far down the runway with all that speed for any forward stick to save it. He'd have to clamp the brakes on with the tail up, modulating the elevator against the brakes, a technique way beyond most taildragger pilots.

 

[Daleandee]

Forward stick would have stopped that circus. Too often pilots are afraid of forward stick fearing they'll hit the prop. Biplanes produce a lot of lift.

It does appear that several times some forward stick would have planted the mains. But Dan makes a great point in that the pilot is too fast and apparently asleep at the stick.

 

[Albany Tom]

Ok, those two videos were tough to watch. The Archer - from what I can tell, that wasn't landing, it was flying the plane down to the runway. Being way too fast is bad, being way too fast, and low, is worse and sillier. The biplane - It looked like he was coming in just fine, and for whatever reason added power, and then reduced power, then added power again. If you're going to land, land. If you're going to go around, go around. You can do the add power thing maybe once, after that, just go around. Both sad.

There's a reason why people use 1.3 stall for final approach, on a good approach angle, and slower on short final. Eventually, you should be able to judge speed by feel, but while you're learning I'd suggest talking w/ your CFI and having a max speed for short final, and if you're over that, go around.

 

[David Megginson]

Many GA airplanes don't float that much, especially high-wing aircraft and shorter-winged of any sort.

True — the wing loading isn't all that different on most utility GA piston planes.

That said, it's all about airspeed — any plane will float for ever if you bring it in too fast, or will drop the last few feet onto the runway hard if you run out of airspeed too soon.

In the Piper community, there are old and enduring myths that the Hershey Bar wing drops while the semi-tapered (Warrior) wing floats, but I suspect it's 99% due to pilots flying the same approach speeds in knots on the 161, 181, etc that they flew in mph on the 140 or 180. If you add 15% to your approach speed, no surprise that you'll float (and float, and float, and …).

 

[dmspilot]

In the Piper community, there are old and enduring myths that the Hershey Bar wing drops while the semi-tapered (Warrior) wing floats, but I suspect it's 99% due to pilots flying the same approach speeds in knots on the 161, 181, etc that they flew in mph on the 140 or 180. If you add 15% to your approach speed, no surprise that you'll float (and float, and float, and …).

The semi-tapered wing has a substantially longer span so ground effect starts at a higher altitude.

 

[Capt. Geoffrey Thorpe]

He probably never got any wheel-landing training.

Or was taught that wheel landings are "bad" and "never use the brakes".

Or, was just asleep at the switch.

 

[David Megginson]

The semi-tapered wing has a substantially longer span so ground effect starts at a higher altitude.

Slightly, but about the same mean chord. The primary handling difference in the longer wing is better aileron effectiveness in slow flight (that's why Piper introduced it), but fans/critics of both shapes have let their imaginations run wild ever since, as you'll see in any Piper-wing debate.

I've owned a PA-28-161 for 19 years, and it doesn't float at all when you bring it in at the correct speed (adjusted for weight). There's rarely any problem making the first turnoff 1,000 ft down the runway at my home airport, often without touching the brakes.

If I bring my 161 over the fence at 70–75 KIAS, of course it will float halfway down the runway, especially if the winds are light and I'm a few hundred pounds under gross. If I bring a lightly-loaded 160 or 180 with the Hershey Bar wing over the fence at 80–85 mph in light winds, it will use up a lot of the runway too.

 

[dmspilot]

Slightly, but about the same mean chord. The primary handling difference in the longer wing is better aileron effectiveness in slow flight (that's why Piper introduced it), but fans/critics of both shapes have let their imaginations run wild ever since, as you'll see in any Piper-wing debate.

I've owned a PA-28-161 for 19 years, and it doesn't float at all when you bring it in at the correct speed (adjusted for weight). There's rarely any problem making the first turnoff 1,000 ft down the runway at my home airport, often without touching the brakes.

If I bring my 161 over the fence at 70–75 KIAS, of course it will float halfway down the runway, especially if the winds are light and I'm a few hundred pounds under gross. If I bring a lightly-loaded 160 or 180 with the Hershey Bar wing over the fence at 80–85 mph in light winds, it will use up a lot of the runway too.

Here is an analysis by someone much smarter than myself:
https://charles-oneill.com/blog/cherokee-tapered-wing-float/

The conclusion is that, "reports that the tapered wing Piper Cherokee PA-28 floats more than the constant chord wings are completely substantiated with the engineering and physics analysis."

I am sure that you are correct that with the proper technique, the tapered wing variety can be landed in an adequately short distance without excess float.

 

[Dan Thomas]

The semi-tapered wing has a substantially longer span so ground effect starts at a higher altitude.

It also had a totally different airfoil along with the tapered section. That will influence behavior considerably.

 

[David Megginson]

Here is an analysis by someone much smarter than myself:
https://charles-oneill.com/blog/cherokee-tapered-wing-float/

The conclusion is that, "reports that the tapered wing Piper Cherokee PA-28 floats more than the constant chord wings are completely substantiated with the engineering and physics analysis."

I am sure that you are correct that with the proper technique, the tapered wing variety can be landed in an adequately short distance without excess float.

Thanks for sharing that — it was an interesting read. It's important to bear in mind that it's not a scientific analysis but just an informed hypothesis by a scientist, and that it's looking at the wing as an idealised abstraction.

Here's one example: he notes that the semi-tapered wing on the PA-28-161 has 6% more surface area than the rectangular wing on the PA-28-181, but then doesn't mention than a fully-loaded -181 is 150 lb heavier than an early -180. Piper also streched the fuselage of later PA-28 models slightly.

The question we care about as pilots isn't the idealised abstract wing numbers, but how the actual Pipers with those wings attach perform. After extensive flight testing with the new wing, Piper did not increase the published landing distance for the models with the newer wing, so from a pilot's PoV it's the same as it ever was:

• if you approach too fast, you'll float
  
• if you approach too slowly, you'll drop
• if you approach at the correct speed, you'll land just right (like the baby bear's porridge )

 

[Albany Tom]

Re the PA-28's, I think it's because the Hershey bar wings don't float much at all, and kind of "drop" pretty quickly if you let them slow, compared to tapered. So you get used to carrying a little extra speed in those, easy to burn it off quickly, where if carry an extra 10k in a taper wing, you're going to float it down the runway a bit. The other is that the published numbers for something like an Archer are higher than that of a Cherokee simply because the max gross is higher. If you base your speeds on max gross instead of being lightly loaded in an Archer, you're going to come in too fast. Lightly loaded, I bring an Archer in over the numbers about 60kts. It doesn't float for me at that speed.

Reading the above again, yep, if you come in just right it's just like the 3 bears.

 

[Dan Thomas]

When I was learning to fly 48 years ago I did some time in a PA-28-180. Old Hershey-bar wing. The popular talk around the airport was that the airplane would float and then finally "punch though the ground effect" and land firmly. I don't remember it doing that, but it was a long time ago. I suppose too much speed, and flaring five feet up and floating there would get you a hard landing. Short wings are famous for that. It's not a stall, it's the sink that can develop quite suddenly.

 

[Domenick]

...I've owned a PA-28-161 for 19 years, and it doesn't float at all when you bring it in at the correct speed (adjusted for weight). There's rarely any problem making the first turnoff 1,000 ft down the runway at my home airport, often without touching the brakes.
If I bring my 161 over the fence at 70–75 KIAS, of course it will float halfway down the runway, especially if the winds are light and I'm a few hundred pounds under gross. ...

David, I too have owned and flown a PA-28-161 for a couple of decades. "Over the fence" at my home drome (S43) means 8 feet over the threshold, as the runway butts up against a major thoroughfare. (Officially, the threshold is displaced 242', but we tend to ignore that since we need to clear the fence at the end of the asphalt). Solo and lightly loaded, how high and what airspeed are you at over your threshold?
Thanks.

 

[David Megginson]

David, I too have owned and flown a PA-28-161 for a couple of decades. "Over the fence" at my home drome (S43) means 8 feet over the threshold, as the runway butts up against a major thoroughfare. (Officially, the threshold is displaced 242', but we tend to ignore that since we need to clear the fence at the end of the asphalt). Solo and lightly loaded, how high and what airspeed are you at over your threshold?
Thanks.

Unless there are strong wind gusts, I fly the published approach speed of 65 KIAS, adjusted down for weight. Before I cross the fence, I've started to decelerate from that (and dropped full flaps).

Once nice thing about our -161s is that Piper actually publishes the weight-adjusted approach and touchdown speeds in the POH, so we don't have to try to guesstimate them. Though, to be fair, "I'm light so I'll take off 2–3 knots" is usually close enough for a simple plane like ours.

For example, if you're lightly loaded at 2,140 lb (300 lb under max gross), your weight-adjusted approach speed should be 62 KIAS according to the chart, and you'll touch down around 41–42 KIAS (so maybe I'd be around 55 KIAS over the fence, slowing for the flare, but of course I'm never looking at the ASI at that point).

 

[oskrypuch]

It also had a totally different airfoil along with the tapered section. That will influence behavior considerably.

Surprising as it may seem, the airfoil is actually the same for the taper and hershey bar Cherokees, the NACA 65(2)-415. I believe it was chosen for its graceful stall characteristics, it is not a very efficient airfoil in terms of L/D.

* Orest

 

[oskrypuch]

Unless there are strong wind gusts, I fly the published approach speed of 65 KIAS, adjusted down for weight. ...

@David Megginson makes a very important point, that is often not taken into consideration. You must adjust your stall speed to your landing weight (and flap position), before you can calculate your Vref.

The difference in stall speed in my plane, between MGW + clean flaps, and just the pilot with vapors and full flaps is 21 knots.

If you calculate your approach speeds for heavy, medium and light (for usual flap positions) and placard it, you will cover most of the bases and will be within a few knots of ideal. If you take note of that speed (or even adjust a speed bug on your panel) and fly it, that will remove most of the mystery of why the plane floats, or doesn't, or drops to the runway, and will allow for more consistency (and safety) in the round out and touchdown.

* Orest

 

[Timbeck2]

Good Gawd there seems to be a lot of engineers in this thread.

OP - what does being in ground effect feel like?
Engineer - well ya see son, floating is caused by …

 

[Domenick]

<hijack>
I am going to assume the "What does ground effect feel like" portion of this thread has been well answered and run its course ...

...
For example, if you're lightly loaded at 2,140 lb (300 lb under max gross), your weight-adjusted approach speed should be 62 KIAS according to the chart, and you'll touch down around 41–42 KIAS (so maybe I'd be around 55 KIAS over the fence, slowing for the flare, but of course I'm never looking at the ASI at that point)....

Thanks. It's interesting that we have arrived at the same rule-of-thumb, although CYRO has hundreds of feet between fence and runway end. Between the asphalt of the approach end of runway 15 at S43 and the asphalt road is 15 feet, in the middle of which is the perimeter fence. I aim to cross the fence at 55 kts too. Thanks for the reality check.

Question: On Google Earth in a image from 2018, CYRO's runway 09 has a huge white 'X' on the end. The 27 end is clear. In the 2021 June image, the 'X' is faded and barely discernible. What's the story?
</hijack>

 

[David Megginson]

Question: On Google Earth in a image from 2018, CYRO's runway 09 has a huge white 'X' on the end. The 27 end is clear. In the 2021 June image, the 'X' is faded and barely discernible. What's the story?

I don't remember the exact history of the markings, but 27 is unusual because it has a big displaced threshold that applies only at night.