The use of ground effect.

[midlifeflyer]

Wait, you're saying the report says Ground Effect was the cause of the fatality?

Please post a link, I gotta see this.

PJ

I don't think he said that. I think he said there were reports where ground effect was a killer. To me that just means ground effect was a factor and the pilot mismanaged it.

Easy to find links. Not all fatal, of course. Just Google NTSB "ground effect" You'll find stuff like this simple non-gory one in which the probable cause of the soft field takeoff accident was "The student pilot's improper pitch technique after rotation during a short field take off, which resulted in the right wing impacting the ground and a nose gear collapse."

add "fatal" to the search and you can find those as well.

 

[Velocity173]

Ground effect can be important in getting airborne early (short field technique) and accelerating to Vx. That’s not what is being displayed in these vids. It’s obvious the aircraft isn’t operating at a high weight high DA. The CJ could’ve easily been airborne and crossed the departure end several hundred feet up. Instead, it’s nothing more than staying in ground effect, building up speed well over Vx / Vy and crossing obstacles at the dept end at an unnecessarily low altitude.

 

[Juliet Hotel]

Ground effect can be important in getting airborne early (short field technique) and accelerating to Vx. That’s not what is being displayed in these vids. It’s obvious the aircraft isn’t operating at a high weight high DA. The CJ could’ve easily been airborne and crossed the departure end several hundred feet up. Instead, it’s nothing more than staying in ground effect, building up speed well over Vx / Vy and crossing obstacles at the dept end at an unnecessarily low altitude.

THIS! This is what I'm saying. Thank you.

As I said before, I am not saying ground effect doesn't exist. What I'm saying is that it doesn't do much. Actually let me revise that. For most pilots, in most of their flying, ground effect doesn't do much and isn't a factor in the performance of their aircraft.

Hot high and heavy, yep I could see it becoming a factor. For most people who are not taking off hot high and heavy, it really not a factor. And in the clips in that video? All I'm seeing a guy building a lot of excess speed and pulling the stick into his gut. The plane will do that at 10' and it'll do that at 100' and it'll do that at 1000'

 

[ElPaso Pilot]

You said you used to fly a Mooney.

Come in 10 knots hot and try to get the gear down on the ground before you bleed off that extra speed. That is demonstrably ground effect.

Are you a proponent of airplanes not being able to take off from treadmills, too?

 

[Stewartb]

When the wind at my cabin is blowing SE (common) I get flying as quickly as possible and gain speed while in ground effect (and sheltered from the crossing wind by trees) until I run out of space and climb over the trees at the best airspeed I can manage. Crossing wind rolling over trees can offer some pretty good sinkers so using Vx is no bargain. Ground effect eliminates that concern. Trying to hold a plane on the ground to gain speed isn't effective in my plane past 60mph. I literally can't hold the plane on the ground past that. The strip is about 1100' and the 100' trees are 150' or so off the end. When the winds blow it'll be rough at the treetops. Airspeed is life. Ground effect is a useful tool. So is a zoom climb.

 

[luvflyin]

Wait, you're saying the report says Ground Effect was the cause of the fatality?

Please post a link, I gotta see this.

PJ

I’ll look. I don’t remember exactly which ones. What happens is without ground effect the plane never would have become airborne and the worst that would have happened is it would have run off the end of the runway if the takeoff had not been aborted. But ground effect allowed the plane to become airborne and is to heavy to climb out of ground effect and flies into something.

 

[luvflyin]

I don't think he said that. I think he said there were reports where ground effect was a killer. To me that just means ground effect was a factor and the pilot mismanaged it.

Easy to find links. Not all fatal, of course. Just Google NTSB "ground effect" You'll find stuff like this simple non-gory one in which the probable cause of the soft field takeoff accident was "The student pilot's improper pitch technique after rotation during a short field take off, which resulted in the right wing impacting the ground and a nose gear collapse."

add "fatal" to the search and you can find those as well.

Yeah, ground effect was a factor might have been a better way to say it. But like I said one post above, ground effect is what caused the plane to fly into something at flying speed instead of rolling into something at a slower speed. Ground effect didn’t cause the accident, but that it exists, and allowed the accident to happen is real

 

[Dan Thomas]

What I'm saying is that it doesn't do much. Actually let me revise that. For most pilots, in most of their flying, ground effect doesn't do much and isn't a factor in the performance of their aircraft.

Yup. Most pilots never operate off pavement. They have neve had to try to fly out of a stubble field or a muddy strip or from long, uncut grass. And many, many pilots land at long runways and never have to achieve the book numbers wrt landing distance, so they approach hot, float for a couple thousand feet, touch down flat and roll forever or smoke the brakes and tires. Ground effect is ignored altogether, even though it is contributing mightily to their long landings.
Fly-ins at rural grass strips sometimes see accidents when pilots use their international-airport techniques on a 2000' grass strip. They've developed a bunch of bad habits during and after training, and their instructors never corrected them. I've seen instructors land like that. Some pilots are happy with their performance. They shouldn't be. Who would be satisfied consistently achieving a bowling score of 75??

 

[MooneyDriver78]

Here is an how to educational video

Tom

 

[SToL]

Ground effect is ignored altogether, even though it is contributing mightily to their long landings.
Fly-ins at rural grass strips sometimes see accidents when pilots use their international-airport techniques on a 2000' grass strip. They've developed a bunch of bad habits during and after training, and their instructors never corrected them. I've seen instructors land like that.

We're getting off topic but, this is a huge problem! Who among us has not seen flight instructors teaching there student's in a C-152 or C-172 and they're doing 747 patterns around the airport. Part of the idea of the traffic pattern, is to make it to the runway in the even of a power failure. Keep that in mind next time your on downwind a mile or two away from the runway or turning final 2 miles away. If you can't chop the power at any point and make the runway, you're in the wrong place

Back on topic, the next problem is speed. This does relate to ground effect in the sense that they float forever down the runway. These are bad pilot techniques taught or allowed by inexperienced instructors.

 

[SToL]

Easy to find links. Not all fatal, of course. Just Google NTSB "ground effect" You'll find stuff like this simple non-gory one in which the probable cause of the soft field takeoff accident was "The student pilot's improper pitch technique after rotation during a short field take off, which resulted in the right wing impacting the ground and a nose gear collapse." add "fatal" to the search and you can find those as well.

This is the point I was trying to make. Ground effect didn't kill anyone or cause the accident. It wasn't even a factor. Leaving it was the factor. Yes we all know ground effect allowed the pilot to get off the runway. But so did turning the key, starting the engine, applying power, pulling back on the yoke.. you see where I'm going with this.

In my opinion, trying to blame the accident on ground effect, or even calling it a contributing factor is ridiculous. Contributing factors would be, Altitude, temperature, weight, failure to know, understand and/or utilize performance charts, all a result of improper piloting techniques. Ground effect has never caused any accident. Attempting to fly out of ground effect without sufficient airspeed has caused many accidents.

I can personally attest to two accidents flying out of high altitude airports, fully loaded on steep down hill departures with tailwinds, where I remained in ground effect and had zero issues. On two separate occasions, airplanes taking off after me crashed. Luckily no one was injured in either case. But ground effect did not cause the accidents. The cause in both instances were the pilots poor piloting techniques, attempting to fly out of ground effect to early. Factors where the downhill departure with a tailwind, the altitude, the OAT and the weight of the aircraft.

PJ

 

[SToL]

Easy to find links. Not all fatal, of course. Just Google NTSB "ground effect" find stuff like this simple non-gory one in which the probable cause of the soft field takeoff accident was "The student pilot's improper pitch technique after rotation during a short field take off, which resulted in the right wing impacting the ground and a nose gear collapse." add "fatal" to the search and you can find those as well.

So I did your google search,NTSB "ground effect" and so far I've read the first 10. None of them, including the one you posted, claim ground effect was the cause or even a contributing factor in the accident.

This would be easier if one of you who believe ground effect causes accidents would just post your link. I genuinely would like to see it.

PJ

 

[SToL]

Crossing wind rolling over trees can offer some pretty good sinkers so using Vx is no bargain.

Boy there's a lot of truth to that statement. I had a harrowing experience once on a strip similar to yours. I was departing in a loaded C-185 and everything was normal. As I climbed off the runway, just as I hit tree top level, about 100+ feet agl, my left wing began to stall.

Everything happened in what seemed like the flash of a second... I was certain we were going to go into the trees on the departure end. I reached for the throttle and pulled it back, pushed the nose down and applied right rudder, instantly the airplane began to level - I immediately re-applied full throttle, holding the nose down and built all the airspeed I could and rotated just before the trees.

I believe what happened was as follows. The end of this runway was notorious for 'squirrely winds'. I was at climb power and climb out speed. I think as I topped out above the tree, my left wing entered some swirling wind that actually caused a downwind effect, thus stalling that wing.

I was certain that flight was not going to end well, but I got lucky that day. I'd like to thank my father for pulling me out of that one. He was a 30 year military pilot who taught me how to fly when I was a kid, and he always told me, "No matter what's going on, there's nothing more important than Flying the Airplane".

PJ

EDITED: I wrote left rudder but meant right rudder. it was a brain fart.

 

[LongRoadBob]

Boy there's a lot of truth to that statement. I had a harrowing experience once on a strip similar to yours. I was departing in a loaded C-185 and everything was normal. As I climbed off the runway, just as I hit tree top level, about 100+ feet agl, my left wing began to stall.

Everything happened in what seemed like the flash of a second... I was certain we were going to go into the trees on the departure end. I reached for the throttle and pulled it back, pushed the nose down and applied left rudder, instantly the airplane began to level - I immediately re-applied full throttle, holding the nose down and built all the airspeed I could and rotated just before the trees.

I believe what happened was as follows. The end of this runway was notorious for 'squirrely winds'. I was at climb power and climb out speed. I think as I topped out above the tree, my left wing entered some swirling wind that actually caused a downwind effect, thus stalling that wing.

I was certain that flight was not going to end well, but I got lucky that day. I'd like to thank my father for pulling me out of that one. He was a 30 year military pilot who taught me how to fly when I was a kid, and he always told me, "No matter what's going on, there's nothing more important than Flying the Airplane".



PJ

I am having a hard time understanding the purpose of pulling the throttle, I feel I also would have lowering the nose, but also, left rudder puzzles me. My inexperienced instinct would have been al, wrong I guess.
I would have left power at full, used right rudder (because of being slow instead of aileron) to try and bring the wing up.

What were the effects of pulling throttle, nose down, left rudder? The theory of how that righted it?
I’d really like to understand that.

 

[SToL]

I am having a hard time understanding the purpose of pulling the throttle, I feel I also would have lowering the nose, but also, left rudder puzzles me. My inexperienced instinct would have been al, wrong I guess.
I would have left power at full, used right rudder (because of being slow instead of aileron) to try and bring the wing up.

What were the effects of pulling throttle, nose down, left rudder? The theory of how that righted it?
I’d really like to understand that.

Hi LongRoadBob,

You're correct, I meant right rudder... not left. I remember it as clear as day, not sure why I said left. I was thinking of going into this long diatribe about how the plane dipped left and hinted of a entry to a left spin. I guess I just had left on my brain, but it was in fact, right rudder. Sorry for the confusion. I should correct that.

First, remember that the sequence of events was really one long fluid motion that occurred in realistically probably a couple seconds. But it seemed almost instant.

I pulled the throttle because I thought we were going down. I didn't want to impact the trees at full power. I was setting up for as slow a landing as possible, power off.

I put the nose down to prevent further stalling (i.e. maintain or increase my flying speed just above the stall)

The left wing stalling was, just that, a stall, and as it began dipping to the left, it could have easily become the dreaded and lethal, stall spin. I simply recovered for a left stall/spin before anything actually developed. This leveled the wings instantly.

Almost simultaneously, I re-applied full power, holding the nose down and building airspeed. It really didn't take much but I held it until I had (from a previous post) Zoom Climb speed and rotated above the trees.

Hope that explains it.

PJ

 

[LongRoadBob]

Hi LongRoadBob,

You're correct, I meant right rudder... not left. I remember it as clear as day, not sure why I said left. I was thinking of going into this long diatribe about how the plane dipped left and hinted of a entry to a left spin. I guess I just had left on my brain, but it was in fact, right rudder. Sorry for the confusion. I should correct that.

First, remember that the sequence of events was really one long fluid motion that occurred in realistically probably a couple seconds. But it seemed almost instant.

I pulled the throttle because I thought we were going down. I didn't want to impact the trees at full power. I was setting up for as slow a landing as possible, power off.

I put the nose down to prevent further stalling (i.e. maintain or increase my flying speed just above the stall)

The left wing stalling was, just that, a stall, and as it began dipping to the left, it could have easily become the dreaded and lethal, stall spin. I simply recovered for a left stall/spin before anything actually developed. This leveled the wings instantly.

Almost simultaneously, I re-applied full power, holding the nose down and building airspeed. It really didn't take much but I held it until I had (from a previous post) Zoom Climb speed and rotated above the trees.

Hope that explains it.

PJ

Hey PJ, thanks for walking me through that. That left rudder left me thinking “damn, I haven’t understood enough!! There must be some force, probably AOA that I’m missing here!” And all that. Nice to hear it was just a mistake

But just to go a tiny bit deeper, if you would, I think actually my instinct would have been to use right ailerons, not right rudder alone, unless I knew I was slow. Were you slow in airspeed at that point? I’m guessing yes, because Vx is slow, relatively so right ailerons would have made the situation worse right?

Also that is interesting with the throttle, and make me think about that so that is a good lesson. I think instinct for me would be to keep full throttle, but then again you do say it was about 100’ AGL, so I would hope I would be thinking the same thing. Reacting quickly to go back to full throttle just as soon as you saw you had the wing up again. I picture that scenario. Thanks for the information!

As for Ground Effect, I thought I understood it at a basic level, but is it such that if one stays in ground effect too long, building up speed, that it can adversely affect the ability to climb? I saw the post about g forces, if you pull up sharp and zoom, I think zooming is the term to describe a short lived climb and if at a high angle the g forces increase stall speed so no win, but can one get into trouble building up speed in GE And then gradually raising the nose?

 

[FastEddieB]

As for Ground Effect, I thought I understood it at a basic level, but is it such that if one stays in ground effect too long, building up speed, that it can adversely affect the ability to climb?

Yes. Parasitic drag is increasing as the square of the speed increase. It’s just induced drag that is reduced in ground effect. Accelerating beyond the desired climb speed, normally Vx or Vy, is less efficient than smoothly beginning the climb when those speeds are reached. Plus, a hard pull to “zoom climb” increases induced drag, making it less efficient than a smooth transition.

 

[LongRoadBob]

Yes. Parasitic drag is increasing as the square of the speed increase. It’s just induced drag that is reduced in ground effect. Accelerating beyond the desired climb speed, normally Vx or Vy, is less efficient than smoothly beginning the climb when those speeds are reached. Plus, a hard pull to “zoom climb” increases induced drag, making it less efficient than a smooth transition.

Thanks, that rings a bell for me. It’s putting it all together that can be a challenge. That helped a lot!

That Drag is split and opposite between parasitic and induced is what I was missing here. You explained it well. Thanks!

I did know that you want to rotate at the right speed, which changes with weight, but also that there is a limit to how much over you should let it go but this puts the why of it into perspective.

 

[SToL]

But just to go a tiny bit deeper, if you would, I think actually my instinct would have been to use right ailerons, not right rudder alone, unless I knew I was slow. Were you slow in airspeed at that point? I’m guessing yes, because Vx is slow, relatively so right ailerons would have made the situation worse right?

I was at takeoff power, climbing out just like I had done literally hundreds (if not thousands) of times from this airport, but apparently on this day, I was slow enough in current wind conditions for my left wing to drop and I recall having the sensation that the nose was moving left while dropping, and a sinking sensation. Remember, it was amazing how fast everything happened, but as soon as I pulled power, (and I don't even think I got the power all the way off) pushed the nose forward and hit the rudder, the plane went level. I immediately followed up with neutral inputs maintaining level-ish to slightly low nose attitude and wings level, re-applying full power.

Also that is interesting with the throttle, and make me think about that so that is a good lesson. I think instinct for me would be to keep full throttle, but then again you do say it was about 100’ AGL, so I would hope I would be thinking the same thing. Reacting quickly to go back to full throttle just as soon as you saw you had the wing up again. I picture that scenario.

Keep in mind, when this occurred my thought process did not begin with "Stall Recovery". My thought process went from, WTF!!! we are going to go into the trees, immediately to, WTF!!! my left wing is stalling, and then just as quickly to WTF!!! why is the nose turning? These things all happened together literally, perceptibly, simultaneously. It might be easy to say, well you just weren't used to that fight regime so it seemed to have happened all at once. The problem with that is I've been done aerobatics since I was a kid as well as teaching stall training to students, and I haven't been a kid for a long, long time. I'm used to unusual flight attitudes. This did catch me off guard in the sense that I was not expecting it to happen where it did, but it did not catch me off guard in the sense that I didn't recognize it or didn't know what to do.

In training we practice stall recoveries as nose down, wings level, and power recovery. In this situation, and again these things happened almost instantly, the plane simultaneously sank (the feeling you get when you raise flaps after take off, but I hadn't done that yet), the wind dipped and the nose appeared to be favoring turning left. Oddly, In this instance, there was no warning of wing buffeting and the stall horn never sounded. We were simply climbing out and next thing we were sinking and the left wing started dropping, all putting us below the tree line. Perhaps if I'd been 1 second slower on my recovery, I might have gotten the horn.

As for Ground Effect, I thought I understood it at a basic level, but is it such that if one stays in ground effect too long, building up speed, that it can adversely affect the ability to climb? I saw the post about g forces, if you pull up sharp and zoom, I think zooming is the term to describe a short lived climb and if at a high angle the g forces increase stall speed so no win, but can one get into trouble building up speed in GE And then gradually raising the nose?

Well first of all, you'll never see 'zoom climb, or zooming' in any aviation manual. That was a term I copied as a joke from a post on here. Unfortunately there is a lot of misunderstanding about ground effect.

Ground Effect is a phenomenon of increased lift created by a moving wing. It applies when an aircraft is within approximately half it's wingspan to the surface. Ground effect allows an aircraft to leave the surface at a slower speed than what is actually be needed in flight. This phenomenon can be helpful if you understand how it works, or it can be detrimental if you don't understand and try to leave ground effect to early, without sufficient airspeed to fly.

1. You can not stay in ground effect too long, unless there is an obstacle in your path. Then it would be advisable to either go around it or climb over it. Lot's of people like to fly around in ground effect all day. It's a blast, until you have an engine problem or hit something.

2. Two things are you friend in aviation. Speed and Altitude. There are two times you do not want one of those things. When you are going to hit something and when you are on fire. You can trade speed for altitude, or altitude for speed. The faster you go, the more lift you can obtain. More speed will never adversely effect the ability to climb out of ground effect.

3. You will not get into trouble building up speed and gradually raising the nose. You can even briskly raise the nose without issue. Don't go crazy and pull the wings off. You can pull a g or two without any adverse issue. In order to stall the aircraft you would have to either hold the climb too long, thus losing airspeed and stalling, or pull so abruptly and maintain the pull, that the aircraft has an accelerated stall.

PJ

EDIT: To alleviate confusion, added "out of ground effect" to #2.

 

[FastEddieB]

More speed will never adversely effect the ability to climb.

Sort of.

But accelerating beyond the desired climb speed (Vx or Vy, let's say) and then converting that excess speed into altitude will result in less altitude than just climbing at Vx or Vy in the first place. They both have the word "best" in their definitions for a reason.

 

[SToL]

Sort of.

But accelerating beyond the desired climb speed (Vx or Vy, let's say) and then converting that excess speed into altitude will result in less altitude than just climbing at Vx or Vy in the first place. They both have the word "best" in their definitions for a reason.

FastEddie, you are absolutely correct, My response was more general and specially towards this comment...

but can one get into trouble building up speed in GE And then gradually raising the nose?

Sorry for the confusion, I never went into 'best climb speeds'. Thanks for checking me on that.

PJ

 

[Dan Thomas]

You will not get into trouble building up speed and gradually raising the nose. You can even briskly raise the nose without issue. Don't go crazy and pull the wings off. You can pull a g or two without any adverse issue. In order to stall the aircraft you would have to either hold the climb too long, thus losing airspeed and stalling, or pull so abruptly and maintain the pull, that the aircraft has an accelerated stall.

You can stall the aircraft instantly if you pull hard enough at a low enough airspeed. See my post (#24) about accelerated stalls. It's the phenomenon seen in a snap roll: yank back hard and stomp rudder to get the yaw. It's a horizontal spin and needs only a split second to develop.
Guys buzzing and crashing aren't usually running out of airspeed and stalling. They're doing the yank-and-bank thing to impress the folks on the ground, and they stall that wing at well above the normal 1G stall speed and spin in without ever realizing what they did wrong. Dead before they figure it out. Google "buzzing accidents accelerated stall spin" and see all the articles and accident reports that come up.

It's one of those things that is, unfortunately, neither well-taught nor well-understood during flight training, and it kills people. Carb ice is another misunderstood threat.

 

[SToL]

You can stall the aircraft instantly if you pull hard enough at a low enough airspeed. See my post (#24) about accelerated stalls. It's the phenomenon seen in a snap roll: yank back hard and stomp rudder to get the yaw. It's a horizontal spin and needs only a split second to develop.
Guys buzzing and crashing aren't usually running out of airspeed and stalling. They're doing the yank-and-bank thing to impress the folks on the ground, and they stall that wing at well above the normal 1G stall speed and spin in without ever realizing what they did wrong. Dead before they figure it out. Google "buzzing accidents accelerated stall spin" and see all the articles and accident reports that come up.

It's one of those things that is, unfortunately, neither well-taught nor well-understood during flight training, and it kills people. Carb ice is another misunderstood threat.

I find this is interesting because even though it's possible to stall at any speed, and the scenario you describe does happen, I would have thought that the majority of those guys buzzing and crashing were a combination of the "too slow, too steep and uncoordinated" accidents. I'm not exactly sure, without video evidence, how you could prove one cause over the other but I would love to know which is more prolific.

PJ

 

[Stewartb]

Low enough airspeed makes a stall? Really??? That’s why we gain airspeed FIRST!

 

[dmspilot]

These are bad pilot techniques taught or allowed by inexperienced instructors.

That's due to apathy, not inexperience.

 

[SToL]

That's due to apathy, not inexperience.

I'd agree with that too.

 

[Dan Thomas]

I find this is interesting because even though it's possible to stall at any speed, and the scenario you describe does happen, I would have thought that the majority of those guys buzzing and crashing where a combination of the "too slow, too steep and uncoordinated" accidents. I'm not exactly sure, without video evidence, how you could prove one cause over the other but I would love to know which is more prolific.

PJ

I know. That's what most pilots think. Too slow, too low, too steep. But angle of attack is waiting for the unwary who think that because they have plenty of speed, they're safe. I have been flying since 1973 and have read far too many reports of some guy buzzing over someone, and the eyewitness says "he passed over at high speed, then he pulled up quickly and suddenly the airplane rolled to the left and dove into the ground."

Classic accelerated stall-spin. And it's almost never mentioned in ground school. Or in the air. Many instructors just teach straight-ahead power-off stalls, and the student thinks "Well, that's no big deal." Instant complacency, instant ignorance.

I have been an instructor, and the lack of AoA awareness among too many pilots is appalling. It's equal to the lack of awareness too many drivers have for the road's surface; they don't slow up and take it easy when the road gets icy, and it bites them.

AOA indicators won't save most of these folks. The stall is achieved very suddenly, as AoA goes from some safe angle to 18° or more, and the AoA indicator alarm sounds as the airplane is rolling/diving out of control. Too late.

A good rundown: http://download.aopa.org/epilot/2007/sa20.pdf

 

[Dan Thomas]

That's due to apathy, not inexperience.

No, there are instructors who are lacking in some critical areas. No experience either in the classroom or in flight. It's not apathy; they often don't know what they don't know.

If they don't care to study and learn, that's apathy.

 

[Jesus]

THIS! This is what I'm saying. Thank you.

As I said before, I am not saying ground effect doesn't exist. What I'm saying is that it doesn't do much. Actually let me revise that. For most pilots, in most of their flying, ground effect doesn't do much and isn't a factor in the performance of their aircraft.

Hot high and heavy, yep I could see it becoming a factor. For most people who are not taking off hot high and heavy, it really not a factor. And in the clips in that video? All I'm seeing a guy building a lot of excess speed and pulling the stick into his gut. The plane will do that at 10' and it'll do that at 100' and it'll do that at 1000'

What you are failing to understand is that the reduced induced drag from ground effect, allows you to pick up speed at a higher rate (accelerate faster), while getting more lift at a lower AoA, thus further increasing your acceleration. You won't accelerate as fast at 100' or 1000' as you will in ground effect. On low wing aircraft, this translates to ~60% induced drag reduction at a height 10% the wingspan, ~30% less drag at 20% height, ~20% less drag at 30%, and becoming negligible at a height half the wingspan. Additionally, the friction between the tires and the runway consumes some non-negligible amount of energy, which translates into an increased acceleration once off the ground.

 

[dmspilot]

No, there are instructors who are lacking in some critical areas. No experience either in the classroom or in flight. It's not apathy; they often don't know what they don't know.

No, any CFI should be able a student to "not float forever down the runway" starting with hour 0 of dual given after their checkride.

 

[SToL]

I know. That's what most pilots think.

Dan, I think you misunderstood my post. I'm well aware of how stalls and possible resulting spins occur.

My post was asking, which happens more, and is there really any definitive way to determine which type it was after the fact?

Relating a witnesses report that they plane flew by really fast and then pulled up really hard still could have resulted in either stall depending on when it happened. For example, did he stall it near the top when the plane ran out of energy/power, and then recover incorrectly and spin it into the ground? It's a possibility.

Can you supply any data other than opinion that the primary cause of these accidents are accelerated stalls and not the typical slow speed stalls? In Alaska we call them Moose stalls because it happens to a lot of pilots who slow down making turns looking down at moose.

Again, I'm not disagreeing with you that they happen, I'm just curious which happens the most?

This does NOT mean I don't think accelerated stall occur or I that I don't understand them.

Personally, I tend to believe more people stall slowly than fast. I have no proof of this, and I'm not aware of any data that proves this. Again, this is just my thinking. I suppose one day in the future when every aircraft has some type of monitoring system, we'll learn the answer to this question. Maybe the reason I think this is because I think for one, there are more people landing, than there are people buzzing houses. And I believe stalling on the base to final leg is one of, if not the top killer of pilots.

Just my thoughts,
PJ

 

[Dan Thomas]

Can you supply any data other than opinion that the primary cause of these accidents are accelerated stalls and not the typical slow speed stalls?
Again, I'm not disagreeing with you that they happen, I'm just curious which happens the most?

This does NOT mean I don't think accelerated stall occur or I that I don't understand them.

Personally, I tend to believe more people stall slowly than fast. I have no proof of this, and I'm not aware of any data that proves this. Again, this is just my thinking. I suppose one day in the future when every aircraft has some type of monitoring system, we'll learn the answer to this question. Maybe the reason I think this is because I think for one, there are more people landing, than there are people buzzing houses. And I believe stalling on the base to final leg is one of, if not the top killer of pilots.

It's dangerous to assume that loss of speed is the biggest factor. I am emphasising to you and to others that accelerated stalls are real, they're dangerous, and that they happen to people who do dumb things.

A 2G pull-up puts the same load factor on the wing that a 60-degree banked turn does. Would you do a 60-degree banked turn at 50 feet? No. But some guys think nothing of pulling 2G after a low-level buzz. Thats what I mean about so many not understanding the dangers of fooling around near the ground, pulling back or whatever.

 

[Dan Thomas]

No, any CFI should be able a student to "not float forever down the runway" starting with hour 0 of dual given after their checkride.

I know they should. But many don't. Just sit outside on a nice day at the airportand watch when airplanes are doing dual-instruction circuits.

 

[SToL]

It's dangerous to assume...

I give up.

 

[luvflyin]

So I did your google search,NTSB "ground effect" and so far I've read the first 10. None of them, including the one you posted, claim ground effect was the cause or even a contributing factor in the accident.

This would be easier if one of you who believe ground effect causes accidents would just post your link. I genuinely would like to see it.

PJ

I’ve looked and didn’t find any that had fatalities. My memory still says I’ve seen them but I couldn’t find my car keys this morning, so much for memory. I found this one http://www.aopa.org/asf/ntsb/narrative.cfm?ackey=1&evid=20140527X11017

Like I said earlier, saying ground effect ‘caused’ the accident wouldn’t be exactly accurate. But the existence of ground effect ‘allowed’ it to happen. Without ground effect the airplane would unlikely have been able to become airborne in the first place and then crash.

 

[luvflyin]

You can stall the aircraft instantly if you pull hard enough at a low enough airspeed. See my post (#24) about accelerated stalls. It's the phenomenon seen in a snap roll: yank back hard and stomp rudder to get the yaw. It's a horizontal spin and needs only a split second to develop.
Guys buzzing and crashing aren't usually running out of airspeed and stalling. They're doing the yank-and-bank thing to impress the folks on the ground, and they stall that wing at well above the normal 1G stall speed and spin in without ever realizing what they did wrong. Dead before they figure it out. Google "buzzing accidents accelerated stall spin" and see all the articles and accident reports that come up.

It's one of those things that is, unfortunately, neither well-taught nor well-understood during flight training, and it kills people. Carb ice is another misunderstood threat.

Yeah. Inertia is a factor in the airspeed vs angle of attack thing. Reaching critical angle of attack is what causes stalls. The airspeed at which critical angle of attack occurs is predictable. That’s why it is common to publish ‘stall speeds.’ But when you start ‘yanking’ on the yoke it’s not that simple. A plane with a lot of elevator authority can change the angle of attack like ‘right now.’ Inertia is going to delay the reduction in airspeed a little

 

[SToL]

I found this one http://www.aopa.org/asf/ntsb/narrative.cfm?ackey=1&evid=20140527X11017

Like I said earlier, saying ground effect ‘caused’ the accident wouldn’t be exactly accurate. But the existence of ground effect ‘allowed’ it to happen. Without ground effect the airplane would unlikely have been able to become airborne in the first place and then crash.

I hear what you're saying, but I don't agree with your assessment that 'ground effect' is a cause or contributing factor.

You believe 'ground effect' allowed it to happen, I believe the pilot allowed it to happen.

You believe; "Without ground effect the airplane would unlikely have been able to become airborne in the first place and then crash." I believe; Without the invention of the wheel, the airplane would unlikely have been able to become airborne in the first place and then crash. <--- friendly sarcasm

In the link you provide, the NTSB FINAL NARRATIVE states;

The combined effects of the tall grass, the limited available engine power, operation near the airplane’s maximum gross weight, the light tailwind condition, and the high density altitude likely extended the required ground roll and degraded the airplane’s climb performance, which resulted in its inability to climb out of ground effect and clear the trees.

To me, the contributing factors where, tall grass, limited power, near max gross weight, a tail wind all at high density altitude.

Ground effect is no more a contributing cause of the accident than the trees were.

In my opinion, this had nothing to do with ground effect and everything to do with inappropriate piloting decision and technique.

PJ

 

[luvflyin]

I hear what you're saying, but I don't agree with your assessment that 'ground effect' is a cause or contributing factor.

You believe 'ground effect' allowed it to happen, I believe the pilot allowed it to happen.

You believe; "Without ground effect the airplane would unlikely have been able to become airborne in the first place and then crash." I believe; Without the invention of the wheel, the airplane would unlikely have been able to become airborne in the first place and then crash. <--- friendly sarcasm

In the link you provide, the NTSB FINAL NARRATIVE states;

The combined effects of the tall grass, the limited available engine power, operation near the airplane’s maximum gross weight, the light tailwind condition, and the high density altitude likely extended the required ground roll and degraded the airplane’s climb performance, which resulted in its inability to climb out of ground effect and clear the trees.

To me, the contributing factors where, tall grass, limited power, near max gross weight, a tail wind all at high density altitude.

Ground effect is no more a contributing cause of the accident than the trees were.

In my opinion, this had nothing to do with ground effect and everything to do with inappropriate piloting decision and technique.

PJ

Yeah. I agree with you. I certainly could have worded that better. At the time, the thread was still about is ground effect real and if it is, is it effective enough to make any difference to anyone. I was trying to make the point that yes it exists and yes it can be significant. I thought @Kenny Phillips put it well in post #17 where he said "It can help a heavy plane on a hot day make it to the accident scene!" I was adding to that

 

[FastEddieB]

In my opinion, this had nothing to do with ground effect and everything to do with inappropriate piloting decision and technique.

I think I disagree.

In a world without ground effect, the plane never would have gotten airborne in the first place, allowing the pilot the option of stopping on the runway. It was ground effect that set the stage. Hence it “contributed”.

But maybe we’re just being pedantic. Was it the ground effect itself that contributed, or the pilot’s inability to recognize the consequences of ground effect. A distinction without a difference?

 

[flyingbrit]

Warning: This post may contain blasphemy.

I always thought of ground effect sort of the same way I think about acupuncture. People use it and swear by it, but I've never personally seen it do anything and as far as I know, science is unable to prove that its use has any measurable effectiveness.

Have you considered how a hovercraft works?