RV-8 Landing With 20? Flaps

Yesterday I nearly bit off more than I could chew with regard to landing the 8 in rather rough wind conditions.

Take off at about 8 am was a none event, clear weather and almost calm wind. Two hours later things had changed. A front had passed the night before and ushered in some nice dry air from the north, I noticed the GRT Sport EFIS indicated 30 knots at 2000'.

I made a tour of the local area as per usual taking in the sites including a couple landings at the 3000' grass strip where I made the first landing on June 16 - really nice near 3 pointers.

Back home just a few miles distant all heck broke loose on the first approach. The 8-26 runway has trees on the west end and along the north side of it. The NW wind was favoring a 26 approach so that was the plan. The EFIS indicated over 30 knots of NW wind at 800 AGL. A couple friends with a radio said it appeared nearly calm at the surface inside the tree line shelter.

I've landed out of this approach at least 10 times but this time the bottom dropped out at about 50', like really big time. The sink rate was amazing, I had no illusions of landing and went WOT to catch the sink just before aircraft would have made ground contact. The nose was quite high, higher than the normal 3 point attitude.

Well that was interesting and decided to try it again.

After 4 more attempts with similar results I was beginning to think this may not work out. There was either a serious wind shear coming into the tree shelter or a vertical down draft. It was in about the same area each time.

I was about to arrange for the guys to come pick me up at the near by grass strip I had just visited but decided to try it one more time with 20? flaps instead of 40?.

I'm just guessing as to the why of it, but with 20 flaps I was able to control the airplane through the sink and make a half-ways decent wheel landing, albeit a little long, and get it stopped before the west end. I've learned to brake the beast with the tail up and as it comes down.

I think what was going on with 40 flaps was when pitch was increased to stop the sink it did not stop it at all, except with a burst of power, lots of it.

Turns out most of the guys here have experienced that sink with a NW wind and avoid flying on such days.

Flew today and it was a completely different story, same weather pattern but the wind at altitude was just 8 or 10 knots.

I will try some 20? flap landings and no flappers also in the near future just to see how they work out. I've been using 40 with the 8 because I've read it is a good thing to do. We shall see about that.

The stall difference from 20 to 40 is miniscule, 40 is mostly drag - not lift.

I almost always use 20 when solo.

Because of my somewhat short strip (1500') I always use full flaps for landing. I have found, with RVs, that full flap landings with a crosswind is never a problem.

My tests show that stall speed is reduced with flaps up to about 28?. After that the flaps add drag but with no reduction in stall speed. My tests were on my -6, but I have found that results are very similar on the -3, -4, -7, and -8.
I have not done these tests on the -9, -10, or -12.

David-aviator said:

I think what was going on with 40 flaps was when pitch was increased to stop the sink it did not stop it at all, except with a burst of power, lots of it.

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Using pitch to arrest sink in an RV close to landing speed is a recipe for disaster! The increased angle of attack will increase sink rate and put the aircraft closer, sometimes below, stall speed.

Pitch controls airspeed, throttle controls sink rate. When the big sink begins, immediately add power, not back stick. The aircraft will already be trimmed for a climb if power is added.

Adding back pressure just increases the amount of power required....as you experienced.

Glad your flight had a good ending.

I'd say the answer lies between the last two post. You were probably much higher on drag at 40 degrees and flying a back side approach, which Sam eluded to; power is required for glideslope control and AOA can cause issues fast as drag goes through the roof with it. With 20 flaps drag was decreased and perhaps you were flying a front side approach, where glideslope corrections can be easily made with attitude.

Ed Kolano wrote an article I found by google flight path stability it was the first result, short wing pipers. I am on my phone and can't copy the link.

Did you happen to note what the ASI did during any of these events? Was there a big drop in airspeed when the windshear occurred? If so, it might have been worthwhile to fly the approach at a much higher than normal speed, so you would end up at an acceptable speed after the wind shear hit.

Sam Buchanan said:

Using pitch to arrest sink in an RV close to landing speed is a recipe for disaster! The increased angle of attack will increase sink rate and put the aircraft closer, sometimes below, stall speed.

Pitch controls airspeed, throttle controls sink rate. When the big sink begins, immediately add power, not back stick. The aircraft will already be trimmed for a climb if power is added.

Adding back pressure just increases the amount of power required....as you experienced.

Glad your flight had a good ending.

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True, Sam, when flying an ILS or VFR slot in relatively still air conditions.

However, recovery from a sudden wind shear or a down burst requires both, aggressively. Increasing power alone will not save it if it is severe. AOA needs to be increased to compensate for loss of lift due to reduced air flow across the wing.

Power alone may have saved it but it did not feel like it at the time. It felt and looked more like ground contact coming with WOT.

Kevin Horton said:

Did you happen to note what the ASI did during any of these events? Was there a big drop in airspeed when the windshear occurred? If so, it might have been worthwhile to fly the approach at a much higher than normal speed, so you would end up at an acceptable speed after the wind shear hit.

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The stall speed with 40 flaps is 47 KIAS, I was flying my usual 60. ASI was not noted during the sink event.

The final successful approach with 20 flaps was at 65KIAS. That may have worked with 40 also. But extra speed is not comforting with a short runway.

David-aviator said:

The stall speed with 40 flaps is 47 KIAS, I was flying my usual 60. ASI was not noted during the sink event.

The final successful approach with 20 flaps was at 65KIAS. That may have worked with 40 also. But extra speed is not comforting with a short runway.

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If I'm reading your first post correctly, the 30 kt wind at 800 ft wasn't a direct crosswind - i.e. there probably was a significant headwind component at that altitude. If the wind was 45 deg off, that is a 20 kt headwind component. 60 degrees off is a 15 kt headwind component. The reported wind at the surface was close to calm. Somewhere between 800 ft and the surface you'd have to lose 15 to 20 kt of headwind. If that occurs suddenly in a windshear, you'd have a sudden loss of 15 to 20 kt of speed, which would have produced one heck of a sink, especially starting at 60 kt. 60 kt is perhaps a bit slow for rough conditions, that often have gusts or shears leading to sudden airspeed drops.

You were concerned about the short runway, so were reluctant to add speed. But, if there is a headwind component at altitude, and a low wind at the surface, additional speed during the early approach is insurance against the wind change that has to occur before touchdown. If the wind changes gradually, with no sudden windshear, you will be faster than you want at the end of the runway, so you go around and try again, with a bit less speed next time. If the wind shear does occur, you'll be in better shape than if you were at your normal approach speed.

I'm very happy you got it safely on the ground. Good work.

X-wind correction

When landing is windy conditions, I use this formula to add KIAS:

My starting point is 55 KIAS which is the final airspeed at light weight and calm wind.
For medium and heavy weight, I add 5 KIAS per "step".

Then I add half the headwind component pluss the whole gustfactor.

Normally I land with full flaps.

andrewtac said:

I'd say the answer lies between the last two post. You were probably much higher on drag at 40 degrees and flying a back side approach, which Sam eluded to; power is required for glideslope control and AOA can cause issues fast as drag goes through the roof with it. With 20 flaps drag was decreased and perhaps you were flying a front side approach, where glideslope corrections can be easily made with attitude.

Ed Kolano wrote an article I found by google flight path stability it was the first result, short wing pipers. I am on my phone and can't copy the link.

Click to expand...

Found it...

http://www.shortwingpipers.org/forum/attachment.php?attachmentid=2306&d=1300202999 Good article out of Test Pilot, Sport Aviation. Linked from the Short Wing Pipers site.

Do you have a AOA indicator installed?

sailvi767 said:

Do you have a AOA indicator installed?

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The GRT Sport has an AOA feature but I have not calibrated it.

It is based on internal computations - not an actual AOA physical measurement like the Dynon D-10. I liked the D-10 AOA and used it all the time in the 7A.

I need to get this one calibrated, up and running, and see how it works.

Related to 20 Degrees...

David, just a little note that is sort of related. I now own an RV6A, recently purchased, my 7A will wait for a Lyc engine package or possibly get sold.

One thing I have noticed in getting used to flying the 6 is the flaps. On my 7A I had installed the flap control mechanism from Show Planes and I guess I had really gotten used to the operation and I really miss it now that I don't have it. With the Show Planes mod I could just hit the toggle and keep my attention on flying the plane and it would go to 10 degrees. Turn base and hit it again and I get my 20 degrees. Then a third touch to go all the way if I chose. Even more so I miss the auto retract feature with a simple flip of the toggle switch.

I found myself climbing away from a touch and go with nearly full flaps as I had automatically just hit the toggle expecting full retraction while rolling down the runway.

Easy to get spoiled I guess.

I am having a hard time deciding how many goodies to steal off my 7A

Randall Crothers

Randy said:

David, just a little note that is sort of related. I now own an RV6A, recently purchased, my 7A will wait for a Lyc engine package or possibly get sold.

One thing I have noticed in getting used to flying the 6 is the flaps. On my 7A I had installed the flap control mechanism from Show Planes and I guess I had really gotten used to the operation and I really miss it now that I don't have it. With the Show Planes mod I could just hit the toggle and keep my attention on flying the plane and it would go to 10 degrees. Turn base and hit it again and I get my 20 degrees. Then a third touch to go all the way if I chose. Even more so I miss the auto retract feature with a simple flip of the toggle switch.

I found myself climbing away from a touch and go with nearly full flaps as I had automatically just hit the toggle expecting full retraction while rolling down the runway.

Easy to get spoiled I guess.

I am having a hard time deciding how many goodies to steal off my 7A

Randall Crothers

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Randy, an ex-Subby guy, good to hear from you glad you're still alive.

David-aviator said:

True, Sam, when flying an ILS or VFR slot in relatively still air conditions.

However, recovery from a sudden wind shear or a down burst requires both, aggressively. Increasing power alone will not save it if it is severe. AOA needs to be increased to compensate for loss of lift due to reduced air flow across the wing.

Power alone may have saved it but it did not feel like it at the time. It felt and looked more like ground contact coming with WOT.

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You have the answer in your own statement, reduced airflow across the wing loses lift. It may sound counter intuitive, but lowering the nose in a sink decreases angle of attack and increases your airspeed, increasing lift.
In an aggressive sink, it may take both; lowering the angle of attack and adding power.
You then have to deal with the extra airspeed, but that is a lot better than bent gear, prop, and engine teardown. (recent occurrence at our airfield where this type of condition exists often).

I try to fly my approaches with a relatively constant pitch for the airspeed I am trying to achieve and use throttle to move myself back and forth on the glide slope. If I sink, I am not afraid to lower the nose to get back to my target airspeed.

Hand on the throttle, always, and be ready to throw it in if you can not arrest the sink. Your airplane will respond to that power far better with a lower angle of attack than it will if your nose high. Dragging it in behind the power curve is not a good place to be in any landing.

PS - I am with Mel. Always a full flap landing for me.

KatieB said:

Found it...

http://www.shortwingpipers.org/forum/attachment.php?attachmentid=2306&d=1300202999 Good article out of Test Pilot, Sport Aviation. Linked from the Short Wing Pipers site.

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Thanks that is it. Not hard to do the testing if you can find some clean air. I suspect you got far on the backside of the backside with the loss of wind. The AOA went pretty high pretty quick resulting in induced drag going up quick.

JonJay said:

You have the answer in your own statement, reduced airflow across the wing loses lift. It may sound counter intuitive, but lowering the nose in a sink decreases angle of attack and increases your airspeed, increasing lift.
In an aggressive sink, it may take both; lowering the angle of attack and adding power.
You then have to deal with the extra airspeed, but that is a lot better than bent gear, prop, and engine teardown. (recent occurrence at our airfield where this type of condition exists often).

I try to fly my approaches with a relatively constant pitch for the airspeed I am trying to achieve and use throttle to move myself back and forth on the glide slope. If I sink, I am not afraid to lower the nose to get back to my target airspeed.

Hand on the throttle, always, and be ready to throw it in if you can not arrest the sink. Your airplane will respond to that power far better with a lower angle of attack than it will if your nose high. Dragging it in behind the power curve is not a good place to be in any landing.

PS - I am with Mel. Always a full flap landing for me.

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Intuitively, I have a hard time pushing forward on the stick if the sink occurs about the time the flare should begin. You see ground coming up quick and react to it.

Perhaps the proof of the pudding is in the end result - no bent metal or unintended ground contact.

Intuitively, I have had a complete engine failure at about 800' and the stick did go forward to maintain flying speed. But to reduce AOA inside of 50' with a good engine, I'd have to reprogram my brain.

....different strokes for different folks...

David-aviator said:

....different strokes for different folks...

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I think what people are trying to (tactfully) say is that you may have been lucky on this one. The laws of physics don't lie, and can't be broken lest the ground come up and smite thee.

David-aviator said:

Intuitively, I have a hard time pushing forward on the stick if the sink occurs about the time the flare should begin. You see ground coming up quick and react to it.

Perhaps the proof of the pudding is in the end result - no bent metal or unintended ground contact.

Intuitively, I have had a complete engine failure at about 800' and the stick did go forward to maintain flying speed. But to reduce AOA inside of 50' with a good engine, I'd have to reprogram my brain.

....different strokes for different folks...

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I've been watching this discussion, but hearing a couple of things feel like I should comment. If I'm landing - no flaps, full flaps, partial flaps - and I encounter a sink at 50' agl, I'm adding power and maintaining attitude.

If I'm at 5' and encounter a sink, I'm raising the nose right now and might add power depending on the degree of sink. It's too late - you just have to protect the plane as best you can with the remaining energy you have.

Under almost no circumstance will I drop the nose in a sink situation near the runway. Sink to me means descending air and/or wind shear. With me, power is the answer. -8s drop like a rock when you get slow. Power/additional energy is what you need when low and slow.

2 cents

Low Pass said:

I've been watching this discussion, but hearing a couple of things feel like I should comment. If I'm landing - no flaps, full flaps, partial flaps - and I encounter a sink at 50' agl, I'm adding power and maintaining attitude.

If I'm at 5' and encounter a sink, I'm raising the nose right now and might add power depending on the degree of sink. It's too late - you just have to protect the plane as best you can with the remaining energy you have.

Under almost no circumstance will I drop the nose in a sink situation near the runway. Sink to me means descending air and/or wind shear. With me, power is the answer. -8s drop like a rock when you get slow. Power/additional energy is what you need when low and slow.

2 cents

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It's always risky discussing flying technique in a forum. Of course you wouldn't push the nose over in flare. As you mention it is too late and you are going to be scrambling to do what you can to keep the airplane flying.
The original OP stated that 50' is where the sink occurred. When you state you are adding power to maintain altitude, I would bet you are at least relaxing stick pressure if not slightly pushing to do so. You probably don't even know it as your instincts take over. Adding power will pitch the nose up, all things equal.

Each circumstance is different and only the pilot truly knows what the conditions where. I have found that most "sinks" end in ground effect. Shear is an entirely different thing and much more unpredictable.

We are blessed with a power to weight ratio in our RV's that allow us to recover from all kinds of situations with power.
I would be curious to hear from some of the experienced glider or turbine pilots we have in the forums. They don't have the luxury of adding power. What would they do?

Snowflake said:

I think what people are trying to (tactfully) say is that you may have been lucky on this one. The laws of physics don't lie, and can't be broken lest the ground come up and smite thee.

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Rob,

As a guy who flew for a living for some 42 years, let me say luck has a lot to do with surviving over the long term and I will take as much of it as I can get.

Sink occurs with all airplanes, dealing with it is NOT cut and dried. It is a matter of physics but in the typical everyday situation the pilot simply does not have enough information as to what is really going on with wind to deal with it successfully all the time. We develop techniques to be successful most of the time.

A burst of power with spun up jet engines usually caught it in time, but not always. The worst days were with a 20-30 knot gusting cross wind with hangars and other obstructions totally screwing with it. Sometimes, if timing was just right, forward stick would cause the gear (way aft of cg) to be on the rise as the aircraft settled on the concrete and the landing was so smooth people did not know we had arrived. That was personal technique, about half luck and half skill. Somedays you had to accept a prang on.

My experience with landing a tail dragger began seriously just recently. All previous history is with nose wheelers, and 98% of that in heavy stuff. So this is a process of developing techniques to deal with whatever comes up, especially in the RV-8.

In spite of volumes of information written on landing tail draggers from lots of good pilots, I am a with "Stick and Rudder" author Wolfgang Langewiesche who in 1944, without apology after explaining how to land a tail dragger 3 points and stalled, wrote wheel landing are safer and better than 3 pointers. So my technique is to wheel land. No big deal, it works for me.

Dealing with wind shear and sink is another matter. A discussion of AOA can get off track and contentious. Yes, it is absolutely necessary to reduce AOA in situations where a stall is eminent - but NOT always. It also may be a successful technique on short final but I am not familiar with it.

Wind shear avoidance, and training to deal with it if in it, was a big deal after the Dallas air carrier accident years ago. If an airplane is caught in a serious down draft close to the ground, what MIGHT save the day is full power, rotate to stick shaker if necessary, and fly out of it. That procedure is stuck in my brain. The thought of forward stick in such a situation does not equate. Anywhere else not close to the ground, yes, forward stick. But not there.

Hopefully, this will clarify the matter from my perspective and get me off the "you do not understand AOA" list.

JonJay said:

It's always risky discussing flying technique in a forum. Of course you wouldn't push the nose over in flare. As you mention it is too late and you are going to be scrambling to do what you can to keep the airplane flying.
The original OP stated that 50' is where the sink occurred. When you state you are adding power to maintain altitude, I would bet you are at least relaxing stick pressure if not slightly pushing to do so. You probably don't even know it as your instincts take over. Adding power will pitch the nose up, all things equal.

Each circumstance is different and only the pilot truly knows what the conditions where. I have found that most "sinks" end in ground effect. Shear is an entirely different thing and much more unpredictable.

We are blessed with a power to weight ratio in our RV's that allow us to recover from all kinds of situations with power.
I would be curious to hear from some of the experienced glider or turbine pilots we have in the forums. They don't have the luxury of adding power. What would they do?

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I'm only speaking about normally powered RVs. Clearly other types and conditions will have varied procedures and handling concerns. Without power, I'll grant you - push for increased airspeed and plan on leveling in ground effect.

Please note, I said adding power and maintaining *attitude*. My immediate concern is assuring the plane has enough energy to keep the flying safely, and then begin deciding whether you can continue or go on to some other course of action.

For the 50' sink, I will have to go try it to see what actually happens. But from this chair, thinking about it, I'm adding power depending on the severity of the sink. If hitting the ground is a possibility, I'm going full throttle and probably relaxing back pressure somewhat to make certain I do not slow the plane more than necessary (holding attitude, stabilize, accelerate, evaluate).

Just not going to lower the nose at that time (if the engine's still running). At 50', in a sink, I'd be afraid of adding complexity to the recovery.

The root of my concern with pushing over at 50' and less, is the accelerated stall. We've said there's an unstable air condition (a sink, turbulence, etc.). We're slow (landing). So to push over in these conditions, and then have to pull again as you get close to the ground, *might* put someone in an accelerated stall situation. Especially if they're excited and over pull.

I've done it. Wasn't excited, but was practicing steep, full flap descents to land. Had turbulent air crossing the end of the runway where I flared. As I pulled for flare, I got what was essentially an accelerated stall at 2-3'. Fortunately, in the half second it took for this to occur, I didn't bend anything and it stalled straight ahead.

But I will try to set up a simulation of both a try next time I'm up. Heck, might even set up a GoPro in the cockpit...

I think your doing fine David, by evidence that you had an issue dealt with it, and figured out how to overcome it.
One thing that I encourage any new tailwheel pilot, regardless of PIC hours in other types, is to get some hours in an antique tailwheel trainer like a Champ or Cub.
RV's are very forgiving machines. It isn't that Champs and Cubs are not, they are sweethearts, but they do tell you right away when control inputs are not correct. They do it slowly and deliberately. They are much more honest than our high powered, stubby winged, relatively heavy RV's in my opinion.
The value in learning to fly in one of these old machines and the instincts engrained are immeasurable.
I think everyone appreciates you posting your experiences. Nobody was there that day but you....but the discussions are not without merit.

Low Pass said:

I'm only speaking about normally powered RVs. Clearly other types and conditions will have varied procedures and handling concerns. Without power, I'll grant you - push for increased airspeed and plan on leveling in ground effect.

Please note, I said adding power and maintaining *attitude*. My immediate concern is assuring the plane has enough energy to keep the flying safely, and then begin deciding whether you can continue or go on to some other course of action.

For the 50' sink, I will have to go try it to see what actually happens. But from this chair, thinking about it, I'm adding power depending on the severity of the sink. If hitting the ground is a possibility, I'm going full throttle and probably relaxing back pressure somewhat to make certain I do not slow the plane more than necessary (holding attitude, stabilize, accelerate, evaluate).

Just not going to lower the nose at that time (if the engine's still running). At 50', in a sink, I'd be afraid of adding complexity to the recovery.

The root of my concern with pushing over at 50' and less, is the accelerated stall. We've said there's an unstable air condition (a sink, turbulence, etc.). We're slow (landing). So to push over in these conditions, and then have to pull again as you get close to the ground, *might* put someone in an accelerated stall situation. Especially if they're excited and over pull.

I've done it. Wasn't excited, but was practicing steep, full flap descents to land. Had turbulent air crossing the end of the runway where I flared. As I pulled for flare, I got what was essentially an accelerated stall at 2-3'. Fortunately, in the half second it took for this to occur, I didn't bend anything and it stalled straight ahead.

But I will try to set up a simulation of both a try next time I'm up. Heck, might even set up a GoPro in the cockpit...

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I think we are exactly on the same page actually. So much of my flying is by instinct, I find it hard to explain sometimes.

"Diving" toward the numbers is rarely, if ever, a good idea in any conditions that I can think of. I see this all the time at our home field as the decent to the West is steep due to tree's and the runway is short and downhill.

I don't think you can capture the subtleties on a camera but I would be interested to hear your observations.

Here is an image the day I had difficulty landing on our RW 26 due to a NW wind across the trees. The sink begins as one gets below the tree line and does get your attention. I probably was already adding power to fly out of there, a later 20? flap approach worked flying through it but it also could have been a brief period of lessor wind. I don't know for sure....it was good to get on the ground and put the airplane away that day.

Photo by Gale Derosers.