Landing Stall Question

Skyhawk4754

Skyhawk4754

Pre-takeoff checklist
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SW Minnesota
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Display name:
Willie
This not a trick question, I'm just a little puzzeled.....

Would you be more apt to have a landing stall when

A) using flaps,10-20 or 30 degree

B) no flaps

C) doesn't matter

thanks
 
As I see it, you're going to have a stall whenever you exceed the critical angle of attack.

Now, does that critical angle of attack change when flaps are used?

A - Yes, the flaps alter the shape and aerodynamics of the wing
B - No, the critical angle of attack does not change regardless of flap position
 
do you mean as you are landing? During my training, I've made approaches and had the stall warning go off on a no-flap landing just as the wheels touched, and nearly consistantly on a normal / soft field landing with 30* flaps.

If you are referring to having the plane to slow during your pattern work,.. turning downwind to base, or base to final, it can stall in any configuration if you aren't coordinated and carefull of your airspeed. Remember, the load factor increases with the angle of bank, which increases the stall speed,... Low and Slow is not a good combination.
 
Skyhawk4754 said:
This not a trick question, I'm just a little puzzeled.....

Would you be more apt to have a landing stall when

A) using flaps,10-20 or 30 degree

B) no flaps

C) doesn't matter

thanks
Click to expand...

Flaps are high drag, high lift devices.

How do they increase lift?

Flaps change the camber of the wing (Answer A in Tim's Quiz above)

If by "Landing stall" you mean the stall warning going off before touchdown -- keep in mind that buzzer is set to go off 5-10 knots before the actual stall.
 
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OK, flaps do change the wing, and while they lower the stall speed, they also LOWER the critical angle of attack. If you've done airwork at altitude you've noticed this.

Fortunately, while you're on the landing approach, you're generally more nose down, so I don't think it's necessarily easier to accidently stall the airplane. But you won't need to point it at the sky at the roundout either.
 
I think you're confusing AoA with Attitude, but I've been wrong before...


TMetzinger said:
OK, flaps do change the wing, and while they lower the stall speed, they also LOWER the critical angle of attack. If you've done airwork at altitude you've noticed this.

Fortunately, while you're on the landing approach, you're generally more nose down, so I don't think it's necessarily easier to accidently stall the airplane. But you won't need to point it at the sky at the roundout either.
Click to expand...
 
Steve said:
I think you're confusing AoA with Attitude, but I've been wrong before...
Click to expand...

I don't think so - the wing is fixed, so unless the relative wind changes, the angle of attack is directly related to aircraft attitude. In a landing approach, the relative wind isn't changing much (unlike in aerobatics, where it's changing frequently).

Go up to altitude, reduce power to idle, and then do stalls clean and with full flaps. I believe you'll find the stall warning going off (or the stall occuring) at a lower pitch attitude with flaps down, assuming the same rate of pitch up.

But it's late and I'm tired.
 
ok, maybe it's angle of incidence, then


TMetzinger said:
I don't think so - the wing is fixed, so unless the relative wind changes, the angle of attack is directly related to aircraft attitude. In a landing approach, the relative wind isn't changing much (unlike in aerobatics, where it's changing frequently).

Go up to altitude, reduce power to idle, and then do stalls clean and with full flaps. I believe you'll find the stall warning going off (or the stall occuring) at a lower pitch attitude with flaps down, assuming the same rate of pitch up.

But it's late and I'm tired.
Click to expand...
 
Skyhawk4754 said:
This not a trick question, I'm just a little puzzeled.....

Would you be more apt to have a landing stall when

A) using flaps,10-20 or 30 degree

B) no flaps

C) doesn't matter

thanks
Click to expand...
It doesn't matter. You can stall in any of the above configurations.

One isn't 'more likely' to cause a stall over the other. You could try to pull statistics that state that most fatal stalls in teh pattern happen with flaps out--but thats pointless because people put flaps out. That'd be the same as saying that most fatal accidents happen because the pilot is wearing a headset.

You're going to stall when you hit your critical angle of attack regardless of your flaps or the type of headset your wearing. I'm not really sure of what else to write--what brings this question on?
 
I'm a no flapper. My son is taking lesson from a younger CFI who teaches at a college.
He teaches 10 degree on down wind right before turning base, then another 10 degree on base b/4 final.
For some reason it just seems odd to me coming in with power so to speak....don't know if this is old school-new school or just different...
It would seem easier stall right before round out if you happen to cut power to soon if you are already at 20 degrees.
Just was wonder what some of the CFI's here had to say

Thanks
 
Skyhawk4754 said:
I'm a no flapper. My son is taking lesson from a younger CFI who teaches at a college.
He teaches 10 degree on down wind right before turning base, then another 10 degree on base b/4 final.
For some reason it just seems odd to me coming in with power so to speak....don't know if this is old school-new school or just different...
It would seem easier stall right before round out if you happen to cut power to soon if you are already at 20 degrees.
Just was wonder what some of the CFI's here had to say

Thanks
Click to expand...
So you don't use flaps? You're missing out on a lot of the short-field ability of your 172. 20 degrees isn't unreasonable--that actually seems odd. Full flaps is more appropriate. Are we talking about a 172?
 
TMetzinger said:
I don't think so - the wing is fixed, so unless the relative wind changes, the angle of attack is directly related to aircraft attitude.
Click to expand...

Or you change the shape of the wing and move the chord line by, say, lowering the flaps.

Draw a line between the leading and trailing edge and the angle changes compared to the attitude when you move the flaps.

Depends on how you define "angle of attack", eh?

Geoff
 
yep and it's a 57 vintage manual flap. It will go to 40 degree, and I have gone there on short field grass strips if needed but not on a normal basis. We have alot of wind here, most of the time it's a X wind and just seems smoother with out the flaps.
 
Skyhawk4754 said:
yep and it's a 57 vintage manual flap. It will go to 40 degree, and I have gone there on short field grass strips if needed but not on a normal basis. We have alot of wind here, most of the time it's a X wind and just seems smoother with out the flaps.
Click to expand...
I suggest you read the following article. There is some good information in here:
http://www.avweb.com/news/pilotlounge/192672-1.html

My opinion is:
In a light single engine airplane, like the Cessna 172, the slower you touch-down the better off you will be. This applies to crosswinds as well.
 
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Thanks Jesse.....I've always said never to old to learn. Also I did read you "slip comments" too
 
For a normal landing, I teach a stable approach from abeam the numbers. For a Skyhawk, it starts with power at 1500 RPM and flaps at 10. This results in pretty close to 500 FPM descent. During the remaining downwind, they lose about 200-250 feet. For the 172M, it's 90 MPH. We turn base with the threshold 45 degrees behind your shoulder, adjusting somewhat for known wind aloft.

On base, it's still at 1500 and another 10 degrees. Continuing descent at 500 FPM, it's down another 200-250 feet. Speed is 80 MPH. Usually, it's wings level just long enough to insure final is clear then turn final.

After turning final, it's full flaps (40 degrees) and speed at 70 MPH. Continuing a stable descent at 500 FPM and 70 MPH keeps them pretty well on glide path. Power at 1500 remains with exception of changing winds/gusts or descent rate changing.

About 15-20 feet above ground, I teach a very gradual "round out" while simultaneously reducing power. At the "bottom" of the round out, your mains should be just a few feet above the runway. The end of the round out should result in about 3-4 degrees of nose up pitch.

During that time, you're bleeding off the energy of airspeed, decreasing lift and continuing the descent the last few feet. If it's even near perfect, you'll be stalled as you kiss the runway.

Edit: (I also teach to ignore VASI or PAPI lights if installed. I've been picking up students who were allowed to dwell on them.)

One problem I encounter are students who fear the runway coming at them and prematurely pull the nose up. Obviously, you balloon and at the same time airspeeds decreases rapidly. So, the student pushes the nose over only to find they are falling. Gravity sorts things out for you rather quickly resulting in a good plop on the runway if not caught. Then, it's telling them to pull the nose up or me grabbing the yoke and softening the touchdown. Rarely has it resulted in adding power. Only once have I had to go around.

The other problem is a perfect round out at the right height above the runway but not continuing and holding nose up. So, landing is more flat and results in varying degrees of a plopping it down.

If it's less flaps or no flaps, the speeds increase and the round out is much less defined but eventually the nose is pitched up to slow down and allow descent and touch down.

For short field and soft field, power is off on short final keeping the descent rate high. Just before round out, a touch of power is added to soften the descent rate and the subsequent touch down. For soft-field, a bit of power is left in during touchdown and beginning roll-out.

This has worked pretty well for me since I started teaching. It was what I was taught during my commercial training but no one had the words to describe what I was doing. I stopped using the "F" word in lieu of "round out" as it better describes what you want to accomplish before touching down.
 
Last edited by a moderator:
Skyhawk4754 said:
yep and it's a 57 vintage manual flap. It will go to 40 degree, and I have gone there on short field grass strips if needed but not on a normal basis. We have alot of wind here, most of the time it's a X wind and just seems smoother with out the flaps.
Click to expand...

The key to consistent, safe landings is to treat every landing as short field landing. This means arriving at the ground with as little energy as possible. This can only be achieved with slow speeds (1.3 x Vso is a good target) and full flaps.

On most aircraft, the first 1/2 travel is added lift with a slight drag penalty. This will allow to wing to fly at slower airspeeds. The 2nd 1/2 of travel is almost all added drag. This helps steepen the descent at the same airspeed.

Many pilots figure out that they can "grease" it on and have all that great visibility by landing fast and flat. That all seems to work at the home 5,000' airport.

Some argue that in crosswinds flaps should be minimal, if used at all since the wind will "catch" the wing.

The contrary argument is that the greater danger is the swerve or ground loop on landing rollout -- both cases much more likely when rolling very fast on tiny wheels.

So I've come to the conclusion that full flaps, every time is the way to go, unless there is some compelling reason not too (In my case, gusts 15 knots or greater, perhaps, where the object is a solid planting of the airplane, not a full stall, nose high regular landing).
 
Skyhawk4754 said:
I'm a no flapper. My son is taking lesson from a younger CFI who teaches at a college.
He teaches 10 degree on down wind right before turning base, then another 10 degree on base b/4 final.
For some reason it just seems odd to me coming in with power so to speak....don't know if this is old school-new school or just different...
It would seem easier stall right before round out if you happen to cut power to soon if you are already at 20 degrees.
Just was wonder what some of the CFI's here had to say
Click to expand...
Yes, your method is "old school." Back in the old days, the FAA pushed power-off landings staying within gliding range of the runway, and using only the minimum flaps necessary. However, based on studies of landing accidents, they changed their tune in the mid-70's to recommending partial power stabilized approaches with flaps. See http://www.paragonair.com/public/docs/Safety_Pamphlets/P8740-48.html for more on that. Thus, your son's instructor is teaching him the way the FAA recommends, and you are showing your age.:)

As far as attitude vs AOA, the change in wing curvature with the extension of flaps (trailing edge moves down) changes the effective incidence angle of the wing, and thus changes the relationship between AOA and pitch attitude significantly. All things being equal, in level unaccelerated flight, you'll stall at a much lower pitch attitude with flaps extended. This is why it's so much easier to bang the tail on the ground when trying to make a full stall landing with no flaps.
 
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Capt. Geoffrey Thorpe said:
Or you change the shape of the wing and move the chord line by, say, lowering the flaps.

Draw a line between the leading and trailing edge and the angle changes compared to the attitude when you move the flaps.

Depends on how you define "angle of attack", eh?

Geoff
Click to expand...

DOH! Right. Next time I'll have my aerodynamics reference handy so I can use the terms correctly. I described the effect correctly, but not the WHY - the change in wing shape DOES affect the angle of incidence. I now will think of the flaps as "tilting" the overall wing chord line in relation to the body of the aircraft.
 
Capt Ron your picture is not clear enough in the avatar to see if you have gray hair or not...:dunno: but yes I'm showing my age and it's good to laugh about it once in awhile as long as I don't let my mind slip I'll be fine. It has been along time since I did much flying and it's a little bit of a challenge for me, but it's coming back more ever day. I'm happy that my son took up the interest or I may have never gotten back into it.

Ok so teach this old dog would ya.... the 57 has the capability of 40 degree flaps, if I'm going to use em give me the skinny starting with the down wind b/4 the numbers, rpm,rate of decent, etc etc.

thanks
 
Skyhawk4754 said:
I'm a no flapper. My son is taking lesson from a younger CFI who teaches at a college.
He teaches 10 degree on down wind right before turning base, then another 10 degree on base b/4 final.
For some reason it just seems odd to me coming in with power so to speak....don't know if this is old school-new school or just different...
It would seem easier stall right before round out if you happen to cut power to soon if you are already at 20 degrees.
Just was wonder what some of the CFI's here had to say

Thanks
Click to expand...

There is no better source of questionable information than a gaggle of flight instructors, and I include myself in that statistic. Have you tried what Cessna suggests in Section 4 of the Pilot's Operating Handbook (Normal Procedures)?

Whenever a CFI suggests/recommends something, ask him or her to show you what the manufacturer has to say on the subject. Don't operate on the basis of opinions. :(

Bob Gardner
 
Capt. Geoffrey Thorpe said:
Or you change the shape of the wing and move the chord line by, say, lowering the flaps.

Draw a line between the leading and trailing edge and the angle changes compared to the attitude when you move the flaps.

Depends on how you define "angle of attack", eh?

Geoff
Click to expand...

I'm another immigrant from RAP. Sounds like some good discussion here.

Lowering the flaps changes the angle of incidence of the inner wingspan, so its AOA increases relative to the rest of the wing. However, the camber is also greatly increased so the stall speed for the whole thing actually drops some, around 5 knots in a 172 at 40 degrees, most of which happens in the first 20 degrees. Most wings are designed to stall at the roots first, so stall behavior with flaps up or down isn't much different except that the deck angle will be lower with flaps extended.
Stalling on final is a rare problem. (Stalling and spinning while turning base is a different problem altogether, caused by skidding the airplane.) Most problems arise out of approaching too fast and getting into ground effect and either floating forever or it gets landed three-point and raises the risk of porpoising or wheelbarrowing or skidding the tires while trying to stop or just ending up in the rhubarb. And too much speed often comes from being too high and diving at the runway to get down. Doesn't work.
The POH has approach speeds listed, and those are plenty high enough. And THAT speed should be bled off close to the threshold before getting into ground effect. It's called the round-out and the textbooks describe it. The flare comes after the round-out. Two different things, but seamlessly put together.
A 172 would have a hard time getting to stall angle in the landing flare. We've had students drag the tail in the soft-field landing flare using a little power. The airplane is still flying. The $40 tail tiedown ring gets busted off. I get to fix those things that get busted by poor technique, and as an instructor as well as an engineer I get a little annoyed at times. Not a happy combination.
Angle of attack is difficult to determine while flying. The airplane's attitude is only part of it; the airplane's flight path is the rest, and you can have a high AOA with the nose level if you're slow enough to be sinking at a good rate. That's where airspeed control comes in.
Good landings start when you turn downwind. Plan ahead, get to the right altitude at the right places and the right speeds and everything improves enormously.

Dan
________
FJ1100
 
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bobmrg said:
There is no better source of questionable information than a gaggle of flight instructors, and I include myself in that statistic. Have you tried what Cessna suggests in Section 4 of the Pilot's Operating Handbook (Normal Procedures)?

Whenever a CFI suggests/recommends something, ask him or her to show you what the manufacturer has to say on the subject. Don't operate on the basis of opinions.
Click to expand...

Another good source of information is the Airplane Flying Handbook (required reading for Private, Commercial, tailwheel, ME and CFI candidates).

Here's one tidbit on flaps from the AFH:

USE OF FLAPS
The lift/drag factors may also be varied by the pilot to adjust the descent through the use of landing flaps.
Flap extension during landings provides several advantages by:

  • Producing greater lift and permitting lower landing speed.
  • Producing greater drag, permitting a steep descent angle without airspeed increase.
  • Reducing the length of the landing roll.
There's plenty more in there...

In a related topic -- Unfortunately, Raytheon Beechcraft dropped short field takeoff and landing in the Normal Procedures section, so for practical tests the default procedure is the AFH and the PTS.
 
bobmrg said:
There is no better source of questionable information than a gaggle of flight instructors, and I include myself in that statistic. Have you tried what Cessna suggests in Section 4 of the Pilot's Operating Handbook (Normal Procedures)?

Whenever a CFI suggests/recommends something, ask him or her to show you what the manufacturer has to say on the subject. Don't operate on the basis of opinions. :(

Bob Gardner
Click to expand...
Agreed. We'll teach the normal application as specified by the POH. But, we also teach what happens when you stray from those numbers... mainly, the difference between a powered glide to a falling refrigerator to a skipping rock with wings.
 
Indeed a good discussion. Thanks to all for all the info.

Hope I didn't scare Capt Ron off with the gray hair comment:confused:

It is a rare evening in SW Minnesota we only have a lite breeze around 8mph so I think I'm going to go out and try some of this good stuff I learned.

Thanks again to all....you too Kate
 
Not scared, just not here at the time -- gimme a chance, as I've flown three hops since my last post.

In any event, I fly a '57 172 about like I fly any other 172:
  • Slow to 70-80 knots on downwind.
  • Abeam the numbers, pull carb heat, reduce to 1500 RPM, and drop 10 flaps
  • Use power to control descent to turn base at 800 AGL
  • On base, drop 20 flaps, slow to 65-70 knots and use power to control descent to turn final at 400 AGL
  • On final, drop full flaps, slow to 60-65 knots and use power to control descent to the runway.
Convert knots to mph as appropriate. Use bottom end speeds when light, top end speeds when heavy.
 
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