Alright, I've an aerodynamics/how-the-wing-things-work question. I've found a HUGE difference between regular stalls (or, how I learned them) and a different sort of stall, which I've heard is called 'accelerated,' but I'm sorta foggy on that whole idea. I read the section in my Jepp commercial book, and I didn't quite get it. I talked with one pilot who's got a good number of hours in an aerobat, and i'm still foggy on the idea. so i'll spell out the two scenarios, ask my question, and i'll be curious to hear what you all know/thing/ponder/muse/opine!

Two scenarios in a 152...

1. From a cruise, reduce power to ~1500 (and pull carb heat on) and hold altitude with the elevator. Eventually comes that lovely "sccccrrrrrreeeeeEEEEEE!!", then the nose drops, usually along with one wing or the other. Ease up on the back pressure & level the wings with rudder, at the same time carb heat off & full power, recover altitude when the plane's flying again.

2. Same thing, but work the flaps out to 20 degrees while slowing down, and when the airspeed comes down to 50, add power for level flight. trim for hands free flight, and tah-dah! Slow flight! Mosey along, practice gentle rudder scootching turns, lots of fun for all, right? yup! now, from that configuration, bring the nose up, stall horn goes and FWOOM! Big nose drop and really big wing drop (left wing, if that's important). I tried this out the other day and it kept me on my toes! Shortly after I started my normal stall recovery steps, I yanked the power out, as my airspeed was climbing pretty nicely, what with that big nose drop and all. the left wing really didn't seem like it wanted to come back up, even with full right rudder. eventually it did, but simply not with the same quickness that i'm used to.

so. here's my only idea: trimming for slow flight adds a boat load of back pressure, which if not accounted for would lead to a greatly exaggerated stall entry. but it seems like there's more going on then an exaggerated stall. it almost felt more like a spin entry...but i was being rather careful to stay coordinated. Hmm.

questions:

a. is scenario #2 an "accelerated stall?"
b. in scenario #2, whatever it is, why the super exaggerated wing drop?
c. am i making any sense? i'm quite prepared to hear a 'no' for this one
d. any suggestions for aerobatics training in the lower 48? i'll be down there for my ifr ticket in a month or so, thinking of tacking on some twirly/spinny training while i'm down there

thanks!
dave

PS: extra request! anybody know of any aerobatics schools/instructors who use 152 aerobats? significantly less cool then a decathlon or citabria, WAY less cool then an extra or pitts, but it would seem (to me...maybe i'm wrong?) that in my goal of make-me-a-safer/smarter/better-pilot, it'd be best to get aerobatics training in the same-ish airframe as the one i'm puttering around in.

Dave, where in the lower 48 are you going to be?

To answer your questions:

a) no, an accelerated stall is when the wing stalls at a higher load factor - like if you were maintaining altitude in a 45 deg angle of bank and performed a stall. You could also yank full aft stick/yoke at an airspeed above your 1g stall speed but below your Va (maneuvering) speed and also produce an accelerated stall because in yanking the stick/yoke, you've increased the load factor and the wing will stall at a higher airspeed. Va is supposed to keep you safe structurally, but I personally wouldn't go around doing that one.

b) in your power off scenario, its likely that you weren't too far on the back side of the Cl curve before you ran out of elevator effectiveness and were unable to pull into a full stall break. With the power on you've got considerably more airflow over the tail, allowing more elevator effectiveness and allowing you to pull deeper into the stall which nets you the sharp break you noticed.

c) It's kind of a combination of a lot of things, but is it possible that you were subconsciously trying to lift that wing with some aileron as well? If so, that would increase the local AoA of the outboard section of the left wing, holding it into a stalling scenario longer and making it harder to lift with the rudder. Also, poor wing rigging could cause this as well. And being trimmed for slow flight, holding elevator forces neutral would put more up elevator inputs via the tab than if you were trimmed for cruise flight. In essence like recovering from a stall while holding aft elevator pressure - makes sense to me that it'd be a slower recovery.

thanks!

what is the CI curve?

i'll be in tucson. hopefully i won't melt!

in my memory, i was positively steller with the ailerons...didn't touch them a single bit. but to be frank, yeah...it's likely i had some subconscious pressure on the yolk happening.

so: not an accelerated stall, because i wasn't increasing the load factor / g's. likely it's a combo of the extra airflow from extra power, the trimmed-in back pressure, and maybe just an eentsy-teeny-tiny bit of subconscious inappropriate aileron use. i buy that.

dpadvo wrote:PS: extra request! anybody know of any aerobatics schools/instructors who use 152 aerobats? significantly less cool then a decathlon or citabria, WAY less cool then an extra or pitts, but it would seem (to me...maybe i'm wrong?) that in my goal of make-me-a-safer/smarter/better-pilot, it'd be best to get aerobatics training in the same-ish airframe as the one i'm puttering around in.

Catherine at KUOS does spin and aerobatic training in a Cessna Aerobat. http://www.aceaerobaticschool.com/

Other than what has been said, don't necessarily have answers. But I will say that some airplanes like to dip a wing in certain stall scenarios, no matter whether they are coordinated or not. And you can find that behavior in one plane, but not another of identical model/configuration. So get real familiar with whatever you fly.


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dpadvo wrote:thanks!

what is the CI curve?

No worries! It's a graph that plots the lift coefficient (Cl) vs alpha, or angle of attack, for a given airfoil. If you look one up, you'll notice that up to a certain point Cl will increase as alpha increases, then as alpha continues to increase Cl starts to decrease, but still stays quite high. The definition of wing stall is the peak of this curve. The airfoil still generates quite a bit of lift for a small alpha beyond stall, but at this point drag goes up exponentially so it's not really usable.

Cam Tom 12 nailed the aerodynamics. Yes, training in the C-150 Aerobat would be more useful to you safety wise. Less power to weight make you more aware of what a normal airplane wants to do. The low powered airplane is comfortable with more than you would think, but it doesn't like to climb so much. It will make you realize the energy achieved in the energy management zoom climb is useful. Pilots who don't believe their airplane will necessarily climb are safer pilots.

CamTom has the essentials, and explains accelerated stalls.

But at least one reason that the plane rolled off to the left in your second scenario is that you said you were using "cruise power". I don't know exactly what you mean by that term, but I assume it's significantly more power than in your other scenario.

In that case, left turning tendency is probably what's causing that rolling tendency. That is a combination of propeller p-factor and engine torque, both of whitch tend to drive the airplane to the left. With the airplane at a high angle of attack, this turning/rolling tendency will be more pronounced.

It's also possible that the airplane is slightly mis rigged, or that it's had some "tweaking" at some point such that it tends to go left a little more enthusiastically.

But, my reading of what you describe sounds perfectly normal for a power on stall.

MTV

DPALVO: Hope I got it right.

I agree with all the above fellas as they are way ahead of my aeronautics memories.
Would like to add just three items:

1: Pull the carb heat on FIRST. Not a big deal in a Lyc. - but can get critical in some Continentals. Once the power comes back you are no longer generating heat for the carb heater to transfer. Relative I know. All the Lycs. I've flown run the intake air UP through the hot oil sump. 1500 is my usual rpm during most landings, gives me some up/down options, have had too many old Continental "choke" and stumble from idle.

2: I usually do that kind of practice with neutral trim. When I need to push forward I do not want the elevator trying to argue with me. I could be wrong but it is one of my old habits.

3: When doing stall with power, (variable settings) I was taught to keep the right foot on the rudder just enough to ensure you are going straight ahead, like on take-off. Counters what MTV wrote about P factor etc. Some instructors want to see almost a half ball to the right on powered stalls. They don't like a fall off either.

Different planes - different pilots - different results.

Geez how old pilots can rag on.
Chris C

MTV pointed out that P factor and torque increase with power. Adverse yaw problems are worse when slower. Keeping the longitudinal axis lined up with a distant target is important in stalls and landing. Slow flight and stalls teach what control keeps the wings level and the nose on target. It ain't the aileron. And like the last post pointed out, the ball has little to do with it.

Since the OP talks about performing stalls in a new to him aircraft, it's worth noting that this is a VERY good process to go through any time you get in a new aircraft type that you're going to be flying. Exploring the stall characteristics of a new aircraft.....even if that plane is the same model you've been flying is a really good idea.

But how to go about it? Here are a couple thoughts:

Obviously, you want to start this process at a respectable altitude. And assume the worst....so a little extra height for Mom is good. I like at least 3000 agl or more

First stall (after clearing the area) is flaps up, straight ahead, power off.....the simplest task here. Take it right to the aerodynamic buffet, then recover.

If everything seems fine, Climb back up, then try one with the first notch of flaps, no power.

If good, try one with full flaps, no power.

If that's good, climb back up, clean it up and try a no flap, power on stall. Most times I don't use full power, because of P factor those MAY get a bit aggressive, and I'm still not ready to trust this bus yet.

Next, I'll try a power on stall with flaps.

If nothing untoward raises its head (like an unexplainable hard roll off, or ??) I climb back up and do a "falling leaf" stall, which is ALWAYS done power off, flaps up. Enter the stall, and at the buffet, bring the yoke all the way to the aft stop, and keep the airplane from rolling off with RUDDER ONLY.

This is best done FIRST till you're comfortable with an instructor who's done a lot of these. And, I HIGHLY recommend spin training prior to playing this game as well......if you're slow with your feet or elevator, that's where you're apt to wind up....pun intended.

If, at any point in this drill the plane rolls off and you can't stop it with rudder, immediately apply nose down input on the elevator to recover. And mind your height.

Doing this I've found virtually identical aircraft, some brand new, with some very different stall characteristics.

Go at it carefully and if at any point, you see something you can't explain, STOP until you can explain it.

Be careful out there, and know thy aircraft before you try those short field landings.....

MTV

Speaking of stalls...I can't count how many times someone has been talking to me about what approach speed to use for a (short) landing, and when I ask what their airplane stalls at they reply "well the POH says...". I usually ask if that's indicated, calibrated or true airspeed. Then I remind them that they're flying the airplane, not the POH. I always recommend that they load the airplane up to their usual flying weight, take it up to about 3000' AGL, and do some approach stalls. Power off, full flaps, just like if they were gliding in to a landing, then start easing the stick back & see where it quits flying. Then they have a valid reference point to work with, and can start out at Vso x 1.3 and start working their way down.

This is best done FIRST till you're comfortable with an instructor who's done a lot of these. And, I HIGHLY recommend spin training prior to playing this game as well......if you're slow with your feet or elevator, that's where you're apt to wind up....pun intended.

If, at any point in this drill the plane rolls off and you can't stop it with rudder, immediately apply nose down input on the elevator to recover. And mind your height.

Doing this I've found virtually identical aircraft, some brand new, with some very different stall characteristics.

Go at it carefully and if at any point, you see something you can't explain, STOP until you can explain it.

Be careful out there, and know thy aircraft before you try those short field landings.....

MTV

In addition to the good stall practice already posted, I like to practice accelerated stalls. Probably not recommended until after you have had spin training, though. At safe altitude, set up a power off, approach to landing stall, when you get slow, go into a coordinated 20-30 degree turn and pull back smooth and steady until it stalls. (It is the opposite of the "energy management turn" taken to its conclusion) In the planes I fly, when I ease up on the back pressure and recover, the wings seek level. It's good practice for what not to do in the pattern.

Yes, practice any and all stalls is worthwhile, no doubt. I didn't note definitively up front that the purpose of the stall series I described is what I use when I get in an airplane that's new to me to determine if the plane has any rigging issues. To accomplish that, no real need to do accelerated stalls, and the sequence I described can be done in just a few minutes.

I once flew a brand new Scout that had VERY ugly stall characteristics initially. A mechanic rigged it per the factory recommendations and it was a pussy cat. We used two C-172-S for spin training at the school. They were brothers, came out of the factory at the same time. One was an enthusiastic spinner....easy to get into a spin (well, as easy as any 172 is) and stayed in the spin as long as you held full in spin control inputs. Then recovered nicely. The other airplane wouldn't spin unless the pilot did something to aggravate it, as in use power and aileron at the stall break..... And, even with full in spin controls, it would pop out into a nasty spiral very quickly. I was able to get it to two turns a couple times, but no more.

Point is, very similar airplanes, yet quite a difference in wing rigging.

But, for flight proficiency, accelerated stalls are good practice.

MTV

This is great!! I could have written this exact post in 1985. First and most important my primary instructor was scared to fly, and especially hated stalls. So off I go on my second solo, first solo out of the pattern. I am practicing slow flight in a 152 dirty, and think to myself "self, you are all set up for a landing stall" except I never pulled the power, now this is in socal and I was carrying a lot of power to maintain altitude. So back I pull the elevator, the burble starts, my left wings starts dropping, and I counteract with my aileron (which I found out later exacerbated the problem. All of a sudden I am in a full blown spin, looking at the ocean. I remembered reading about spins and that the first step was to pull the power, so I did that and the wonderful 152 pretty much came out of the spin by itself, however, I got a little excited and pulled back on the elevator, and boom! secondary stall. Got that sorted out, and flew back to the airport.

The first instructor that I found in the FBO I asked if he did stalls and spin training, he said yes and I did my next flight with him. That is when I found out about the rudders. I never soloed a student without spinning them.

My buddy asked if I was scared, I told him I really didn't think so but somebody crapped in my pants.

Dave, I'm a little concerned that you're this far along in your flying life (you said you're about to go for your IR, so I'm assuming you have your PPL) without a better understanding of stalls. You've gotten some good advice here which is 100% on target, but it's really basic stuff that you should have been taught already. Granted that accelerated stalls are a commercial requirement and not a private requirement, you really might want to get with a good instructor and play with all the kinds of stalls, much like Mike (MTV) described.

A 152 is an excellent airplane for practicing all kinds of stalls, and it will spin like crazy. Its only real fault is that its spin characteristics change after several turns, which throws some people off a bit. How good it is as an aerobatics trainer, I don't really know. My own aerobatics training was in a Super Decathlon; the most I've done in 150s/152s is several turn spins. But you can certainly learn a whole lot about airplane control in any basic aerobatics course, no matter what aerobatic airplane is used.

Cary

cary - thank you for the wisdom & concern, i really appreciate it, as well as the tactful manner of expression .

i've had something of a hunch that my stall comfort-level/ability-level isn't exactly where it ought to be. i'm almost completely comfortable with power off "regular" stalls, a bit less comfy with power on stalls. i'm almost...but not quite...comfy enough to do spins on my own. i read something somewhere about simulating (at altitude) a stall in a uncoordinated turn to final...that sounds like something i want to do with an instructor! sounds rather spinny.

i hope a mix of careful/gradual practice on my own and liberal doses of good & targeted stall/spin instruction will get me to a more comfy place .

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headoutdaplane - hah! i'll think of that next time a stall recovery doesn't go as smoothly as i would've liked it to!

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all - thank you for sharing experience/wisdom! if there's any more out there, keep it coming!

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random thought: so...full power, flaps at 10 degrees, nose high attitude, trimmed for takeoff (so, 65-ish knots at full power)...if bringing the nose up into a stall can very very easily turn dramatic quickly...that would then mean that short field takeoffs with flaps at 10, trying to clear an object at the end of the runway, could turn really, really really ugly in a hurry with a misread/miscontrol of the aircraft. hmm. seems like a hell of a good reason to get confident in that sort of configuration/situation...

dpadvo,

Stall practice helps us understand the airplane in high pitch up situations both with and without power. The objective in landing is actually to stall at the desired touchdown point while just off the ground.

The objective in takeoff, however, is to accelerate as quickly as possible and to clear any obstructions with as much speed (not altitude) as possible. We don't want our comfort with stalling to become comfort with near stall speeds on takeoff when greater speed would be available in ground effect and just clearing the obstruction. Assuming you are beyond PPL, go with a soft field type takeoff but don't let the airplane climb above low ground effect (six inches to three feet) until near the obstruction and then zoom over with confidence. If you do Patrick's potato count. With a 152 at sea level and sixty degrees, the nose wheel should be off within four or five potatoes or abort. The mains should come off in another four or five potatoes or abort. Set the flaps before you start but you will have to haul the airplane off when it will fly in low ground effect, not when it will climb out of ground effect. Don't let the airplane climb right away. Level the nose to stay in low ground effect. Wiggle the control wheel fore/aft a bit to get the feel for where you want to be. Finally just stay put in low ground effect until near the obstruction or well above Vy. Vx has no place in the short field takeoff over an obstruction except in the zoom up after the level run in low ground effect.

During power stall practice, do everything slowly and notice that your 152 is descending in a mush before the stall. This mush, at a high pitch attitude, is what gets pilots in trouble with obstructions. The only correction for this mush is to push forward on the control wheel. On takeoff, you will have full power. There is no more to add. Climbing too soon and at a higher pitch attitude than necessary is what causes mushing on takeoff, especially at high density altitude.

Keep going up,

contact

Jim's right. I've said for years to students that you don't need to clear an obstacle on takeoff by fifty or a hundred feet.....you just have to miss it.

MTV

Let me add, that it's a lot easier to stay in low ground effect on the short/soft take off if you have a little nose down trim to start with. As an airplane gains speed, it tends to climb, but if it climbs out of low ground effect before it has reached Vx, it won't climb at all thereafter unless it has gobs of extra power, which a 152 does not have (obviously ). It'll just mush along at 50-60' AGL, and that's a very uncomfortable situation--both speed and climb stagnates.

If you start with a little nose down trim, you'll find yourself pulling on the yoke to keep from touching down again, but I think that's easier than pushing to stay low. Then when your airspeed has increased to somewhere between Vx and Vy, you can pull back enough to climb out not slower than Vx and trim for the climb-out. The really neat thing about staying in low ground effect is that the airplane will accelerate much more quickly than if it's either on the ground or climbing, because there's significantly less drag.

Cary