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Power on stalls


chanik

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On a recent trip to Sedona, diverted to Prescott due to lightning, I had occasion to talk to a grey-beard flight instructor at Guidance who specializes in LSA and mountain/high-desert flying. He made the point that 'everybody' is wrong about landing planes with flaps, specifically that you should always land with 30-40 flaps especially in LSA and especially if you have gusty or crosswind conditions. The argument comes down to much lower stall speed and more drag so the plane will stick on the ground once down and be more forgiving of a tail gust creating a stall. He said Cessna is mostly to blame for discouraging full flap landings but their reason (he claimed) was not that it wasn't better for landing but that it is very bad to leave them in if you need to do a go-around. His point WRT to LSA is that they are much more forgiving of full flap go-around so you have plenty of time to switch back to 15deg. I said I like the extra speed so extra control authority, countered with the idea that the real risk is being stalled near landing or popped in the air with a gust. That vulnerable transition to below flying speed is shortest and safest with full flaps is the idea.

 

The one easily testable part was stall speed. I did a battery of power-on stalls at 15 versus 30 degree flaps and do find a large difference in true stall speed. The indicated is only 40Kts down to 39kts but using the GPS ground speed on the same course, my true speed went from 38kts at 15deg down to 33kts using 30deg. Indicated is way off when the pitot is slow with a high angle of attack. BTW, full power stalls at 30 flaps are pretty interresting.

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The guy has obviously never landed a CT with full flaps and a 15 kt direct crosswind! It is not a good idea at all! You want a higher approach speed to maintain more directional control.

 

Especially with our flaperons. With full flaps and a crosswind the wing you are trying to lower will have the aileron nuetral and the other will be extremely low creating a bunch of drag on the wrong side. Also with the bigger difference in angle of attack because of the flaperons one wing will stall and fall out on you.

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Hi Kurt,

I'm with Tom and Eric. He evidently hasn't flown many very light aircraft. I have been flying only light aircraft since 1980 and a 1000 hrs in the CT alone. Landed in lots of winds and some in excess of 30+ mph. This guys needs to be in more light aircraft with full flaps in high winds and actually try 100 landings and then comment. He made comments just like other CFI's and GA mechanics. He compared it to Cessna and other heavier aircraft. Many of the landing accidents in the LSA community have been exacerbated by full flaps. If you are at 30 or 40 flaps you can still do a go around, I have done it in practice. The flaps in high cross winds will also give the wind a surface to act upon and leverage to get a wing up. Landing too slow and next to stall in high winds will get him in trouble one day. Like you said, full flaps in high crosswinds at stall speed gives little to no control surface authority or maneuvering speed. Plus if you are sitting at stall had you have a serious problem you have no speed or time to save yourself.Let the old CFI that says everyone else is wrong go his own way and hope he doesn't cost some new unsuspecting pilot his landing gear.

 

This is kind of like the mother watching all the solders parade by and telling the person next to her that everyone Else is out of step except her son.

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They fly Sportcruisers over there, not even any high-wing LSAs. I do somewhat enjoy arguing with super-opinionated old codgers. I didn't really agree with him either but he made some interesting points. He was correct about how much lower the stall speed is.

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Hi Kurt,

 

That's what flaps are supposed to do, lower stall speed. I'll take the little higher speed with better control and safety margin over bent gear any day. I'll meet you up at Love Field next time and we can double team him for fun.tongue.giflaugh.gif Then go to breakfast.

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Low wing aircraft, I think, generally handle a cross wind better than a high wing.

 

As for flaps/higher speed or not in a cross wind, lets talk about tail wheel airplanes of which I've owned many, given lots of dual, and received same from some of the best. The way I was taught, used and instructed was a little higher speed, wheel landing, and minimal flaps. The wheel landing, as opposed to a three point full stall, gave the extra speed with which to maneuver. Less flap, therefore less drag, made it a little easier to keep the speed up. Once on the ground forward stick kept the wheel landing attitude and firmly planted the plane on the ground.

 

All of this is contrary to what this guy is saying. It throws everything I have successfully used over 47 years out the window. I think he is wrong. I use the tailwheel example because it clarifies this, at least in my mind, and the concept applies equally to tricycle gear. Just don't try to plant it with more abrupt forward stick like you would in tailwheel.

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Flaps 30, at least on my airplane, is the sweet spot for lowest stall speed. Stall comes at least 2 knots higher at flaps 40. I respect a flaps 40 landing and definitely keep it in my bag of tricks, but prefer flaps 30 if crosswinds are moderate and not gusty.

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Low wing aircraft, I think, generally handle a cross wind better than a high wing.

 

As for flaps/higher speed or not in a cross wind, lets talk about tail wheel airplanes of which I've owned many, given lots of dual, and received same from some of the best. The way I was taught, used and instructed was a little higher speed, wheel landing, and minimal flaps. The wheel landing, as opposed to a three point full stall, gave the extra speed with which to maneuver. Less flap, therefore less drag, made it a little easier to keep the speed up. Once on the ground forward stick kept the wheel landing attitude and firmly planted the plane on the ground.

 

All of this is contrary to what this guy is saying. It throws everything I have successfully used over 47 years out the window. I think he is wrong. I use the tailwheel example because it clarifies this, at least in my mind, and the concept applies equally to tricycle gear. Just don't try to plant it with more abrupt forward stick like you would in tailwheel.

 

Totally agree, I use to fly L-19 bird dogs with 60 deg flaps, great for short field three pointers but when the winds got crossed up, no more than 30 deg and always wheel landings with higher speed and better control. Every aircraft is different but using less flaps in high crosswinds has been successful for me, and we get a lot of crosswinds here at Bisbee!

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Eric,

 

Did you fly the Birddog in the Army? All my time in them was with AK CAP. Great aircraft. National HQ CAP decided they all had to go since too many were groundlooped. Didn't have that problem myself. They went straight so long as you paid attention.

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I would opine that it is all about running out of rudder control in the crosswind. That happens sooner with more flaps, because at the slower stall speed with more flaps the crosswind component is larger. The stronger the wind and the higher the gust, the less flaps I use. WF

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I do nearly all my landings, including cross wind landings, at 30° flaps. I do more at 40° than at 15°. Did two at 40° today, one a dead stick and one at idle.

 

I went up with a friend one day and did over 50 approach (power off) stalls in every conceivable flap configuration. How you do the stalls affects stall speed. That is, if you fly straight and level, pull power and try to hold altitude till it stalls, it's different than if you establish an approach speed and pitch, then slowly pull the nose up (simulating trying to stretch the glide) till it stalls. The second is the way it's taught in AFH and will stall at a lower speed. In any event, because I'd seen some earlier discussion that 40° flaps stalled faster than 30°, I paid particular attention to it.. I found that in every single case, 40° stalled slower than 30°, just like the CTSW POH says.

 

Airplane Flying Handbook is a very good discussion of how to fly. It applies to Piper Cubs and DC-3s and more. What I see in the LSA movement is a tendency to bring up techniques learned in the ultralight field and apply them to heavier airplanes, rather than apply protocols that are time tested with airplanes that have been in the LSA field for 75 years. The result is a tendency to correct for landing challenges by a faster approach and touchdown than is traditional.

 

Several challenges with landing any airplane include side loading and a smooth touchdown. Flying faster increases the rudder effectiveness so you can handle a bigger crosswind or you can handle the same crosswind with less finesse.

 

Flying the airplane on gives you more airspeed to deal with the sink. To some extent, pilots avoid dealing with a flare at all. Why not fly all airplanes on? Because one of the most dangerous aspects of a landing is the speed of it. If something goes wrong, the faster you go the more energy there is available to damage things. Landing fast means a gust of wind can pop you back in the air. AFH teaches to touch down at the slowest possible speed.

 

I fly like the old CFI, except that I don't use full flaps in max crosswinds. I'll try to keep my speed down.

 

I find it amazing that SP trainers want to throw out everything we've learned over 100 years of flying all kinds of airplanes, including ones with very low weight and very low wing loading.

 

Tail wheel airplanes are significantly different because of the different placement of the CG. One gets plenty of arguments about wheel or full stall landings in gusty conditions, as the old time tail wheel pilots will admit.

 

 

 

 

 

 

 

 

 

 

 

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Eric,

 

Did you fly the Birddog in the Army? All my time in them was with AK CAP. Great aircraft. National HQ CAP decided they all had to go since too many were groundlooped. Didn't have that problem myself. They went straight so long as you paid attention.

 

I flew them as a Chase plane for the UAS I fly. We also had a T-34 and a Varga Kachina, the Bird dog was the best though. I flew them over 500hrs and found they did everything great except go fast! Didn't have any ground loops either, but saw another pilot have one trying to land in a quartering tailwind..not good! The T-34 was good for loops and rolls though but to fast for our UAS!

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I find it amazing that SP trainers want to throw out everything we've learned over 100 years of flying all kinds of airplanes, including ones with very low weight and very low wing loading.

 

Well put Jim,

 

I still approach at idle with full flaps more than 95% of the time. In my CTSW I virtually never run out of rudder attempting to land in crosswinds so why increase my speed and increase the potential for damage and injury?

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In a perfect world, the "lots of flaps" method can result in very nice, low-speed, short landings. It's a thing of beauty. But it requires more precision and a touch of luck. When the energy runs out... you better be within a couple inches of the runway. And beware of any gusts, pockets, dust devils, or such. The "fly it in" method seems to result in a higher percentage of good landings. Yes, they take up more runway, but most of us have lots to spare. I see the new Plane & Pilot, special Sport Pilot edition, suggests "flying onto the runway, rather than the traditional GA full-stall technique" especially for those with less experience. I can control my experience level, but I can't control gusts, winds, etc. They suggest the fly-it-in method even for experienced pilots in crosswind situations. (under "Tips from a veteran" one expert's opinion)

I practice full flap landings, and use them in short, dirt strips. And I'll certainly use full flaps if I ever have an emergency landing. I just prefer using 15/30 for my everyday landings, as they seem to give me a higher percentage of better landings.

After watching the Olympics, I'll put it this way... Full-flap landings are like the super-extra-difficult routine that can result in extra points... when executed perfectly,it'll get you the most points. But when you screw it up, you walk away in shame (or limp away with a bent gear). I prefer that less-complicated routine that has a higher percentage of execution.

Tim

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I'm in the full flaps camp. My CFI taught me to do this and his reasoning is that in windy or gusty conditions, full flaps keep you on the runway due to the high drag. I carry speed with pitch and/or throttle until it's time to touch down. Always have my hand on the throttle, ready for power when needed. So much control with the CTSW and also great recovery with applied power if speed gets too slow. The way I was taught was to just get down near the runway and fly it with full flaps. At the start, my CFI would work the throttle and I'd just fly. See what the plane's doing. Don't worry about landing but get it to 55 kts and fly the runway and see what it does. Work with the x-winds if there are some. When one gets to the point where they're comfortable with landing, pull some power and let it settle if there's a long runway. If not enough runway, go 'round and try this again.

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Hi Dick,

 

It's not always about the flying part. You can still being flying on the ground. 30-40 flaps give the wind something to push against while on the ground and lift the wing. Just like trying to carry a large piece of plywood in high wind. Keep it flat and level (zero flaps) and the winds blows over and you stay on two feet. Place the plywood flat against the wind like a large flap at 40 and the wind has a surface to push against. The flap down won't let the wing dump the wind pushing on it.

 

Here's the next fun question. We ask this one a few years back.

 

If the wind gets up under the right wing and starts to lower the left wing into the ground what is the fastest way to get the left wing back up before it strikes the ground and lower the right wing? (flaps or no flaps it won't matter)

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Fastest way to lift a wing is your rudder. If you landing with a high degree of flaps with or without wind get fht flaps to 0 straight away to decay lift. I never use 40 degrees even with a 2000' strip, 30 max. Usually use 0 or 15 deg. another fun approach technique is to chop the power at the numbers and dive towards the runway and get down omn the ground asap. (short approach)

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