Dirt,

I think you made my point .. the flap extension doesn't "weaken the wing" as some say. As I said in my post, extending flaps changes the loading on the wing (how much, it's location, and the change in tortional moment imposed on the wing structure). Which is why the top of the white arc on your airspeed indicator is the max. flap extension airspeed (Vfe) for your particular aircraft, which is well below your placarded maximum structural cruise airspeed.

So if you're flying above Vfe, you should not extend your flaps, whether you're turning or not. And if you're flying up canyon and approaching the point of no return, you also should be flying slow anyway, far below Vfe, because of the simple fact of the much larger turn radius at high indicated airspeeds.

Not to mention the fact that at high DA, the true airspeed (and thus, "true turn radius") is much higher/longer for any given indicated airspeed at low DA.

But the fact that full flap extension limits maximum structural airspeed is irrelevent to the Canyon Turn, which as described by those who instruct on it, is a turn conducted at slow indicated airspeed (by anyone's definition, that's always going to be well below Vfe) .. and also performed with minimum wing loading, because you also relieve the elevator backpressure - which also reduces angle of attack to prevent an accelerated stall.

Duane

nmflyguy wrote:I dunno - this notion of a wing being weakened by extended flaps sounds like complete BS and old wives tale stuff to me.

Somebody show me the error of my way

All slowed up, full flaps (in the Husky . . . which is also take off flap setting), cranked over at 60 plus degrees, full throttle and hauling back on the elevator . . . I don't think it's possible to overstress anything except ones sphincter muscles.

Perhaps not germane to the discussion, but wing loading does vary with the application of aerodynamic controls. Consider an extreme case with a Nimbus 4 glider in a nose down attitude following an inadvertent upset (perhaps stall) in turbulent thermal conditions. Modern gliders accelerate very fast when nose down. In this case, the pilot applied spoilers (doubtless full spoiler as in most designs they will rather violently open all the way, once they are unlocked, if going really fast). The spoilers are located inboard, and whatever lift was being generated by that section of the wing is now dumped, instantly transferred that share of the load to the outboard wing (which was, according to witnesses already bent up like a "U"). The wing failed with outer panels shedding, and unfortunately neither elderly occupant was able to bail out.

So, to the extent that aerodynamic controls add or detract from lift, they will have an effect on wing loading. And as drag forces are transferred back into the structure, that too will affect loading on the structure. . . though I suspect in most cases, especially when below maneuvering speed, those forces are not going to be of much consequence.

Disclaimer: I ain't no engineer and wish I was a farm boy again.

nmflyguy wrote:Dirt,

I think you made my point .. the flap extension doesn't "weaken the wing" as some say.
Duane

Well then, glad I could help.
As wing load and g force apply to the canyon turn this "weakening" thing of course does not exist as damage to the wing even with a lower rated 3.8 g plane. Theoretically though the wing is "weaker" at 40 degrees in its ability to carry load in the C 150 vs the increase to 1670 pounds in the 152 if that plane is limited to 30 degrees. So Cessna, to achieve an increase in payload the cheap way took away the 40 degree position. Not that the wing suffers damage or becomes weakened but is weaker in the sense it cannot be rated to carry as much load. Like one simple skinny farm boy is weaker and cannot lift as much as a big simple farm boy. However if both stay within what the skinny simple farm boy is rated to lift, then no FAR's are busted. Even if no damage occurs , everybody knows the skinny one is weaker.

This would be giving the boys who chose the word "weakend" the benefit of course, if this is what they meant. I did not read their post on the subject. Again my disclaimer is I am just a farm boy although I have much experience to draw on as the simple skinny one.

Actually, the certification standard in Part 23 for Normal category aircraft requires that the structure meet the 3.8 G standard.

BUT, with flaps extended (any deflection) the structure need only meet a 2.0 G load standard.

So, the wing IS typically weaker with flaps deflected, and generally, that is because the flaps are attached to the aft wing spar. Air loads on deflected flaps impart a severe twisting moment to that aft spar, not really weakening the spar, but placing VERY different load paths onto the structure.

The reason Cessna reduced max flap deflection on ALL their aircraft (not just the 152) from 40 to 30 had nothing to do with increasing Gross weight. It had everything to do with numb nuts pilots continuing to crash perfectly good Cessna airplanes because they couldn't figure out how to fly them with flaps deployed to 40 degrees in a go-around. The entire Cessna line went to 30 flaps at the same time.

I'm not sure what Cessna did to increase the GW of the 152, but I doubt it had anything to do the structural loading on the flaps--more likely the improved climb performance with less flap hanging out there.'

At 60 degrees of bank angle, in a level turn, you will impart a 2 G load to the airframe. That is where I want to be in a Canyon turn, no more, no less.

And, you can't TURN the airplane unless you load the wing, folks. You can bank the plane all you want, but until you increase the pitch to load the wing, you're not going to turn much at all.


MTV