SaultFresh wrote on Jan 15^th, 2010 at 3:23pm:

I dunno... tail stalls are more of a jet thing; I'm not sure. But it sort of makes sense (pitching up)- most horizontal stabs are angled relative to the fuselage so that they provide a downward force ("negative lift"). If that surface has stalled, that probably means its leading edge is too low (or ice accumulation is having the equivalent effect). So pitching up should reduce that "negative angle of attack" so that the stab starts doing its thing again.

Another indication that this is why is the fact that if that stab is providing down force, if it stalls, it stops producing down force... so the nose of the plane will try to pitch down, requiring you to pull back anyway.


Ask him if that's why... I'm curious myself, and probably wrong, because it seems so simple...   

Getting back to the heavier plane climbing scenario:

Let's forget the obvious problems associated with weight and its effect on takeoff roll and breaking out of ground effect... let's assume each pilot is already established at the desired climb rate to go from Point A to Point B, with Point B is at  higher altitude, over a specific distance. Like, for instance, each plane is cruising at 1500 MSL, and starting at a highway intersection, they must begin climbing so that they cut a ribbon on poles atop a ridge at 5000 MSL, exactly 5 miles from the highway intersection. They must each climb exactly 3500 feet over 5 miles. We know they can both do it (we're assuming the heavy airplane is within limits, not over gross). But something will have to be different, for sure. Each plane will have to blend airspeed and vertical speed in different ways to achieve the same goal of alt/distance.
We know damn well that if the aim is to get to 5,000 MSL sooner, the lighter plane will win, because the thrust and A of A is less hampered by weight. But the goal is two-pronged: a specific altitude and a specific distance, at a specific angle, just like the gliding-to-land scenario. There is no time requirement.

I am certain that the heavier plane will have to climb at a higher airspeed to reach a given altitude over a given horizontal distance (all V-speeds go up with weight, even Vx and Vy, so whatever the desired rate of climb is, the heavier plane will need more airspeed to do it, assuming the same available thrust as the lighter plane).
But will it take less time? I don't know. I think it will, but I'm not sure. Can the heavy plane match the lighter plane's rate of climb, and still move forward faster? Or will it have to compromise, logging the same amount of time as the lighter plane... or more? 

We know  that the indicated airspeed shows the velocity of the relative wind, so airspeed in a climb is not the same as groundspeed with no wind, as it would be if you were flying level between two points at the same altitude. Most of us figure our time-to-climb  based on horizontal distance... works well enough with a light single most of the time, but this is not entirely accurate, unless our climb angle is such that the hypotenuse of the triangle (the actual path through the air) equals the base (the distance over the surface). And it rarely does. 

 So... maybe that is where the tale is told... but wait, no; each plane is flying a path fixed by the dimensions of the same right triangle... the actual path traveled in this steady climb represents the same distance. A higher airspeed, it would seem, should yield a shorter time along that path. But can a heavier airplane really do this trick faster? Doesn't seem right. I am an empiricist by nature... I'd have to fly the two planes myself before I can answer that.

Whatever the difference, I think in most cases it would be negligible. The lighter plane will have an advantage initially, during the time it is accelerating, on the ground and in ground effect, as it approaches the speed required to yield the desired climb rate. The difference could be very pronounced, so I think from a dead stop on the ground to the altitude/distance waypoint (Point B), the lighter plane would complete the task in less time, even if the heavier plane can climb at a higher airspeed at the same vertical speed once the climb is established.

We're gonna have to discuss this stuff over a beer sometime.    You attack this stuff a lot like I do.. your attempt to understand it yourself, is driven from the perspective of explaining it to others.  'cept I'm more likely to accept the mysterious, aeordynamic stuff, and put hard math aside (ala that debate over what causes an airplane to fly..    )

There's a "Devil's Advocate" glitch in my attempt to fog the gliding scenario.. because I  DO  accept that the gliding distances are effectively equal on paper. My statement that our stored energy is a constant is flawed. Your explanation on climbs kinda points it out. Gravity itself is a constant, but the climb to get the heavier airplane up there, has stored more energy. It took a longer application of engine thrust. So the heavier airplane has more energy at it's disposal (eaten up by the higher airspeed during the glide). When the dust settles.. the conservation of energy dictates that both airplanes can glide equal distances.

HOWEVER..  my countless times going from TPA to a runway, in every load-range imaginable, STILL has me believing that the 172 with just me in it, will make the runway after engine failure on base, when the 172 with two freinds and a bunch of fuel will not. 

Quote:


If point B is distance from takeoff, AND an altitude.. the heavier airplane would need more thrust than the lighter.. AND bigger wings to get to the same point, at the same time.

Brett_Henderson wrote on Jan 16^th, 2010 at 6:16am:

But what if Point A was not takeoff, but some random point when climb is firmly established?

Brett_Henderson wrote on Jan 16^th, 2010 at 3:15pm:

Right...that shows that there is a rate of climb beyond the capability of the heavier aircraft (which actually jibes with common sense, whew!) .

But in our exercise, we're not merely trying to get the best rate of climb, or even the best distance to climb... we're trying to fly the same path at the same angle. It's a vertical and horizontal distance problem.

The assumption is that the heavier airplane will need to fly at a higher IAS just to climb fast enough to manage it... but will it get there faster? 

That's all I will say about this for now; it's making my head hurt.
this is what happens when you don't get to fly often enough...   

beaky wrote on Jan 16^th, 2010 at 7:31pm:


Definitely agree with this... haha... all this bad weather is ironically keeping me from an instrument rating... haha...