Rob - I was answering Gordon. I have no crop dusting experience.
wasted thrust, not wasted energy..
I think you want to convert thrust into some form of energy. Potential energy is what you need when clearing the trees. Kinetic energy is what you get when you go fast - but remember drag increases as the square of airspeed, so in the runup to the zoom, you are converting some of your thrust into heat, when it would be better to convert it into potential energy (altitude).
Someplace in my deep distant past I remember studying zoom climbs as opposed to Vx climbs. I think it was part of a private pilot study course. That stuff is gone forever - folks are being taught to climb at Vy + 10, which sort of makes 180 hp engines and Borer props a waste of time and money. And they are taught to do so at flaps 10, because flaps mean lift and lift is what makes you go up. I am the odd man out - I believe that excess thrust is what makes you climb, and less drag = more excess thrust. At least for rate of climb . . .
Well Bob, you like the tech stuff, so here goes with my thinking: You're pretty close - - More generally, excess
power is what makes the airplane climb. Excess power delivered to the mass of the aircraft is net thrust times velocity, where net thrust is thrust minus drag. At a constant speed that excess power is linearly proportional to rate of climb. That's because rate of climb is linearly proportional to rate of change of potential energy and by definition, power is the rate of change in energy. Total power, then, is the sum of the rates of change of the various energy regimes, notably drag power (drag times speed - the rate of converting mechanical energy to heat, as you mentioned), and the rate of kinetic and potential energy changes. So assuming constant drag coefficient and velocity, all excess power must go to altitude (and noise!).
So best rate of climb occurs at a speed and configuration of maximum excess power. A speed higher or lower than that consumes more power as drag. So as speed decreases, excess power decreases and vertical speed decreases. But between best rate and best angle, horizontal speed decreases faster than vertical speed - hence, angle of climb increases. At a speed below best angle of climb, vertical speed starts decreasing faster than horizontal speed.
I know you know this stuff, so why am I reciting it? Well, it's the basis for why I think the takeoff / climb sequence I mentioned is optimal. The natural conclusion is that it's best to keep the overall drag minimized until the plane reaches at least Vx. That way excess power is maximized and available to increase kinetic energy as rapidly as possible, until an efficient climb speed is reached. THEN redirect that excess power to potential energy and get the hell outta Dodge.
I never meant to imply zoom climb (but I guess I did) - that's a different situation (which killed my friend), I only meant to describe a way of getting off the ground in a short distance, then as promptly as possible begin a
sustained max performance climb, whether 'max performance' in a particular instance be best angle, best rate, or cruise climb. I think Ag-Pilot Dave described the sequence better than I did - -- Anyway, as you said, certainly no flaps for best rate - - - Hmmm, I think I might see a mini-project looming for my AP physics class - - - give 'em a rate of climb / airspeed profile and have them play with excess power, drag power, best angle. Poor me - I'd have to go flying to collect some data for them - - -
I've noticed in the 737s I've ridden in, that a little bit of flap is left deployed for quite a while after takeoff. Is that a Control Zone speed limit issue, or angle of climb for noise abatement, or just bleeding them off slowly for smoothness (i.e. passenger comfort) or ???
Oh yeah - a number of times you've commented on the scary deck angle of a Vx climb. This afternoon I was exploring the slow flight regime in my 12, which is different having added leading edge cuff and VGs. So at altitude, I was playing with that extreme nose-up, full-flaps climb, at a deck angle much greater than Vx, maybe 60 deg or so. IAS was 20 mi/hr. Then cut the power. Yep, it goes DOWN in a big hurry, and ya better push it over before it does something really silly at that deck angle. But I was surprised to find that I could recover (flare to zero sink or slight climb, power-off) in about 200 ft, maybe slightly less. But man, if the fan stopped at less than that altitude, there wouldn't be much more than a grease spot on pilot's seat. Yep, get airspeed in ground effect first!!!
Sheesh, I better shut up - I haven't written this much since the downwind turn epic thread!
