I got this question recently and often in the past. My practice and teaching is to stay in low ground effect until obstacles or terrain force us up. Because of airspeed indicator indoctrination, most pilots want a number. Most assume what is now in the PTS, "Vy or Vx as appropriate."

It would be very scary pulling an overloaded spray plane up and over a wire at such a slow speed. It is only comfortable at maximum full throttle speed. I don't know of any Ag instructor who teaches anything less, and certainly not Vx or Vy.

Which will provide more zoom reserve for climb: Vx,Vy, or as fast as it will go in low ground effect?

Well Contact - I will take a personal shot at it.

I have never used Vx except to pass my private check ride. I have always considered it close to dangerous.
My best example would be Thomas Crick in Idaho. At the normal down stream take off direction, just as you cross the end of the runway, the river makes a turn underneath the plane bringing with it a bit a cold tailwind.
A good place for Vx to either get ya wet, or paint the plane green in the brush on the far bank.

Of the two choices you offer. My personal choice would be Vy as a minimum, (Vx MEETS Vy when hot and high), and shoot for as close to Va as possible while judging the rate of closure between me and destiny.

Wannabe

Good grief Jim, I do hope you're not suggesting that any of the assembled company would fly an overloaded airplane!

Staying in ground effect seems like a no-brainer, but to every rule there's probably an exception. I'm struggling to think of one, but Valloire Bonnenuit might be it. It's an alpine one-way, where staying in ground effect with a tailwind would take you through a venturi in the bottom of the valley. Maybe better to climb above that kind of feature at Vy with a wingtip right against the north side, especially if there's a bit of sun on the rocks?

Same with my home airfield with a southerly wind. It's a one-way, with no obstacle whatever on departure, but staying low for longer than necessary means flying through turbulence off the adjacent hillside.

contact flying wrote:...Which will provide more zoom reserve for climb: Vx,Vy, or as fast as it will go in low ground effect?

Ah Jim you bring back fond memories of flying my first airplane in our hot Texas summers, a wood prop 220hp Stearman. A 100 fpm climb rate was excellent when it could be achieved. Better flown like a powered glider riding thermals to gain altitude.

The answer to your question ("until obstacles or terrain force us up", and a one-way would be a one-way because of either obstacles or terrain) is of course building up as much speed as possible in ground effect for a zoom climb. Did that many a time with that Stearman. Which reminds me of a story I heard:

Seems like this new pilot replaced the wood prop on his Stearman with a Ground Adjustable McCauley. One day, after buying a nice digital level, he decided to adjust the prop for better climb performance as the hot summer days we approaching. He adjusted the propellor to such a precision that only a digital level would afford. It was a cool morning when he lifted off his home runway and headed for Llano, a normal routine for this intrepid new aviator.

The thrill of flying a Stearman is unequaled by any other airplane and he played all along the way, reaching Llano as the temperatures were rising. He fueled the Stearman for the return flight that would occur after a hearty lunch. With a full belly, our aviator climbed into the cockpit to head back home. It was now Texas hot.

He back taxied so he’d have the full 3,000 feet of grass to use for takeoff. The air was still as he swung the plane around, pushed the throttle forward, and started his long takeoff roll. The Stearman seemed slower to pick up speed then usual. Our young aviator decided if she wasn’t flying by the 2,000 foot mark he’d abort the takeoff, but at the 2,000 foot mark she was light on her gear and about to fly so our aviator pressed on. As she neared the end of the 3,000 feet of grass she was finally airborne but remained in ground effect.

Fortunately there were no obstructions for as far as the eye could see which was a good thing because she was still stuck in ground effect as she crossed over the highway and proceeded out into the Texas ranchlands. Ever so gradually her speed increased until she was finally able to break free from the grip of ground effect and with a sloth-like rate, over many miles, she climbed and climbed and climb eventually achieving 1,000 feet AGL. As she leveled off our new aviator realized she was cruising 15 mph faster then he’d ever seen her fly before.

Once back on the ground our aviator took out his trusty digital level to see if the prop blades had somehow moved, perhaps he’d not tightened the bolts adequately. It was at this point that the light of knowledge shown down upon him and he realized that the digital level indicated two entirely differently measurements when placed on the prop first facing him, then flipped opposite away from him. Of course it had been much easier for him to read it when it was facing him as he adjusted the blades.

At least this is how the story was told to me.

Barnstormer,

Great story. Reminds me why we gunship pilots hated the concertina wire around every firebase in Vietnam.

Contact

Climb out at more just less than Vfe with flaps,or upon reaching Vfe retract the flaps and climb when an obstacle makes you?

The reasons I can think to climb Vx is because the CFI told you to and you don't feel like being told that you stayed to long in ground effect.
Another may be to see if the afore mention overloaded plane would climb before running out of runway. Or the runway is simple so long.

Getting the mains off as quickly as possible, into low ground effect, gives us so much more runway ahead to look at. If not off really early, we can abort. It only gets better from that point, if we stay level in low ground effect.

Not for recreational flying, but on short spray field situations there is no consideration of an abort. If possible we have something set up toward the end to give us a bump off into low ground effect. No obstructions in that kind of work. We accelerate over the desert on the way to the field. Fabens, Texas was set up by farmers for crop dusters so that we could take off 34 from the loader and land on the taxiway between 08 and 34 back to the loader. On takeoff on 34 we crossed 08 just before the end of 34. If we weren't off by then the crown in 08 would bounce us off into low ground effect. From that point we stayed in low ground effect and made a left rudder turn to get going down hill into the Rio Grande Valley.

In the 172 on the pipeline, I didn't use flaps and stayed in low ground effect until obstructions or terrain forced me up. Only one forced landing on takeoff, but at one foot AGL it was a nada.

Off topic Contact, but the mere mention of Fabens makes my mouth water for a huge steak with beans and all the fixings and brings back the beautiful sunsets from the porch at Cattleman's.

I could only afford Cattleman's when Dennis Ivy, Gail Surratt, or one of the other big growers took me. Best steak ever.