Thanks MTV. Both techniques require skills. We both have been with students who started too early or tried for too much clearance and bled kinetic energy. We can load a Cub to max gross with fuel and student but there is no way to fully prepare him for the first time he has to get out heavy , hot, and or high and then get to the field without hitting anything and then get into and out of a crop surrounded by tall trees several times before he gets some of the load sprayed. You could possibly math all that out and come up with a reasonable load, but those numbers would not keep you in most seats.

These guys are paying pretty good attention to your wise cautions, but things happen. I have found the extra kinetic energy of low ground effect for as long as practicable to save me many, many times over. The early extra altitude gaining with a Vx or Vy climb when that shows on the ASI is not easily converted into maneuvering speed when facing high trees. And once climb is began, the extra energy of low ground effect is gone and cannot easily be regained.

I have never had to grab the stick, at the end of a spray run. I have often had to make students stay down a bit longer. When loaded they must just get over. Often leveling is required on top of the obstruction. We could start early and then level and then fly level to the obstacles. Things happen, however, and once we have used up our zoom, descent is entirely possible.

I have never been comfortable with the idea that once established, Vx or Vy or any V is guaranteed.

Some brief comments that hopefully will be worthwhile. Owned two Citabrias, one 115 7ECA and a 150 7GCBC. Always replaced the airspeed with something with an expanded range at low airspeeds. Stock is really cramped at low speeds and meant for cruise and caution areas I assume. I like to know how fast I'm going at low airspeeds. Periodic pitot/static checks insure the system is tight and clog-free of debris, water, and ice. Now with GPS in level flight/no wind they can be checked.

Never made an intentional Vx except for check rides so can't comment. Never had to even flying off small lakes on skis (on both models) and floats surrounded by trees (7GCBC). If I wasn't in the air by a certain point and accelerating to build speed I redid the takeoff. Turning takeoffs can be learned. I like building speed after liftoff and prior to climb. Tall trees and uneven terrain can do strange things to surface winds and I want as much in the airspeed bank as possible.

Reading and accepting the POH written with new planes flown by experts from a hard level surface does not guarantee in the real world. Inclined surfaces, snow of varying depth and consistency, grass or brush of different height and density, and surface roughness (potholes, snow drifts, or rough wavy water) can work the plane's gear and change expected performance. On skis one can make repeatable tracks and measure the actual takeoff. Timing a takeoff can offer a rough estimate of roll progress or walk it out and mark the go/no go spot before hand.

Last obs. Flew a C-85 Taylorcraft off short farm fields 40 some years ago. As the grass grew so did the takeoff run. Finally after I and my mom drove through some tall willow trees after takeoff I learned about the effects of surface drag and clumps of draggy grass stuck on the gear. A few weeks later got a PA-18 on 25" tires and never noticed the grass effect much. Power sometimes prevents "P" poor performance.

Gary

Folks,

For those who may think I'm opposed to the low ground effect/zoom climb procedure to get out of Dodge, please understand that I'm really not at all.

This has been a good discussion, but a couple of takeaways:

1. In aviation, like most things there's nearly always more than one way to skin a particular cat. Is one better than the other? It depends on a lot of variables.

2. Working truly confined areas demands a certain level of skill and competence in the aircraft, regardless of the procedure one uses.

3. That level of skill by definition comes from experience and practice of the chosen technique in an area that is NOT a truly confined area, and using some physical benchmarks which will help you measure your efforts.....not that easy to do.

4. In later model airplanes that were equipped with a Flight Manual (and that is often different from a "Operators handbook) the factory test pilot has tested and given specific parameters and performance. You'll be well advised to consult that info if available. If you've got an older plane without such info, it's up to YOU to develop such performance data.

Most of all, be safe, and take it a bit at a time.

MTV

I suggest following the Flight Manual/OP Handbook if available. But planes do vary in performance and various STC'd configurations may not duplicate the factory parameters. And as MTV notes not all older aircraft have documented flight operations available. My Taylorcraft does not so it's been up to me to explore them.

Here's some suggested tests from the EAA that may help determine the range of indicated performance options. Use with caution of course.

Vx and Vy: http://eaavideo.org/video.aspx?v=3192335455001

Vso: http://eaavideo.org/video.aspx?v=3232093608001

GPS <> Airspeed calibration: http://eaavideo.org/video.aspx?v=3426915181001

And here's the FAA's AC regarding flight testing of amateur built aircraft that's mentioned in the videos: https://www.faa.gov/documentLibrary/med ... 90-89B.pdf

Gary

contactflying wrote:The Airworthiness Directive system works well because mechanics use it. ...

Does the AD process work because mechanics report issues, or these are issues discovered after accidents? Or maybe both? It seems like I see a lot of references to accidents when I read ADs.

Both. The point is that we see that there is a problem and attempt to fix or at least mitigate it. Concerning technique, not so much. Once the Administrator decides on a best technique, he is reluctant to see problems with the technique. Pilot error is cited even when ineffective technique is a major factor. Look at how little has changed with PTS in its 45 or so years of existence.

I know it's an old thread, but I have found it very useful and informative. Given that I have read every page up to this point, I have a couple of general questions.

I have a low hp (100hp) LSA cub (600kg MTOW) with big wheels and slats etc. So we are talking low intertia and high drag.

I have concluded from reading this thread, that lifting the wheels off early and staying in ground effect until at least VX will give the best obstacle clearance (big trees at end of runway). I also assume that accelerating much past this speed may be a little pointless as the inertia is small and the drag is high. This aircraft has a VR 32knots, VX of 56knots and a VY of 60knots and a typical cruise of 70knts, I have lots of time to think.

1. Do I have it correct in my assumptions above?
2. Also, if I have a steepish down hill slope (with trees at the end), is it still best to get up to at least VX in ground effect and trade some altitude (as it is downhill) or transition out of ground effect a little earlier ?

Thanks
ps. I do agree that VY is preferrable in most circumstances and if you need VX, you probably have got yourself in too deep.

Damiens,

1. Yes, assumptions basically correct. A young man from Kansas City came down with his 100 hp Savage. I was very impressed with the slow speed characteristics, but we didn't do any of the hover taxi out of ground effect stuff you see in video. When the engine quits on a helicopter, autorotation keeps the same pressure of airspeed on the continuing to rotate wings. He was impressed with the energy management turn and Valdez quality takeoff and landing using the basic low ground effect takeoff and the apparent brisk walk rate of closure approach to landing.

2. Three things makes pilots occasionally leave low ground effect too early on a downhill slope into high trees: First, we often have a tailwind but are on a one way slope. Second, we get off quickly driving downhill (gravity thrust or just umph for aerodynamics guys.) We have to really pitch down to stay in low ground effect. Third, it takes a little more time to bring the nose up from level in ground effect to level with the horizon to Vy or Vx pitch up.

Like MTV says, when we have no extra runway length, we will have to pitch up to Vy or Vx as appropriate just as soon as we arrive at Vy or Vx speed in low ground effect.

A big advantage to teaching in low powered airplanes is that certain things like leveling the airplane in low ground effect have to happen. With your airplane's higher engineered wing, not absolutely necessary. Your airplane will not autorotate, however.

Downhill takeoffs are a whole mother kettle of fish. Taking off downhill on a glacier, a steep downhill, can instill religion in an atheist. It’s really hard to shove that nose over and hold it in ground effect as you head downhill.

MTV

Lots of downhill into trees spraying in the Ozarks. I just screamed and gritted my teeth at the same time. Kind of slobbery but you're alone in the cockpit. Having enough runway to get up and over with plenty of zoom reserve in airspeed (not altitude) would make his downhill into trees more comfortable.

Plenty of times my high time engine quit. I was always glad to have zoom reserve in airspeed rather than try to autorotate from 100' and Vx. It is nice to have maneuverability to make a near better place. I was always able to zoom up to 100'and still have zoom reserve in airspeed left. Always had to slow rapidly to make the beginning of the near LZ.

Okay, Jim, here’s a question for you: How do you determine when to initiate the climb over obstacles in your “Hold it in low ground effect” procedure. More to the point, how do you teach someone to make that determination?

MTV

On level ground, I demonstrate a pull up late that degrades good zoom reserve. Next I demonstrate a smoother pull up. From there, I allow them to pull up when they feel they should and evaluate how much too high and too slow they were at the trees. Nobody pulls up late to start with. They start out pulling up early and work it down to a smooth, not energy zapping, pull up just over the trees or wire.

It is easier and smoother to start a little early and pull back a bit slower than having to rush it when late. Rushing waists zoom reserve. Like John Wooden told his UCLA basketball team, "Be quick but not hurried."

Downhill into trees? Like an old instructor I admire just said, "Downhill takeoffs are a whole mother kettle of fish. Same with Ag training. They ain't going to be real good at first. And I ain't going to push them from on the floor in the back seat of a Super Cub. With cushions, I can barely see out.

Thanks all for the clarification and a huge thank you to Jim for the book (at the bottom of his signature block). I just discovered it and I am half way through. Great read. Thanks again.

My technique is to get the plane in the air as soon as possible and aim just above the tops of the trees, it has worked...so far.

I have flown just too many planes that have been crashed, modified, tweaked etc that I just don't believe in the airspeed indicator and book numbers. As MTV said there are a lot of techniques out there, this one just happens to work for me.

The New Testament covers grace in more detail than judgement, but seems to say there is a special place in hell for false teachers.

For safety reasons, the FAA builds cushions into hard numbers like max gross weight and V speeds.

So they think they have us covered with Vx or Vy as appropriate. On paper, there is a little extra in there. The problem is when they dictate the number on the less than perfect gauge rather than simply dictate "just over the obstacle." Not false teaching but incomplete teaching, which has the same effect. No, not spiritual death, just physical death.