Take-off to clear obstacle. Whats your method?

[integritywood]

My instructor taught me after lift off, level and accelerate to vx then climb at vx till clear. He said the old bush pilots around advocate lift off, accelerate in low ground effect as long as possible, then pull up just in time to clear obstacle. The theory being you waste less energy accelerating in ground effect so have more stored energy by the time you reach the obstacle? There's gotta be some opinions on this, maybe a good discussion.

[blueldr]

As done in a C-170B with an engine that is about 600 hrs over TBO.

Open throttle to ffffFULL. Then, as airplane attempts to accellerate, recite, not too slowly, "Our Father Who Art---etc."

[WSHIII]

Food for thought.

http://www.avweb.com/news/pelican/182089-1.html

[GAHorn]

John Deakin is certainly an experienced pilot, and he's paid well for his writings, much of which is right on target.
Not this one though.

He does create some insight to the difference between certification flights by test pilots versus everyday flying by others, ...but his suggested techniques aren't really very useful at all for several reasons.

We all rely upon the certification data for predicting our ability to clear the obstacle or get airborne within the takeoff run distance available. To toss in imaginary differences in everyday operations using ad hoc techniques ...is equivalent to tossing out all the valuable test-data obtained by the certification process. I.E., the only way to rely upon the certification data is to duplicate the recommended techniques.

This is supported by his story about the Sacramento Ice Cream Parlor crash.
First, he denounces the FAA comment: "Remember that an attempt to pull the airplane off the ground prematurely, or to climb too steeply, may cause the airplane to settle back to the runway or into the obstacles."
...Then he states "Not exactly. This is true only if the performance is marginal, as at high elevations and density altitudes, or with very underpowered airplanes, which is pretty much the same thing. "
...then he supports his denouncement by using examples which exactly prove the FAA comment. He uses a 172 in Colorado that cannot continue to climb due to density altitude, and a Sabre jet which tries to fly by rotating prematurely thereby creating excess drag which in-turn prevents acceleration to flying speed...
...exactly what the FAA comment implies.

He denounces takeoff configurations which begin the roll with unnecessary drag...then recommends full flaps application for the shortest possible takeoff rolls.

In another contradiction, he seems to endorse the idea of "popping" flaps immediately prior to the end of the takeoff roll and/or obstacle. How does that compare with the full flaps takeoff he recommended earlier? And what about the excess speed (which equates to unobtained/lost altitude) using that technique?

In my opinion, the reason many pilots like the flap-popping technique is because it reduces the amount of time exposed to the emotional concern of "will this work?" (The relief of excess speed being available to hop-up over the obstacle is more reassuring than the Vx struggle to do the same....completely overlooking the fact that arriving at the obstacle with excess speed means the obstacle is cleared with less altitude to spare.)

He criticizes FAA for recommending a "safe altitude"...questioning whatever that definition might be...then states unequivocally " ..a "safe" altitude is anything from about ten feet above the runway on up. ..." Huh? I thought we were discussing obstacle-clearance.

He questions the technique of a taildragger using a "tail low" technique for shortest take-off run... then shifts to using only examples of tri-cycle gear airplanes for proving his points.

He demeans the FAA recommendation of accelerating to a safe "flaps up" speed, then retracting the gearr... by scolding the "dog"... and then he recommends virtually the same technique several paragraphs later : "...at least until some speed is gained, the flaps can be eased up to a "high lift, low drag" position, and the gear retracted."

This article is good for inspiration to THINK about the subject. But it offers nothing new, or particularly good, for the everyday operations by line pilots. IMO.

In my B-model,
Soft field/Short field:
1-Keep rolling. (make a properly-leaned, power-on U-turn if it helps) 2- Use takeoff flaps and full power as recommended by the OM and documented by the AFM. 3- Let the tailwheel come up naturally (i.e. use nuetral elevator until it lifts the little wheel clear of the mud/grass, then keep it there) until the airplane lifts up/out of the soft-field. 4-Accelerate to Vx or Vy (as obstacles require) to a "safe altitude", retract takeoff flaps while accelerating to your preferred climb speed, but only after close-in obstacles are cleared.

[WSHIII]

George

John Deakin is certainly an experienced pilot, and he's paid well for his writings, much of which is right on target.
Not this one though.

He does create some insight to the difference between certification flights by test pilots versus everyday flying by others, ...but his suggested techniques aren't really very useful at all for several reasons.

We all rely upon the certification data for predicting our ability to clear the obstacle or get airborne within the takeoff run distance available. To toss in imaginary differences in everyday operations using ad hoc techniques ...is equivalent to tossing out all the valuable test-data obtained by the certification process. I.E., the only way to rely upon the certification data is to duplicate the recommended techniques.

This is supported by his story about the Sacramento Ice Cream Parlor crash.
First, he denounces the FAA comment: "Remember that an attempt to pull the airplane off the ground prematurely, or to climb too steeply, may cause the airplane to settle back to the runway or into the obstacles."
...Then he states "Not exactly. This is true only if the performance is marginal, as at high elevations and density altitudes, or with very underpowered airplanes, which is pretty much the same thing. "
...then he supports his denouncement by using examples which exactly prove the FAA comment. He uses a 172 in Colorado that cannot continue to climb due to density altitude, and a Sabre jet which tries to fly by rotating prematurely thereby creating excess drag which in-turn prevents acceleration to flying speed...
...exactly what the FAA comment implies.

He denounces takeoff configurations which begin the roll with unnecessary drag...then recommends full flaps application for the shortest possible takeoff rolls.

In another contradiction, he seems to endorse the idea of "popping" flaps immediately prior to the end of the takeoff roll and/or obstacle. How does that compare with the full flaps takeoff he recommended earlier? And what about the excess speed (which equates to unobtained/lost altitude) using that technique?

In my opinion, the reason many pilots like the flap-popping technique is because it reduces the amount of time exposed to the emotional concern of "will this work?" (The relief of excess speed being available to hop-up over the obstacle is more reassuring than the Vx struggle to do the same....completely overlooking the fact that arriving at the obstacle with excess speed means the obstacle is cleared with less altitude to spare.)

He criticizes FAA for recommending a "safe altitude"...questioning whatever that definition might be...then states unequivocally " ..a "safe" altitude is anything from about ten feet above the runway on up. ..." Huh? I thought we were discussing obstacle-clearance.

He questions the technique of a taildragger using a "tail low" technique for shortest take-off run... then shifts to using only examples of tri-cycle gear airplanes for proving his points.

He demeans the FAA recommendation of accelerating to a safe "flaps up" speed, then retracting the gearr... by scolding the "dog"... and then he recommends virtually the same technique several paragraphs later : "...at least until some speed is gained, the flaps can be eased up to a "high lift, low drag" position, and the gear retracted."

This article is good for inspiration to THINK about the subject. But it offers nothing new, or particularly good, for the everyday operations by line pilots. IMO.

In my B-model,
Soft field/Short field:
1-Keep rolling. (make a properly-leaned, power-on U-turn if it helps) 2- Use takeoff flaps and full power as recommended by the OM and documented by the AFM. 3- Let the tailwheel come up naturally (i.e. use nuetral elevator until it lifts the little wheel clear of the mud/grass, then keep it there) until the airplane lifts up/out of the soft-field. 4-Accelerate to Vx or Vy (as obstacles require) to a "safe altitude", retract takeoff flaps while accelerating to your preferred climb speed, but only after close-in obstacles are cleared.

Respectfully, IMO you could benefit from revisiting the article again. I think you've completely mischaracterized, misinterpreted, most of what Deakin said.

Et al: It's a common mistake to mix the two techniques up, soft field and short field, when discussing one or the other. But to be fair, the original question was about "obstacle clearance", not soft field technique, i.e., intentionally keeping the tail low and or stopping on the runway.

[Bruce Fenstermacher]

I haven't found the power on u turn that much more effective and in actuality probably hurts. Maybe because I don't practice it. I've come to the conclusion that it is just as effective to u turn slow and controlled then full power when aligned down the runway. I also don't pop flaps as I'm just as likely to lose any improvement to over or miss control as I reach for the flaps. On a A or B model I'd use 20 degrees of flap to depart and clear an obstacle them reduce to 10 and eventually to zero flaps.

[docfoley]

Basically I use George's method. Experimenting with 2704C I found that 20 deg gets off the ground shorter than 10 deg and I get over obstacles faster. Popping flaps makes no sense to me at all. The induced drag at low speed for the flaps is negligible and I bet you can't measure the difference in acceleration to speed. However, it would be easy to measure the crash caused be reaching forward to grab the flap handle...

20 deg, Full power, let the tail come off the ground and keep it low. Take off in a 3 point attitude and climb out at best angle of climb. I retract the flaps when it's safe and a moment of inattention or excess rudder or brake won't kill me. There is always some element of crosswind and wind shear.

[lowNslow]

Not saying Mr. Deakin's theory is incorrect but the fact that he offers no test data to validate his opinion makes it suspect. His article would have been more convincing if he had done a number of takeoffs using both techniques with an observer to record the results and averaging the data to come up with some actual proof that his way is better. Lacking any test data his theory is just that, a theory.

[pdb]

My instructor taught me after lift off, level and accelerate to vx then climb at vx till clear.

I think your instructor basically has it right. Refinements like keeping all the weight on the mains on hard paved surfaces or keeping the tail a bit low on soft may be appropriate in those conditions to optimize lift off.

He said the old bush pilots around advocate lift off, accelerate in low ground effect as long as possible, then pull up just in time to clear obstacle. The theory being you waste less energy accelerating in ground effect so have more stored energy by the time you reach the obstacle? There's gotta be some opinions on this, maybe a good discussion.

This is basically the technique that Deakins advocates for obstacle clearance. I understand accelerating in ground effect to Vx but I don't think Deakins really makes the case that accelerating beyond Vx to Vy before pulling up and zoom climbing until reaching Vx achieves additional climb performance. The climb angle you will have to achieve doing this will necessarily be greater that that achieved in a steady Vx climb since you start the climb farther down the runway. Does the benefit of a bit more acceleration in ground effect from Vx to Vy more than offset the reduction in climb angle between Vy and Vx? I don't know but Deakin merely asserts it. I suspect that engineers and test pilots solved this one a while ago and I will stick to a climb at Vx as soon as I can achieve it.

[WSHIII]

Pete,

My instructor taught me after lift off, level and accelerate to vx then climb at vx till clear.

I think your instructor basically has it right. Refinements like keeping all the weight on the mains on hard paved surfaces or keeping the tail a bit low on soft may be appropriate in those conditions to optimize lift off.

He said the old bush pilots around advocate lift off, accelerate in low ground effect as long as possible, then pull up just in time to clear obstacle. The theory being you waste less energy accelerating in ground effect so have more stored energy by the time you reach the obstacle? There's gotta be some opinions on this, maybe a good discussion.

This is basically the technique that Deakins advocates for obstacle clearance. I understand accelerating in ground effect to Vx but I don't think Deakins really makes the case that accelerating beyond Vx to Vy before pulling up and zoom climbing until reaching Vx achieves additional climb performance. The climb angle you will have to achieve doing this will necessarily be greater that that achieved in a steady Vx climb since you start the climb farther down the runway. Does the benefit of a bit more acceleration in ground effect from Vx to Vy more than offset the reduction in climb angle between Vy and Vx? I don't know but Deakin merely asserts it. I suspect that engineers and test pilots solved this one a while ago and I will stick to a climb at Vx as soon as I can achieve it.

Well, you have to do, what you have to do, in order to clear the obstacle. And if the circumstances require climbing out at Vx to clear them,then so be it.

The point Deakin is trying to make, and I'll grant you he doesn't provide many details on why in this article, if the circumstances will allow you, accellerating too and climbing out at Vy is a much safer, better way, than what the FAA advocates.

It's all about risk management, and climbing out at Vx, while hanging on the prop, has more risk involved than climbing out at Vy with excess energy stored in the airplane. If you lose the engine climbing out at Vx, the airplane is going to stall almost immediately and while climbing out at 100 feet, its game over. While climbing out at Vy, and excess energy stored in the airplane, maintaing postive control of the aircraft after an engine failure is less critical. I think we'd all agree, losing the engine in either case is not going to be fun but, given the choice, a controlled crash almost always has a better outcome than stalling out and going straight in from a 100 feet.

In broad general terms, it's better, safer, to clear the obstacle at 10 feet at Vy, then to clear it by 100 feet at Vx.

[bagarre]

That was going to be my point as well. I almost always keep the plane in ground effect for the free airspeed and security of an engine out (on takeoff). Having an engine out at 50 or 100 feet at Vx or Vy isn't something I want to experience.

BUT, I also don't go into places that need the AFM and a wiz wheel to figure if I can get out of.

Vx is the airspeed where you will get the most height in the shortest distance (at gross weight on a standard day) so it makes sense to fly out of your driveway at that speed as soon as possible once off the ground in order to miss your neighbors house. In an engine failure, each technique only means the difference of going thru your neighbors house at a higher or lower speed.

[Bruce Fenstermacher]

I think David hit it about right. I think it feels better clearing the obstacle by 10 feet at v,y and as a helicopter pilot use to clearing things by 10 feet, it is my preferred method. However I don't think it any safer than being at 100 ft and vx in the same situation. Unless of course that extra 100 ft allows you to see the little gap between the houses or trees, you can stick the plane through with less damage and maybe a better survival situation.

[integritywood]

I've really enjoyed reading different perspectives on this. Jim Dulin in his book "Contact flying" makes the point that in a climb at vx you are vulnerable to degraded performance from wind shear or downdrafts. His theory is the reduction of induced drag in ground effect allows you to store more energy as airspeed which can then be used to more safely "zoom" over the obstacle. I guess probably for most of us lacking the blind unflinching faith of BL we look for other methods of accomplishing the same thing

[Bruce Fenstermacher]

I aim for the top 1/3 of the obstacle and just barely miss it. Came from a CFI who also flew helicopters.

You had a good instructor.

[WSHIII]

Kimball

I've really enjoyed reading different perspectives on this. Jim Dulin in his book "Contact flying" makes the point that in a climb at vx you are vulnerable to degraded performance from wind shear or downdrafts. His theory is the reduction of induced drag in ground effect allows you to store more energy as airspeed which can then be used to more safely "zoom" over the obstacle. I guess probably for most of us lacking the blind unflinching faith of BL we look for other methods of accomplishing the same thing

Don't take anyones advice, mine included, go see for yourself. Make your own mind up which way makes more sense. It's easy enough to simulate why you'll have a much better chance of maintaing control after an engine failure climbing out at Vy, rather than Vx.

Go to a safe altitude and try it. If your not completely comfortable trying it alone, take an instructor along. Pitch to VX and climb out at full power. When you get 100 feets or so above your new "hard deck", pull the power, count 1 Mississippi to approximate "WTF just happened"? And see if you can regain control of the airplane and flare in any meaningful way to stay above your "hard deck".

Now try the samething at Vy. Its a night and day difference. Engine failure at Vy is almost a non-event compared to "airshow" your going to put on when it happens climbing out at Vx.