PilotEdge Forums

https://youtu.be/vV4tni4fFow

Great video, about 20 minutes. Good description of route planning and weather at the start.

Even better video about their departure from L85:
https://www.youtube.com/watch?v=aOlSPtexCsA

Ooops typo....L35

Quick reaction, and very sensible decision! Phew........

Ok. I'm hoping that I'm not having a senior moment. But I'm having a hard time understanding why a tailwind (only) causes the plane to gain airspeed more slowly after lift off.

I understand how a tailwind increases the length of take off roll as well as increasing the airplane's ground speed needed to achieve Vx speed. But once the airplane has achieved Vx speed, how does the tailwind keep the airplane from acceleration normally (assuming the motor is generating full power)?

I also understand why a tailwind lowers the effective climb angle after lift off (obstacle clearance).

Or is it possible that the pilot lifted off before the airplane achieved the necessary airspeed for the conditions (flaps, weight, density altitude) and that's what retarded the airplane's acceleration? Or perhaps over rotated in an attempt to climb faster?

I was also trying to figure out why the use of short field take off technique on a 5850 foot runway. Again adding to the thought that they were so concerned about obstacle clearance that the rotation was too soon.

For example consider an experience shared by Chris Palmer from Angle of Attack. Note how much effect on climb performance an early lift off had on the airplane's rate of climb (or near total lack of climb).

http://www.flyaoamedia.com/aviation/my- ... s-a-pilot/

There's a note in the following link about increasing the take off airspeed during gusty tailwind conditions.

http://www.experimentalaircraft.info/fl ... ance-4.php

I think he made a good call on the aborted takeoff.

As to why it wasn't climbing...3 possibilities spring to mind:
1) incorrect mixture. It was leaned, but I don't know if it was leaned for best power.

2) gusty tailwind. The momentary gusts result in a loss of indicated airspeed, the pilot compensates by increasing the angle of attack at a fairly sensitive point in the climb when it's already at a relatively high angle of attack

3) increasing tailwind. Given how stiff the actual winds were on the ground, it's not unreasonable to think that there was a strong wind gradient above, resulting in an even stronger tailwind. Climbing into an tailwind which is growing in strength can be a real challenge. I've seen the opposite during takeoffs into a strong headwind.

Keith Smith wrote:I think he made a good call on the aborted takeoff.

As to why it wasn't climbing...3 possibilities spring to mind:
1) incorrect mixture. It was leaned, but I don't know if it was leaned for best power.

2) gusty tailwind. The momentary gusts result in a loss of indicated airspeed, the pilot compensates by increasing the angle of attack at a fairly sensitive point in the climb when it's already at a relatively high angle of attack

3) increasing tailwind. Given how stiff the actual winds were on the ground, it's not unreasonable to think that there was a strong wind gradient above, resulting in an even stronger tailwind. Climbing into an tailwind which is growing in strength can be a real challenge. I've seen the opposite during takeoffs into a strong headwind.

4) An airport elevation of 6750 ft probably didn't help matters either.

yes, Hence point number 1

For sure Keith. And certainly not contradicting your point, but hoping to add to the discussion here . . . Besides the decrease in "engine performance" of a normally aspirated engine, even if leaned correctly at high density altitude, there is also the decrease in airfoil and propeller performance. I was surprised that in the video the emphasis was focused on the wind direction, yet the airport elevation was not discussed as a likely large contributing factor to the inability of this plane to gain altitude. In the previous video he had discussed going to Big Bear for the lower fuel costs, so I assume he filled up - possibly to max gross, and that potentially plays into the lack of climb rate too.
He definitely made the right decision and was well done for sure.

Here's a video of a guy that should have done exactly what Mr. Aviation did . . .

https://www.youtube.com/watch?v=OVM3RRd1vf0

Was thinking the same thing. I've taken off and landed F-14's at that altitude and even in that airplane the density altitude has a big impact on roll and climb. You guys have much more GA experience than I do but in a C172, there are soooo many factors in this one (alt, terrain, xwind / tailwind potential, IMC wx looming) that would have scared me into calling a cab in the first place. Nice job of recognizing an uncomfortable situation fast and getting it safely back on deck.