Where's the eight in a lazy 8?

[gismo]

Tom Turner (ABS technical editor) included a diagram (attached) in an article that purported to show what a lazy eight (performed per the commercial airplane PTS) looks like when viewed from the Earth's surface. I can't see how this maneuver could ever resemble anything even remotely like the figure '8' from any perspective. Viewed from the side (along a line perpendicular to the entry path) I think it should look like the profile of a shallow bowl or a wide 'U' and from along the line of the entry path I think it would appear to be an adjacent pair of slightly narrower inverted 'U's neither which reminds me of the shape of a figure eight. Even when viewed from above the pattern would resemble adjacent 'U's with alternating direction. I suppose that if you performed two lazy 8s back to back with the second one beginning with a turn in the opposite direction of the first the plan view could be thought of an '8' but it wouldn't be lying on it's side per the oft stated description.

So where's the eight?

 

[tonycondon]

ive always thought that the eight was from the path the nose would carve along the horizon.

 

[ScottM]

ive always thought that the eight was from the path the nose would carve along the horizon.

ditto

 

[Areeda]

ive always thought that the eight was from the path the nose would carve along the horizon.

That's what I've read too but I've never been able to see it.

Oh and that diagram is from the Airplane Flying Handbook. here's the text to go with it

This maneuver derives its name from the manner in which the extended longitudinal axis of the airplane is made to trace a flight pattern in the form of a figure 8 lying on its side (a lazy 8). [Figure 9-4]

Joe

 

[gismo]

ive always thought that the eight was from the path the nose would carve along the horizon.

That's not what some of the texts say, at least some say "when viewed from the side" or something similar. And what horizon? Are you talking about a the intersection of the longitudinal axis of the airplane with a vertical cylinder who's axis is centered on the starting position of the maneuver? That would also resemble a distorted sine wave, not a figure 8.

 

[gismo]

That's what I've read too but I've never been able to see it.

Oh and that diagram is from the Airplane Flying Handbook.

But that diagram doesn't look like a lazy 8 at all, it looks suspiciously like a cuban 8.

here's the text to go with it.

OK, but I've drawn out that line and it's not an eight as far as I can tell.

 

[Areeda]

That's not what the texts say, they all say "when viewed from the side" or something similar. And what horizon? Are you talking about a the intersection of the longitudinal axis of the airplane with a vertical cylinder who's axis is centered on the starting position of the maneuver? That would also resemble a distorted sine wave, not a figure 8.

Lance,

I believe if you were to keep a grease pencil on the windscreen at the horizon while the other pilot flew the maneuver you would end up with an ∞ when you were done.

I've looked for it without success.

Joe

 

[poadeleted20]

If you had a grease pencil on the spinner point forward, you'd have a wrapped around (like drawing on the inside surface of a tin can) sideways 8 on the horizon covering 180 degrees field of view.

 

[bobmrg]

I always taught it as the path described by the prop spinner above and below the horizon. Never had a commercial or CFI applicant fail that maneuver.

Bob Gardner

 

[gismo]

If you had a grease pencil on the spinner point forward, you'd have a wrapped around (like drawing on the inside surface of a tin can) sideways 8 on the horizon covering 180 degrees field of view.

OK, I can kinda visualize that although I think the beginning and end of the '8' would be displaced by twice the radius of each turn.

 

[poadeleted20]

OK, I can kinda visualize that although I think the beginning and end of the '8' would be displaced by twice the radius of each turn.

I suppose that's true, but given the vastness of the distance to the horizon compared to the radius of turn, it would be a small discontinuity.

 

[wabower]

As luck would have it, I rode with three CFI's while working on this maneuver. The first guy, usually a pretty reliable source, had it all twisted up. I don't know if he understood it or not, but he couldn't put it in words that made sense to me. The second guy was even worse, and the third guy was closer than the first two but I was still in the dark.

So when the examiner asked me about the manuever, I just told him I could do it three ways, none of which I had confidence were correct. He laughed and gave the description Bob and Ron provided, said it wasn't unusual to hear other theories. The interesting part to me was that the actual control inputs and aircraft position/orientation during the maneuver wasn't significantly different no matter which method I used, and the the path flown was about the same. It was just interesting to observe how much difference there could be in the description vs. that for all the other maneuvers that seem to be much more consistent among CFI's.

 

[TangoWhiskey]

That diagram is LOUSY! Is it really from the FAA's Airplane Flying Handbook?

Can you just see a student trying to pull the Cessna into a vertical, as pictured at the far right?! ;-) [See CFI need new pants]

 

[Dave Krall CFII]

That diagram is LOUSY! Is it really from the FAA's Airplane Flying Handbook?

Can you just see a student trying to pull the Cessna into a vertical, as pictured at the far right?! ;-) [See CFI need new pants]

Indeed, very poor diagram! The maneuver's lazy 8 (on its side) is readily apparent from the ground when the aircraft is flown generally towards the ground viewer from a distance, especially when at not too much AGL.

 

[TangoWhiskey]

The maneuver's lazy 8 (on its side) is readily apparent from the ground when the aircraft is flown generally towards the ground viewer from a distance, especially when at not too much AGL.

That should be easy to demonstrate using Flight Simulator or X-Plane, recorded using the Tower View or a different camera.

 

[flhrci]

If an of you use Itunes, look for a group of podcasts from the University Of North Dakota called "University of North Dakota Aerocast." Among others, there is a great video with plenty of animation and live demonstration of the lazy 8 and other maneuvers. No need to simulate this any more than has already been done.

http://www.undaerocast.com/ has msot of the videos, but not this particular one. Lots of good stuff there.


David