8's on

[beasly]

The point of it was, you don't need the wing if you fly the maneuver as it should be flown. I don't let my students use the wing other than to take a peek every 15-20 seconds to verify. I have taped my sectional to the left window on multiple occasions to make them do it without and lift it periodically to show them they can fly perfect w/o the wing.

I will look into that, thanks.


b.

 

[shdw]

I don't agree with that at all. I love the extra ground speed picked up by pitching over for the descent.

Try what I said, a constant power setting descent with an aircraft with GPS. Your groundspeed is not changing, what your changing is your altitude to keep the perceptual look at the point the same. Pitching is not changing ground speed, we just see ASI going up so we think, "great this is what we need," ehhhhhhnnntttt wrong, GS is what you need. Unless you increase power, your not getting anymore of that needed GS.

Since when?

You can, but shouldn't need to if you perform the maneuver properly. I personally hold my students to +/- 5 degrees to show them this.

 

[shdw]

Eights on Plyons....This post will start a holy war and run for days!

Likely the truth, let us see if we can all be civilized.

I had to look it up to see, so here, Civilized: having an advanced or humane culture, society, etc...humane...ha

 

[tgrayson]

Pitching is not changing ground speed, we just see ASI going up so we think,

You still haven't explained how this is physically possible given basic trigonometry.

 

[shdw]

You still haven't explained how this is physically possible given basic trigonometry.

Don't know, what I know is what my GPS showed me, if anyone sees otherwise I would love to know, I will go test it again when I am back at home. The trig, for the ground speed versus airspeed, doesn't work, I can't explain why.

The trig for the distance from the point I will work out in the am and see how that turns out, for now, it is bed time.

 

[tgrayson]

The trig, for the ground speed versus airspeed, doesn't work, I can't explain why.

Well, it does work. More than likely, your GPS doesn't display brief changes in GS. Trigonometry is a lot more reliable than technology.

 

[Douglas]

Try what I said, a constant power setting descent with an aircraft with GPS.

Well, I did one earlier today and pax pointed it out to me, "Hey look at that ground speed!". We did 10,500 to 1,250 at 500 fpm with constant power in a beautiful bonanza/G...there is no try...only do.

 

[EnRoute]

Doesn't it stand to reason that the reason that the ground speed is not increasing that much as you pitch down to capture that pylon that you are falling behind, is because the reason you are falling behind it is that you are now flying into a head wind, which is inherently slowing your ground speed down to begin with?

I find it hard to believe that if you are flying straight and level at a constant airspeed with a constant wind, whether it be tail, head or cross, and you pitch over and start a descent, your ground speed isn't going to increase considerably. I just can't subscribe to this notion.:insane:

 

[shdw]

Well, it does work. More than likely, your GPS doesn't display brief changes in GS. Trigonometry is a lot more reliable than technology.

This was a constant rate descent out of 11,500 if I remember right. We set up a 500 FPM descent with the ASI increasing 20 knots and the GPS GS only increasing by 1 knot. I was back seat doing radios and spent the last hour of that flight trying to figure that out. I did the trig then and found it didn't work, but still have been unable to explain why.

I will have to go try it again a few times and see.

I will get the other trig up tonight, I don't know how to draw pretty pictures of triangles to post and have to figure that out first.

Your post, tgray, where it shows the "same angle" would explain it fairly well. If you increase height (h) than distance (d) must change (increase) to keep that "same angle," the same, vice versa if you decrease. So, assuming you keep the bank angle the same, the only reason to change height would be due to an increased or decreased distance from the point.

You can see this by holding a string out off of a point on a table at a given angle. Depending on your distance from the point will depend where on that string you will be or in other words, the height you will be above the ground.

 

[nosehair]

the only reason to change height would be due to an increased or decreased distance from the point.

The other reason to change height would be a change in groundspeed.

Imagine an airplane holding the same bank, with verry long wings, so that the inside wing is actually tethered to the pylon.

There are 3 pitot tubes (or GPS groundspeed sensors, if you will) located at each wing tip and in the cockpit.

The cockpit speed is 100k, the inside wing speed is 1k, the outside wing tip is 200k.

Imagine the cockpit can slide up and down along the axis of the wing, necessarily speeding up and slowing down as the altitude changes.

 

[tgrayson]

So, assuming you keep the bank angle the same, the only reason to change height would be due to an increased or decreased distance from the point.

No, it's not that simple. It implies that there are an infinite number of pivotal altitudes, one for each distance away from the pylon, which is false. While all of those altitude/distance combinations will keep the pylon nailed at one instant in time, only one of those altitudes will tend to keep it there, because only one of those altitude/distance combinations has a distance equal to the turn radius of the chosen bank.

 

[tgrayson]

Imagine the cockpit can slide up and down along the axis of the wing

That's an interesting metaphor. One point of discontinuity is that it implies the aircraft needs to change its distance away from the pylon at different pivotal altitudes. This is only true if you want to keep the same bank angle, which is unrealistic. Once pivotal altitude is reached, there are an infinite number of radii and bank angles that will work. There will be one that works at your present distance from the pylon and your best bet is to find it, rather than trying to change your distance from the pylon.

 

[shdw]

This is only true if you want to keep the same bank angle, which is unrealistic.

Don't we have any WWII pilots on here that can better explain the origin of this maneuver. The guy I spoke with explained it as being a constant bank throughout. He explained that changing bank requires the gunner to change the gun up and down. On the other hand if the pilot can hold the bank perfectly and only pitch up and down based on drift from the point, then the gunner will have to do little to no work, thus improving their accuracy.

Maybe you can shed some light on this though tgray. I don't get how pivotal altitude is derived. I would think that it would only work for a given bank angle, meaning that formula would only give pivotal altitude for say 45 degrees. Then you would need another formula for pivotal altitude at differing degrees, do you see where I am going with this?

After reading all these posts, I believe I am confusing how pivotal altitude works. For some more research I went here: http://www.auf.asn.au/magazine/pivotal_altitude.html but that didn't help to much. Basically, can you better explain the math behind this so I can see/understand how it works.

 

[tgrayson]

Don't we have any WWII pilots on here that can better explain the origin of this maneuver.

The origins of the maneuver is interesting, but in the end, it's not that relevant to how we perform it. We perform it the way the Airplane Flying Handbook describes it.

I would think that it would only work for a given bank angle, meaning that formula would only give pivotal altitude for say 45 degrees. Then you would need another formula for pivotal altitude at differing degrees, do you see where I am going with this?

If that were true, it'd make the maneuver impossible. We only have one formula and no assumed bank angle, so we know it can work for any bank angle. I think you're assuming that pivotal altitude is just the altitude where a given bank angle will target our pylon. That's a necessary, but not sufficient requirement of the altitude. There is a whole cone of such altitudes available, as the author shows in that first diagram in your link.

For some more research I went here: http://www.auf.asn.au/magazine/pivotal_altitude.html but that didn't help to much. Basically, can you better explain the math behind this so I can see/understand how it works.

The author is simply using the equation for the bank angle and throwing in the equation for the radius of turn (based on TAS and load factor) and solving them simultaneously for the altitude. The other variables (bank angle, distance from pylon) cancel during the algebraic manipulation, leaving only TAS. You can find a similar analysis in Bill Kershner's Flight Instructor Manual. The initial analysis I posted says pretty much the same thing, but I intentionally left out the algebra.

Because there are two equations which must be satisfied, the cone of possible altitudes collapse into one altitude that depends only on TAS. At the proper altitude any bank angle will work, as long as the airplane initiates the maneuver at the proper distance from the pylon.

 

[lhornaday]

BANK angle changes only because of distance from the pylon. Not used to maintain a radius. Bank is held constant unless distance changes. Make the steepest bank of the maneuver between 30 and 40 degrees. Radius will remain constant unless there is wind.

ALTITUDE depends on groundspeed. Entry estimated altitude can be estimated under no wind conditions using TAS formula. It is up the pilot to correct for groundspeed changes. For every groundspeed, there is only one correct altitude to be at (pivotal).

Entry is downwind where altitude is highest. When turning upwind, groundspeed decreases if there is any wind. The airplane must descend becuse pivotal altitude is lower when directly upwind. Pitching down will not cause the groundspeed to increase very much when only descending 200-300 feet.

If the airplane were to enter the maneuver at pivotal altitude with no wind and then somehow subjected to a constant 15 knot headwind, the airplane would have to descend to reach the new pivotal altitude. It would then level out at the lower altitude and fly around the pylons in level flight until a new groundspeed is encountered.

Getting to the altitude where the pylons stops moving is what the maneuver is all about. The faster you fly, the higher you'll have to be to observe no relative motion. Think about flying at 30,000 feet and looking out the window. No noticeable movement at 200 knots. At 300 feet, even a c-152 at 80 knots looks like a rocket moving over the ground. Put both of those airplanes into a bank and imagine what you would see looking down the reference line.

:deadhorse: