Debunking Glider Spoiler Turns Causing Spin Thinking

"Holding your breath does the same thing.
Try it, you'll feel lighter.
Jim "

Wow! That really works, just tried it here in my chair!

What's wrong?!? I did it, but right up until I turned blue and passed out, I
actually felt heavier...air from the big breath I took first?

It is always amusing listening to pilots discuss aerodynamics.

It's proof that the monkey does not need to know how the machine works, as long as they know what button to push and when.

I'll remember to use the breath hold in the future.

Todd Smith
3S
Educated and practicing aeronautical engineer.

On Thursday, June 11, 2015 at 1:44:11 PM UTC-4, wrote:
It is always amusing listening to pilots discuss aerodynamics.

It's proof that the monkey does not need to know how the machine works, as long as they know what button to push and when.

I'll remember to use the breath hold in the future.

Todd Smith
3S
Educated and practicing aeronautical engineer.

Such an individual has no place on this site!
UH

It's always good to consider extreme cases.

Consider a terminal velocity dive, where the flight path is vertical.

I stand by every word I've said so far, so I won't say them again.

I get the impression some folks are reading this in the form of individual emails and missing the context of the whole thread? Because points that have already been answered keep getting raised over and over again. Here is the whole thread: https://groups.google.com/forum/#!to...ng/svCmIstyZPU

S

The only caveat I'll add (again repeating something said already) was that I'm using G-loading to mean lift force / weight. That's quite close to what we'll read on a panel-mounted G-meter. I won't quarrel if you want to use G-loading to mean something else, that's fine, there is at least one other very reasonable definition of G-loading, but if the parameter of interest is lift force or lift force/ weight, then absolutely you do it reduce it, in the long run (steady-state case), by deploying spoilers or landing gear.

Again consider the terminal velocity vertical dive-- what will your panel-mounted G-meter read?

Why people are suddenly talking about airmass movement is beyond me-- I wasn't.

S

What is this - war on physics ?!

LOL
Bert TW

On Thu, 11 Jun 2015 21:26:29 -0700, Tango Whisky wrote:

What is this - war on physics ?!

Total misunderstanding of high school physics is more likely, coupled
with the sort of subject changing typical of trolls.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Thursday, June 11, 2015 at 5:38:16 PM UTC-7, wrote:
The only caveat I'll add (again repeating something said already) was that I'm using G-loading to mean lift force / weight.


Maybe this is a clearer system of terminology:

Total g-loading = net aerodynamic force / weight

Lift-wise g-loading = lift / weight. This is the g-loading component that acts in the direction of the lift vector, i.e. perpendicular to the flight path. A conventional panel-mounted g-loading measures something very close to this. Excess amounts of this kind of g-loading is usually the reason pilots pull the wings off in clouds.

Drag-wise g-loading = drag / weight. This is the g-loading component that acts in the direction of the drag vector, i.e. parallel to the flight path. This component of g-loading is large in very steep dive. This component of G-loading has little effect on a conventional panel-mounted g-meter.

In unbanked steady-state flight in a glider, L D and W form a closed vector triangle. Thus the magnitude of L is dependent on the L/D ratio, and increasing the drag coefficient by opening spoilers or lowering landing gear does decrease L and also does decrease the lift-wise component of g-loading.

I don't know if the recent reference to trolls was aimed at me, but see my June 3 post and my June 4 post presenting the table of lift/weight at various bank angles and L/D loadings-- I was responding directly to Dan Marotta's question. I was not trolling for contradictory responses. Nonetheless several people disagreed with these posts, and away the discussion went in a typical internet spiral.

For high L/D ratios, we can substantially increase D and cause only a tiny decrease in L, unless the bank angle is really extreme. I never said otherwise-- the table I posted on June 4 shows it-- yet there is still SOME reduction in L, and to say otherwise is to ignore the L D W vector triangle. For much poorer L/D ratios, increasing D makes a much larger reduction in L, especially when the bank angle gets above 45 degrees or so. The terminal-velocity dive is an interesting extreme case where L/D is zero, and thus either L is zero or D is infinite. It the real world it is always the former case.

All this is kind of peripheral to looking at the immediate effects of deploying the spoilers, because the decrease in L is quite small when we deploy the spoilers starting with a typical sailplane L/D ratio, and I said as much in my June 3 reply to Dan. If folks hadn't wanted to argue, the discussion wouldn't have spiralled so far away from the original topic.

S

On Friday, June 12, 2015 at 6:16:31 AM UTC-7, wrote:


All this is kind of peripheral to looking at the immediate effects of deploying the spoilers, because the decrease in L is quite small when we deploy the spoilers starting with a typical sailplane L/D ratio,

Better would have been written "All this is kind of peripheral to looking at the long-run or steady-state effects of deploying the spoilers, because the final or steady-state decrease in L is quite small when we deploy the spoilers starting with a typical sailplane L/D ratio."

The immediate or short-term decrease in L can be much larger, as was well explained in the couple of posts by "sant..." immediately above.

S

On Friday, June 12, 2015 at 6:16:31 AM UTC-7, wrote:
On Thursday, June 11, 2015 at 5:38:16 PM UTC-7, wrote:
The only caveat I'll add (again repeating something said already) was that I'm using G-loading to mean lift force / weight.


Maybe this is a clearer system of terminology:

Total g-loading = net aerodynamic force / weight

Lift-wise g-loading = lift / weight. This is the g-loading component that acts in the direction of the lift vector, i.e. perpendicular to the flight path. A conventional panel-mounted g-loading measures something very close to this. Excess amounts of this kind of g-loading is usually the reason pilots pull the wings off in clouds.

Key point-- this is the g-loading component that is normally of greatest interest to pilots, because this is the g-loading component that affects the stall speed. When someone says that doubling the g-loading increases the stall speed by 1.4, they really ought to specify that they are talking about the lift-wise component of g-loading. We don't often use this language in actual practice. So when a pilot talks about g-loading, the listener ought to suspect that he may be talking about the lift-wise component of g-loading. As was the case in many of my previous posts.

It's really simplest to just leave g-loading out of it and simply talk about L and D and L/ weight and D/ weight. Then there is no possibility of confusion. So long as we understand the L D W vector triangle.

S