Loose Change - Part IV

[MarkyX]

Use http://www.imageshack.us/

 

[Darth Rotor]

You are mixing vertical speed and the velocity vector that is measured on the airspeed indicator, which is the speed of the aircraft relative to the airmass.

If you hold power constant, and weight is more, changes in pitch attitude will of course change both speed and rate of descent. If you hold airspeed and thrust constant, more weight will tend to cause higher RoD since to balance forces and come up with the same airspeed, your AoA is slightly different (nose attitude) for the heavier aircraft.

For the constant glide slope at constant power setting, your heavier aircraft will have to fly slightly slower since to prevent higher RoD than glide path allows, you have to adjust nose attitude.

The aim, in this exercise, is not to fall (vertically) but to move laterally and hit a target.

DRHey now, some of find this boring sh[rule8] interesting![/QUOTE]
Draw the triangle on a piece of paper. Bottom is long leg, length 24,000 feet (4 nm) Short leg of right triangle is 2000 feet. Hypotenuse represents actual flight path (desired) to impact point. You are moving far more "laterally" than "vertically" on this glide path. Consider 460 knots in Feet per minute, and compare to the 3000 FPM RoD.

460 knots = 6000 x 460 feet per hour / 60 minutes per hour = 46,000 feet per minute.

DR

 

[ktesibios]

Speaking of plugs, Mike W has my essay up at 911myths
http://911myths.com/html/what_s_new_.html

Well done!

My area of expertise is audio recording and reinforcement electronics, not avionics, but I had no trouble understanding your essay. I think it should be accessible to anyone with a general electronics background or even anyone who has a clue about what happens when they flip a light switch.

I noticed that a few of the diagrams seem to be missing from the pdf (notably the first two). You might want to check that.

Also, what's "monkey motion" (I assume that it's industry slang)?

 

[TjW]

No, given the overall weight of the aircraft, the power setting, and the apparent attempt at max speed, the speed difference, while finite, isn't as pronounced at high speeds as at approach speeds, where you are dealing with stall margins and high angle of attack, high induced drag, etc.

At the higher speed, form drag is a more significant source of drag than induced drag. (drag from creating lift) and I don't think you'd have flaps or spoilers out (which add lift) when making a high speed run. As I mentioned above, I'd assume a clean configuration for the attack run.

To be honest with you, I don't know if the difference would be 3 knots, 7 knots, or what, I'd have to look at a 757 performance chart, from the manual, know the temp and barometric altimeter, the max gross weight of the plane in question, at both fuel loads, to give you a precise answer. I am pretty certain that my order of magnitude is correct: single digits.

DR

EDIT: the remark "(which add lift)" was supposed to be "(which add drag)" and thanks go to apathoid for pointing that out to me. Of course, flaps also add lift . . . I'm having a beer. Been too long since I taught this to newbie pilot trainees.

In general, the speed differences of the same aircraft at different weights will be related by the square root of the change in wing loading. i.e. twice as heavy means you'll fly 1.41 times faster -- in both forward and sink velocity.
This is why gliders ballast up with water in strong conditions.

 

[apathoid]

You are mixing vertical speed and the velocity vector that is measured on the airspeed indicator, which is the speed of the aircraft relative to the airmass.

If you hold power constant, and weight is more, changes in pitch attitude will of course change both speed and rate of descent. If you hold airspeed and thrust constant, more weight will tend to cause higher RoD since to balance forces and come up with the same airspeed, your AoA is slightly different (nose attitude) for the heavier aircraft.

The aim, in this exercise, is not to fall (vertically) but to move laterally and hit a target.


DR

Emphasis to the bolded part.

Ok doke, but what if the autopilot was keeping the RoD exactly the same in both cases?
Think of it like this, if the airspeed and thrust was exactly the same between a "heavy" 757 and a "light" 757, and they stayed the same with autopilot help: How would the vertical speeds compare?

For the constant glide slope at constant power setting, your heavier aircraft will have to fly slightly slower since to prevent higher RoD than glide path allows, you have to adjust nose attitude.

Again, completely agree. But, as I said above if you could fix variable with autopilot help, then what would happen?

Anyhow, Bill(zilla) got back to me. He flies left seat on the 747.

Cool Yeah, thats pretty much as I thought. But, essentially they are telling me that :


Airplane A: 757 at 255,000 lbs, at 50% N1(or even idle), in a 2000 fpm descent
-and-
Airplane B: 757 at 140,000 lbs, at 50% N1(or idle, same as above), in a 2000 fpm descent

..will accelerate(or decel) at the same rate and I just dont know about that. I remember talking to a 767 pilot about VNAV and he was telling me that the plane will speed up in a descent closer to MLW and will sometimes bust VNAV constraints if the descent started a little late. I never gave it much thought, but the physics guys I'm debating seem to think he is wrong. I'm not a physics guy or a pilot, so I don't know.....it seems logical either way I guess.

Now that I think about it, a heavy aeroplane will tend to over-speed more easily. The pilot sounds like he's right.

 

[T.A.M.]

Apathoid:

No, Eli says he doesn't have the cash to make the trip. We are both 1500 Miles from GZ, so it is a bit of a jaunt, even by plane. I will be there (with the Debunkers) in spirit, and watching on TV.

 

[Dog Town]

Me too, stuck in studio 2-21 !

 

[apathoid]

Well done!

My area of expertise is audio recording and reinforcement electronics, not avionics, but I had no trouble understanding your essay. I think it should be accessible to anyone with a general electronics background or even anyone who has a clue about what happens when they flip a light switch.

I noticed that a few of the diagrams seem to be missing from the pdf (notably the first two). You might want to check that.

Also, what's "monkey motion" (I assume that it's industry slang)?

Thanks !
I really, really watered it down and cut out 3 pages on autopilot servos. I couldve written another 20 pages on autopilot, IRS, etc...maybe I'll do a pt II

Thanks for the heads up on the missing images.

Oh, monkey motion is A&P slang referring to seemingly unnecessary linkage in the flight controls. But Boeings are nothing compared to MD-XX aircraft

 

[Brainache]

I'm down here at the other side of the world and I'd be very surprised if this GZ rally or whatever they are calling it doesn't turn nasty very quickly.
I would advise anyone who plans to attend to be very careful.
But all I can say is good luck. People like them need to see that they aren't fooling anyone but themselves.

 

[LashL]

Here's hoping they can read english

Most of them can. I've been to Turkey and had no problem communicating in English. I can't speak a word of Turkish and it wasn't an impediment

So the very fact that they posted your Screw Loose Change video in English is terrific, Marky, even if neither you nor I nor most of the rest of us here can read the accompanying text in Turkish

ETA: they reproduced the video in English on the site even though the text on the print page is in Turkish. They would not have done that unless they knew that lots of Turks would understand the English video. Like I said, I didn't know a word of Turkish before I got there and didn't need it to communicate.

So, again, congratulations!

 

[ktesibios]

Thanks !
I really, really watered it down and cut out 3 pages on autopilot servos. I couldve written another 20 pages on autopilot, IRS, etc...maybe I'll do a pt II

If you want to produce an edition that's designed for technicians and engineers, that would be really cool.

Of course, my idea of "cool" is kind of warped- years ago someone I knew said to me "you look at them electronics books like I look at a Hustler"

 

[Dog Town]

you look at them electronics books like I look at a Hustler"

That sounded prettee'er than a 2 dollar whore!
What would we do without either of ya????

 

[apathoid]

If you want to produce an edition that's designed for technicians and engineers, that would be really cool.

Of course, my idea of "cool" is kind of warped- years ago someone I knew said to me "you look at them electronics books like I look at a Hustler"

Sure!!
I'll run that by Mike and if he likes the idea, I'll "geek" the current version and use wiring prints/schematics over block diagrams and purdy pictures.

I actually want to try a theoretical sabotage of a 767 FCC when I get a chance. I'm thinking of pulling a few inhibit/discrete lines, powering up the MCDP and see how it responds and what EICAS messages/ Maintenance messages pop up. I've already got a pretty good idea though as I've done it accidentally before!!

 

[Gravy]

So, what ever happened with Gravy's debate of (with?) Korey Rowe?

His challenge seems to stand, and I remember Gravy sending him an email about it ...

Did Korey back out?

He says he's too busy with 9/11 activities. He was excited, though, about the "arguments" we could have at Ground Zero. I reminded him that that's day of remembrance for me, not a day for shouting matches for the sake of video cameras.

I'll try for October.

 

[Gravy]

Sure!!
I'll run that by Mike and if he likes the idea, I'll "geek" the current version and use wiring prints/schematics over block diagrams and purdy pictures.

I actually want to try a theoretical sabotage of a 767 FCC when I get a chance. I'm thinking of pulling a few inhibit/discrete lines, powering up the MCDP and see how it responds and what EICAS messages/ Maintenance messages pop up. I've already got a pretty good idea though as I've done it accidentally before!!

Hmm...Apathoid...Atlanta...Delta? You wouldn't happen to know the mechanic who, when I was waiting in a Delta plane in Atlanta, pulled up a ladder, climbed up to the side of the plane beneath my window, scratched his head, called down to his buddy, was handed a mallet, and started wailing away with it at something on the plane?

'Cause I'd really like to talk to him.

 

[MikeW]

I noticed that a few of the diagrams seem to be missing from the pdf (notably the first two). You might want to check that.

Oops. Only the first two? Which page(s)? Anyone else see this? Try saving the file to your desktop and view it from there (if that's not what you're doing already). Then click in the space where the image looks like it ought to be. Still nothing?

 

[Class]

Hmm...Apathoid...Atlanta...Delta? You wouldn't happen to know the mechanic who, when I was waiting in a Delta plane in Atlanta, pulled up a ladder, climbed up to the side of the plane beneath my window, scratched his head, called down to his buddy, was handed a mallet, and started wailing away with it at something on the plane.

'Cause I'd really like to talk to him.

There's something, something, on the wing!

 

[gumboot]

[brief derail]

I just want to clarify, for the "aircraft speed" discussion, I thought the discussion was about rate of descent - the train of logic being:

1 - heavier aircraft descends faster
2 - why?
3 - because it's heavier
4 - laws of gravity, all fall same speed, blah blah...

Hence my comment....

Which can as easily be explained by the following experiment:

Take an A4 sheet of 80gsm paper...

That's 21 cm x 29.7cm = 21*29.7 = 623.7cm^2

Total weight = 80g for 1m^2 = 10000cm^2

Weight per cm^2 = 0.008g

Sheet of paper = 4.9g

Now take an A4-sized slab of lead weighing 1kg

Attach each to a fan with a 1m long piece of wire.

Extend wire to maximum length, and let go.

What happens?

Lead slab falls onto fan, piece of paper doesn't.

Now, in each case, the wind resistance on each is identical. The reason the lead slab falls faster is because it is heavier, therefore has higher gravitational potential energy, therefore requires higher resistance to keep it in the air.

Hence, all else being equal, a heavier object falls faster in air than a lighter object.

Now, there may be some confusion, are we talking about the aircraft's rate of descent, or its airspeed?

And on a possibly more pertinent note... why exactly are we arguing this again? Is it to determine impact speed? Because as I understand it we have the FDR, so this discussion is pointless?

I'm sure someone mentioned somewhere why this is being discussed, I just can't remember...and am feeling lazy...

-Andrew

 

[defaultdotxbe]

Hence, all else being equal, a heavier object falls faster in air than a lighter object.

while techinically this is true, the most important thing to be equal is surface area, its the weight/surface area ratio that determines what falls like a brick or flutters like a peice of paper (not entirely certain how that will apply to the current discussion, just felt like pointing it out)

 

[Gravy]

[qimg]http://www.rodserling.com/theystartedontz/0220K.jpg[/qimg]
There's something, something, on the wing!

A pictographic representation of the mallet incident: