A Critical Analysis of JDX's math (split)

[Anti-sophist]

I might also add, I dont even think its possible to arrest a 4000 fpm descent rate on a 255,000 lb object in one second without hitting a wall or something.

Again, your intuition is failing you. I've proven it to you time and time again (mathematically, using the laws of the physics) that a simple 3G pull-up, for 1 second, will do the trick.

Can you stop your car in one second from 45 mph (66ft/sec)? What would the G's be if you did?

Why do you keep asking questions I've already given you the answer to. You would experience 2Gs (forward) for that entire second, if you were in a car that did 45mph -> 0 mph in 1 second.

 

[qarnos]

G Force is a Force. F = ma.

Basically, by your claims, a 757 would take the same amount of G's to pull out of a 4,000 fpm dive in one second as a Learjet. I highly disagree.


Besides the fact that the csv file never shows 3 g's for one full second, anywhere.

But, I do admire your work and thanks for the input. What kind of student are you? Physics?

Did you claim earlier that you are a pilot???

Sorry if I have my wires crossed, but I thought you mentioned you were.

 

[weedwacker]

the aircraft shows a 3960 fpm dive at time stamp :44. The G's after that show no correction. It actually shows less than 1 G. Where is the correction to start pulling out of the dive?

The G's shown prior to the :44 second time stamp are pulling level from 5960fpm to slow the descent rate.

09:37:25 AM
1.3 1690 altitude

1.26


1.24


1.16


1.13


1.08


1.03


0.96

09:37:26 AM
0.93 1647 altitude

0.88


0.84


0.84


0.85


0.88


0.92


0.91

09:37:27 AM
0.95 1596

0.97


0.98


0.98


0.98


0.99


0.99


0.99

09:37:28 AM0.971545

0.97


0.96


0.99


0.99


0.98


0.93


0.87

09:37:29 AM0.811494

0.75


0.7


0.65


0.63


0.6


0.6


0.61

09:37:30 AM0.631432

0.63


0.63


0.64


0.62


0.6


0.52


0.46

09:37:31 AM0.391362

0.34


0.31


0.32


0.31


0.36


0.35


0.52

09:37:32 AM0.541263

0.65


0.69


0.74


0.77


0.82


0.88


0.89

09:37:33 AM0.911158

0.92


0.94


0.99


1.01


1.04


1.11


1.26

09:37:34 AM1.391049

1.51


1.6


1.67


1.66


1.57


1.52


1.52

09:37:35 AM1.56955

1.45


1.42


1.27


1.31


1.21


1.15


1.2

09:37:36 AM0.94869

1.01


1.01


1.03


0.86


0.92


0.83


0.72

09:37:37 AM0.72786

0.67


0.7


0.64


0.72


0.56


0.36


0.61

09:37:38 AM0.56685

0.79


0.93


0.97


0.75


1


1.12


1.14

09:37:39 AM1.29592

1.17


1.38


1.21


1.39


1.43


1.35


1.43

09:37:40 AM1.45496

1.52


0.97


0.93


0.86


0.9


0.9


1.06

09:37:41 AM1.27399

1.31


1.28


1.12


1.1


1.25


1.22


1.28

09:37:42 AM
1.4 307
5520fpm here
1.7


1.71


1.75
<pulling G's to slow descent rate

1.72


1.62


1.58


1.55

09:37:43 AM
1.52 239
<4080fpm here
1.13


1.22


1.13


1.23


1.04


1.03


0.88

09:37:44 AM
0.66 173
<3980 fpm here
0.62


0.63


0.69<doesnt show any G's to level the 3980 fpm descent.


0.76


0.61


0.72


0.62

09:37:45 AM

 

[Anti-sophist]

the aircraft shows a 3960 fpm dive at time stamp :44. The G's after that show no correction.

Why do you keep insisting that the plane hit the pentagon when it was level, and therefore HAD to correct for the 4000fpm descent?

All I've said is it's not _impossible_, I didn't say it happened.

 

[Anti-sophist]

But, I do admire your work and thanks for the input. What kind of student are you? Physics?

And to answer this question, I graduated recently with my Master's Degree in Electrical Engineering.

 

[weedwacker]

But I now also understand JDX's 480MSL based on local pressure correction. Wow.

I really have to look into this further. Thanks for all the help everyone.

I'll continue to post so observations.


Yes, I'm a retired Airline pilot from Independence Air. Haven't thought much about flying since except for buzzing around in a 172.

It good to get the ol' noggin working again. I'm going to try to contact this JDX guy and see if he worked for FLYI.

 

[weedwacker]

Why do you keep insisting that the plane hit the pentagon when it was level, and therefore HAD to correct for the 4000fpm descent?

All I've said is it's not _impossible_, I didn't say it happened.

The 5 frames video that shows it level just above the lawn. I firmly believe the 757 hit the pentagon. We have people from FLYI that say they saw it on the way in to work from DC. But this FDR is very interesting. Did this really come from the NTSB?

 

[Anti-sophist]

Oh dear. How exactly can you tell the plane is level from 5 frames of video, when only one of those frames shows the plane? (and it shows it rather poorly). Certainly the 3 frames of explosions aren't helping.

 

[qarnos]

Yes, I'm a retired Airline pilot from Independence Air. Haven't thought much about flying since except for buzzing around in a 172.

Can you provide any credentials to back this up?

 

[weedwacker]

haha, on the internet? Sure, right after you provide your birth certificate.

Do you think I'm a fake? As I said, I can take my posts back over to flightinfo. No sweat off my back. It already seems some of you people attack anyone that comes here and obviously this JDX guy has many of you so riled up. My best advice is to get some whiskey. Go out and see a movie. Enjoy your life. Don't let one person get so under your skin. Especially one that you don't know and one that you obviously disagree with. How many threads are here on this guy alone? You don't even know him?

If I seem protective of him, it's because if he did work for FLYI, it was one big family and we all went through alot with that airline. But, that doesn't excuse his claims if they are wrong.

Good luck all. Try not to let one person get to you.

 

[bignickel]

Here here. Let's all take a breather (well, not me, I just started posting in this thread, and I don't know NTSB from NSTB).

WW said he was going to check out some numbers on JDX site; after he does, he can get back to us with what he discovered. In the meantime, we can discuss this and that, of whatnot and happenstance, of cabbages and kings, and where the sea is boiling hot.

(BTW, WW, I suspect that JDX likes the band X. If you do know him, tell him to get a new moniker please)

 

[Gravy]

haha, on the internet? Sure, right after you provide your birth certificate.

Do you think I'm a fake? As I said, I can take my posts back over to flightinfo. No sweat off my back. It already seems some of you people attack anyone that comes here and obviously this JDX guy has many of you so riled up. My best advice is to get some whiskey. Go out and see a movie. Enjoy your life. Don't let one person get so under your skin. Especially one that you don't know and one that you obviously disagree with. How many threads are here on this guy alone? You don't even know him?

If I seem protective of him, it's because if he did work for FLYI, it was one big family and we all went through alot with that airline. But, that doesn't excuse his claims if they are wrong.

Good luck all. Try not to let one person get to you.

I think the issue of credentials is only relevant if someone cites their experience, rather than evidence we can check (argument to auto-authority?), or if they get things wrong that someone with the claimed experience should get right. JDX has done both of those things at times, so asking him to show his credentials is to be expected. I don't see why Weedwacker should be asked to show credentials unless he makes questionable claims or doesn't seem to know what he's talking about. I've seen no evidence of that behavior.

 

[qarnos]

I think the issue of credentials is only relevant if someone cites their experience, rather than evidence we can check (argument to auto-authority?), or if they get things wrong that someone with the claimed experience should get right. JDX has done both of those things at times, so asking him to show his credentials is to be expected. I don't see why Weedwacker should be asked to show credentials unless he makes questionable claims or doesn't seem to know what he's talking about. I've seen no evidence of that behavior.

My concern was raised by the confusion over G Force, which is absolute grass-roots basic stuff for a pilot.

You are correct, however, that Weedwacker did not cite his experience. That was my oversight.

I apologise if anyone took offence or thought I was out of line.

 

[R.Mackey]

I'm coming to this party late, after a pleasant evening sampling the premier oeonphiliac products of the free world with the wife... so forgive me if this doesn't make sense...

An accelerometer reading of zero G's probably doesn't mean that the aircraft is freefalling. The accelerometer doesn't know about Earth's gravity. If the aircraft is flat and level, experiencing no net acceleration, the accelerometer reads zero G's.

If the accelerometer reads -1 G, it means the aircraft is diving at freefall.

If it reads +1 G, it means the aircraft is climbing.

You have to treat the aircraft itself as its own Newtonian reference frame for this to be consistent. If the aircraft doesn't accelerate at all, it means zero G's. That means flat and level flight.

Also, for what it's worth, I've found weedwacker's comments to be completely reasonable. I could care less what his background is, it's the quality of his arguments that matter. That goes for every person here. Let's not make the mistake of the CT's, and let everyone have their say. Thanks.

 

[einsteen]

G-force is indeed no force but acceleration. The ratio with the famous factor g is always used (think about roller coasters)

I didn’t know about JDX math stuff, it looks like that parking camera information is used in your analysis, some people claim that that frames are edited but even if that info is genuine you have to know something about the accuracy of the frames. The frames are crappy, crap in crap out. Even my dad has a better camera for his business bought at the local store for a few euros.

Normally when you have n points you can estimate the “real” trajectory by a polynomial of order n-1, I think a 2nd order estimation is sufficient for an airplane, because the heavier they are the straighter the trajectory will be. But of course if there is a lot of force available the momentum (hence velocity) can change rapidly. I assume the acceleration of a plane is public and available information that can be found somewhere?

Once you have the position of function of time the velocity as function of time is nothing more than the time-derivative and the acceleration is another time-derivative. Be careful because an initial error in position will strongly affect your end result.

 

[qarnos]

I'm coming to this party late, after a pleasant evening sampling the premier oeonphiliac products of the free world with the wife... so forgive me if this doesn't make sense...

An accelerometer reading of zero G's probably doesn't mean that the aircraft is freefalling. The accelerometer doesn't know about Earth's gravity. If the aircraft is flat and level, experiencing no net acceleration, the accelerometer reads zero G's.

This is something I would be interested to know for sure.

I would have thought that a stationary accelerometer at MSL would read +1g since it is, after all, experiencing an accelerative force (gravity).

By this logic, zero G's would mean free-fall.

An accelerometer does not "know" what the source of the acceleration is. It has no way of segregating gravitational acceleration from any other kind because this is simply not possible and is, in fact, one of the corner stones of relativity.

The only way to construct an accelerometer which would read zero G's in the above scenario is to artificially compensate for the expected gravitational force.

Perhaps the FDR data has been adjusted for this. I don't know.

If the accelerometer reads -1 G, it means the aircraft is diving at freefall.

If it reads +1 G, it means the aircraft is climbing.

You have to treat the aircraft itself as its own Newtonian reference frame for this to be consistent. If the aircraft doesn't accelerate at all, it means zero G's. That means flat and level flight.

The lift generated by the wings is an accelerative force. And in level flight at MSL lift equals exactly 1g.

Also, for what it's worth, I've found weedwacker's comments to be completely reasonable. I could care less what his background is, it's the quality of his arguments that matter. That goes for every person here. Let's not make the mistake of the CT's, and let everyone have their say. Thanks.

Agreed. I jumped the gun. Badly.

 

[Obviousman]

I'm coming to this party late, after a pleasant evening sampling the premier oeonphiliac products of the free world with the wife... so forgive me if this doesn't make sense...

An accelerometer reading of zero G's probably doesn't mean that the aircraft is freefalling. The accelerometer doesn't know about Earth's gravity. If the aircraft is flat and level, experiencing no net acceleration, the accelerometer reads zero G's.

If the accelerometer reads -1 G, it means the aircraft is diving at freefall.

If it reads +1 G, it means the aircraft is climbing.

You have to treat the aircraft itself as its own Newtonian reference frame for this to be consistent. If the aircraft doesn't accelerate at all, it means zero G's. That means flat and level flight.

Also, for what it's worth, I've found weedwacker's comments to be completely reasonable. I could care less what his background is, it's the quality of his arguments that matter. That goes for every person here. Let's not make the mistake of the CT's, and let everyone have their say. Thanks.

Correction there. The accelerometer will read +1 in normal, straight & level flight. If it reads zero, then you are actually in freefall.

Here's a piccie of one:

Notice how it is reading 1 in 'normal' condition, and that marking is thicker than the other lines?

That's why the DFDR data will show '1' vertical acceleration a lot of the time.

So the last DFDR data showed 3960 fpm rate of descent, and about 0.6G during the last recorded second. That's to be expected because the the aircraft was descending, thus lower G.

Still, DOH! himself has said that 4000 fpm is not "excessive" for an airliner, so he would have to admit that pulling out of that descent is quite possible - especially some 400 feet above the ground (very rough figure, and assuming DOH! is correct with his calculations) when you are not concerned with overstressing the aircraft.

 

[Obviousman]

You know, what this does go to show is that you need to be a professional trained in this field to properly analyse the DFDR data.

Regardless of DOH!s pilot experience, he is not (I assume) qualified to analyse DFDRs and give an accurate conclusion. There are lots of factors of which the layman - and pilot - is unaware, and must be considered with this stuff. There are no doubt a few, highly qualified people who can look at this correctly. Flight test pilots & engineers would have - most likely - the necessary backgrounds to properly evaluate the data.

 

[MRC_Hans]

I think an accelerometer will be reading zero in normal gravity. Of course, it is really in 1G, but this will be its reference. So an accelerometer will show the differential G value.

There is a technical reason for this. The accelerometer has to be set to zero, somehow. The transducer types used for this are not capable of holding an initial setting indefinitely, so you would either have to take them for frequent recalibrations or you set them to zero when there is no differential force.

What the reading in an FDR is, I don't know. It could have one G added, but I somehow doubt that. It wouldn't be of any use, since what we are interested in is the differential G.

Hans

 

[Obviousman]

I know it might seem counter-intuitive, but they read 1 normally:

...accelerometers are commonly calibrated to read 1.0 g-units when stationary on the Earth's surface...

http://media.wiley.com/product_data/excerpt/59/04713714/0471371459.pdf

So if the DFDR says +1.5G, you are pulling +1.5G but are experiencing +0.5 differential G.

So normal weight is say 100kg, so at 1.5G you would "weigh" 150kg.