Jet engine sim for testing 9/11 planes

reply to post by ULTIMA1


I read all your posts (when I come across them, not in some stalkerish kind of way).

You're intelligent, thoughtful and very (compliment, not a dig) opinionated. You have served your country honorably and were a Crew Dog for, what I think, is the sexiest aircraft of all time. An F-4 is simply beautiful and I can't think of another airframe that had so many versions, so widely used. The fact that you were a part of that is something that I hold you in very high regard for.

You are obviously a good guy and we all know it – truly.

Originally posted by Pilgrum

Originally posted by ULTIMA1

Originally posted by Pilgrum
I think there's at least one who says he had to drop to the ground for fear of being hit but that action would have minimised the effect on him and it was grossly exceeded by the explosion a moment later.

Yes the same person who claimed he was 6 feet away, who would have been blown away by jet blast.

But at what point was the jet blast perfectly directed at him considering he was lying prone on the ground?
If he'd remained standing he'd have experienced more of it but lying down, he avoided it.

It's an interesting point but again, it doesn't provide positive proof of anything unless we rely on enough negatives adding up to a positive which just doesn't happen.

If a jet is moving at 500mph, and the jet blast is exiting the engine at 520 mph, for example,...what is the speed of "jet-blasted" air which will be felt by someone whom the jet is passing? 20mph. (It's like throwing a baseball backwards out of a car that's moving forward.)

Jet blasts are more dangerous at takeoff & low speeds, because the plane is not yet moving, so the blast is not offset by the forward speed of the aircraft.

Originally posted by Zaphod58
A plane flying high speed, low level, in a clean configuration, is going to have WAKE TURBULENCE causing more problems than jet blast,

Please correct me if i am wrong. Major wake turbulence is caused at low speed (landing) with gear and flaps down, usullay under 200 mph.

The official story states the plane at the Pentagon was flying clean, (gear and flaps up) so the wake turbulence would not have been as major.

According to the NASA engine sim, a turbofan engine at 60 feet doing 486 MPH is putting out just over 65,000 lbs of thrust.

I do believe that 65,000 ibs of thrust even at several feet about the cars would still be enough to rock them.


[edit on 10-4-2008 by ULTIMA1]

Originally posted by SlightlyAbovePar
An F-4 is simply beautiful and I can't think of another airframe that had so many versions, so widely used. The fact that you were a part of that is something that I hold you in very high regard for.

The F-4 was a true workhorse and 1 of the few planes to ever serve in all 3 flying branches of the service. Also used by several other countries.

If you are interested you should check out the National Vigilance Park in MD.

It is a memorial for recon aircrews lost during the cold war that at the time their missions were classified and no infomratoinwas given out to the families about what happened to them.

Originally posted by ULTIMA1
.

According to the NASA engine sim, a turbofan engine at 60 feet doing 486 MPH is putting out just over 65,000 lbs of thrust.

I do believe that 65,000 ibs of thrust even at several feet about the cars would still be enough to rock them.


[edit on 10-4-2008 by ULTIMA1]

the speed of that jetblast is also reduced by the forward movement of the aircraft. (relative to the ground)

[edit on 10-4-2008 by nicepants]

Originally posted by nicepants
the speed of that jetblast is also reduced by the forward movement of the aircraft. (relative to the ground)

Modern jet engines, like on B 757s, have a double exhaust flux : hot gases, coming out from the high pressure stage on the center, cold air pushed by the front low pressure fan at the exterior. These two fluxes have different speeds. The central hot flux speed is something like two times the speed of the annular cold flux which surrounds it. This later cold flux speed is approximately the full speed of the aircraft, i.e. something like 650 mph (near sound speed).

There are, near the exhaust, two turbulence zones created by the mix of gases : one at the hot flux / cold flux interface zone, and one at the cold flux / exterior air interface zone. Behind the aircraft, (say ~30 ft behind the engine) the hot and cold fluxes mix. Their speed decrease because they spread in a growing section cone. Thus it is reasonnable to think that when this cone met the ground on rd 27, the average relative speed - regarding to the plane - of the turbulent gases was something like 500 mph, and not 1500 !
The plane was said to fly at ~350 mph when it hit the Pentagon. Thus, I think that when the cars on rd 27 were blown by the blast of the engines, this blast had a relative speed of ~150 mph regarding to the ground. As explained above, this did not last a long time. Cars were shocked and moved a little sidely. As they were all stopped or nearly stopped in a traffic jam, this did not cause any accident by itself.

[edit on 10-4-2008 by ULTIMA1]

Originally posted by ULTIMA1

Originally posted by nicepants
the speed of that jetblast is also reduced by the forward movement of the aircraft. (relative to the ground)

Modern jet engines, like on B 757s, have a double exhaust flux : hot gases, coming out from the high pressure stage on the center, cold air pushed by the front low pressure fan at the exterior. These two fluxes have different speeds. The central hot flux speed is something like two times the speed of the annular cold flux which surrounds it. This later cold flux speed is approximately the full speed of the aircraft, i.e. something like 650 mph (near sound speed).

There are, near the exhaust, two turbulence zones created by the mix of gases : one at the hot flux / cold flux interface zone, and one at the cold flux / exterior air interface zone. Behind the aircraft, (say ~30 ft behind the engine) the hot and cold fluxes mix. Their speed decrease because they spread in a growing section cone. Thus it is reasonnable to think that when this cone met the ground on rd 27, the average relative speed - regarding to the plane - of the turbulent gases was something like 500 mph, and not 1500 !
The plane was said to fly at ~350 mph when it hit the Pentagon. Thus, I think that when the cars on rd 27 were blown by the blast of the engines, this blast had a relative speed of ~150 mph regarding to the ground. As explained above, this did not last a long time. Cars were shocked and moved a little sidely. As they were all stopped or nearly stopped in a traffic jam, this did not cause any accident by itself.

[edit on 10-4-2008 by ULTIMA1]

Either way the effect was minimal. Don't forget to post your sources

Originally posted by nicepants
Either way the effect was minimal. Don't forget to post your sources

But enough to rock the cars as originally stated.

The source is the same as the original post.

[edit on 10-4-2008 by ULTIMA1]

Originally posted by ULTIMA1

Originally posted by nicepants
Either way the effect was minimal. Don't forget to post your sources

But enough to rock the cars as originally stated.
[edit on 10-4-2008 by ULTIMA1]

It certainly could be, yes.

Originally posted by nicepants
It certainly could be, yes.

Well at least 1 person can can state a could be.

reply to post by nicepants


nicepants, you deserve a star for that one!!!

Somewhere there is a graphic that shows the flow patterns behind engines....of course, this refers to engines on the ground, since that is the real 'problem' of 'jet-blast'....it is only important during ground operations, as it pertains to what damage can be done by using too much thrust during taxi, and the proximity of persons or equipment. That is why, when we taxi, we are very careful of using power to 'break away', as the term is used...this refers to thrust necessary to start initial movement...once momentum is underway, idle thrust is sufficient to maintain taxi speed.

WW

Originally posted by weedwhacker
That is why, when we taxi, we are very careful of using power to 'break away', as the term is used...this refers to thrust necessary to start initial movement...once momentum is underway, idle thrust is sufficient to maintain taxi speed.

But there is still jet blast in the air.

I have seen a student pilot throttle up to move out of the parking space and then pull throttle back to idle but pulled back to far and shut off the engines. OOOPS !



[edit on 10-4-2008 by ULTIMA1]

reply to post by ULTIMA1


Yes, MAJOR wake turbulence is in the landing configuration. However, in ANY configuration you are still going to have wake turbulence. It doesn't stop because the flaps and landing gear are up. It doesn't make ANY difference how much jet blast is being produced by the engine. Unless you can tell me how it's going to go from travelling in a straight line out the exhaust, to curving into the ground to rock the cars, it's NOT going to be a factor, or rock the cars. The WAKE TURBULENCE will do that.

reply to post by ULTIMA1


ULTIMA, not sure what jet you are referring to....but the jets I flew had idle stops, the mechanical place where the throttle stops...and the difference between 'ground idle' and 'flight idle' is determined by the air/ground sensing switches.

The way to shut down the engines was different....the fuel cut-off levers...or, in an emergency, the fire handles, since that's how they teach airport fire department personnel.

WW

Originally posted by Zaphod58
Yes, MAJOR wake turbulence is in the landing configuration. However, in ANY configuration you are still going to have wake turbulence.

So you agree that major wake happenes at slower speed and gear, flap down.

So that could mean the jet blast is another reason for the cars rocking then the wake, snice the wake would not have been as major.

Something pretty simple states that the jet flys low over the cars the jet blast contacts the cars. I mean how loarge is the blast coming from a large turbofan?

Originally posted by weedwhacker
ULTIMA, not sure what jet you are referring to....but the jets I flew had idle stops, the mechanical place where the throttle stops...

Well i guess you never flew in a T-38A military trainer.



[edit on 10-4-2008 by ULTIMA1]

If you had actually READ any of the links we have posted, jet blast comes out of the exhaust in a cone of approximately 20 feet wide from the back of the engine IIRC. You didn't even have to read the links! We put it in POSTS in the thread.

reply to post by ULTIMA1


ULTIMA, that is correct, I never flew a T-38. I never flew any military airplane, of course. I have flown the B727, A-300 and DC-10, right seat....I am type-rated in the B737, DC-9/MD-80 and B757/B767.

I also flew a few turbo-props...reverse on a turboprop requires one to bring the throttles up, over the flight idle stop, and into the reverse region.

Modern jets have levers, built in, forward of the thrust levers, that you pull up with your fingers, in order to activate reverse thrust.

Of course, reversing with a turbo-prop is different than reversing with a jet. A turbo-prop uses the propellor blades, and of course, a modern jet engine just redirects some of the exhaust airflow forward....hence, this is how modern jets work.

WW

Originally posted by weedwhackerit is only important during ground operations, as it pertains to what damage can be done by using too much thrust during taxi, and the proximity of persons or equipment. That is why, when we taxi, we are very careful of using power to 'break away'

Indeed, our chief pilot once prooved that even a 737 can do serious damage to ground-equipment hitting TOGA leaving the stand.

After that little incident autothrottle was moved from before taxi to before takeoff flow.

[edit on 10-4-2008 by Freaky_Animal]

reply to post by ULTIMA1


I already did correct you. The most wake turbulance is created when the aircraft is CLEAN, HEAVY, and SLOW. Why? Because that's obviously the configuration that created the biggest wingtip vorticies. Also, it's in the FAA link you said before.

Wings are always going to be creating lift equal to the weight of the plane (plus some from the tailplane pushing down). There will ALWAYS be severe wake turbulence behind an aircraft. Why is this being argued anyway? They don't limit anything on jet blast, they limit distance because of wake, as described in your on link.

[edit on 10/4/2008 by C0bzz]

Originally posted by Freaky_Animal

Originally posted by weedwhackerit is only important during ground operations, as it pertains to what damage can be done by using too much thrust during taxi, and the proximity of persons or equipment. That is why, when we taxi, we are very careful of using power to 'break away'

Indeed, our chief pilot once prooved that even a 737 can do serious damage to ground-equipment hitting TOGA leaving the stand.

After that little incident autothrottle was moved from before taxi to before takeoff flow.

[edit on 10-4-2008 by Freaky_Animal]

LOL! LOL! LOL!......Oh, my, glad to see ya again, Freaky!!!

Yup, that happened so many times at my airline, at least on the B737....it is now a 'before take-off' item as well!!!!

On the MD-80, it was on the 'taxi' checklist, but things are different for each airplane.

I can't remember what we currently do on the 757/767 fleet, if I remember, we just 'call' for the N1, and the NFP engages for us, after engines are stabilized. In fact, the protocol is, if the AP is disengaged, the FP calls out everything, and of course, monitors and verifies. If the AP is engaged, the FP notifies, and receives verification from the NFP, so there is agreement on the action taken.

That's the official story, and I;m sticking to it!

WW

[edit on 4/11/0808 by weedwhacker]