Jet engine sim for testing 9/11 planes

Originally posted by HLR53K
No, of course it doesn't "disappear". I just believe jet blast becomes less and less of a factor on objects on the ground as the airplane goes higher. Wake turbulence takes over as the primary force.

But doesn't the FA have a rule for takeoff distance becasue of jet blast on the ground and in the air at takeoff?

Thanks for being truthful about the jet blast not disappering.

But wake turbulence is at its highest at slow speed, gear and flaps down, wake turbulence decrease as speed increases. Where jet blast would be a constant.


[edit on 27-4-2008 by ULTIMA1]

Originally posted by weedwhackerGear Operating' limit airspeed on the B757 is 220 knots.....this is because of the load limits on the gear doors, during the cycle. The 'Gear Extended' speed is 250 Knots

Are there differences from the 200-300's?
I have some old sop's and manuals from back when my company operated the B757 that say max operating speed 250 and gear ext. 270.
(757-300 that is)
Im not rated on or have any experiance on the 757, just curious.

reply to post by HLR53K


HLR....the signs to denote Runway Hold points, or to denote taxiway designations....are frangible for a reason...in case they don't become a hazard to an airplane that may already be in distress.

Yes, a particularly inattentive pilot might 'blow' a sign down, break it.....but if standard procedures are followed, and no one acts like a 'TopGun' yahoo....the signs won't get broken.

MAYBE.....maybe....an international airport, in some backwater part of the World, where a Jumbo comes in rarely....they lost a sign. Not likely to be from the wingtip vortices, though....they aren't that strong.

Just thinking....

WW

Originally posted by ULTIMA1
But it also places the plane closer to the cars.

Well about as close as the tops of the light poles placing the plane about 30' above the cars and even higher above the Pentagon lawn at that point so it had considerable descent to accomplish in a very short time in order to impact near ground level. The engine thrust would be directed upward for that, not downward.

reply to post by Freaky_Animal


Yeah, Freaky......I could be off, I didn't look up the FOM, just going from memory.....might have been B737 limits......

Ya know, the limits, along with flap speeds, are mounted on the Instrument panel.....we memorize them for the type-rating oral.....then, well....you know......

WW

Originally posted by weedwhacker
Not likely to be from the wingtip vortices, though....they aren't that strong.

But aren't wingtip vortices strongest on landing role?

Isn't that why there is a distance rule for planes comming in behind a "heavy"

Here's an interesting bit I found:

aircraft wake turbulence as a product of lift

Many people think of aircraft wakes in terms of “prop wash” or jet engine exhaust. The inflight turbulence associated with the power plants is actually short-lived. The principal cause of the trailing vortices which constitute the wakes is the lift generated by wing surfaces. As proof of this, wake turbulence is present behind unpowered aircraft and even birds in flight. Geese are believed to adjust their positions in formation flight instinctively to achieve maximum lift from the vortex wakes generated by their mates, the energy saved permitting longer-range flight. (Presumably, the birds take turns in the lead position.) Helicopter pilots in Southeast Asia (SEA) refueling operations are reported to be using the wakes of tanker aircraft to decrease rotor workloads during hookup, an obvious range-extending maneuver. (Helicopters themselves generate powerful [and dangerous] vortex wakes which have been useful in fog-clearing operations in SEA, a technique tested at the Army’s Cold Region Research and Engineering Laboratory and developed at AFCRL.)

www.airpower.maxwell.af.mil...

Originally posted by Pilgrum
The engine thrust would be directed upward for that, not downward.

But if the engines were close enough to the cars it would not matter if the blast was directed upward, jet blast would still hit the cars.

Originally posted by ULTIMA1I will ask you the same queston.

What happens when the gear is lowered above 500 mph at 60 feet or less above the ground?

Well as weedwhacker have stated damage to the gear doors and hydraulic systems, as well as increased drag.

In few words loss of control.

Originally posted by HLR53K
Helicopters themselves generate powerful [and dangerous] vortex wakes which have been useful in fog-clearing operations in SEA, a technique tested at the Army’s Cold Region Research and Engineering Laboratory and developed at AFCRL

I have seen photos of helicopters used for fighting fires by hovering over the fire and using the wake to try to blow out the fire.

Originally posted by Freaky_Animal
In few words loss of control.

So the pilot of the plane would be fighting to try to control a plane and keep it on course and altitude?

[edit on 27-4-2008 by ULTIMA1]

Originally posted by ULTIMA1

I have seen photos of helicopters used for fighting fires by hovering over the fire and using the wake to try to blow out the fire.

Helicopter propulsion is completely different from airplanes.

Airplanes use lift from the wings to keep them in the air. The engines push parallel to the fuselage of the airplane. The speed resulting from the pushing of the engines gets airflow over the wings.

Helicopters use their rotors to actually push air downwards. Their form of lift/propulsion requires the air to be pushed perpendicular to the fuselage. In this case, it would be like using an high-speed fan to blow on the fire.

I bet if you flew and airplane over the fires, it wouldn't really do anything.


I posted the link because of the beginning sentence of that section of the document. It states that the engine exhaust power effects are short-lived while the airplane is in flight.

[edit on 27-4-2008 by HLR53K]

[edit on 27-4-2008 by HLR53K]

Originally posted by HLR53K
Airplanes use lift from the wings to keep them in the air.

Yes i know how a plane works thanks, i was a crew chief in the Air Force.

Actaully a plane flies due to a mathamatical principal.



[edit on 27-4-2008 by ULTIMA1]

Originally posted by ULTIMA1

Yes i know how a plane works thanks, i was a crew chief in the Air Force.

Actaully a plane flies due to a mathamatical principal.



[edit on 27-4-2008 by ULTIMA1]

L = 1/2*ro*Cl*S*v^2

ro = Air density at altitude
Cl = Coefficient of lift (due to the airfoil characteristic; camber, etc.)
S = Planform area of the wing (surface area looking straight down on it)
v = Velocity of the aircraft

I know it all too well.

[edit on 27-4-2008 by HLR53K]

reply to post by ULTIMA1


ULTIMA....yes, I lready posted this.

The vortices are strongest when 'slow and heavy'

"Slow" only occurs in the Landing Configuration. 'Heavy' refers to any airplane that is 'capable' of a GTOW of 300,000 lbs or more. The B757-200 is not designated a 'heavy' (the B757-300 is) but it is treated, by ATC, with the same separation standards as a 'heavy', bucuase it has been determined that WHEN IN THE LANDING CONFIGURATION, the B757-200 exhibits a wake turbelence vortex, from each wingtip, similar to airplnes of ahigher weight ctegory.

(FYI....COA has equipped most of their B757s with winglets....for increased fuel efficiency, but has the added benefit of reduced wake turbulence. Of course, the separation standards, by ATC, remain the same, regardless.)

A 'Heavy' requires 5 miles horizontal, as does a B757 (and B767, since it automatically qualifies as 'Heavy' anyway!)

This, I say, is in what is called the 'Terminal' area....generally below 10,000 feet near the airport, where the TRACON has control. Other min separation is 3 miles. It is always 1000 feet vertically, for airplnaes on an IFR flight plan, unless you can say you have your 'traffic in sight'. VFR airplanes operate at 500 feet off the IFR altitudes.

Example....you are flying Westbound, on an IFR flight plan, in a Cessna, say....you will be at an even altitude, depending, of course, on the MEA for your route....(MEA is 'minimum enroute altitude') But, it will be 6,000 or 8,000 or whatever. If you are VFR, you will be at 6,500, or 8,500,,,,etc.

Eastbound is odd, of course.

This concept is based on your Magnetic Course, not your Magnetic Heading....just to clarify.

WW

Originally posted by HLR53K

L = 1/2*ro*Cl*S*v^2

I know it all too well.

Bernoulli's Principle

Originally posted by weedwhacker
ULTIMA....yes, I lready posted this.

The vortices are strongest when 'slow and heavy'

So a plane going 500 mph and clean would not create strong wingtip vorticies? (but there would be vorticies, just not as strong)

Originally posted by ULTIMA1

Bernoulli's Principle

Modified from:

P1 + 1/2*ro1*v1^2 = P2 + 1/2*ro2*v2^2

That's the general, simplified lift equation. There are many more complex forms which require partial differentials. But I won't get into that. Far outside the scope of this thread.

Originally posted by HLR53K
[That's the general, simplified lift equation. There are many more complex forms which require partial differentials. But I won't get into that. Far outside the scope of this thread.

Yes, as stated i know what makes a plane fly.

Originally posted by ULTIMA1

Yes, as stated i know what makes a plane fly.

Would you like to see the partial differential equations relating to the vortices? Those are even worse.