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Originally posted by darkbluesky
14 CFR 23.303 FAA Airworthiness Standards - Factor of Safety
An airframe certificated for 2.5G must be designed to 3.8G. The aircraft designer will also apply their own safety factor on top of the FAAs.
posted by darkbluesky
BS- more intentional disinfo. All air liners can withstand 6-7 Gs.
§ 25.301 Loads.
(a) Strength requirements are specified
in terms of limit loads (the maximum
loads to be expected in service)
and ultimate loads (limit loads multiplied
by prescribed factors of safety).
Unless otherwise provided, prescribed
loads are limit loads.
(b) Unless otherwise provided, the
specified air, ground, and water loads
must be placed in equilibrium with inertia
forces, considering each item of
mass in the airplane.
§ 25.303 Factor of safety.
Unless otherwise specified, a factor of
safety of 1.5 must be applied to the prescribed
limit load which are considered
external loads on the structure. When a
loading condition is prescribed in
terms of ultimate loads, a factor of
safety need not be applied unless otherwise
specified.
(Amdt. 25–23, 35 FR 5672, Apr. 8, 1970)
An airframe certificated for 2.5G must be designed to 3.8G.
NATIONAL TRANSPORTATION SAFETY BOARD
N National Transportation Safety Board
Washington, D.C. 20594
Safety Recommendation
Date: September 4, 2003
In reply refer to: A-03-41 through -44
Honorable Marion C. Blakey
Administrator
Federal Aviation Administration
Washington, D.C. 20591
Background
On November 17, 2002, at 1800 eastern standard time, a Canadair CL-600-2B19
(CRJ-2), N868CA, operated by Comair as Delta Connection flight 5109, a scheduled passenger
flight from Atlanta, Georgia, to Washington, D.C., encountered severe turbulence while in a
descent near Rockville, Virginia. There were no injuries to the crew or passengers. The airplane
was returned to revenue service on November 18, 2002, after it was visually inspected for
damage in accordance with the procedures for severe turbulence or extreme maneuvers outlined
in the Canadair Regional Jet (CRJ) Aircraft Maintenance Manual (AMM).
The National Transportation Safety Board’s examination of information from the flight
data recorder (FDR) indicated that large vertical accelerations occurred during the turbulence
event. Further analysis by Canadair indicated that during the event, the wing, pylon, and
horizontal stabilizer to vertical stabilizer attachment structure experienced loads outside their
certificated design envelopes. Specifically, this analysis revealed that the airplane experienced
vertical accelerations ranging from 4.3 G positive to 1.9 G negative, resulting in internal loads
well in excess of the certificated limit load for these structural components.
For example, engineers typically design composite tail sections of commercial airliners to withstand a stress 2.5 times greater than the maximum stress anticipated during their service life—a factor of safety of 250%. With a better understanding of the stress states and long-term performance of composites, aerospace designers should be able to significantly reduce this factor of safety.
Originally posted by johnlear
Originally posted by darkbluesky
Do the math. A level 75 degree banking turn exerts approx 4 Gs on the airframe. This maneuver is possible.
To talk of anything over 3 G's in a modern airliner is ridiculous. They are not certificated for the kind of load maneuvering. They are certificated to +2.0 and thats it. 2 g's is lot of g's in an airliner. During their entire lifetime they will rarely see that.
Originally posted by johnlear
3 g's is absolutely not seen ever. 4 g's is what aerobatic aircraft are stressed for.
Originally posted by johnlear
The airplane in its lifetime will probably never see 2 g's. Airliners are carefully flown by professionals and other than an occasional thunderstorm with strong vertical currents it will never even see 1.5 g's.
Originally posted by johnlear
If you want to worry about the pilot remember that at 4 g's a 180 pound pilot weighs 720 pounds! And if you think that a Arab hijacker with minumum time is going to be able to sustain a 4 g turn weighing 720 pounds then you just don't understand what is is like to weigh 720 pounds or what it is like to try and hold on to a control column when you arms, wrist and hands weigh 4 times normal.
Originally posted by johnlear
Not even possible. And not to worry, the airplane won't be flying at 4 g's!
Originally posted by johnlear
To state that this maneuver is possible is to have no understanding of the flight dynamics involved or to have any understanding of the physiological ramifications of trying to function as a pilot at 4 g's.
Originally posted by tinfoilhatman
This question has been asked repeatedly and NOT answered so I will pose it again.
What part of a differing flight plan PROVES that the plane DID NOT hit the pentagon?
That is stated by Jack multiple times yet no proof is offered. Is there some geographic feature that makes it impossible for the plane to hit the building if the flight plan is different? Seems to me that given the head on nature of the flight path that Jack is selling (and I'm buying) grants an easier target to hit than the angular "official" flight path.
So the question remains, how does the new flight plan equate to a non pentagon strike?
Originally posted by darkbluesky
Originally posted by johnlear
Not even possible. And not to worry, the airplane won't be flying at 4 g's!
Really?
.
Now lets look at someone trying to fly a Boeing 757 one hundred feet off of the ground at from 350 knots to 450 knots. If he pulls the maximum of 2 g's, which the airplane is certificated for the wing will be generating enough lift to support twice the aircraft's weight which we'll say is 250,000 pounds. So twice that is 500,000 pounds of lift is being generated to keep the airplane level. Now lets say the pilot is one hundred feet off of the ground and pulls 3 g's in a turn. The weight that the wing will now have to support is now 750,000 pounds and it is not designed to do that. As the weight, caused by the excessive g's is increased, the airplane will begin to buffet because it can no longer support the weight it is being asked to support with the available lift being generated frrom the wings. The buffet is caused by the air over the wing separating from the wing and no longer producing lift. As the buffet begins lift instantaneously decreases. At 100 hundred feet off of the ground there is not much room for error. I would estimate much, much less than a second between the time the high speed buffet began and the airplane descended wing first into the ground.
posted by darkbluesky I thought carefully about making this post, but since my understading of flight dynamics and physiology was dismissed, and my knowledge and integrity were challenged, I felt I had no other option.
Airliners are carefullly flown by professionals and other than an occasional thunderstorm with strong vertical currents will never see more than 1.5 g's.
Originally posted by johnlear
Darkkbluesky. Please don't mix apples with oranges. The number of g's a Boeing 757 could sustain came up because we were talking about making the violent turns at 100 feet agl just before it allegedly hit the Pentagon. We are not talking about vertical loads sustained by aircraft due to turbulence at 35,000 feet.
During their entire lifetime they will rarely see that. 3 g's is absolutely not seen ever.
Now lets look at someone trying to fly a Boeing 757 one hundred feet off of the ground at from 350 knots to 450 knots. If he pulls the maximum of 2 g's, which the airplane is certificated for the wing will be generating enough lift to support twice the aircraft's weight which we'll say is 250,000 pounds. So twice that is 500,000 pounds of lift is being generated to keep the airplane level. Now lets say the pilot is one hundred feet off of the ground and pulls 3 g's in a turn. The weight that the wing will now have to support is now 750,000 pounds and it is not designed to do that.
As the weight, caused by the excessive g's is increased, the airplane will begin to buffet because it can no longer support the weight it is being asked to support with the available lift being generated frrom the wings. The buffet is caused by the air over the wing separating from the wing and no longer producing lift. As the buffet begins lift instantaneously decreases.
At 100 hundred feet off of the ground there is not much room for error.
The fact that the Boeing 757 would not still be flying, as I stated, is not due to vertical loads sustained due to clear air turbulence.
It is due to the fact that at 4 g's the wing will not be creating enough lift to support the weight of the aircraft.
You have also failed to address the issue of how a pilot with limited experience would be able to fly these violent maneuvers at 100 agl without a g suit. Remember, a 180 pound pilot would weigh 720 pounds!
As to my statement:
Airliners are carefullly flown by professionals and other than an occasional thunderstorm with strong vertical currents will never see more than 1.5 g's.
I stand by this statement. You posted 2 incidents which occurred during the past 28 years. Like I said 'occasional'. These incidents are rare and the only reason the airplane survives is that it has thousands of feet of altitude in which to recover.
Thank you for your withdrawal of your statement that airliners are designed to 6 and 7 g's.
The Airbus 380 is requesting certification for 2.5 g's. Ultimate load factor would be (150% ultimate load) 3.75. The wing failed between 3.70 and 3.75 when is was bent up approximately 24 feet.
I will email Boeing tomorrow to see if we ca get an answer to the ultimate load factor to which it was tested. As you may know, for FAA certification the fuselage is secured and by hydraulic lifts the wings are lifted up to the proposed failure point, that is, if the airplane is requesting a maximum weight of, say, 300,000 pounds and they are presenting an ultimate load factor of 4.0 g's then the upward load has to equal 4 times 300,000 pounds or 1,200,000 pounds. This is just an example for clarity. 2.5 g's is normal certification and 150% of that is 3.75 g's.
Originally posted by darkbluesky
I just want to point out that certificated max load and ultimate load obviously do not match actual load bearing capabilities as the 2.5g certificated 727 demonstrates.
Limit load is established by a mixture of FAA certification criteria and Boeing design requirements. Coupled with a safety factor, this establishes the strength at which we design and build the airplane.