jacking cases need ultimate factor?
jacking cases need ultimate factor?
(OP)
Hi guys,
just a confirmation... for large aeroplanes (CS25), when the plane is in Jack position; does it need to withstand just limit loads, isn´t it? So, once I have put the adequate reaction factors stated in CS25.519 in my analysis, no need for applying the typical UF=1.5 on top of them...
just a confirmation... for large aeroplanes (CS25), when the plane is in Jack position; does it need to withstand just limit loads, isn´t it? So, once I have put the adequate reaction factors stated in CS25.519 in my analysis, no need for applying the typical UF=1.5 on top of them...





RE: jacking cases need ultimate factor?
STF
RE: jacking cases need ultimate factor?
I guess that, for some failure scenarios, limit load capability is enough for certificate the structure because load level is known (or accepted) not to overcome the associated to the failure case. So, isn´t this rational valid for jacking (where loads are known, controlled and without any "unexpected" exceedance)? Do you know any practical UF people use for Jack? is UF=1.5 widely used even though?
thanks again!
RE: jacking cases need ultimate factor?
On many aircraft they are also used for holding the aircraft down when stored outside.
Now the loads aren't so easy to predict.
The "unexpected" exceedance should always be expected. Do you think no aircraft has ever been dropped off of its jacks? You should spend more time in hangars - it won't take long to hear some stories.
Go look at the jacking points of an aircraft that's more than 20 years old. They probably look a little beat up.
If memory serves... There is a life-extension package for a certain type of aircraft requiring certain members to be installed only when the aircraft is on jacks with thousands of pounds of lead stacked on the wing, in order to pre-set the load on the spar while a reinforcement member is installed. (If anyone can jog my memory on exactly which aircraft that is, I'd appreciate it.) Anyway the point is that who would have foreseen the need for the jacks to support that load?
STF
RE: jacking cases need ultimate factor?
" CS 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 loading condition is prescribed in terms of ultimate loads, a factor of safety need not be applied unless otherwise specified.
RE: jacking cases need ultimate factor?
RE: jacking cases need ultimate factor?
Aircraft structures must be very light, so they are designed and analyzed to very slim margins. If you consider just how heavy a commercial aircraft structure is, and how high the forces/moments applied to the jacking points can be, you would appreciate the design and analysis factors used. The 1.5 FoS required for analysis is used to account for any inaccuracies in the analysis procedures. If an excessive load was applied to a jacking point, it could damage the fuselage structure and the damage might go undetected. A good example is that of the DC-10 engine pylon failure of AA flight 191, that was allegedly caused by excessive loading on the engine pylon structure during maintenance.
RE: jacking cases need ultimate factor?
RE: jacking cases need ultimate factor?
Once the aircraft is on jacks, it becomes part of a "workplace". I may be using North American terminology here. Think of your local civil building and worker safety codes. When a load is elevated, the people working in it and under it become vulnerable to injury or death if it falls. Assurance that the support points have adequate strength in that situation must be shown to people responsible for worker safety, not flight safety. They live by their own set of rules. I don't know much about them. What's the difference between jacking up an aircraft for maintenance, or a truck, or a bulldozer? Not much to the guy whose leg is pinned under it, if it comes off the jacks.
STF
RE: jacking cases need ultimate factor?
i don't know where 3g comes from ... i'd've used (without thinking about it) 1g ??
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RE: jacking cases need ultimate factor?
Lufthansa had this happen to a 747-200... scary. Thank God the the remaining jacks/jack-points didn't catastropically fail.
http://avtales.wordpress.com/2004/02/16/lufthansa-...
http://www.airliners.net/aviation-forums/general_a...
Regards, Wil Taylor
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RE: jacking cases need ultimate factor?
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