Engine Mounts

[phoenix 23684]

A few months back a thread was posted and people were wondering wether turbine mounts had a point of failure where due to extreme engine vibration or damage the engine would fall of in an effort to minimize damage to the aircraft.

I just came back from an interview with P&W and out of curiosity I asked that question and I'm here to clarify that there is no such thing, the bolts used are made out of titanium and it takes them months to make these bolts and was told that those engines are made to stay on the airplane no matter what. Basically the wing would have to fall off with the engine.

I got a tour of the engines they make, and it was quite impressive to see them specially the A380

[Dan208B]

I was told in groundschool that our engines (CFMs) were designed to break free from the aircraft if vibration got too bad. They said the idea was that they would fall free rather than taking the whole wing.

[tgrayson]

Originally Posted by phoenix 23684

I'm here to clarify that there is no such thing, the bolts used are made out of titanium and it takes them months to make these bolts and was told that those engines are made to stay on the airplane no matter what. Basically the wing would have to fall off with the engine.

That was probably a thread that I was involved in.

My research indicated that first, Airbus and Boeing are different in this regard. Airbus engines are designed to stay attached to the airframe no matter what.

Boeing's are designed to detach under certain conditions, such as ditching at sea, in order to protect the wing from getting ruptured fuel tanks and catching fire. My research indicated, however, that even Boeing's engines are not intended to detach merely due to engine failure. However, they sometimes do and it's been regarded as a design flaw or maintenance failure. Boeing keeps beefing up the attachment structures to keep this from happening. The goal appears to be that the engines should not detach in flight under any circumstances, but having the engines designed to detach during crashes makes them vulnerable to separation in flight when subjected to large g-forces.

[Minuteman]

I won't claim to know more than an engine manufacturer, but, turboprop engine mounts are often statically determinate to keep structure weight down and thermally isolate the engine.

The down-side is that all mounting points are necessary to keep the engine in-place. A failure in any one point allows a line of rotation to form about the remaining mounting points and the engine can move enough to cause the remaining attachments to fail if ignored.



Turboprop engines "breaking away" go back to the Electra and was suspected by ALPA as the cause of a 1991 accident involving a 1900C. In fact, Conquest Airlines had enough difficulty with downtime for repairs to their 1900Cs' engine mounts that they eventually sold them all and bought Metroliners.

So there is an engineering push in opposing directions to make an engine mount as "insubstantial" as possible while still being strong enough to hold the engine for all reasonably conceivable conditions.

As far as intentionally designing engines to breakaway, I don't know. There do seem to be lots of patents for lighter methods for hanging turbofan engines from the wing structure. It's probably the same situation: the push for lighter weights and ease of maintenance has made the attachment point evolve in a way that they are not intended to be strong against abnormal loads (outside of reasonable and certifiable, at least).