Is there any standards or at least typical values of aircraft engine displacement and rotation relatively to the wing in flight? Actually I'm looking for that values at Boeing 747-400 RF or ERF.

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1 Answer 1


There is no standard. Even for a single plane and a single engine, there will be literally hundreds of different possible displacements depending on the condition. The engine manufacturer will split these into several categories.

First would be static versus dynamic loads. Static loads are the loads (or displacements) caused by gravity, thrust load, maneuvers or wind. Dynamic loads are transient events caused by rotor unbalance, bird impacts, blade loss, etc.

The second category is the severity of the load. There are several levels here. First is a fatigue load. The engine will experience this level of load (or displacement) on virtually every flight. Therefore, all parts must be able to withstand this load and not have a fatigue failure. The second level is a "limit" load. This would be experienced by the engine say once every 4000 or 5000 flights. E.g. a very rapid maneuver or a particularly hard landing. For this level, fatigue is not a concern, because the engine won't experience it very often. Just have to make sure no parts yield. Final level is "ultimate" load. This is the highest load that will ever be experienced by any engine in the lifetime of the entire fleet (e.g. a fan blade out condition). Yielding may be allowed here, as long as nothing breaks.

Depending on what you are looking for, the answers could vary between 0.001 inch and several inches. I'm not sure that you will be able to find exact values, as the airframer and engine manufacturers will regard this as proprietary information.

  • $\begingroup$ Consider you've designed an engine mount so that it is strong enough being as light as possible... but the engine moves 30 inches down and rotates 20 degrees downward due to it's own weight as soon as it is attached to the mount (figuratively). Obviously that's not acceptable. Construction is strong enough but not rigid enough. The question is how much more rigid you should make it? $\endgroup$
    – Bzhenko
    Mar 31, 2017 at 23:47
  • $\begingroup$ Engine mounts are usually sized by the ultimate loads mentioned above. An ultimate load may be significantly higher than normal operating load. e.g. a 747-400 engine weighs ~10,000 lbf, but may experience, say, 6g during a very hard landing, or 10g during fan blade out, so the vertical load is now 100,000 lbf. Usually a mount that is strong enough to take the ultimate load will end up being stiff enough anyway. But to answer your question, I think a few degrees / few inches would okay. Since it will be a known displacement, the aero lines can be compensated for this. $\endgroup$
    – Daniel K
    Apr 1, 2017 at 0:41

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