How to build a complete fuselage loads FEM for a helicotper and correlate with FLS data

Are the FLS results in terms of accelerations?
To apply inertia loads you have to model all of the masses, structural and non structural, and apply accelerations.

Automotive experience is that accelerometer data is too far removed from what you want, forces and stresses and strains. I don't know how many years were spent pursuing 'fatigue loads from accelerometer time histories', they got to some sort of ballparky figures, but I'm pretty sure the standard method is still force transducers and strain gages.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

Hello,

FLS data is in load, moment, strain in some point, and accel on high vibrating point.

I allowed to use inertia relief at aircraft CG SUPORT point connected to mast base.

But how to find out which limit loads? What to apply where and then how to validate with FLS data?

I would start by applying unit accelerations in the 3 translations and 3 rotations, in 6 separate subcases. Then with the results from those cases at the points where you have FLS data, figure out the factors to apply to the set of unit load case results to match 5he FLS data.

Thank you so much.
So that sound like good start.

But FLS data is from many maneuver that include many things, rolling pull out, pushover, turn, dive, pull up etc. not just one direction g load. So how to do it?
TY,
KS.

Each maneuver point is a separate load case. So you have to find the correct load factors for each of those cases. Then you will apply all of those cases to your FEM, and analyze every case.

So let us take one maneuver. In that maneuver, for example, say I have measurements for moment on two locations in tailboom, moments in two sides of horizontal, moment and torsion at two locations on vertical, moments at two locations on mast tube, many other measurements on main and tail rotor blades, control system and others. So you see its not just G load, but I know the peak G load in this maneuver, The peak value in each of the measurement no exactly at same time during maneuver. So how to apply all loads when one load may cause another?

This is where you need to talk to your peers and management. I know how I'd do it, but I use different tools to you.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

Ok.
First, the title says fuselage model, so ignore all of the rotor data; those get analyzed separately.
Second, not sure what you mean by control system, but probably ignore that also, as it will get separate design and analysis.
Third, you need to sort it out for a single fixed time value.
Fourth, get your forces, moments, strains, G’s for a given maneuver and time value.
Then as mentioned above, get the unit load case results at the same locations as the data in step 4.
Then see if there is a single set of 6 factors to apply to the unit load model data so the model matches all of 5he data from step 4.
Repeat for every time value and maneuver.
Probably can be set up in a giant spreadsheet.

Right, rotor and control system, drive system all are separate, just wanted to mention. But inertia relief, g load no do anything, right? Forces or pressures etc. will work.

Agreed, use the forces, moments pressures. The G’s maybe become a sanity check against the unit load factors in the FEM.