There is an old RAE document which details a method of designing a wing leading edge to resist birdstrike. This can safely-ish be used for curved inlet LEs. It's good for metallic LEs. It works quite well for preliminary sizing and weights, and will probably pass a test. (Or an explicit FE can be used (one of the Dynas, Dytran or Abaqus Explicit), though last time I was involved (2000) the authorities still needed a test.) The document is Royal Aircraft Establishment Technical Report 72056, "The Design of Leading Edge and Intake Wall Structure to Resist Bird Impact". There is also a BAC report which is partly based on this, "BAe Bird Strike Design Manual", GEN/B44/30210.
The main reaon for keeping a bird out of an inlet is because you don't want it blasting back through the inlet aft bulkhead and potentially shutting down the engine by ripping off a FADEC box or whatever, or, worse, rupturing a fuel line and starting a nacelle fire.
I haven't got a copy of the full RAE report. If anyone knows of a digital copy please let us know.
However, I do have the GEN/B44/30210 report, and also a more concise Hawker Siddeley report which have most of the relevant data in them.
The GEN/B44/30210 report is 64 Mb; if you can receive this by e-mail then let me know a contact e-address suitably encoded (ROT 47 encoding worked well enough last time I did this). The Hawker report is just 1/2 Mb, but doesn't have the stuff in it about calculating the forces and pressures and doesn't account for material other than 2000 or 7000 series Al alloys, whereas the BAC report does all those things, plus it has a ton of references and background plus the workings for the various equations.
However, you may not need the whole document; the basic equation from the RAE report, as stated by the BAC report is:
Vp = 3127*t / cube_root(W*cos(alpha)^2) * antilog10(0.83 / (r^2 + 1.16*r + 1.56)) * 0.8*Ftu/63
where:
Vp is penetration speed in knots,
t is thickness in inches,
W is bird weight in lb,
alpha is LE sweepback angle,
r is LE nose radius,
Ftu is material ultimate strength in ksi.
NB: Antilog10(x) is aka Exp(x).
For the force, the BAC doument says that the RAE report has an empirical formula:
Fav = 1.18 * M^(2/3) * V^2 * cos(alpha)
where:
V is impact speed in knots,
M is bird mass in kg,
alpha is LE sweepback angle,
Fav is the average force in N.
(Apologies for mix of units here.)
I think this translates to
Fav = W^(2/3) * V^2 * cos(alpha) / 6.39
Fav in lbf,
W in lb,
V and alpha as before.
These average forecs are based on measurements during tests, and so aren't too bad. If you spread the force out from the LE back to the inlet attachment, take the distance around the attachments equal to the distance from the LE to the attachment station. NB: this assumes that the bird is comletely stopped by the LE.
