Which would cause more damage and why? I'm particularly interested in how the fan blades and compressor stages will be affected by the difference in materials.
There is a numerical study on the topic at VirginiaTech, where they simulated a 5kg drone being ingested by a turbofan, some pictures related to the study below:
On the same Aerospace America Article it can be read that:
- FAA will begin testing of drone ingestion next year
- The metric for danger is the density of the material, so metallic parts are more critical than the bird bones/tissues. Modern drones have more aluminum parts, but the most critical component of a Drone ingestion would be the batteries.
Comparing different sizes, a commercial quad copter is around 1.4kg, while the most frequent bird impact (from FAA database) is around 1.8kg.
This is not the worst case scenario since larger drones are commercially available, and a goose, which can weight up to 6kg.
Birds are soft; drones tend to have at least some parts that are hard metal. If a small bird goes through the fan blades of an engine, it gets pretty cleanly sliced, and often causes no damage at all. (A bigger bird going into the core is a different matter -- ask Captain Sullenberger!) I'd suspect that the metallic parts in a drone would cause far more damage to the fan blades than the bird would -- not necessarily anything immediately catastrophic, but nicks in the leading edge of the fan blades would probably be visible when looking at the shut-down engine, and those take maintenance action to resolve.
Anything going into the core is more involved than if it went only into the fan blades, and the difference between bird flesh cooking and getting spit out versus the metal & plastic of the drone melting & causing clogs & damage is probably another point of difference -- the bird may cause damage, but the drone would probably be more likely to cause damage, and would probably cause greater damage.
To what extent the crew could tell the difference in flight, is hard to say. (The experience with bird-strikes to the engines is pretty wide-spread, at least in terms of corporate knowledge; the number of drones-in-engines is far, far fewer.) Knowing that something is wrong with a motor, and dealing with it, isn't the same as knowing the cause -- at least until you're back on the ground and the engine gets inspected.
While a collision with anything during flight would be bad, please keep the fear of drones in perspective. the OP's scenario has never happened.
There have been more than a million hours of flight of small drones, yet there is not one verifiable report of a collision between a personal drone and a manned aircraft. Not one.
There is also not one verifiable report of a drone crash in the U.S. that resulted in a serious injury as defined by the NTSB to someone not connected to the flight. Not one. It is a safety rate that all other segments of aviation would be jealous to have.
The only significant metal in most consumer drones is the motors, about the size of a large hailstone. The batteries feel dense, but they are mostly a liquid polymer electrolyte.
Yes, the FAA plans to include a drone in their engine ingesting tests next year. The problem I see is which drone? The333.org has examined 5469 Exemptions through 7/12/2016 and the data contains 902 Models of UAS from 256 manufacturers. So, which one is "typical"?