A viewer asked my opinion on the subject of damage cause to airliner engines from colliding with UAVs/drones. Here is the description and list of questions sent to me:
" Recently, I was asked what the effects would be if a drone collided with the engines of an airliner (no particular engine specified). I've started to second-guess what I said and am wondering if you would be able to provide some insight on the matter. The following is my answer and the reasoning behind it:
My initial response was that the results would not be good regardless of whether it's a tiny drone (15-20cm across; 0.2-1.2kg), medium drone (60cm across; 4kg), or large drone (114.3cm across; 7-14 kg). I'm pretty confident that the largest drones we're tracking would do a ton of damage to even a moderately-sized, high-bypass engine. In the case of the smaller drones, I said that it wouldn't likely cause a major flight safety issue (uncontained failure, uncontained fire, etc), but could potentially cause a compressor stall if ingested into the core. In the case of regional jets with low/lower-bypass engines, it seems that the likelihood of the core ingesting it increases dramatically, in part just because of the change in size relative to the drone, but also because the bypass duct is going to be much smaller.
Aside from the motors, wiring, circuit boards, battery, etc, the construction of the drone is primarily molded plastic, 3D-printed composite, or carbon fiber. I think it would melt very quickly. As an example, the 3D-printed composite construction of one of the drones we're using has a melting point of 193 C. Based on my understanding, the air already exceeds that temperature before the combustors. Ignoring the melting issue, the strength of the plastic parts would probably be more than enough to cause damage to the entire compressor. For carbon fiber, I think it would splinter apart long before the glue could melt. Given how abrasive CF is, I assume that there would also be some abrasive damage regardless of whether or not the compressor was damaged when it broke up the material.
I would guess that the strength of the fan blades (at least in medium-sized, high-bypass engines) would be more than enough to survive the impact. I do question whether the parts of the drone would actually make it to the core, or if they would just get kicked out to the sides and go by in the bypass duct (assuming solid particles behave similarly to water). The reason I think they may make it into the core of larger/higher-bypass engines is because of the much steeper pitch of the fan blade near the root/center.
In short, the answer I gave was that it would cause damage regardless of the engine, and that you would almost certainly need to overhaul/rebuild (not sure of correct terminology here) the entire engine because the I figured FAA wouldn't let you fly with an engine that had ingested something of appreciable size. I said that the "worst-case" that was likely to happen was that the compressor would stall and the pilots would treat it like a compressor stall caused by anything else. I do not think a compressor stall caused by damage from ingesting something would be the type of stall that you could recover from just by reducing engine power and adding it back (as opposed to a compressor stall caused by temporary airflow disturbance somewhere ahead of the compressor).
Some questions:
How accurate/realistic is my initial prediction?
If a drone impacted near the perimeter of the fan and caused (not sure of terminology here) a rotating compressor stall (localized to the damaged blades), would that stall always propagate to the IP and/or HP compressor, or could the engine function "normally" enough in some instances that it would be able to provide most of its rated thrust?
Would a drone impact of any type require an inspection/rebuild of the engine?
If a drone (or FOD of any type) did damage part of the LP compressor to an extent that warranted a rebuild of the LP compressor, would you also be required to inspect/rebuild the IP and HP compressors (if three-spool)?
If the impact of a small drone wouldn't damage and/or stall the compressor of the engine, how big of a drone would you need to cause enough damage for an engine failure? I know this is a somewhat loaded question because of how many parameters can impact (pun maybe intended) the result of a situation like this.
Is a three-spool engine more prone to compressor stalls than two-spool?
Would the volatile nature of the LiPo battery increase damage in any appreciable way, or is the engine resilient enough to heat and pressure to not be affected?"
0 Comments