So sorry to hear about Challenge. RIP
Most of the sounds are clean, IMO. There's really not much I would change. They may even still be my files. Some of them I seem to recognize, but it's been a long time. The biggest issue I had was getting recorded audio of the exact plane or gun it belonged to.
If I remember right, without even looking, the Engine start, run and stop, all had to be found. Back in the day the intardnet was not quite as robust. When I found them most were quite dirty and distorted, many had to be trashed and re-found. Not only were the recordings old skewl mics and techniques, then the compression used in like MP3 files destroyed them more. Old recordings using tape, degrades over time just sitting there. When converted digitally, you got what time left you. Bringing them back to life, every file had to be dealt with individually, each one had it's own issues. It's time consuming to get it right.
The only way I see to make improvements would be to find modern digital recordings in original uncompressed .wav file, many come from air shows, some from documentaries. Some planes don't exist anymore in running condition.
I don't see a major overhaul here, I just picked out very few that could be tweaked.
If peeps don't know how to process sound files, but can find *and verify authenticity*, I'd be willing to work them into the existing set, as long as they are better then the default. They have to be improvements.
I have the time to process files, probably not the time to find new ones. It could be more of a group effort.
If players want to dump some in my lap, I or WE as a group could pick out the best of the best and then I'd process those. If peeps can find sounds of the motors/hydraulics used for flaps and wheels, that goes even deeper into authentic immersion, those are even harder to find. That said, I won't waste time on any file that is not authentic.
I'd be willing to pick up where Challenge left off with his, as long as they are authentic and not computer generated. He took on a huge task, I hope it was a good therapy for him. Maybe we can make his work live on and not go wasted and keep his name attached to them, he earned that credit.