So far I have participated in a number of airdrop campaigns, but I have not received any awards. I think it's all scam.
There is no scam airdrops as you were participating on it for absolutely free. You did not risk single cent on it, so how could you say they are scam? It can be called as scam if you need to pay something to get the airdrop but the project is not running as planned. You should never hope too much from anything called airdrop, it is free coins/tokens but they may have no values at all.
I think it belongs to the scam category, a scam does not mean deceiving people to spend money but they can also make other people work and they are not paid at all from the they have promoted. The way airdrop works so far is they offer a product to be promoted by many people, usually through Facebook, Twitter and other social media. At least with this promotion there will be some people who are interested in participating and even becoming an investor, maybe from here we will see them committing fraud against others.