David Axe wrote about the use of Syria as a testing ground:

• The Syrian conflict is a relatively low risk one for US fighters, with the enemy being targeted lacking serious anti-air capabilities.
• The Air Force is thus using the battle to test out aircraft it might consider for future operations.
• Interestingly they’re not testing the most cutting edge in technology. Instead they’re looking at the performance of propeller aircraft from the Vietnam war.
• Such aircraft are substantially cheaper than jet fighters, costing just $1,000 per flight hour, versus $40,000 per hour for an F-15.
• They require less maintenance and can take off from rough airfields, which future battlefields may be full of.

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Source: MSN