The main drawback to this design is the power loss on the upward stroke of the piston caused by the exhaust valving. 主要缺点是这种设计的功率损耗的向上中风活塞所引起的排气门。
The jet engine requires a huge scavenging system sometimes using half as much power as the tunnel itself in order to keep contamination low. 喷气发动机试验要求庞大的排气清除系统,以减轻污染,该系统有时要耗去风洞本身功率一半之多。