Can a car engine be used for a helicopter?

Answer

It is possible to use an automobile engine to power a helicopter, but the thing better be light (have an aluminum block and heads) and have a high horsepower to weight ratio. But it can't be a hot rod engine either. It absolutely must be set up to run extremely reliably or you'll be autorotating down every week. A light plane or gyro-copter may be easier to build from scratch, but you may have figured that out already.

The Lycoming engines (O-235, O-290, O-320, O-360,...) used in light aircraft have been adapted for use in a number of home brew or kit rotorcraft. A lot of two-seater helicopters are built using them. But they cost. A more modest power plant can be used to power up a single-seater. You can pay $3K to $4K just for a Lycoming core (the whole engine, but outside its hours and needing to be rebuilt).

Are you going to design the thing and build it from scratch? Or use a plan to construct it? Plans aren't free, but they have a singular advantage - they have been proven, have been engineered to work. Plus, critical parts can be purchased instead of built (machined). If you plan to fly this thing, what's your life worth?

Have you looked at the Adams-Wilson Choppy plans? (The A/W-95 is the current run, if memory serves.) They use about the smallest airframe and a modest power plant to lift one person (about 250 pounds) clear of the ground. These have been built and flown so they're relatively safe. The whole thing is doable at home. (Which is why it was designed.) Plans cost about a hundred bucks.

There are mini helicopters and gyrocopters that have motorcycle engines adapted for use to power them up. Hit the www and check it out. If you're not already surfing the net for info, you should be. What you waitin' on?

There are going to be severe limits on what you can do unless you have a machine shop. The swash plate and pitch linkage is not something that can be "welded up" from scrap. It has to be machined. The main rotor hub must be adequate. And what about the tail rotor drive mechanism? You lose a tail rotor and you won't be autorotating the vehicle in. (Your loss of control will yield a high probably of serious injury or death, and probably the latter.)

And if you haven't looked into FAA regs regarding home builts, you need to. These aren't local cops; they're Feds, and they'll kick your butt for fooling around with uncleared (uncertified) aircraft. Any flying machine can fall onto a citizen or a house or other structure. It can be much worse than a car crash. You don't want to be crashing or even autorotating into someone's back yard and a kid's birthday party there, do you? A flying machine puts people at risk like no vehicle can. You been warned, ait?
Links are provided to get you started and give you some things to think about. And there is always Wikianswers for other questions.