ORIGINAL: bentgear
They are great on buggies and trucks that you can pull right up to your feet quickly after a hard run and get a reading. Have not figured out how to do that with a plane except to crash it.
No need to wreck an airplane just to check the temps
Run it hard on the ground while being held by a helper, and measure it while running if the engine is open. On the larger gas engines measure it immedately after shutting it down and check both cylinder heads. Consistancy is the key if you are going to measure differences for tuning, baffling, cooling, etc. Ie, if you lower it 20 degrees on the ground, than you most likely lowered it 20 degrees in the air as well, even if the ground temp is different from the 'in the air' temp.
ORIGINAL: *Crash*Johnson*
I don't think airplanes are as sensitive to heat as the prop usually supplies enough air over the head to keep it cool.
If the air is not directed over the cylinder heads properly, it will not cool the engine. The air will take the path of least resistance, which unfortunately is not usually through the fins. Many gasoline airplanes are fine without any baffling, but many do require baffles to direct the air through the fins and not around it. The temp guns allow you to determine if baffling is required, as well as measure how effective the baffles were after installation. I've seen easy an 50 degree drop when I installed some baffles on one of my airplanes.