I need to calculate the frequency of a flat spring. I need to make reed valves for a pulse jet engine. I read online to use Hooks's Law but this is not working. F = force. x = the amount spring moves. k = spring constant. I have a flat spring made of .010" spring steel. Spring is .375" wide by 1.250" long. I have no clue what k is for flat spring steel? It seems to me Hooke's law does not tell me the frequency of a spring. If I tie a string to the ceiling that hands down 6' with weight on the end I can get the weight swinging and count the swings per min. No matter how much the weight is changed Hz is the same. If I change the distance of the swing Hz stays the same. If string is shortened to 3' frequency changes. Now I can do math to calculate frequency if string is 1.250" long. I don't think my experiment & math applies to metal that is spring steel. If I cut a sample piece of spring steel, clamp it in the vise, flip the end it is too fast for me to count the Hz I can hear is buzz like a tuning fork. NEXT the pulse jet engine is 40" long I can use the formula to find the frequency of a tube to get Hz of the tube. It has been 7 years since I worked on this project I don't remember the frequency of the pulse jet engine body which is a tube closed on the valve end. If the frequency of the tube is 180 Hz the spring steel reed valves also need to be 180 Hz also. I could probably use some type of electric device that listens to tuning forks to listen to my valve to tell me what the Hz is if there is suck a thing? After a lot of trial and error I have an engine that runs very well but maybe it could be better. Watch the YouTube video of my engine running. I have run this engine for many hours the valves have no damage and no signs of getting hot. This engine produces 20 lbs of thrust running on propane or gasoline. A mix of 80% gas + 20% diesel engine produces 24 lbs of thrust. Running on methanol 34 lbs thrust. Methanol + 5% water = 34 lbs thrust.