I get the impresson people are trying to overcomplicate a relatively simple answer to a relatively simple question vis "How to experimentally determine max endurance speed in a piston engine aircraft?" Fuel flow for practical purposes is ~proportional to power in a piston engine so:
Go flying on the smoothest, most calm day you can find. In level flight, progressively & slowly reduce power to reduce speed until level flight can only just be maintained. Any slower and more power will be required to maintain levle flight so the aircraft must be flying at Vmp. Whilst FF is not exactly proportional to power it's close enough to give a workable solution.
Add in the usual caveats about mixture leaned, an oversquare MP/RPM combination if possible, minimum drag configuration, aft CG, light weight, low density altitude and the like.
To correct something the original poster described in his or her method: It's not correct to increase power at the point where there is a greater proportional reduction in speed for a given amount of power reduction. If it can fly S&L at that lower power setting then *any* increase in power setting moves you further away from Vmp. It doesn't matter how much the speed reduces per unit of power reduction - what matters is finding the minimum power with which you can maintain level flight irrespective of the eventual speed. You should find, however, that once in the region of the bottom of the power curve you can make a small increase in power with a correspondingly small increase in fuel flow but realise a proportionally large gain in speed. Won't be at Vmp any more but the difference is small.
Last edited by Tinstaafl; 21st Jan 2009 at 19:41.