chart program lookitup
I assume you meant gal/hr not gal/min (gpm). To get FF v. % power you need to do some flight test and nail down some variables, not the least of which are you full rich, lean rich of peak and by how much or lean lean of peak. Also RPM is what it is because its a fixed prop. Fixed props vary, climb prop v. crusie prop will give different % power for a given RPM and altitude.
This the nomagram and gives you HP. Divide calculate HP by max engine HP (180) and you get percent. This nomagram has also been boiled down into look up tables which I am sure you have seen. Of course without manifold pressure (MAP) you are flying a little blind. Do you have MAP? Also it does not have 2,800 rpm because red line is 2,700. However the relation ships are still there. Depending on altitude 100 RPM is about 3-5 HP more.
There was an article about this in kit plane just this or last month about doing approx power based on MAP/RPM/FF.
I just know my standard power settings (MAP/RPM), my "Go-To" power settings. The only % power I really care about is being approx at or less than 75% power so I can lean. Takeoff is full power to 1,000 ft agl and than climb is 25 square, putting around is 23" and rpm set to 2,300-2,500 rpm. With a constant speed prop I can control a precise RPM at any altitude independent of throttle postion (with in reason of course). I usually set 2,400-2,500 rpm for cruise and know when MAP is less than 23.5" at sea level or 21.5" at 8,000 ft DA, for those RPM's, I am at or below 75% power. There is a whole world of RPM and MAP settings, but knowing the basics mentioned above and a few others I really don't care what % power is.
My main goal is fly at or less than 75% power. The decision is made for me by 8 or 9 thousand. Down low (sea level - 3,000 msl) I know 23 square or less, 21/2300 I am at about 61% tp 63%. The more I fly at 65% to 55% I know my wallet will feel better. Once below 75% I know I can lean the living heck out of my engine with out fear. The LOP subject goes along with this but is a whole norther ball of wax. (see LOP - lean of peak treads)
I also have an Excel spread sheet program I copied from Kevin Horton that runs on my handheld Ipaq. Enter altitude, MAP, RPM you get % power and FF. It is a "look up" program, using standard tables or data from the Lycoming manual; the program looks up and interpolates the data. It's pretty slick. Kevin has other programs and "scripts" to replicate the Lyc data.
Here is his web site:
http://www.kilohotel.com/rv8/
(On the left scroll down to TOP LINKS and down load excel spread sheet for power charts for (I)O-360 -A -C. It's in a zip file. Once down loaded and extracted, open it and run it on Microsoft Excel. Do some flight test, record data and than plug what you know into the spread sheet (RPM, MAP, ALT, TEMP) and make your own custom tables. Anything above or about 8,000 ft will be less than 75% power WOT.
Again with out MAP gauge you are flying blind in my opinion (unless you do some flight test and get those RPM/FF v. Altitude relations and percent power).
