Formula to calculate % power

[walkman]

I'm building a little spreadsheet so that I can track performance over time. I want to enter observations such as indicated altitude, airspeed, OAT, rpm and MAP, fuel burn etc and have it calculate density alt, true airspeed, % power etc.

This will help for some planning, but mostly to identify trends over time, potentially catch problems, and will help quantify any performance changes due to any changes I make.

I've got all the calcs except for % power. I have a power setting table but I'm a bit stuck on how I would use that in Excel. I'd really like to find a formula for calculating % power based on density altitude, rpm, and MAP. Any ideas?

This is for an O-360.

[n5lp]

Kevin's Website

Look down the left side for "IO-360-A, -C, -D, -J, -K and AIO-360 Power Spreadsheet"

[walkman]

Thanks. The Kevins sheet for some reason throws all sorts of errors and doesn't work for me.

I think what I'll do is create a separate curve for each RPM in {2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700} for pressure alt vs MP. then use curve fitting to approximate the formula for each.

[gtmule]

Originally Posted by walkman

Thanks. The Kevins sheet for some reason throws all sorts of errors and doesn't work for me.

I think what I'll do is create a separate curve for each RPM in {2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700} for pressure alt vs MP. then use curve fitting to approximate the formula for each.

Search Excel help for "look up tables"...

[walkman]

found an older version that works. go figure. I'll utilize that. thanks for the pointer.

[rocketbob]

control-A, right-click, select Unhide, and you can see how Kevin put this spreadsheet together.

[MauiLvrs]

(RPM/max RPM) * (MP/Atm P) * Rated HP = HP


(HP / Rated HP) * 100 = % power

[walkman]

Originally Posted by MauiLvrs

(RPM/max RPM) * (MP/Atm P) * Rated HP = HP


(HP / Rated HP) * 100 = % power

Well that's giving my wildly different results than either the lycoming power setting tables or Kevin's spreadsheet.

Example. 9,000' msl indicated, 30.18 in the window, gives me an absolute atmospheric pressure of 21.6". Running at 2,400 rpm and 21.9 map. Your calculation gives me 90% power whereas the others give me 75%.

Am I missing something?

[MauiLvrs]

Originally Posted by walkman

Example. 9,000' msl indicated, 30.18 in the window, gives me an absolute atmospheric pressure of 21.6". Running at 2,400 rpm and 21.9 map. Your calculation gives me 90% power whereas the others give me 75%.

Am I missing something?

atmospheric pressure not corrected for altitude.
Try 30.18

[walkman]

Originally Posted by MauiLvrs

atmospheric pressure not corrected for altitude.
Try 30.18

ah gotcha....cheers