Pietenpol-List: Weight & Balance Spreadsheet
Posted: Sun Mar 23, 2014 2:32 pm
Original Posted By: "H. Marvin Haught"
Okay, Here is a spreadsheet that I developed to be able to compute weight &balance for a generic Pietenpol. It requires the plane be completed, but itcan be used to determine when the wing has been moved back far enough. Ihave input the values from my Pietenpol, so you will need to just type overthose values with the weights and measurement from your own airplane Inputvalues are red, calculated values are blue.The procedure is pretty simple. All of the measurements are made using thefirewall as the datum, so you can make most of the measurements with thetail on the ground, which is easier (and safer) than when the tail issupported on a stool or sawhorse. The only measurements that must be madewith the plane in level flight attitude are the distance from the firewallto the wing leading edge, and the distance from the firewall to the maingear axle and tailwheel axle. For these three measurements you will need touse a plumb bob and a tape measure. Strive for accuracy, because smallvariations in distance can have a large effect.You will to measure the distance to the middle of the fuel tank(s) whichmust be estimated to some extent. You will also need to sit in the cockpitand make note of where your belt buckle is (the belt buckle is very close tothe C.G. of a human body in a sitting position), then measure from there tothe firewall. Same for the front seat passenger (you will be surprised howlittle a passenger affects the CG position). If you have a baggagecompartment and/or a helmet box, measure from the firewall to the center ofthose spaces (or, if you really want to be conservative, measure to the backof each of those compartments to get worst case).You will need a good set of aircraft or race car scales. Bathroom scalesare worse than useless - most do not go up to 300 lbs and unless you havebuilt your airplane exceedingly light, your main gear wheels will weigh over300 lbs eac. Besides, bathroom scales are notoriously inaccurate -particularly at the extremes of their range. While building mine I weighedit several times with digital electronic bathroom scales. My estimatedweight turned out to be within 80 lbs of my finished weight on aircraftscales. You need better accuracy than that.Position the plane in level flight attitude on the scales after setting thetare to include the weight of any supports and chocks that are on thescales. Enter the data in the spreadsheet and then input weights for pilot,passenger, fuel and baggage. The spreadsheet will calculate the CG positionwith respect to the firewall, the CG position with respect to the wingleading edge, and the CG position as a percentage of Mean Aerodynamic Chord.You can play around a bit, inputting different weights to see what effectthey have on the balance. You will have to do trial and error to find themax weight pilot that will keep the CG ahead of 20" aft of the leading edge- I don't have the fancy algorithm that Ryan and William put in theirprogram to determine this automatically.This spreadsheet is in Excel 2003, so unless your software is even olderthan mine, if you have Excel on your computer you should be able to use thespreadsheet.Good luck and don't hesitate to ask questions if it is not clear how to useit.Jack PhillipsNX899JPSmith Mountain Lake, Virginia________________________________________________________________________________
Okay, Here is a spreadsheet that I developed to be able to compute weight &balance for a generic Pietenpol. It requires the plane be completed, but itcan be used to determine when the wing has been moved back far enough. Ihave input the values from my Pietenpol, so you will need to just type overthose values with the weights and measurement from your own airplane Inputvalues are red, calculated values are blue.The procedure is pretty simple. All of the measurements are made using thefirewall as the datum, so you can make most of the measurements with thetail on the ground, which is easier (and safer) than when the tail issupported on a stool or sawhorse. The only measurements that must be madewith the plane in level flight attitude are the distance from the firewallto the wing leading edge, and the distance from the firewall to the maingear axle and tailwheel axle. For these three measurements you will need touse a plumb bob and a tape measure. Strive for accuracy, because smallvariations in distance can have a large effect.You will to measure the distance to the middle of the fuel tank(s) whichmust be estimated to some extent. You will also need to sit in the cockpitand make note of where your belt buckle is (the belt buckle is very close tothe C.G. of a human body in a sitting position), then measure from there tothe firewall. Same for the front seat passenger (you will be surprised howlittle a passenger affects the CG position). If you have a baggagecompartment and/or a helmet box, measure from the firewall to the center ofthose spaces (or, if you really want to be conservative, measure to the backof each of those compartments to get worst case).You will need a good set of aircraft or race car scales. Bathroom scalesare worse than useless - most do not go up to 300 lbs and unless you havebuilt your airplane exceedingly light, your main gear wheels will weigh over300 lbs eac. Besides, bathroom scales are notoriously inaccurate -particularly at the extremes of their range. While building mine I weighedit several times with digital electronic bathroom scales. My estimatedweight turned out to be within 80 lbs of my finished weight on aircraftscales. You need better accuracy than that.Position the plane in level flight attitude on the scales after setting thetare to include the weight of any supports and chocks that are on thescales. Enter the data in the spreadsheet and then input weights for pilot,passenger, fuel and baggage. The spreadsheet will calculate the CG positionwith respect to the firewall, the CG position with respect to the wingleading edge, and the CG position as a percentage of Mean Aerodynamic Chord.You can play around a bit, inputting different weights to see what effectthey have on the balance. You will have to do trial and error to find themax weight pilot that will keep the CG ahead of 20" aft of the leading edge- I don't have the fancy algorithm that Ryan and William put in theirprogram to determine this automatically.This spreadsheet is in Excel 2003, so unless your software is even olderthan mine, if you have Excel on your computer you should be able to use thespreadsheet.Good luck and don't hesitate to ask questions if it is not clear how to useit.Jack PhillipsNX899JPSmith Mountain Lake, Virginia________________________________________________________________________________