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________________________________________________________________________________
Pietenpol-List: Weight & Balance Spreadsheet
Pietenpol-List: Re: Weight & Balance Spreadsheet
Original Posted By: "dgaldrich"
Great picture of this, thanksKeith goffSent from my iPad> On Mar 22, 2014, at 10:24 PM, santiago morete wrote:> > Here is another idea> > Santiago> ________________________________________________________________________________Subject: Pietenpol-List: Re: Weight & Balance Spreadsheet
Great picture of this, thanksKeith goffSent from my iPad> On Mar 22, 2014, at 10:24 PM, santiago morete wrote:> > Here is another idea> > Santiago> ________________________________________________________________________________Subject: Pietenpol-List: Re: Weight & Balance Spreadsheet
Re: Pietenpol-List: Re: Weight & Balance Spreadsheet
Original Posted By: Gary Boothe
Waaiiit a minute. Moving the location of the wheels should have very little, ifany, effect on CG. What DOES change, from a CG perspective, when you move thewheels forward is the weight on the tail wheel. A couple of pounds increasemakes a large difference since the arm is so long and moving the wheels forwardincreases it. Using Jack's spreadsheet, I added just 5 pounds to the tailwheelweight and it moved the CG aft by 1 inch. That's 20% of the total allowablerange. A Scott 2000 tailwheel from a Piper Cub is about five pounds heavierthan an original BHP tail skid. As Jack, and others, have said, accuratemeasurement is important. Bathroom scales are for my fat ass, not aircraft.You have correctly noticed that moving the wing also has almost a 1 for 1 relationshipto CG. Moving the wing aft 1 inch moves the CG almost 1 inch forwardand is by far the most effective way of achieving a correctly balanced airplane.That's one of the advantages of this design is that it's relatively easy todo since the cabanes are equal length and parallel, more or less.DaveRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Re: Pietenpol-List: Re: Weight & Balance Spreadsheet
Waaiiit a minute. Moving the location of the wheels should have very little, ifany, effect on CG. What DOES change, from a CG perspective, when you move thewheels forward is the weight on the tail wheel. A couple of pounds increasemakes a large difference since the arm is so long and moving the wheels forwardincreases it. Using Jack's spreadsheet, I added just 5 pounds to the tailwheelweight and it moved the CG aft by 1 inch. That's 20% of the total allowablerange. A Scott 2000 tailwheel from a Piper Cub is about five pounds heavierthan an original BHP tail skid. As Jack, and others, have said, accuratemeasurement is important. Bathroom scales are for my fat ass, not aircraft.You have correctly noticed that moving the wing also has almost a 1 for 1 relationshipto CG. Moving the wing aft 1 inch moves the CG almost 1 inch forwardand is by far the most effective way of achieving a correctly balanced airplane.That's one of the advantages of this design is that it's relatively easy todo since the cabanes are equal length and parallel, more or less.DaveRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Re: Pietenpol-List: Re: Weight & Balance Spreadsheet
Pietenpol-List: Re: Weight & Balance Spreadsheet
Original Posted By: "dgaldrich"
Jake,Nice. Really nice!Are you doing bungees or die springs?--------Semper Fi,Terry HandAthens, GAUSMC, USMCR, ATPBVD DVD PDQ BBQRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: Weight & Balance Spreadsheet
Jake,Nice. Really nice!Are you doing bungees or die springs?--------Semper Fi,Terry HandAthens, GAUSMC, USMCR, ATPBVD DVD PDQ BBQRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: Weight & Balance Spreadsheet
Original Posted By: Brian Kenney
Gary, that's precisely my point. Moving the wheels has virtually NO affect onCG in flight, all else being equal. That's why you can change a Tripacer intoa Pacer or vice versa. Same wing and fuselage.In theory, you don't even have to put the scales under the wheels to get a validCG. You could put a fork under the prop and a knife edge stand under the pilotsseat and calculate a CG with accurate scales and known tare weights of thesupports. The only other necessary missing piece is their location in relationshipto whatever datum you choose. Weight x Arm always = Moment. Total weightand total moment determine CG. My point was that you can't change just one thing in Jack's spreadsheet withoutat least considering its affect on the others. Moving the main wheels forwardWILL slightly increase the weight on the tail while on scales but the calculatedCG will stay almost static. DaveRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________
Gary, that's precisely my point. Moving the wheels has virtually NO affect onCG in flight, all else being equal. That's why you can change a Tripacer intoa Pacer or vice versa. Same wing and fuselage.In theory, you don't even have to put the scales under the wheels to get a validCG. You could put a fork under the prop and a knife edge stand under the pilotsseat and calculate a CG with accurate scales and known tare weights of thesupports. The only other necessary missing piece is their location in relationshipto whatever datum you choose. Weight x Arm always = Moment. Total weightand total moment determine CG. My point was that you can't change just one thing in Jack's spreadsheet withoutat least considering its affect on the others. Moving the main wheels forwardWILL slightly increase the weight on the tail while on scales but the calculatedCG will stay almost static. DaveRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________
Re: Pietenpol-List: Re: Weight & Balance Spreadsheet
Original Posted By: Steven Dortch
Subject: Re: Pietenpol-List: Re: Weight & Balance Spreadsheet
Subject: Re: Pietenpol-List: Re: Weight & Balance Spreadsheet