W&B spreadsheet... with a twist

[BackPacker]

I'm looking for a W&B spreadsheet, but with a twist.

I want to be able to input the empty weight/balance data, the pilots weight, the maximum fuel capacity and moment, the moment arm of the front/aft seats and the max W&B graph points, and then get a textual plus graphical output of the max variable weight (passengers, mostly), assuming half full and full tanks, plus the allowed weight distribution of those pax front/aft.

Assuming a standard 4-seat club aircraft (PA28, C172, DR400 or similar) with just one fuel tank (or two with the same moment arm) and no complicated W&B restrictions.

This is so that I can rapidly set up a few of these calculations in advance, without having to recalculate the W&B every time. But it needs to be done for multiple aircraft so I want to automate things as far as possible.

Now I appreciate that this may not be readily available, but if somebody has done an Excel or OpenOffice spreadsheet that does a graphical display of a normal W&B calculation, that would be a major step in the right direction already. Anyone?

[Intercepted]

I have one you can have if you send me your email address.

Something most applications/calculations forget is the fact that front seats move back and forth on a runner with a big impact on moment arm.

[Big Pistons Forever]

Originally Posted by Intercepted

Something most applications/calculations forget is the fact that front seats move back and forth on a runner with a big impact on moment arm.

Which is why the POH will specify the mid range of the seat track as the arm.
A seat position ahead or behind that will not move the CG enough to matter.

[Intercepted]

A seat position ahead or behind that will not move the CG enough to matter.

You are wrong and you don't even refer to type when you make your statement.

I can send a copy to you as well, and you can have a play with the seat position?

You might be surprised how substantially you can see the CG move back and forth in the graphical representation for a standard Cherokee, especially with two heavy persons upfront. Something to think about if you want to do spin training.

Quote from Piper Aircraft Corporation Service Bulletin 753:

The pilot and co-pilot seat location of 85.5” as specified in the A.F.M.2 is the centre position of the seat track. This may vary from a full forward position arm of 80.5” to 90.5” at the most rearward position. Each hole from the centre position of 85.5” changes the arm of the seat location 1.25”.

The seat position to be used for spins should be determined and the correct arm should be used in calculating the aircraft weight and centre of gravity prior to beginning the flight.

80.5" to 90.5" is what I use, and yes it does matter!

[Big Pistons Forever]

Silly me, I made a comment about a practical reality that applies to 99% of light aircraft flights and someone immediately jumps in with the 1% scenario. Yes in a standard Piper when the purpose of the flight is to conduct the spin manoever and when both occupants are both short and weigh more than 24O pounds the seat position might actually matter. For all the flights where you are not intending to do spins and the pilots are not inordinately fat and short/tall, or are in a Cessna.....or in other words ordinary loading with ordinary people to go out and do and ordinary flight ......the seat postion just does not matter. In fact I will go further and say in the weight and balance calculation it is the weight that is by far the most important and for most flights a balance calculation is not required. Instead chosing a CG location from a set of "CG for stock loadings" for 4 or 5 of the most common loading situations is more than adequate for almost all flights. On the odd occasion that an unusual situation comes up (eg 2 pax in the back but only one up front, a heavy baggage load, or somebody unusually light/heavy) than yes a proper balance calculation should be carried out.

I would suggest any loading where the seat position is the differnance between being in or out of the allowable CG range, is reason enough for a major rethink of the loading plan.

[Intercepted]

Silly me, I made a comment about a practical reality that applies to 99% of light aircraft flights and someone immediately jumps in with the 1% scenario.

Yeah, but this thread was about spreadsheets and I happened to have one taking care off adjustable seat positions

I also managed to convince a CFI once that we didn't need to have 50 liter of water in the back seat of a PA28 to stay within CG limit during a test.

[Big Pistons Forever]

Originally Posted by Intercepted

I also managed to convince a CFI once that we didn't need to have 50 liter of water in the back seat of a PA28 to stay within CG limit during a test.

I have to ask when was the last time the aircraft was accurately weighed ? I bring this up because small errors do accumulate during and after the weighing process. I still think fussing over seat position is ultimately as meaningless as those elaborate PLOGs which result in fuel burns calulated to the tenth of of a gallon.

if you want to put seat position into your W & B calculations there is no reason not to, just understand that for all but the most unusual loading situations it will not have any practical effect. To imply that it is negligent not to use seat position in every calculation is an idea which I think you will find is not supported by very many people.

In any case for the same reason one should assume greater than book fuel flows and slower than book cruise speeds for cross country planning, loading to the exact limit (especially the aft limit) is to place an unwarrented faith in the absolute accuracy of the aircraft data ( in this case the aircraft empty weight and moment), and should IMO therefore be avoided.

[24Carrot]

The seat runner effect is easy to ballpark without a spreadsheet.

Two heavy people could be about 20% of the aircraft weight. Moving 1/5th of the aircraft mass 5 inches moves the CofG 1 inch.

PS. This is an illustration. Obviously, there are some A/c types which do not weigh the same as 10 heavy people.

[Katamarino]

Backpacker; I have one I've been working on. It's not exactly a market-ready product, but it displays a graph of the weight and balance, and it has all the data for most of our club aircraft already in it. If you want to have a look, PM me the required details.