Weight & Balance - Pilot location

[Tony Spicer]

Brian,

I'm 5' 10" with a 29" inseam and weigh 188.

Seatback is 1" forward of aft hole at the bottom and 3" forward at the top. Back cushion is 3" thick. With the stick full aft, the grip is just brushing my cojones. A full stall landing with it any further forward at the bottom would be interesting. Short legs and an aft position of the seat back required the rudder pedals to be mounted full aft. I also have 2" balsa blocks under the pedals for heel rests.

Bottom line is I don't think it makes a rats ass where the seat ends up. Just run the numbers with min fuel and some baggage to be sure you're inside the aft limit.

Tony

[sowell]

When I calculate my pilot position (using both the spreadsheet and my own calculations), I find that my pilot position is 91.5 inches aft of datum. I used certified scales and expert assistance. I weighed it again using a different scale for the tail to double-check, and I got a very similar --almost exactly the same -- result. The spreadsheet says the pilot range is 84.25 to 89.75. Since it is further aft than what the spreadsheet lists, I just wanted some validation that 91.5 inches for pilot location is a reasonable number. It has nothing to do with the CG of my plane in total, what engine I have, or anything else than what I asked -- just the pilot arm results of other builders.

Since my calculation is so far behind what SPA says is the range, I thought I should do my due diligence and asked what other people who have weighed their panthers have gotten, along with how big the pilot was who sat in it and what their seat position is -- two things that affect this arm calculation. As many times as Paul weighed his sample in order to come up with the spreadsheet, I would be remiss to not to consider the possibility that the spreadsheet might not be accurate with respect to that range listed. A sample of 1 builder is not a big sample, so I have asked for the results of others to get a bigger sample size.

But as forums go, instead of getting what I asked for, folks clog up this thread with dissertations on how to weigh a plane, how not to use spreadsheets, and now comments about the 'shame' of my facebook page. All of these serve only to make the thread so long that it is less and less likely that any builders see and respond to my query.

I will not post another reply, and I also ask that no one else to do so either unless you are an actual builder of a panther who has done your W&B, and can give me your pilot arm result, your seat location, and your weight and height. Otherwise, this thread is a lost cause.

[GlenNJ]

Brian,

Are your concerns that the weight and balance calculations are wrong, or is your airplane actually tail heavy (possibly the motor mount not extending far enough forward)? Does your Panther have the o-235, or the Corvair engine? I know you have a Facebook page, but it's so unorganized that it makes it hard to find things. I stop looking at it a long time ago. It's a shame, because from what I remember, you had some great pictures.
Glen

[sowell]

i just want some validation of the range listed in the spreadsheet. I know how to calculate W&B. Just saying.

[Exhaust guy]

Weight and balance is a very simple thing to do if you use the standard like setting a datum and use weight times arm equal moment, instead of the computer generated Buck Rogers approach like I'm seeing here. No thanks, I will do mine the old well proven way. Just saying, I'm not a computer guy and never plan to be one. Example, what happens when the site goes down? Bet there's a lot of older guys that think like I do. Now I feel much better. Larry v.

[sowell]

Thanks, guys. Tony, if I remember correctly, you are about 5'11" and maybe 200 lbs, right? And with your pilot location coming in at at 89.5 inches, you are only .25 inches ahead of the rear most range in the W&B spreadsheet. If you can confirm your size for me, that seems like validation that my 6'2", 225 lbs being 2 inches further back (91.5) seems like a reasonable result.

[psalter]

Brian,

I don't have information on the other pilot's locations at my fingertips. I will check to see what I can find out this weekend.

Tony is correct in that the pilots moment arm is assuming a 2-3" cushion or parachute. So seat cushion should be in place when weighing/measuring pilots moment arm.

While the prototype aircraft did have a limitation on seat back location, this was due to interference with the seat belt attachments. We changed the seat back and seat belt attachments for production aircraft. Seat back positions in the last 3 holes does require a low profile pin or bolt, to minimize seat belt issues. Production aircraft does not have a limit that I know of besides the Aft CG limits of the aircraft itself.

One other thought, you probably did this, but just to be sure, did you measure the moment arms, especially to the tail wheel? We have received tail wheel springs from the manufacturer with variations on taper, which affected how they are trimmed to fit in the sockets. That can cause the tail wheel itself to be slightly off from one aircraft to another. Usually the difference is about an inch or less, but that far back and being the primary measurement for CG location, it can affect the CG if the measurement is assumed to be the default value in the spreadsheet instead of an actual value.

[Tony Spicer]

Brian,

Mine is 89.5"

Notes on the W&B spreadsheet refer you to W&B instructions contained in the BM. They are either no longer there or I have a case of male blindness. As I recall, there was a restriction as to how far aft the pilot could sit. Spacing was to be provided with a backpack 'chute or seat cushion.

Could be that your position is too far aft.

Tony

[sowell]

Have you seen other panther's ( perhaps those that are flying) W&B Paul? Any idea what their pilot arm's are?

[psalter]

One item I forgot to mention, it is best to have someone else check the scales. If you have to move around, to see the readouts, you are going to cause some errors. I found this to be significant during my testing.

Probably not the case for your problem, but a caution for others.

Sit back and relax, let someone else do the work