Weight and balance Hippert's plane

buck toenges · 3 October 2009, 03:42 PM

I have loaded current pictures of Hippert's DVII being reassembled in Auburn Indiana, Here is the link: photobucket.com/hippertDVII

Now, help me weight and balance this plane. Here is what I have so far:
Plane is fully loaded without pilot.
Oil tank holds 3 gal. Fuel tank is 20 gal (I think).
Left main = 824 lbs
Right main = 814 lbs
tail = 94lbs
wheel arm = 55"
tail arm = 265"
fuel tank center is 66"
seat center = 109"
pilot weight = 200lbs

What else do I need?

Buck

3 October 2009, 04:53 PM

Buck,

W&B is so critical, that as an A&P, I can either do it for you, or inspect what you've done on site. To talk one through remotely, is to invite mistakes.

So,...I will refer you to the "holy grail" of reference material on the subject....

http://www.faa.gov/library/manuals/a...-H-8083-1A.pdf

It's quite comprehensive,..you've just got to love Uncle Sam!

jumpinjan · 3 October 2009, 05:05 PM

Do you need help calculating the CG? What about your Center of Pressure (CP)? I have written a spreadsheet to calculate the CP, mostly based on Jeff Brook's work, but I have recently found some new formulas & processes with more accurcy with biplanes.
Jan

Jeff Brooks · 3 October 2009, 07:05 PM

Buck,
where are you putting your datum? how far is that datum from your wheels & tail skid?

jumpinjan · 4 October 2009, 07:29 AM

The datum looks to be the front of the airplane.
CG distance from datum= sum of moments/sum of weights
Cg distance = (55*1638 + 265*94 + 109*200 + 66*124) / (1638 + 94 + 200 + 124)
CG = 70.5" (you may want to double check my calculation)
Jan

Jeff Brooks · 4 October 2009, 08:20 AM

I have heard different folks use different things for the datum. The firewall, the leading edge of the bottom wing, or the prop.
I first saw this last night while I was at work, so I couldn't get to work on this, but this is the exact info I have been looking for to compare mine to others.
I will spend some time reviewing this and post what I found.

jumpinjan · 4 October 2009, 08:32 AM

Jeff,
Buck is at 2,056lbs now and the numbers indicate its tail heavy (based on your CP calculations)
Jan

Jeff Brooks · 4 October 2009, 08:58 AM

Quote:

Originally Posted by jumpinjan

Jeff,
Buck is at 2,056lbs now and the numbers indicate its tail heavy (based on your CP calculations)
Jan

how did you get oil? I saw no arm for the oil?
and the calculations I posted were based on 25% where a biplane should be 23% ... which could put him further aft.

jumpinjan · 4 October 2009, 12:50 PM

Jeff,
Yeah, I forgot the oil tank and yes, for biplanes we need to use the 23% MAC. I have reference material that verifies that amount.
Jan

Jeff Brooks · 4 October 2009, 01:01 PM

Using the 23% cord reference, I calculate the CG should be somewhere around 62.16" using buck's datum line.

Jan, I agree with your numbers, Buck's CG (from the numbers he posted here) is somewhere around 70.52" aft of datum. His' CG is aft by some 8.36"

Now to correct this, it would be better to remove weight from the tail, than to add weight to the nose.

The original Fokkers avaraged 880 Kg fully loaded, that is 1940lbs. With this aircraft at 2050, adding weight should be a last resort. the Gypsy is still not as strong as the BMW or Mercedese, so keeping it light is a plus.

I would love to see how much the tail feathers on this aircraft weigh individually. Buck, would you consider unbolting the horizontal stab, elevator, rudder and weighing them individually?