Need help with conflicting weight/balance arm data.

Please assist... I have some conflicting arm data for my Kitfox IV-1050 that I am hoping to get straightened out.

I have a number of aged records on my aircraft that state the following arms:

Original Paperwork
Empty Aircraft 12.1 (560.7 lbs)
Pilot 16.3
Rear Header Tank 45.9 or 46.4 (which one is right?)
Wing Tanks 16.47
Cargo Bay 40.5

2006 Weight and Balance - paperwork suggests an aviation shop did the work
Empty Aircraft 12.91 (632.0 lbs)
Pilot 15.8
Wing Tanks 15.97
Baggage 24.00

My big concern is the conflicting ARMS for the Pilot, wing tanks, and baggage between these two read outs. Would love any input that get help get the correct numbers I should be using for my calcs.

Thanks!

~Jason

Jason,

1) My Kitfox is a later model so I am not going to relate any of my measurements you your situation.
2) The Science and Theory of W & B can be applied to any aircraft once you know your datum plane, have the aircraft set properly for for empty weight and arms.
3) Do you have the construction manual for the plane?
4) Do you have access to Scales

The weight gain from 560 to 630 needs to be checked out. Either the plane gained weight over time (happens all the time as stuff gets added) or the conditions for checking the empty weight were wrong the first time ,the second time or both times -or the plane gained some weight and the conditions for empty weight were not right - sheeesh! - all adding up to no reason to trust either set of numbers New W/B needs to be done.

The difference in the arms - To the best of my knowledge, all kitfoxes use the leading edge of the wing as the datum plane - BUT YOU HAVE TO KNOW THAT FOR YOUR SPECIFIC AIRPLANE - NOT GUESS. Next problem - the arms? They don't change unless - I am going out on a limb, but I doubt that the wing tanks moved or the fuselage shortened itself - Again - no reason to trust what you are looking at - either set of numbers. Now - how can a person get shorter arms measuring from the leading edge? Do the first measurement with the fuselage level then do the measurement with the tail on the ground the second time - that will make them shorter. The baggage numbers - pretty crazy unless one is measuring from the front of the baggage area and the second is to the back of the baggage bay - 24 vs 40.5 is more than enough to get you killed if a big enough load is put back there under the wrong assumption.

Just my opinion - 1) no reason to trust the numbers you have 2) get the W & B section from your builders manual for the plane - that is the holy grail - it will tell you what the arms are supposed to be and how to set of the fuselage and the empty weight 3) Get some accurate scales and start with a new W & B under the correct conditions with the correct arms.

You don't want to mess with bad W & B data.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp

The weight and balance form on the Kitfox LLC site for the Classic IV 1050 gross weight matches closely to your original paperwork.
Your numbers
Original Paperwork
Pilot 16.3
Wing Tanks 16.47
Cargo Bay 40.5
Rear Header Tank 45.9 or 46.4 (which one is right?)

Kitfox LLC numbers

Pilot 18.3
Wing Tanks 16.5
Cargo Bay 40.5
Rear Header Tank (not listed)


Why there is exactly a 2 inch difference in the pilot location, I can't say. Perhaps it is a typo on your original work.


I would measure the actual distance from the wing leading edge to the header tank to get an accurate figure. I don’t believe your header tank is aft of the baggage.Simply level the airplane and use a plumb bob and tape measure to locate the CG of the header tank and any other items you feel are suspect.

John Pitkin
Greenville, TX

Were there any mods to your plane? namely the plastic leading edge added? It is easy to get the #s off if the shop doing the work is not real careful. I paid 279 bucks to have my W&B done by a "real aircraft shop". They did not level it properly nor drain any fuel etc. I went back and had them do it again while I watched and got the correct leveling set up myself as they figured a couple degrees was close enough. If your dropping a string line to get the actual measurements for your plane, then close enough is not good enough. It needs to be leveled properly.

I am definitely going to get a new W/B on the machine.

I pulled the weight and balance data from the Kitfox website and it says that that min/ax CG limits are 10.2 and 16.0 respectively for the IV-1050. Can I get a confirmation from a fellow owner or two?

I ask because I have builder's paperwork and prior owner's paperwork that says 14.78 is the max aft. You can barley load the airplane with a 14.78 max aft so something seems off.

Thanks for everyone's help.

Here's the service letter that changes the aft CG limit of all model 4s to 16 inches. http://www.kitfoxaircraft.com/suppor...ters/sl30a.htm