K3 Weight and Balance

[bbryan]

Does anybody know what the Extreme AFT CG for the Kitfox 3 is. My old book for the K2 says its 14.28" but I heard rumors it was updated to 16". Its gonna be tough for me to stay below 14.28" and carry anything but a bag of peanuts. Also what numbers are you guys using for the weight of a gallon of fuel. Trying to get my W&B paperwork done for my DAR inspector

[Dave S]

Can't help you on a kitfox III CG...however...Gasoline is 6 pounds per gallon

Dave S

[DesertFox4]

Bob- one U.S. gallon weighs approximately 6 lbs. That is what most pilots use as a gallon weight when figuring W.& B. calcs. and likely what your DAR will look for.

[bbryan]

10-4 on the 6 pounds for fuel. I didn't realize that aviation fuel was heavier. When I googled it, Av gas was almost a half pound more than car gas. Maybe its the lead in the fuel.

[rv9ralph]

I recently did a W&B on my model 3. I used the worksheet from the Technical FAQ link on the Kitfox Aircraft website, it will do the math. However, the aft CG is based on a percentage of the MAC, which is based on the airfoil. The 2 and 3 used the same airfoil, it was changed on the model 4. The spreadsheet shows an aft CG of 16. Do not use that. The proper Aft CG for Model 3 is no larger than 14.28. Weigh the aircraft, measure the Arm of the data points and plug them into the spreadsheet. Then you can adjust the weight of fuel and pilots in the spreadsheet to see what your loading limits are.

[bbryan]

Thanks for the info. I will plug the numbers in, who knows, I may be able to giggle the numbers around and get in 2 bags of peanuts. I think I should have put the battery up front instead behind the seat. One other question, when I do the dry weight do I have the header tank behind the seat full or empty. I dont see anything in the calculation for that. Empty would sure make my numbers better looking. Right now my loaded AFT CG is looking around 14.75. About 13.12cg dry weight

[avidflyer]

Empty numbers don't mean a whole lot in a way, other than to base your flying calculations off of. You won't ever want to fly with an empty header tank, (unless you like gliding) :-) I would fill it myself. Jim Chuk

[cgruby]

Does anybody know what the Extreme AFT CG for the Kitfox 3 is. My old book for the K2 says its 14.28" but I heard rumors it was updated to 16". Its gonna be tough for me to stay below 14.28" and carry anything but a bag of peanuts. Also what numbers are you guys using for the weight of a gallon of fuel. Trying to get my W&B paperwork done for my DAR inspector

Bulletin #30 updated the aft CG to 16" for models IV -1200. It does not apply to the model III, so therefore 14.28 "/28% is correct for the model III.

Cheers,

[Dave S]

Technically, by definition (and for the purpose of your required current W/B record which must be on the plane,) Empty weight with regard to fuel includes only unusable fuel.....not unusable for practical purposes, but when the system is empty of all fuel which could be pulled through to the engine.

Then there is your legal reserve....1/2 hour for day VFR which would include what could be sucked out of the header tank by the engine down to the pickup fitting.....However, I never calculate for 1/2 hour reserves so no, that half hour of usable fuel isn't very practical.....I am not going to be flying around and planning to land with 3 quarts in each wing tank + what is held in the header tank for minimum reserves. But, empty weight is still defined as zero usable fuel.


Sincerely,

Dave S
Kitfox 7 trigear
912ULS Warp Drive

[KFfan]

From my model 2 documents

1. Datum Line Located At Wing Leading Edge
2. MAC Most Forward Limit Must Be More Than +10.2 Inches And Not Less Than 20% Of MAC
3. Most Aft Limit 14.28 Inches and 28% of MAC

FWIW