Weight and balance

[TJay 1041]

Hey guys I just did a quick weight and balance to see where I can place my battery, tell me if this sounds right, it has been so long since I have done one,

Right Main=261

Left Main=258

Tail wheel=40

total 559

From leading edge

Mains are 2 inches behind

Tailwheel is 155 inches behind

if I did it right comes out to 12.94

If i'm doing it way wrong feel free to tell me, like I said its been a long time, I think the last one was when I got my license a few years back,

 

Edited 12 Nov 2016 by TJay

[tcj 150]

Check your math.

[EDMO 1078]

Agree - TJay you were off by .008121 !  ;<)   Interesting tho - I think Avids have the mains in front of the datum instead of 2" behind?   You did level the plane to weigh it?   Just checking - others have weighed them with tail down...   EDMO

Edited 13 Nov 2016 by EDMO

[lostman 198]

I hope that this means you're getting close to flying it? Can't wait to see the report and video. You ARE taking video right?!  

[1avidflyer 1983]

Just dug up my Kitfox 1 WB sheet, and I show 1/2" in front of datum for mains, and tailwheel at 151 3/4" behind the datum.  My main landing gear is supposed to be from a Kitfox 4 according to an entry in the log book.   I think I would keep the battery back as far as I could, these planes are supposed to fly better with a rearward CG.  Also, if your mains are 2" behind, it may want to tip on it's nose that much easier with hard braking.  Just remembered, you have the bush gear, that could account for the difference from mine.  For some reason my brakes are super good, I can hold a full throttle run up real easy, and I notice the tail wanting to come up on braking.  Just something to keep in mind.  (one more thing to worry about! ;-)  Jim Chuk

[EDMO 1078]

Jim,  What is the Empty CG range on the KF1, or does the book give it?  What is your ECG?  My KF1 book only tells how to weigh it, and the MTOW.  EDMO

Edited 13 Nov 2016 by EDMO

[1avidflyer 1983]

I'm showing 10.2" forward, and 14.28 aft.  I think that aft location is extremely conservative.  Avid went to 16"  and it's been tested way further back.  My ECG is 11.32"  EW is 502 with 4 qts oil, and GW is 950.  JImChuk

[EDMO 1078]

I think I figured the % of the forward and aft flying CGs for the 51" chord at one time -

Seems like 20% forward, (about 10"), and 30%, (15.3") to 33%, (17"), for the aft, which corresponds somewhat with my design book.  Some say they fly best at about 17" aft.       EDMO

Edited 13 Nov 2016 by EDMO

[TJay 1041]

yeah bush gear and plastic leading edge maybe has something to do with it along with a 3 leaf tail spring and 8 inch matco probally pushes the tail measurement back a bit, my battery only weighs 4 lbs ill play with it a bit in different spots see what it does, I would rather not mount it far back, I hate all those extra heavy 4 gauge cables adding weight,

[tcj 150]

I would keep the battery as far forward as possible.  In front of the fire wall if there is room.  Fuel, Pilot, passenger, baggage, everything you put in the plane when you fly will push the CG back further.

The Good book says, "Thou shallt not put weight at the extremes of the airplane"  ie, propeller, wing tips, or tail.  There is much more to weight and balance than balancing a teeter totter.

[1avidflyer 1983]

At 4 lbs, it wont make much difference, and not running lots of cable makes sense.   I just punched in numbers, and if you have 450 lbs at 16" back (which is about where people and fuel end up being) your CG ends up at 14.3".  An Avid baggage compartment is at 57"  and so I used that moment, not knowing where yours is at.  If you had 50 lbs there plus the 450 at the 16" moment, your CG is then 16.32"   JImChuk

[TJay 1041]

Thanks Guys, I did a better check today and I made a mistake my main axles are .75 inch rear of the leading edge, which doesn't make much difference for what I was checking, also did some playing with the battery location, way upfront on the firewall it makes the rear scale read 39.5 lbs. if I stick it in the baggage area it reads 41.5lbs, think Ill stick it up front, thanks for the help guys,

[EDMO 1078]

TJay,  Do you have one of those "Burn-Fast" batteries?  IMO, the front of the firewall is the only safe place to put them.  EDMO

Edited 13 Nov 2016 by EDMO

[TJay 1041]

TJay,  Do you have one of those "Burn-Fast" batteries?  IMO, the front of the firewall is the only safe place to put them.  EDMO

They don't burn, they explode or melt ha, ah Im not worried hook them up to the right system and there fine,

[EDMO 1078]

TJay,  Do you have one of those "Burn-Fast" batteries?  IMO, the front of the firewall is the only safe place to put them.  EDMO

They don't burn, they explode or melt ha, ah Im not worried hook them up to the right system and there fine,

Just hoping you didn't have to breath all that toxic smoke - as you look for a place to land!    EDMO