Weight and Balance Issues, Ballast.

[B757Rus 0]

I am almost done with my rescue Kitfox II /III hybrid (larger tail feathers, rail type engine mount for a 582, IVO prop, E-box).  I performed the weight and balance. It's a little on the heavy side at 567lbs empty weight. The best I can tell from other posts this is fairly common for KFIII.  The tail is 40.2 lbs which I guessing is due to the larger tail surfaces (I'm seeing approx 28 to 30 for the standard tail).  The cg is barely in the accepted range aft at 14.1.  

I've read some threads about adding ballast, but would like to see some solutions others have done.  I would like to get it a little more in the mid CG range between 10.2 and 14.28 to make the DAR more agreeable.    I am considering moving the battery from behind the seat to up front behind the firewall but it's not much weight due to upgrading to a LiPoh.  

Any one out there with this same issue ?  If you used ballast, I am looking for examples of what others have done.  La Saupe, Tjay, Jim Chuk ?  I've seen some previous posts alluding to this issue.  

Any input is much appreciated.

B757Rus

 

 

 

 

 

 

 

[1avidflyer 2006]

I believe there was a service letter that moved the rearward CG to 16 or 16.5"   Here is a link to the service letters.  Look at # 30.  JImChuk

Service Letters – Kitfox (kitfoxaircraft.com)

[B757Rus 0]

JimChuk,

I saw that reference #30a in another post (LSaupe I believe).  I see in the download header they included M1 M2 M3 M4 C4  for the revised CG letter, however in the applicability section of the bulletin they still only call out  "All Model IV-1050 and Model IV-1200 Kitfoxes".    I'm wondering if anyone has clarification that the early models are retroactive to those limits as well.  If so, I'm golden.  Don't know if it's Skystar just not wanting to take responsibility (liability) for Denney planes. I would rather not have to add ballast and decrease my useful load.

In any event I just want to be ready to prove to the DAR my numbers are within limits. 

[1avidflyer 2006]

Well the service letter does list the early models.  Also, the Avid Flyer wing is almost identical to the early model Kitfoxes and it's rear CG is 16.5"

[B757Rus 0]

JimChuk, 

The 30a revised letter I can download only includes IV models both 1050 and 1200.  Do have you have another version showing applicability for the M3? I know the download page says it includes m1, m2, m3, c4 but when you download the letter it only shows mIV versions.   I've see this issue hashed out in other forums, but no conclusive document was ever produced that I could see.  If you have a copy of the letter could you send it to me ?

I sincerely respect your experience and advice,  I was just hoping for documentation in black and white. The way the service letter is presented contradicts itself. 

 

 

 

[1avidflyer 2006]

I don't have a different letter.  I would wonder if this is really an issue anyway.  Has the DAR raised this topic or are you just trying to dot all the eyes, and cross all the tees?  JImChuk

[B757Rus 0]

Crossing tees and dotting eyes. I haven't been to inspection. No DAR yet.  This issue has been a concern to me as I fill out my weight and balance form.  When calculating the adverse CG limits, I will be outside of the documented aft limit of 14.28, however I will be good if I apply the inferred limit of 16 in.  If my DAR looks at my W/B form and asks the question, how do I respond ?  I'm sure the inferred limit is safe, there is enough personal experience out there to show that, but nothing official. The experimental world is uncharted territory for me.  I live in the Part 121 world. I'm a little tainted. Everything is either in black and white or you're in trouble.

I'm really looking for advice how to document this on the form that I will file with the FAA and present at inspection.  Just use 10.2 in fore and 16.5 in aft as the envelope and be done with it ?    B757Rus

 

 

 

 

[1avidflyer 2006]

I don't think you file a weight and balance form with the FAA.  Can you show me different?  The best bet is to talk to the DAR you are going to use and get it straight from the guy who will say yes or no.  JImChuk

Edited 14 July by 1avidflyer

[nlappos 415]

Let me recommend a possible rope out of the tree. You can get airworthy by temporarily ballasting within the 14.28" aft cg, and then flight test your way back to the 16.0" I believe the larger horizontal tail and vertical tail will let you go farther aft because you will have more horizontal tail volume to control the aft cg.

So temporarily ballast to 14.28" with weights hung on the engine mount. Then during the initial 40 hours test further aft by reducing the weight as you test the critical conditions (slowing to unaccelerated stall, landing flare, cruise speed longitudinal stability).

All legal and all wise.

How much bigger is your horizontal stab?

[B757Rus 0]

Not sure about horizontal stab,  the vertical is larger as in the later model 3s from what I have read to compensate for yaw issue.  I am still fairly new to the kitfox world and still have much to learn.  I do not have any information to gauge the changes from the 2 to the 3 other what the person I bought the kit from.  It's a 2 by sn 634 however it was modded with the III engine mount, 13 gal wing tanks and tail from the information I was provided. It was about 75% when I bought it.

If anyone has the tail size increases from 2 to 3  I could compare.  Dimensions anyone ?  All I know is it is definitely heavier than reported 2s. 

Your advise is sound and I plan on adding ballast and doing what you are suggesting. 

If anyone out there has a 3,  what were your experiences and solutions ?  

Many thank yous for the replies.