KF5 weight and balance

[Kitfoxkerry]

I bought a KF5 that had been completed but phase I not flown off. In checking the empty wab it is near the aft limit. The plane flies fine and behaves in all stall configurations and phase I is complete. Still I am concerned about loading the plane up until I have a better understanding of the cg as everything I put in the plane will move the cg farther aft. Has anyone else had experience where the weight distribution for a model 5 is differs significantly from the example in the builders manual?

[kmach]

Hi,

With 230 lb pilot 220lb passenger ,144 lbs fuel , 120 lbs cargo my model 5 outback's c of g is at 15.88"aft still below the max aft of 16.0"

the forward min c of g is 11.37" .
the max aft c of g is 16.0"
these are for a wing with no wing sweep, (rotax 912 engine)

[Dave S]

Kitfoxkerry,

Might be well to provide some additional data on your W/B question to help others in supporting your question....What engine are you running; and, do you have the wings with the forward sweep to accomodate a heavier engine? or are the wings straight? Any unusual accessories or battery location? ....there is a different value for sweep or no sweep.

Our S7 W rotax & no sweep, is similar to 5s of the same configuration. I found that max weight and max aft CG of 16" resulted in no bad behavior. It is also apparent in working a few W/B problems for the airplane, it is nearly impossible to exceed the forward CG while it is entirely possible to load the plane in a way that would exceed the aft CG.

If something does not seem right, since you did not build the plane, it might be worth redoing the empty weight to assure that the W/B is correct for the plane.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp

[jiott]

I agree with Dave, that with most heavy loadings you will be at or near max aft CG. You have to be careful because it is easy to exceed the max aft CG if you put much weight in the cargo area. I also have flow at max gross of 1320 lbs and max aft CG of 16" and noticed no bad handling, but it does definitely feel different in the landing approach and flare.

[Kitfoxkerry]

Thanks for your comments, Kevin, Dave and Jim. The configuration is Rotax 912 ULS, Warp Drive prop, Grove gear and 6" matco tail wheel and light on avionics (com and xponder). I added the Grove gear and the tail wheel which added some to the empty weight and a bit to the rear cg. I expect to redo the weight being careful to level the plane and also to verify where the main gear actually sits relative to the wing root leading edge. The plane behaves well in a no-flap stall with a pilot and full tanks so I think we will sneak up on the loading of the plane monitoring how the stall behavior progresses. Since the flaps move the center of lift back significantly I feel comfortable that a bit of flaps can clean up a no flap stall if that is indeed a problem. If, after another pass on weighing the plane the cg still appears to be too far back I will have to figure out why and what to do about it.
Again, thanks for your comments and as a Kitfox newbee I hope we may run into one another some day.

Kerry S

[JSR13]

Heres a quick formula to determine weight and balance.

1. Add weight of aircraft, passengers, baggage and fuel.
2. Determine total weight to be within limits
3. Multiply weight by arm for moment. (W x A = M)
4. Add individual moments for Total Moment.
5. Divide the Total Moment by the Total Weight to determine the loaded
C/G. (TM/TW = LCG)
6. Determine the loaded CG. to be within limits.

Maybe that'll help, JON

[t j]

Is the main gear in front of the wing leading edge when the place is leveled. If so, are the main gear arms negative on your weight and balance form?

[Kitfoxkerry]

Thanks Tom - good question that I wondered about too. Also the fuselage may not have been quite level on the first weighing - next time do it paying more attention to details before deciding that there is a problem.