Mass Balance Weights

[TJay 1041]

Anybody know why the early foxes and Avids had a spade looking weight and the later foxes have the nicer looking weights, I bought some a long time ago from Airedale for the Avids but not sure I like the looks enough to install them, thinking bout making some nicer looking ones, like the kitfox weights anybody see a issue with this?

[Av8r3400 1179]

The early Kitfox and all the Avid weights are just tube filled with lead. 

Kitfox later went to a aero-shaped piece of steel filled with lead, on a stick, which looks kind of like a spade or spoon.  With the IV-1200 they went to two smaller weights on each flapperon instead of one large one to lessen the torsional vibration and flutter at higher speeds. 

[Dusty 126]

Any more information on the dual weight option,the STI appears to have them.My 4 1200 has only one outboard each side,is the dual weights a necessary mod?

We recently have had an avid break a flapperon in flight (by the turtledeck hinge and possibly unrelated to oscillations) but it does make one wonder!

[Av8r3400 1179]

The dual weights started as standard equipment with the IV-1200.   All Kitfoxes have been this way since.  Maybe yours is a very early 1200?  

This change was associated with the increase the the airspeed redline from 125 to 140. 

[EDMO 1078]

I've got a pair of Ercoupe weights - they look like an egg on the end of a tube.   Don't remember if I have any of the Kitfox T shaped ones.  I am going to have an internal balance on my ailerons by weight in the leading edge tube.  Ailerons are short compared to the long AvidFox flaperons - I can see the need for two balance weights on flaperons, but one full-length weight to balance is considered better.  EDMO

Edited 6 Jan 2017 by EDMO

[dholly 718]

The early Kitfox and all the Avid weights are just tube filled with lead. 

Kitfox later went to a aero-shaped piece of steel filled with lead, on a stick, which looks kind of like a spade or spoon.  With the IV-1200 they went to two smaller weights on each flapperon instead of one large one to lessen the torsional vibration and flutter at higher speeds. 

Larry, I think you may be mistaken about the addition of dual MBWs on all (or even most?) KF4-1200s. Every single one I've seen had only one outboard weight per flaperon, including my s/n #1901. I believe the model change from 4-1050 to 4-1200 occurred at s/n #1723, so wouldn't really think mine qualified as a 'very early' 4-1200. Actually, I'm 99% certain both my 3s, my 4-1050 and 4-1200 all had the exact same size and location weights. I thought just the windshield thickness was changed for the higher Vne somewhere along the KF4 line, but not sure when.

[1avidflyer 1983]

Something in the back of my mind is telling me that the speedster Kitfox 4 classic went with 2 weights, and the flaperon maybe had the skin cut in the middle of the flaperons.  I don't have my manuals handy to find it right now though.  Both of my Kitfox 4 classics have a single weight for each flaperon.  Both are long wings though.   JImChuk

PS    I reread my post, and if it wasn't clear, I meant to say 2 weights per flaperon (4 total)

Edited 7 Jan 2017 by 1avidflyer

[Dusty 126]

The vne theory sounds right as my redline is only 125.

[Av8r3400 1179]

 

Larry, I think you may be mistaken about the addition of dual MBWs on all (or even most?) KF4-1200s. Every single one I've seen had only one outboard weight per flaperon, including my s/n #1901. I believe the model change from 4-1050 to 4-1200 occurred at s/n #1723, so wouldn't really think mine qualified as a 'very early' 4-1200. Actually, I'm 99% certain both my 3s, my 4-1050 and 4-1200 all had the exact same size and location weights. I thought just the windshield thickness was changed for the higher Vne somewhere along the KF4 line, but not sure when.

 

I would stand by my comment.  My IV-1200 has dual weights, as has every other IV-1200 I have ever taken note of.  Mine is a "Classic 1200".  There are three other non-Classic IV-1200s (I don't know the SNs) in my chapter that all have dual weights.  I forget now who told me of the dual weights was part of the redline speed increase, if it was McBean or one of the other guys at Kitfox.  What was the redline speed of your 1200?  Is it possible those were not the original flapperons on your plane?  Is it possible that they were ordered specifically with single weights?  There may be more progressions between the 1050 and 1200, it wasn't just a "line in the sand" change over.  With an experimental kit there are alway anomalies.  

My IV-1050 had single weights on each wing, so I do not doubt that was the way of the "early" IV planes.  Maybe the change was not instantly at the 1200 mark, but I was told that was one of the methods of telling the difference. 

[EDMO 1078]

Something in the back of my mind is telling me that the speedster Kitfox 4 classic went with 2 weights, and the flaperon maybe had the skin cut in the middle of the flaperons.  I don't have my manuals handy to find it right now though.  Both of my Kitfox 4 classics have a single weight for each flaperon.  Both are long wings though.   JImChuk

You are correct about the Speedster Kitfox had the skin cut in the center - I don't remember the 2 weights, but can check my manual.   EDMO

[tcj 150]

Lots of different information on the kitfox mass balance weights.  Here's mine.  Classic 4 Long Wing kit rolled out of the factory Sept 1994.  It has one weight on each flaperon.  The mass balance weight installation section in the manual states that the Speedster has two weights per flaperon and instructs to slit each flaperon in two places and cover the slits with  fabric so that it can flex at the higher speeds.

According to the Kitfox Model 4 Pilot's operating handbook, Model 4 1200 and Classic 4 Vne with 582 and 912 engines is 125 mph.  Classic 4 with 503 Rotax is also 125 mph.  Model 4 speedster Vne is 140 mph.

I have a foggy memory of a comment by the factory back some time ago that they started building the small mass balance weights only and would be including 4 of them with all  kits from that point on.

 

Edited 7 Jan 2017 by tcj

[TJay 1041]

So if I end up using my Avid weights which get mounted in the center do I need to slit the flaperon too?

[EDMO 1078]

So if I end up using my Avid weights which get mounted in the center do I need to slit the flaperon too?

You should not need to slit the flaperons - but make sure you put the weights in a different location on each side so they don't interfere with folding the wings.  I read that in the manual.   I would temporarily place them and do a test run before riveting them on.   EDMO 

Edited 7 Jan 2017 by EDMO

[Av8r3400 1179]

Something in the back of my mind is telling me that the speedster Kitfox 4 classic went with 2 weights, and the flaperon maybe had the skin cut in the middle of the flaperons.  I don't have my manuals handy to find it right now though.  Both of my Kitfox 4 classics have a single weight for each flaperon.  Both are long wings though.   JImChuk

Mine is not a speedster, its a long wing and has two weights.  Also, the skin of the flapperons is continuous one end to the other.  Splitting the skins would be s sure fire excuse for disaster.  IMO, you would definitely have flutter issues.  The skin is most of the torsional stability of the flapperons.

[TJay 1041]

Yeah thats kinda what I thought, with the flat bottoms they can flex more than enough, I can see with a convex top and bottom, that would make them way more ridged,

got them finished up today and the primer is drying as we type.

Edited 7 Jan 2017 by TJay

[EDMO 1078]

Something in the back of my mind is telling me that the speedster Kitfox 4 classic went with 2 weights, and the flaperon maybe had the skin cut in the middle of the flaperons.  I don't have my manuals handy to find it right now though.  Both of my Kitfox 4 classics have a single weight for each flaperon.  Both are long wings though.   JImChuk

Mine is not a speedster, its a long wing and has two weights.  Also, the skin of the flapperons is continuous one end to the other.  Splitting the skins would be s sure fire excuse for disaster.  IMO, you would definitely have flutter issues.  The skin is most of the torsional stability of the flapperons.

The skin was only slit on the Speedster according to the manual.  Guess there was a reason Kitfox did that?   I assumed it was to keep them from binding?   Those short wings had a heavier wing loading than the long wings.   Here are 3 pages from the Kitfox 4 manual.   The last page is for TJay showing that the weights are offset from each other.  EDMO

Edited 7 Jan 2017 by EDMO

[1avidflyer 1983]

I guess my (maybe alzheimers assisted) memory isn't as bad as I thought, hey Ed.  :-)    Thanks for digging up the manual pages.  According to the first page, the slot is there to keep the flaperons from binding under heavy load conditions.   Second page says the Speedster gets the 2 weights per flaperon.   JImChuk

[EDMO 1078]

I guess my (maybe alzheimers assisted) memory isn't as bad as I thought, hey Ed.  :-)    Thanks for digging up the manual pages.  According to the first page, the slot is there to keep the flaperons from binding under heavy load conditions.   Second page says the Speedster gets the 2 weights per flaperon.   JImChuk

Enjoy it while you got it Jim  - it don't last forever!  That's why I keep the manuals handy!   ;<)   I wonder how the pages got copied now - I didn't put them on this post?    EDMO

Edited 7 Jan 2017 by EDMO