kitfox 3 vs 4

What are the differences between a 3 and 4?

I'm interested in getting a Kitfox, used. I was told the one I'm looking at is a 4. Now it's a 3. So I'd like to know the difference. Thanks much.
Jim

Jim, The model 3 had a different wing and flapperons than the 4. The 3 wing has undercamber to the bottom side of the wing for more lift but is a slower speed wing. The 3 has a shorter rudder than most 4's although the earliest model 4 has a shorter rudder too. The gross weight on a 3 is 1050 lbs. The shorter ruddered model 4 also carries the 1050 lbs gross weight. If it has a 1200 lbs gross weight and tall rudder , and no undercamber to the wing it's a 4. Also the control mixers are different for the 3 . If it's a model 3 (more complicated) you won't have to disconnect the flapperon control rods to fold the wings. There are other small diffs. but these are the most apparent. Both the 3 and 4 used Rotax 912 four stroke and 582 two stroke engines so the engine it has or is set up for will not help much.

Model 3
1. Under-cambered wing. (Slower cruise speeds but high lift wing)

2. Shorter vertical stabilizer/rudder
3. Gross weight of 1050 lbs.
4. More complicated control mixer/ no disconnecting flapperon control rods to fold wings.
5. VNE of 100 mph or less (mine was 98 mph)
6. Airfoil shaped flapperons(models 1,2 & 3)

Model 4
1. Flat bottomed wing. (faster cruise speeds with this wing)
2. Early 4's have shorter rudder. Later 4's have taller rudder.
3. Early 4's 1050 lbs. gross weight later 4's with tall rudders 1200 lbs.
4. Simpler control mixer. Must disconnect flapperon control rods to fold wings.
5. VNE of 120 mph or faster depending on Speedster mods and windshield thickness.
6. Symmetrical flapperons.

Jim, if I've forgotten any major easily spotted differences someone will respond.

Not bad Desertsfox I give you an 8/10 for Kitfox Model knowledge.

The Model three also had wooden Aileron hinge attachment points these were a continuation of the actual wing rib. The Model 4 and onwards departed from this method and employed separate metal fittings which attached to the ends of wood ribs to serve the same function.

I also understand that the later model 4 had thicker carry through tubes for the wings attachment and thus the heavy load capability. The struts on the Model 3 and 4 are the same and attached at the same point along the wings spars. The 3 and 4 are very similar in structure almost the same.
Aerodynamics and the flaperon mixer were the main differences.

I'll be happy with a 5/10

some of the 3's were retrofitted with metal reinforcements on the wing rib/flapperon attach points so that may not be a definitive item for qualification of a 4 over a 3 unless the buyer knows what a 4 bracket looks like and a repaired 3. That was a recommended repair procedure for any flapperon attach point that was broken in an accident. The carry throughs may not be apparently bigger to a novice so I was keying in on very apparent differences but your points are spot on if the buyer is really up on his Kitfox models.
I do think though that the struts were beefed up also on the later 4's. 3/4" to 1" struts maybe. I could be remembering wrong. I am getting old.

Jim - other things to consider if deciding between a 3 or a 4 are what kind of flying you intend to do. If you want to fly with other Kitfox's and they are 4's , 5's - 7 SuperSport then the 3 will have a tougher time keeping up with them even with the 912 Rotax and a controllable prop. The model 4 will do pretty much everything the 3 can do and fly quite a bit faster in cruise. The 3 will cruise at 80 to 90 mph real well and the 4 will do 110mph pretty easily. I'm comparing with a 912 installed. The 582 will be slower on both models. The 3 gets off extremely quick with the 912 but the 4 will probably climb as quickly. I loved my model 3 but the the 4 was quite an improvement in speed with little or no sacrifice in climb and can carry more load.

Hi, my model III Had the metal aileron brackets attached at the time of construction, I thought it was a factory upgrade. I wouldn't have an aircraft with out them.

Hello the group,
I had one of the early to mid Model IIIs.
SN 1951 I think. ( Shamefully not finished yet ).

There were two variants of the Model III.
As I said, I had one of the early ones It was a Model III.
This model was later re-designated the Model III-1050 when the Model III-1200 was introduced.

I have two Model IIIs hanging in my hangar.
One is a Model III-1050 and the other is a Model III-1200
The -1050 is mine, the 1200 is an orphan. ( mostly mine - don't ask )

Flaperon attach points:
My -1050 had the AL flaperon brackets right off, these were not retrofits for me.

The Model III-1200 had two main differences:
1) Various reinforcements to allow for an increased GW ( 1200 lbs of course )
and
2) A thicker windshield so that the higher cruise would not cave in the lexan.

Under chamber:
Note: I can not speak of the Model IV, but the III-1200 also had the under cambered wing. You could get either the droop tips or the "Speedster" tips.
I got the "speedster" tips with mine.


Spar:
I do not know and have not measured the thickness of the spare tube material, but the diameter is the same as far as I can tell.

Spar "I" beam at the strut attach points:
My recollection, based on the rivet pattern, is that the reinforcements are about the same length between the 1050 and the 1200.
However I can not speak of the thickness of the "I" beam or the basic spar tube.

Lift Struts:
The III-1200 struts are significantly beefier than the III-1050.
I seem to recall that the threaded element on the ends of the struts are the next stud size up as well.

Carry throughs:
The cabin carry throughs are were beefier to allow for the higher GW.
These included the spar carry throughs on top as well as some of the tubes in the floor at the attach points for the struts and landing gear. The ODs of the tubing do not seem any different, so the differences must be in the gauges of the tubing walls. Makes it tough to tell which it might be.

Which one is it, a 1050 or a 1200???
The surest way is to look at the lift struts, if they are side by side, there is no missing the larger "look & feel" of the 1200 struts.

Assuming that all Model-IVs were -1200s ( I can't imagine anything else ), then from one of the earlier posts, it seems that the the easiest way to tell a -III for the -IV would be the under chambered wing.

Happy flying.
Kevin

Kitfox never offered a III-1200. History

The 1200 didn't appear until the model IV, and then it was the later variation.

Hi Kevin,
Your III's are most certainly Model IV's, one 1050 and the other 1200 gross.

The Model IV wing is more desireable than the undercambered III wing. You'll probably want to update your sale posting and put up some pics to go with it.

I Humbly stand corrected.
Chalk it up to age and that it has been to many years since I have spent any time working on it. Sometimes it is nice to be just flat wrong. In this case, I have a IV-1050 instead of a -III. Not a bad way to be wrong.

I also concede on the "under cambered" wing.
I have not worked with other wings and there is a "slight" (1/2" ) of under camber in the wings I have. ( Along with the plastic nose extension ). But it clearly is not deeply under cambered like many of the Avids that I have seen.

Thanks for the corrections,
Sincerely,
Kevin Hanna

P.S. Thanks Av8r-Sed for the corrections.

I have N505KF which was built in 1993. It says it is a Kitfox 3 but has the Kitfox 4 flat bottomed wings and has the shaped (not flat)horizontal stabilizers in the tail feathers. I hear talk of short and tall rudders. I will measure mine tomorrow but meanwhile can somebody give me the dimensions of "Tall and Short'? Do I have a 1050 gross or 1200? A Kitfox 3.5?

I have model IV sn 1563 was delivered in November of 1991 and is a small tailed 1050. The construction manual is a mix of III and IV instructions . Sorry , don't have the measurements handy

My 1992 Model IV-1200 rudder is 53" tall at the hinge.

i had failed to mention that there are some pictures in my album of the mod i did to the tail to install a 1200 rudder that show the difference in vert stab .

John at the factory says I have a 1050. I guess that is the final word. My rudder at the hinge is 47" and 14' at its widest. I assume that is the size of a Kitfox 3 rudder. Any comments? Thanks in advance. BTW I have enjoyed this forum right from the start. Doug