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Kitfox IV modifications list

18 posts in this topic

Posted (edited)

I may be able to get a Kitfox IV project close by where I live. It is uncovered and I wanted to get a list of modifications that you guys that have been flying Kitfoxes and Avids for a while have made and feel are worthwhile.  I'm interested in hearing about all modifications, but especially those that are considered mandatory and need to be done before covering. Don't think that any mod is too trivial or simple because I want to try to think of all and incorporate the ones I want during the build rather than try to add on later. I'll start the list below.  If you would when you post let me know if you think a particular mod is mandatory, nice to have, etc. Just so you know some of the parameters, the airplane will be a tailwheel airplane powered by an 80 hp Rotax 912. I'm going for light weight as much as possible.

Modifications List

1. Comply with all Kitfox service bulletins and service letters

2. Reinforce fuselage sides where landing gear mounts

3. Reinforce landing gear truss where bungees attach

4. Different main landing gear (Grove, cabane type, other) (I'll probably go with cabane type gear)

5. Larger pneumatic tailwheel  (Probably a 8" Matco)

6. In flight adjustable elevator trim tab. (Electric or manual)

Added to list from suggestions:

7. Beef up tailspring mount area.

8. Inspection ring near tailwheel spiring bolts

9. Ground plane for antenna mount

10. Widen fuselage at seat back (Murle Williams kit or other)

11. Relocate shoulder harness mount so that straps don't fall off shoulders. 

 

 

Edited by 109jb

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Posted


That's tough the model 4 is a pretty good one already.  The only thing that's looks cheap to me is the stock landing gear.  Maybe the height of the vertical and rudder.

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Posted

Yeah, the basic airframe is good but I'm looking for any kind of mod. Even something like an extra welded tab for a whatzit isn't off limits.

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Posted (edited)

First thing is to figure out exactly what you want your Fox to do. Then do the mods to make it do that mission. Adding mods just because you can, adds a lot of unnecessary weight if their not really needed for your mission. Trying to have an aircraft to do it all usually ends up doing everything just so-so and nothing well. Kit builders have been searching for the do-it-all kitplane for years and still hunting. A standard model 4 is a pretty good all around airframe as it is. It can be made better for certain missions but just not all.

Edited by Allen Sutphin

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Posted

Yes, I will decide if the mods  people suggest fit my mission and if I will incorporate them, but quite frankly that is not something you need to know. It is something for me to know and to decide.  I am intentionally not listing my exact mission specifics because I don't want to limit responses.

Also I am not only looking for airframe modifications, but all modifications. Nothing is too trivial.  Heck, even something like "weld a tab for a go-pro mount here" is welcome.

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Posted

I really don't give a crap what your mission is. I just didn't want you to end up with a flying brick. You'll hear no more about it from me!

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Posted

The tab that is welded on the vertical stab, which holds the tailspring from lateral movement is a weak point.  I've seen several of them fail.  Avid's mount is better IMHO.  We built that sort of mount for one IV and it is holding up well. Also built a plate that mounts under the spring for another where the tabs had bent but not broken but had been bent.  The issue presents itself because the spring doesn't have a good flat surface to mount to.  With side pressure the spring rolls to the side bending the main bolt and bending or breaking the tabs.  Otherwise I have to say I'm pretty impressed with the KF 4. Faster that the Avid just a tiny bit slower to get off the ground.  Not a fan of the Grove gear or the so called bush great with the heavy springs, still waiting to see if Leni's suggested fix with the snogo springs will cure the issue.  I'm using the Roberts Rage gear with my own gear leg design and I like the TK1 gear of Tony's but both are not cheap.  Larry's beefing up of his fuselage surely would be on my list also for both the KF and the Avid. JIm Chuk and many others also documented ways of beefing up the cockpit area of the fuselage,there are a lot of good options out there.

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Posted (edited)

I really don't give a crap what your mission is. I just didn't want you to end up with a flying brick. You'll hear no more about it from me!

I'm sorry if I somehow offended you because it wasn't my intention. I just wanted to make clear that I don't want anyone ommitting any potential modification due to some perceived mission profile.

Edited by 109jb

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Posted

The tab that is welded on the vertical stab, which holds the tailspring from lateral movement is a weak point.  I've seen several of them fail.  Avid's mount is better IMHO.  We built that sort of mount for one IV and it is holding up well. Also built a plate that mounts under the spring for another where the tabs had bent but not broken but had been bent.  The issue presents itself because the spring doesn't have a good flat surface to mount to.  With side pressure the spring rolls to the side bending the main bolt and bending or breaking the tabs. 

Good to know. I'll definitely look at beefing that tailspring area up.

Not a fan of the Grove gear or the so called bush great with the heavy springs, still waiting to see if Leni's suggested fix with the snogo springs will cure the issue.  I'm using the Roberts Rage gear with my own gear leg design and I like the TK1 gear of Tony's but both are not cheap. 

Yeah. I'm not looking for monster gear with 37" tires. The 21" Nanco's on my current kitfox are fine by me. I'd just like a little wider gear than the stock. The Grove does that and eliminates bungy failure concerns, is lower drag but from what I understand a bit heavier. A cabane gear is probably a good compromise and I'd probably build my own. Again, not looking for monster tires or even a taller stance for that matter, just wider for a little better ground stability. Quite honestly the gear decision can be made later since the gear designs I'd consider wouldn't require anything affecting the fabric.

Larry's beefing up of his fuselage surely would be on my list also for both the KF and the Avid. JIm Chuk and many others also documented ways of beefing up the cockpit area of the fuselage,there are a lot of good options out there.

Definitely doing this as it is ounces of material for improving the strength of a known weak point.

Keep em coming.

 

 

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Posted

Added a few more to the first post.  

 

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Posted

Yes I forgot about the seatbelts, that is annoying as hell.  I tie the end of the seatbelts across my chest to keep them on.

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Posted

Yes, I will decide if the mods  people suggest fit my mission and if I will incorporate them, but quite frankly that is not something you need to know. It is something for me to know and to decide.  I am intentionally not listing my exact mission specifics because I don't want to limit responses.

Also I am not only looking for airframe modifications, but all modifications. Nothing is too trivial.  Heck, even something like "weld a tab for a go-pro mount here" is welcome.

I would be hesitant to offer any advice for mods based on this.  Your right, its none of our business so why bother.

I think it safe to say that a mission should be in mind when building or modding a bird.  Why should I waste time listing out a ton of mods that you have no use for?? Why beef up the fuse and make it big tire ready when you have no use for big tires?  why mention mods for float use when you would never put it on floats :dunno:

I think you can see where I am going with this in as nice of a way as I possibly can... this is after having a few days to really think about my reply.

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Well OK.  The primary mission is the typical mission for a Kitfox IV. Mostly just bombing around airport to airport, paved strips, grass strips. Ocassionally I will be landing on unimproved landing areas from time to time, mainly farm fields (sometimes a bit rough), and pastures of friends and family I have, and I'd like to take it out west at some point too. I'll be retiring in about 5 years and after that want to do a lot of grass-roots flying and experiencing as much as I can. Basically doing the flying that I couldn't do for the past 30 years raising kids and such. I want it to be a fast as is possible but that isn't a determining factor in the mission or modifications except that I'll do some lightweight fairing of things. I have a SES certificate so throw some amphibious floats on it at some time or another too. I like to build so will probably do Zenith amphibs. Because of where I live and where I want to fly I will have to have ADS-B out, Mode-C transponder, and comm radio, but the rest of the panel will only be a  G5x, an appropriate engine monitor and a tablet for navigation. No fancy heavy upholstery, just comfortable and lightweight. Covering I would love to do Oratex if it is in the budget when I get to that point, again to save weight as I don't consider oratex to be pretty. Modifications I want to do are those that are worthwhile for any of the above missions that are worth the weight penalty. Again I don't want to build an 800 pound Kifox IV so I will assess each suggestion very carefully.

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Posted

Yeah, the basic airframe is good but I'm looking for any kind of mod. Even something like an extra welded tab for a whatzit isn't off limits.

Sounds like you wanna build another Mangy Fox.

IMG_4541.thumb.jpeg.dc6e66058bd7ed4eaaba

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Posted (edited)

I have definitely drooled over your airplane and love the mods you have done.  Can I ask what your Mangy Fox came in at for empty weight and what engine you have in it?

Oops. I see it has a 912UL with the 105 hp zipper conversion

Edited by 109jb

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Posted

She a thick girl at 700 empty....

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Posted (edited)

She a thick girl at 700 empty....

Some guys like thick girls....pretty sure you like the Mangy Fox! 

Edited by lostman
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Posted

She a thick girl at 700 empty....

Some guys like thick girls....pretty sure you like the Mangy Fox! 

 

2 people like this

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