Another Kitfox IV rebuild project

32 posts in this topic

Posted

So I finally got a chance to get my project airplane home today. This is a Kitfox IV speedster powered by a 80 hp Rotax 912 UL that I bought from an insurance auction. It actually belonged to an acquaintance of mine and was located only about 30 minutes away. The airplane suffered a loss of engine power followed by a forced landing to a waist high bean field, which ended in a rapid nose-over.  The vertical tail struck the ground and the aft fuselage got bent as did the vertical stab. The horizontal and elevator look OK as do the wings and struts. The plan is to rebuild the airplane while incorporating a few key modifications which will include these main mods but also a lot of little weigh next to nothing mods:

1. Landing gear area reinforcement

2. Tail spring mount reinforcement

3. Fuselage widening (Murle Williams style)

4. Provisions for future autopilot servo mounting

5. Upgraded panel with only engine monitor, Garmin G5X, tablet computer for navigation, intercom, radio, and transponder.

6. Upgraded baggage area.

It will probably be a little while before I can really get into it as I have to clean out and sell my father's house since he passed away recently. He was a pilot too and I had wanted to get him airborne in the other Kitfox I have but his health never got well enough. I know he would have also loved to see the rebuild of this project airplane.  I learned most of what I know about fabrication, welding, machining, and general mechanicing from him.

Anyway, Here are some pics of it stuffed away in the storage part of my barn.

 

 

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Posted

Built by a left-handed owner who flew from the right seat. It's cursed! :P

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Posted

Yeah. When I'm done it will be setup for left seat flight primarily, but will have enough that right seat flight would be easy too. Main thing for me would be switches easy enough to reach from both sides. I can still remember doing solo right seat practice  for my CFI and having to lean way over from the right seat  in the C152 to reach the switches. I'll probably have a home brew digital ASI/Altimeter/Tachometer on the right for convenience but not really necessary.

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Posted (edited)

Finally got some time to mess with this one and got the Rotax 912 running today.  I know the guy this airplane used to belong to and it was a afternoon flight in late August last year when the engine quit when he was at about 1,500 ft agl. I didn't really do anything to get it running.  I just ran a hose from the pump inlet to a gas can on the ground, put some run out blades in the prop hub and it started pretty much right away.  The only things are:

1. The temp and dew point (23/15 deg C) are right in the middle of the "moderate icing at cruise power"/"Serious icing at descent power", so I guess it is possible it was carb ice, but this Kitfox has the short filters back at the firewall which everyone say are not ice prone. I guess the reasoning is that with the carbs back there they are drawing in warm air from inside the cowl.  I wonder about that theory though.

2. The other thing I notice is that this airplane doesn't have a fuel return line as called for by this Rotax Safety Notice.  I wonder if this could have been a case of vapor lock.

Anyway, I'm happy it runs and for the price I paid I'm really happy. To let the cat out of the bag, I paid $5100 for the whole airplane and it looks like the only real problem is the little kink in the fuselage. It has a newish Garmin SL40 comm radio, a Terra transponder with encoder, and a flightcom intercom. I figure those are worth about $1500 all together.

Edited by 109jb

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Posted

Got a second run in today. Ran fantastic. Only issue is that I have the prop pitched too high and could only get 4800 static.  Really really happy.

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Posted

I also had a chance to get the fabric off the aft fuselage and eye up the truss damage. It isn't as bad as I thought. I think all but 2 tubes can be straightened but maybe 3.  The one picture with the colored lines shows the bent tubes and the green ones are ones that can be straightened, the yellow might be able to be straightened, and the red will probably need to be replaced , or at least the kinked section sleeved.

 

 

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Posted

That sure is a nice looking KitFox. 

It is a speedster?

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Posted

Yep. Speedster it is.  

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Posted

That's what mine is

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Posted

109jb,

Nice airplane!  Good luck.

Can I suggest you mount a boost pump to feed the engine, and leave it on constantly. A good one from Aircraft Spruce, with 4 psi. It is a great insurance against excessive quietness.

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Posted

Yeah I was thinking about an electric pump. Will have to do some research.

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Posted (edited)

Didnt some of the earlie 912 have fuel pump problems? And there was a service bulletin to replace it with one with a return line so u dont get vaporlock, Jonas Marcinco had that happens to him he has a utube video on that happening to him and he crashed on takeoff, May check that also. 

Edited by Buckchop

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Posted (edited)

Yes, the Rotax pumps themselves were problematic, much more so than the earlier Pierburg pumps. Mandatory pump replacement for SLSAs w/ Rotax pumps a number of years back and it caused a massive shortage of new pumps from Rotax. I had a pump start weeping on my KF4 at the same time and ended up grounded for weeks. Separate issue but I believe all new 912 installs now require the return line, although there are still a ton flying fine without retrofitting. Personal decision I guess for E-AB. FWIW, I recently put a fuel system schematic for 912 w/ return line in the Technical Tasks forum.

Edited by dholly
fix file location

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Posted

Doug, I looked for that 912 fuel schematic and didn't find it.  Got a link?  Thanks,  JImChuk

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Posted (edited)

The Rotax 912 mechanical fuel pumps have a 5 year replacement interval so all of the bad pumps "should" have been replaced by now. This airplane is going to get the return line when the engine is re-installed. when I do the install I am going to follow both the Rotax install manual and the Kitfox manual, but in cases of a conflict the Rotax manual will win.

I was thinking about going to a dual electric pump setup and eliminating the mechanical pump but I see the Rotax pump is only priced like it is silver plated, not gold plated.  I'll probably stick with a electric-mechanical setup, but my experience with electric-electric is good. My Sonerai has electric-electric and has been flawless.  I've got plenty of time to think about it though.

Edited by 109jb

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Posted

Did some more work. It has been a pain moving the airplane around with the wings folded, so yesterday I made a towbar. Would have just bought one but the prices are outrageous.

I also made a tube straightening tool that I've already put to use with excellent results. There are  some pictures of it in use on the airplane and a before and after of the fuselage after straightening. I was able to get the longerons straight and they won't need to be replaced. Two of the truss diagonals have a little kink in them, so I'll have to splice or sleeve them .  Looks like I need 2 6 inch long pieces of tube to fix this one.

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Posted

Doug, I looked for that 912 fuel schematic and didn't find it.  Got a link?  Thanks,  JImChuk

Sorry Jim, it was in the Technical Task forum. Previous post fixed.

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Posted

I finally got some other things done and was able to get the ball rolling on this rebuild. I've attached some pictures, one of which is just the fusealge moved from the cold storage side of my barn to the work area with my other project I've got going.

I also started working on the repairing the cowling that got damaged during the nose-over. I probably should have just bought a new one but I'm too cheap and I've also made it sort of a game with myself to see just how inexpensively I can get this airplane flying again. The lower front cowl took the brunt of the damage and had a lot of cracks. So many and so large that it could not hold its own shape correctly. Fortunately I had the other Kitfox IV, so I used its lower cowl to make a plywood template for a jig to hold the broken cowl in position for enough repairs to make it rigid again.

The cowl was placed in the jig and internal repairs done with epoxy and biderectional cloth using several internal layers. Every time i thought I had all of the cracks taken car of I found another. There were so many. Once the cowl was rigid enough to hold shape I continued glassing cracks as I found them and also put a couple layers on the outside after sanding down to the bare glass. I used enough externally to insure that after sanding and fairing the outside that each crack would still have an external layer of fresh glass.

The upper cowl wasn't as bad but still ad some cracks.

It is really  amazing how long this takes. I have about 20 hours into the cowl repairs and still not done. Then I have to move on the the aft cowls. They fortunately only have a couple minor cracks and shouldn't take much.

More to come but likely a little slowly at first.

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Posted

So per my other thread, I made a set of cabane landing gear for my Kitfox 4  project. For design, I made my own decision on width and height, but I didn't re-invent the wheel and did a lot of internet searching for tube sizes. It came down to a combination of looking at other airplane designs, other kitfox landing gear designs, etc. It was a lot of internet sleuthing. To save someone else from having to go down the same road, I decided to make a pdf showing how I built my gear. It was built in place on my fuselage, and I don't know how close it would be on other Kitfoxes. I've attached that pdf here. I had a chance to get a better picture of the gear with the airplane outside showing how the gear came out. Since these pictures were taken I have decided to make a couple changes, namely, I am going to add a tube between the front and rear legs about half way down, and I am going to change the lower shock strut mount. The current arrangement was chosen so that I could use the the wheel penetration skis I have. I put the skis on and realized that I could just extend the axle a bit farther inboard, through the inboard mount of the ski and put a yoke on the bottom end of the shock tube. This should alleviate some of the bending moment in the gear leg during landing.

 

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Cabane Landing Gear for Kitfox 4.pdf

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Posted

Well you put a lot of effort into making this gear and the PDF as well.  Hope it works out for you and does all that you ask of it.  JImChuk

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Posted

Have a question. For the rudder cables there is a section next to the seat that has a 5/16" O.D. plastic guide tube that gets inserted into short pieces of 3/8" x 0.035 tube at either end. These pieces are about a foot long or so. Is that tubing something special or just run of the mill polyethylene tubing from the hardware store?

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Posted

Thanks Jim. Run of the mill polyethylene it is.

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Posted

John. Thanks! I immediate saved your .pdf via Facebook. I also spent nights studying cub-style landing gear. As both commercial options (groove and cabane gear) are out of scope, I probably also will end up making my own...Thanks again for your time creating the file.

Question regarding the bungee. Is your planing to go with the wraps? What about using fabricated rings? Both options: How to determine correct force/tension?

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Posted

John. Thanks! I immediate saved your .pdf via Facebook. I also spent nights studying cub-style landing gear. As both commercial options (groove and cabane gear) are out of scope, I probably also will end up making my own...Thanks again for your time creating the file.

Question regarding the bungee. Is your planing to go with the wraps? What about using fabricated rings? Both options: How to determine correct force/tension?

So for the bungees I haven't settled on a diameter or number of wraps. What I can say is that on my particular design the bungees will need to provide about 1.58 times the force of the original bungee setup to provide the same amount of "cushion". I plan to figure out the amount of stretch the original bungees had and then tailor the new bungees to provide the same amount of force. This is based on the geometry of the gear as shown in this drawing.

 

 

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