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Subaru is a better choice in a 5-7 Kitfox or an Avid that has had the fuselage mod (16" stretch) to accept the weight.

A Kitfox 4 with a (light) Subaru is a single place airplane.

The motor itself may be fine, but its not for this application. Keep looking.

Thanks for that bit of info Paul We as in those who actually have a plane flying are pushing the limits as to how far these planes were designed to ggo and how far they make it. For a design that was built 30 years ago and meant to get people flying cheap while landing on a grass strip, it is amazing how far we have taken them. I went through the other group and wrote down all of the modifications Steve Winder put down and with those I was able to upgrade my fuselage to Mark IV specifications with the B model width and then made my own copy of Merle Williams fuselage widening kit. I have been meaning to write them down here, At the same time I have been looking at the damage done to the planes and re-engineering a few things, I have an I dea on the bush gear to put the strength in that it needs, But I need to Know what size tubing the gear is made out of,and preferably how hard the landing was that caused the damage. I have priced out 18 inch travel Rok Shocks and have an idea there, but I need to know what the weight comes to, designing it as a bolt on could be a bear butsince there is no fabric around that area of the plane It should be do=able with minimal welding, Now I just have to look at Steve Winders Numbers again.

    The gear I dsigned for my own kept the same positioning back from the leading edge, but went out 14 inches wider and 8 inches taller, those he had put tubing specs down for, now its on to uncharted territory, and money, The one thing I Know is that up to the Highlander, they used the same 2 1/2 by .063 tubing for the spars and were willing to sell the inserts at a reasonable price. I used 1/4 inch plywood in mine figuring the original load test was done without anything in it. I should have kept building but at the time I was looking for a 2 place airplane and had some weight to lose, now 210 lbs lighter The Avid Became a 2 person plane even if I had not made any modifications.

Another weak point that needs a triangle is horizontal on the lower longeron and just ahead of the seat truss under the floor boards. My MK IV has a triangle formed by tubes at that point that I filled with plywood after repairing the structure there.

Yeah, that mount looks different than mine. Because my muffler actually mounts to a mount coming down off the engine mount itself. So the engine and muffler vibrate/move at the same frequency whereas with this set up because the mufflers attached the firewall and the engine vibrates around the firewall, it looks like you're asking for a leak. Bryce

Chris,

Great!  Let's chat, could you PM me your phone #?  I can possibly swing by this weekend, even if weather's not lookin up it would be worth a trip.

I have talked to ChrisB about the nosewheel - He liked the spring-loaded nosewheel attached to the steerable linkage best - If I remember right - this nosewheel is no longer made - I have one and have shared photos & dimensions of it with Steve and Amie. There are videos of it on a Challenger(?) and photos of it on Chris' plane.

I know this don't help answer about your springs.

Can you lighten the springs?

EDMO

I think the Pipers have survived the hard landings where the Avids/Foxes have gotten bent up because Piper longerons are a lot bigger and heavier than the Kitplanes - not engineer - just observing.

EDMO

How hard do you have to hit to bottom out the spring or the bungee gear? Taking the lead out of the tail and the 150lb engine off the front would be a good place to start. Like I said before, fly the airplane on to the runway! The hell with the full stall landings. Like Leni said once before, you are decending at around 1000ft per minute, If you don't judge the flare just right something is going to bend if you hit hard. I can't imagine the stress on the rest of the plane. My door latches easier on the ground than in the air. So the airframe must twist and turn while flying. It really must twist on a hard landing.

Perfect, thanks guys

The NSI is a very heavy engine. Parts and support are also not available for it. My plane had an NSI on it when we bought it and it reamained unairworrhy for many years until we saved it and yanked all that stuff the nose, removed the 40lb weight off the tail, and put a 582 back on it.

Slightly off topic, but is that a stock motor mount? Mie looks nothing like it on the engine mounts but I don't know if mine is correct or not. They used to sell just the ball and sockets for the 2 stroke exhaust it might be time for a new set, they do wear out eventually.

Mark,

I'm back in town. Could not access this site while gone. Any time you are in the area I would be happy to show you my planes, introduce you to my two other local Avid owner friends and get you a test ride/drive in one.

Chris

My opinion and $5.00 might get you a simple coffee at Starbucks, but I am a believer in the 912 all the way for the kitfox 4-7's.

The additional weight of the big direct drive 4 strokes will kill performance way beyond what you can imagine. Most of these planes whether Avid or Kitfox that have Continental or Lycoming conversions require additional weight in the tail to reach an acceptable weight and balance. I have seen first hand the difference. Flown in a 100 HP 0-200 powered KF 5 and a 80 HP rotax KF 5 and would choose the 80 HP Rotax powered hands down for short field performance and useful load. The ONLY place the 0-200 powered KF 5 outperformed the the 80 HP rotax was solo flight cruise speed.

Chris

Great topic since I have been researching gear design for the last week.

John Roberts said the front gear leg takes the greatest load and is in compression so that is why it needs to be beefier and braced like your new version is to prevent it from collapsing.

Extending and widening the gear also requires bigger diameters and wall thickness to prevent tube failure on compression.

Roberts also said the gear and cabane attach points need to be designed so the forces are applied inline with the longerons instead of twisting the longerons.

That explains why most cub style cabanes use separate attach points from the gear leg.

I was surprized to see at the High Sierra fly in that Pops Dory was not using bungees on his new Cub.

As long as the springs have enough travel to prevent metal on metal for reasonable hard hits, they sure look like the way to go.

My off road car has 2 springs per shock.

When lighter spring bottoms out the stiffer second spring takes over for progressive action.

Hi Willis!

It should be the same as model A-D, and Magnum.

Chris Bolkan

I'm back looking for opinions.  I have web-found a KitFox 4 with a Subaru E-81 NSI engine.  I have heard mixed reviews on this engine.  Anyone with experience or heard credible reviews? Mark in Sun City West, AZ

Willis,

How does the Fat Avid compare to the Magnum? I have the W&B specs for the Magnum.

EDMO

This has been somewhat of a hot topic lately so i thought I would post some various gear designs to hopefully spark some discussion from someone much smarter than me on it. The discussion is on the strength of the cabane strutted spring gear.

Airdale gear

Version two contains lighter springs a thicker wall tubing the addition of a cross brace between the front and rear leg where another set had failed.

New brace the first set didn't have

HighWingLLC gear

Super Cub Geometry on Pops Dory latest cub using springs instead of bungees

Murphy Bush Gear

Rans Brand New "Monster" Gear

Roberts Bush Gear

So it's obvious there are subtle differences between every set, but generally speaking they are all similar. So what makes one set work and another one not???

There's nothing high tech about the reinforcement.

You just cut triangles from plywood and hysol them onto the openings in the truss. Make note of where the bungees pass through and don't fill in those openings.

Bandit, my avid isn't going anywhere.. The $450 fuel for 4.3 hrs flying is going to put a dampner on my 180 just for fun time! Holy cripes!

239 572 0021

Yes, there's more things to do, call Rotax ric

The Avid Model C that I measured to find out how the gear placement compared to a Kitfox had an upside down 582 with cheek radiators.

I now understand why the upside down 582 in an Avid allows the cowl to be lower than a Kitfox for better visability.

It appears that the  top 4 of the 6 Avid 582 engine mount bolts would come  close to fitting the Kitfox.

Otherwise the Avid and Kitfox engine mount attachment to the fuselage firewall are not even close to interchanging.

Without a custom engine mount I will not be lowering my Kitfox cowl for the better Avid visability. 

I measured an Avid Mark 4 and an Avid Model C today and you are correct, the gear attach points on the longerons are almost Identical to within a 1/16" of my Model 2 Kitfox or less and could be adjusted with a file.

All 3 aircraft are within a 1/2" of axle placement in relation to the leading edge of the wing when the fuselage lower longerons are level as when doing C. of G. calculations.

Av8r3400 said his friend recently ordered a swept forward gear for his Model C Avid, which according to Trackwelder and my measurements should fit the early Kitfox's that do not have the forward float attach points.

According to Grove's website, their Avid Mark 4 TD gear costs $300. more and weighs 8 pounds more than a Model 3-4 gear.

The reason for the increased weight is the extra material needed for the forward swept feature of the gear and that it is 5" instead of 4" wide where it clamps to the attachment brackets.

Av8r3400 said the Grove gear on his Model 4 increase  his empty weight 12 pounds over the stock bungee gear which I could live with.

Since my Kitfox would require the swept forward gear, the weight increase would approach 20 pounds which I do not think I can live with.

Thanks for all the comments to help me come to a conclusion.

Where do I find Steve Winder's posts on how to reinforce the seat-bungee truss?

Thanks  Herman

 Hi guys, well things are getting closer with my fat avid and i.m just wondering if the datum line and formulas  on it, is like the avid c . I have the manual walking you threw it and have a friend thats did them before but want to make sure the extra 18" in length dont affect  using the avid c method of doing the W & B. Randy if you happen to have any of your numbers handy and get a chance to post them ,that would be appreciated, Thanks Willis