Model 2 adverse yaw?

[herman pahls]

I have hundreds of hours on my model 2 Kitfox.
The first 14 years with a Rotax 532 (C.G. was near the rear of envelope).
The last 2 years with a Jabiru 2200 (C.G is near the front of the envelope).
I like flying behind the Jabiru engine but find that in windy and gusty conditions coordinated turns are almost impossible and therefore dangerous. The 532 seemed to have much less adverse yaw (much easier to keep the ball centered). I am tempted to reinstall the 532 to determine if this is all in my head.
I added 4 pounds to the tail to move the CG more to the middle and still do not like how it flys.
I started flying a Piper Pacer 3 years ago and coodinated turns are a non issue.
When I found this model 2 kit in a barn 17 years ago I was advised to hold out for a model 4 because of differential aileron action on the improved model 4 controls.
I would like opinions from the undercambered Avid and kitfox flyers about what I am experienceing and is there a fix.
Are the model 4's handling vastly improved?
Thanks Herman Pahls Oregon 541 404 6464

[SkySteve]

Herman,
I fly a model I with a 912, 80 HP. I cut the vertical off, replaced it with a model IV vertical & rudder. Huge difference in a good way.

[rogerh12]

My model 2 with a 582 engine had horrible adverse yaw. People seem surpised when I say that, but I'm glad someone agrees with me. Maybe it was because of the heavier engine, I don't know. All I know is it was bad.
Now I have a model 4, for the reasons you mentioned before (but it's now flying yet)

Roger

[jiott]

I believe the Model 2 did not have aileron/flaperon differential. The differential (less down than up travel) makes a big difference in reducing adverse yaw because the drag on the outside wing is reduced in comparison to the inside wing. I don't know, but maybe the Model 2 flaperon linkage could be modified to provide differential.

Jim

[Av8r3400]

I believe the I-III flapperon mixer is virtually a direct copy of the Avid Flyer units. There is a modified part offered by Airdale (http://www.airdale.com/) that adds an amount of 'differential' to the aileron control. The part is something like F-7a or similar. Brett would know off the top of his head. This may help your situation.

Additionally, is there built in vertical stabilizer offset in the early Kitfoxes? If so, wouldn't this be in the opposite direction when going from a two stroke to a four stroke Jabaru (Prop rotation direction). Could this be part of your problem?

[toekh]

I have about 100 hours in my Kitfox 2 behind Jabiru. There is no weight added when they did the conversion from Rotax 532 to the Jabiru engine. The start battery is placed about 3 feet behind the seat. I have wing tanks.
I have very little adverse yaw, almost none. When some of my buddies try to fly my plane, almost everyone of them overdo the rudder movement. In the other hand I have to push right rudder a little bit constant to fly in a straight course.
One of my friends formerly owned an Avid Flyer, similar to my plane. He also had a Jabiru engine in his plane. He was able to trim his aircraft flying hands off in every plan and his method was changing the engine angel with some shims in the engine mount.
Must say that I love the Jabiru engine, even if it takes a few more feet’s to go off the ground compared to a Rotax 532/582. In the other hand it sounds like a real airplane and burn 2-2,5 gph at 55 kt. And it looks like a jewel ;)

[dholly]

I believe the I-III flapperon mixer is virtually a direct copy of the Avid Flyer units. There is a modified part offered by Airdale (http://www.airdale.com/) that adds an amount of 'differential' to the aileron control. The part is something like F-7a or similar. Brett would know off the top of his head. This may help your situation.
Looking at my KF-III mixer, I do not believe these parts are directly interchangeable. The Avid mixer differential mod consisted of:

- replacing (2) existing p/n F7 bellcranks with (2) new p/n F7a bellcranks (the new bellcranks have noticeably more curve, as seen in the attached comparison).

- replacing (2) p/n F37 straight ~2-1/2" long threaded-end rods with (2) new p/n F37a bent ~5" long threaded-end tube rods.

I've also attached a pic of the (unpainted) F7a and F37a modification parts installed in my old Mk-IV mixer.

[FoxDB]

I have been interested in the differential flaperon mod by Airdale for my Kitfox 1. I have not checked to see if the Airdale parts would fit the Kitfox Mixer. If not I am planning to do a CAD layout to investigate the motion. I have Raven drawing that detail the Kitfox/Raven parts. I just need info on the Airdale parts. If anyone has additional info on this please post.
Thanks Dave

[herman pahls]

I want to thank those who responded with possiblities why replacing the Rotax 532 with a Jabiru 2200 would induce more adverse yaw on my Model 2 Kitfox.
I recently spoke with Joey who posts on this forum ( Avid flyer with 582 and E-box) regarding what he feels may be off with my Model 2's rigging now that a Jabiru has replaced the 532.
Since I had just flown the Kitfox I was reminded that the flaperon forces are much higher with the Jabiru than with the 532.
The flaperons have a very effortless feeling when checking control freedom at run-up.
Joey mentioned that flaperon reflex can cause higher aileron stick forces.
With the 532 I adjusted pitch trim with the flaperon lever.
With the Jabiru the flaperon lever is all the way down to trim which would give more up on the trailing edge of the flaperons than what I flew with the 532 for years.
So is more flaperon reflex when the trailing edge is higher?
The Jabiru added 30#'s bringing the empty weight to 520 #'s which moved the CG forward versus the CG of the 532 which was towards the rear.
The 532 and Jabiru CG's were or are in the envelope.
The only other change made when installing the Jabiru was going to 1 inch unfaired lift struts from the original 3/4 faired lift struts.
Some of you questioned Vertical fin offset and wing twist as possible issues.
Any further ideas why I no longer enjoy or feel comfortable flying this Kitfox ( especially in gusty wind or turbulence) with the much higher flaperon forces and the almost impossible ability to keep the ball centered in turns?
Thanks Herman Pahls Oregon 541 404 6464

[cap01]

herman , i think there is something to that vertical stab offset . i have a very early model IV 1050 with a 912ul , thats right at the change from III to IV . i have the same problem with the ball . i have over 300 hrs on it and havent mastered it yet , just live with it and havent spun in yet . i pretty much eliminated a rigging problem and even installed a rudder trim tab which helped a little . appears to be more pronounced when banking to the left where the ball takes off to the right . ive flown speedsters that dont do that . the idea of replacing the tail sounds good if a person had one .

[C5Engineer]

Herman try Pulling on some flap at cruise speed. You will get a nose down moment but see if your roll forces lighten up. The more positive ( trailing edge up) on your dlapweons the stiffer your roll rate will be. This is what I do when I am yanking and banking down low. It's out of trim but when your maneuvering you won't really notice it.

[herman pahls]

Joey
My prop is off getting repitched so I will have to wait to experiment with the roll pressure on my Kitfox.
Dave (FOXDB) from Idaho reported to me that by pulling part way up on the flap handle on his model 1 the aileron control pressure became very light in comparison to when the lever is all the way to the floor.
Joey, I am curious how you knew this was the problem.
I assume having the flapperons up too high on the trailing edge would act like a spoiler and decrease lift and increase stall speed.

I have room to move the leading edge of the horizontal stab down another 1/2 inch.
Hopefully that will be enough trim so the flaperons can return to the position that has minimal stick pressure in roll.
Hopefully repostioning the flapperons will make ball centered -coodinated turns like they were with the 532.

Does anyone know if these early Avids or Kitfoxes have offset vertical stabs that would counter act for P-factor?
All those years with the 532 I never considered a rudder trim tab.
The Jabiru prop rotates opposite from the 532 and I have a 6" high by 2" long rudder trim tab bent at 40 degrees to reduce right rudder pedal pressure.

I want to thank those who offered suggestions and shared experiences.
Herman

[C5Engineer]

Herman I learned this theory by experimenting. I found that if I rigged my flaperons to where I had nose up trim using flaps the roll was far too stiff. I experimented until it would just maintain level flight in cruise. The roll is still a little stiff but in cruise it's no big deal. Like I said if I want to go play I just pull like 1/4" on the handle and it greatly lightens the roll forces but then it wants to pitch nose down. I'm in the process of adding some VGs to my tail which is suppose to help this dilemma. My Avid manual states that with some positive relflex it will increase cruise speed. I think I ended up with right around 5 degrees. This is with the mixer mod like what is posted in this thread..max in the directions with that mod was 6. Without the mod the manual stated to rig them at 2-3 degrees I think.

I don't' know about the Kitfox but the early AVIDS did have a tail offset to compensate for the Right turning Rotax 2 stroke. Your not the first person to have issues going from a two stroke to a 4 stroke. You can probably fix this with some shims on the motor mount. If not I made a tab with a scrap piece of aluminum and I stuck it to the rudder with some 3M double sided tape and rattle canned it to match my paint. Took me all of 30 minutes to make and works great.

[skelly]

Hi,

I know that this is an old thread but I wondered if anyone had a solution for making a differential flapperon action for the Mk2 Kitfox.

Any ideas ?

Cheers,
Skelly.

[avidflyer]

A few guys have changed out the mixer controls to the Kitfox 4 style. But it's a lot easier to have your slip skid ball in a good spot to see it and use it till your butt tells you what you need to do. Adverse yaw isn't that bad if you use your feet. JImChuk

[av8rps]

The early Avids for sure had the vertical fin offset. When they originally had the Cuyuna engine in them, and then later changed to the Rotax 2 stroke you were told to remove the offset and reweld it centered on the fuselage. I've flown a lot of Avids and Kitfoxes in my life and have to say that flying the early ones taught me how to use my feet better than any airplane I've ever been in (I learned how to fly in a J3 Cub).

As the models changed and improved / evolved they became a bit more stable in yaw, but overall might still appear a bit "twitchy" and unstable for your average Cessna or Piper pilot. Few will be able to keep the ball centered until they get a few hours in it (with someone that can teach them what to do and not do). Unfortunately, many will walk away in the first hour thinking these planes fly badly and aren't worth owning. But the ones that stick with it and learn how to adapt their skills to fly the plane correctly will really enjoy the airplane, recognizing its nimble flying qualities and the off the charts fun factor. But that is common with many airplanes that do some things other planes can't. Examples of that I have experience with, a Pitts Special and a Lake amphibian. Both can be demanding to learn, but awesome airplanes once you get past the difficult learning curve.

So I learned to love the adverse yaw as foolish as that may sound. Overall I felt the early Avids and Kitfoxes were more maneuverable because of it, but that is just my opinion. I flew Avids with and without the F7 differential kit and overall didn't think it did much. But again, I had learned to offset the shortcomings of the design by adapting my pilot skills to the airplane, more than thinking I would ever be able to get the airplane to fly more like a Piper or Cessna.

Avids and Kitfoxes are short fuselaged, long winged airplanes (aka High Aspect Ratio). Adverse yaw is inherent in those designs. Over the years Kitfox has improved it some, but it is still there. I own a couple early Avids yet, and a Model 4 Kitfox. Yes, the Kitfox is a bit tamed down compared to the early airplanes, but it is my opinion that if they got rid of all of the things some pilots don't like about the design, they would kill much of the fun that we love about these airplanes. I own a Highlander also, and it is a great flying airplane that feels more like a cross between a Kitfox and a Cub. A bit more conventional feeling you might say. But the Kitfox has a much sportier feeling to me that makes it a bit more fun to fly. So you have to choose your battles...

I personally love all of the various offshoots of the original Avid Flyer design. They all have their pluses or minuses, but in the same family they are all GREAT airplanes that I have never gotten bored with (unlike my experiences with most all the "trainer-like feeling" Cessnas and Pipers).

With that said, the earlier parts of this thread indicated some issues associated with other issues that indicated some flapperon, rigging, W&B, or engine offset issues. That would only make things worse to the point of making some of the known idiosyncrasies of the design potentially intolerable for even the best of pilots. So my comments above are based on airplanes not having any of those issues.