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KF III rigging

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Posted

I'm working on the final rigging of a KF III rebuild project before I start covering. Seems the instructions in the builders manual are pretty skimpy or maybe it's just me. Is there any information on the amount of travel(in degrees) the flapperons should have when functioning as ailerons/flaps? Do you just set it up the way they say and get what you get? I'm also having trouble understanding why they say the left wing is non-adjustable it has the same rod ends as the right wing, do the mean you just adjust the right wing to match the left. Any ideas, suggestions ?

thanks

EG

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Posted

I'm working on the final rigging of a KF III rebuild project before I start covering. Seems the instructions in the builders manual are pretty skimpy or maybe it's just me. Is there any information on the amount of travel(in degrees) the flapperons should have when functioning as ailerons/flaps? Do you just set it up the way they say and get what you get? I'm also having trouble understanding why they say the left wing is non-adjustable it has the same rod ends as the right wing, do the mean you just adjust the right wing to match the left. Any ideas, suggestions ?

thanks

EG

Sounds like the manual you have is still talking about the model II where the left strut was fixed and you could only adjust the right wing. The initial twist in the wing is built in. Just make sure that you level the fuse and wings per the manual and make both sides match for initial flights (if you find that it wont fly level hands off you can adjust one wing or the other to get it perfect). As far as the flaperon action, you should set the flaps for a maximum of 15 degrees, and what ever you get for aileron action is what you get. It is easier to do all your adjusting now before the plane is covered than once it is done. I finished mine in the winter time and did not have room in the garage to put both wings on so I did the final after it was covered and it makes it a little tougher to get to some of the bolts, but not too bad if you pull the seat out.

:BC:

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Posted (edited)

EG-

It sounds like we have the same M-III 'Manual', more like a mish-mosh of earlier manuals with lots of revisions and even 'final installments' of the M-IV manual. At first I thought it was an improvement over my sketchy Avid Mk-IV manual but, after going thru it all, I dunno...

In any event, you're right, CF-17 refers to left wing lift strut as non-adjustable. However, Step (24) pg. W-21 of the 1 Sept 90 M-III Manual says to install (4) rod ends etc. Also, the rigging info I have on pgs CF-17 and CF-18 are for Model "Kitfox" (with no model # designation), pg. CF-17 is noted Revision 2 and dtd 19 Nov 85, and pg. CF-18 has blank revision or date notations. If the pg just says Kitfox with no model designation, I assumed it was for earlier models. That does call into question the 'instructions' on pg. CF-18, as well as the continuation of Steps (71) and (72) on it's backside, pg. CF-19. Interestingly, my pg. CF-19 says Kitfox M-II, Spinner Assembly, Rev.3, 31 Aug 89 but contains only the flaperon rigging info.

Clearly, the manual is light on info but I agree with Leni's 15* degree suggestion. Most everything I've read leads to it. The original builder of my M-III penciled in copious notes and, on Fig. CF-12, he drew in flaperon down deflection of 0*-23* degrees from neutral but I intend to check deflection and reduce to 0*-15* degrees if necessary.

A couple other items to note:

- a short blurb in the attached Kitfox Owner Newsletter states:
"The flaperons neutral position, as shown in Fig. CF-12 page CF-18 of the construction manual, can be safely set at 1-3/4" below the front spar. This may greatly facilitate the rest of the rigging procedure."

- when setting flaperons to neutral, the fuse leveling procedure is on pg. F-21 of the 01 Nov 90 M-III Manual, took me a while to find it and it is different than leveling procedure for later Kitfox models or the Avid.

- post by another M-III owner:
"When I got my model III the flaperons were set so that a deflection of the ailerons would cause the flaperon setting to reduce to about half. I thought that was probably putting unnecessary stress on the mixing box so I adjusted the flaperon so it would just start to reduce the flaperon setting with full aileron deflection. The results of this adjustment were: the flaperons can now be used as a slight attitude adjuster... The nose goes up slightly with flaperons fully retracted. As for the use of the flaps I noticed no difference at all."

I saved some info when rigging my Avid Mk-IV. Because the KF-III and Avid have an almost identical mixer and flaperon setup, it may be helpful for you. Just keep in mind, part numbers are different but rigging procedure will be similar.

- post by another Avid owner:
"Thinking it over, I dug out the destructions and there was an update! This plane and others with “flaperons†use a mechanical contraption to provide aileron control and flap, but in reality, they are “Trimerons†as using too much flap input reduces the effect of the aileron control and will cause control reversal with too much flap deflection.
AVID warns not to use more than 15* degrees, but they also suggest starting with a negative 6* degrees to provide more trim effect, rather than use the elevator trim. The verbiage also said that this would make the aileron control HEAVY! AHAH..... back to the first set of blurb, and they say to use minus 3* degrees, which I reset them to. I also made certain I had just 13* degrees of travel
, as the flaps don't work like conventional do."

The following is credited (with many thanks) to Graham Laucht:

"This is the text from a note I wrote for our locals builders several years ago to help identify the necessary steps in setting up the flight controls particularly the flaperons. The builder's manual never quite seemed to deal with the essentials.

Flaperon rigging

1.. Assemble the Control Column so each control stick (F16) is parallel with its neighbour. Adjust the length of the Connecting link F18 to arrive at this point.

2.. Check the angular movement of the control stick is equal each side of centre (+/-30 degrees). Trim any excess metal from the "doghouse" if necessary.

3.. Assemble the U joint assembly F47, F5, F39 etc and temporarily assembly the Front Bellcrank F5. Check that in the full range of the control stick the U joint remains free and is not bound up or in contact with the Control Column Housing F15. Re-assemble the link assemblies, change bolts to Clevis heads if this helps. Cutting off the port end of F15 at approximately 45 degrees helps eliminate a lot of foul ups with the moving parts. Placing packing beneath the half round wooden supports and the end pivot bracket might help in obtaining smooth motion. Adjust the vertical position of the front bellcrank with washers if necessary.

4.. Temporarily assemble the F19(A) Aileron push pull tube with the front rod end joint F40 and lay the tube so that the aft end is near the aft bellcrank but disconnected. Ensure the rod end bolt doesn't foul with the carpet or floorboards.

5.. Adjust the links F38 & F39 until the relative movements of the push pull tube are equal for control stick deflection.

6.. Assemble Bellcrank F6 to the Aileron push pull tube and with the control stick locked in the vertical position adjust the rod end fitting F40 until the bellcrank pivot bolt and output link forms a line parallel with the mixer pivot bolt.

7.. Hopefully by now the angular rotation of the F6 bellcrank is equal about this imaginary parallel line for deflections of the control stick. If not adjust the fitting either side of the front bellcrank until this is satisfied.

8.. Assemble the mixer pivot arm F1 and connect the male and female rod end fittings F39 and F38 adjusting them so that with the control stick vertical the mixer pivot arm is perfectly horizontal. Check that the angular rotation of the pivot arm is equal about the horizontal for deflections of the control stick.

9.. Now connect the Flaperon bell cranks F7 to the mixer arm with the male and female rod ends F37 and F38 from the flap bellcrank F8. Initially adjust them so that the Flaperon bell crank inboard arms are parallel with the mixer arm. Check with the control stick locked vertically that the Flaperon bell cranks are parallel by laying a straightedge across them. Adjust the rod end links from the flap bellcrank until this is true. Check the angular movement of each flaperon bell crank is equal for control stick deflection. That is to say that the amount of up travel matches that of the opposite arm and likewise the amount of down travel. Because of slight differential action here the amounts of up and down travel are unequal.

10.. Assemble the Flaperon push pull tubes F21 and temporarily fix the Vertical swivels F51 etc so that the Flaperons can be connected.

11.. With the stick locked in the middle the neutral angle of each flaperon must be equal. If not adjust the length of the push pull tube by adding AN4 washers between the push pull tube and the swivel. If gross errors are adjusted by altering the lengths of the threaded rods F37 then the mixer will be unbalanced.

12.. Check the angular movement of the flaperons is equal for deflection of the control stick. Again the movement up and down will differ due to a degree of differential action.

13.. Finally set the flap handle in the neutral position so the top end of the flap bellcrank is parallel with the mixer pivot bolt. Use the Flap push pull tube F10(A) F40 rod end to make this adjustment.

14..
Adjust the threaded links equally until the flaperons are set to zero degrees incidence and check the actual angles. Pull the flap handle until with the control stick locked vertical the flaperons droop by 15* degrees and adjust the stop bolt.

15.. Check the angular movement is equal for deflection of the control stick allowing for differences due to differential action.

16.. Fit the turtledecks and check that the movements are equal and not affected by excess friction from the nylon bearings.

17.. Eliminate any lost motion through slack or loose bolt assemblies and similarly remove any source of binding or excess friction from the system.

This is an ideal situation but takes no account of build errors particularly in locating the flaperon hinges on the wing ribs. Similarly inexact drilling of the

U joint blocks F2 can throw out the accuracy of the system. Sometimes compromises have to be made to ensure the wings fold properly.

- This text is from another missive on identifying potential problems:

Normal problems are generally a failure to assure the system is working symmetrically due to errors in the cockpit assemblies or in the mixer main arm. If this area is remedied then often the residual problems are soluble. One problem that is not easy to solve is due to dynamic changes to the rigging in flight. One example in particular trued out on the ground but was a nightmare when airborne. This turned out to be additional friction in the flaperon bearings and especially the turtledeck bearings which was developed asymmetrically in flight. Ground checks showed appropriate opposite flaperon deflection with stick input but airborne only one flaperon was downgoing on one side but upgoing on both. The result was very poor control harmony and a lethal turning stall characteristic where instead of the aircraft rolling out of the stalled wing it rolled in.

Another showed unusual pitch effects with roll control and was found due to gross errors in drilling the front spar carry through holes resulting in one

wing being swept back and the other swept forward. Simple test for imbalance, time the period between rolling from 30 degree bank left to right and the other way about. It should be the same. At approximately 70mph with the stick held central pull on the flap lever in stages and determine

which way the aircraft rolls. It should remain wings level and only pitch down. Yawing or rolling would imply imbalance.

Stall the aircraft clean and with flaps set. It should stall straight ahead or have similar benign characteristics at any setting. This assumes the port wing strut rod end bearing has been adjusted to eliminate any nasty wing dropping tendencies.

Stall the aircraft in gentle co-ordinated banked turns with various degrees of flaperon set and ensure it rolls level and does not have any tendency to "tuck in" to the turn.

Ensure that at maximum flap setting there is no tendency to control reversal or asymmetric stall. Experience has shown that this may occur above 15* degrees on some examples.
"

Graham Laucht

Hope that helps some.

[edit] wrong attachment

Kitfox_O_News_Sept1989.pdf

Edited by dholly

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Posted

thanks guys, that helps alot.

EG

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Posted

Well I found why mine were set as they were. The KitFox M-III Operator's Manual pg. 7 says to set flaperons at 0-23* degrees. I posted a copy of the OM in the Kitfox III forum.

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Posted

Here's another helpful rigging tip from the May 1990 Kitfox Owners Newsletter:

Flap Limit Stop

In the June, 1989 issue of the Newsletter, we showed you how to build a Flap Limit Stop; to find the proper degree of flap for your "stop", first find the neutral flap position as shown on page CF-18 Fig. CF-12, of your Construction Manual and mark that position for the "zero flap" setting. Next, move the control stick all the way to the left (or right) until it stops. While holding the stick in this position, slowly pull the flap handle up until it starts moving the control stick toward the center. When the top of the stick has moved toward the center 1-1/2 inch, that is Max Flap. This step can be completed after you have finished the rigging process on pages CF-17 through CF-19 of the Builders Construction Manual.

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