How can i check the dihedron of my KF2 ?

[GDN]

Still searching about why i have to put a left stick constant force for not taking roll i'm going to check the dihedron of my wings.

Is anybody have a simple solution for that ?

Thanks

[Av8r3400]

Roll-trim adjustments are made at the rod-end bearings where the lift struts mate to the wings.

[GDN]

OK but how can i check the good settings ?

[Geowitz]

Easiest way is to use a "smart" level. It's usually a 4 foot long level with a digital readout. You can use a standard level with spacers as well(but not nearly as easily) if you can't get a smart level. I'm not sure what the standard angles and washout is for a model II, but you should atleast see if the wings match each other. First level the plane in all directions using the bottom of the fuse as a datum. Then place the level in the same spot on top of each wing lengthwise and see if the dihedral angle is the same on both. Then place the level chordwise undernieth each wing rib near the cockpit and make sure that is the same. Then place the level chordwise undernieth the last rib on each wing and make sure the angles match. The angle of attack of the outboard rib should be less than the inboard most rib. Probably around 1 degree less. If everything matches up you may want to look elsewhere for your problem. If you can't find the problem anywhere else it may be a warp somewhere and you can adjust the rod end bearings of the lift struts to trim the left stick force out. This would be accomplished by either raising the back left wing fitting or raising the front right wing fitting. Just make sure you preserve the washout of 1 degree(need to confirm correct washout degree though), Go 1/2 turn of the bearing at a time and try it out. It won't take much. You're basically turning your whole wing into an aileron.

[Lion8]

Is it possible to use a lazer level?

[Geowitz]

I suppose it's possible, but not realistic. I would imagine that the setup and measuring would be extremely hard to duplicate on both wings and get accurate measurements. You could probably find the dihedral, but it's the washout(twist) that would be very hard to get relative to each other.

I would think it would be easier to just use a regular 4 foot level and measure the distance to level from the surface you are checking. Basically you hold the level level and against one side of what you are measuring and then measure the distance from the object at the other end of the level. Kind of like in this picture. Here I was checking washout with the smart level, but also had a ruler on one end to measure the actual dimension of one degree of washout.

Another note - A wing with different dihedral on each side won't necessarily cause a tendency to turn. The fuse will just hang off to one side to compensate and find equilibrium.

[Dorsal]

And the wings will not line up when folded. (an easy check)

[GDN]

Sure when i unfold my right wing (to put it in flight position), i have to push up the tube to insert the cotter pin to safety it ?

So perhaps the problem is located here ?

[Dorsal]

Not likely, I think you should be looking at washout or the relative angle of atack on the outboard end of the wing. I found this was best done with a digital level as others have suggested and is adjusted with the rod ends on the lift struts.

[Geowitz]

Yeah, you really need to at least try and locate a digital level and check the washout/twist of the wing. That is the most likely cause of your issue.

[Geowitz]

It is definitely a possibility that your issue with having to push up on the right wing is a symptom of your problem as this indicates a lower angle of attack on your right wing thus causing a bank to the right. You could shorten the back right fitting which will cause the spar to raise up where it gets cotter pinned to the fuse so you won't have to push up on it. However, you want to make sure you still preserve the washout of the wing so your stall tendencies remain friendly. This where the smart level is really the best tool for this job. You want to make the plane fly level and have as close to 1 degree of washout as you can get to maintain good stall characteristics.

[avidflyer]

A smart level would be nice to use, but a 4' level and a tape measure will tell you the amount of twist/washout in each wing just as well. Just put the level up against the bottom of the wing at the fusaloge, lower the one end of the level till it reads level while holding the tape measure at that end. Read the tape. Do the same at the other end of the wing and subtract the inboard dimention from the outboard one and you will have the amount of twist in the wing. I don't remember what all the earlier post said, so sorry if I just repeated someone's elses thoughts. Take care, Jim Chuk

[GDN]

Thanks for all this answers will check this when i'll become less busy ;-)

[jeffcoaj]

I have been looking, but I haven't found a definite dihedral angle prescribed for the kf2. I am getting 1.6 degrees for each wing on kf2 ( measured on the front spar on both sides.) Is this correct? I've noticed on the kf4 and up to the ss7 that the dihedral is considerably less, no more than 1.2 degrees. close to 0 for the ss7. Thanks.

[t j]

You're not going to chnage the dihedral much once the wings are built. You can change the twist a little with strut adjustments. I would adjust them to where it flies straight and not worry about the dihedral.

[jeffcoaj]

Thanks for the response.. I am still at the point of attaching the strut brace to the spar, I can still attacH the spar wherever needed to adjust the dihedral. I also have not drilled the bottom holes yet to the spar. Is 1.6 in the ballpark?

[Av8r3400]

I was under the impression that dihedral was set to a given distance measurement, rather than an angle. Similar to how the washout is set during the buildup of the wings.

Like 2" at the center via a string from tip to tip… ?

[jeffcoaj]

Yes, there is a distance that the strut brace is set from the root. A small adjustment significantly changes the dihedral. as a sanity check before drilling holes, I wanted to see if 1.6 degrees is close.

Thanks for the quick replies!

[n85ae]

Very easy to use a laser level, wish I would have used one when I built my
Fox it would have simplified a lot of things. My plane is very true, but I didn't
use a laser level. I have used one extensively with the new plane, and it is
the superior tool.

Just have to use the right combination of (1) figuring out what you are trying
to do, and (2) do it with the laser level.

I also cross check the lines from the laser level with a regular level.

If you work in a hangar where you can dim the lights that's the thing to
do.

Jeff


Is it possible to use a lazer level?

[t j]

I would say you are in the ball park. I am doing my condition inspection right now, I'll go check and get a couple photos and make some measurements. Mine is a model 4 but will give some numbers for reference.

Okay here's what I have. I stretched a string tight between the high points of the outboard ribs (Right at the trailing edge of the false ribs).

Measuring from the top of the root rib to the string is 2-7/8" on each wing. Using a smart level I get 1.3 degrees on the right wing and 1.2 degrees on the left wing.

Note: At first it measured 1-3/4 on each wing then I sighted down the string and it had a sag in it. I had to pull it really tight to get the sag out then measured 2-7/8".

I was holding the tape with one hand and the camera with the other and didn't get the shot straigt on level with the string. It is 2-7/8" when you look straight on.
7800

This is what it looks like. I have had people ask if there is any Dihedral. It is hard to see without the string. Flys beautifully hands off.
7801

[jeffcoaj]

Thanks

That is interesting, this way of measuring was not listed in the KF2 manual. I really appreciate it. you guys are awesome.

[n85ae]

What Tom is doing with string, I would use the laser level to do, but the string method works well. The string doesn't really sag but, it can the laser
casts a perfectly straight line. You can just put a rule on like Tom is doing
and just move it slightly so the beam hits it and measure the dip.

I think the string method was what I did as it was prescribed in the builders manual.

Jeff

[cgruby]

I had a similar question regarding my type III. The factory could offer no information on my plane, however said the newer planes were 1 degree.

I think I found the answer to my question in Service Letter #25. A 4 foot level beneath the front spar should read between 1.1 and 1.4 inches.

If you want to get that in degrees, then the Tangent of 1.3/48=0.0270. The angle whose tangent is 0.0270 is 1.1 degrees. That's for each wing. Mine measures 1.25 degrees. I think that's close enough for me.

Cheers,

[jeffcoaj]

I could not tell if bulletin 25 would apply to KF2 since the initial distance from the root was different from the value listed (96.75 and 97.75). For the KF2, the initial distance is 86.125 inches from the root to the support hole on the strut brace.

So the dihedral is a little more pronounced on the KF2. Also with the KF2, the only adjustment rod is on the right rear wing, so I have less tuning available.

[jeffcoaj]

Looking at bulletin 25 again, it is giving a rule of thumb for twist. I think I will look at that again and do the 1.137 thing to see if the front and back follow this rule.

Thanks again-
Joey

[t j]

The 1.137 number is for 1/2 inch of twist on the model 4 and later wings. Look through your builders manual and see if you can find how much twist is built into the model II wings.