Wing Incidence

Question for the group:

I'm working on a 2003 classic 4 fuselage and one thing that is notable is that the rear wing attachment is much lower than on my KF III. Looking over another builder's 1995 vintage KF 4 fuselage his rear wing attachment height looks the about same as the KF III.

So when was the wing incidence angle increased and why? Can't make it go faster so is it to get off the ground quicker? This 2003 fuse has brackets for tricycle gear so is there a connection?

Just curious,

Mark Napier

not positive,..but a possibility,..is your kit a high lift wing kit?

you can check the incidence or angle of attack,..by leveling the tail horizontal stab..then take a level and lay it accross the top of the wing mounts,.. if you've got as scientific calculator ..you can check the angle , once you have the dimensions ,..using sine cosine and tangent dimensions to get the angle or just get a protractor :),.

most GA aircraft have a 6 degree incidence,..you'd have to ask John @ kitfox what the model 4 classic incidence is suppose to be and if there is a difference between the standard and high lift option.

if a high lift wing option was available for that model


Chase

Mark, here's a measurement from a 1994 vintage Classic 4. I am curious to know if it is different than your 2003. From the top of the front spar attach lug to bottom center of the front float fitting and from the top of the rear spar lug to the wing strut attach fitting are both 39 inches.

good idea TJ ,..but now measure from top front to bottom rear ..and top rear to bottom front ..this will show if there is a difference,..it can still be the same measurement top to bottom on front and rear ..but diagonally will tell the angle..
because the wing folds,..the pivot of the strut and the rear wing mount should be in line paralell to each other,..the difference from bottom rear, or pivot of the strut,.. to top front will give difference for the angle.

unless the whole plane ,,,meaning pivot of the rear wing mount and strut mount is tilted ..then to get the righjt AOA ,..you need to go to first post and level tail horizontal stab ..then take a level and set it on top of the wing mounts ,,hold the level at level and measure the gap between rear wing mount and bottom of level ,..then do the cosine sine and tangent measurements to get angle of attack,..

I'm guessing it is around 4.5 degree's

didnt do the math ..just a guess

Chase

Probably Saturday when I get back to the hanger but will write down some measurements then. I may already have those written down in my book.

I do remember that it is hard to get a good number for the rear because the door frame is in the way.

I'll try to get a couple of pictures too. The difference in the lengths of the tubes just above the side windows and the angle of the tube bracing just below the top rear carry through is very evident.

Cheers,

Mark

let me know the dimensions and I'll figure your AOA or incidence for you ..

sounds like someone might have modified it or ..that model did offer the high lift wing set up.

Chase

Mark, the measurements I took are not to establish what the incidence is, just to verify if there was a change in the later classic 4. My plane is finished so on the rear measurement the tape measure was around the outside of the fuselage. the front float fitting is a few inches ahead of the front spar and was just an easy place to measure that you can duplicate.

For what its worth. I can say from my experience rigging the wings and checking washout that there isn't hardly any and maybe no positive incidence on my Classic 4 anyhow.

Mark,

I'll take a stab at this one...

Way back when in the model II and III Kitfox days they had changed the wing incidence in an effort to be able to see over the nose better in flight. In fact I have a magazine cover somewhere showing a Kitfox 2 or 3 flying alongside another airplane that looks almost funny because the tail is so high in the air. Now I'm not sure what the dimensions were for those with that incidence, or if it was all in the wing or in the tail, but it is one of the reasons I believe that some 2's and 3's have very low top speeds compared to the 4's (aside from the obvious wing design changes).

Anyhow, it's free info, so take it for what it's worth. I'm sure someone may have some better, more exact specifications that may explain this better

Paul S
Wisconsin
M4-1200 Amphib
& M4-1050 soon to be a "Super Speedster"

Quote:

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Originally Posted by napierm

Question for the group:

I'm working on a 2003 classic 4 fuselage and one thing that is notable is that the rear wing attachment is much lower than on my KF III. Looking over another builder's 1995 vintage KF 4 fuselage his rear wing attachment height looks the about same as the KF III.

So when was the wing incidence angle increased and why? Can't make it go faster so is it to get off the ground quicker? This 2003 fuse has brackets for tricycle gear so is there a connection?

Just curious,

Mark Napier

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Hey Tom Jones,

It was snowy in Georgia (big deal here) on Saturday but I did get those measurements. They are pretty close to what you mentioned.

From the top of the front wing attach to the "flat" of the front float attach fitting is 39 1/16".

From the top of the rear with attach to the "flat" of the strut attach fitting is 38 11/16".

Mark

39.0625 minus 38.6875 equals .375 or 3/8" ..depending on the distance between the 2 points between the wing connection points,...let's say it's 27.5 inches center to center on the wing connect points,. that gives you a little over "2" degrees AOA if the pivot point's of the wing and the lower front measurement point is at 90 degree's to each other,and the horizontal stab is in the level position or perallel to the front and rear measurement points on the bottom ..

due to the style of the wing on the kitox,..this is not an accurate way to measure the AOA of the wing ..just the connect points the wing connects to on the fuselage.

Chase

Quote:

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Originally Posted by napierm

Hey Tom Jones,

It was snowy in Georgia (big deal here) on Saturday but I did get those measurements. They are pretty close to what you mentioned.

From the top of the front wing attach to the "flat" of the front float attach fitting is 39 1/16".

From the top of the rear with attach to the "flat" of the strut attach fitting is 38 11/16".

Mark

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Thanks Mark. I would venture given my crude measuring technique that there has been no change in the position of the Classic 4 wing attach lugs.

given that it was said that the points looked different compared to other kitfox's,.. especially the rear wing connect points ,...if you question the positions I would seriously check with John McBean on the exact postions of the wing connect points,..especially if the kit was pre owned by another ,..the pre owner might have been building a glider tow plane using a kitfox kit ,..or hang glider tow plane ,..this could explain a change in the wing incidence.
If it has been changed ..all written performances of the wing would be null.

but if a "crude way of measuring " gives you a warm and fuzzy feeling about the connect point positions ,.or AOA ,..don't sweat it

I personally would certainly check with John if I had any doubts

Chase

Photo of the rear wing attachment from my KF 3 and the ~2003 KF 4. It is much lower in this area than a model III and an ~1993 vintage IV I looked at for comparison.

Also, the tubes in this whole area and around the door are larger. The fuse is notably heavier.

A better way to know if the incidence really is different would be to put a straight edge across the top of the horizontal stabilizer, letting it extend all the way to the front of the door along the side of the fuselage. Then measure the distance between the bottom of the frt and rear wing attach pins and the straight edge. That would be the best way to know the true incidence numbers between any of the various kitfoxes. Of course you do have to take into account that you can adjust the horizontal stabilizer with the extra holes in the front attach bracket in the tail.

I'm not sure how much the 3 and 4 are different, but I'm pretty certain you will find a big difference between the model 2 and the Model 4.

It would be very interesting to see how different all the models would compare. And yes, this would be easiest to do if you had the original jigs to measure for all the various model fuselages, but I'm not sure they even exist anymore?


Paul S

for the individual aircraft av8rps that is a good way to check the AOA of the horizontal stab ,..because the leading edge of the horizontal stab can be placed in different locations depending on desired cruise speeds and weights of different motor/prop configurations,..

Chase