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extended leading edges

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Posted

Hi all

I have been super busy and not had time for the mk4 lately.

I found thaT I have extended leading edges on mine.What does that do to the cg?What is cg range without them?With them??

Brian in MO

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Posted

Hi all

I have been super busy and not had time for the mk4 lately.

I found thaT I have extended leading edges on mine.What does that do to the cg?What is cg range without them?With them??

Brian in MO

While the listed CG range really does not change, it moves it forward the same amount of you leading edge. Guys with heavier engines were adding to the leading edge to move the CG forwards to help with the nose heavy condition. While the published aft CG is something like 16.8" Dean Wilson says to run it at 18-20" and you will like the plane much better. He does not recomend stalling it without flaperons full on at a CG of more than 21" aft. Without full flaperon, you may not have enough down elevator to push the nose back over when she stalls.

I like flying mine at 18", STOL is much better!

:BC:

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Posted (edited)

Hi all

I have been super busy and not had time for the mk4 lately.

I found thaT I have extended leading edges on mine.What does that do to the cg?What is cg range without them?With them??

Brian in MO

Depends on amount of extension - If it is only the plastic Kitfox LE, or a short aluminum Avid LE, then all should be about the same. You can use factory measurements from the front of the front spar where it attaches to fuselage, or add the 1/2 LE.

If you extend 4 inches, like mine, then you remeasure the wing chord - Aerodynamic Center (AC) should be at about 25% Chord - Forward CG at about 16%, and aft CG at about 30%.

If wings have been raked forward, then your figures are all Kapoot! Then, you have to calculate averages.

For weight and balance computations, use the factory measurements from original front spar, or add your extension to factory numbers and measure from new LE.

ED in MO

Edited by Ed In Missouri

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Posted

While the listed CG range really does not change, it moves it forward the same amount of you leading edge. Guys with heavier engines were adding to the leading edge to move the CG forwards to help with the nose heavy condition. While the published aft CG is something like 16.8" Dean Wilson says to run it at 18-20" and you will like the plane much better. He does not recomend stalling it without flaperons full on at a CG of more than 21" aft. Without full flaperon, you may not have enough down elevator to push the nose back over when she stalls.

I like flying mine at 18", STOL is much better!

:BC:

Thsnks

that is just what i need to know

Brian

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Posted

Any chance of posting some pictures of the 4" extentions you have on your plane? I would be curious to see them. Is this your own idea or does putting the 4" extentions on cause the shape of the wing to copy another previously designed wing? Thanks, Jim Chuk

Depends on amount of extension - If it is only the plastic Kitfox LE, or a short aluminum Avid LE, then all should be about the same. You can use factory measurements from the front of the front spar where it attaches to fuselage, or add the 1/2 LE.

If you extend 4 inches, like mine, then you remeasure the wing chord - Aerodynamic Center (AC) should be at about 25% Chord - Forward CG at about 16%, and aft CG at about 30%.

If wings have been raked forward, then your figures are all Kapoot! Then, you have to calculate averages.

For weight and balance computations, use the factory measurements from original front spar, or add your extension to factory numbers and measure from new LE.

ED in MO

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Posted (edited)

Any chance of posting some pictures of the 4" extentions you have on your plane? I would be curious to see them. Is this your own idea or does putting the 4" extentions on cause the shape of the wing to copy another previously designed wing? Thanks, Jim Chuk

JIM,

If you got to forum index and scroll all the way down until you see "files and forms" where Doug Holly posted the Harry Ribblet letter and the drawing of his extended leading edge and rib for the Soob engine drivers, you will see about what I have done - although I stayed with the original profile and my ribs still have the undercamber. There is also a letter there about putting VGs on BOTTOM of LE, and gave the guy 10 mph more cruise with undercambered ribs.

I posted a photo of my 1 1/4 inch .032 aluminum tube LE with plywood supports somewhere in all these posts. Maybe you can find the photo. If not, let me know. Got the upper 1mm plywood on top now, and starting on bottom - 12 inches top - 6 inches bottom - extended LE 4 inches per Riblett. Planning to cover plywood with polyfelt before fabric.

ED in MO

I have a hard copy. ED

again: Well, Dummy here just found "files and forms" in forum index, and it is first article there, and Doug posted a picture and rib coordinates there. My photos are on page 4 Avidfoxflyers Hanger, halfway down page.

Edited by Ed In Missouri

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Posted

Jim, Look on page 4 of this site and you will see photos I posted of my LE extensions in progress.

ED in MO

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Posted

I'm sorry, but wasn't able to find your pictures??? Thanks, Jim Chuk

Jim, Look on page 4 of this site and you will see photos I posted of my LE extensions in progress.

ED in MO

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Posted

I'm sorry, but wasn't able to find your pictures??? Thanks, Jim Chuk

I have a meeting in an hour that will last a couple hours, when I get back I will see if I can find the pics and link them.

:BC:

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Posted (edited)

I have a meeting in an hour that will last a couple hours, when I get back I will see if I can find the pics and link them.

:BC:

Leni - NOT that it really matters - but this site is KOOKOO on post times - one time I get on and your post above is listed as 11:30 AM, and the next time I see it, it is listed as 4:30 PM in the index.....And, believe that my time is somewhere in Mexico or China, and one time it will agree with my clock and others it may be 8 hours off.

AS I SAID: NOT THAT IT REALLY MATTERS! JUST WONDERING WHY? At least we can still communicate well.......

ED in MO

P.S. 1030 PM here and still waiting for you to get out of that "couple hour meeting" since about noon today, OR - have I been waiting since 4:30?????????! Dont take much to confuse me....I sleep days - sometimes!!!!!:lol:

Edited by Ed In Missouri

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Posted

Leni - NOT that it really matters - but this site is KOOKOO on post times - one time I get on and your post above is listed as 11:30 AM, and the next time I see it, it is listed as 4:30 PM in the index.....And, believe that my time is somewhere in Mexico or China, and one time it will agree with my clock and others it may be 8 hours off.

AS I SAID: NOT THAT IT REALLY MATTERS! JUST WONDERING WHY? At least we can still communicate well.......

ED in MO

P.S. 1030 PM here and still waiting for you to get out of that "couple hour meeting" since about noon today, OR - have I been waiting since 4:30?huh.gif?huh.gif?! Dont take much to confuse me....I sleep days - sometimes!!!!!smilielol.gif

ahhh.. you have to love the oilfield. One meeting turns into 3 these days and every job is an emergency...

Not sure what to say on the post times. They are correct for me on every computer I have used in the last week to check this place out. That would be my home computer, my laptop and 4 differnt computers here at work. I think you have a gifted computer :lol:

:BC:

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Posted

Ed's LE ext. thread

For the record, it was showing as on page 6 on my computer so it all depends on how many topics you have set per page as to what page it may be on.

:BC:

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Posted

Thanks Leni for finding the pics for me. I have some drawings from Lee Dubay that show how to do an aluminum leading edge extention that goes out about 1 1/2". The 4" extention would give about 9% more wing area over a standard wing and move the CG in a way most Avids need it to go. I do wonder what it will do to the wing in regards to flying and stall characteristics though. I'm not saying it would be worse, just wondering. Take care, Jim Chuk

Ed's LE ext. thread

For the record, it was showing as on page 6 on my computer so it all depends on how many topics you have set per page as to what page it may be on.

:BC:

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Posted (edited)

Thanks Leni for finding the pics for me. I have some drawings from Lee Dubay that show how to do an aluminum leading edge extention that goes out about 1 1/2". The 4" extention would give about 9% more wing area over a standard wing and move the CG in a way most Avids need it to go. I do wonder what it will do to the wing in regards to flying and stall characteristics though. I'm not saying it would be worse, just wondering. Take care, Jim Chuk

It should get off quicker and stall slower - I hope for better cruise too! My wing has the old twist which dont help.

If you read the Riblett letter about getting rid of the undercamber, the new rib eliminates the 100 mph wall that the Eppler rib seems to have because of the bubble that forms in the undercamber. The VGs UNDER the LE are supposed to help if you keep the undercamber, which should slow you down faster.

Look at the late Kitfoxes cruise speeds of 120, or so, and that rib is an intermediate between the two designs, but they float and dont slow down like the Eppler ribs.

I will gain more than the 4" (9%) on my wing, because I am not a flaperon fan - I am splitting them into 6 foot differential ailerons and 6.5 foot flaps, about 14 inches wide. Seperate controls - just KISS as best I can. But this engineering change sure extends the building time, as well as my injured shoulder which has cost me another year.

ED in MO

Edited by Ed In Missouri

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