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Different wings

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Posted

DOUG, THANKS - But I just have to guess that the Speedwing rib is flatter than the Kitfox 4, because the other rib is not labeled, and doesn't look like Riblett to me. Guessing is not my best asset.

EDMO

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Posted

Guessing why Ed? That is indeed a KF 4-1200 rib, You asked about the profile of an Avid speed rib vs.Kitfox 4-7 (Riblett) rib and that's exactly what you got. The pics posted were taken personally in my shop and show each rib with their lower surfaces against a straight edge to best highlight the profile differences. I'm not certain which you might define as "flatter", however, if you look closely you can see several notable differences between the lower surface profiles. Hope that helps.

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Posted (edited)

Guessing why Ed? That is indeed a KF 4-1200 rib, You asked about the profile of an Avid speed rib vs.Kitfox 4-7 (Riblett) rib and that's exactly what you got. The pics posted were taken personally in my shop and show each rib with their lower surfaces against a straight edge to best highlight the profile differences. I'm not certain which you might define as "flatter", however, if you look closely you can see several notable differences between the lower surface profiles. Hope that helps.

Thanks for the clarification Doug - I just wanted to be sure about the Kitfox Riblett rib.

I can see the differences.

EDMO

Edited by Ed In Missouri

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Posted

I just picked up a new heavy hauler wing kit that a guy had but never put together ,I am thinking about extending the wing when I build it for the fat avid,Is there any plans for this or has anybody did it and is there anything else I should think about when I start this project. I would think about changing over to the kitfox ribs but sounds like alot of work

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Posted (edited)

Score! Now you go from 1050 to 1150 or 1200 lb. MTOW, big plus with your FWF. You won't find any aluminum extruded stiffeners for the .083" spars but check the A+ forum for pics and rational of the quick and easy wood stiffener mod I did. I think it would be easy to add a 12"-24" wing extension using simple internal tube sleeve joints on the spars when you are starting from scratch. Two or three additional ribs and a drag tube per side, essentially. I would use a set of non-droop KF 3 tips (slight modification required) and make them removable to use with or without the wing extension in place. It certainly is easy enough to use the Riblett KF4 ribs instead of the Avid HH ribs, but then you'd need the KF flaperons. I don't see why the KF wings/flaperons wouldn't work with our teleflex cable flaperon controls, although it might require repositioning the flaperon control horns or perhaps different length cables. To be honest, I think that airfoil is so superior that it might be worth the trouble.

Edited by dholly

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Posted

I have a set of Hoerner wingtips or a set of Kitfox droop tips if you are interested.

EDMO

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Posted

Thanks guys for the info, maybe I will l price out some kitfox Ribs and flaperons ( Kitfox 4 is what i would be after I think) I will have to read  up on it again but if I remember I would gain alot of airspeed and still have the same   stall speed. I may take you up on that Ed but probably wont get nothing started till winter, to dam busy right now.

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Posted

Yes, you want the KF 4-7 Riblett airfoil. KF 1-3 airfoil is almost a dead nuts copy of Avid HH airfoil, great STOL performance but both hit an aerodynamic wall around 90-95 mph due to the significant under camber. Anything more you are burning thru exponentially more fuel for incrementally smaller speed gains. The Riblett airfoil will get you in the air almost as quick but efficiently cruise at 110-115 mph all day long. If you use that airfoil, you also probably won't need the wing extensions as the 144" spar tube length you have is almost as long as the KF wing. Obviously, many KF 4-1200 Speedsters flying with the Riblett airfoil on shorter spars just fine!

FWIW, I am using KF 4-7 Hoerner tips on my A+ wings with Avid speed ribs @ 12" o.c., the tips will add an additional 6-8" of wing length without the need for a separate section of wing extension. The KF wingtip design also makes it easy to fabricate removable tips, something the oem Avid tips do not. This is a plus for internal wing inspection, storage considerations (buddy here would remove wingtips in order to fit shorter, folded plane in his barn for winter storage, or just plain fun (I also have KF droop and KF standard non-Hoerner tips to interchange when the mood strikes).

Keep in mind, KF wing tips for models 4-7 cross closely to Avid speed/Aerobat rib profile, NOT Avid Heavy Hauler/STOL rib profile. If you use the Avid HH ribs and are looking for alternatives to the oem Avid fixed tips, you will need to modify the oem tips or source the KF 1-3 tips for under cambered ribs. As Ed mentioned, most of these KF 1-3 tips were the 'droop' style tips but I do believe Skystar also offered the smaller, standard non-Hoerner tips sometime during model 3 production as an option. Just make sure it is for the under cambered rib as the current wing tips are much harder to modify In my experience.

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Posted

Thanks Doug always appreciate the knowledge you have stored up. I will seriouly look at the kitfox rib now that you mention not having to worry about extending the wing and which ever way I go will be using the removable kitfox wing tips, Thanks again

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Posted

$.02 of advise is to use the Kitfox Flapperons as well as the wing.  They are part of the system that makes the wing work.

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Posted

If you can get the symmetrical flaperons, you may be better off - Riblett said that the flat-bottom flaperons were a drag just like the undercambered ribs.

EDMO

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Posted

Doug , would it be possible to add a flat bottom on the undercamber HH riblettes I have to build them like a speed wing riblette, It would add a little weight but dont think it would be to difficult but not sure if that would cause other issues, I know I would have to also deal the fuel tanks.

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Posted (edited)

I added a modified Riblett Kitfox 4 profile to the bottom of my undercambered witngs - Just a 1/4 (6mm) rib extension and new capstrips, leaving the old capstrips on except at the wingtip - the profile is posted on here, I think, in "files and forms" and a few photos somewhere.  I can post a photo if needed.  The only other thing I had to do was replace my rear jury strut attachments with longer ones.

And, I cut some old rib material aft of the rear spar and shortened the ribs by about 1 inch and relocated the trailing edges.

YOU DON'T WANT a flat bottom!  The Kitfox 4 bottom is not flat.

EdMO

Maybe modifying your ribs and building like Avid, you wont have to buy Kitfox flaperons.

EDMO

Edited by Ed In Missouri

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Posted

Thanks Ed, I will check them out ,I will probably get a riblette to copy so I get it right

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Posted (edited)

If you print the drawings I posted in files and forms, then  go to UPS or a copy store, they can enlarge them until the yardstick is actual  size - Lots cheaper than buying a pattern rib from Kitfox.  Just make sure your spar holes are the right distance apart.

EDMO 

Edited by Ed In Missouri

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Posted

Doug , would it be possible to add a flat bottom on the undercamber HH riblettes I have to build them like a speed wing riblette, It would add a little weight but dont think it would be to difficult but not sure if that would cause other issues, I know I would have to also deal the fuel tanks.

Willis - sure, you can change the lower profile of the Avid HH rib but it won't turn it into a Riblett airfoil. Even if you make the lower airfoil profile similar, the top airfoil profile, flaperon rib hinges and spar hole cut outs in the rib webbing are all different. Easier to buy a set of KF4 ribs or make your own than trying to modify the Avid HH ribs you have.

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Posted (edited)

Doug,

     I believe he has good HH wing ribs - The only difference I have seen in the top profile is that my early Kitfox rib had just a tiny bit higher curve on the top - should give more lift?  I think his easiest, but maybe not perfect way to go, would be modifying what he has and he doesn't have to buy flaperons if he sticks with the Avid modified ribs.

EdMO

Edited by Ed In Missouri

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Posted

Maybe I missed this when I was skimming through this thread but I bought the aluminum stiffener insert for .083 tubing from Just aircraft. Pretty sure that Just uses .083 spars in their highlander. 

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Posted (edited)

IFMT,

     How much were the 083 stiffeners from Just?  If their spars are priced like their tanks, I cant afford them!

EDMO

Edited by Ed In Missouri

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Posted

It's been a few years and I can't remember. Had to repair the left wing after a ground loop. I was getting material from a few places so I don't know exactly. Give them a call. Might not be that bad.

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Posted

My understanding is that Just buys the extruded stiffeners from Kitfox.

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Posted

^ That's what I understood too. And, unless something changed, I believe both Skystar and KF had extruded aluminum stiffeners for the .065" spars only, not .083" spars. According to Steve Winder, Avid and [old] Airdale were able to source extruded aluminum stiffener material that fit the .083" thick spar tube at one time, but it was so expensive given the small amounts ordered that they dropped it. I've never heard of or seen a definitive source since then.

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Posted

Doug,

     I believe he has good HH wing ribs - The only difference I have seen in the top profile is that my early Kitfox rib had just a tiny bit higher curve on the top - should give more lift?  I think his easiest, but maybe not perfect way to go, would be modifying what he has and he doesn't have to buy flaperons if he sticks with the Avid modified ribs.

EdMO

 

Well Ed, I'm not an aeronautical engineer so I can't say what effect changing any one or multiple combination of characteristics to the HH airfoil will have. My comments are limited to trying to modify the Avid HH rib airfoil to mimic the KF 4-7 rib airfoil exactly. I'll leave the 'close enough', mix 'n match stuff and test flights to others.

 

I think you might be surprised at how different the two airfoils actually are, it's not just "a tiny bit more curve on the top". The top airfoil, the lower airfoil, the rear spar hole location and leading edge are all notably different, as are the leading edge and capstrip width. I think modifying HH ribs into KF 4-7 rib clones would be a LOT of work. IMHO, it would be easier to just route out a new set.

 

Some more pics that might be useful...

 

These show a KF4-7 rib against an Avid 'transitional' rib (speed rib lower profile with HH upper profile). The special transitional rib is used to mate Rib #1 on an Avid Speed wing or Aerobat to the butt rib on the fuse). Avid rib has oval cutouts in the web, KF rib has truss like cutouts. Clearly, the top airfoil surface of the Avid HH/STOL rib is quite a bit different than the KF4-7 Riblett airfoil. Even though it doesn't show well in the pic, the Avid capstrip actually sits directly on the spar. Capstrip on the KF rib sits ~1/4" above the KF rib. While it might sound insignificant, it created huge issues when I used the old Skystar slip-in wing tanks in my Avid Mk-IV HH wing.

 

post-53-0-22555700-1408575462_thumb.jpg

 

post-53-0-59393600-1408575460_thumb.jpg

 

post-53-0-41602400-1408575461_thumb.jpg

 

These pics show the underside difference between the KF4-7 rib and my A+ butt rib (Avid's HH/STOL top and bottom airfoil profile).

 

post-53-0-58382800-1408575900_thumb.jpg

 

post-53-0-23635900-1408575901_thumb.jpg

 

post-53-0-12707000-1408575902_thumb.jpg

 

HTH

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Posted (edited)

Doug,

     I understand what you have shown - I am not debating it.   However, like you were saying, changing ribs can be a real pain if your tanks don't fit - His Avid tanks may give him trouble with real Kitfox 4 ribs, or Kitfox tanks may not fit Avid ribs because of the spar hole location in the ribs.  He needs to use the rib hole location which makes his tanks fit.

     I am not afraid of the modified undercamber ribs - The NASA rib design turned out to be a dud, and they are supposed to be smarter than me!  Just look at how many "bad" designed ribs that have flown without failure.

     Harry Riblett even recommended doing that same modification to the undercambered ribs, and even suggested using his 35 inch rib pattern to replace the original Kitfox shorter ribs.  His letter and drawing and dimensions were posted on our "Files and Forms" section.

EDMO

Even the Clark Y rib, like on early Pipers, with a flat bottom, should be an improvement in cruise over the Eppler Avid and early Kitfox undercambered rib.  Barnaby Wainfain published an excellent little book on rib designs.

EDMO

Edited by Ed In Missouri

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Posted

Well those are interesting pictures Doug, what´s that? eurofox? aerotrek? I thought, making the ribs on aluminium and riveting them to the spar was more easy than glue and plywood, but then again, the AVID/FK wings are one of the most easy to build wings ever.

 

Regards

Dimi3

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