leading edge cuff on KF 3 undercamber

[6320012s 12]

Well, Im underwhelmed.  I was hoping for 5-7 mph cruise increase, but it looks like if anything, I only got 2-3.  At 6000rpm I get about 82 mph with me and full gas.  Was hoping for closer to 90.  But on the bright side, I got a new paint job, rejuvinated fabric, an epoxy liner in my fuel tanks and a header tank that doesn't leak.   Hope John isn't spinning in his grave over the changes.   Have a good 4 hrs on it now, and had a great flight practicing beach landings and slow flight from Nikiski to Anchorage.  Maybe for fathers day I'll get a Gopro to make some video.

[1avidflyer 1983]

Did you put the Kitfox plastic leading edge cuffs on? Got any pics? I've got to rebuild a set of Avid wings and am thinking about leading edge cuffs as well. Plane looks nice! Jim

Edited 7 Jun 2013 by Jim Chuk

[BryceKat 125]

John Miller streamlined his tail bracing and got 3-4 mph, I think. Maybe he'll chime in.

[dholly 718]

Good looking Kitfox! Your experience adds one more data point which echos what has been discussed many times before. Tough to push these under cambered wings through that aerodynamic wall, eh? I think the extruded PVC leading-edge cuff was designed as an integral part of the new Riblett airfoil used on Kitfox models 4 and up. When added onto any flat bottom airfoil like Avid Speed/Aerobat wings, the cuff should produce measurable benefits due to increased chord. A higher angle of attack is possible with lower aspect ratio without a stall. Plus the lift to drag ratio also goes down which results in a slightly higher cruise and better stall speeds. This is not the case on KF 1-3 and Avid HH/STOL airfoil due to the significant amount of rib under camber. Too much drag to overcome apparently. I have seen more positive comments reported with the aluminum Dubuy (sp?) LE cuff that was specifically designed for the Avid under camber airfoil. This extended the LE even further than the KF cuff and produced better results, but still not enough to be adopted by Avid builders. Empirical evidence says the primary benefit to a LE cuff on the Avid and early KF under cambered wings is simply cosmetic. Does cover the lift strut bracket and rivet heads that would otherwise show through the fabric on the spar for a nice, smooth finished look. I've never seen a negative comment (my performance is WORSE) or safety issue (spin stall), and I'm more neat than weight freak, so I would probably add the KF cuff when building new Avid or KF under camber wings if my wallet allowed.

[akflyer 1427]

Hey Dave,  Is that on one of the pipeline strips in the Mystery creek area?  The plane is looking good, and I am CERTAIN that John is smiling knowing the plane is actually being flown and enjoyed!  It killed him that he was not able to get out very much and fly it, but we did get him out a few times in those last few years..

 

Bob put the cuffs on his too with about the same results.  It is more cosmetic than anything else on our undercambered wings like Doug said.

 

Randy Tyler also did some work streamlining his tail braces and jury struts with a nice increase in speed noted.  one of these days, I am going to make new tail brace and jusry struts using the stream lined aluminum tubing from Carlson Aircraft.  I think that will be a nice fit and finish and be pretty damn cost effective!

 

http://www.carlsonaircraft.com/struts.html

 

The Jury strut material is what I was looking at for all the bracing.  It should be stronger than the 4130 round tubing we have now using 5/32" Stainless steel plate bolted in the ends for the mounting tabs.  I could have the metalurgist here run some numbers for me, but I am sure that 5/32" aluminum plate would be plenty strong for the tabs also.

 

[6320012s 12]

Picture was taken at Bold Airstrip on Eklutna Lake. While I had the struts off, I should have put on some Balsa wood Farings.  I think that with a heat shrink tubing cover would be a nice addition.

[akflyer 1427]

Yes Sir.

,  Balsa and some coverite would do great for fairing the struts in..

 

[EDMO 1078]

Have you considered putting the VGs UNDER the LE? One guy said he had a 10 mph increase with them.

I am hoping someone else will try that and give a report. I plan to do that after I get some cruise figures without them first.

EDMO

[SuberAvid 617]

Dave,

 

Your plane looks great!  Now tht you are back in the air, we need to do some flying together.  Jeff and I have had a lot of fun out on the gravel bars and strips lately.

 

On my fairings, I just bent up some aluminum to make the faring for my jury struts and tail braces; a V shape with about 1/8" turn in on the the edges of the open end.  Then just drilled them and zip tied them onto the tubing.  The picture shows them pretty well.  The biggest benefit was a measurable decrease in fuel burn at the same speed.  When it comes to speed, the prop change was the biggest for me.  My plane went from an 80+ mph cruise to a 90-95 mph cruise with the change from my Warp Drive to my IVO Med. IFA.

 

Hmmm, cant seem to find the attach button...

[akflyer 1427]

Dave,

 

Your plane looks great!  Now tht you are back in the air, we need to do some flying together.  Jeff and I have had a lot of fun out on the gravel bars and strips lately.

 

On my fairings, I just bent up some aluminum to make the faring for my jury struts and tail braces; a V shape with about 1/8" turn in on the the edges of the open end.  Then just drilled them and zip tied them onto the tubing.  The picture shows them pretty well.  The biggest benefit was a measurable decrease in fuel burn at the same speed.  When it comes to speed, the prop change was the biggest for me.  My plane went from an 80+ mph cruise to a 90-95 mph cruise with the change from my Warp Drive to my IVO Med. IFA.

 

Hmmm, cant seem to find the attach button...

Randy,

 

Click the "more reply options" button.

[SuberAvid 617]

Thanks Leni

[6320012s 12]

Randy, are you going to be out flying this afternoon/evening?   Promised my son to go play.  Farings look like a simple solution, but I can see that the IVO is what I am looking for.

[C5Engineer 1170]

This is the stuff that John Miller used on his covered with Monokote

 

http://www.aircraftspruce.com/catalog/mepages/trailedge.php

 

Balsa seems like it would be easier to work with and lighter too. If a guy were to glue balsa onto a painted jury strut would we he use? Leni? CA/Epoxy? Gorilla glue? I'm gonna do  this mod when I get home. Sucks sitting half a world a way from your plane modding it in your head!

 

You can get this stuff in just about every size

 

[6320012s 12]

Randy, If the weather is good We are going to go up to kinik river flats this evening.

[6320012s 12]

Jeff, you going to be out playing today ?

[EDMO 1078]

Joey,

My original Strut fairings were a hardwood with a U-shaped radius to match the tube, and glued on with epoxy, and covered with fabric. Where can you buy long strips of the balsa?

ED in MO

[Mendlerr 4]

My plane went from an 80+ mph cruise to a 90-95 mph cruise with the change from my Warp Drive to my IVO Med. IFA.

 

2 or 3-Blade and what length?  I'm topping out at 75-80mph in my KFIV with the 68" GSC 3-Blade

 

I've also been working on streamlining some things.  I got some StolSpeed VG's.  Smaller then I expected them to be for sure but I got enought to do the wing and the tail.  When I get more time in the plane and record some stall speeds, ect. I will install them and do a comparison

[C5Engineer 1170]

Ed my main struts and gear legs are faired the same way. I'm looking to fair my jury struts and the struts on the horizontal stab. I googled Balsa Wood trailing edge and the top find was the site that picture came from. They were selling it in 36" lengths. If you have a RC hobby shop nearby most all of them sell balsa in various forms as well.

 

Anybody have a theory on the angle the fairing should be on the horizontal stab struts to be streamline? Maybe I should put them up a little bit for some more lift back there

Joey,
My original Strut fairings were a hardwood with a U-shaped radius to match the tube, and glued on with epoxy, and covered with fabric. Where can you buy long strips of the balsa?
ED in MO

[EDMO 1078]

Joey,

I would think that the rear strut fairings should be about the same level at the top as your HS - Cant believe they will take much pressure -

EDMO

[EDMO 1078]

Yes Sir.

,  Balsa and some coverite would do great for fairing the struts in..

 

What is "Coverite"? What is "Monocoat"? Is that the new stuff for model planes?

Now - on modifying the undercamber ribs like the Riblett drawing that Doug posted, I cant run the new ribcap completely underneath, because I couldn't get my strut bolts into the attachments on the rear spar - I can only run them from front spar to rear spar, leaving a drooping trailing edge from the rear spar to the TE....Anyone think this will help get rid of the bubble he describes that forms the "90 mph wall"?

EDMO

Edited 11 Jun 2013 by Ed In Missouri

[SuberAvid 617]

Randy, If the weather is good We are going to go up to kinik river flats this evening.

Hey Dave,

 

Sorry I didn't see this until today; I was flying most every day of the weekend but was trying to catch a fish.      It looks like a good week ahead so let me know if you are going to be out flying and we will try to meet up.

[Nico 2]

Have you considered putting the VGs UNDER the LE? One guy said he had a 10 mph increase with them.

I am hoping someone else will try that and give a report. I plan to do that after I get some cruise figures without them first.

EDMO

A friend of me, actually my flight instructor, has put VG's under the hor. stab approx 4 inches before the stab/elevator separation. It gave him an astonishing 20 kM/hr max speed increase at his 912 powered apollo fox. Speed was 180, is now a little over 200 kM/Hr

[EDMO 1078]

A friend of me, actually my flight instructor, has put VG's under the hor. stab approx 4 inches before the stab/elevator separation. It gave him an astonishing 20 kM/hr max speed increase at his 912 powered apollo fox. Speed was 180, is now a little over 200 kM/Hr

Thanks - That is interesting - I thought the only benefit for the HS was better elevator control - same thing for VS and rudder. If you haven't read Doug Holly's post in files about the VGs and the Harry Riblett modification, then you should read it.

Good Flying,

EDMO