Paint or cover my strut fairings?

[C5Engineer 1170]

Finishing up my MK4 and prepping it for inspection. Wood fairings are glued to the powdercoated struts already. I can either use some polyfill to make them pretty and epoxy varnish and paint em with epoxy paint or wrap them in fabric. I have some fabric but I'll have to get some more polytak and some polytone and wait for warmer weather. Easier way would be to just paint em but I'm curious if what the strength difference is if any between the two methods. I've painted the ones on my gear legs the last two sets of gear but that's a much smaller length of tube. Thoughts?

 

[Av8r3400 1179]

I don't know how much structural strength fabric will provide other than strength to hold the farings in place.

[EDMO 1078]

I don't have much faith that fabric and dope will keep moisture out of the wood or add much strength.  A good coat of epoxy will do that better.  My suggestion is a coat of West System or other epoxy, followed by fiberglass cloth and a final coat of epoxy for added sealing.   Max strength and stiffness being to add a layer of carbon fiber, but that would probably be overkill and too expensive.   EDMO 

Edited 2 Jan 2017 by EDMO

[tx_swordguy 20]

I think Joey was asking if the fabric will hold the fairings to the strut stronger than the glue alone. At least that was my take on the question. I think the answer would be yes it will but in actuality may not be needed. If the glue is solid the only thing I can see happening is a hard landing or some sort of jolt flexing the strut enough to "pop" the glue. Whether that is  a realistic issue or not I don't know. Simple paint would be the best weather proofing I would think. If the gear legs held up I would sure think just painting the struts would too.

 

[C5Engineer 1170]

I've just had the wood glued to my gear legs on the last 2 sets and they've done a lot more flexing than my struts ever will. I was more concerned with it adding and strength structurally to the strut. 

[TJay 1041]

I would say almost no strength to the strut, But blends in with the rest of the plane nicely, Im piping in here because I am wondering what I should do also, I got my Brake out and bent a sample piece. May do this instead of wood, But not sure yet, I like the strength of wood and the look of fabric but aluminum only comes in at 3.648lbs to do all the struts minus the rivets and paint. Wood may be a couple pounds more,

[lostman 198]

If you used the correct species of wood it shouldn't weigh any more than what you are doing with the aluminum. Balsa or spruce are extremely light when talking about just a trailing edge fairing. 

How do you plan to attach the aluminum fairings to the struts? 

Personally I think if the dang streamlined strut material wasn't so expensive I'd remake the struts and have the lightest and strongest available. Of course I'm cheap and am not willing to spend $12 per foot for that stuff when I could use factory struts faired with wood and covered in fabric then painted.

[TJay 1041]

If you used the correct species of wood it shouldn't weigh any more than what you are doing with the aluminum. Balsa or spruce are extremely light when talking about just a trailing edge fairing. 

How do you plan to attach the aluminum fairings to the struts? 

Personally I think if the dang streamlined strut material wasn't so expensive I'd remake the struts and have the lightest and strongest available. Of course I'm cheap and am not willing to spend $12 per foot for that stuff when I could use factory struts faired with wood and covered in fabric then painted.

Same way you attach plastic a little glue and rivet them together. If you want to build some nice cheap struts Wag-Aero has some streamline tubing for 3 bucks a foot I bought some a wile back, Nice stuff,

[TJay 1041]

Joey what glue did you use to attach them, It doesn't look like Hysol looks more like a polyurethane construction adhesive, I guess on another note what is everyone using to glue these on?

[EDMO 1078]

Joey what glue did you use to attach them, It doesn't look like Hysol looks more like a polyurethane construction adhesive, I guess on another note what is everyone using to glue these on?

All of mine were originally glued with 2116 (Whatever the old glue was) or 9460.  EDMO

Edited 8 Jan 2017 by EDMO

[jackak 20]

Interesting discussion. I know that the goal seems to be fairing the lift struts with the lightest material that will get the job done and be fairly durable, but, is or was there something in the construction manual that included a comment that the fairings were needed to provide the required strength for the struts? It seems that there was also a message from Avid, perhaps Steve Winder, that stated that the fairings provided strength. Doug H., do you remember the discussion and perhaps have a copy of the message?

Jackak

 

[EDMO 1078]

Interesting discussion. I know that the goal seems to be fairing the lift struts with the lightest material that will get the job done and be fairly durable, but, is or was there something in the construction manual that included a comment that the fairings were needed to provide the required strength for the struts? It seems that there was also a message from Avid, perhaps Steve Winder, that stated that the fairings provided strength. Doug H., do you remember the discussion and perhaps have a copy of the message?

Jackak

 

Jack,  Not trying to butt in, but we have had this discussion before, and I remember the statement you refer to.  Maybe Doug has it?   Something further to add to this, at least with the Kitfox flyers, and maybe Avids, is that the original struts were 3/4" and thin wall, but have been evolving to stronger 7/8" and now 1" diameter and .049 wall, or in my and Leni's case, .058 wall, so the struts themselves have gotten stronger.   Of course the weights of the planes have gotten heavier too.   Evidently, Kitfox gets by with some plastic fairings that snap onto their struts now.   Leni has them too.  I don't know how the strength of them would compare to the wood fairings, but for the price that Kitfox gets, I will be looking for an alternative.   Hello TJay?   EDMO

Edited 9 Jan 2017 by EDMO

[dholly 718]

Jack, Ed - Joey posted the Avid AD's onsite somewhere, but I looked quick and couldn't find them to link. Avid AD #007 said the wood lift strut fairings must be installed to provide necessary structural strength under compression loading "within the next 25 hrs flight time", or something to that effect. So, not critical enough to ground each ship immediately, but Avid obviously did consider the bonded on wood fairings mandatory. I don't know if the early build manuals actually said the fairings were required or not, but I'm pretty certain my Mk-IV manual did. I do think Ed has it right, the early Avid models simply had smaller, lighter, thinner wall lift struts vs. 1" struts which are strong enough to stand alone with or without the snap on plastic fairings.

[jackak 20]

Thanks guys. I thought I remembered something about them.

Jackak

[EDMO 1078]

Aside from strengthening the struts,  the fairings seem to take some drag off of the struts, so they are beneficial.  EDMO

[RobS 52]

This rather old video clearly shows the improvement made by fairing a round tube. 

[C5Engineer 1170]

Stick a broom handle out the window going 75 mph and then try it faired with something even cardboard duct taped on. Made me a believer. 

[EDMO 1078]

8 or 9 times the drag on a round tube vs the drag on a streamlined tube - very impressive!   EDMO

[TJay 1041]

Ha I did that same type test with an electric leaf blower, Just holding a stick in my hand I was amazed, 

[lostman 198]

That's a great simple yet detailed analysis of the different shapes. Makes me want to fair everything on my Pietenpol and get flying wires instead of cables. Although it's not ever going to be a really fast airplane and wasn't meant for it. I may fair the struts to reduce the drag though. I figure if the drag is reduced it equals less RPM for the same speed, which in turn is less fuel and cheaper flying. Makes perfect sense to me. 

[akflyer 1427]

That's a great simple yet detailed analysis of the different shapes. Makes me want to fair everything on my Pietenpol and get flying wires instead of cables. Although it's not ever going to be a really fast airplane and wasn't meant for it. I may fair the struts to reduce the drag though. I figure if the drag is reduced it equals less RPM for the same speed, which in turn is less fuel and cheaper flying. Makes perfect sense to me. 

take off and climb performance if where you will notice the fairings the most.. at least that is where I really noticed it on my avid..

 

Joey, get some super coverite.  its fabric and will look 100 times better than monocote.  It may be called oratex these days.  At any rate, simple iron on covering that will come super close to matching your paint already and its a 1 hr install if your dicking around drinking beer while you do it.  If you just get after it it will take less time than that..

 

 

[TJay 1041]

That's a great simple yet detailed analysis of the different shapes. Makes me want to fair everything on my Pietenpol and get flying wires instead of cables. Although it's not ever going to be a really fast airplane and wasn't meant for it. I may fair the struts to reduce the drag though. I figure if the drag is reduced it equals less RPM for the same speed, which in turn is less fuel and cheaper flying. Makes perfect sense to me. 

probably less vibration and stress on the attachment points too.