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 Thorp T-18
 Wing
 wing root seal
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irapilot

USA
19 Posts

Posted - 03/12/2010 :  23:27:34  Show Profile
ok hombres, what are some of your ideas on what type of wing root seal to install. and how hard would it be to making my own.
open to all suggestions.
thanks, ira.

Bill Williams

USA
336 Posts

Posted - 03/13/2010 :  05:15:12  Show Profile
I used clay and formed a seal using a large soup spoon, dipping it in Marvel Mystery Oil and forming a mold then laying up in fiberglass.
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leewwalton

USA
1041 Posts

Posted - 03/13/2010 :  06:10:10  Show Profile  Send leewwalton a Yahoo! Message
You can also use ACS PN# 05-01500 if you don't feel like digging into the fiberglass bin!

Lee Walton
Houston, TX
N589LW,N51863
KDWH
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Tom Hunter

USA
59 Posts

Posted - 03/13/2010 :  09:29:55  Show Profile  Visit Tom Hunter's Homepage  Send Tom Hunter a Yahoo! Message
For those who hate fiberglass, but want a composite wing root fairing. Here are the steps I used. And my fairings go from behind the flaps completely around the leading edge, so they are pretty long.

Materials: 5 ply aircraft plywood. 5 minute epoxy, close cell foam that sands easily, saran wrap (get it in a colored variety, then when people ask what that is on your plane, you can tell them it is "Aircraft grade thin film". Cardboard to make patterns. Pencil. Scissors, Painters tape. Fiberglass clothe, 1 hour epoxy, Body filler.

The logic behind this. The purpose of a wing root fairing is to fill in the void between the junction of the wing and the fuselage. If you think about the cross section of this "fairing" on the Thorp, it would be a very odd triangle. Two legs would be straight and one would be curved inward towards the other two. This cross section would be consistent along much of the cord.

Using cardboard templates, I created a series of sections about 20 inches long starting from behind the flap up to the wing spar carry thru doubler on the fuselage side. That would become the first assembly to work on. The second assembly would be the remainder of the faring.

It was necessary to divide the fairing into two parts for fabrication since the bulk of the effort with this method of construction takes place off the airplane with the fairing resting on your lap as you sit in the hangar and answer the passerbyers questions of "What in the heck are you doing now".

OK, so what about the ply wood you ask. Well, that thin five ply (got it from ACS) is the base of your fairing and gives the fairing rigidity as you sand away the foam to get the desired cross second.

Using your cardboard patterns cut out a series of plywood sections and label them with a marker. Do the same for the foam that gets glued
onto the two legs of the triangle.

Since the space over the flap and behind the wing is more difficult to "fill in" with your fairing, I am going to leave that out for now, and look just at what you do generically.

Tape your aircraft thin film in place. This is easier said than done
but if you are patient you can get it in place on the section you are working on. The reason for the "thin film" or TF is to prevent the 5 minute epoxy from bonding to your aircraft.

Ok, now with TF in place, place your approximately 20 inch ply wood on wing and on fuselage. Coat the two faces of the foam that contact the wood with 5 minute epoxy making sure that you do not spread the epoxy too close to the outside edges of the plywood. Press the foam into place and hold for 5 minutes. If you don't want to hold it in place, then bucking bars are handy to hold it while the epoxy cures.

You need to incorporate a way to link each section to the next that gives the fairing rigidity since you want to be able to take it off the airplane and do your finish work.

Once you have the rear section completed, you can sand the foam to get the desired cross section. Then you wrap the fairing with a single layer of fiberglass. Again, you can use fast drying epoxy to do this so you are not sitting around waiting for things to dry. You are going to be very pleased with how strong this structure is at this point.

After the part completely dries, you go to work on it with a good quality body filler. I used Rage Gold because you can apply it and sand it within 15 minutes.

It took me approx. two months of week ends to do this project. Quite a bit of that time was spent trying to figure out the next step. And one side went much faster than the second. If you decide to try this project I'll be happy to answer any questions.

Tom Hunter
805-202-4261
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Rich Brazell

USA
911 Posts

Posted - 03/13/2010 :  11:27:21  Show Profile
Tom ! I've made it half way thru your post and I need a nap! Muey Grande!
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irapilot

USA
19 Posts

Posted - 03/14/2010 :  23:28:01  Show Profile
Thanks guys for your great ideas,man i love this forum.
thanks, ira
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leewwalton

USA
1041 Posts

Posted - 03/15/2010 :  10:38:38  Show Profile  Send leewwalton a Yahoo! Message
the wing root fairing is partially cosmestic on the t-18. the primary purpose is to seal the leading edge to fuse juncture thus keeping the relative wind from hitting the flat plate of the spar web. so yes there is a big aerodynamic benefit.

Lee Walton
Houston, TX
N589LW,N51863
KDWH
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Fraser MacPhee

USA
277 Posts

Posted - 03/15/2010 :  10:49:58  Show Profile
As a senior household aerodynamic posterior postulator, it is my humble opinion that if the abrupt intersection of any two surfaces purpendickular to each udder can be blended or smoothed, there is aerodynamic benefit. My2yuans.

Fraser MacPhee
N633PM
Draper, UT
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leewwalton

USA
1041 Posts

Posted - 03/15/2010 :  11:54:55  Show Profile  Send leewwalton a Yahoo! Message
you may get some comments on that one frase. i think the rule is that if two surfaces are in fact perpendicular to each other there is in fact no aerodynamic benefit. something tells me mr. thorp knew that one. that being said, on the thorp there are other factors at play that come into view (as previously noted). )

Lee Walton
Houston, TX
N589LW,N51863
KDWH
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Jim Mantyla

Canada
126 Posts

Posted - 03/15/2010 :  12:57:23  Show Profile
Guys,

There is an aerodynamic benefit to the wing root fairing. Let me simply explain.

Imagine if you will that as the wing passes through the air the molecules are forced upwards over the wing. At the same time as the fuselage goes through the air, other molecules are forced sideways. The two sets collide and an increase in pressure results. This pressure increase can be reduced with the wing root fairing. The larger the fairing radius, the lower the pressure increase. The best example I can think of is the B1B bomber. It has huge fairings. It's almost a flying wing. John Thorp was pretty smart in his design in that he made sure that the thickest portion of the wing is not in the same place as the thickest portion of the fuselage. This was a conscious decision he made to reduce the pressure increase and associated drag as the plane travels through the air. Remember pressure increases take horsepower and result in drag.

The fairing are more than ornamental.

Jim Mantyla
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leewwalton

USA
1041 Posts

Posted - 03/15/2010 :  15:44:46  Show Profile  Send leewwalton a Yahoo! Message
Jim,

I'll agree with that on wings with dihedral at the fuselage (RV) but I'm pretty sure I read somewhere that a 90 deg. wing/fuse intersection actually has less drag than a sculpted one. Really a moot point anyhow as we've already determined why it's nessessary. I'll see If I can dig up the article.


Lee Walton
Houston, TX
N589LW,N51863
KDWH
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mattst18

USA
32 Posts

Posted - 03/15/2010 :  17:01:54  Show Profile
I have a simple rubber seal on the wing root to keep the relative wind from hitting the flat plate of the web spar. :)

I read an article like that also but I have no idea when or where so good luck finding it.

Matt Smith
Des Moines, IA
55RC
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leewwalton

USA
1041 Posts

Posted - 03/16/2010 :  20:42:46  Show Profile  Send leewwalton a Yahoo! Message
Should have known this one ... found the 90 deg/wing fillet comment ..

"The non-tapered wing on the T-18 has a dihedral break at the center of each panel, utilizing an aerodynamic principle that once was the secret of race pilots. This outboard dihedral wing makes a 90 degree intersection with the fuselage, avoiding the tangling of wing and fuselage flow fields, reducing drag and eliminating the use of complicated fillets that try to do the same thing. Another racing axiom was to never put the maximum wing thickness at the same point as the maximum fuselage width, again to minimize drag. If you look at the T-18 fuselage profile from above, it is quickly evident that each half strongly resembles a slice of an airfoil."

Dick Cavin Sport Aviation 9/1986

Lee Walton
Houston, TX
N589LW,N51863
KDWH
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