Drag Anti Drag Wires

[Darren Thorpe]

Hi

I'm in the process of recovering my wings, during the inspection of the top wing we found that one of the anti drag wires was loose.  It's not a big problem to resolve, although I don't know how it would have come loose.  It does beg the question though how can the drag wires be inspected without removing the fabric.  I guess the obvious answer is to add inspection ports, however can't recall seeing with a Pitts or an Eagle with inspection ports on the top wing.

Does anyone have any advice.

Cheers

Darren

G-EGLE

[Ronald K. Stevens]

The anti-drag wire is loose due to a broken and/or loose anti-drag block.  It is a (relatively) common occurrence on Pitts/Eagle type aircraft.  What happens is that the anti-drag block breaks and/or comes loose, and then under flight loads the hollow rib slowly gets crushed.  The result of the movement of the anti-drag block is the looseness that you're seeing in the anti-drag wire.  The anti-drag blocks are merely glued into place.  There is no mechanical attachment other than the anti-drag wire itself that penetrates both the anti-drag block and then the spar.   This is due to the design of the anti-drag blocks - which are a two piece design. (One on either side of the (hollow) rib.  The front drag blocks do not suffer the same concerns.

 

The fix - if the block is broken - is to remove and replace the block. Usually with a solid one piece block.   Usually this means a recover.  However, if the blocks are not yet broken and/or loose, there are prophylactic means to address the inherent weakness of the two piece anti-drag block design.  This is usually  accomplished by filling the voids in the hollow rib with a non-compressible material - usually an epoxy of some sort either injected via needle through the fabric or via holes drilled into the side of the ribs (via access through inspection panels - think building a ship in a bottle)

 

Oh, if you're planning on injecting epoxy through the fabric wing skins...you'll have to balance the aircraft on its nose.  Otherwise, you'll end up filling the entire rib with epoxy which would be way heavy :-)

 

Cheers,

 

Ron

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[Dave von Linsowe]

Hi Ron,

The two piece drag/anti-drag blocks on either side of a hollow compression rib are unique to the Eagle.  The Pitts (at least the S-2) uses a one piece block and the compression rib isn't a factor.

Dave

[Ronald K. Stevens]

Hi Dave,

 

You're correct.  On later Pitts & Eagles, they've gone to the one piece block.  But, I've seen a couple of S-1's with this exact problem - detached/broken anti-drag blocks.   And my hanger mate's S-2B had this problem as well.  I don't know exactly what year(s) they made the change - but if memory serves, it was in the early 90's.

 

I wish my Eagle had the mod.  But, I've filled the voids in the ribs with Hysol/flox.  Hopefully, this will mitigate any future problems.

 

Cheers,

 

Ron

[Dave von Linsowe]

Hi Ron,

I would like to hear more about your hangar mate's S-2B problem.  I've got a '92 B now and it's got the one piece drag/anti-drag termination blocks and my wires are on the loose side.  But my issue seems to be caused by the wing shrinking.  The airplane had spent 5 years in a Vegas hangar and the wires were pretty loose.  Now that it's back down in Florida the wires tighten up when it's warm and humid and go a little loose when it's cold and dry.

I believe the '81 S-2A I use to have had the same setup as my current B.  The nose ribs of the compression ribs are not sheeted with plywood like the Eagle is.  The drag/anti-drag blocks are captured by the spruce upright that locates the rib to the spar.

If you ever wondered what the creaking and cracking noise coming from the wings is when you push your airplane out of a cool hangar into the sunlight, it's the different expansion rates between the aluminum LE and the wood wing.

Regards,

Dave

[daz.t...@gmail.com]

Thanks for all the advice guys. I'm recovering the wings so at least
I don't have to worry about cutting fabric.

The thing that I'm worried it about is how will I check the wires at
next years annual, the manual doesn't talk about inspection ports on
the top wing. I think I'm going to ask my fabric guy to put in
inspection port rings over the wire intersections, then at the annual
I'll cut out the fabric and check the tension. The only problem is
I'll have to path and re-paint.

I don't suppose anyone has any ideas?

Cheers

Darren

[bruce...@juno.com]

My plane has inspection rings on the bottom of the top and bottom wing at the wire intersections, I was under the impression that the manual said to put them there and to cut them out at the first annual and to use inspection covers. I know that many Eagles that I have looked at either don't have the rings or have them, but they have not been cut out. In my opinion, even if you fix the hollow rib problem, checking those wires is a great indicator as to internal problems with the wings. I would much rather find out about that on the ground than in the air.

Bruce Green
Eagle N110GM

---------- Original Message ----------
From: "daz.t...@gmail.com" <daz.t...@gmail.com>
To: Christen-Eagle <christe...@googlegroups.com>
Subject: Re: Christen-Eagle Drag Anti Drag Wires

Cheers

Darren

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[Kurt Haukohl]

On wooden or metal leading edges I suggest drilling an exact 1" hole
in front of the spar. (before covering) I have plugs that are flush
and screw in tight just in case I ever needed to get in front of the
spars with a wrench. Similarly I have two holes pre-drilled in the
center spar box below the wing for access to the bolts and wires. I
am sure that because we did this explains the reason, I never needed
to gain access later. You can feel them be you cannot see them other
than a couple small divots in the fabric on the bottom of the center
spar box. We installed inspection rings as do most people on the
bottom of every wing at the intersection of the drag wires. I made a
special large plate at the control rod bracket so I could get two
hands up in there and change the control arms and bearings. This was
essential on my plane and used many times over for rigging and
adjustments to the control systems.

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Kurt O. Haukohl
2612 South Denison Avenue
San Pedro, California  90731-6502
iPhone:  (916) 825-3102
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[daz.t...@gmail.com]

Guys thanks for the advice

I'm going for inspection wings on the under side of the top wing.

I already have holes drilled in the leading edge alli, so that they
are there if I need them.

Cheers

Darren

http://www.facebook.com/album.php?aid=153769&id=226658832381

[Dave von Linsowe]

Hi Darren,

What did you find out about how tight to make the drag/anti-drag wires
and should they be tensioned with the flying and landing wires loose or
tight?

I have found that because of the geometry of the landing and flying
wires it will have an effect on the tension of the drag/anti-drag wires...

Thanks,

Dave

[Dave Lyjak]

I'm an Eagle wannabe, but in my antique biplane experience, you *must* put inspection rings in the bottom of the top wing when you cover it so that you have access to the drag/antidrag wires.  You don't have to cut them out right away, but they're there when you need them down the road (or runway).
Dave Lyjak

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[Mark Mattioli]

[daz.t...@gmail.com]

Hi Guys

My nice new anti-drag wire arrived from Aviat today. Unfortunately my
2nd set of manuals has a crucial page missing, does anyone know the
correct tension for the port inboard anti drag wire?

Many thanks

Darren

[daz.t...@gmail.com]

[Daz]

Got it now, thanks Rick.