Wing trammeling and drag wire

I have made a lot of progress on my fuselage and I am now stating o look at the wing covering. But before I have to do one last step on drag wires "tightening".

Did some one have an idea to tighten the drag wire a the proper "force" ?

What "charge" should I use ?

Thanks
Best Regards
Pierre

The A&E who signed off my Taylorcraft wing build checked by the sound they made. You want the same tone when strummed from all of them. So, all the same, that's obvious, how tight I won't try and explain, other then take all the play out, but not too tight. Snug, no play or sag, would maybe be the proper descriptive terms.

16-18lbs at 1/2" deflection in the middle of the wire.

Thanks !
Great !

Not in the manual, but I stretch a string along the front spar, then trammel the bays. I found that just trammelling might not guarantee a dead-straight spar, even though mathematically it ought to.

That's the way I was taught too, Bob. One of my old mentors used to say, "strings don't lie". I lay a string (usually orange or black thread) on front and rear spars... keep it in the middle of the spar and it's plenty "true".

Folks

This is my first time trammeling a 16 rib Cub wing.

Having read many posts here plus the Dakota Cub support sheet it all seems to be pretty simple in my mind.

However having squared and tensioned the drag wires in the first bay outboard of the tank I find the spars are neatly curved (see photo).

Will this correct itself as I trammel the other two bays or is there a trick I am missing?

Also, how is it that if one bay is square and with parallel spars the other bays have curves? - beats me!

Thanks all

Frank

Never seen that but never paid attention until I had done all the bays.

coxcub;803968However having squared and tensioned the drag wires in the first bay outboard of the tank I find the spars are neatly curved (see photo). Will this correct itself as I trammel the other two bays or is there a trick I am missing? Also said:

55853[/ATTACH]

Click to expand...

If the first bay is square and it does not appear to be so in this picture, the rest of them are not.

coxcub said:

Folks

This is my first time trammeling a 16 rib Cub wing.

Having read many posts here plus the Dakota Cub support sheet it all seems to be pretty simple in my mind.

However having squared and tensioned the drag wires in the first bay outboard of the tank I find the spars are neatly curved (see photo).

Will this correct itself as I trammel the other two bays or is there a trick I am missing?

Also, how is it that if one bay is square and with parallel spars the other bays have curves? - beats me!

Thanks all

Frank

View attachment 55853

Click to expand...

Not sure about how you are doing this, as I don’t see any reference points marked on the spars to check to. I will put a bit of masking tape over the spar where the compression strut attaches. Then mark dead center of the spar over the center of the attachment bolt passing below. I use the tape as the pointer of the tram doesn’t slip much during checking. Checking and adjusting to these points is what needs to be done. It will come out strait when done. (Unless someone has replaced the spars with improperly positioned holes. )

Back in 1970 an engineer suggested stretching a string along the front spar. I tram carefully, but always stretch that string. Straight spars are stronger than curved spars.

Yup, tram carefully, than eyeball for straight, that's how I did my T-Craft wing. I got lucky maybe but it trammeled and then eyeballed perfect.

Wing Trammeling

Here's a copy of Dakota Cubs Instructions.

coxcub said:

Folks

This is my first time trammeling a 16 rib Cub wing.

Having read many posts here plus the Dakota Cub support sheet it all seems to be pretty simple in my mind.

However having squared and tensioned the drag wires in the first bay outboard of the tank I find the spars are neatly curved (see photo).

Will this correct itself as I trammel the other two bays or is there a trick I am missing?

Also, how is it that if one bay is square and with parallel spars the other bays have curves? - beats me!

Thanks all

Frank

View attachment 55853

Click to expand...

Make sure the other drag wires are loose or they fight each other. Make sure the the drag tubes are square to the spars before you start.

Here is cubcrafters method, your mileage may vary.

Ensure the 1” X 1” X 6” block is under the rear
spar per sawhorse setup in prep section. The block
should be under the rear spar for the rest of the wing
build. Trammeling (squaring and straightening) the wing
is a critical part of the wing build.
Start by loosening all of the drag-anti drag wire nuts.
Start at the #2 compression tube, and check using
your modified carpenters square to assure that the
compression tube is square with the rear spar. It is
critical in this process to make sure that it is square.
If necessary, move the rear spar in or out to achieve
square.
After the wing is square, lightly tighten the nuts in
the first compression bay (this bay will have the fuel
tank in it, later). The wires at the #1 rib should
protrude from the fitting 1”. Once you have 1”
protrusion on the #1 rib wires, you will not move
these nuts.
Recheck the wing for square. Continue if the wing
is still square. If not, tighten one of the nuts at the
second compression tube to achieve square. After
checking square again, tighten both nuts at the
second compression tube 1/2 turn and recheck
square, then repeat this process (see next
paragraph for goal)
USE THE SQUARE TO CHECK THE #2 COMPRESSION
TUBE FROM THE FRONT SPAR AND THE REAR SPAR. THE
COMPRESSION TUBE WILL BOW SLIGHTLY WHEN THE
WIRES ARE PROPERLY TENSIONED. MAKE SURE THE OUT
OF SQUARE CONDITION IS THE SAME ON THE FRONT
AND REAR SPAR.
After 2 full turns with the wing still square, check the
tension. Find the center of the small wire. Proper
tension will result in 1/2” (you will notice that we start
at the 1” mark on the rule) deflection equaling 13 to
15 pounds. Keep repeating the previous step until
tension is correct and the wing is square. Once you have
finished and the tension is correct, verify the wing is still
square.


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I assume you have a good trammel tool that you can adjust to the correct lengths. I bought a good set for about $100 and used an aluminum bookshelf bracket rail you would normally use to put the “L” bookshelf brackets on as my trammel arm. And with a drill punch I punched a tiny indent in identical positions on the top and bottom of the spars that the tip of the trammel tool would rest. That setup gave me the precise measurements needed to correctly square up the bays. I always mounted the wing on the plane with the flaps and ailerons for trammeling and started on the inboard bay to make sure the wings would fit the wing attachment points, that the flaps and ailerons fit, and that the wing was perpendicular to the fuselage. Worked great.

Much better that eyeballing it with crossed fingers hoping you got it close enough for piece work. FYI, I did one set of wings before I bought the tool and ended up with a unique swept-wing Cub. Getting the ailerons and flaps to fit those wings was an added chore. That was a lesson learned the hard way. I always wondered if the subsequent owners ever noticed the error.

If you don’t have a good trammel tool let me know and I’ll dig out mine. It isn’t an easy or quick job for someone without prior experience.

Best wishes,

Paul Heinrich

Very many thanks everyone - lots of useful tips - I will start from scratch again.
I had marked both spars with a bolt through the root fittings and used trammel points to square the first bay but hey ho - off we go again!

Frank

Did that wing get hit from the front between the #2 and#3 compression tubes? I’ve seen front spars permanently bent and the smaller rear ones pop back perfectly straight once the tension is released during disassembly.

I believe the cross brace that goes through fuel tank must be installed also.
Can’t tell by the picture? Just a thought.

Update on my neatly curved spars - Post #7

After much head scratching I discovered the lower leg of the N brace was 1/8" short ie. same length as the upper one - great rebuild earlier in the wing's life!
Fitted a new one and wing became square easily
Frank

If I remember right one side is shorter to go in a certain way to clear the aileron cable


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What Chuck posted, plus what Tom remembers is if the N struts installed backwards the aileron cable will rub as we saw on Miss Daisey before the wing rebuild and recover.

I remember the one on Miss Daisy. I found it during an annual and he was getting close to covering the wings anyway. It had been that way a long time.