Drag Wire Tensions
Control cable tensions are set with a relatively inexpensive device. Drag wire, anti-drag, and flying wire tensions are set with a similar device.
Drag wire tensions are NOT set by measuring the torque on the end nut.
Here is an explanation of the tension-measuring process from the Yahoo! group.
From: Jerry Jackson
Sent: Wednesday, November 09, 2005 11:48 AM
Subject: Re: Tail brace wire tension
When the wire diameter is much, much smaller than its length it is easy o
calculate the tension from measurement of the deflection caused by a known force. The relationship is T=(L*F) / (4*x) where:
L=length of wire between supports
F=force applied at midpoint of wire
x=deflection of wire due to the force
For example, consider a 30 inch horizontal wire that has a one pound weight suspended at the midpoint and suppose the dial indicator shows a deflection of 0.05 inches. Then the
tension is : T=(30*1)/(4*.05)=150 pounds
That relationship will be accurate so long as:
(a) the force and deflection is applied and measured at right angles to the wire
(b) the ratio of length to wire diameter is so large ( say 100 or more) that the wire stiffness does not affect the amount of deflection.
(c) the force is small compared to the tension (no larger than a few
percent) so that the amount of deflection is much, much smaller than the wire length.
The problem with this procedure on a Stinson is that the wire stiffness DOES affect the amount of deflection. To do it right requires the correct tool. A Holloway Flying Wire Tensiometer http://www.radialengine.com/flywire/flywire2.htm ) is available from Aircraft Spruce (part number 12-12500 http://www.aircraftspruce.com/catalog/topages/flywire.php ) for $226.00. You can read about the use of this tool at http://www.radialengine.com/flywire/index.html .
Do it right. One pilot of a Fly Baby died because of improper drag wire tensioning, according to the NTSB report.
This brings up a very good point. I am nearly to the point in my restoration where I need to tension my anti drag wires. I have talked to Mr Holloway about his tool, and he has assured me that the lower tensions required on the Stinson wings can be measured with his tool, even though the scale he publishes doesn't go down far enough. He says to just extrapolate the tensions needed by the Stinson. Fine, whatever. My question is: how did Stinson build them? Where are the tools the old timers used for this? How do home builders set their wings up? Sometimes it feels like I'm the only guy in the world who ever wanted to tension my wires "by the book". I've asked the old timers, and they say just twang em, which I suppose is fine if you're just checking them, but in cases like mine where I've had to replace the false spars, I have nothing to start from. I would think that if the old timers used the method you specify, it would be in 43-13 or CAR 3. What am I missing here? From an engineer's standpoint, it seems more important to have the spars square to each other, with at least a certain minimum threshhold of compression on the compression members, than to have the tensions right on the book figure. Obviously, too much tension would be detrimental, even if the spars were still trammelled. Insight, please!
It is just a guess on my part, but the Stinson's contemporaries were Stearmans, Wacos, and Ryans that had lots of flying wires and tail bracing wires. I would expect that every self respectiong mechanic had a heavy duty tension meter that he purchased at a war surplus store for a buck or two. I was there at the airport when the Stinson was new but I was too young and dumb to have paid close attention.
My name is Brad. I was wondering if anyone had any recent information on this topic. I am involved in a restoration of a Stinson 108 and am to the point where I need to tighten the drag wires. I have been unable to find the tool listed above 12-12500, so I was curious about any thoughts of the best method or if anyone had any contacts for that tool.
I've used the Holloway tool on two sets of wings, and it works well. Here is the website: radialengine.com/flywire/index.html To use it for a Stinson, you'll need a pretty small inch/pound torque wrench.
And don't forget to trammel!
Could this be used?
I would think not. Cable and wire tensions are two different things. Cable bends easier than wire, so the reading would be different. As I understand it.
So. After doing a bit of digging, the Holloway tool doesn't seem like it is available. I could not reach Holloway Engineering by phone or email and a phone call to Spruce confirmed that it doesn't appear like they are doing business anymore unfortunately. I'd still like to go with this tool as it seems like the best affordable option, but I just have to find one.
I didn't see any for sale on controller or trade a plane so i was wondering if anyone here may have one I could purchase or rent when i go to tension my drag wires?
There is little tension on the wire itself. You could never stretch a solid wire with the toggle or end fitting. You only need to get the wire tight enough to not have any slack in the fittings. If you over tighten things you are only distorting the spars and compression struts. I really doubt they used any kind of meter back in the day.
Drag wires absolutely should be tensioned and properly measured. Having said that, it is possible to calculate the tension based on the "twang". It's well established science (my family are stringed instrument makers) but a little knowledge can be dangerous since the note created by a certain tension will be different based on the length, diameter and material of the wire. There's a myth out there about E flat for flying wires but on which wire, which aircraft? They would have used a rod tension meter to do it originally.
Loos sells an obviously uncertified gauge made for sailboat rigging but I'm not sure it could fit in between the ribs or that it's got the right scale: rod-rigging-gauge
You can make your own meter using an inch-lb torque wrench and some careful rigging. I might look into this since I have to do mine too. I'll keep my eyes out for a Holloway tool too.
For convenience, the drag wire tension page from the Stinson general service manual is attached.
Marcus Sabathil: Owner of Skookumchuck Voyageur 108
That's great info. I'm finishing up a rear spar splice on my model 10 and need to adjust the wires. I wonder if the model 10 and 108 spars etc are about the same? There is a musical quality to the wires but my ears are shot. It's great that there is a proper tool but I've been around since forever and have never seen anybody use one. You can get a pretty good idea from measuring deflection with an accurate scale.
I have rigged a sailboat and that tool works ok on a sailboat. I can't remember if it would fit between the ribs in this wing.
Did you see the size of that tool? OMG checkout the video https://youtu.be/pFf5QovoY_w
I wonder if this would work? $99
This may be a Model 10 etc, kind of thing. In the inner fuel tank bay, the drag and anti drag wires are different length! It took me a while to figure this out, having 2 wings helped. To trammel, you need to establish 2 reference points at the but end of the spar, equal distance from the outboard fittings and not use the end of the anti drag wire.