Introduction
Monocoupes use either 5/8" or 3/4" shock cord wrapped around each gear leg and the fuselage frame as shown in the picture above.
The only print that I have is shown below and a handwritten note calls for 5/8" shock cord. Many of the 110 Specials (clipwings) have been wrapped with 3/4" shock cord due to the increased weight of the Warner 185 and propellor.
Notice that the drawing calls for the shock cord to be wrapped with 100 pounds of tension. More on that later.
Here are some instructions, written by Bud Dake, for the Monocoupe Club Newsletter which describe his method for installing the bungee cords. This gives a very good introductory overview. Study this first.
Where to get the shock cord and how much to order?
You can order the shock cord from Aircraft Spruce. They seem to only stock up to 5/8" diameter.
If you need the 3/4" shock cord, then you can order it directly from the manufacturer:
Superior Bungee Corporation
429 West Laurel Street
Scottsboro, AL 35768
Phone: 256-259-3770
Email: info@superiorbungee.com
For my Model 110, I ordered 25 feet of 5/8" shock cord and had about 5 feet left over after completion. So plan accordingly. It somewhat depends if you want to leave some extra length in the fuselage in case you need to unwrap and rewrap them at some time in the future, which is what I did.
The best thing to do is to get some 5/8" rope and simulate the routing and wrapping of the cord, including the starting and ending loops, and measure what you need.
Starting and ending loops
The shock cord gets secured to an adjacent fuselage from member using a starting loop.
I used rib stitching cord. The final lacing should be covered with varnish to help preserve the cord.
Here is an example of a starting loop on a Model 90A:
How many wraps and how tight?
The monocoupe assembly manual calls for:
The number of wraps you will be able to get depends on the diameter of the cord used and on the Model and vintage of fuselage frame and landing gear being wrapped. Some frames (ex: 90A) are wider and using 5/8" cord you will be able to get 8-9 wraps. On the narrower 90 and 110 frames you might only get 6-7 wraps.
There are a lot of opinions on how tight the shock cord should be wrapped. Some people insist on wrapping the cord as tight as possible.
The drawing at the top of this page calls for 100 pounds of tension. I called tech support at Superior Bungee and talked to them about this. Their website contains a document with the specifications of their cord. Here is a link to the Superior Bungee Specifications.
From that document, you need to stretch 5/8" cord to get 100 to 180 pounds of tension:
If you are using 3/4" shock cord, then stretching 50% will get you 200 to 350 pounds of tension:
I used 50% stretch on 5/8" shock cord on my Model 110 with Warner 145 and it is working very well.
Cushion that Landing Gear!
Before you wrap the gear, insert a piece of rubber material, approximately 1/4" thick, between the landing gear and the fuselage frame for cushioning. The picture below shows this. Less banging when you drop it in!
Wrap, Stretch, Clamp, Repeat
Once you do a starter loop attached to the fuselage frame, you then make your first wrap and use your method of choice to stretch the cord 50%. Bud Dakes article linked above gives one suggestion on how to stretch the cord. The picture below shows the method I used. A boat trailer winch on a square steel tube attached between the landing gear legs.
While you have tension on the cord, it is very important to tap the cord where it wraps around the frame with a rubber mallet to help the cord stretch around the frame. When you tap the cord you will see it move around the frame to get even tension.
Next clamp the cord tight against the frame. The photo gallery shows several methods to clamp the cord. How you do this will depend on your fuselage frame and the space available to get a clamp on the cord.
Once the cord is clamped tight, free it from the stretching device and wrap another wrap.
Repeat the whole process 6-9 times depending on how many wraps you are able to get on your ship.
When done with the wraps, stretch the cord around the adjacent frame member for the termination loop. Lace as before. You can cut the cord close or leave some extra length for removal if required in the future.
Install a Safety Cable
When you are all done, don't forget to install a safety cable just in case the bungee cords break, you will have the cable to keep the gear mostly upright. See picture below.
Here is the photo gallery with all my Monocoupe bungee photos.
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