How To Install Rail Guides

Usually the top rail guide is well above the motor mount completely and access is not an issue at all...

The bottom rail guide is only an inch or two from the base of the airframe
( according to the diameter of the airframe )... 
This article addresses access to the inside of the airframe to make a solid installation of this lower rail guide..

All work with epoxy should always be done with a bottle of rubbing alcohol and a roll of paper towels on hand,, wet epoxy is alcohol soluble .. No matter how much trouble it is cleaning wet epoxy off of somewhere you didn't intend to get it,, it is a thousand times easier then after it has hardened...


Assuming your dealing with 3 CR's,, that's most common..

Lay out and careful measurement and marking of the mm tube is very important....

The top CR is epoxied 3/8" or 1/2" down from the top of the mm tube with the stainless eye already in it,, hardware ground so all fits well...

Now epoxy the next CR at the position on the MM tube so that when you put the fins through the airframe the forward most part of the fin will touch that 2nd CR...

On this 2nd CR epoxy a good fillet around the top of the CR but not the bottom,, the bottom must remain clean so that the fin will go all the way into the corner between the CR and the MM tube..

When you’re doing this marking and laying out with your pencil,, the motor retention must be slipped onto the mm tube as that's what determines how far into the airframe the mm tube goes..

Now you have the mm tube with 2 CR epoxied on and you know exactly how far into the airframe this assembly goes..

Take the 3rd CR,, drill 2 very small holes 180 Degrees apart, opposite each other,, put a 2" long black thin Sheetrock screw into the holes,, just a bit,, 1/4" or so,, enough so they won't come out till you take them out..

Now slide the MM tube assembly into the airframe to the correct depth,, put the 3rd CR onto the mm tube so you can use the 2 screws to position it,, I use a very large hose clamp from Home Depot and put it around the base of the airframe right on-top of the 3rd lowest CR,,

Now nothing can move all is solid and in the correct place,,    check and recheck this....

Stand the airframe up,, use black electrical tape to tape a syringe to a 1/2" dowel,, mix a batch of epoxy and fill the syringe with epoxy,, have someone else hold the airframe and shine a flashlight down into it,,

Reach down into the airframe with the syringe on the dowel and push the plunger with another dowel,,  
Do not get any epoxy on the inside of the motor mount tube,,  leave the airframe vertical till hard,, 
then drill 2 holes in the airframe 180 degrees apart dead between the top CR and the 2nd CR,,
they are usually very close to each other,, invert the airframe,, inject these 2 holes,, the bottom of the top ring is now done, wait till hard,, turn the airframe right-side up again, inject the same 2 holes,, 
wait till hard the top of the 2nd ring is done,,
Lay the airframe horizontally with one hole up and one hole down,, in the hole facing down, shoot a little epoxy and cover with masking tape, wait till hard,, if you worked clean,, when the epoxy is hard and you peel the masking tape that hole has vanished..  Roll the airframe so the 2nd hole is facing down and inject it with a little epoxy and cover with masking tape... You must wait for a full cure before peeling the masking tape or you'll be able to see that there was a hole there, if you wait the full cure it's harder to tell.......

Now,,, all is hard and solid,,,,,, pull the hose clamp off the airframe from around where the 3rd, lowest CR is,, grab the 2 -- long Sheetrock screws and pull the 3rd CR out,, it will come right out.. you now have total access to the lower rail guides position on the inside of the tube.... I use a blind nut or you may know it as a Tee nut,, turned upside down so the flat face faces the inside of the airframe, drill the hole for the rail guide,, put some grease on the threads of the screw so epoxy won't stick to it.. put the screw in through the hole and into the flat face of the Tee nut tighten very gently,, just a touch firm, you don't want to pull so hard that your digging into the glass airframe, use any epoxy you like mixed with chopped or milled fiberglass and make it fairly thick,, embed the entire back of the Tee nut all around, under all over,,, when this is hard you have a steel thread to screw your rail guides into and change them whenever you wish,, in order to rip this rail guide off you will have to exert enough force to tear out a chuck of the airframe the size of the mound of thickened epoxy you put around the Tee nut,,, that's not going to happen,, this is the best most solid mount I've ever seen and is completely removable ( the rail guide ) in case you'd like to change them... I install the top rail guide the same way..

Now you can put the 3rd CR back in and epoxy or do the fins if you wish and use a very thin dowel to aid in spreading the epoxy on the internal fillets.....................

Remember,,

A glass build is all about "Order of events"...........

Teddy