Retracts Install - Very Basic Question
 

Hi All,
About to start on a 1/6th scale '47, using Sierra gear. First time installing retracts, so this may seem like a silly question...

What do you use to mount them to the rails? Some particular type of screw or drill through rail and use bolt/nut? Considering landing forces, weight, impact, etc,.. seems that using the right mounting hardware would be kind of important, but I can find nothing other than hooking up lines and such. Opinions and suggestions appreciated!

I typically tap the wood or ply for machine screws.. tap. then wick thin Ca in,, the run the tap again, might have to do it twice to get a solid feel,,

good luck

You'll probably get as many different opinions as there are replies to your thread. I do mine with machine screws and blind nuts.

mate I have used both of the methods listed.

My Vailly 90" & 42lb Seafury uses bolts with capitive nuts. Holds them securely but if you have a heaving landing it will tend to rip the mounting and supporting structure out plus do damage to the retracts.

My smaller P51 82" and 21lbs uses self tapping screws. Again it holds them nicely but on a few occassions I have had heavy arrivals and it has pulled the screws out, sometimes with a little sheet damage but not substatial and the retracts have not been damaged.
The rails tend to split and will need to be repaired or replaced. Not really a big repair.

Pros and cons to both methods.

On a smaller model like yours I think the self tapping screws would be a good option.

Hope it helps.
cheers
P

Mounting rails provide support however there is a better method using the rails and a plywood plate. Mount your gear on the plate and that attach it to the rails. Or you can eliminate the rails and go with the plate. Meister Scale uses the plate method and that is a company that invests in engineering principles other manufactures neglect.

What is the benefit of using a plate with the rails?

-Ed B.

Increased structural integrity.

plate pulls out leaving the rails intact.

I've used that as well and it can work well. Depends on the model and how much room you have.

@RD
Plates flex before failing giving the structure a chance to absorb the impact and distribute the forces. A rigid mount assembly will transfer the load to the next weakest point.
If you cant use a plate then use good coarse thread sheet metal screws in predrilled holes. You want the drill size to be smaller than the minimum screw diameter (minor pitch dia) to make a pilot hole. The screw will then cut a nice clean thread in the wood. Unscrew them and use thin CA glue to toughen the wood grain. Assemble the gear and check fit.
If you use a blind nut and dont have access to the back of the rail then the blind nut will aid in splitting the rail because it has a larger diameter shank. You must predrill the hole on the back side to clear the shank diameter to do it right. It will be a stepped hole not a clearence hole all the way thru because then the screw can move within the diameter of the large hole.

Using a machine thread which is a fine pitch thread is ok but not ideal. The threaded wood doesnt offer as much leverage to compress the assembly when you tighten the screw. If its long then yes it does a better job but if its a short screw then I would change to a coarse thread sheet metal screw.

If the retract flange is about 1/8 in thick then you want a screw that is a minimum of 1/2 inch or longer if your using washers also.

Post a photo of your retract install and the guys here will be happy to give you better suggestions.

Thats some great info. Chris, much appreciated. I'll see if I can post this pic.. I havent relieved the area around the rails yet, the rail extends about another 6" to front spar. The flange is 1/8th. Basically planning ahead so when I'm done testing and ready to mount I'll have the materials on hand. Thanks again!

For .60 size Sierras I used No.6 cap screws 3/4" to 1" depending on the rail thickness. The Sierra case is stouter (and heavier) than a lot of the other retracts, so I liked to screw them in good and a hex cap seem to work better than various screw type heads.

For other retracts (Robart air and various mechanical retracts) I use 3mm self tapping screws I get from Airborne Models. Generally the cases on these retracts are not as strong. If the rails are not exactly square, pulling them down really tight will put them in a bind. May hang up then. 3 x 14 for .46 planes and 3 x 18 for .60 planes. These screws come with Airborne's planes with mechanical retracts and seem to hold better than others I have tried. Don't know why.

I use the pilot hole and CA method mentioned earlier.

The Sierras for my GS TF P-51 came with a solid, rigid base plate the retracts screwed onto. I think the rigid plate/heavy retract case spread the landing shock out more evenly across the rails. I did not have any problems with retract rails after I installed these Sierras.

Brian

There is not always room for a plate, and even if there was, the original bounting beams are often installed so closely together, that any eccessive force (hard landing) will cause the retract unit to bend/break the beams, even if an additional mounting plate is used. I have several 40-50lbs jets/prop, and I use wood screws in them all. The screws just barely peeks through the beams/blocks/plate. As mentioned above, something has to give, and I want to "control" that as much as I can.

If you secure the retract rock solid with machine screws and nuts, the mounts might hold up on a hard landing, but on inspection you might very well discover that the struts are slightly bent;(

Other modellers might prefer this..

I prefer to fix the screw holes and put in some new screws:)


btw, l/g issues seems to be the most common trouble area in this hobby, if I jugde by my experience.

Hmmm, just looked at your photo Radical. Personally, I would cut out a good bit of the wing skin around the mounting beams, and reinforce or maybe change the stock ones completely. The wing skin part can either be glued back on, or made to function as a big access hatch for future possible retract repairs/maintainance. You can do it now, when everything is clean and new, or later when you have a mess after a hard landing /off the field landing.

Just a thought;)

I'm going to be cutting the area away, just haven't got to it yet, getting all the things I need together so when I start I can keep moving right on along. Planning on using G10 to make covers. Putting some reinforcement around the existing rails is no big deal, can do that. Sierra sent the wrong size wheels, got tired of dealing with Darrell and got right size from Robart, and now they've been delayed. Really not wanting to get too far along until I can make sure I have the wheels centered. Hurry and wait! Trying to figure how I'll get the inner doors to work is whats been keeping me bamboozled.. but that's another topic...

Thanks to all for the great responses, not sure if will use plate, will have to see how things go together, but I know now what hardware I need to bolt'em on. Thanks again!!