Access hatches
 

How do you do your access hatches? I need info on how you attach the hatches, ie type of support,screws, thread inserts, etc, (balsa construction). All sugesstions greatly appreciated.

Thanks,
Pete Killingsworth
Peshtigo, Wisconsin

RE: Access hatches
 

Depends somehwat on thier purpose. Some may just provide a cosmetic cover, others may be structural. For cosmetic covers, very little is required to hold them on. Even tape works to hold a cover on. However, if the cover is structural, you need to take any loads into consideration.

What I typically do is create a tab or pin and socket at one end and then have a fastener of sone type at the other end. A tab would typically slide under some structural item. A pin and socket could be a simple as a small dowl and a drilled hole. For fasteners, all sorts of stuff will work, I've used some spring loaded captive locks before, but I typically just use a screw of some type. Sometimes with a blind nut, or insert, or even threaded wood. There is no reason why you couldn't use screws all around, but I find it easier to use the panel if I have less screws to mess with. As for material, again it depends. Balsa is a little flimsy for something that will get some abuse, so I typically make my own plywood or composite. Easy to do, just sheet 1/16" balsa with fiberglass or 1/64" aircraft ply. The final result is a very thin and light hatch, but stiff. You can also laminate over a curved surface, such as a mailing tube to create a curved hatch. You can also make a fiberglass (or other composite like carbon fiber) hatch fairly easily. But there is no reason why you can't use light ply or aircraft ply.

RE: Access hatches
 

Generally speaking, unless the hatch is thick balsa, then it should be made with the grain going in the short direction. You can put dowels in the balsa hatch and drill through them to provide hard points for screws. You can also put some squares of plywood on the underside of the hatch and counter-bore the balsa down to the ply for the same purpose.

Inside the plane, you can put squares or triangles of 1/4" plywood or hardwood to thread the screws into. Another way which I like is to glue 3/8" - 1/2" long pieces of inner NyRod into the balsa on the plane and use #2 wood screws or servo screws. You don't need to glue hardwood in if you do this because the NyRod holds a thread well.

Just drill a 1/8" hole in the balsa where you want the screw to go, put in an over-size piece of the NyRod and then put a couple drops of thin CA next to it. The CA will wick in and hold the NyRod in place. Then trim off the excess. It's neat and light.

JohnWillman was right in saying there are a lot of ways to do it. Once you've built a few models you'll learn all kinds of ways to make hatches. But, the more you know, the less hatches you need. :)

You should avoid hatches whenever possible because they weaken the structure while making it heavier. But they work and if you need one, you need one.

Harry Higley has a book called "Mostly Mounting." It covers some of this, but I didn't think it was worth paying for because there was nothing in it that I didn't know already or felt I had a better way of doing. But for a new builder, it will give you a jump start on some techniques.

RE: Access hatches
 

Many thanks to all who replied, your input was most helpful. Now I feel I do my hatches with confidance. I really appreciate you taking the time to respond.

Pete

RE: Access hatches
 

Just thought I would show what I did to my Super Sportster 60 to gain access to the fuel tank and battery compartment. Being that I had to mount the battery forward near the firewall, and the model was already built and covered, I had to cut a portion of the top section of the nose out. I used a plastic hinge (same as my control surface hinges) and very small nails with epoxy to hold it all together. I did my cutting inward at an angle so there is a cross section like \_/. I may have problems with monokote pealing in the wind, but I have yet to fly it to find out. As long as your hatch opens against the airflow you should do o.k. I don't know if this is what your looking for, just my .02 [8D]