DIRTY BIRDY “60”

Joe Bridi’s Dirty Birdy is one of my favorite planes. There have been numerous discussions of problems with the instructions so I thought that while I built a replacement for the one that I killed last year it would be a good time to keep some notes and post a few corrections. Let me start out by saying that this is not a difficult plane to build. If you’ve built a few planes the Dirty Birdy shouldn’t present any real challenges. However due to a few errors and some changes to the kit through the years, the instructions can be somewhat confusing. I hope that these instruction updates will help eliminate some of this confusion

Let me say that I am not now nor have I ever been associated with Joe Bridi or Bluejay Models. These instructions are just my take on building this plane. If you don’t understand something that I say and if you’re cool with the instructions as they are, by all means follow the original or do things the way you think best. Additional insight into the evolution of this plane and the plans can be gained from looking at the original construction article http://www.trentonrcflyers.com/patte...rdyArticle.pdf .


A few general construction notes:

This plane has lots of shaping to be done. In many places the instructions tell you to sand to shape. A razor plane gives much better control, shapes faster and makes less mess. If you don’t have one, go buy one right now and practice with it. I use the Master Airscrew razor plane but any one will do.

When you need to shape a block next to sheeting (LE, wing tip, etc.) protect the sheeting with blue painters tape. Now you can carve away without damaging the sheeting. Carve flush with the sheeting first, don’t try to round it right away. When you start tearing the tape you’re getting close, treat that area with caution. Once you’re just about flush with the entire surface, then you can start rounding. But go slowly, it’s easy to get too aggressive and leave a flat spot. Only use the razor plane to get close. Then switch to a sanding block to even things up and finish shaping. Leave the tape on even for the early sanding. Finally remove the tape and finish sand. If you’re really tearing the tape up, it’s doing it’s job and you’ve saved your finish. Remove the tape and apply a new piece.

When you’re carving something long like a leading edge or an aileron bevel, use long strokes, each one the full length of the part. This will help keep the shape constant.

I do lots of filleting with microballoons and epoxy. The trick of protecting the wood with tape while sanding works great around fillets too. It keeps you from cutting into the wood. You can see some of my microballoon filleting in the pictures of the Wing Filler and the Tail and Hatch.


A few things need to be taken care of before starting assembly. The original kit had pre-cut stab slots in the fuselage sides. But the current fuse sides do not have the slots pre cut and the instructions don’t tell you to cut them. You will do well to mark and cut them now and it’s much easier to do before the fuse is assembled. I use tracing paper to trace the outline of the aft end of the fuse sides and the slot from the plans. To cut both slots exactly the same I use a little Scotch double stick tape to hold the two fuse sides together, then double stick tape the tracing in place. Then it’s an easy job on the band saw to make the slot. Or each fuse side could be marked and cut by hand with an X-Acto knife.

The fin slot in the fuselage top is also no longer pre-cut but I find it more accurate to cut this slot after the fuselage is framed and squared.

Be sure to make the cutouts shown on bulkheads #2 and #3. Again, the instructions make no mention of this. I think these cutouts may have been precut in an earlier version of the kit.

You also need to determine if you need to move the firewall position based on your engine selection. These planes tend to come out nose heavy so moving the firewall back a little is not a problem. Determine the required distance from the firewall to the spinner based on your motor mount/engine/spinner combination and if necessary mark the new position on the plans.

Another thing you need to start considering is wing incidence. A note on the instructions says the wing should have 1/64” positive incidence which works out to 0.068 degrees. The instructions say you should have 1/32” positive incidence (0.137 degrees). But if you measure the plans it actually shows 7/32” positive incidence, right about 1 degree positive. And the parts exactly match this. I don’t know which is right. The instructions will have you adjust the incidence when you mount the wing but it’s difficult to make large adjustments once everything is done so it’s best to decide now what you want. On my first Dirty Birdy I shot for the 1/64” positive incidence but wound up with 1/32”. This plane needed significant up elevator trim to fly level. My second plane I went with the stock 7/32” incidence which gives you just about one degree of positive incidence, many people consider this to be ideal. With one degree incidence the second plane required four clicks down trim, about 1/16”. And this will increase as I move the CG aft. Of course both planes flew fine.

So which incidence was the original design and which was the update? I don’t know. You’ll have to decide for yourself which number to use. Having tried both I think the best answer is somewhere in between but who knows what other things affected the trim on my two planes.

Whatever incidence you choose, adjust the wing saddle now or step 14 will be a major headache. Read step 14 of Completing the Wing to determine how the incidence is set, you’re just going to measure the front and back of the saddle to the top of the fuse side. Remember to include the shape and thickness of the leading and trailing edges. Trace the wing saddle and adjust the saddle to your desired angle before you start building. You’ll be way ahead.