Seagull Boomerang taildragger mod

[Martin 0]

A couple of people have asked me about my taildragger mod for my Boomerang, and so I'm posting it here so it's archived.

 

I have tried a few versions of this, and this is the one I'd recommend.

 

Unfortunately I don't have photos of it, so I'll try to describe as best I can. I might also try to get some photos of the installed one, but they're unlikely to come out well inside the fuselage (if only I'd taken photos as I did it).

 

If you're modding a brand new airframe, do this as your first action on the fuselage assembly. It'll be much easier and you won't risk damaging the tail assembly while fiddling around! In any event, you need to not have the fuel tank in place.

 

The undercarriage I used was just described as "Dural undercarriage for 40 size planes" or similar at Inwoods. It's basically the same as a WOT4 undercarriage. I think the one I have may have been Irvine branded. I can't find the exact one I bought listed on their site any more, but any model shop should be able to sort you out with something appropriate.

 

I mount the undercarriage with two M4 nylon bolts. These seem to be just about right, breaking on abnormal events (like running too fast off the end of the runway) but not normal landings. M3s were definitely too weak with only two. If you reinforce everything as described here you might also be OK with steel bolts as the undercarriage mounting is probably the strongest part of the whole airframe!

 

The Boomerang has a fuselage former just forward of the leading edge of the wing. There is another former about 2 inches in front of this, which also supports the rear of the fuel tank. I mount the undercarriage between these two formers, so the rear edge of the undercarriage lines up with the rear of these two formers (and hence also the leading edge of the wing).

 

Cut a piece of 1/4in ply that exactly fits the floor of this space. I measured the distance between the formers inside the fuselage, and determined the width of the space by measuring the external width and subtracting two thicknesses of the wood used for the sides. (Note that the wing seats are doubled, so if you measure those only subtract one.)

 

Mark the centre line on both the undercarriage and this piece of ply, and then use the undercarriage as a drilling jig to drill two holes to take M4 T-nuts. Fit the former inside the fuselage and use a 4mm drill bit between finger and thumb to drill the holes through the 1/16 balsa on the bottom of the fuselage.

 

This piece of ply needs reinforcements to attach it to all four sides, but paying particular attention to the front and rear. I have successfully used beech strip (which Avicraft sell for engine bearers and servo mountings), and also 1/4in ply mounted vertically (when I didn't have enough beech left). I haven't tried balsa, but it might be OK as long as you mount it with the grain VERTICAL. Balsa is very weak in tension across the grain, and a hard landing with a bad flare would rip the front of the reinforcing plate downwards. If you use balsa with the grain horizontal then it's not adding much strength in this direction.

 

Make sure that whatever you use on the forward edge doesn't impinge on the tank hole in the former! Dry fit everything to make sure!

 

Hammer the T-nuts into the reinforcing plate, then epoxy the plate into the fuselage. Pay particular attention to the edges of the plate rather than the bottom, as these are the bits in contact with strong structural members. Epoxy the reinforcing strips (beech or ply) in place and leave the whole lot to set. Make sure that the reinforcing strips are well glued to both the plate and their respective formers.

 

For the rear, I currently have a simple wooden tailskid. I cut out the sheeting from the floor of the rearmost fuselage compartment and cut a piece of 1/4in ply to fit (so there is a strong floor to this compartment too). I cut a triangular tailskid from 1/4in ply, sanded to have nice rounded corners, and both epoxied and screwed it (with small brass woodscrews) to this floor piece. I then epoxied the assembly into the bottom of the fuselage and painted the whole thing with warmed-up epoxy to mud- and fuel-proof it.

 

(If you're concerned about the weight being added to the tail, remember that you've added a big metal undercarriage in front of the CG. Without a little extra weight in the tail you might otherwise find that the plane is a little nose-heavy.)

 

On my first Boomerang I had a non-steerable tailwheel. I only used a tailskid on this one as I forgot to buy another tailwheel assembly. If (heaven forfend) I need a third, then I would definitely put on a steerable tailwheel. There is a spare pushrod tube already fitted inside the fuselage going from in line with the rudder servo down into the rearmost fuselage compartment, exactly where it would be required. I haven't yet tried this, though.

 

Well, that's come out a bit longer than I expected, but at least it's now written down. I hope someone finds it useful!

[snakeyme 0]

hi martin, im curious s to how big is the rudder on a boomerang, meaning if it full length or is it just the size of the fin itself.

 

the reason why im asking is becoz im wondering if it would be possible to attach a rear landing wheel which uses a pin drilled and glued into a rudder for steering as this would (i imagine) save alot of trouble with more linkages.