Hello,

Many years ago, I started to build an ElectroFreshman; a kit from the now defunct Premier Balsa Products. It was to have been my first aircraft of this type. Then a house move got in the way, and the project was shelved.

I recently rediscovered the forgotten, half-built 'plane in the loft, and a brief search finally turned up the rest of the kit. I think the time has come to finish it, since I've had it since 1991...

Trouble is, I only have half the model plan. I have the (very scanty) instructions, and plan and elevation for the fuselage, but I appear to have lost the top half of the plans, probably still pinned to a building board and left behind during the house move.

I have already built the wing centre sections. I have a full set of ribs, and I know the total wingspan, so I think I can deduce enough to get the outer wing panels built.

The fuse and fin/rudder are no problem - I have the parts and plans.

What I don't know is anything much about the horizontal stabiliser. It's made from sheet, not built up. Nice and simple, but I have no idea what its span ought to be.

Model's vital statistics:
72 inch wingspan
53 inch length
approx 550 sq/inch
approx 22 ounce<div id="TixyyLink" style="border: medium none ; overflow: hidden; color: rgb(0, 0, 0); background-color: transparent; text-align: left; text-decoration: none;"></div>...and that's about all I know. Anybody care to hazard a guess at the dimensions or surface area of the empennage? Is there a formula I should use to determine this?

Any thoughts appreciated!

The optimum would be if someone has a set of plans for you. But barring that it sounds like you've got enough to come up with a plan that'll work.

I'm guessing that this was a poly or tip dihedral design. If so then it shouldn't be too hard to at least make up a resonable model. The tips would use the same rib spacing as the center section so that'll fix the span of the tip panels. Then to make things easier I would suggest that the tip panel spar be in line with the center panel spars. From there the ribs will set any taper that may be in the tips and now much, if any, sweep there is. And if you can find any pictures of the model that can also provide a guide.

Tail size isn't all THAT critical. It won't be hard to figure out a suitable size. The length is a goodly portion of the span and if the nose and tail are of average proportion I'd suggest you should have a stabilizer of about 85 to 90 square inches. Use the chord of the stab from your fuselage plan to figure out what the span of it should be. And although you don't remember it being built up I would suggest you make it this way to keep the back end lighter. 1/4 inch would be a good thickness with the "spar" or hinge line strip being from 1/4 x 1 and the leading edge from 1/4 x 3/4. 1/8 x 1/4 strip ribs holds the parts together. The elevator can then be made from 1/4 x 1 trailing edge stock or carved to a similar shape from sheet stock.

And I trust that you're not planning on using the 1991 motor and battery technology at this point in time. Lighter tail structures combined with our far lighter brushless outrunner motors should make this old girl really sit up and sing sweetly.

Thank you for the advice. It is indeed a poly dihedral model, and your comment about the rib spacing has helped me a great deal. There's virtually no mystery about the wings now.

I've resumed building, on this kit originally started 19 years ago. And wow... how things have changed! We're really spoiled nowadays, with CNC-cut parts and so on. This is a very different beast, starting with how you can't build with the model pinned over the plan, or you can't see a thing. Some of the dotted line detail is more than a little vague, too. Fortunately, I'm not a complete beginner and I think it's going OK.

I'm pleased by the thought of finally getting this model into the air, but it's proving to be hard to love. The boxy shape of the fuselage and wing is meant to make construction easier, I suppose, but I've seen newer kits that manage to be simpler and quicker to build, while still having some nice curves.

Still... let's wait and see how it flies. With 21st century electrics, naturally. I plan to cover this ship old-style: something of a wolf in sheeps' clothing!

If ever I manage to tease out the warp that the aged balsa seems to be forcing upon the fuse, that is. (Heat? Steam?)

Scalding hot water works well. Pour it over the wood and then immediately set it onto a drying rack of shims as mentioned next. Another option is to soak it in full strength ammonia and then lay it across a bed of shim strips to elevate the side up about an inch. Load the other side with shims and some light weights that hold the side flat. Allow to dry out for about 24 hours until you cannot smell even teh slightest whiff of ammonia.

The idea is that the ammonia softens the lignum that forms the walls of the wood's cell structure. But when it evaporates away the lignum is fully restored.

For obvious reasons you won't be a household fan if you do this indoors. So out in the garage with lots of airflow is the way to go. About a 5 minute soak should do the job. But pull it out and test for flexibility

Thanks again! I'll give it a go, since I have nothing to lose with this old kit.

I did try to build it nice and square... with bricks on the building board and several clamps... but it's as if the two fuse sides were completely different grades of balsa. (Does it degrade over time, I wonder?) One of 'em bends readily, and the other one really doesn't want to flex. Hopefully, with your method, I can relieve the stress before I skin the top and bottom.

While this may well level a warped piece of wood it won't aid in the two sides flexing equally. If the mismatch is extreme you may well need to cut one or even two sides from new wood.

An old trick from the books I read on model building showed how to compare sheets for similar stiffness for matching things like sides. It involved holding the sheets so that they hung over the edge of the bench like two diving boards with only about 2 inches held onto the bench. For wood up to 3/16 inch you look for the wood to sag by equal amounts to show that they were about the same bending stiffness. This is more effective with wood of 1/8 inch or less. With 3/16 stock I suspect it would work as well but you would want to position a little extra weight at the end. Something like an oz perhaps? That would cause them to sag enough that it would be far easier to see what their relative stiffness' are like.

Thanks for your encouragement. The build has gone very well. There's still a slight warp, but nothing I can't compensate for elsewhere.

Can we talk battery, prop and motor combo, now? I haven't covered the model yet, but I don't think it's going to be overweight.

I'm assuming I'll use a 10g receiver, and an ESC with a BEC. Top it off with HS82mg servos (which look absolutely tiny in that big fuse)... at a mere 19g each. This ship is going to be nice and light... but what brushless motor would you put on a 72" span motor glider?

I have fitted an Overlander Thumper V2 (T35/36/8 480 watt kv1000), and a 3-cell LiPo. Complete overkill in terms of climb performance I expect, but it filled out the nose of the model perfectly, and put all the weight up front. Plenty of room for an oblique-mounted camera or two, amidships.

Steering this old thing with its three channels and massive amounts of dihedral isn't going to be exactly exciting, so we have to do what we can to jazz it up.