Tutorial Advanced - Orta Saint - Hubert G - 1

[Gearup]

Reducing the wing blank thickness
The wing can be thinned using a hand plane, bandsaw or handsaw as available to just under 1/4 ". To plane it to thickness, the wing is double side taped to a work surface and planed down to its thickness.

I used a table saw and I attached the wing blank to a sturdy and straight stick with double side tape. I set the saw fence to 7/32" from the blade and I made a few passes raising the saw blade until it was through the full thickness. (IMG_0195.JPG)

You may see that the wing profile has been cut out already. On consideration it is better to thickness the wing while it is still in a squared flat block as it makes handling much easier.

[Gearup]

Applying the paper templates to the wing and tail blocks with reference holes

(IMG_9789.JPG) (IMG_9790.JPG) (IMG_9803.JPG)

Now apply a thin layer of glue as before to the top of the wing block and apply the plan of the wing. I defined the block top as the smooth side since future work thinning the block will be from the bottom side.

Mark and drill the four reference holes as shown . Two define the centreline and two more are reference points located at the outer end of the ailerons.

For the tail surfaces, note the grain direction on the maple scrap used. It is best to have the grain running parallel to the span of the horizontal stabilizer and to the height of the vertical fin. This is far stronger and actually mimics the direction the spars run on the real aircraft.

[Gearup]

Rough cut wing and tail surfaces

(IMG_9796.JPG) (IMG_9795.JPG) (IMG_9811.JPG)

Using a bandsaw, scroll saw or coping saw the wing blank is sawn out. Here I am using a scroll saw as the wood is thin and easy to cut.
Cut to the outside of the line as shown. Sometimes it can get a bit confusing if there are other lines in the vicinity that can pull you off course. Pausing and standing back to check your progress can help you refocus on the line to cut. Notice the bright light close to the blade and the sharp shadow it is casting. It will help you to keep track of the blade as it cuts as well. Also the air blower helps keep the area clear.

Cut out the tail surfaces using the same technique . A small cut at either end of the centreline on the horizontal stabilizer ensures that the centre is not lost during further shaping and thinning. (IMG_9818.JPG)

[Gearup]

Sanding the wing and tail to the line.

A stationary belt sander is a great tool to trim and shape parts. It can work as fine as splitting a pencil line or can remove the waste wood around a large bock very quickly. Here, the horizontal stabilizer has been sanded to the line using a belt sander. (IMG_9818.JPG)

Remove the paper patterns from the wing blocks. Use a heat gun (hair drier) to soften the glue under the paper and scrap it off with a putty knife.(IMG_9821.JPG)

[lastvautour]

Coming along nicely Fraser.

Lou

[Gearup]

Thanks Lou. Like tying your shoe laces, it's actually easy to do but difficult to describe the process.
Fraser

[Gearup]

Wing guide marks

Some of the marks can be measured from the plan while others are made using a general rule-of-thimb method to define the airfoil.

First a centreline is drawn on the wing connecting the alignment holes with a line on both top and bottom.  It is also marked on the verticals of the leading and trailing edges.(IMG_9921.JPG) (IMG_9923.JPG)

A measurement from the wing plan center line to the point that the wing starts to sweep forward and back is taken with a compass. Transfer the tick marks to the leading edge and trailing edge of the wing as was measured from the centre line. Connect the ticks with lines fore and aft (wing chord) and vertically along the thickness of the leading and trailing edges.

Mark a line at the wing tip alignment holes parallel to the centre line of the wing on both top and bottom. I used a sliding T bevel gauge for this. (IMG_9924.JPG)(IMG_9925.JPG)

[Gearup]

Wing lower surface layout for taper

The Orta has an interesting wing. It is a straight wing with no dihedral typically made by raising the left and right wing tips up a certain amount. Dihedral is a stability design found on nearly all aircraft. However, it looks like the way the Orta's wing was designed, the lower surface tapers from the root to the tip while the upper surface remains straight, creating a type of dihedral.

This tapering is easy to do. Double side tape the wing, bottom side up, onto a suitable length of wood to act as a holder while planing. Looking at the plan, the wing tapers in thickness from the root chord lines drawn in the step above.

Mark point on the front  face  of the wing leading edge tip chord-line half way between the top and bottom surfaces.  Now on the front face of the wing leading edge, draw a line connecting the bottom root chord to the tip chord line the halfway mark. You should have a taper drawn on the from leading edge from root to tip. Repeat on the other wing leading edge and on both wings trailing edges. (IMG_0205.JPG) Shown partial planed. Sorry I forgot to add the arrows for a few pictures, but you are basically drawing a slope from the wing root to the tip to define the lower surface .

You should now see a wedge of material that needs to be removed from the lower wing surface.

[Gearup]

Wing lower surface -  planing the taper.

Using a soft (HB) pencil, lightly mark chord wise lines (lines running fore and aft)on the wing spaced about 1/2" apart between the tip and the root chord line. Straightness of the lines nor the spacing of them is not critical. Draw them free-hand and don't press down on the pencil. These lines will be used to control where you are removing material with the plane and allows you to control the taper.(IMG_0199.JPG)

Work the handplane on the wing moving from the root line to tip direction. Initially hold the back of the handplane (heel) up so you are just shaving the surface of the wing about 1/2 inch back from the tip.

Take a look and you should see that one or two of the lines have disappeared. This is the start of the taper. If the lines are partially gone and only the forward or aft portion of the line remains, you are removing the material chord wise unevenly (tilted across the wing). Take a few more passes with the plane and adjust your stroke to favour the portion of the  marks that are still remaining. This should even it out. Still keep the heel up to work only on the end of the wing or now.

Remark the missing chord wise lines again in the area where you have removed them. Now raise the heel a small amount and plane again. You should see that you have again removed the new lines and probably some of the other lines you marked originally . Continue remarking and planing the wing with progressively longer strokes. Now check the sloped line you drew on the leading and trailing edges. The line should be parallel with the planed surface. Use this as a gauge to determine whether you need to adjust the angle of the cut you are making to bring the planed surface match the lines slope. Mark, plane, check repeat.(IMG_0203.JPG)(IMG_0204.JPG)

You will eventually reach the root chord line but don't shave it off. If you shave it off, remark the line accurately and try to avoid removing material from the centre part of the wing beyond that line. (IMG_0205.JPG)
The picture of the plane sitting on the wing seams to look totally tapered beyond the root cord line, but it is an illusion from the photo. (IMG_0206.JPG) Repeat on opposite wing.

When done, remove the wing from the board. Here is the final wing taper showing how the dihedral was formed. (IMG_0207.JPG)
Wing upper surface airfoil layout

[Gearup]

Wing upper surface airfoil layout and guide marks

A generic curve for the top of an airfoil can be achieved using guidelines drawn on top.
All of the marking made now will be only on the top surface of the wing. The bottom wing surface remains flat.

A bit of measuring and arithmetic is used to lay out the guidlines. The airfoil is roughly in thirds: leading edge to wing top surface and trailing edge to wing top surface.  Measure the chord of the wing at the root and divide by three. (1.5" / 3 = 0.5" = 1/2"). Do the same at the cord at the tip where the last rib would be, that is at the alignment hole in the wing tip. (1.25"/3 =0.375" = 3/8")  Ignore the rounded tip as it will form its shape as the wing is shaped.

Mark the 1/3 divisions on the root chord (1/2" spacing) and tip chord (3/8" spacing). Draw a pencil line connecting the forward root chord and tip chord marks along the length of the leading edge. Now mark another line span wise along the leading edge halfway between the leading edge and first 1/3 line. The leading edge is a steeper curve from the nose to the first mark and flattens to the 1/3 line where the wing is relatively flat, and this will help mark the shape the leading edge curve. Do the same on the other wing. It is a one piece wing, but there is still a left and right wing. Make sure to mark the wing into thirds on the centre section ( the straight section between the two wing halfs)

Now do the same with a 1/3 line for the aft part of the wing to define where the trailing edge meet the upper part of the airfoil.(IMG_9927.JPG)

[Gearup]

PAUSED for now
I will have to pause work and recording of the Orta build due to an unforeseen circumstance. Shortly after I started a vacation, our neighbour discovered that the dish washer had flooded the kitchen. Now that I am back, the repair of the damage is underway but it will make it difficult to provide construction updates. 

I will resume the construction  when the kitchen is in a usable state. Sorry about the delay in updates.

Fraser

[Gearup]

So where did I leave off.... Its been a bit of a break for summer vacation and kitchen repairs, but I digress...

Wing airfoil shaping with block plane

Now that the guidelines for the airfoil have been marked out, it is time to shape the wing. Again I am going to use a nice sharp block plane to take even and thin shavings. I find it best to work a few strokes on the left wing and then take the same number and position of strokes from the right wing. This will help keep the material removed symmetrical.

I usually start at the leading edge. I've shaded the area where I will start with. Use an HB pencil or soft charcoal stick as it gives a nice dark mark that is easy to renew. Shaping will initially start with the upper forward edge of the leading edge and work the length of the wing with the grain. In fact all work for this part is moving the block plane with the grain. Take a few stroke with the block plane held at a constant shallow angle to the chord of the wing. Now take the same number of strokes on the opposite wing leading edge. Change the angle slightly flatter to remove the angled corner to produce a faceted shape of the leading edge . Now do the same on the opposite wing.  Use the charcoal to mark the facets to give a clear visual to help in making the cuts.

The idea is to gradually work the leading edge to get a multifaceted curve back to the first "third" mark on the wings aft of the leading edge centre mark. By making only small facets at this point, it is easier to achieve good symmetry of the wings and to get a gradual curve from the centre of the leading edge to the top of the wing. 

When you have a nicely facetted upper surface leading edge, flip the wing over and give the lower leading edge a few strokes to facet the lower leading edge.
When planing the wing, do not remove any material from the very front edge or trailing edge of the wings as this will change the plan shape of the wing.

Now work on the aft third of the upper surface. This part of the wing, although slightly curved on an actual wing, can be planed to a flat wedge from the aft third at the top surface to the trailing edge. Use the charcoal frequently to make slash marks on the planed area as you remove material to give you an indication of the progress of the material removed. Plane until the wedge slope forms a surface from the aft third mark to a consistent trailing edge thickness of about 1/32" from the bottom of the wing. If it gets too thin, it gets very fragile, especially in softer woods.

Now the wing is ready for further shaping with sandpaper.

[Gearup]

Wing airfoil shaping
more pictures

[Gearup]

Wing airfoil shaping with sanding stick

Make a sanding stick from a piece of wood 10" long and 3/4" square. Use double sided tape or glue to attache a 3/4" wide strip of 80 grit sandpaper (course) to the length of the stick.

Look at the wing from end on and you will see that you need to blend all the facets into a fair curve on the upper surface. Use the sanding stick as if it is a violin bow across the chord of the wing. You do not need to apply a great force on the sanding stick. Work the wing surfaces equally left and right gradually blending the wing surface into a smooth curve. Don't work on getting one spot to the right shape, rather work the whole wing along the span to get a nice smooth shape. Notice in the  picture that the wing that is partially sanded has a dirty and clean surface. The very top surface of the wing is barely touched and marks will remain there until final sanding. Work on blending the center section cut out and it does not come to a sharp trailing edge, but is a rather blunt curve.

When you are satisfied with the overall smoothness and shape of the wing you can sand it to 220 grit. I use a 2" square of sand paper double taped to a square of "craft foam" sheet. This is an inexpensive foam sheet that is fairly dense yet flexible that you can get from a dollar store. It makes for a great model sanding pad.

Work the sandpaper pad down the length of the span with the grain until you have a smooth wing, top and bottom. At this point there is no need to go finer in grit as sealing and primer will adhere better.

[lastvautour]

The wing is looking good Fraser.


Lou