Autogyro, can meh?

29 December 2023

Spinning propeller. spinning rotor

Keep the disc of propeller or rotor spin true, or just less wobbly. That means the bearing holes must have some play but not too much and be spaced a good distance apart.

Bearing structures could be made from thin aluminium sheet with the holes pierced then folded to the hub.

The hub may be 2 identical sheet balsa pieces to anchor and spaced apart the folded bearing structures.

Since the hub is sheet balsa, it will provide good gluing surfaces to the 2 blades.

Distance between bearings, the "height" or "depth" of sheet hub, may be 1/4" for 3-7" prop and 1/2" for 20" rotor. 

Propeller shaft is perpendicular to sheet hub. Rotor shaft can be angled to create a conical disc.

Propeller and rotor shafts may be flat to glue directly onto the sheet hub or they may be thin carbon fibre rods so that the angle of attack may be adjusted. If adjustable rods are used, the holding structure may be tissue/paper, pressed over the rod and glued with superglue on to the sheet hub.

To fold the bearing structure, a former can be used. A former can be 2 pieces of hardwood (ice cream stick), with one edge square and a pin perpendicular to the edge to locate the hole in the bearing structure. Then a plier to fold the aluminium over the same edge.

The blades may be like a paddle where there is no twist between root and tip. Or, the blades may be twisted to form something of a helical pitch.

There is no perceivable benefit to have tip weight to the propeller blades but it may be beneficial to have tip weight to the rotor blades to introduce some momentum stability while the rotor spins.

Rotor constructed above does not have flapping hinge.

Thin rotor blades may bend under flying load and cause something like flapping hinge but there's hardly any control of the hinge axis.

Flapping hinge is beneficial to rotor blades to avoid roll-over.

The flapping hinge may be set at an angle to introduce negative angle as the blade hinges up.

The limit of hinge may be a pair of simple thin aluminium bracket at the flapping point.

6 July 2023

Foam blades with CF rod as spars

1. Blades from foam dinner plates. 
2. Glue CF rod to blade.
3. Balance.

Cardboard hub

1. Draw and mark hub strip on cardboard. 
2. Punch holes according to mark.
3. Fold ends to form isoceles triangle.
4. Make aluminium bearings from drink cans. 
5. Cap the top of the isoceles triangle cardboard hub with the top folded aluminium bearing and add the bottom bearing to the base of the isoceles triangle.

Assembly

1. Insert CF ends of the blades through the isoceles triangle hub.
2. Insert Shaft through the bearings.
3. Adjust and balance.

If the isoceles triangle is used with the base as the top, we have a flat top bearing surface which is better since the lifting/dragging force pushes against the top stop of the shaft. The sides are used as tensile members. The ends of the sides can be lapped to the counterpart side.  

3 July 2023

Paper blades

1. Rectangle blanks, equal lengths, width at 150% of chord. 
2. On underside, mark at 50% chord along span.
3. Crease fold the longer 100% of chord width, the crease line will be 50% and the long edge meets the marked 50% chordline.
4. Slit along marked chordline, glue paper tabs to secure, top of chord and bottom of chord. 
5. Cut 1/32" balsa spars to width of 40% chord.
6. Insert balsa spars to paper blades' pockets, ensure they are identically placed in each blade.
7. Spot glue the balsa spars to the tip and root of the paper blades.
8. Join the balsa spars to the hub and a rotor disc is formed. Could use the balsa spars itself to make the bottom hub.

22 March 2023

Today I am thinking about leverages for pitch roll and yaw stability.

If the rotor is flat, it can't provide any leverage.

Pitch stability

It could be an elevator at the back or a lifting plane at the front. Which is more effective? In the front lifting plane, it would be at the verge of stalling. Front fin would destroy yaw stability, so my choice would be a rear elevator.

A wing can be pitch stable itself, this involves having lifting portion and stabilising portion of the wing front and rear respectively.

A rotor with a dihedral angle will have this form of pitch stability as well.

Yaw stability

It would be a fin at the back. 

Roll stability

It could be by the center of gravity, but more likely some dihedral is required so that together with the fin, there will be less slip.

A dihedral rotor ought to have roll stability too, but I am thinking it is not constant and need supplementation.

To supplement, I think the pitch and roll stability can be enhanced with a lifting plane just in front of the rotor.

So actually, the rotor could be flat without any dihedral if the pitch and roll stability are mainly by a lifting plane. Using the spinning rotor as a additional lifting/dragging device. 

In a beautiful world, a conical rotor only need a fin (for yaw stability).

Differential thrusts changes the pitch, the yaw and affects the roll slightly.  

3 March 2023

Paper blades and ribs.

Ribs: Glue halved paper ribbons to spar.

Blade area: Cut blanks, do a fold, glue to spar and ribs.

That way the ribs can be adjusted for incidence and curled for airfoil.

1 March 2023

Conventional: Tube bearing, bent up tabs, strings and disc

As many rotor blades as needed is made identical with longish spars. 

At root end of each spar is secured an aluminum tab from aluminum can.

Have the central plastic tube surrounded by the aluminum tabs and secured the exposed aluminum tabs against the tube and open up the spars like petals around the pistil. Then glue the blades on each spar, secure with a central disc and adjust.

If the blades are already on the spars, just arrange them with a jig on the tip of the blades.

A disc of card, foam or anything like that with a central hole, is used to lock the tube's perpendicular position, the position of each blade around the tube, and the dihedral angle.

Spars can be made from balsa strips, or carbon rods.

Tabs or joiners to the tube, can be aluminum sheet as mentioned above, or cotton thread.

28 February 2023

How about a cone as the rotor?  It wouldn't spin. What makes it spin? Oblique airflow pushing the blades forward. So what is needed? Some openings in the cone for the air to rush by obliquely? Or just some negative incidence? But there appears to be zero incidence blades and why not?

Try a paper cone with 50% cutouts, the root and the tip will be solid rings. At the top is paper cross pattern to locate the central hub which is a paper tube. Acting like flat blades and adding area to rotor surfaces.

An inverted cone = some camber, more chord = more camber. Very draggy.  But autogyro is draggy and drag contributes lift?

Will location of opening affects anything? It's a 360 conical disc, why should it? Shape of openings? Is circular holes, oval holes, triangular holes, half circles one way or the other way or root or tip? 

27 February 2023

Hub for 3 or 4 bladed rotors, with a different assembly

1. Cut out the top and bottom aluminium shape, punch hole in the centre. In case it is a 4 bladed rotor, the hub piece is a cross-shaped sheet. If it is to be a 3 bladed rotor, then there is 3 spokes.
2. Make a work base that will support the spindle, glue the work plan over the work base.
3. Lay the bottom hub piece through the spindle, over the plan and line it up to the work plan.
4. Glue the arms over the hub piece (don't need chamfering, think of it as adjustability).
5. Bend up the arms to dihedral height over the work base, use a dihedral jig. Start with one arm, then turn and do the bend on the next arm until all arms are bent to the dihedral jig.
6. Remove the arms and bottom hub.
7. Lay the top hub upside down through the spindle, over the plan and line it up to the work plan.
8. Bend up each spoke of the top hub to a jig, fold down the tab and remove.
9. Re-insert the arms and bottom hub to the spindle.
10. Drop the top hub to the spindle and glue the tabs to the arms.
11. Strip identical spacer strips (same height as the jig) and glue to top of the arms and the bottom of the top hub. Alternatively, a tube can be used but it shall be inserted between steps 9 and 10.
12. If the top spokes are too weak, glue balsa strips to reinforce the top diagonal spokes.
13. Remove assembled hub from work base.

Hub for 3 or 4 bladed rotors, with a round tube as upright

1. Cut out the top and bottom aluminium shape, punch hole in the centre. In case it is a 4 bladed rotor, the hub piece is a cross-shaped sheet. If it is to be a 3 bladed rotor, then there is 3 spokes.
2. Make a work base that will support the spindle, glue the work plan over the work base.
3. Lay the bottom hub piece through the spindle, over the plan and line it up to the work plan.
4. Glue the plastic hollow tube to the hub piece, vertically.
5. Glue the arms over the hub piece (don't need chamfering, think of it as adjustability).
6. Bend up the arms to dihedral height over the work base, use a dihedral jig. Start with one arm, then turn and do the bend on the next arm until all arms are bent to the dihedral jig.
7. Chamfer a piece of balsa sheet to meet the vertical tube and the arm, strip to make the corresponding number of diagonal struts.
8. Glue the diagonals to the work piece.
9. Lay the top hub piece through the spindle, over the tube and bend to meet the diagonals and glue in place, 
10. Remove assembled hub from work base.

Hub for 3 or 4 bladed rotors, built up 

1. Cut out the top and bottom aluminium shape, punch hole in the centre. In case it is a 4 bladed rotor, the hub piece is a cross-shaped sheet. 
2. Make a work base that will support the spindle, glue the work plan over the work base.
3. Lay the bottom hub piece through the spindle, over the plan and line it up to the work plan.
4. Glue uprights to the hub piece.
5. Lay the top hub piece through the spindle and over the uprights. Bend to meet the uprights and glue in place, 
6. Glue the arms over the hub piece (chamfered for dihedral).
7. Bend up the arms to dihedral height over the work base, use a dihedral jig. Start with one arm, then turn and do the bend on the next arm until all arms are bent to the dihedral jig.
8. Chamfer a piece of balsa sheet to meet the upright and the arm, strip to make the corresponding number of diagonal struts.
9. Glue the diagonals to the work piece.
10. Remove assembled hub from work base.

10 January 2023

hmm.... just a criss and have the blades as the cross. Reinforce with aluminium strips for the bearing points.

6 January 2023

Foam blank with 45degrees bent to provide negative incidence and dihedral

Tin can aluminium strips with double 45 degrees bend to support the blades at top and bottom.

The bottom strip may be bent at the axle hole or bent into a curve.

The axle passes through the bottom strip, foam blank, and top strip, anchored at the bottom, guided by a wire loop, through the rotor assembly, a single bead and secured at the top with a 90degrees bent or stopper.

Foam blank may be extended with paper sails supported by strips which are glued to foam blank, treat the foam blank as a spar.

6 December 2022

No suitable nozzles? How about carbon rods, paper clips and some ready at hand stuff? 

• A short piece of carbon for the blade shaft and at both ends, tie a Z bent paper clip
• Glue blades on the Z bent wire flat over the table
• Bend for dihedral and twist for incidence
• Glue the spindle rod perpendicular to the center of rotor, reinforce with thin card patch or other means.

5 December 2022

Re-using Covid ART nozzles for spinning Hub and dihedral blades. 2 blades rotor.

If the chosen carbon fibre rod fits tightly in the nozzle hole:

• ice cream stick with hole in middle
• thin aluminum strips to ends of ice cream stick and blades
• Bend the aluminum strips to give equal dihedral and angle of attack 
• Covid ART nozzle hotglued to ice cream stick, over the hole, I prefer bottom.
• insert carbon fibre rod through the nozzle and the ice cream stick

If the rod spins freely (but not too wobbly) in the hole in the Covid ART nozzle kit, insert the rod through one nozzle, sandwich the icecream stick and then another nozzle. Once satisfied, glue the nozzles to the ice cream stick.

11 November 2022

Spinning Hub

• A piece of round or square cardboard with a centre pivot hole. Or a pyramid formed from 4 triangles or ring of 4 triangles, so that this pivot hole is set above the cross-piece pivot hole. (can also have a square cardboard supported by 4 perimeter cardboard spacers or a central single piece spacer with a larger hole in the centre) 
• A piece of cardboard cut to a cross shape with a centre pivot hole.
• The 4 arms are bent to 15 degrees angle, superglue applied to lock the 15 degrees dihedral and decalage.
• The ends of the 4 arms are cut to 15 degrees angle.
• The pivot holes are cored to fit the shaft and reinforced with superglue, since they are made from cardboard.

Flapping Blades

• Root of each blade (4 in total) is a small triangle with a 15 degrees cut to match cross piece.
• Leading edge is a piece of balsa or foam, glued to the root piece.
• Root chord and tip chord is balsa or bamboo.
• Covered on top with 70 g/sm photocopier paper
• Flapping hinge is a trapezoidal piece of flexible foam.

Assembly:

1. Pin the hub in the centre pivot hole, use the same 15 degrees jig to raise and superglue the 4 arms so that the arms is raised to 15 degrees. When one arm is set, rotate the hub and do the next arm.
2. Remove pin, place scrap pieces of flexible foam under the cross piece and re-pin. This raises the entire cross piece, letting the blade to slid under,  
3. Glue flapping hinge to underside of each blade, slip and glue the flapping hinge under the cross piece, make sure a gap of 3mm is between the cross piece and blade root.
4. The 15 degrees jig will support the blade while the glue set.

23 September 2021

Sure Fire Autogiro

Rake: 3/8" over 6"

Slant: nil

Dihedral (each blade): 2.3/4" over 13"

Angle of Attack: 0

Blade x2 clockwise: 11" x 2.3/8" paper

Downthrust: similar to Rake

With horizontal stabiliser

Cierva Autogiro

Rake: nil

Slant: nil

Dihedral (each blade): nil

Angle of Attack: negative 1/8" over chord

Blade x4 anti-clockwise: built up

Downthrust: nil

With roll paddle and elevator

Can't find more.

If blades can be set zero, one less to get wrong.

Rotor hub can be made from a piece of flat wood, paper clip bent to give dihedral where blades are patched.

Blades can be balsa built up with paper

22 September 2021

How about plastic tubes for the hub? If doing a very light version, bent plastic tubes from cotton bud may be enough. 

Bend 2 lengths of plastic tubes in their centre by crimping. (the dihedral effect)

Glue bent plastic tubes at right angle to each other. (4 rotor blades)

Prepare jig to hold the crossed plastic tubes evenly.

Example of a jig: one centre pin, 4 spacers to support the crossed tubes.

Pierce centre, enlarge for shaft.

Use a temporary shaft, tie the crossed tubes with thread and glue.

Prepare 4 rotor blades.

Using previous example of jig: add a triangle to one of the spacer. The triangle set the angle of attack of each blade. Can add blocks so that each blade will be located at the same place.

Glue each blade in turn.

Or, to make the angle of attack adjustable by gluing a bamboo stick to each blade and insert the bamboo into the tubes. Doesn't fit? Sand down before gluing to blade or split the tubes' ends.

A 2 blade rotor with doweled blades would be:

1. Pierce a hole in the centre of a plastic tube, enlarge hole to shaft diameter.

2. Bend up for dihedral, not in the centre of the tube, just a short distance away to avoid skewed hole.

3. Insert blade, adjust to angle. Just eyeball and spin the rotor.

Shaft shall be from a paper clip? It is easy to bend.

9 April 2018

On Sunday, I tried Version 2. Version 1 had a bamboo boom and vertical tail. Version 2 had foam fuselage, horizontal stabilizer and 2 tip fins and  affixed to the other components of Version 1.

I tried running start to spin the main rotor fast at full throttle. The initial launches rolled right and crashed within a foot away. I finally got a left arc about 2 m away after having adjusted the model to have left rudder, left weight, and left rotor. The 8.5mm motor and 56mm propeller seems incapable of overcoming the drag.

The fooling around stopped after I noticed my sewing pin is bent. Maybe next time, I can try rotors with flapping tips. From the anticlockwise prop (from front), anticlockwise rotor (from top), I can have left thrust, left weight, left rudder and left rotor. Or I am also thinking of normal elevator and rudder and if one rotor does not balance, twin rotors. I need also better pushrods then the soft wire can afford.



Version 2

These did not grip the thin soft wires I am using and the nuts get loose easily.



Version 1, as the motor stick is screwed, thrust direction is adjustable. The hotglued boom came loose easily and the bamboo size lacks torsion strength.




While making Version 1, I originally thought of making it a pusher.

5 October 2017

Previous was using plastic tubing, how about just beads?

This will limit the contact of the axle to the two points on the hub.







The ice cream stick option has the blades at 0 degrees. Pack with beveled pieces at the blade holding area, or instead of beveled pieces with balsa blocks that has angled saw cuts (similar to sketch on right), the blades will be held at an angle. Or, maybe we can leave it at 0 degrees, and use flat blades that have toe-in/toe-out near the tips by angling it upwards, which ought to propel the blades.

Or how about a spinning disc, spun by peripheral winglets? The centre area is slow anyway and can't possibly have much difference whether it is spinning slow, fast or not at all. When the disc stop spinning, it's still a larger flying surface than is possible with the normal blades' area.

Change the kite to an autogyro? I think a tractor propeller and a large tail is good.

1 February 2016

Even-Bladed Hubs

Too much theory only ends in theory and I get confused. Maybe just try the following. If I set the blades carefully, I could have some coning too.

2mm dowels from Daiso (Basswood?) for hub and blades leading edges.
2mm foam blades (from Daiso) are glued to the 2mm dowel leading edges and wrapped in "Scotch" tape.
Large heat-shrink sleeves to set the angles and dose of superglue when set is as desired.

How about a Cootie but with this blade hub?

16 September 2015

On the following chain of thought, of which all hypotheses are without any substantiation or even personal experience:

1. Negative angle of attack is necessary to get the rotor spinning in the correct direction against the model's direction.
2. Lift or drag of the rotor amounts to the same thing, it lifts the model so long as there is some element of vertical vector.
3. Negative angle of the rotor blades is not too critical, even if it is at -45 degrees, there would still be 'lift' (point 2 above), except that we shan't go there because everyone will tell you it's wrong and I won't be needing that! (And also for point 12 below.)
4. The angle the entire rotor is presented to the wind has to be positive. I think this is the most important aspect. If it were negative, the model sinks instead of rising.
5. Combining point 3 and point 4, if there is not enough negative angle of the blades, at some point it could become a positive blade angle to the wind if the positive rotor angle is excessive. If a blade angle is positive to the wind, then it would retard the spinning rotor because it would attempt to spin in the opposite direction. The rotor would then stall, and hence a faster spinning rotor is safer than a slower one.
6. Carrying on from point 5, this mean that the negative angle of blade must be greater than the positive angle of rotor.
7. The torque of a free spinning rotor is unlike a motorised rotor. The torque is in the same direction as the rotor direction. Hence, if a tractor propeller has left torque, the rotor should spin clockwise when viewed from top because the blade going against the direction of the wind will create more lift, in this case, the left half of the rotor has more lift then the receding right half of the rotor.
8. Since the rotor is functioning as a wing, dihedral would be desirable if we are using rudder to turn the model. Air flowing through the rotor will tend to cone the rotor in the correct direction, yet the faster it spins, the more centrifugal force of the blades will flatten the cone.
9. Should the blades be like a normal flatbottomed airfoil or should it be mounted inverted instead? If it is mounted like a normal airfoil then the rotor would have more lift because of the downwash. If it is mounted inverted, we are having air directed upwards and therefore there would be less lift and more drag.
10. Carrying on from point 9, the main objective should be to have the blades advancing with the least drag and therefore, a thin non-cambered foil is desirable. Something that has a smooth entry and exit.
11. When the model flies faster, the rotor spins faster and the model rises, so downthrust is required to 'lift' the tail.
12. If there is no elevator to lift the tail, the flyable CG range is very limited and the downthrust has to do the 'lifting' of the tail. There is no lift when downthrust equals negative angle of blade and hence the tractor propeller should be set at a greater negative angle.
13. For a simple rotor, the negative angle of the blades shall be fixed. If the positive rotor angle is 8 degrees and we desire a negative effective angle of 3 degrees, this means the blades are set at 11 degrees and the effective downthrust angle is 3 degrees.
14. When the propeller is lower than the rotor, and assuming it is not a very long way infront of the rotor, there is a upwards turning moment. Therefore the downthrust angle has to be set greater than 3 degrees. However, if we have a stabiliser set at a positive angle leewards of the propeller, the stabiliser would have some downthrust to pitch the model down when forward speed is increased.
15. A simple autogyro with the following parameters: A coned rotor with blades set at 11 degrees negative is set 8 degrees positive (round disc don't really stall) to the datum line. Motor is set at 3 degrees negative and stabiliser at zero degrees.

HWC small foam wings

22 December 2023

I have a short 6" bow cutter and cannot use it with rib templates.

6" is wider than most chords of small foam wings for wingspan of perhaps up to 20". So may be I can use it to cut triangular airfoil on expanded polystryene foam blocks.

• Block the wing planform, except that the leading edge is left straight for now and slightly oversized.
• Place trailing edge over table's edge and use root-tip span-wise LE template 1 at the straight leading edge to taper cut.
• Cut the leading edge sweepback on the wing planform, if any.
• Place leading edge template 2 over table's edge and use another root-tip span wise template 3 at the trailing edge to taper cut. 
• Trim to wing planform.
• Sand to trim the wing planform and airfoil.

The templates has to be stable and self supporting.

• LE template 1: Could be a taper if the thickness is to reduce at tip
• LE template 2: If there is no washout and no change in thickness, then it is a thin strip. Use a taper strip if there is washout, higher at the root. Use a more tapered strip if there is both washout and thickness change.
• TE template 3: The highest template. Not tapered if no thickness change and constant chord. Tapered strip to cater for tapered planform and change in thickness.

Washout is introduced at the leading edge; the trailing edge is left flat.

Elliptical planform led me to think of planform template.

Also, the high point is important. 

If the front and rear tapered slopes maintains throughout span, it means same airfoil throughout the span even though it looks thinner at the tip. 

Slicing curved strips

21 December 2023

1/16" x 1/16" laminated curved ribs from 2 x 1/16"x1/32" strips

A former of 1/16".

From 1/16" balsa sheet, cut according to the curvature to separate upper (concave) half and lower (convex) half.

1. On the assembly plan, draw parallel lines, inner set being width of upper laminate, lower set being width of total chord and tape to building surface.
2. Cut equal sets of upper and lower laminates, soak for 5 minutes.
3. Pin upper former over the plan.
4. Start layering laminates: upper, lower, upper, lower with thin white glue between upper and lower but not lower and upper.
5. Pin lower former over the plan, pushing against the sets of laminates.
6. Adjust the upper laminate so they match against the inner set of lines and the lower laminates so they match the outer set of lines.
7. Leave to dry. 
8. Remove laminated sets and clean up.
9. Trim the lower laminates by using spacer/s, cut perpendicular.
10. Cross-pin laminated ribs, push to match leading edge follow by the trailing edge.
11. Remove wing and trim lower laminates.
12. Sand smooth.  

Since the laminate is from 1/32" thick balsa, use scissors for quickness, razor blade for accuracy to cut and some sandpaper to trim.

Since the curvature is slight (for camber of 2-6 degrees), perhaps a jig using 3 pressure points is good enough. This type of jig would not be suitable for wing tips, exact shapes or multiple curves. 

Since the laminate is from 1/32" thick balsa, must the laminates be wetted, must white glue be used? Perhaps strips can be dry-laminated with superglue, which will be fast and maybe good enough?

14 December 2023

Going back to the idea of laminated ribs: 1/32" leading and trailing strips and ribs from 2 laminates of 1/32".

• A piece of 1/32" balsa sheet to the length of the overall chord and marked with 2 parallel lines showing the back of leading edge and front of trailing edge.
• A piece of 1/32" balsa sheet to the length of the 2 parallel lines.
• Glue the 2nd sheet to the first sheet and while wet, tape/bound to a round cylinder. No need to bound all around because the rear chord has less curvature. Leave to dry.
• Strip for ribs from the formed laminated blanks.
• Pin and glue the ribs to the leading and trailing edges, one edge at a time.
• Trim/sand the ribs to the leading and trailing edges. 

Instead of a former, if the wet blank were pinned to well placed strips, it would achieve the same result.

The ribs can be laminated upside down, with pinnings on the leading and trailing spacers (which determined the height of the camber) and then pinned down to the building board. Reversing for use, the rebates preferably be at bottom.

The ribs can be laminated upside up with a single spacer (which determines the height of the camber) and the leading and trailing edges pinned/clamped down to the building board. The rebates are at the top, naturally.  

13 December 2023

For a curved strip (non-preformed; sliced from flat sheet), the two ends may be vertical, horizontal but hardly likely to be notched (because it can be avoided).

For vertical ends, such as those with substantial leading edges (unlikely for the tapering trailing edges):

• Prepare and cut a flat sheet to the chord length,
• Cut the curved ribs from top down.

For horizontal ends, such as those with tapered trailing edges:

• Prepare and cut a flat sheet wider than the chord length,
• Mark the chord length,
• Mark the horizontal lines,
• Cut the curved ribs from top down, leaving them connected at the waste area,
• Cut the horizontal lines from the bottom of the rib blank individually.

4 December 2023

The solution of 18 August 2023: Having notches (and gaps) in the leading and trailing edges is using more material (=weight & more stress points). 

18 August 2023

Cut using template going down each time results in strips' ends at an angle that doesn't fit leading and trailing edges strips that were laid flat.

If each rib's end is trimmed square, only one edge can be attached while either the leading or trailing edge is flat on the building board, meaning that the ribs are built 'up-side down'.

By laying the leading and trailing edges with packing underneath can allow the strips to be installed 'right-side up'.

By having recesses at the leading and trailing edges, the strips can be assembled 'right-side' in the hands and then pinned to glue and there is no need to trim the ends of each rib. However, it won't fit perfectly when it is assembled in the air, so packing material underneath the leading and trailing edges will ensure accuracy while one tries to adjust each end of the rib.

 

Fold and Roll: Polystyrene foam sheets

5 December 2023

Whether it is a skeletal or a solid structure, the outerskin is the finish, adds integrity/stiffness and is necessary. The outerskin is usually coloured tissue further decorated with lines and symbols. Since it is used throughout, it cannot be omitted if any standard of visual representation is required and there is no different in weight except for the gluing area.

For flat flying surfaces, the structural weight of a foam sheet or balsa built up is about the same, but obviously, the foam sheet is easiest.

For solid surfaces, foam blocks, folded/rolled sheets is fastest. 

21 February 2022

Tissue-foam technique might just be ideal for (under-)cambered wings for light models. :

1. Cut a tissue sheet that is an inch wider all round, use the leading edge of the wing as the guideline;
2. Glue the tissue onto the leading edge of the wing blank;
3. Tape the excess tissue at the leading edge down on a large cylindrical former;
4. Apply glue stick to the other 3 borders of the wing blank;
5. Stretch the tissue to curl the foam around the former, start at the middle of the trailing edge and tape down, carefully pull/reposition and tape the tissue all around;
6. Cut an oversized piece of baking paper and use the household laundry iron to roll over this baking paper that is set over the tissued foam. This will hopefully set the glue and perhaps a bit of the foam curvature, apply alcohol and repeat the ironing process;
7. Release from former and trim the tissue.

The above is for top covered wings. Tissue is used primarily for aesthetic, it also adds a bit of strength. By skipping out covering the bottom of the wing, a little bit of weight is spared and the covering work is halved. If tissue shall cover the bottom of the wing, then the tissue shall be bonded to the underside of the wing first, and this has to be throughout the entire bottom side of the wing.

Notes:

1. The grain direction in tissue sheets means it is weak across the grain and it is easier to curl across the grain.
2. When the tissue is bonded to the underside of the foam sheet, curling the composite sheet to form an (under-)cambered airfoil will not tear the tissue because the force is compressive and it is more flexible than the foam; if tissue is also bonded to the upperside, then the tissue will probably tear along the grain.
3. The top tissue should be applied after the foam is curved. The bottom tissue can either be applied before or after the foam is curved. 

 3 January 2022

Balsa is nice but you need to buy it and the wood differs. Foam is relatively consistent, cheaper/free and flexible but does not come readily available in thin sheets.

1. Fix/screw/pin/tape/glue 2 dowels (bamboo, wire, anything that will not snag on the cutter wire) to my blue foam building board or any corrugated cardboard that is purpose-cut to width for the bow cutter.
2. Cut a polystyrene foam block so that it fits loosely between the 2 dowels.
3. Weight/press the polystyrene foam block.
4. Drag bow cutter along the dowels and the resultant bottom sliced sheet will have a thickness slightly less than the dowel's diameter.
5. Remove sliced sheet from the polystyrene foam block, repeat steps 2 and 3 for more sliced sheets.
6. After a few slices, clean the bow cutter's wire by swiping the wire with a damp sponge, the one that is used for cleaning soldering iron's tip.

 I think I can make a lot of model planes using thin polystyrene foam sheets.

Wing lift drag

4 December 2023

Making a flat wing, but the tissue over the rib hover over the leading and trailing edges.

1. Lay down overlength strips (ribs), say 1/32"x1/16" (or greater but at the same 1/32" thickness) at the rib positions.
2. Glue on the 1/32" or 1/16" leading and trailing edges over the ribs.
3. Sand chamfer on the 1/32" ribs over the leading and trailing edges.
4. Cover with tissue/film. 

Not pretty but easiest.

21 November 2023

Design without ridges so that airflow over and under the wing has no obstruction. Leading and trailing edges are thicker and will obstruct, make slim. Thickness of chord will obstruct, make thin. Spars will obstruct, avoid ridges. Smooth is better than rough.

Curve is better than segmented. Drag increases with lift. Lift is the displacement of air downwards.

There has to be sufficient chord for curve/segment to take effect. 

Narrow chord with flat plate might be better than narrow chord with curved plate because the drag is reduced. On a curved/segmented wing, at zero AOA, the front deflected the air upwards (drag), turns back to zero (drag), turns to down (drag). On a flat wing, at zero AOA, air not deflected (no induced drag).    

Materials and Tools

• 1mm: 1mm EPS: 20gsm
• 1mm: 1mm XPS: 30gsm
• 1mm: 1mm Depron: 40gsm
• 0.09mm: 1 pc Paper: 70gsm (A4 is 5g per piece)
• 1mm: 1mm Balsa: 160gsm (10lb/ft3, medium density)

Paper is 11 times thinner than any other 1mm material. Tissue is thinner. Weight of 1mm balsa is equivalent to 8mm EPS, 2.3mm XPS, 1.75mm Depron. 8mm EPS ought to be stronger than 1mm balsa. XPS (Extruded Polystryrene or Styrofoam) has its Compressive strength of 250 kPa, Tensile strength of 450 kPa and Shear strength of 250 kPa. Since I am taking 20gsm for 1mm EPS, while general EPS has compressive strength of between 40 and 72 kPa, the particular 1mm EPS ought to have compressive strength of 20/30*250kPa = 166 kPa.

Gms/m2:
Monokote 75
Doculam 42
Litespan 28
Cellophane 24
Reynolds 14

XPS (Extruded Polystyrene or Styrofoam) has its Compressive strength of 250 kPa, Tensile strength of 450 kPa and Shear strength of 250 kPa.

 Candidates for modelling use.

Covering:

• A4 paper, printer
• Store bought coloured paper and tissue

Structural:

• Expanded or extruded foam (EPS, XPS comes in various density)
• A4 paper, cardboard
• Incense sticks, disposable chopsticks, ice-cream sticks
• Stapler, paper clips
• glue, CA, tape, double sided tape
• Disposable plastic cups
• CF rods, bamboo
• thread

Tools:

• Pencil, pens, markers, paint, brushes, tape, masking tape, double side tapes
• Tracing paper, saranwrap, rubber bands
• NT cutter
• Files, sanding blocks, sandpaper, plane
• HWC
• Ruler, compass, divider
• Pins, thumbtacks
• foam board, corrugated cardboard, wood
• Soldering iron and solder
• Cutting mat
• 
  

Structure

Tension, Compression, Torsion

Triangle frame has torsion resistant.

Rectangle frame has no torsion resistant.

Thick end frame gives a bit of torsion strength, so does making similar triangular gussets.

Catastrophic failures are:

Wing fold, at dihedral joint and outwards. Wing twist. Wing break due to impact.

Fuselage folds. Fuselage cracks.

EPS, XPS, depron, compressed foam. XPS can be prepared in sheets and sanded

Unit weight (gsm) comparison of material

• 1mm EPS: 20gsm
• 1mm XPS: 30gsm
• 1mm Depron: 40gsm
• 1 pc Paper: 70gsm (A4 is 5g per piece)
• 1mm Balsa: 160gsm (10lb/ft3, medium density)

Balsa

Use of 1/16" balsa wood: 

Small sections unless made of firm wood are fragile and does not have insufficient strength, maybe to use larger section, for example if it calls for a 1/8"x1/16" 9lb/ft3 density and I don't have that heavy a wood, increase the size to 3/16"x1/8", this will require some structure changes to the layout to accommodate the larger section.

Use of 1/32" balsa wood:

Even though it is convenient and easy to cut out the entire shape from sheet wood, bear in mind that a frame structure of 1/16" will be stronger and more resilient. This thickness is especially useful for making laminations for curve parts. As 0.8mm is very thin, go with 3 laminates of 1/32".

Windex

I read that windex and other glass cleaner makes the balsa more pliable then with plain water. I don't think I'd use saliva and I have also read that soaking the balsa strips in windex for a few hours is good.

Gussets

This could be from balsa sheet or even bond paper. 

Tweezers

I think a pair of tweezers is a useful tool for handling balsa. However, I also think that using tweezers made from metal might crush the balsa. I have read that crushed balsa may be recovered by dipping a bit of water on the affected wood. Maybe a better pair of tweezers may be made from bamboo chopsticks or a folded piece of plastic card?

Other tools

The biggest tool may be the building board. For my case, I think a piece of 1" blue foam is ok. 

A tool that may surpass the building board in size would be a frame for stretching tissue. I think there's no easy way to get the tool made, so I think I could just buy a frame from Art Friend. Might as well buy 2 at least, because there's bound to be more than 1 coloured tissue needed. I think I should also get a smaller frame for doping trimmings, A4 sized. To attach the tissue on a wet day, have the frame coated with dope and use thinner to attach the tissue. Any leftovers on the frame may be sanded off and re-doped.

Dope replacement, I think I'll just use thinner and EPS. It is not for doping the completed model, it is only for the attachment of tissue. For final protection, I think I'd just buy a rattlecan of clear lacquer.

Coloured trims will need to be firm enough to handle and crisp enough to cut neatly. I think a doped piece of coloured tissue is good and it can be attached with thinner. I will try this, it may be better than white glue or glue stick. I'll experiment with the dope replacement and the rattlecan. I think the rattle can is also thinner solvent.

Intricate photos may be printed, treated, cutout and applied in a similar manner. Hence the need for a small frame of A4 size.

Kitchen plastic wrap would protect the plan from CA and the underlying building board is also protected.

Pins will be needed, I think the regular tailors' pins are good enough. Other pins and thumb tacks are also useful. Locations requiring temporary anchors may be pinned, against the transferring load or to both sides of the transferring load. 

Right angle braces can be made from blue foam and pinned to the board to hold the sides together or to hold the former perpendicular. Is 10 degrees a good dihedral for free flight?

Glue applicator. I normally used excessive glue, I used offcuts of sticks but they lumped easily and seems not to be able to carry sufficient glue. I think I could use the eye of a largish needle to be a glue applicator. Maybe the eye should be cut/grounded as I have read? Or maybe I can just use a soft wire and make the eyelet, seems less 'dangerous'. A 'O' sized nylon brush should also work very well for water solvent glue, it might be ruined and have to be replaced frequently if using superglue.

Slab flyer

20 July 2023

Diamond airfoil = 1st point Leading edge, 2nd point Trailing edge, 3rd point Upper ridge, 4th point Lower ridge.

Triangle airfoil = 1st point Leading edge, 2nd point Trailing edge, 3rd point Upper ridge.

1st to 2nd points = chord.

3rd to 4th points = thickness. 

Cambered diamond = higher 3rd point Upper ridge than 4th point Lower ridge (or flat if triangle airfoil is)

Angled diamond = higher 1st point than 2nd point.

26 October 2021

1s, 3 channel, direct drive, indoor wing, minimal work.

Wing from 1/2" expanded foam, it has sufficient strength without spars or ribs. It has to be a wing, for extra area and chord. Leading edge can be sanded roundish but trailing edge is better tapered, leave the fuselage area square. A reflexed airfoil is just tapered on top leading edge and bottom trailing edge. Use thin foam for elevons.

Approximate foil will do, most of the shaping is at the back half of the chord. Say it is for a tapered or parallel chord wing with cambered foil and here's a method using a short bow cutter:

• Use some double sided tape on a steel rule to stick on the trailing edge, line the trailing edge about 6mm away from the steel edge.
• Use some double sided tape on another steel rule and line one edge to around 40-50% chord of the wing.
• Use a short hot wire cutter across the two steel rules to cut the tapered waste. The trailing edge will be a few mm thick, it can be feathered down or just lightly rounded to give the edge some ding resistant. 

Fuselage from 1/2" expanded foam, any profile is ok, the only caring bits are the wing joint to minimise glue. Fin is thinner foam butt glued to fuselage or wing tips. This is the profile fuselage with minimal work.

Using WLToys all in one board, cut a clearance slot at fuselage and wing joint, just below the wing seating. No need to cut if separate servos, receiver etc.

Stick a bamboo to gearbox, or bind motor to bamboo. The bamboo can glued in slit of wing or fuselage.

Tissue or tape, over 1/2" foam will give strength.

Small gliding Planes

26 May 2023

I glued a piece of folded cardboard over a styrofoam fuselage blank for nose weight. Then the colour profiles were glued first to one side, trimmed the foam/cardboard and then the other side. A small slot cut at bottom for hooking on a rubber band.

  

5 May 2023

Blow through a launcher tube and the plane shoots out. It's a blow powered glider. This is not new, decades ago, some modellers have devised and flown such models. Let's hope that we are not spitting saliva.

A length of plastic straw (or rolled paper tube) has the front capped and is affixed to a model. A blow pipe which fits inside the previous straw and by blowing into this blow pipe, the model is propelled forward.

The article I read has the straw longer than the length of the model. I think the straw can be shorter because I don't think a very long length helps to propell it further or faster.

I think a modular system is good fun.

• Find 2 plastic straws, one fitting smoothly over the other. The bigger straw is the one to be glued to the model and the smaller straw is the blow pipe.
• Cut a few 3-5 cm length of straw with a foam or balsa cap glued on one end. 
• Model is made from thin paper (printed or unprinted): cut the planform and glue the side profiles.
• Strip of paper glued around the straw and the ends glued to the bottom of the model.

 Don't hyper-ventilate, don't spit and be civil.

Example, artwork from www.cybermodeler.com:

UFO thrust

 13 February 2023

Need thrust to fly (up). Inefficent flying objects just need more thrust. Autogyros, flex wings, quad drones and blimps. My idea of a model blimp is a blimp look-a-like that is small and has no helium or other lifting gases. It just looks like a blimp and relies on the thrust to climb, when the thrust is reduced it glides down. Today I am thinking about differential thrusts without controllable surfaces.

In order of increasing exotic-ness, lifting surfaces crafts like: aeroplanes, rogallos autogyros, blimps. The thrusters should be a distance from the centre of lift to create a pitching moment. By angling the thrusters and if the thrusters are a distance in front of or behind of the centre of lift, the same pitching moment can also be created.

Pitching is to the centre of lift or centre of drag? I think centre of drag has greater influence. In practical terms, having adjustable angle of thrusters will help trim without changing centre of gravity. Having adjustable positions for thrusters will also behave the same except that the centre of gravity changes. 

If full efficiency is desired, it'll look like an airplane. If full curiousity is required, that'll either be the blimp or the autogyro. A blimp is cool as it is a recognisable single object, but if it is thinned down for less drag then it's not that cool anymore. An autogiro is cool because of the spinning disc.

Maybe a thrust platform with options of different lifting surfaces.