Carving a 1/12th scale pilot silhouette for the Flying Flea

Start with a block of foam and decide the approximate dimensions of the pilot figurine. I want a 1/12th scale with height of 5'9", i.e. in model size, 5.75".
I drew the outline on paper.



Cut a piece of L-shaped foam block and trace the outline on one side and the backside, and carve. The shorter length of the L is for the arms.

The carved pilot turns out to be a muscle man, and appears more than 6 feet in scaled height.



Start trimming by lessening the shoulder and chest. Now the carved pilot of approx. 5' 9" of scaled height looks like a child because the head is big compared to the slimmed shoulder.

I could carve the head smaller, but never mind.

I would check it against the Flying Flea first and play around with it.

This torso is a silhouette figurine, it will be glued on a 1/16" balsa sheet, the assembly will be glued into the cockpit, leaving a space between the back of this figurine and the cockpit rear former in the plane.

The space is for slotting in the 2s 500mah lipo battery as I think I might have to have my battery against the cockpit rear former . The battery will be held in placed by friction and compressible foam figurine.

I used grey-black foam because:

1.  that was what my IT colleague has on his table and it is light, plenty of air in the foam; 
2. I don't intend to paint or do details; and
3. grey-black offers great silhouette shading. It ought to be visually pleasing when the Flying Flea is flying (if it comes to that stage). 

Maybe I should install 1/4" balsa rails into the cockpit and mount the assembly on that instead. The assembly could be mounted with magnets or velcro, something like that, then I will be able to remove and change the position of the pilot assembly anytime.

Broken wing pivot

The wing pivot didn't break, the plastic horn broke, and the attachment to cabane struts also broke.

The wire in the ez-connector allows length adjustment of the pull lines. Because the pull line is in " \/-\/ " fashion, with the "-" being hooked to reduce the two "\/", very fine adjustment can be made, every unit length at the hook equals 1/4 to the wing displacement, approximately.

Repair:
The plastic horn has been replaced without the pvc cabane attachment. I am relying on superglue, but maybe I will wrap some thread around to secure.

The many crashes of the Flying Flea on Sunday

Sunday morning, I decided to go out to the centre of the field where there's sandy ground and do a few taxis. Directional control not good, I suppose I will have better chance if the tail wheels were of softer material than ply discs so that instead of skidding over the place, the tail wheel could roll along instead. Maybe next time an opportunity present itself (such as lost of tail wheel?)

There were a couple of nose over if I go too fast.

In the afternoon, I thought about it and think that that is probably because the rear wing is providing lift, so I zeroed in on the wing incidences.

I fabricated adjustable pull lines, and I think I have both wings along the same incidence.

In the evening, the wind was even stronger, too strong in fact, but I gave the wing some more incidence (+25 in the digital trim), hand launched and it looped, inverted for a moment and crashed.

This happened twice before the pivot horn snapped.

Now I have to replace the horn and probably do up the whole rigging again before the next test flight.

The many crashes of the Flying Flea on Saturday

On Saturday:

1. Acceptable wind condition, hand launched, nose dived and smacked the ground, nothing broke.
2. Moved the 2S500mah battery out of the intended battery slot compartment, placed it in the cockpit. Acceptable wind condition, hand launched, nose dived and smacked the ground again, one of the rigging tabs came loose, together with a strip the tracing paper covering.
3. Glued back the rigging tab, taped the battery just in front of the rudder. Acceptable wind condition, hand launched, looped and smacked the ground once again, the wing pivot made of 0.25mm clear PVC sheet broke, the hinge at the fore wing pulled out of the foam.

Back at home, I placed the damaged model on a table, a gust of wind flipped the model, sending it on its fourth crash upside down and broke the rudder hinge.

I removed the 0.65mm nylon fishing line rigging wire and pull lines, took a small plastic horn and glued it to the apex of the cabane struts to use as the wing pivot. This took the front wing forward and higher. Deemed desirable based on the internet search of  a forum for full size Flying Flea.

It listed a few key points:

1. CG to be  23-26% of the total chord.
2. The front wing must not overlap the rear wing.
3. Use latest reflexed airfoil (which I can do nothing about it unless I want to do a new model).
4. More than quarter chord vertical distance when the front wing is at maximum angle.
5. 0 degrees incidence for rear wing, 0-12 degrees incidence for front wing.
6. Not to use older designs (which I happened to based my model on, well, can't do much there).

 The plastic horn will bring the front wing forward and higher, while not in keeping with at least one key point, it ought to improve the dangerous dive somewhat.

While trimming the sheared off rudder hinge, the rudder lug points broke. These items were fabricated from 0.25mm PVC clear sheet. I think it is not flexible enough. Another lug point at the wing had the lines pulled out of the centre hole too.

So I repaired the broken lug and horns with more 0.25mm PVC clear sheet, as that is what I have and tried using tape hinge for the rudder. The taped hinged rudder looks ok, but on testing, it was too inaccurate, the rudder cannot centre well because the hingeline is only 2-3cm. I sewed on figure 8 thread hinges with yellow thread (the fuselage and rudder is sprayed yellow) and this is fine.

Using white thread, I rigged the model. I did not have to use aluminium tubing anymore. The thread is more flexible than the 0.65mm nylon fishing line and a few half hitches do the job admirably well, more importantly, no curved lengths of rigging which lead to spongy lines.

In the evening (after a trip to jethobby in the afternoon to buy a non-in-stock replacement motor shaft for the AS2816 and ended buying a FMS mini Mustang of 800mm, and assembled the Mustang), using excel determined the CG to be at 2.75" from the front wing's leading edge.

Flying Flea

Last night fitted 2 extension arms to the wing actuating mechanism.
Just 2 short pieces of thin wire, formed into eyelet at one end of each wire piece, and heat shrunk in place.

Then I proceeded to lace up the pull-line.
In order to have it taut, it is necessary that at all bending points, it has to be made sharper.
The problem it gave was that the wing would be pulled down in the process of tightening and if you held the wing, the wing actuating arms would be pulled upwards.

One hand on the loose end of the pull-line (did not relegated function to a foot this time) and adjusting the pull-line through the bends to make it taut.
One hand assisting the tightening and alternately holding on to the wing.
I don't have another hand to hold the actuating arms stationary, I relied on the servo's holding power instead, quite risky.

Then a short test and found that the wing actuating mechanism was not functioning properly: the centering is very bad.

I ripped it out, the aluminium bearings were jammed with white glue, the slit tube connecting the internal perpendicular horn was loose.

I'll have to do another wing actuating mechanism.
This time with longer actuating arms, straighter connecting rods, made from thinner wire (that's the only thickness I can form an eyelet), maybe replace the 3mm aluminium tubing bearing to some smaller plastic sheath. I don't think I want to solder the internal perpendicular horn and will just superglue it with short 3mm aluminium tubing.

Flying Flea, insufficient throw at the main wing.

The flea is dependant on the wing incidence of the main wing for attitude of the plane.
If hooked up as it is, I think the change in angle of attack of the main wing is insufficient.
Yesterday, I thought of moving the lug points closer to the wing pivot.
I could do a temporary lug with temporary pushrod to see how the flea flies.
An alternative is to extend the actuating arms.

The actuating arms are approx. 17mm long and the throw is approx. 10mm.

The distance between wing pivot point and lug points is approx. 65mm and the distance between wing pivot point and trailing edge is approx. 90mm.

If I want the throw at the trailing edge to be 20mm, then the actuating arms should be approx. 24mm.

I don't fancy additional lugs, I don't fancy changing the actuating arms, so maybe I should extend the actuating arms instead.

A bit of nylon fishing line to form an eyelet at the end of 25mm long carbon fibre rod of 1.5mm diameter, heat shrunk to existing actuating arms might be good enough.

How long should my wing pull wires or pushrods be? How to make it adjustable? How much of wing incidence when neutral?

The first thing to answer should be the fore wing incidence, relative to the rear wing. Do I want the rear wing to exert a downward depressing (stabilising) force like a normal flat plate horizontal stabiliser or to utilise the rear wing to provide some lift as well? Since the rear wing is already a lifting section, I choose that it should contribute to the overall lift. So if it is going to lift and I don't want the front wing to underwork either, I shall arrange 0-0 degree decalage (if you consider treat both wings to be a set of biplane). Motor is also at 0 degrees, so increasing the power to the motor should accelerate the model causing both wings to increase lift due to increased speed and minimal loss or correcting force.

With everything at zero degree, how shall I have adjustable pushrods/pull-lines? If it is pushrods, I could use collet, I could take use heatshrink (which 'ought' to be tight enough but I have no way of knowing until I try), or I could just have a kink. If it is pull-lines, I could use loops and aluminum tubing.

I think I could also just use one actuating end with kinked wire pushrod to determine the length after flying it.  Then when it is flying ok, to fit the other actuating arm extension and to replace the kinked wire with pull-lines, and if found that push rod is required, to heat shrink on a carbon fibre rod to one of the pull-line.

Or shall I just install 2 actuating extension arms and use pull-lines without adjustable feature? Relying on quick and stable jabbing of the transmitter?

Stringed up Pou du Ciel

There are 3 stringings.

The first is the " /\/\| " configuration when viewed starboard side.
This braces the top wing, giving it lateral restraint.

The second is the " /-\" configuration, again when viewed from starboard side.
This braces the planforms of the wings.

The third and final stringing is the "\/-\/" configuration when viewed headlong or from tail view, connecting the incidence horns.

During the first stringing, while tightening the lines and preparing to lock it down with 3mm aluminium tubing, the end line pulled through the pvc lug.
So it is determined that 1) the lug ends are the weakest point, 2) the anchoring of the lugs is strong enough, 3) the line is strongest.

To repair this torn lug, I could 1) replace the lug, 2) reinforce the lug.
To keep things fast and simple, I cyano'd a small washer onto the lug, should be strong enough.

First stringing done, I admired the handiwork and found that some lugs are lifting the tracing paper covering. This won't do, the tracing paper is relatively weak and could give way easily. So, I poked holes around the lugs, through the paper/tissue and injected superglue (foamsafe of course). A bit of kicker and hold it in position until the lugs, or rather the underlying paper/tissue don't come loose.

Initially, I thought the 2nd stringing should come before the 1st stringing because the line has to pass through the main wing's lug before the 1st stringing. Then I figured that they are non-interfering, and I should get the most part of the stringing done first, that is, the one that uses the longest line.

For simplicity, I did not follow the full-size stringing practice which entails individual lines (of which I perceive). Instead, I used a continuous line for the first stringing, relying on friction to hold in position, which means I can adjust the wing's lateral tilt easily, and only 2 ends in the whole 1st stringing exercise to contend with.

It seems like I should do the 3rd stringing before the 2nd stringing, even though 3rd stringing is 'shorter' because it seems that the throws I am getting from the wing actuation horns are small and will not change the incidence of the main wing by more than a few degrees.

With such short throws, the incidence of the main wing can only be controlled to a few degrees, how would I ensure sufficient control authority?
Assuming I want -5degrees and +10degrees, it is a total of 15 degrees. The servo operates say 60 degrees. On account that somehow my wing actuation horn travels only less than 10mm, I think that the 'original' wing pull locations at the main wing is too far back.

I should do some measurements on the throw I am getting from the wing actuating horn/s. Maybe I'll just put in a pushrod and connected to a point on the wing much closer to the pivot point of the same wing.
For this temporary pushrod, how shall I make it adjustable?

Completing the Flying Flea

Here's the main wing from pink foam.

 

 Here it is with the tips sanded, ready for sawing for the polyhedral. The bow is actually the wooden spar for the main wing.

Pasted tracing paper over the wings and fuselage.







Result is not good, I re-learned the knowledge and practise the technique:

• to glue only small sections
• to glue on edges, leaving centre bare

I think it ought to be better if I had used pre-wet tissue on full glue surfaces but I have not got around to experiment it because I couldn't figure out how to 'hold' the pre-wet tissue. Also, I have no spray mister, I was using a 2" brush.

Then I fabricated the rudder horn of 5mm carbon fibre strip and pvc report cover sheet and linked up the pushrod/s (one actual, one dummy) and used more pvc report cover sheet as hinges for the rudder and cyano'd the rudder in placed.

Turned-on the transmitter the rudder functions but the wing rocking mechanism is not working. I had to aid the elevator servo a bit by bending the mechanism until it came loose enough to operate.
Not too good though, because the centering seems to be lousy.
Next time I ought to devise access to the servos.

Last Sunday, I went to the flying field and did some spray painting with  a $2.90 rattle spray can. Result is not good, the nozzle clogged and the paint came out in splutters. So I ended up with sprayed uppers of the wings, top and sides of the fuselage.
This leaves the bottom of the fuselage partly painted and both undersides of wings unpainted.

Never mind.

I used some red coloured packing tape for the fuselage bottom and decide to leave the wings alone.

In the evening, while listening to the National Day Rally, I fabricated the lug points of the wings, glued on the rear wing, glued on the cabane structure to the front wing and glued in turn, the cabane structure to the fuselage.

Now I only need to string the whole flea together.

Should I use more 3mm aluminium tubing, or should I use heat shrinking electrical tubing to afix the nylon lines?