Kwik Fli IV

[Martyn K]

Last nights and this mornings efforts - some may call it progress..

Following Sam Wragg's guide on his Arrow build, the tube for aileron cable was cut using a sharpened tube (actually the wing joining tube for the Glass Slipper which is now ballasted with a foam insert )

You can see the aileron extension lead just tucked into place,

The aileron extension lead was joined to the servo lead using a short length of heat shrink tubing. Much better than the clips for this sort of application. I spotted the idea in an old (1993) RCMW while I was researching yet another build..

Undercarriage beam next

Following the plan, the beams were cut from 3/4 x 1/2 beech, the wing carefully marked ensuring that they were actually square allowing for the wing taper

The holes were cut. I am not sure the best way of doing this. I don't have a router, so I used my scalpel to cut a 1/2" slit all the way round, then carefully removed about 15mm of waste wood and foam from underneath at a time.

Lots of Gorilla Glue in the slot and PVA on the wood > wood join and then clamped it up hard so that as the Gorilla Glue expanded it wouldn't force the beam out.

Left it overnight to dry/harden

This morning, it was time to attack the aileron horns. The ailerons are quite thick and I didn't want bolts all the way through which wouldn't align anyway because of the converging angles of the two surfaces

The approach I adopted was to use 6mm ply plates with a captive nut on the back, the screw for the Tornado horn screwed through from the rear and then trimmed to length

Like this.

These little plates are then inserted into the ailerons. You can't remove the screw unfortunately but secured with Gorilla Glue, PVA and a little Cyano (holding it together while the other glues dry) it should be strong enough and look quite neat

I then managed to glue left and right horns in place on the wrong sides ..

It just means that the fit isn't quite as good as expected, but I felt it was too risky to try and remove/reposition them. Leaving them to dry until lunchtime..

DOH!

More to come

Martyn

[Jack Banner]

Just a quick recommendation from experience Martin. With that heatshrink holder on the servo join, I would use a longer piece so that it is longer than the plastic section. Then when you shrink it, the corners of the servo plugs dig into the heatshrink and there is no way it is coming loose. I did one the way you have and, whilst tight, it did move given a good tug.

[IanN]

For "hidden" extensions like this which don't need to accessed or undone I simply tie the plug and socket together with several turns of cotton

[Martyn K]

Thanks both

I need to remove the servos and extension leads anyway - when I cover the wing. I'll replace the heat shrink with a longer length although it does seem pretty secure at the moment.

Nice tip about using thread - I never would have considered that Ian

Thanks

Martyn

[Martyn K]

Last nights nocturnal activities.

I had glued on the wing tips - laminated from 2 pieces of soft 3/8 balsa - at lunchtime using gorilla glue and PVA. A short 1/16" ply insert at the aileron boundary adds a lot of extra strength and a nice edge to trim film to.

Sanded to shape. I have decided to keep the edges square. Hope that doesn't upset the purists too much..

The remainder of the evening was spent bending the undercarriage legs and then joining the wing halves together. I'll cover the undercarriage separately/later as I am exploring options of making the fixed legs removable.

So onto joining the wing halves.

I join them upside down. The plan says 1" dihedral under each tip. However, the tip section is 1/2" thinner than the root, so when joining upside, the centre only needs propping up by 1/2"

My approach is to:

First check that the we have the correct amount of sweep on both panels. I had one panel that was 1/2" out measured at the tip. This was corrected by a slight trim at the root.

Prop the root up by 1/2" and then sand square to the building board - I use a long Permagrit block - making sure that the wing is at 0 degrees incidence (by eye)

When both panels line up when butted together I then jig the wing so that both panels are at the same incidence at the wingtip

Using the aileron hinge line as a reference, the X axis shows -4.2 degrees on the right panel

and -4.2 degrees on the left panel..

We also have -2.9 + 0.7 = 3.6 degrees total dihedral on the lower surface (ignoring the fact that the building board isn't actually level).

With the wing secured and weighed down so it doesn't move and Gorilla glue used as the panel to panel adhesive, the lower glass bandage was added, coated in epoxy resin and allowed to harden overnight

There are small balsa blocks under each tip (by the aileron) to make sure that the wing doesn't move. A bit like building tabs.

This morning, the resin had hardened, the wing flipped over and bandage added to the upper surface. No need to jig this, its very rigid already

I can't touch that until tea time at the earliest..

More to come

Martyn

[Jack Banner]

It is great to see that you have built this wing completely from scratch, including the foam cores. You are making it look very easy indeed. It has also highlighted to me how I need to start checking accurate angles and incidences more when I build. I may get well flying models more often if I do that!

[Martyn K]

Thanks Jack

I spent a lot of time on the Magic getting the wing panels built with no warps. This is something you take for granted when flying free flight competition models - then I seemed to forget all about it when building R/C models. I used a spirit level on the Magic, using this little Bubble Applet makes life so much easier.

When I recently cut and reset the wing (to reduce the dihedral) on the Gangster a couple of months ago, I was amazed how far out of true the panels were. Despite the fact that I had followed the instructions carefully for the self jigging wing, they were nowhere near accurate when I eventually measured it. The result was that it always tried to screw out of bunts - usually just after the power went on at the bottom of the loop. (Far more than the simple torque increase). Since I have straightened it up, its much better now.

The Magic is much better, I can pull loops (almost indefinitely) without having to touch the ailerons. The wing was also carefully balanced laterally as well. Unfortunately, these panels are slightly different weights (about 30g) so one tip will need a little additional weight to get them to balance correctly.

However, as they say, the proof will not be in the pudding but in the eating (or something like that)..

M

[Steve Houghton]

Martyn,

I follow most of your blogs with interest, but rarely contribute. Great work.

With regard to your 'pivot' method for cutting the wing cores, does this produce reverse tapered LE and TE thicknesses? The wire is coming from the TE (LE) height at the root up to a higher point (wing Thickness) at the pivot, so the tip TE (LE) must therefore be thicker than the root. Did you find this, or have I missed some cunning twist in the geometry calculations?

I also appreciated seeing your cowl production, which I might adopt for my PSS Zlin build where I need a fake spinner with a strange shape. Did you make the pink foam mould slightly undersize to allow for adding the thickness of the fibreglass?

[Martyn K]

Hi Steve

Wing Cores. If you can imagine a pantograph

this produces an exact scale replica from the object you are tracing to the reduced (or enlarged) replica.

As I am cutting/tracing around the root rib, the tip rib will be an exact scale copy. This means that not only is the TE and LE tapered in thickness, it is also tapered in width

So the TE tapered from 1" wide at the root to 3/4" at the tip and the LE tapered from 1/4" at LE to 3/16" at the tip.

In both cases this is not strictly accurate as I had a 1/8" wide false LE and TE which should also be included in that but it demonstrates the point.

The other problem with this solution is that you can cut warps if your root rib is not perfectly aligned and you cannot have a different tip section to root section. Obviously, you cannot cut a parallel chord wing either.

When I measured the wing last night, I was delighted to see that the root section was 2" thick and the tip was exactly 1.5" thick.. The system does seem to work and I find it much easier than using a bow. I am going to make my lash up system a bit more robust and have a better way of temperature control before I do the next wing. As far as I could see, the trick was to move slowly and as you cut extend the virtual line through the wing to the tip and back to the pivot to make sure its not dragging, In practice, I found the tip was always about 6mm behind the root and I had to allow it to catch up before changing direction. Using extended templates would probably be a good idea.

Regarding the cowl.

My 'plug' was cut exactly to size. The 2 layers of tissue add very little width, the 170gm cloth adds about another 1.5mm - so I would guess that it is slightly oversize by about 2mm all round

However, the cowl is too long - it has had cloth added behind the spinner and at the moment, it appears that about 6mm will need to be taken from the length (to allow for an air gap behind the spinner). As the cowl is tapered in all directions, I am hoping that I will lose that 2mm oversize when I take the excess off the back end.

The next job is to fit the engine and cut the cowl to shape. I'll find out then whether I am lucky or very lucky.

On a discussion on Facebook, one contributor suggested that I should have Vac formed a female using the foam plug and then made a conventional F/G cowl using that mould. I never considered that but it is something that I will try next time

Martyn

[Steve Houghton]

Martyn,

Yes, I see it all now - thanks!

I had misread your description of setting the pivot point at 'EXACTLY the same height as the centre of the foam core', and thought it said 'same height as the top of the foam core'. I had also assumed, for some odd reason, that you'd turn the core over before making the second cut. Combined with an offset centre point this might have had the effect I was concerned about. So, I must read more carefully!

Glad it all worked out so well, and I have taken note for any future cores I attempt to cut.

I think the cowl is great, and will be interested if you ever try the vac formed moulding method in the future.

Looking forward to seeing how your build progresses.

[Martyn K]

WOT! No updates for 3 days. He must have retired..

Well, not quite. Thursday evening I was mending a Taranis the n checking over a new fliers models before he tried to fly it. Friday, I went flying - actually instructing, so a only a little progress over the weekend as time has been reprioritised into Gardening and Decorating.

Still - by getting up early, I have still managed to spend at least 10 hours in the shed this weekend

Back on the cowl.

The engine has been temporarily fitted

Hardwood blocks added to locate the cowl

Wrong sized spinner but currently it fits like this

Managed to chip the glass when trimming down to size but that has subsequently been redone

Its not too bad - weighs 80g.

The next job was to get the wing to fit.

The chord is 1.5" wider at the root than the standard Kwik Fli III wing. The 2 pager out of RCM&E doesn't actually say how to make the change. The root wing section is also somewhat different to the mk III as well so a certain amount of trial and error and sanding etc. to get the wing to fit at the same time at getting the wing level with the tailplane.

A thick ply wing plate has been fitted - using slow dry epoxy and the wing drilled for 2 M5 Nylon bolts. I then realised I cant measure.. and managed to display one of the bolts by 5mm

I am so cross with myself over that stupid error. Its not too noticeable with the wing fitted though.

This morning, I started fitted out for the radio gear. 3mm Lite ply plates on 10mm sq Pine runners and cross beams

After the usual faffing around

The receiver will replaced with an X8R this week (I hope).

More to come

Martyn

[Martyn K]

One of the problem I have had to address was measuring the wing incidence. This was especially important as I have had to fit the wing 'by eye'. Not the best method of guaranteeing accuracy.

I decided to make an incidence gauge based upon the standard sliding bar but using the smartphone as the clinometer.

I didn't take enough photos to create a full build blog for this but broadly:

The frame was manufactured from 2 laminations of 4mm building ply. Each piece was nominally 30mm wide.

One of the arms is permanently fastened, the other slides along the beam. By doing this there is less scope for error.

The two arms were cut together so that they are identical.

The 2 'vees' are checked using a square

While it was assembled (in one piece) a square was used to make sure that everything remained square while the glue dried.

The photo is on its side but it shows the arrangement. The beam has been waxed with 'G' Wax and the other parts are treated to linseed oil

A 4mm iPhone shaped platform is glued and pinned to a recess on the top of the bar. The elastic band pulls it together when clamped to the wing. It will cater for a wing with 14" chord

So - this evening, the model assembled on the stand

And another one, I like it when they are like this...

However, I need to check the wing incidence

We already established that the tailplane is parallel with the datum. so put the phone on the tailplane and press the zero button

Put the phone onto the incidence measuring jig platform

0.4 degrees positive. The plan says for the MkIII it should be +0.5, so that is pretty close. Certainly close enough to risk flying it and then assess.

To sanity check, reverse the jig. If the jig is accurate, the incidence should be exactly the same (it was).

It looks aligned as well. No obvious tail tilt

And it weighs this much so far. Probably looking at an AUW of 3Kg

More to come but the end is in sight

Martyn

[Martyn K]

The last couple of days have been spent adding detail, sanding down smooth and making a better job of the wing seat. Not much in the way of photos, so yesterday I decided to cover the model and now it looks like this.

and

A contrasting (and much simpler) colour scheme underneath

It's been Tangoed!

This morning I completed the installation of the Radio Gear, everything appear to work in the right direction but it will get final checks before its let loose..

The canopy is on order from Vortex - hopefully, that will arrive today, the cowl needs another coat of paint and the undercarriage needs fitting.

I am also waiting for an M3 tap so that I can make the necessary alterations to the HK sprung legs that I plan to fit. I don't think it will be ready to crash for a few days yet.

Not much more to come..

Martyn

Yaaay - the Canopy and the Taps have just been delivered

[Jack Banner]

Looking great. Glad to see you have some orange on it!

[Martyn K]

Its was tangoed Jack...

Final build posting.

I wanted removable undercarriage legs if possible. I was quite aware of the torque reaction when my Magic lands. Ideally, I wanted a simple clip system as suggested by Braddock in a separate thread, but I couldn't drill through (the annealed) piano wire. Eventually, I settled on using two set screws, with one located in a recess ground into the leg.

The HK legs that I had were 100mm long. However, I need to reduce these down to 80mm.

Remove the screw that sits in the slide, remove the spring, reassemble and then set the length to 80mm A new hole was drilled at the base of the slot (bottom stop). Disassemble and tap M3. I drilled straight through, this means that the leg could be rotated and the original blind hole is now invisible at the back of the 'oleo'

The spring was cut back to 25mm - this gives a nice action although there is now only about 10mm of travel. If I had a lathe, that could have been extended quite easily by turning down the leg near the spindle

As you can see, not a lot of travel.

Conventional (if very short) 8G torque legs have been bent up. 8G is about 4mm dia, however, the orifice in the top of the oleo is 5mm so the leg (about 15mm long) was padded out with a length of 0.5mm wall brass tube, hammered into place. The lower set screw location now located in a slot ground into the leg. It seems quite sturdy, time will tell

And that is the undercarriage done. Its actually not too heavy as the oleo and leg are manufactured from aluminium. Probably a bit more draggy though. If it doesn't work, its very easy to revert to conventional 8G piano wire legs.

The cowl has been painted - KlassKote - thanks Andy Green - I painted (sprayed) it and the 'Magic' this morning (the white bits). Its a 2 pack epoxy paint and sets hard in about 6 hours on a warm day.

So now, with the undercarriage done, the cowl fitted and spinner fitted its ready for its maiden. I have a Taranis X8R receiver on order although currently it has a V8 fitted, I have decided to wait for the receiver that I want to use.

CG is a guess as no CG shown on the mods diagram. Currently set about 20mm in front of the main wheels.

The Canopy came from Vortex and sprayed Matt black on the inside after it was cut to fit. A small balsa former cut to the inside front and rear and this was used to glue it to the fuselage. The seam was sealed with Canopy Glue. Looks quite a neat installation.

and

and

It's Ready to Crash.. Aurora 60 next....

3 weeks and 3 days since the first part was cut.. It really is an easy build

I'll let you know if it actually flies..

Best wishes

Martyn

 

 

Edited By Martyn K on 05/07/2015 21:17:09

[Chris Barlow]

Looks great Martyn. I'm very impressed with the colour scheme especially the red and blue bars.

I did the same with the undercarriage on my Flair Harvard and converted it with HK oleos, using brass tube to shim out the piano wire and giving it more rake forward to reduce its terrible nosing over! The Harvard is quite heavy so uses lots of the available travel in the oleos but rolling landings are now smooth and planted.

[Martyn K]

Thanks Chris

I am really pleased with the trim. It is Solar-trim on top of an eBay sourced film (which is really excellent). The black trim lines are vinyl go faster stripes from Halfords. The eBay film is very similar to World Models Toughlon or Lite-Tex - at a fraction of the price.

(And you have just reminded me that I have not sealed the trim yet... )

The U/C mod was much simpler. I really didn't want to use set screws, I am thinking of replacing those screws with similar threaded bolts but with a 'Tommy Bar' head.

Best wishes

Martyn

 

 

Edited By Martyn K on 05/07/2015 22:12:22

[Martyn K]

I maidened the Kwik Fli last night.

Apart from managing to split the fill tube resulting in spraying fuel into the fuel bay, it was quite an uneventful experience.

This is a very gentle and smooth flying aerobatic aeroplane. It needed a couple of clicks of up to get it trimmed and a couple of clicks of left aileron. Its much slower flying than the Magic - as you can probably imagine, however in the few minutes of getting a feel for it, loops and rolls were absolutely no problem, rolls especially are very axial, far better than I expected.

I only managed one flight as my ancient (35 year old) electric starter to chose to die on me with an internal short but at least its out of the way.

Very happy with it indeed.

Martyn

[IanN]

Congrats, looks great, glad it flies as well as it looks

[Colin Leighfield]

It looks great Martyn, a real classic model design. I only wish that I could build as fast as you do.

[Jack Banner]

Great! How is the rudder authority on it?

[Martyn K]

Thanks all, it was rather an anti-climax - which for me I guess is rather a good thing. Having trashed three Aerobatic models this years (so far) I am getting a bit apprehensive about flying anything, even though none of the write-offs were directly attributable to dumb thumbs.

Rudder Authority, I tried about 5 seconds of knife edge, and although not especially successful (lack of lateral side area), the model was definitely inclined nose up. I need to experiment more, but I would say its OK, bearing in mind the model was designed 45 years ago.. It doesn't look like a 45 year old design in the air though although compared with a modern F3A - say a 30 year old design , the tail moment arm is noticeably shorter.

I am going to enjoy flying it. Last night the conditions were slightly worse than ideal, it was absolutely flat calm, I like to see how they behave in turbulence and with a cross wind but I am sure I will get plenty of opportunity for that soon enough

Martyn