STOL-X(perimental)

[Martyn K]

A bit more done last night

Added all the sheet infill in the fuselage sides

You can see the 1/16" ply undercarriage reinforcement plate in the shot.

The Trailing Edge has been chamfered down to about 1/2 thickness

A bit of filler will be used to finish off the blending

Started work on the main undercarriage. The plan shows a 12G main leg assembly with a rather convoluted suspension system. However the 3" wheels I got had an 8G hole so I have settled on a simpler 10G main leg with a 18G front torsion bar and bushes in the wheels.

Bend the main leg to shape - I use a 'Wirebender' not cheap but a very worthwhile investment. This is loosely attached to the bottom plate with clips and drilled through....

...to a 3mm lite ply plate underneath (or rather on top - inside). You can see where the 18G torsion bar has been soldered to the main leg. I used 5amp fuse wire wrapped around the leg and the torsion bar. There are two secrets to good soldering (if I told you it wouldn't be a secret).

Oh OK then..

• An iron with a high enough wattage to get all the metalwork up to temperature. You will know it is up to temperature when you can melt solder on the thickest piece of metal in the joint 6mm away from the joint
• Cleanliness - I mean clinically clean - polished - all residue removed and then don't touch it with your hands
• Practice

A steerable tailskid assembly has been produced. The plan shows the skid bound to the 1/16" ply plate. I have used 3/32 sq spruce frame - this will be capped with a 1/16" ply plate and it will all be epoxied together.

At the tailplane, I was unhappy with prospective joint to the fuselage

There is not much glue area there. My solution to this is to add a couple of 3/32 balsa plates on the tailplane lower surface that will give a good contact area to the fuselage and also to your chosen covering material

and

Moving on and back to the fuselage

The final reinforcement pieces have been added. The plan shows 3 sets of 3/32 balsa doublers. 2 pairs behind the wing - upper and lower fuselage and 1 pair underneath the tailplane.

These need to be cut to fit inside the structure - this isn't very clear on the plan.

For example, the lower fuselage pair look something like this when cut..

and when fitted..

and

and at the tail reinforcement

When cutting these, use the plan as a guide only. I found that the easiest approach was to place my piece of sheet on the outside overlapping the longeron and the spacers and then mark and cut each piece to size. The tailplane fuselage doublers are a bit more tricky because they fit into a slot in the former. It's not difficult, just time consuming. Check twice and cut once.

You can also see in the front fuselage shots above how the 3/16" sheet infill blends into those 3/32" doublers. This provides a smooth transition in the load/stress path.

The upper of this set of photos shows some additional gussets that I have added. The two inside cabin gussets are shown on the plan but I have changed the relative sizes of them slightly. I have added 2 more on the top and 2 more behind the cabin.

Apart from finishing off the undercarriage and fitting the radio gear, that basically finishes the fuselage construction. Still got to:

1. Make the Slats

2. Fit the Radio Gear

3. Finish the undercarriage and tailskid

4. Cover it

5. Crash it

More to come...

Martyn

[Braddock, VC]

Please hurry to the crash bit , just joshing, btw.

[Martyn K]

I have to crash it to check that its been built properly. Its not worth adding all those extra bits if I don't crash it..

[Levanter]

At this rate Martin you will be on your second before I even start mine! Very interesting blog and very clearly explained.

[Martyn K]

A bit more last night.

I have started work fitting the fuel tank, radio gear and the ply coaming behind the cowl

Starting with the tank. I have elected to use a 6oz SLEC square tank. Looking at the plan, the recommended location means that some surgery will be required on F1. PR suggests (implied) cutting away part of the former and simply supporting the tank on 2 off 3/16 sq beams. My approach is slightly different. I want to maintain (as much as possible) the integrity of the bulkhead so I am going to place my tank in a 3mm lite ply frame and secure this into the cut away area.

Cut the frame to fit inside and centre and mark the position of the tank. Cut to the inside of the line and then trim back with a scalpel to get a snug fit.

Cut away the inner former - its easier than it looks with a razor saw - the gap should be the same width as the tank or thereabouts.

Test fit.

At this point I stopped. I am really unsure just how high to mount the tank. For a small F/S engine (OS 26FS), should the centre line of the tank be lined up with the carb or with the crankshaft? Is it very critical? If so, I'll make the plate removable/adjustable.. Answers on a postcard please...

Moving on to the Radio Tray

I want to mount the servos as low as possible to keep space above clear to mount the UAV sensors and computing hardware. Fortunately, the design provides a pair of rails to locate a servo tray at just the right height.

My standard method of mounting radio gear is to have one tray for Rudder and Elevator and a separate tray for the throttle servo.

The R/E tray also holds the receiver and the flight battery. I cut this from 3mm lite ply and in this case, it is cut to fit across the top of the infill sheeting in the cabin area - and notched for the spacers

Servos positions are marked and holes cut. I am not sure if I mentioned this earlier, but when cutting holes or any form of internal corner, always cut from the corner inwards - it takes 8 cuts to make an oblong hole. This helps prevent the knife overrunning and weakening the object that you are cutting.

On the back of the tray, I use 3mm birch ply 'beams' to take the servo mounting screws. These need to be spaced about 2mm from the edge of the servo hole to allow wiggle room for removing or inserting a servo. You will need to pilot drill the plate before putting the screws in to prevent the wood splitting though.

Glue it into place and allow to dry before drilling holes

I also started work on the coaming last night.

Unusually, there are no templates shown on the plan for the coaming. TBH, it looks like a little bit of an afterthought by PR.

My method is to make it in two halves. Cut two oversized triangles something like this. They will need the strange angle to get the edge around the curve of the firewall. The bottom edge of the triangle shown on the photo fits against (on top of) the longeron

Glue and clamp one edge to the upper longeron below the cabin and allow it to dry.

When dry, dampen the outside edge of the ply, lots of glue around the top of the former then wrap one piece round and trim to the centre line, wrap the other piece round and trim to fit then clamp in place and allow to dry for several hours (assuming you are using PVA). Mine is still clamped and will remain like that until lunchtime or this evening before I release the clamps. It will need a little filler to blend the edge into the fuselage.

The final job last night was to fit the mounting plate for the switch. I now use large switches with integral charge points. This will be mounted flush on the port side of the model. A simple plate and support have been cut and glued into place.

More to come...

Martyn

[Martyn K]

I had the longest single session working on this model in the shed last - and probably the least to show for my efforts. The biggest puzzle I had was linking up the tiller arm for the steerable skid to the rudder. I was originally going to use snakes but could not work out the best way of doing this.

Anyway - a couple of catch-up shots..

The radio bay - I have added a servo mount for the throttle - the only place it could sensibly go, I was rather hoping that I could get it further forward.

Same technique, lite ply plate and ply bearers underneath

I have also fitted the fuel tank. The 1/2 x 1/4 balsa frame helps support the tank. Regarding the height, the mid point is a bit of a compromise, its between the crankshaft and the needle valve. If it needs moving, it's accessible enough to get it out with care

The coaming with all the clamps removed - quite pleased with that. I have added a small piece of 1/32" ply under the same - about 12mm wide which you can just see. I haven't trimmed this back to the firewall yet - I'll see how the cowl fits when I get round to forming it.

The rudder and tiller arm linkage. I eventually decided to uses a 1/4" dowel pushrod. This is drilled, the wire end are added and then bound with thin sea ranger braided fishing line - a bit more heavy duty than cotton and I fine better to use than monofilament fishing line. It absorbs PVA glue very nicely and when dry gives a very strong bonding.

The tiller arm linkage is formed from about 100mm of 18g piano wire - drilled through the push rod and with a washer soldered on the far side. This allows the link to move independently up and down while still being controlled by the rudder servo.

The end is terminated in a clevis with the pin removed. Slide the clevis over the arm like this and it becomes self locking.

Finally, I couldn't resist a couple of assembled shots, it helps keep me motivated..

and

More to come..

Martyn

[David Davis]

Looking good Martyn!

[Martian]

that's looking really good Martyn

[Martyn K]

Thanks both, much appreciated

M

[reg shaw]

Looking very nice Martyn. A lovely looking machine indeed. My mojo has up and went but those last pics have perked it up a little!!!

Any thoughts on covering and colour yet?

Ian.

[Martyn K]

Hi Ian

I am absolutely skint at the moment = overspent on a house extension by £15k which has totally drained me of any financial resource I thought I had and the rest came from the financial resources I don't have..

Covering will be cheap. I have some black film (LightTex I think) for the Fuselage and Dark Red for the flying surfaces. May indulge myself with a bit of colour trim though.. Cabin windows will be silver trim - function over form in this case.

I am not the best coverer in the world, that part of the blog will be glossed over I am afraid. Hopefully I will get it ready for flying some time next week. That's the plan anyway..

Martyn

[John Keywood]

Realy good blog. Inspired me to get on with mine.

Well done.

John

[Chris Barlow]

Always nice to follow other peoples builds and pick up some new tricks & ideas.

Looks very nice and looking forward to seeing it dressed & with wheels.

[Martyn K]

OK - a bit more progress.

I have completed the radio installation in the fuselage.

I am using a goldenrod snake to link the elevator. This is supported using a small liteply plate at the front and the middle and a slight sheet balsa box around the exit

You can see the binding for the rudder and tailskid in this shot

The centre support. Initially just glued to the upright but I have subsequently added a piece of 3/16 squreon the inside to give it a bit more contact area

And the exit. Although this is epoxied in place, it will be fully braces after the model has been covered. The surrounding box is made up of scrap 1/16" balsa

Place the tailplane on top and check that the tube lines up with the hard area for the elevator horn. The trick with using snakes is o keep the runs as straight as possible - despite the name suggesting you can wrap them into knots

Add a little bit of infill to flair in the tube to the fuselage. This is 1/16" balsa tapered using a round file from underneath

Bolt and plumb the engine. Now is the time to sort out any routing issues

The throttle linkage is a length of 20g piano wire. To help keep it stiff, I run it inside a length of goldenrod inner as shown

The link at the throttle arm is a 'Z' link. I don't use Z pliers for this, for small gauge wire I find that it is quite easy to make my owns Zeds..

One thing I have noticed that as I have been working in the fuselage is that the uprights in the cabin area need a little extra support so I have added a few extra gussets.

This shot also shows quite nicely the bend in the throttle pushrod to get the alignment sorted.

[Martyn K]

With the radio gear sorted, next job was to fit the slats.

The aluminium sheet was purchased from an eBay supplier - by pure chance it was exactly the correct width. The strip was cut with tin snips. A guillotine would be better but I don't have access to one of those. If you don't have tin snips, use a sharp pair of heavy duty scissors, The trick is to cut at least 25mm at a time but never let the jaws of the snips close - that will leave a little kink.

Cut them and deburr them then round the corners. The easiest way to deburr aluminium is to drag a steel straight edge - like the BACK of a Stanley blade at 45 degrees over the edge of the aluminium, it will leave a nice smooth edge. Remember, you are dragging, not cutting into.

The shape is formed by rolling a piece of dowel over the cut pieces - the aluminium will slowly start to curve inwards.

The section (on the plan) shows a classic plate aerofoil with maximum curvature at about 30% of chord. This means you will need to roll it asymmetrically. It should look something like this

 

Back to the plan..

The LE of the slat is 3/16" above the bottom of the wing. The TE of the slat lines up with the rear edge of the LE

We need to make some supports from 1/4" dowel..

6 of these are required with an angle cut to match the angle of the slat against the horizontal. Again - measure directly from the plan

Mark where the dowel will intersect the LE - 10mm back from the top edge (from memory)

Pilot drill the LE in 3 places.

You can see from the plan that the dowel lines up with the top edge of the LE. Because it is off centre, I find it easier and much neater to cut into the LE and open the hole out with a round file.

Then glue the dowels into place make sure they are all horizontal and all line up.

This has obviously weakened the LE at this point so when dry, add a length of 1/2 x 1/4 above the dowel and sand back to shape.

This is the central mounting dowel - offset slightly because it would clash with the wing rib.

Weigh the wing down so its flat on the board and locate a couple of 3/16" spacers in front of the LE

To mark the drilling spots for the securing screws, I put a dollop of paint on the end of the dowel and placed the slat against it. this will leave 3 nice centering circles to drill - 1mm pilot, then use these as a template to back drill into the supporting dowels

I am intending to use 1.5mm rods with a flat head (aka nails) to hold the slat into place with a liberal dose of epoxy.

and

 

The next instalment will have a public health warning

 

More to come.

Martyn

Edited By Martyn K on 02/02/2015 10:25:28

[Martyn K]

3rd post today

After a while prevaricating on how the wings should be fasted - (bands or bolt) I decided on the bolt method. The main reason is that the flaps run very close to the fuselage side and a slipping band could cause damage.

so..

 

2 6mm diameter dowels in the LE and a single M6 Nylon bolt holding the TE down.

a 3mm ply plate fitted between the two uprights - which I had deliberately not cut down and a piece of 1/2" sheet in front for a fairing. Drilled and the wing dowel positions marked and the LE drilled accordingly.

Unfortunately, I forgot to take some photos here so you will have to settle for a description. I had already beefed up the wing in the area behind the LE with some 1/2 x1/4 balsa. This was doubled up and sanded to section. This large block of balsa supports the dowels quite well and is adequate for a model this size.

At the TE, a 1/16" ply plate (30mm wide) was inlaid between the TE and the rear spars and centre drilled. I had already sheeted the lower area underneath this. Finally, a 1/8" ply plate is fitted across the fuselage and underneath the longerons and centred on the mounting hole. A M6 Captive Star Nut holds the wing down.

HEALTH WARNING - THOSE OF A NERVOUS DISPOSITION MAY WISH TO SWITCH OFF THEIR COMPUTERS NOW.

OK. my choice of colours were dark red wings and black fuselage and I had a couple of rolls of Solarfilm in stock.

Now ,I am comfortable with my (hetero) sexual disposition and friends say that I am in touch with my feminine side but the dark red Solarfilm is actually PINK! And I mean PINK - Cranberry PINK... its also see through.

Reminds me of a tarts boudoir.

It wasn't obvious until after I started covering the model. Avert your vision if you have got this far

.

.

.

 

A bit of a jumble of photos. 'L' plate showed me how to fit furry hinges using a pin to centre the hinge and stop it from slipping, so the ailerons and flaps were covered and fitted. At this stage, I couldn't pre-cover the bottom of the flap as the flap torque rod needed to be fitted..

Basically, the rod is epoxied into position and a gusset placed on top to secure it. Glue it and allow to dry then finish off covering the flaps

You can see from this shot that the hairy hinges have been located sideways and how the pins maintain a nice even gap.

When fitting the tailplane, strip the film from the bottom so that we are gluing bare wood to the top of the fuselage.

The horn has also been pre-fitted - much easier to do this before the tailplane is glued down. You will also need to remove film from the bottom of the fin where it glues into the tailplane slot.

When gluing, make sure that the tailplane and fin are mounted centrally and are square. BEB described a triangulation method in his 2014 Dawn Flyer build (I think). It really is worth having a read of that..

Now I know that this had gone horrible when my current wife walked in to the sacred place known as the Shed and said "oooh that's nice - I could fly that" - I wasn't feeling any better at this stage.

So a couple of assembled shots showing WIP..

 

 

and

Detail around the front end.

Mandatory - (for my models) Silver and Black chequerboard on wing tips and rudder

Still to do.

• Aileron and flap servos and linkages
• Cowl
• Fasten the wheels on
• Crash it

I have a problem with Pink..

More to come (if I can face it again)

Martyn

 

 

Edited By Martyn K on 02/02/2015 13:30:47

[Chris Barlow]

You're gonna need a can of spray paint for that Martyn!

Been waiting for someone to make a start on slats so I can get some ideas for the cub. They look nice and straightforward.

[Martian]

very nice Martyn, pretty in pink

[trebor]

Not sure about the pink ! Although it's the same colour as the pot of nail varnish I have in my flight box.

[Martyn K]

mmm. Not sure how it will go down at the club. The South Cheshire RCS members are a hard lot - up here, men are men and the sheep are especially attractive.

Still - onwards and upwards Gungadin.

Fitted the aileron and flap servos last night and terminated the ends with Ashlocks. Andy Green put me onto these - they are not cheap but they are a very reliable and simple method of joining multiple wing servos into a fuselage based receiver. You can start with wire and pins and make up both ends, but I tend to use longish extension leads - cut them where they need to be cut and crimp the special pins/sockets and fit them together. Its a bit fiddly - I use magnified reading glasses to get them right but its worthwhile

The Fuselage connector (in my case) contains the sockets

and the wing connector has the pins..

I use the HK crimp tool - really unbeatable value for money.

The other thing I did last night was fit the wheels. I wish I could find the same style that PR used. The WWI air wheels from flair are similar but rather heavy - these are very light foam wheels.

A brass sleeve sits over the shaft and the wheel runs on that. I use a short length of fuel tube behind the wheel - then a M4 washer, then wheel, another M4 washer and the wheel is secured by a length of copper wire wrapped around the shaft and soldered into place. It will look OK when I have filed it down to a circle..

Finally, here are the missing wing securing shots

The rear plate holding the captive star nut

The rear 1/16" ply plate in the wing (under the covering)

The beefed up LE blocks supporting the pegs - again through the covering

Finally, the additional support for the cabin 'frame' at the front - I have raised the fuselage at the front of the wing to accommodate the front mounting plate.

More to come - but not much more

Martyn

[Martyn K]

The last 2 nights work.

The aileron and flap linkages have been done.

The Ailerons are very simple - a 20g wire with Z link at each end. I am using 1 channel per aileron so fine adjustment can be carried out using the subtrims.

A bit of camera shake there - sorry.

The flap linkages are also fairly straightforward. The end of a length of brass tube has been gently flattened and drilled. This is filled with solder then soldered onto the actuating arm - 2 will be required. The arms are connected with Z links and brought back to a common servo

the arms are clamped using one of these screw type clamps. You can just get 2 rods in the hole.

Another shot of the flap actuating arms

The bit I absolutely hate - fitting the glazing. I have cut the windscreen (using the template off the plan) from a pop bottle and glued/clamped/pinned it. Using Canopy glue, I have left it overnight to dry. I have had a look this morning, I am not happy - it will need to be redone.

I also started work on the cowl last night. The template was copied to a sheet of A4 and used as a master for the aluminium sheet. The plan says use .010" aluminium, I only had .020" that I acquired for the slats so have used that.

The template - this is cut oversize and trimmed back. I had to make adjustments for the exhaust on the OS26 which inconveniently sits right down the cowl line

Now working with aluminium

Gently fold it around a suitable object. I used the nose of the model to make sure it was the right size. It tapers towards the spinner, this causes the sides to move backwards - obvious when you do it.

This shows the cut out - still WIP progress for the exhaust. Filing this material is difficult - its too thin and its actually quite easy to tear if you hae been too enthusiastic with the tin snips

Hardwood blocks have been glued into place for securing screws. I am trying to work out whether I can get a small grill at the front and not lose access to the engine. Its rather open at the moment

Don't skimp on these blocks - they get a lot of abuse.

A bit more to come.

Martyn

[Martyn K]

Final build post... Yaay

The cowl has been completed.

A 3mm liteply former - spinner sized - has been cut for the front of the cowl. This also has a 3mm liteply backing ring

Hardwood blocks added so it is all glued and screwed together. Probably not the best photo as the building board underneath confuses the image a bit

From the other side - painted in black acrylic paint and fuel proofed.

All fitted and with the spinner in place I think it looks pretty good

Amazing what 5 minutes on a buffing wheel and Solvol AutoSol will do for aluminium

and

and

I am *really* pleased with that cowl.

So - the finished model - ready for its maiden..

Flaps down for take-off

Finally

That's it - all done. Ready for its maiden crash. Ran the engine last night - started almost instantly so the fuel tank appears to be OK at the almost empty level

No more to come.

Best wishes

Martyn

[Martian]

Excellent Martyn looks very nice and good luck with the maiden. I feel I should get cracking with mine need to order some balsa and other bits had to sell a plane for funds

[Martyn K]

Thanks Martian

I forgot to mention.

AUW - was less than 1.1kg Dry = 0.79kg Fuselage/Tail/Engine/radio gear and Flight battery and 0.25kg wing and flap and aileron servos. Not bad - a 25 sized model at 2.25lbs or thereabouts. I suspect that will be the main reason for the STO bit of STOL

Martyn

Edited By Martyn K on 09/02/2015 10:46:59

[john stones 1 - Moderator]

That looks good for me Martyn, I like bold colour schemes they work in the sky

John