Weston Capiche 50cc Build

[Gary Manuel]

I spoke to Alan, who made my exhaust header at Weston UK today. He had assumed that the AGM-55 was the same dimensions another engine he had a jig for, which resulted in the problem I have with mine. He offered to re-shape mine to my requirements if I returned it to him. I asked if there was any way I would be able to do it at home without damaging anything.

He suggested that if it only needs bending by 5-6mm or so, it should be OK to do it at room temperature with the flange end in a vice and a tight fitting wooden pole or similar in the open end of the pipe. Pulling on the pole to bend it to the required shape should be reasonably easy.

Fortunately, I found a short length of carbon tube that was a nice tight fit on the inside and a longer aluminium wing tube that was a tight fit on the outside. A few pulls on the wing tube later and it was sorted.

Silencer supported on temporary suspension tube (new tube not arrived yet).

Alignment much better now.

[cymaz]

Well done that man !

[Gary Manuel]

I'm planning on using the tunnel in the model to full advantage. This will include blocking the cheek holes in the cowl and cutting cooling holes directly in front of the engine fins. Baffles will be added in front of and above the rear of the engine to force air over the engine fins, down the back of the engine, through the tunnel and out of the rear end - That's how I'd like it to behave anyway. Time will tell whether the air behaves itself in practice.

My first job is to prepare the tunnel. At the moment, there is no provision for air to flow through.

Covering cut away to expose a hole where I want the hot air to exit the model.

Covering ironed into the hole. At the moment, the tunnel ends in a 90 degree end.

Balsa sheeting cut to create a ramp which will form an angled exit for the hot air. The sheeting is in two parts as it needs to be passed through the exit hole, which is narrower than the full fuselage width. 1/4" border added / shaped to increase strength and surface area for gluing.

I also shaped a piece of balsa to form a lip on the leading edge of the tunnel outlet. My theory here is that this will deflect the airflow underneath the fuselage, creating a negative pressure area to help "suck" air out of the tunnel.

The ramp front face and lip (not shown) were covered with white Hobbyking covering.

Here's the tunnel exit before adding the ramp and lip.

Ramp fitted.

Finished exit hole with ramp and lip in place.

[Gary Manuel]

Here's the inside of the tunnel. There are three of these wooden rings. Note that the rear two rings do not have lightening / air holes at either side of the rings.

My silicone tubing has now arrived. Twelve short lengths cut from the length of tubing.

Tubing added to the rings. This does not leave much space for cooling air on its way down the tube .....

..... so I've cut some. The slight reservation I have about this, is that these formers are also the ones that the undercarriage fits between. I may add some fibreglass reinforcement later.

I needed to remove the engine to get the silencer in, but here it is fitted.

[Gary Manuel]

Could somebody remind me what the make of craft foam is that someone recommended for baffles. Something like dickies as I recall. There was some special glue that works with it too. Done a search but can't find it.

 

Edit - found it - "Darice Foamies"

Edited By Gary Manuel on 19/02/2018 19:46:02

[Peter Jenkins]

Gary, did you say you were going to exhaust the engine cooling air via the pipe tunnel? If yes, then you do need to make sure that the intake area is matched by an exit area that is twice as much. Looking at the size of the holes you have made in the pipe supports it may be marginal. I had an exit I cut in the bottom of the cowl to exhaust the engine cooling air. I also blocked off the intakes either side of the spinner and cut a hole in the cowl to allow air straight onto the cylinder head. This was on a Capiche 140 which had a DLE35 RA with canister. The pipe tunnel cooling was just to keep the canister cool.

[Gary Manuel]

Peter.

I am aiming to making the exit hole area THREE times the area of the air intakes to allow for volumetric thermal expansion of the air. I'll estimate the inlet area once I've done the baffling and see whether I have enough outlet area then - more by eye than by calculation though. I also suspect that I will finish up some elongation of the holes where the exhaust pipe outlets are, due to the need for the one piece cowl to physically slide on from the front. I can play around with this and make it bigger if I need more area.

The key to getting this right in my mind, is making the inlet area small enough and in the right place so that the majority of air is blowing over the engine fins. What you don't want is air passing through the cowl without actually doing anything - hence blocking the cheek holes and adding baffling. It's worked OK on other models I've built, so it should be OK on this one.

[Rich too]

Nice work Gary. It is odd that no cooling holes are provided in the cannister rings. Just personal preference, but I favour rear exit canisters so that the exhaust mess is further down the fuselage.

[Gary Manuel]

Thanks Rich.

I would have preferred rear exit canisters too, but if you think about it, it would be no good in this type of tunnel with built in support rings. The canister needs to be slid through the three support rings from the front. If it had the exit pipes at the rear end, it would not be possible to do this.

[Gary Manuel]

The two formers I drilled out earlier for cooling have now had a layer of heavy duty fibre glass applied to each side to resolve any weakness I may have introduced when I drilled them. I'll leave it like this for a couple of days for the epoxy to cure before I clean it up and cut the holes out again.

[Gary Manuel]

Aileron servo fitted and a line drawn on masking tape perpendicular to the hinge line to mark the centre line of the control horn.

Very nice quality push rod fittings .....

..... and aileron horns.

Note that the large washers have a concave protrusion which is a nice fit into the concave ends of the cone and special washer. This allows the large washers to take up any angle that the control surface might be without "digging in" at the thick end as is quite often the case. In my eyes, these are quite simply the best control horns I've ever seen.

This is how I make sure that the wing is level and the aileron centred .....

,,,,,, when marking the control horn hole position (I settled on 12mm from leading edge of the aileron) ....

.... but more for drilling a hole through the aileron that is perpendicular to the wing centre line.

I like to have the wings nice and level so that when I drill through the aileron, all I need to do is keep the drill level and (hopefully) the small pilot drill comes out of the other side the same distance from the leading edge that it went in. This one was spot on at 12mm, meaning that the control horn should be perpendicular to the wing centre line.

One thing I really like about this model is the attention to detail that Weston have made. Once the hole is drilled through the aileron (and other surfaces), the manual asks for the hole to be drilled out, not to the diameter of the control horn threaded rod, but to the size of a length of carbon tube what is a nice snug fit over the threaded rod. Here's the carbon tube pushed into the hole.

The carbon rod isn't just fitted any old how, it's cut at the same angle as the aileron taper, so that the ends of it are angled the same as the aileron surface.

The length is gradually reduced until it is SLIGHTLY LESS than the aileron thickness. It is then pushed into the hole and the covering cut back at both sides to allow a few drops of thin Cyano to be applied.

This may seem like a lot of messing about, but it results in the ability to tighten up the control horn cone really tightly onto the carbon tube, with the large washers just slightly compressing the balsa without distorting it too much. I got the impressing that this control horn is in for good and will not cause any problems in the future. I'll definitely be using this method on other models in the future.

Note that there is one more step to do here later. I need to slide and glue a length of carbon tubing of the right length over the stainless steel push-rod to stiffen it up.

Geometry looks spot on to me.

This is what the underside of the aileron looks like.

Edited By Gary Manuel on 21/02/2018 19:42:59

[cymaz]

Fab...u.....lous

[Gary Manuel]

Ailerons finished off by cutting and sliding a length of carbon tube over the push rod and glueing it in place.

I also put my gynaecological skills to the test, cleaning up the fibre glass strengthening I added earlier.

Edited By Gary Manuel on 25/02/2018 19:38:37

[Gary Manuel]

Throttle servo fitted. This servo is a bit over the top for what it's doing, but it was the only metal geared one I had available. I have used the supplied threaded metal rod and outer snake, but instead of using a 90 degree bend and the supplied swing keeper at the servo end, I've soldered a threaded adapter on and used a ball link. Nothing wrong with the supplied fittings - just not to my preference. Snake outer has been rough sanded and epoxied in place.

Note that there is a slot cut out for a choke servo, but I won't be using it.

Here's the throttle end of the push-rod. I've replaced the supplied plastic clevis with a ball link. A lock nut will be added later once I'm sure that the engine doesn't need removing again.

Here's how the throttle push rod passes through the engine box. No bending was needed.

I've opted for a simple manual choke.....

.... which is held in place by a home made 1.6mm glass fibre bracket. The end of the choke push rod will be bent at 90 degrees on the outside of the cowl and finished off at a later date. It should exit the cowl through the cheek holes, which I'll be blocking.

[Gary Manuel]

I've moved on to the rudder pull-pull control now.

This the the fuselage laid on its side. The steel straight edge is marking the path of the rudder control wire between the servo end and the outlet in the fuselage side. The exposed wire continues in a straight line, back to the rudder, where the wire position is marked on a piece of masking tape. The aim here is to mark the position of the rudder control horn in a position where the pull-pull wire will be as straight as possible.

In the past, whenever I've tried to drill a control horn hole through a tapered control surface using judgement alone, I've finished up with the hole drifting from the perpendicular in one direction or the other. To overcome this, I've started laying the model on the bench in such a way that I just need to drill vertically to guarantee that the hole will be perpendicular to the model centre line.

Masking tape at front of fuselage with fuselage centre line drawn on it is 87 mm from the bench.

Rear end packed so that rear centre line in also 97mm from the bench i.e. centre line of fuselage is parallel to the bench.

Rudder taped to the fin so that the rudder is also parallel to the bench.

Position of the control horn hole marked such that the control horn ball link is aligned with the rudder hinge line.

Hole drilled over-size and a piece of tapered carbon rod glued in place, similar to the ailerons.

Rudder control horn fitted and everything tightened up.

Now this next bit is a bit counter-intuitive. It would make sense to prepare the servo end of the pull-pull wires first and do the rear end last because it's easier to get to the rear end to make the tricky length adjustment. I want to make sure that I get the right geometry of all pull-pull wires, which may mean playing around with the shape of the servo control horn (straight or off-set). I'll try loose fitting of the wire at the servo end to make sure I get this right before making final adjustments and cutting the wires. Hopefully I should finish up with straight servo horns, but I'm not confident you. Metal horns are ordered but still in the postal system somewhere.

Finished rudder control.

[Ron Gray]

Nice work Gary, love your attention to detail, but in posting your details you leave yourself wide open to smart ar*es like me, did you mean to have the centre line at 97mm at one end and 87 at the other?

[Ron Gray]

Your photo of the cannister tunnel reminded me to upload some shots of what I did with my GP Giant Revolver. It didn't have a tunnel for a can so I cut out the formers and formed holes through for the pipe. Conscious of the fact that the fuel tank sits right on top of the proposed location for the can I lined the underside of the tank platform with balsa and aluminium heat reflective foil but to get rid of the heat I left the underside of the tunnel open and fitted an aluminium grille to it. The end result doesn't look too bad but it really does work well. the only thing I have to watch is if I put the fus on a stand it tends to flatten some of the gils in the grille!

[Gary Manuel]

Posted by Ron Gray on 26/02/2018 18:32:33:

Nice work Gary, love your attention to detail, but in posting your details you leave yourself wide open to smart ar*es like me, did you mean to have the centre line at 97mm at one end and 87 at the other?

No I didn't, but I'll blame Mrs M for shouting me for dinner before I had chance to check what I'd written. Fortunately, she doesn't go into my shed, so I got the actual measuring right.

[Gary Manuel]

I like the grille Ron.

You should get plenty of air flow through that.

[Gary Manuel]

One last job I managed to get done. The manual asks for a bead of epoxy to be run down the sides of the servo blocks. The rudder servo sits in the cut-out at the bottom of this photo.

The starboard elevator servo sits on the port (left) side of photo between the two blocks, with the wires crossing over within the rear of the fuselage. Note that the left servo sits a little higher than the right.. The manual is silent on this, but I assume that this is to make sure that the servo arms do not catch if extra long arms are used. I had initially thought that it was to avoid the wires rubbing as they cross each other within the fuselage, but all six wires are within dedicated snake tubes for the full length of the fuselage.

I must say that I am well impressed with some of the design details that Weston have applied to this model - and I'm not easily impressed.

If a job's worth doing, it's worth over-doing!

I used lengths of triangular stock to add a bit more strength. The two servos that will be on these blocks are capable of moving almost 50Kg between them, so they need to be well secured.

[Ron Gray]

When assembling the GP Giant Revolver I picked up a tip from a guy in the USA when wanting to strengthen joints, instead of using triangular stock he uses string stuck with cyano. You lay the string in the angle of 2 pieces to be strengthened then flow cyano into the string. The result is a very strong joint taking up very little space. I know it’s strong because I tested it first as I was unsure how good it would be! It also looks rather neat!

Edited By Ron Gray on 26/02/2018 22:49:36

[Gary Manuel]

Never thought of using string Ron - one more option to consider next time, though in this case it wouldn't have worked as well as the triangle. What I didn't mention (or take any photos of) is that I needed to trim some of the triangular stock back off in order to get the servos to fit onto the servo blocks.

[Gary Manuel]

Elevators fitted with control horns in exactly the same way as the rudder.

Four wire ends prepared, leaving the other ends unfinished and ready to slide into the snakes.

Ball joints screwed onto the threaded ends and wires threaded into the snakes.

Tail plane halves fitted and controls connected.

Here's a photo of Porthcurno Cable Station. Better not get the cables mixed up!

It would actually be pretty difficult to get the cables mixed up because the other ends are already connected to the moving surfaces and it's easy to work out which servo arm they belong on.

As mentioned earlier, the reason I have connected the tail surfaces first,making the much more difficult final connection even more difficult, is to allow me to check the geometry before I commit to cutting any wire to length. I can always disconnect the wire at the tail end if I need more cable length while I'm crimping the wire end.

Here are the three servos installed in their final positions. The photo is taken with all three control surfaces in the centre position. Note that the two elevator servos are not centred with respect to the fuselage sides. They are centred with respect to a line drawn from the servo centre to the control horn centre, which is necessary in order to achieve correct geometry.

I have taped all wires to their respective servo arm and made the wires quite tight so that I can check whether they loosen too much, or worse, tighten as the servo is turned away from the neutral position.

I've just noticed while looking at this photo that I'll need to shorten the rudder snakes a bit to avoid the threaded ends from striking them when the servo at full travel.

I am happy to say that all three servos remain at roughly the same tension throughout their movement. This is due to the care taken in ensuring that the ball joints are aligned with the hinge centre line when marking out the hole centre position for the control horns. The geometry is not guaranteed to be perfect when I add the proper fitting because there is a bit of "give" in the cables as I have taped them in place. I'm reasonably confident that they won't be far off though, and hopefully I'll be able to use the standard straight servo arms I have fitted at the moment.

Note that I will be changing the rudder servo arm for a longer aluminium one anyway, which should give a bit more rudder movement. It's ordered but still in the post.

Here's the servos at somewhere approaching full movement in one direction .....

..... and here's how this affects the tail surfaces. The pulling and pulled wires are still fairly tight.

[Rich too]

I always do the control surface end first on closed loop - I just find it easier.

[iqon]

Youve put me off it now Gary, dont like pull pull and to put them elevator as well ..is there an alternative with this plane