Weston Capiche 50cc Build

[Gary Manuel]

I'm not at the panicky stage yet and I've not re-checked the CoG since putting the undercarriage on.

My main reason for checking it was because I thought it might actually be nose heavy. I was rather surprised when the tail dropped. When I balance it proper, it will be with everything on (including the missing rudder servo arm). That's when I might get panicky, if it's still tail heavy.

The spinner is one of the Hobbyking uncut carbon fibre ones with the Alloy backplates Adrian.

[Gary Manuel]

I've had another go at balancing the model.

Ignition unit and ignition battery taped in position as forwards as I could practically get them.

Cowl fitted. Prop drilled and fitted. I've not cut the carbon spinner yet, so this is just taped to the prop for now.

A large model like this is not easy to hold up in the air at arms length in order to check the CoG, so I've made a pair of hangers out of scrap ply. The hangers locate onto the wing dowels and the large cut-out is just to clear the wing tube.

Two 3mm threaded rods bolted through the hangers at 225mm and 240mm from the leading edge, which are the suggested limits of CoG position.

Oops!

I miscalculated the position of the rods. They are not clear of the fuselage in the original positions.

New holes drilled and rods moved.

Hangers in place ready for balancing.

With no receiver battery fitted, the model balances almost perfectly .....

..... on the 225mm rods.

It is obviously nose heavy .....

..... when suspended from the 240mm rods.

I'm aiming to be able to adjust the CoG by just moving the receiver batteries, if possible - initially from the 225mm position and later (if all goes well) towards the 240mm position.

With the two receiver batteries positioned as far back as they will go within the cockpit, the model is still nosing down when suspended from the 240mm position. Looks like I've positioned the ignition battery / ignition unit too far forwards.

Edited By Gary Manuel on 14/03/2018 18:59:52

[Peter Jenkins]

Gary - excellent technique. However, I note that you didn't have the canopy hatch installed. On my Capiche 140 the pilot I used weighed 100 gm! That had an effect on the CG! You might want to check the CG of the canopy hatch to see if it falls forward or aft of your chosen balance point.

[Gary Manuel]

Cowl etc removed, ignition battery removed and the ignition unit repositioned at a more natural position.

Receiver batteries positioned somewhere close to where I would like them to finish up.

Ignition battery now repositioned inside the canopy adjacent to the ignition switch.

That's pretty level ......

.... at the 240mm position.

I'm happy with that - but I'll recheck it once everything is in it's final place and bearing in mind that this is balancing without the canopy being fitted, but I don't think that will have much effect.

I'll probably position the receiver batteries here, or further forwards than this for the maiden flight. They can go as far forwards as the inside of the engine box if necessary although this would mean extending the battery leads,

Turns out the model is naturally balanced after all and I won't be needing any added lead.

[Gary Manuel]

Posted by Peter Jenkins on 14/03/2018 18:40:01:

Gary - excellent technique. However, I note that you didn't have the canopy hatch installed. On my Capiche 140 the pilot I used weighed 100 gm! That had an effect on the CG! You might want to check the CG of the canopy hatch to see if it falls forward or aft of your chosen balance point.

Stig is not very heavy but I have already considered the effect of the canopy.

[Martin McIntosh]

I have built a couple of the Island Hobbies originals for other people. These had the very heavy mg elevator servos at the rear, just in front of the tail, YS 140 and 160 powered which were much lighter than petrols with all the associated bits and pieces so I suspect that this may be the cause of your cg problem, or perhaps the Weston version uses heavier construction. Plenty of room in there to move the battery packs to suit I would have thought.

[Gary Manuel]

I don't think I've got a CoG problem now Martin.

I just had a horrible thought yesterday when I tried the CoG that it looked tail heavy. Now I've had another go and tried moving the batteries around, I'm reasonably confident that it will balance OK.

[Gary Manuel]

The next problem to resolve is to mount the heavy duty ignition switch.

The fuselage has cut-outs at the front and rear of the wing on both sides, but they are for the two common rectangular switch types - not the ones I'm using. The sides of the fuselage have lightening holes wherever possible - which is a good thing, but doesn't provide anywhere solid to fix an over-sized switch like I'm using.

A piece of scrap lite-ply was cut, shaped and glued in place to tightly fit into the lightening hole where I wanted to fit my switch.

I really like these switches. The problem with them is that the cut-out shape is not easy to do and unfortunately, no template is provided with the switch.

I've done this several times on previous models but this time I AM going to make a decent template and keep it for next time.

First step is to draw round the switch perimeter onto a piece of cardboard and then hand draw the cut-out shape, using the switch as a guide.

Once the shape is cut out with a sharp scalpel, it will inevitably not fit properly, so the next step is to use the first template to mark out another template and cut this one out after making the necessary adjustments.

Keep going until the template fits the switch. My second one was OK.

I WILL keep this template so that I don't have the same problem again.

I'll be basing my cut-out around this original one.

Template used to mark the cut-out shape onto the fuselage side.

Covering removed to reveal the wood underneath. Note the joint between the original balsa and my lite-ply infill.

Dremel put to good use.

Switch fitted. Note that the Kill switch LED is fitted close to the switch, taking advantage of the lite-ply infill.

Ignition unit attached to the engine box using velcro and tie-wrap. I'm spiral wrapping all the wiring as I go, to give a durable / nice and tidy finish. I'll revisit later to add a few dabs of hot melt glue where needed e.g. where the sensor lead passes over the end of the engine box.

The kill switch is sandwiched between the inner fuselage box and outer skin, close to the ignition switch.

Ignition battery fixed in place with Velcro and tie-wrap. I'll revisit this to connect and secure the battery leads / balance leads later allowing access for charging, although I can use the charge socket on the switch for the occasional non-balanced charge.

Edited By Gary Manuel on 16/03/2018 19:51:23

[Gary Manuel]

I've decided to make a closed loop servo arm for the rudder. Made from 1.6mm fibre glass bolted to a servo wheel.

The wire run isn't quite right for the rudder. I'm also concerned that the wire end adapter / ball link assembly will extend rearwards beyond the slotted ply plate which could result in snagging. I can't really see the point of the ply plate to be honest - there's no real strength to it and the stake tubes are not fastened to in in any way so .....

..... I've cut the ply plate to resolve both issues. It's not in the way now.

Completed wire end in the neutral position.

Fully turned in one direction ......

...... and the other. Wires are reasonably tight throughout with very little free play at either sides. Note how the wire ends extend rearwards of where the ply plate was. Also notice that I've trimmed the elevator servo rail to provide plenty of clearance for the rudder servo arm.

[Gary Manuel]

There are still some slots between the exhaust tunnel and the fuselage bottom, presumably for tie-wrapping any equipment that may be fitted there.

I won't be needing the slots, so they've been covered up.

Fuel tank installed.

I've also covered the large round hole in the front of the fire wall .....

..... and the top of the engine box ......

..... and the bottom. I'll fuel proof these pieces of balsa sheet later and then glue the HT lead and ignition sensor lead to keep them out of harms way. I've had enough for today as my shed heater can't compete with the Beast from the East!

Edited By Gary Manuel on 18/03/2018 16:16:41

[Ron Gray]

Hmm, not too sure about blanking off the firewall hole as that is where the carb intake is isn't it? I've found that air coming into the carb via the fus is more balanced and cooler than that from the engine bay and gives smoother running.

[cymaz]

As I understand it the carb needs space so the air can enter smoothly. If it were me, I would open the hole at the rear.

[Gary Manuel]

I must admit that I blanked the firewall off with a degree of trepidation - I deliberately cyano'd it just around the edge in case I needed to remove it.. Peter Jenkins made a suggestion to fit a trumpet to the inlet manifold extending into the fuselage, which I thought was a great idea. If I had a trumpet, I would probably have used it - but I don't.

I've always sealed the engine box on other models and never had a problem, but I do understand that the pressure and temperature within the cowl may not be ideal. Maybe I've been lucky in the past?

Should I just open up the hole in the firewall or do I need a trumpet? I'll sleep on this question but would appreciate any feedback.

P.S. I understand that there is a mod that can be done to the carb diaphragm casing - to add a nipple and vent this to the inside of the fuselage too. Any thoughts?

Edited By Gary Manuel on 18/03/2018 20:48:14

[cymaz]

Gary, if you intend to sleep on it, may I suggest some bedtime reading? I have one in my box of bits ( unused/ rainy day stuff) . I had a problem with an engine going rich in flight with the cowl so I will experiment with my velocity stack to see if there is any improvement...

[Gary Manuel]

Still not asleep yet.

The way I understand it is that a trumpet is used when the natural airflow is across the mouth of the air intake (i.e. side mounted carb). It's purpose is to reduce suction caused by the venturi effect from syphoning fuel out of the carburetor. With a rear mounted carburetor, I'm not convinced that there is a significant airflow across the air intake, and therefore whether the trumpet would serve any useful purpose. Hence why I've had no trouble before with rear mounted carbs.

I can see however, that extending the air intake into a space where the pressure / temperature is more stable would make the carbureters job of fuel / air mixing a lot easier.

I'm feeling sleepy now.

[Ron Gray]

The main benefits from the use of a rear mounted trumpet are to extend the intake into the fus plus you can easily fit an air cleaner / filter to it, which is what Peter did. You don’t actually need a trumpet 🎺 (unless you want to fit a filter) but I would certainly open up the hole in the firewall.

[Gary Manuel]

I understand what you are saying Ron and I might just do that.

The way I'm thinking is that the air in the fuselage is more stable than the air in the cowl. Trumpets are available to fit the air intake but the trumpet shape would be of no real benefit . I just need some way of venting the air from the fuselage into the carb. I also don't want the positive pressure that will be present at the front of the cowl to act upon the interior of the fuselage - I want that air to move towards the negative areas of pressure I've created at the two air outlets.

Watch this space. I have a the seeds of cunning plan germinating.

[Peter Jenkins]

Well, the major reason for using a trumpet intake extension is to get a steady stream of air into the carb. The DLE carb ends with a flat face and if there is a bulkhead close up to it there will be undue turbulence introduced as the carb draws air in. A trumpet intake stops this happening. The wide intake provides a smooth entry for air which is then smoothly accelerated as the trumpet cross sectional area reduces to match that of the front of the carb. This provides the drop in air pressure that is required to enable the fuel to be sucked into the intake (actually it's the atmospheric pressure in the float chamber that pushes the fuel into the carb intake). The air temperature is also generally lower than that being drawn in from the engine compartment. Whether you choose to fit a "Brian Wnch" style air filter or not, the fact that the air intake is now inside the fuselage will also attenuate the intake roar - ever listened to your car engine running without the air filter fitted? Darn noisy!

So, there are many benefits to fitting a trumpet intake to the standard carb.

You still awake Gary?

[iqon]

Gary I would have given you a finger or two if you would of asked for balancing, also from previous reading etc you need 1/2 " at back of carb, personally I would leave front open and make a box inside

[Gary Manuel]

I'm awake now Peter.

This is my cunning plan. The idea is have the carb getting it's air supply from the inside of the engine box, whilst minimising any cooling air from using the fuselage as an exit.

Start out with a piece of scrap balsa of the same thickness as the gap between the firewall and the carb.

Cut a hole in it.

Cut to size and cut out slots for the carb bolts.

Cut in half to allow it to be slid into place without removing the engine.

Trim to give clearance for throttle and choke mechanisms and the petrol pipe.

Two halves glued in place.

Checked to make sure that the throttle opens OK and airway is clear......

..... and that it closes OK.

Happy with that. Time will tell whether it works OK.

[Gary Manuel]

Posted by iqon on 19/03/2018 13:23:19:

Gary I would have given you a finger or two if you would of asked for balancing, also from previous reading etc you need 1/2 " at back of carb, personally I would leave front open and make a box inside

I had just less than 1/2". I think it might have been OK without opening it up, but it's better safe than sorry.

[cymaz]

Oh that’s thinking inside the box!

[Gary Manuel]

Posted by cymaz on 19/03/2018 17:38:45:

Oh that’s thinking inside the box!

Yes - what I've basically done is add a trumpet without adding a trumpet.

Thanks for all the advice fellas - Like Frankie said, I did it "My Way"

[Gary Manuel]

I've done a bit of tidying up.

Batteries perched up front after double checking CoG (with canopy and everything else in place). This gives a balance point mid-way between the recommended MIN and MAX settings. I'm expecting that I'll move the batteries further backwards later.

Receiver installation. This isn't actually a receiver as it gets it's signals from from between 2 and 4 remote receivers (Satellites).

I'm using 3 satellites. One in the X axis ....

..... one in the Y axis ......

..... and one in the Z axis.

The satellite on the X axis is on a long lead and positioned behind what I expect will be the final battery position. This has been done to make sure that the batteries can never block the transmitter radio waves from reaching all three receivers.

The other little job I've done is to cut a hole in the cowl for adjusting the carbureter needle valves.....

..... and fitting a grommet.

Edited By Gary Manuel on 19/03/2018 19:33:49

[Martin McIntosh]

If I may digress a little I see that you say that the 922 requires satellites to work. I have a few JR921`s, some of which will operate by themselves and others only with a satellite. On speaking to McGregor they say that at least one satellite is needed. Ideas anyone because I am a bit confused? I presume that it must be a s/w change along the line somewhere.

Meticulous build by the way.