Martyn's Chippie RCAF 671

[Martyn K]

Posted by Andy Muckley on 06/01/2017 20:04:47:

Hi All. I t would be a great event to fly ,or even maiden them all together somewhere, sometime, like The Master said.(sorry danny) it's like eating an Elephant , one bite at a time. Maybe we need a date/ venue to aim for regardless of quality of finish. what you guys think ?

Hi Andy

I think we originally said we would meet up at GA last year... possibly next year (2018) may be a better option - a builders and survivors meet. If I get to GA this year. I'll happily bring the chippie along.

[Danny Fenton]

I will be at Greenacres this year, and next year too, Lord willing.

We could also display "where we are up to" in the marquee during the day if that would be of interest? I would have to clear it with young Jim, but usually the marquee is empty during the day unless we are sheltering from the rain in it!!! But we wont have rain will we

Cheers

Danny

[Nev]

You certainly crack on when you put your mind to it Martyn.

Nice wings.

Nev.

[John Timmis]

Hi Martyn

I'm in the Crewe /Nantwich area. Not too far/

Cheers John

[Andy Muckley]

Hi Martyn, that sounds like a plan 2018,

[Martyn K]

Still kofin and splutrin and the Hornet Moth is a distraction.

Progress is slow but its been a time to think. I wasn't happy with the U/C layout so I have added a much larger u/c block and a deep slot to hold the 8g torque arm

This will have a long ali plate over the length of it. The torque arm will be retained by a screwed down steel saddle clamp as per the plan.

That looks - short - the arm is 25mm long.. Optical dillusion.

Also following Danny's lead for retaining the legs onto the torque arms. Drilled a 4mm hole to accommodate the 4.1mm 8g arm - an interference fit. Drilled through and tapped M3 and two cap screws (which will be trimmed back) and hidden in the U/C leg fairing

I have also reduced the length of the oleo spring by 2 turns, but that is not enough. It takes 3kg down force to settle the leg so it sits naturally in the oleo so I'll remove another two windings and try again.

More to come but its slow...

Martyn

[John Timmis]

Hi Martyn

I think that's a much better way of fixing the under carriage. I didn't like the tin straps shown on the plan at all & used this method on both my Chippies. They have both survived all my arrivals so far. I turned the torque arm round to face the rear so that the torque reaction would be absorbed by the mainspar. The photo shows my 2nd chippie.

Love the Hornet Moth, a real work of art.

Cheers John

[Martyn K]

I agree - that's much better John.

As soon as I shake of the remnants of the Flu we'll have a meet up and compare notes.

Martyn

[Martyn K]

A minor update

Eventually managed to get the torque rods and plates and bolts done for the undercarriage

One half likes like this.The plates sit below the skin. I dont think that it will move. The clamp at the end is holding a small beech block (1" x 1/2 x 1/4) to spread the impact load on the block so that is spread more evenly. No excuses - lots of glue to keep it all together.

One more hurdle out of the way. I can get on with sheeting and that wonderful fuselage fairing now

More to come

Martyn

[Simon Feather]

Good stuff, Martyn - my Chippie is still in its box in the wardrobe awaiting its place in the build queue, so maybe I'll get onto that after the KF3 and the MB that I signed up to are done.

Simon

[Martyn K]

Part 1

While the Hornet Moth has been on the go, progress on my Chipmunk slowed down, nonetheless, some progress has been made.

The wing, flaps and ailerons have now been completed - all very straightforward. As Danny has suggested, I have sleeved my hinge points with brass tube to reduce wear. Basically, this part of the build is very straightforward.

and

and

I was really looking forward to doing the swoopy curves under the wing. As it happens, they were actually quite simple, the hard bit was cutting the wood to size - and that wasn't really difficult.

My wing securing method is a single M4 Stainless steel bolt with 2 dowels as suggested on the plan

Slightly different to the plan - I have used hardwood blocks to keep it all together in the fuselage but the wing is basically as drawn

Wing tips added and 99% of the wing LE sanded to shape. I am not bothering with shear webs, the wing is quite heavy and I have used spruce rather than balsa spars.

That was plonked in the corner while I scratched my head on the fuselage - and more importantly, the power plant.

I keep changing my mind on the power plant. Originally, I was going to put an Enya 60 FS in then electric, then an OS70FS then electric again. The Enya 60 is about 25-30 years old and an eBay bargain - if it runs. So - 3 years after I bought it I thought I had actually better test it.

It ran sweetly and will have a remote clip so decision made..

I then got very worried. The engine bearers are quite long. They are located at the front in a 1/4" ply former that only seems to hold the cowl in place - yet 2 formers back they are located in 1/4" balsa! This is where the load is really carried and I am convinced that should have been at least 3mm ply. Probably a drafting error.

So, a bit of re-engineering. The bearer simply run between the front 2 formers and obviously forward of that to support the engine. A 3mm ply shelf (for the fuel tank runs back to the balsa former which now has a 1.5mm cover - slotted to take a tongue from the 3mm ply shelf.

and

a second 3mm ply shelf then fits from the lower side of the fuel tank bay and is glued - and with a 6mm square obechi reinforcement to the wing mounting plate. This is much stronger and of course the plates support the fuel tank and are multi functional. A 10oz fuel tank is fitted

With the engine in place..

and

I have had to move the front former back about 6mm to accommodate the rear intake - which has blocked access to the needle valve - hey ho..

With that done and the fuselage halves glued together, I then worked on the rest of the fuselage - the plan is to get it ready for glassing later this week hopefully.

And the fus is now all in one piece.

 

 

Edited By Martyn K on 20/03/2017 10:18:27

[Martyn K]

Part 2

So - the rear swoopy bits of the fairing that seemed to cause so many problems and here was drafting error number 2..

Clearly the plan was incorrect as the outer curves were shown as being convex rather than concave

The flaps were refitted and the parts held in place and suddenly there was a 'Hallelujah' and a light came on.

This is how I did it although I think that everyone is now past this point.

1. Extend the lines of the wing so that they meet to a point, drawn on the fuselage.

2. Check from the Fuselage C/L that they are both at the same point on opposite sides of the fus.

3. The long edge of ply curvy bit of the rear fairing is slotted into the fus

4. The short edge should be slotted into the triangle that fairs into the edge of the flap. I didn't spot that until after I had cut mine down

5. Fit the balsa former to support the balsa sheeting.

and here is a photo sequence

and

and (there are spacers between the flaps and the end triangle. These will be replace with a lite ply rib to protect against dings).

What was hard about that?

More to come

Martyn

[Martyn K]

A bit more progress

The fairings have been sheeted and are well in the way to being blended in - the solid block upper were cut to shape on the bandsaw then hollowed out with a dremel and drum sander then finished with various sanding blocks.

and

The underside isnt quite finished yet, needs a bit of filler and some thought on how I am going to fill the gap..

More to come

Martyn

[Dwain Dibley.]

Good progress Martyn....

Those fairings can be pretty tricky Matey, but you seem to have nailed it...Well ....er.........glued it....

D.D.

Edited By Dwain Dibley. on 25/03/2017 00:00:48

[Colin Leighfield]

Martyn, those wing fairings have been the subject of debate, I thought the same as you at first, but actually they really are convex. Look at Danny's thread.

[Martyn K]

Thanks both. Fairings now removed, reversed and reglued . It is very tricky, looking at the 3v plan view they look concave, the side elevation they look convex I'll go with the flow snd reverse them

 

Martyn

Edited By Martyn K on 25/03/2017 13:50:07

Edited By Martyn K on 25/03/2017 13:51:09

[Danny Fenton]

Now you are officially in the Chippy club

[Martyn K]

Lol. Don't know what DHC were thinking when they did those fairings but they look better wrong

[Martyn K]

Still working on the wing fairing, probably the biggest and most complex modelling job I think I have ever done. This really isn't easy.. I have corrected the rear part of the fairing and am pretty convinced that the curves are too big but I am stuck with that. Now trying to sort out the curve around the LE and the underside - which I think is far more difficult. The LE bit is OK although I need to add some more wood, it's the underside that I am puzzled about

I have cropped one of Danny's WP912 images. (Hope thats OK Danny..)

If you look at this image, you can see the 'swoopy' curves that blend into the rear fuselage and rear fairings. When I built my wing and fairing, I used the parts supplied, however, it appears that the side curves extend towards the Leading edge and that there is a reduced wing thickness as per the arrows in the following photo.

Because of the way the wing has been built, I cant see how to emulate this.

Has anyone here cracked it? Or is it something else I should just ignore

Thanks

Martyn

[Danny Fenton]

Hi Martyn you have found the area of the plan where it is not exact scale. If you treat the wing root as a given, and the fuselage as a tube you are nearly there. I think the problem is due to the wing sitting wrong in the fus. I built the underside of the centre section up with sheet to correct this. Take a look at my build pics.....
Yes its difficult, but that was the objective
Cheers
Danny

[Martyn K]

Thanks Danny

I think my wing is sitting about 3mm low anyway for some reason. I was actually thinking of stripping the planking from the front two formers and redoing in 5mm balsa then blending it back in again. That would give me about 3-4mm to build up under the wing and then blend in the sides... I have a 3v that actually shows this part of the fus curving downwards in the side profile.

All very messy though and wouldn't really emulate the inflowing curves.

I'll have another look later

Martyn

[Colin Leighfield]

Martyn, I think you are about where I was when I stopped. I have built wash-out into my wing (the full-size has it) and that means that I have a greater angle of incidence at the root, raising the leading edge. I'll have a look at it later today.

[Martyn K]

Thanks Colin

I built mine as per plan. Gordon Whitehead asked me "where is the washout?" when he saw it last week He knows his aeroplanes..

Martyn

[Colin Leighfield]

This is mine now, I've no excuse for not finishing it, although at this stage I was a bit demoralised by it! I messed up the convex bit of the root fairings first time and that is what I have to get back to next.

[Martyn K]

That looks OK underneath Colin...

This update is slightly disjointed.

Before I got too bogged down with the swoopy fairings, I sorted all the linkages out. It didn't help that I managed to add all wing root sheeting and had forgotten to put in the flap bell-cranks. So - a few steps backwards - there seems to be a theme developing here..

This is the aileron linkage. Fairly straightforward. I have used 2mm c/f push-rods. One thing I did change was the position of the horn on the aileron. In the original position it was binding very slightly

So - I moved it in by about 25mm Its made from an aluminium horns designed for an indoor model

and epoxied to a small block of wood. I have now removed the F/G horn from the end rib. It works much more smoothly. Far happier with it this way. The flaps use the standard horns which as you all know are separate from the hinges. No rocket science there..

I was concerned that the wood around the wing mounting bolt was getting a bit battered so epoxied in a small length of ali tube to protect the wood

My rear fairings have now been reversed. IMHO, I think that they are too wide. I also havent quite got the upper line correct although the lower line looks OK Ho hum. If you look at the 3v there is a slight kink as the curve reverses slightly just before the junction with the flap. That ding is intentional..

But on the top, the fairing bends very slightly upwards. My OCD is going into overdrive now - and I even started on the rivets

Another shot - its too wide..

This is the centre bay with flap and 2 aileron servos. All works very smoothly I am pleased to say.

FWIW - this is the Flap bell-crank and linkage

I have started sheeting the cockpit The R/E servos are boxed in under the front pilots seat. It may have been a better idea to use ultra slim wing servos that are used for gliders. Most of the box will be lost by the seat and the pilots bum (or lack of as the case may be). The floor is also a little high but I have carefully tilted it downwards so I can get some detail in there.

Back to the fairings. I have started building up the underside fairings.A ring of 5mm balsa just in front of the LE then 3mm up to the front former then sanded back and blended in. Behind that ring of balsa a 3mm balsa doubler added and blended nto the central swoopy fairing in the rear part of the wing. It looks better than the photo - for a change.

However, the fairing that sits around the LE isn't correct so I have started building that up as well. The difficult bit is deciding what needs to be part of the wing and which bit is attached to the fuselage

Added some 1/4" pieces to the LE. I think there will be a second piece to be added and then I'll sand it all away again.

You can also see the balsa ring and front balsa filler in this shot. I think that its quite subtle and I am pleased with that.

I'll be glad to see the back of these fairings though..

More to come

Martyn