K5682 - Martyn's Fury

[Martyn K]

This is the aircraft that I am planning to build for the latest Scale Mass Build Master Class.

It will be powered by an ic engine, I have managed to acquire an almost new RCV90SP which should be a good fit and match without any protruding lumps

I haven't actually got my hands on it yet, but it may mean that firewalls will need a little tweaking. Nothing insurmountable - hopefully.

I have to admit that I am worried about cooling - I am not sure how I am going to address that - and I think the electric powered models may have the same problem. I think that will be one of the bigger logistic challenges.

Other challenges - silver paint can be challenging to get a nice even coat.. I will almost certainly use Klass Kote for paint - at least for the silver. Getting the correct shade of blue for the trim may be more difficult but it will be finished with Klass Kote clear anyway

Construction however, looks fairly straightforward except for the "new to me" challenge of lots of bent wire for struts and things like that. If you get the wheel axle a couple of mm short then no-one will notice, A twisted or asymetric cabane will cause big problems.. One of my projects on the go is a Free Flight Scale Bucker Jungmann which is just about ready to start the wire-work. It will be good to practice on.

My background. I have been building and flying model aircraft for almost 50 years but only comparatively recently been bitten by the scale bug. I am still building my Chippie (from the last Master Class) but that will hopefully be fully painted before we start this.

I will never be as good a builder as Danny and the other scale masters so will not be trying for a Class A scale model but what I do want is a good Stand Off Scale with lots of detail to satisfy those who want a closer look. It will have to look 'right' even though it may never satisfy a judge.

Hopefully, it will be under 5kg and will therefore qualify for the new BMFA Light Scale Class.

What I would love to see is a squadron of Furies at a show in perhaps a couple of years time. I think that would look awesome and be a great credit to our honourable leader and mentor, Mr Fenton.

More to come..

Martyn

[Manish Chandrayan]

Signed on Martyn

[Danny Fenton]

Looks a great choice Martyn. the cooling issue will need careful consideration.....

Cheers

Danny

[Martyn K]

Its quite a safe choice Danny. The paint detail on some of the schemes - although very attractive - would frighten me to death if I actually had to paint them

[David Davis]

I'm subscribed too Martin.

[Martyn K]

My RCV90SP turned up (courtesy of placing a wanted ad in the BMFA classified). Only run in and never flown. Nice and oily.

It looks like it will be a perfect fit

and

It is certainly a weird looking engine. One of the nice things is that RCV provided details of the right sight size vents and how to direct cooling air. I'll probably mount it needle valve pointing downwards - it depends on where I route the exhaust. Getting quite excited now. That is one big hurdle out of the way

More to come

Martyn

[Danny Fenton]

Looks a very good fit indeed! And they turn big props

Cheers

Danny

Edited By Danny Fenton on 04/07/2018 16:40:10

[DaveyP]

How does that engine work then ?? looks like the shaft is coming out of the top of the cylinder head....

Edited By DaveyP on 04/07/2018 19:07:58

[Martyn K]

There is a video here that shows how it works.

No embed code for some reason

Youtube

[Colin Leighfield]

I could never get used to the idea that the cylinder rotates around the piston? Seems to work but you get mixed reports on them. One big advantage is that the prop rotates at 1/2 of crankcase speed, is that right? So you can use a nice big scale prop.

[Martyn K]

Hi Colin

Yes - that is correct. It will turn an 18x14 prop. Available from Just engines at eek pounds each. It also has a nifty rear starter point using an Allen socket. Not sure if I will use that though

I do hope its reliable. It wasn't cheap - even second hand..

Martyn

[Colin Leighfield]

I think it's a fascinating design and apparently the rear starter point is handy. I've got no experience of them at all, but I've heard that they're mechanically noisy, shouldn't matter if it's drowned by the exhaust noise? Also they run hot, so the cooling needs to be spot on but that's already been pointed out. A test for your ingenuity so I know it's not going to be a problem! I've done no preparation for mine yet, still no clear thoughts on motive power.

[Martyn K]

Getting severe withdrawal symptoms watching all these tail surfaces and fuselages being built so I thought that I had better make a start.

My Fury will have a few minor changes. I was at our local club (SCRCS) a week or so ago and watching Grand Maestro, the Honourable and Venerable Gordon Whitehead flying his lovely DH82a Tiger Moth. When he came to pack it up I was astounded on how easy it was to de-rig and dismantle. The secret of course was the 3 piece wings held in place by the active rigging. I was already toying with the idea of splitting the wings - but primarily for storage so the scene had been set. I just had to make a few tweaks to the Fury design

While I was still thinking this through, I started on what appears to be the easy bit, the lower wing.

Every project has to start somewhere

The 1/16 balsa TA was cut and a strip of 1/4 x 1/16 spruce added to the upper surface (instead of balsa. I have gone for spruce to add a bit of ding resistance. By the time it has been sanded to profile you wont notice the weight.

I also made my first mistake - didn't take long. I didn't lift the underside spar to allow for the 1/32 packing to help keep the covering off the spars. Danny spotted this almost straight away, but I was puzzled why I missed it. The shop bought 1/4 x 1/8 balsa strip was a good deal thicker that 1/8 so when I seated the ribs, they fitted perfectly - no alarm bells raised.

Blindly carrying on and feeling pretty pleased and mentally noting how well everything fitted

 

A few pointers. The rear part of the rib sits flat with the lower spar (supposed to be) packed up by 1/32". The front spar is about 6mm in mid air and will need spacers. I didn't have the thick spar problem as this one came from a different batch.

When I cam to fit the wing tip, the ply and balsa parts fitted great. However, the tip ribs appear to have the slot cut in the wrong place. You can see from the plan. The cut away should be over the ply inner perimeter. It was easy to trim back about 2 or 3mm but that has made the front of the rib short. mmm I didn't think that through as I cut back and glued it into place

So you can see where I was up to on Friday evening when I packed up.

I had a BMFA council meeting in Leicester yesterday, so only an hour in the shed before I had to leave

Started work on the centre section.

B5 & B6 are cut from ply and hacked into 3 pieces.

The front and rear of the ply boxes glued into place with the intermediate part of the ribs

Likewise the outer parts are glued onto the end of the wing half. Note the upper spar is just temporarily inserted while the glue for the brace dries.

 

 

Edited By Martyn K on 14/10/2018 21:13:23

[Martyn K]

....continued

The spars are 1/4" wide. The idea is to have carbon fire (5mm diameter) stubs permanently fixed into each wing half. These fit perfectly into 1/4" OD brass tube. The stubs and tube fit into one bay each side of the wing break, the stubs therefore are 2 bays long.

So for the centre, a dummy spar was created that holds the tube in a curved cradle, so it is parallel with the spar - i.e point straight out.

Its a bit of a faff getting it to fit and leave enough space for the upper spar which will encapsulate the tube so it is supported top and bottom. It took me 4 or 5 hours to get all 4 correct. 2 front and 2 rear). The tube is aligned just under the upper spar, not centrally...

The epoxy was gently heated and the top spar and other ply B5/B6 in the centre was added

then it was all clamped up while the PVA dried. The resin can take its time because it isn't going to move

The CF rod in the outer will need to drop about 3mm to accommodate the 4 degrees dihedral in the lower wings (2 degrees dihedral in the upper wing).

So pack up the wing and cut a length of carbon fibre rod and insert into the tube.

Align the wing so that its not swept back or forwards. You will need to pack up the wing tip packing to line up the front spar. Carefully sand the spars and TE (LE not fitted yet) until you get a good joint and secure into place - I used a mix of pins and weights. I then added the dihedral rib breaks with the inner (centre section) ribs vertical - not canted at 2 degrees as you may expect. I had to cut a couple of extra ribs for this so used some nice 3/32" balsa for the two inner ribs in the outer panel.

The next job was to cut wedged in balsa to support the CF rod

Its a 3mm drop so quite easy to sand that down from a piece of 1/4 x 1/8 at the rear and 1/4 square at the front

Wedges not shown on this photo but its clear where they will go.. (Hopefully)

Finally glue and clamp up and keep your fingers crossed that no epoxy has seeped into the tube...

This photo shows the upper wedge fitted before the rear top spar was added afterwards. You can also see the centre ribs fitted. These will have ply cap ribs fitted.after the wing has been sheeted

More to come

Martyn

[Danny Fenton]

Well done Martyn, glad to see you have got started :}

Cheers

Danny

[Tony Bennett]

nicely done, though a bit too complicated for my small brain to fully take in.

Tony B

[Martyn K]

It's the way i build my gliders tony. Makes for a strong and reliable joint. Its not easy to describe - and it is a bit of a faff but I think worthwhile persevering with

Edited By Martyn K on 14/10/2018 22:15:25

[Martyn K]

Some more progress. Haven't been feeling too well this week and working away Monday and Tuesday slowed things down a bit.

Following on from the wing tip problem noted above, this is what it looks like at the LE.

Interestingly, the ribs were the correct length at the LE although the slot is incorrect. What I think is wrong is that the ribs are common for upper and lower wings, but the upper wing has slightly greater chord..

False LE added, sanded to profile and the upper and lower sheeting added. When unpinned, the wing had bowed - about 25mm across the length of the panel which was a little distressing. Up until now, I was unsure whether I was going to add webs. This made my mind up..

So 45 minutes this morning and the panel was webbed, front and rear spars.

Note the weights holding the wing flat while they were inserted. I may also give it a gentle spray of water

Close up.. Note the vertical grain for anyone who hasn't fitted webs before.

Work on the centre panel continues

Upper side has been sheeted slightly, The upper and lower ply plates have been drilled - along with a fuselage plate - I am going to use star nuts with M4 steel bolts .A strip of balsa lies over the spar to fill the small gap between the spar and the sheet to provide some compression resistance

I am having to move the rigging retaining for the lower wing into the centre panel to stop the lower wings easing outwards with flight loads. The beech hard points will have some new brass plates added which will extend over the inner panel slightly so the rigging point is in the correct place.

I haven't glued the lower plate into position yet but I have tapered it slightly (a slight wedge) so that it fits into place. It sits slightly proud of the underside sheeting at the rear if you don't taper it back slightly

More to come

Martyn

[Colin Leighfield]

Interesting stuff Martyn. I think I will leave the wings until last! I still have Chipmunkwingitis and it's left me with a twitch.

[Jose L. G.]

Nice Progress, Martin.

I was also thinking on three panel wings, but first I have to work on the fuse a bit more. Later prepare cabane and so on.

Cheers

José Luis

[J D 8 - Moderator]

I have run an RCV 60 in a Seagull SNJ [navy texan] for several years,and it is different from normal engines.

There is a lot of mechanical noise that reminds me of a full size radial running but that is normal. Make sure your firewall bulkhead is well strong and firmly fixed,there is a load spreader plate that comes with the engine and should be used. The large prop exerts considerable forces. Use locktite on all bolts and fixings.

Follow the cooling baffle instructions,it is important to get a good air flow across the engine and have plenty of exit area. I see you having air entry on the bottom of the cowl just behind the spinner then a baffle directing air over the fins to the top of the motor,it would then travel down over the rear of the motor and out through a slot at the bottom. It may be possibe to run a duct to the scale radiator but I am not sure about this.

I always start at the rear,a standard starter is fine but from the front something more powerfull may be needed with a 90. All the best with your build . John.

Edited By J D 8 on 18/10/2018 20:08:30

[Martyn K]

Thanks for the advice JD8. I appreciated the amount of force from the big prop when the motor became slightly detached from the workmate that was holding it when I was test running it.

Mine was mechanically fairly quiet, but it is almost new. Being slow revving, its an awesome sounding engine.

 

Edited By Martyn K on 23/10/2018 09:39:25

[Martyn K]

A bit more progress. I have made a start on the Right hand wing, following (almost) the same process as the left hand lower wing.

The differences are that the upper spars and webbing were added before the dihedral was set to prevent the wing from bowing. I did manage to get the bow out of the left lower wing with a little moisture and weighing it down for 4 days. Adding the webs while the wing was flat undoubtedly helped as well.

Personally, I think the webs are a great asset to the wing, they have stiffened it up considerably. So my final structure looks like:

3 of 1/4 x 1/8 spars plus 1 of 1/4 x 1/8 spruce upper front with single full length 1/16 sheet webs (grain vertical) at the rear of the spars

TE is laminated with 1/16 sheet as per plan with 1/4 x 1/16 balsa lower trebler and 1/4 x 1/16 spruce upper trebler

Some progress photos

Right wing assembled and dihedral setting while epoxy hardens. Note webs and spars have been done. LE will be fitted when the wing gets separated

The fixed carbon joiners are 'boxed' in using the cut (dismembered) parts from the ply braces

Started work on the cap strips on the LH lower wing. A very tedious exercise.

However, the section tapers away too sharply at the tip. Look at the light passing through the gap at the rule edge. I think this is due to the three tip ribs being designed for the upper wing rather than lower although they are supposed to be common.

The fix (I think) is quite simple, double up the cap strips then sand back to section which is what I did this morning

Now waiting for glue to dry

More to come

Martyn

[Solly]

Hi Martyn, it might be worth giving Weston UK a ring with the serial number of your engine and asking if it is one of the later upgraded examples. I have both an early 90 and one of the later ones and there is very noticable increase in power with the latter. I suspect an early engine would struggle a bit to fly your Fury, I use mine for flying vintage models, but the later example has flown a 13 pound model without problems using a 4 bladed prop.

[Martyn K]

Thanks Solly

Will do. Great advice.

Martyn