DB 60" Sopwith Pup

[Chris Freeman 3]

Still following with interest, this kit is very well thought out and must take a lot of time to cut with all those lightning holes in the structure, would add quite a lot to the costs to make it. This will be a nice size as well.

Is that an Avian in the backround?

[Geoff S]

Well spotted, it is. I bought it for restoration at a knock down price but it doesn't match the set of drawings I got for it at the same time. I forgot to add it to my list of 'to do' projects in an earlier thread last week

The other model is the Ryan ST I built from a kit I 'found' in the club hut and bought to contribute to club funds (part of the kit bank of a sadly departed member). Without doubt the worst kit I've ever made. Still to be test flown - the weather beat me.

All the lightening holes in the Pup are from the CNC procedure. In the case of the wing seat soft balsa perhaps over done - but I'm not a designer. The kit has its issues (what doesn't?) but I'm still enthusiastic about it and would certainly recommend it. I know it'll be easy to assemble at the field and I confidently expect it to fly well

Geoff

[George P.]

Posted by Geoff Sleath on 10/11/2019 21:04:12:

I seem to spend hours doing very little - or perhaps seeming to achieve very little but the model does actually grow

Last night I epoxied the firewall in place. I opted to use the 60 minute version to avoid panic as I tried with some success to clamp it securely - I even used an elastic wing band! I modified one part to allow me to add some extra glueing area by adding some 0.5" triangular stock outside the main central box.

The balsa sheet is there to provide a location for the stringers that support the 0.4mm ply which forms part of the tapered cylindrical shape characteristic of the Pup's fuselage. I cut away enough to allow the triangular parts to glue both to the firewall and the outside of the box sides. Probably not necessary but I like my firewalls well attached and the extra weight, especially so far forward, is irrelevant.

The first job this morning was to fit the bottom wing 3mm T nuts so that it was properly fitted in its final position before I tackled the cabane for the top wing. So I clamped it in place and checked for square by my usual method of a bit of string attached to very rear of the fuselage and checking to each wing tip. It was pretty well spot-on so I bit the bullet and drilled a 3mm hole through the brass tubes of the wing and into the attachment plate. After drilling the first hole I dropped a bolt in to ensure nothing moved as I drilled the second.

I opened the holes to 4mm and contersunk the back to accept the T nuts. Glueing was once more 60 minute epoxy (taking care to apply Vaseline to the threads.) The wing fits perfectly and the 3mm bolts drop straight into the T nut threads.

I deviated slightly from the instructions and plans when fitting the 2 parts of the fuselage together.

The top longeron has a big support triangle shown on the drawing. I couldn't find it so made my own. Subsequently I came across them but instead of part # 128 it looked like 123 and moreover was much smaller - so future builders be aware. I prefer mine

The other change I made is at the bottom where I added a long triangular support piece to spread the load. The balsa here is very soft - ideal for the wing seat but, IMO, not quite so much for a critical support component. I've effectivly added a 0.8mm ply doubler to the inside. You can see it clearly here on the port side. If I were building another, I'd leave the blanks in the lightening holes and actually glue them in. The balsa here is so light the weight increase would be difficult to measure. Just my feelings. No reflection on DB - I don't think I've ever slavishly followed instructions or plans on kits I've built. Going a little off piste is part of the fun IMO.

Geoff

Edited By Geoff Sleath on 10/11/2019 21:07:23

[George P.]

Great progress, Geoff.

I am very familiar with the feeling of working for hours and not seeming to achieve very much. Although, for me, I am more aware of a feeling of constantly deciding to do 'that job that should take fifteen minutes' only to discover that it has taken at least two hours or more.

George

[Geoff S]

I've suicceeded after much measuring and repeated remeasuring to get the the cabane supports stitched and epoxied together I think accurately. It's very close anyway.

Here's the stitching technique I used. Masking tape over the piano wire then stitching 3/per set of holes then, before moving to the next, glue with Cyano (Poundland's best! Nothing's too good for my Pup!). Then, after yet another check on the angles, 60 minute DeLuxe Materials epoxy.

Before fitting the top wing I soldered the diagonal 18 swg (1mm approx) piano wire. I found this quite difficult and took lots more time than I expected. The first bend was OK but trying to get the second bend right to conform to cabane at the other end was a nightmare. I went for an "it'll do" in the end because it's going to be disguised with hardwood/thin ply and so won't be seen but I'm not proud of it.

Fitting the top wing is another time for repeated measurent befor committing to anything permanent. Because there's no real limit where it can go on the flat ply platform it's just a matter of measurement and eyeball. It's surprising how tiny alignment errors show up just by looking.

There are 4 wooden hooks that restrain the wing l/e on a hardwood strip. I fitted the 2 central ones before drilling at the t/e for the 3mm T nuts. The hooks are glued and scewed (15mm countersunk woodscrews) so are very firm. To make wing removal easy the back is chamfered to clear the main spar and allowing the wing to be tilted forward and lifted clear.

So I now have a biplane, which was the original idea so I suppose that counts as a success.

Geoff

[George P.]

The pictures and write up bring back memories, Geoff. The issues you describe were the same I experienced. Further more, the wires were a perfect push fit into the saddle clamps to attach to the top centre wing section. When you factor in the solder and wire to bind then this does not work. I was able to modify and purchase larger saddle clamps to overcome this. Hopefully you will not have this issue as it is a removeable top wing?

The weather appears to indicate that it is time to stay indoors and get building but I have ran out of space and so promised myself that I will not build anything until the Pup and Chipmunk have flown. I suppose I will just have to get on with all those household chores!

[Geoff S]

Next job was to add the the framework stringers for the tapered cylindrical section from the circular firewall to the square section fusleage which takes over just behind the cockpit.

There are 2 formers which are laminated together. The forward one supports the back of the 0.4mm ply sheeting which represents the metal part of the fuselage immediately behind the cowl and the rearward one supports the stringers that support the fabric covering. (parts 106/107 for anyone building the kit).

I fitted the front set of 1/4"x1/4" strip Ok but whe I came to fit the continuation of the taper from the rearward former there was a sharp change of slope when there should be a straight line. On investigation I found the 2 formers to be 3mm taller than shown on the drawing - not much, but enough to make the slope change.

I took the photo after I'd removed the work I'd already done. The stringers should meet the fuselage in a straight line from the former to just behind the wing's t/e.

My solution was to make a new former and use continuous stringers all the way from the firewall to the fuselage.

The originals were slightly damaged when I removed them. The new former is soft 6mm balsa and actually weighs less than the two 3mm formers it replaces. I also had to cut new stringer support sockets (and fill in the old ones) on the former glued to the firewall.

In the process of studying the pictures and 3 views on the Windsock data file I saw that there are 3 further formers on the full size between the end of the plywood/metal section and the point where the taper meets the fuselage, so I put some in. These aren't part of the kit or shown on the drawings because they aren't actually needed and their abscence wouldn't be noticed except by over critical nerds

At this point I think I got infected by the Danny Fenton virus ( a very mild attack because the full blown version would have me trying to do things far beyond my skill set). Sitting looking at the model I became concerned that the stringers looked too fat compared to the full size. The stringers show through the fabric as thinnish lines not great lumps of timber - so I sawed off the 1/4"x1/4" stringers together with the dummy formers. I replaced them with 3x10 mm strip with 4.5mm formers to achieve an effect I'm hoping will closer represent the full size.

The worrying point about the DF virus is that I'm also considering putting inspection windows in the wing leading edges with totally decorative pulleys (which on the full size carry control cables to the ailerons) and even dummy aileron horns sticking out the top of the top wing ailerons with elastic control cable. I need help!

I think it looks better - especially as the fabric (Oratex) covering will (hopefully) conceal my crude woodwork. It actually looks better in real life. The bottom 1/4"x1/4" stringer is there for additional support for the 0.4mm ply - none of those larger stringers will be seen as they'll be sheeted in. Just the other side to do.

Geoff

[Geoff S]

Just fitted the cowl fixing blocks to the firewall. Something I learned - best to have been done before the firewall was attached to the front of the fuselage. As it was, I held the fuselage vertical by holding the top wing platform in the bench vice and resting he tail on a handy piece of blue foam.

Glued and screwed the plywood blocks. Richard, at DB reported that he'd melted lead into the aluminium cowl to get it as far forward as possible. I'm not keen on the idea but, just in case I change my mind, I made sure the blocks were firmly attached.

Earlier ( a week or two back) I tried the motor and batteries on the plan for size abd it didn't look like the kit motor box would suit as it pushed the motor too far forward.

So, whilst gravity was on my side for a change, I temporarily fitted the motor box ...

... and fitted both the cowl and the motor just to see how serious the problem is. It seems not as serious as I thought because the cowl is deeper in real life than it is on the drawing. I've ordered the vacformed motor from DB so I'll see how much the motor sticks out the 'crankcase' and decide how much needs to be trimmed from the box.

DB specify 2 degrees downthrust but no side thrust. On my Gypsy/Cirrus Moth there's both down and right thrust and it flies perfectly. On my Tiger Moth, DB specify no right thrust and IIRC no downthrust either but stall turns to the right are all but impossible because the verticals use all the rudder before the turn is attempted. To get the prop in the centre I need to offset the motor mount and angle the mounting (ie the box sides) the right amount. It won't be something easy to correct if it doesn't work out. I'm very tempted to go for 2 degrees down and right and cut the box sides to get that. A bit of simple trigonometry will work out the offset needed.

Geoff

[Alan Hilton]

Hi Geoff

I have the big one and it needed a lot of nose weight .I used self adhesive car wheel balancing weights inside the cowl which have stoo the test of time (and glow fuel )

Alan

[Geoff S]

Thanks, Alan.

I usually beg a few wheel weights whenever I go to the local tyre place (had a few punctures recently!) and they're fine for minor adjustments but I think I'll need a lot for this model. I have a lot of lead left over from some roof repairs a few years back so I'll probably cast what I need and screw it to the firewall. I'm hoping having 2 x 4S 4.5AH LiPos immediately behind the firewall will help to keep ballast to a minimum. It's just the idea of hanging all that weight off the front of the cowl and relying on the essentially tempoary fixing to hold it that fazes me.

A clubmate has just about finished a 1/4 scale DB Pup which is going to fly on 6S. He's got 2 batteries in and I think he needed more weight to get the CoG where it needs to be. It'sready to test fly when the weather gets warmer (ie next spring).

Geoff

[Geoff S]

I received the dummy rotary engine from DB last week. It's not super detailed but I think with a little additional fetling it'll look OK. I intend to mount it on a 3mm birch ply disc as weight is no problem (in fact an advantage this far forward).

I marked out a disc by drawing round the cowl and cut it out on my scroll saw. I'm not brilliant at cutting accurately so I just made sure I was near the line as the disc needed to fit inside the cowl. I then worked away with a Permagrit sander while holding and turning the rough disc as I went. I was amazed how perfect a circle I ended up with.

A bit of 1st form geometry (the right bisector of any chord passes through the centre of the circle) got me a reasonably small 'cocked hat' (familar to amyone who's done any plotting for navigation at sea). So I was able to cut a suitably sized hole at the centre with a hole saw.

and, after trimming the hole in the centre of the 'engine' I got this:

Before deciding how the 'engine' was going to be positioned I want to fit the motor so this was laid aside for a while and I fitted the 0.4mm ply round the cockpit. Velcro battery straps as well as clamps came in handy.

I made and fitted the instrument panel first as I thought it would be easier. The supplied panel kit isn't truly accurate and the dials are about 20% too small but a bit of jiggery pokery with Photshop and printer sorted that out. It looks good enough for the sport scale model I'm building. I also cut out the cockpit opening before fitting the ply. I was a bit wary of doing that because I thought it might make the curve distorted but it worked perfectly. Because the rear fusleage taper to the tail starts just behind the cockpit opening there is a little kink in the ply but not enough to cause any problems once the paint and covering is done.

I made a frame for the top hatch cover - in fact I made 2 because the first hatch cover I made was rubbish. The second one isn't perfect but it is better. It's easier making hatches with balsa sheet as you can sand the top to fit - with 0.4mm ply there's no room to bodge; it has to perfect first time.

The cover uses a tongue at the back and 3 magnets at the front ( held in by a 0.4mm ply cover) which attach to a lump of steel sheet from the scrap drawer epoxied to the fuselage opening.

As seen here:

 

That's about where I am so far. I said I was a slow builder. I'm not sure if anyone's following this but it's more of a personal diary, anyway - so thanks RCME for giving me the space.

Before I finish this episode you might like to meet Sydney, my pilot. He's named after my uncle who was killed in WW1 when on a wire cutting expedition. He wasn't a pilot, just an army corporal but I've elevated him literally (I hope) as well as metaphorically. My middle name is in his memory, too.

Anyway, Sydney flew in this afternoon from the home of Real Model Pilots in nearby Nottingham and I thought I'd show him his future seat. He looks a bit off colour afer his trip via RM but I'll bring some colour to his cheeks before he's entrusted to fly my Pup.

 

Geoff

Edited By Geoff Sleath on 30/11/2019 22:27:59

[Former Member]

[This posting has been removed]

[Danny Fenton]

Coming along great Geoff, showing my ignorance, I didn't know (or had forgotten) about the right bisector of any chord passes through the centre of the circle. Had to find a scrap circle and try it. By golly you are right mind you by the time I wake up tomorrow I will have forgotten again

Cheers

Danny

[Geoff S]

Thanks, Tom. This kit is sold as sixth scale but at 60" ws and the full size is 26' 6" ws it's actually 1:5.5 and that's Sydney's scale though his shoulders had to be kept to 95mm wide to avoid painful amputation to get him to fit.

Danny, geometry was my favourite subject when I was 11/12 years old. Euclid was a clever bloke and his geometry is so elegant and simple. I really prefer to get the right bisector just by using a pair of compasses to do the construction but that's difficult on an isolated disc of ply as the construction goes outside the circle. I resorted to using a ruler and my wife's school geometry set square (it still has her name and Boston High School written on it!).

What I found amazing was how just by holding the disc to my chest and turning it as I sanded the edge it ended up such a perfect circle. In a similar way I made a round mast for a a boat from a length of square hardwood strip just by holding the end and turning it as I sanded with a piece of sandpaper in the other hand curled round the wood. It was as perfectly round as a piece of dowel and tapered as I wanted it.

Not quite up to your standard but it'll look reasonably OK at 50' At least I don't have to attempt sticking aluminium foil onto the fuselage as my scheme is blue all over.

Geoff

[Danny Fenton]

Ahh Geoff that is because the force is with you. I have paved the way for to foil to your hearts content

Cheers

Danny

[George P.]

Great progress, Geoff.

I like your pilot and how he fits in the cockpit. Mine is still awaiting amputation on account of the closed loop being in the way for a seat or his ass!

Sad story regarding Sydney but so nice that you can do him the honour and shows you are thinking of him.

[Geoff S]

Some choice to make, George - operation of the rudder or operation to the pilot. Just make sure there are plenty of swabs available when the poor chap is unmanned.

If you look at my chosen scheme the whole fuselage is blue (the Oracover I have is Corsair Blue - at the time it didn't occur to me at the time but that's the colour of the Vought F4U is usually - or often - painted). That includes the cowl, which is polished aluminium as supplied. I have some Humbrol Midnight Blue which is very nearly the same colour - at least close enough to try - but I suspect it won't take well on the polished surface. What's the best way of making the paint stick? I've thought of rubbing down with fine wire wool or is there an etching primer I might use?

Geoff

[George P.]

I have in the past used Prymol which is an etch primer and worked brilliantly although it stinks to high heaven and so best as an outdoor job. Dries very quickly if I remember correctly and you only need to wipe on then wipe off. Used it to paint over film, tex and on piano wire. I think you can still get it.

[Danny Fenton]

I have always used a specific aluminum etch primer and have a tin from LAS its not cheap and the shipping is part of the problem. Zinc Chromate I think it is. I use it for aluminum spinners, where the paint has to stick very well!

Cheers

Danny

[Geoff S]

Thanks for the paint suggestions.

I went to B&Q with my roll of Oracover Corsair blue and it was scanned by one of the staf. I came away with a 236ml tester container of Valspar interior silk paint which matches the Oracover very well. I've used Valspar before and I like the water wash for brushes. I sprayed my Tiger Moth cowl with it using my very old and very cheap single action Badger airbrush. I've had it for years and it's far easier to use than the much expensive double action Iwata which I've never had much success with - probably my fault because I've always tried to use ordinary paint and suffered regular clogging.

I also bought a small tin (250ml) of Fortress white special metals primer which the label claims is suitable for non-ferrous matals, including aluminium. I've done a preliminary trial brush painting first the primer (after cleaning the metal with fine wire wool) and then the Valspar and it seems to stick quite well. It's water clean up, too. I'll spray both when the time comes. The match is as good as I'm ever likely to get. It also helps that fuel proofing isn't an issue.

Not huge progress on the model itself but I've fitted the cowl and changed the securing screws with 3mm machine screws by fitting 3mm T nuts to the mounting blocks. It looks like I'll be putting some lead in the cowl on the "engine" mounting 3mm plywood disc so I need the cowl/ firewall fixing to be as strong as possible.

I've also fitted the ply side panels to the front sides of the fuselage:

As you can see, Velcro battery straps come in very handy here.

The supplied 0.4mm ply are ready cut to shape to go round the wing leading edges but some trimming is needed because of the tapered shape. There is very little wriggle room because the parts are barely big enough. In the end I used some 0.8 mm ply from my stock, fitted it over size and trimmed it after glueing.

It's obviously heavier but it's mostly in front of the CoG so it's not really an issue and it's a bit stiffer and stronger in a vulnerable part of the model that could be damaged by transport or handling.

I tend to seize up when building and get to a tricky but inportant part that I'm not sure how to tackle. I put off the job for a while and find a displacement activity (eg buying paint or just reading ). That's the main reason for the gap in updates.

Next job is manufacturing elevator and rudder horns from 1.5mm fibreglass board for the closed loop. Then it'll be fitting servos.

Geoff

PS Just realised the picture is a mirror image!  It happened when I rotated the picture because I took it with the camera in portrait orientation   I don't suppose it matters  btw they are Eachine straps in case you're puzzling.

Edited By Geoff Sleath on 13/12/2019 17:58:19

[Geoff S]

I won't be adding to this thread and all the images have been deleted.

Goodbye

Geoff

[Former Member]

[This posting has been removed]

[Denis Watkins]

Posted by Doc Marten on 20/12/2019 20:46:52:

???

What? Why?

Edited By Doc Marten on 20/12/2019 20:47:36

Geoff has this evening

Been upset by something in the

Updating Horus OpenTX thread

[McG 6969]

???

... what's happening, Geoff... ?

Cheers

Chris

[cymaz]

Geoff definitely broke the C O C on the Update Horus thread. That’s all I’m going to say and end the matter there.