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DB 60" Sopwith Pup

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G194006/11/2019 20:15:28
3523 forum posts
1 photos

Hi Alan

It's just a sheet of 1mm (approx) steel about 450mm x 1000mm in area, hough, it can be any size to suit the user. The magnetic blocks are very accurate triangular wooden blocks with a 6mm magnet embedded in one face. I think the wood is beech but I'm no expert - it is quite hard.

Someone was selling the blocks at Cosford last year as well as sheets of steel (though, of course, you could get the steel anywhere). I bought 20 blocks which is just about enough but I'd like another 10. Unfortunately the guy selling them wasn't there this year. I'm fairly sure he was an LMA member. I suppose I could make my own but I don't think I could match the accuracy of the ones I bought. There's always the opportunity to make other blocks for special purposes because the magnets are readily available - I use them for holding catches on models.

Much better than pins (though I sometimes use pins to hold parts together - eg holding the ribs down onto the leading edge) because, after a build, the drawings are as good as when you started as no adhesive seeps through the pin holes in whatever you use to protect the plan (I use cling film).

HTH

Geoff

 

Edited By Geoff Sleath on 06/11/2019 20:15:50

Alan Hilton07/11/2019 12:29:35
114 forum posts

Thanks Geoff

Alan

G194009/11/2019 00:23:20
3523 forum posts
1 photos

You're welcome, Alan.

Now a bit more progress on the fuselage. I completed the front section but before I glued it all together I did a dry run and found a couple of components that were easier to glue together before full assembly. So to help other builders (if there are any here).

fuselage 7.jpg

These fit right at the back of the wing seat and are tricky to fit in when it all looks like this in the jig.

fuselage 3.jpg

fuselage 4.jpg

Then I ended up with a complete forward section except for the firewall, which I opted to leave until later because it will be fixed with 60 minute epoxy (it tkes longer than 60 minutes to set completely so best left overnight.

fuselage 8.jpg

and here

fuselage 9.jpg

The rear section of the fuselage is frame structure rather like a vintage model. Each side is built flat on the plan from 1/4" x 1/4" strip. It's fairly straight forward except for the diagonals which I find a great pain to get right. The joints are reinforced with 1mm ply semi circles. I built the second side over the first, separated with cling film, in order to be sure of 2 identical parts

After some thought I decided the easiest way to join front to back accurately was with the front inverted because the top is dead flat. The top longeron goes right from the back to the firewall, and the slanting bottom longeron ends at the back of the front structure.

fuselage 11.jpg

... and here it is. Looking almost like an aeroplane fuselage for the first time.

I couldn't resist trying the bottom wing to see if it fitted. It's perfect! I checked and it's absolutely square with the fuselage. The only tiny problem was that it was a bit too tight at the t/e and a couple of strokes with a Permagrit file and that went away. I think I may need to ease the fit a bit more to allow for covering but I'm pleased with it so far.

Geoff

Danny Fenton09/11/2019 00:37:33
avatar
9312 forum posts
4125 photos

Excellent Geoff the model is coming along well

Cheers

Danny

G194010/11/2019 21:04:12
3523 forum posts
1 photos

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.

fuselage 10.jpg

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.

fuselage 12.jpg

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

G194010/11/2019 21:24:09
3523 forum posts
1 photos

Today part 2.

Cabane fitting, next. The part that supports the front cabane mount is held back from the firewall by the extra 3mm ply which allows for the glow engine mount. As mine is electric I don't have that and that means the fixing point is further forward than shown on the drawings. To get the structure to agree with the drawing I've inserted a piece of 3mm balsa and taken about 6mm off the plywood itself. Because I'm intending to use the top hatch to fit my batteries I want it to be as big as possible. I also added some exta support underneath. I used aliphatic.

fuselage 14.jpg

The drawing has a diagram showing the angle for the front cabane support. I made a pair of jigs from the glow firewall 3mm ply supplied and fitted them on the fuselage with tie wraps. Where the piano wire is stitched and glued (epoxy) the instructions suggest wrapping with masking tape. I've used that method before and it works surprisingly well. I did the same with the rear supports - again tie wraps help a lot.

It's important to get the incidence of the top wing exactly right so I got out my trustly parallel rules, blew off the dust (well they got me across the North Sea before such luxuries as GPS navigation aids!) and made the measurement.

fuselage 13.jpg

There was me thinking they'd be parallel and all the measurement aid I'd need was a spirit level. I know it's only 1 degree but that comes at 5mm over a 250mm length. So it looks like myRobart incidence meter will be in use sometime soon.

I've also been thinking deeply about battery installation/changing but that's for later.

Geoff

Edited By Geoff Sleath on 10/11/2019 21:27:45

Dove from above10/11/2019 22:44:34
20 forum posts
3 photos

Hi Geoff, really enjoying this build, i am a newb so loads of great stuff here to learn from.

I would like to comment on the Slec jig, I got one of those and find it not that great. The plastic uprights are not vertical! at first I thought I was tightening the bottom to tight to the board but ruled that out. Have no idea why the tops flair out

G194010/11/2019 23:09:34
3523 forum posts
1 photos

Dave: Glad you're enjoying it. So am I

Just checked my uprights and they are quite square. However, the main advantage of the jig is in keeping the fuselage under construction, straight. The uprights can be held in place using the SLEC plastic clamps which fit exactly in the grooves and using a normal square to check vertical. I've had mine for 20 years. It's on a piece of MDF board with battens screwed on the bottom to keep it flat.

Geoff

G194011/11/2019 20:54:36
3523 forum posts
1 photos

I've got some Oratex covering but I'll need some matching paint for the cowl. Do you know if anyone supplies such a thing or am I goingto have to try B&Q for a special mix or a local art shop to try acrylics?

Geoff

G194012/11/2019 10:17:15
3523 forum posts
1 photos

I fitted the cabanes and top wing platform (I even put the top wing roughly in place just to see it looking like a biplane for the first time).

Checking that the front cabane is square before stitching and glueing with slow epoxy.

fuselage 15.jpg

I stole a needle form my wife's sewing box (one with the biggest eye), cut off the point and used it to thread the super strong thread I use for jobs like this. It comes from a cone of thread that my wife rescued when she was working in a factory that manufactured clean room clothing when it was thrown out. No idea what it is but it's incredibly strong and I have literally miles of it I think. It'll last me out! DB supply a bobbin of thread for the purpose but I opted for my own which is a bit thicker, I think. My technique is to 'sew' 3 times for each hole and then fix it with a drop of cyano. My jig held everything firmly in place.

Binding and soldering the top was very easy and nothing shifted. There are often queries about what soldering iron to buy so I thought I'd show what the one I use for heavy soldering looks like.

soldering iron.jpg

I've had it for 60 years. I think my dad gave it me - either that or I stole it from him. It's 125 watts and has a wooden handle, though I'm sure newer ones will have plastic It's 125 watts and has a big enough thermal capacity once heated to make soldering piano wire a piece of cake. Not ideal for soldering integrated circuits, of course, but I have a smaller one for that!

The incidence of the platform is 1 degree +ve relative to the top of the fuselage (and the bottom wing).

fuselage 16.jpg

Here it's very slightly over 1 degree but the rear cabane is still held with tie wraps and a slight adjustment will be made before sewing and glueing.

Geoff

Chris Freeman 312/11/2019 10:54:25
315 forum posts
445 photos

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?

G194012/11/2019 12:11:23
3523 forum posts
1 photos

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.12/11/2019 17:20:44
54 forum posts
20 photos
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.

fuselage 10.jpg

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.

fuselage 12.jpg

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.12/11/2019 17:32:07
54 forum posts
20 photos

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

G194015/11/2019 16:19:13
3523 forum posts
1 photos

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.

fuselage 17.jpg

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.

fuselage 18.jpg

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.19/11/2019 09:33:35
54 forum posts
20 photos

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!

G194019/11/2019 12:18:59
3523 forum posts
1 photos

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.

fuselage side 1.jpg

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.

fuselage 19.jpg

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

fuselage 20.jpg

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!

fuselage 22.jpg

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

G194020/11/2019 23:28:45
3523 forum posts
1 photos

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.

motor 2.jpg

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.

motor 1.jpg

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

motor 3.jpg

... 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 Hilton21/11/2019 09:37:27
114 forum posts

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

G194021/11/2019 11:04:27
3523 forum posts
1 photos

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

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