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DB 60" Sopwith Pup

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Geoff Sleath06/11/2019 20:15:28
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3434 forum posts
297 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
102 forum posts

Thanks Geoff

Alan

Geoff Sleath09/11/2019 00:23:20
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3434 forum posts
297 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
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9213 forum posts
4063 photos

Excellent Geoff the model is coming along well

Cheers

Danny

Geoff Sleath10/11/2019 21:04:12
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3434 forum posts
297 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

Geoff Sleath10/11/2019 21:24:09
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3434 forum posts
297 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

Geoff Sleath10/11/2019 23:09:34
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3434 forum posts
297 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

Geoff Sleath11/11/2019 20:54:36
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3434 forum posts
297 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

Geoff Sleath12/11/2019 10:17:15
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3434 forum posts
297 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
273 forum posts
355 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?

Geoff Sleath12/11/2019 12:11:23
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3434 forum posts
297 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
33 forum posts
12 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
33 forum posts
12 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

Geoff Sleath15/11/2019 16:19:13
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3434 forum posts
297 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
33 forum posts
12 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!

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