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DB 60" Sopwith Pup

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Geoff Sleath04/10/2019 21:07:45
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3423 forum posts
295 photos

I bought one of the new DB Pup kits a few months ago and, as the weather seems to be more building than flying I've made an early start to my winter build project. The road to hell is paved with good intentions so I can't promise a blow by blow, step by step account but I'll endevour to update from time to time.

The quarter scale Pup DB already sell is just too big for me. I know it would end up as a hanger queen and rarely get flown but the recently introduced 60" version is the perfect size for me. Big enough to fly well and be easily seen in the air and small enough to transport easily. The 2 58" ws Moths I have (Tiger and Gypsy/Cirrus) get flown a lot and both are quckly assembled at the field and take little longer than a simple monoplane. I don't expect the Pup to be any different.

I intend to power it electrically and there is provision and parts for a battery box as an option. It will be sport scale (I'm no rivet counter) but I will add a little scale detail. I intend to operate the elevator with 2x closed loops from one servo as I've done with both the Moths rather than a non-scale push rod. There's already a quite neat dashboard/instrument panel in the kit. In fact the kit is very comprehensive. I was asked when I ordered it what hinges I prefered and chose pinned and all the supplied accessories look perfecly usable and what I'd choose myself anyway, unlike some kits I've had in the past.

There's a set of instructions which are more of a guide than a step by step approach because this insn't likely to be a first build by anyone. There are 2 huge drawings. One for the fuselage and another for the wings - all the wings ie no need to build one wing at the back of a drawing made transparent by some means. I'm afraid I've cut up the fuselage drawing to make it more manageable to separate the tailplane drawing and a few assembly sketches illustrating the battery box, the cabane construction etc. I'll probably cut up the wing drawing, too when I get to it.

This is the scheme I'm looking at. It's a bit different from PC10 and, as it's a trainer, I won't need to buy or make a Vickers gun

kiwi.jpg

You must admit it'll be easier to see than an all PC10 one.The instructions suggest starting with the tail so I'm breaking te habit of a lifetime and complying.

Here's the fin on my magnetic building board.

fin.jpg

... and here already hinged to the rudder. I like to glue and pin hinges to the control surface before covering and then attach them to the model. So, to save a long job doing all the hingeing in a single session I decided to hinge as I went. There's an attachment on my French plane (which uses Stanley knife blades) for planing 45 deg angles which makes decent surface hingeing a doddle - something I used to find quite difficult.

fin and rudder.jpg

The tailplane is quite complicated and has an aerofoil section. The CNC cut components make it easier but I'm having to be careful to keep it flat. This is a dry assembly. I'll have to take it apart to glue it with aliphatic white glue.

tailplane  1.jpg

It'll be slow progress, I'm afraid. I have a model to test fly - the Ryan ST is flyable at last!

Nigel R04/10/2019 21:26:29
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3099 forum posts
479 photos

That really is quite a short nose! How far forward can you get the lipo? Can that big cowl can hide it?

Geoff Sleath04/10/2019 21:32:29
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3423 forum posts
295 photos

I'm afraid church roof, lots of it, will be needed just as it would with a glow engine. I'll try to reduce lead and add batteries but I don't expect to get away with none. It's a near scale model so there are sacrifices.

Geoff

Ray Wood 404/10/2019 21:59:09
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88 forum posts
9 photos

Hi Geoff,

Will be watching with interest, your right I had the 80" one just to big, sold it !

regards Ray

Geoff Sleath07/10/2019 12:59:47
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3423 forum posts
295 photos

 

 

A bit of progress over the weekend despite its being my wife's birthday (she's very tolerant). I completed the tailplane. It's huge! It could almost be used as a small funfly wing with elevators as ailerons.

tailplane.jpg

It took rather longer than I expected but it worked out OK. I added extra balsa where the hinges are located from scap wood from the plan and also extra corner supports to the outer elevator halves also for scrap balsa. As I'm intending to control the elevator with 2 separate closed loops I haven't used the elevator joiner wire which has saved a bit of weight where it matters. The hinges will be glued and pinned to the elevators before covering.

There was minor fettling needed to fit the fin to the tailplane.

fin tailplane fit 1.jpg

So I adjusted it.

fin tailplane fit 2.jpg

 

Now the whole tail assembly is complete except for horns. I'll make ones for thr the elevators from 1.5mm glass fibre board and probably for the rudder, too, even though there'll be a ply one somewhere in the box.

tail complete.jpg

The magnetic building board is useful for awkward assembly jobs like the battery box.

battery box assembly.jpg

Here it is complete and offered up to the firewall. It's quite big. Not sure if it will take 2x 4AH 4S LiPos. The more battery weight the better to keep lead ballast to a minimum. (some will certainly be needed with that short nose)

battery box complete.jpg

 

battery box firewall 2.jpg

 

I also (with some difficulty) separated the 4mm plywood motor box components and did a rough assemby to the front of the firewall. The batter box will butt up hard against it, so the batteries will be quite well forward.

motor box 1.jpg

 

I have yet to decide on a motor/battery combination so I'm not sure if the supplied motor box will be suitable but it looks OK so far. I'm hovering between a low kv motor and 6s and a higher kv and 2x 4S in parallel (assuming the 4AH ones I have will fit. I think I'll need around 800 to 1000 watts becaue I think the model will be in the region of 4kg (8+ lbs).

Geoff

 

Edited By Geoff Sleath on 07/10/2019 13:02:05

kc07/10/2019 13:14:38
6052 forum posts
169 photos

Does a scale WW1 plane need 100 watts per pound?

Geoff Sleath07/10/2019 13:25:31
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3423 forum posts
295 photos

Perhaps not but it certainly needs the weight up front. I can always prop it to suit the power I need. The prototype had a Saito 65 four stroke glow. I'm going to see what prop/rpm they like.

Geoff

Martyn K07/10/2019 16:20:43
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4978 forum posts
3624 photos

Hi Geoff

This is on my wish list so watching with interest. Have you compared the outline with a 3v to test its accuracy? I think it would make a great candidate for the new BMFA Light Scale class

Martyn

Geoff Gardiner07/10/2019 17:06:56
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410 forum posts
709 photos

Hi Geoff.

I converted a Flair Puppeteer to electric and managed to get the correct CofG without using any lead - just a 5S 5000mah battery. So you may be OK.

Geoff...

Geoff Sleath07/10/2019 17:17:34
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3423 forum posts
295 photos

I haven't checked it against a 3 view but according to the Windsocl Datafile Special I have the DB quarter scale Pup is very close. According to the the instructions this 60" version is very near scale. The deviations are that both wing and tail areas are sightly bigger and the fuselage is very slightly longer. The wing section is nowhere near scale and is more like a Clarke Y in that it's flat bottomed unlike the full size which has a concave underside and is very thin.

I like scale models and I'll add some scale detail to this (like the elevator closed loop) but I'm not a 'real' scale modeller. I'm almost a Peter Miller style scale modeller - ie 'if it looks OK at 50', I'm happy'. Actually I'm hoping more for 10' but we'll see.

Geoff Gardiner:  But the Puppeteer has a much longer nose precisely (I assume) to overcome the CoG problem with the full size's much shorter one.  Pity the engines in 1914/18 period were so heavy.

Geoff

Edited By Geoff Sleath on 07/10/2019 17:21:14

Robert Parker07/10/2019 18:25:20
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912 forum posts
1172 photos

Watching with great interest, my building board is empty right now too.

Regards

Robert

Geoff Sleath09/10/2019 00:49:25
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3423 forum posts
295 photos

I've mostly built the upper stbd wing panel. Strangely, of the 2 spars the main is 2 x 1/4" balsa joined with balsa web but the secondary one, which also carries the aileron is 2 off 6mm x 3mm spruce with a balsa infil between the ribs and to my untutored eye, much stronger.

wing 1.jpg

I tied to be clever with these infills by measuring the bay width and cutting them accurately with the aid of my bandsaw and the handy little Aldi disc sander I bought last year. Luckily I only made 3 before checking as there are 3 different sizes - a triple, a double and two that are different from either. However it was still useful to make them all before I started glueing because they kept the ribs vertical towards the back.

The main body of the wing panel went together OK without too much drama but the tip was a puzzler as there's only a plan view with no end elevation to show how it's supposed to look. The photos on the web site helped but I winged it a bit.

First I put the infill between the lower spar and the leading edhe using scrap balsa.

wing 2.jpg

Then, after joining the 2 wing tip parts, I fitted them.

wing 3.jpg

The 6x6 mm (I'm going to use metric units despite the fact that I think the balsa dimensions are Imperial!) is my addition to support the end of the wing tip as is the extra 6x6mm parts between th spars at the l/e.

I'm not sure how it's supposed to shaped but, by referring to the 3 view I have, the taper starts at the last full rib down to the tip itself. I suppose if I do all 4 tips the same it'll look OK.

I suspect I'm the first to tackle this kit (it is quite new) and especially with electric power, so it's an added challenge. Still pretty happy with it, though. The wood is good quality but it's marred a little by the burn residue from the CNC cutting, the dust of which makes parts look a bit grubby. That, of course, doesn't really affect the build nor the finished model and is just a minor drawback of CNC cutting.

Geoff

Chris Freeman 309/10/2019 07:48:25
272 forum posts
355 photos

Watching this with interest, looks like a great kit, very different from the original DB kits that were all hand cut. I built an original 1/4 Pup in the late 80's. I bought the kit from Henry J Nichols shop in 1989 on my first ever overseas trip.

Cuban809/10/2019 10:01:51
2758 forum posts
13 photos

Will be following this build closely, I can feel a WW1 fighter coming on once my existing projects are complete and the DB kit has a good reputation for quality. I can see the attraction of electric and have several sports and aerobatic models of 350W up to 1500W, but I'd go down the petrol route for a scale model of this type myself. Plenty of room for effective silencing, a large prop that wouldn't be required to be turning at silly RPMs, given the model's and full size's flight performance and much reduced cleaning compared to glow. Personal choice, as always.

Danny Fenton09/10/2019 10:35:47
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9200 forum posts
4044 photos

Really enjoying following along Geoff, will be a cracker, and very tempted myself with one of these

Probably tempted to make it into a Dove

Cheers

Danny

Edited By Danny Fenton on 09/10/2019 10:36:13

Geoff Sleath09/10/2019 12:29:30
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3423 forum posts
295 photos

Chris: A clubmate is very near the completion of a 1/4 scale DB Pup. I'm loking forward to see it fly. He's been building for quite some time and said that if this one had been available he would have chosen it over the bigger one. His is also electrically powered which is an added attraction for me.

Cuban: WW1 fighters are great - specially biplanes (tri-planes are a step too far IMO ) If DB had a similarly sized SE5a I'd have gone for that but the Pup is certainly growing on me.

The proto-type of this model was tested with a Saito 65 but I suppose a small petrol would fit OK. I just like electric - perhaps because of my background. I'm aiming to be able to turn a 13x6.5 (or a 14x7, perhaps) at 7,000 rpm and I'm specifying the drive train accordingly but I'm still thinking.

Danny: A Dove had crossed my mind, too but making an extra cockpit fazed me a little so I decided to build a trainer version and the Kiwi is quite colourful and a change from all dull old PC10

I just hope you'll delay building one and putting my meagre efforts to shame. As I said earlier, this is definitely a stand off a long way scale.

Geoff

Danny Fenton09/10/2019 12:37:34
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9200 forum posts
4044 photos

Geoff I always love seeing your models. You always strike a great balance between the level of detail and practicality. I envy you

Your yellow moth is still one of my favourite models, and makes me smile whenever i see it flying. Ticks all my boxes.

I am bogged down with three C/L models, so a Dove would have to join the back of the queue

Cheers

Danny

Danny Fenton09/10/2019 12:38:48
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9200 forum posts
4044 photos

Grrr double post lol

Edited By Danny Fenton on 09/10/2019 12:39:29

Geoff Sleath09/10/2019 14:52:06
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3423 forum posts
295 photos

Thanks, Danny. That's quite a compliment from you. The Gypsy Moth is my current favourite model. I've flown it a lot. I 'stole' one of the photos of it you took at Buckminster to use as my PC wallpaper. It replaced one of my Tiger Moth.

Geoff

Geoff Sleath10/10/2019 16:49:05
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3423 forum posts
295 photos

I've completed the first wing panel of 4 so there won't be many updates untill I've done the rest as (I hope) they'll be straight forward now I know what I'm doing - really?.

 

wing 4.jpg

 

This is how the tip ended up. Not sure whether or not some more fettling (a posh word for bodging) will be needed or some extra covering support will be needed (probably Solartex, I have a a few rolls still).

wing 5.jpg

 

When making te ailerons it's necessary to ensure the right supplied plywood horn is fitted.

wing 6.jpg

This the upper wing so is slave driven from the bottom and needs its horn to point downwards. There's a ply backing plate so the aileron rib is sandwiched between the 2. Secure and neat.

I did have a minor issue with the aileron build. These are the main components for each of the 4 ailerons.

wing 7.jpg

As you can see thereisn't a socket for the 4th rib on the leading edge part 240.  DB are aware and I'm sure the error will be corrected in the next kit batch.  A sit is, it took me about 2 minutes to cut one with a scalpel and needle file.  I was a bit confused at first because I hadn't found the tip part and didn't appreciate it fitted in the 1/4" square hole at the end.  All's well that ended well with a perfect solution. I may be paying a small price for being an early builder of this particuar kit.

As a slight deviation I though I'd have a look at the drive train.  I have a suitable motor that I'd used in my Ezee Pezee Paper Aviation trainer I sacrificed as a test model for the Laser 62 I overhauled over Christmas 2018. It's a XYH 5055/05 700 rpm/volt motor which should provide more than enough power on a 4S pack. Here it is on the fuselage drawing.

motor 1.jpg

As you can see it doesn't fit well with the optional motor box provided as it pushes the prop too far forward out of the cowl.  Good for CoG but not for appearance as a scale(ish)  build.  If I move it back, as it is here, the battery box won't fit. 

My proposed solution is to cut the battery box sides to allow the motor to be in a better position.  As I'm intending to put some side thrust in (about 2 degrees) I'll be able to offset the motor mount and angle the box by having one side bigger than the other (or, as an alternative, one side smaller than the other ) to bring the prop back to the middle of the cowl and the dummy engine I intend fitting.

That leaves battery mounting.  I've put a couple of 4S 4AH batteries on the drawing just behind the firewall so I hope to be able to that in reality. They could be either across or in line (as shown here).  They'll still be entirely forward on the CoG and, having 2 in there should increase the range.  There's already provision for a hatch at the top, I think, so that will hopefully allow access for battery changing

Geoff

 

Edited By Geoff Sleath on 10/10/2019 17:14:43

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