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Balsa USA Sopwith Pup 1/6 scale

100 years of the Royal Air Force this year and I want a reminder of its roots

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Simon Knight08/03/2018 08:08:23
127 forum posts
201 photos

Throttle servo done thanks, just wanted to be sure there was no hidden science I was unaware.

Anther silly question maybe, but now how can i secure a fuel tank tha has no real way of wedging it in foam or in a box? I could try and build a frame for it to slide into but can it be securely velcroed to the side of the fuse on the left of the below picture? Any suggestions of how people have fitted tns into these short nosed ac would be appreciated, and it’s if possible thanks.


DaveyP08/03/2018 09:17:31
189 forum posts
47 photos

I have an old DB models 1/6 Sopwith Pup kit that I haven't started yet, in that, the fuel tank (metal) is designed to fit in the cowl next to the engine....

Jon - Laser Engines08/03/2018 10:26:19
3920 forum posts
151 photos

If you build a simple tray for the tank to sit on you can then cable tie it to said tray with some foam under the cable ties. Dont forget the fuel proof all of the inside before building yourself into a corner

Simon Knight16/03/2018 20:54:12
127 forum posts
201 photos

Ok so have done a bit of colour this week to reduce the amount of dust in the “workshop”. Used white solartex for the undersides and painted them Linen, and used Olive drab Solartex on top. Added some decals because they were there and wanted to make it look a little more colourful too.

Bulkhead and top deck waterproof stained mahogany and further sprayed with polyurethane varnish for protection. Starting to look better now. Not all of that top deck will be Mahogany, but got carried away.

I now have all of the remaining parts I need to build her and just need to get on with it. Next challenge is to work out where to affix the remote glow start as I can’t access th one on the engine.


Simon Knight18/04/2018 08:36:18
127 forum posts
201 photos

Well that has been a break in comms for a bit sorry. I haven’t been neglectful of the Pup but each time I hit a challenge I procrastinate and what turns out to be a quick job cold have been done earlier. Anyway, after having a colour break I did crack on and sort the pushrods for the elev and Rudd. Needed to work out where they had to exit and how which was difficult without the actual surfaces fitted so it was a case of balance them in place and cross my fingers. Didn’t want to fix them until the rest of the fuse was covered. Once they were in, the fuel tank was secured an things look like they are getting there now. (Going to my pc as can’t add photos easily with this iPad and the inability to see all the pics in one go and the random sorting it does from the album)


After sorting the fuel tank it was time for more covering and a bit of spraying to make up for the lack of availability of Solartex Antique or Linen. The end result isn't perfect but happy that it looks tied and worn which will do for me. Very happy with how easily the Solartex applies and shrinks, makes up for some inaccurate application faffs.


Undersides done and need to sort the wing wiring and servos before covering the upper surfaces. First I decided to complete the fuselage and add the decals because i had them and wanted to see how they went on. Pyramid models, did them for me  1/6 scale which were only available at  1/4 scale before so thank you.



You will note i have sprayed the cowl and wheels red also; may as well whilst having the compressor set up. Again, the Solartex went on beautifully and I am really happy with its finish and look. Rather than use the aluminium sheets supplied with the model, I decided to use Aluclad as recommended earlier in the thread and I wanted more coverage than just the cheeks. It went on pretty easily and I think does just the job. Plenty of spare for another kit should I have space become available. Starting to look like a Pup now.

Edited By Simon Knight on 18/04/2018 08:51:18

Simon Knight18/04/2018 09:06:33
127 forum posts
201 photos

Next was the wing electrics which again went in well and no hassles. Longest part was threading the y harness through the centre of the wing. Should probably have fitted it in when building that part but didn't think that far ahead. Anyway it covered nicely.


Next competed the top wing and decided to go for the centre cutout for a bit of interest. May look to get the gun that was used in it once I have flown her and all is good.


Applying the decal on the upper surface went really well though maybe a bit too far to the wingtip. Undersides for some reason the decals don't take totally and it may be because of the painting. not sure. Will see how they fair on first flight and may have to apply extra glue if they lift.

Next was to hide the wire work and add bulk out the cabane struts and gear legs. Did this with the pieces provided and a bit of spare balsa I had. Covered the gear in Solartex and the cabane in tissue and stained them. Seems to make a big difference on appearance so happier than just bare wires.


Same balsa and tissue stained method for the tail skid. Works on my DVIII so fingers crossed here too.


Used the rubber band method to secure the spreader bar without affecting the natural spring in the gear struts. Not scale but it works


Simon Knight18/04/2018 09:14:35
127 forum posts
201 photos

So this week, with all this progress I felt energised to try and finish her. Bolted all the bits together and all seems fine. The CofG needs an extra 280 ish grams of weight up front (BUSA said they needed 230 so not too bad). Haven't added the rigging wires yet, but will. Need to work out the best (and safest place) to add the remote glow plug as it seems a little close to the prop for my liking.


Would she fly as a monoplane? Looks ok


And finally a Pup! though the upper wing looks a little too high and why do the scale pilots always look so small?



Shes isn't 100% yet, but we are nearly there. I now have to tidy the back bedroom before adding that last detail and deciding on where the remote plug goes. Cowl or gear strut, both pretty close to a spinning prop so will need steady hands when removing it. More to follow when complete and hopefully after a successful maiden in the near future.

There are quite a few more pics from the whole process in the album so please feel free to look at those if you wish

Edited By Simon Knight on 18/04/2018 09:15:34

Jon - Laser Engines18/04/2018 21:04:40
3920 forum posts
151 photos

I hate you. now I have to build mine :'(

Looks awesome

Simon Knight18/04/2018 21:29:56
127 forum posts
201 photos

Thanks Jon, I look forward to seeing how you do yours wink

Some outdoor pics from this afternoon.




Simon Knight20/04/2018 08:54:17
127 forum posts
201 photos

Ok, remote glow fitted (not this photo) with enough room for hands and prop clearance and now trimmed; 310 grams of lead up front. A little more than the BUSA model but not too bad and it fitted neatly in the fuselage up front.


Now need to run up the motor and tune it before heading to the field for her maiden! I will do a video.

Simon Knight24/04/2018 18:34:44
127 forum posts
201 photos

SO the weather is stopping me going to the field and finishing off the tune and test flight so I have been fiddling. Not a fan of the big open front end and fancied a radial engine. Can't afford a real one and don't have the patience to build a dummy so here is my offering:


used a photo from a google search, printed it onto OHP slide so that the ink is under a protective layer and then fixed it to plasticard.


As with my Hangar 9 P47 I have cut a suitably sized hole for cooling and think that should do the trick. Don't have any issues with the P47 so fingers crossed it works on this model too.


If the weather doesn't improve, I may end up fitting the rigging lines too before she gets he first flight. Still no weapon to mount though, at this time.

Jon - Laser Engines24/04/2018 19:46:53
3920 forum posts
151 photos

She looks fantastic, and cooling will be just fine. I keep meaning to do the same as you for the dummy radial on my nieuport. I just keep forgetting to sort it out.

Simon Knight25/04/2018 17:03:57
127 forum posts
201 photos

Rigging lines fitted, Vickers gun ordered...


Simon Knight27/04/2018 17:19:01
127 forum posts
201 photos

Bad weather means no flying means more fiddling. Got the Vickers gun from Inwood Models today and have now installed it so she’s finished! Gun was nice and easy to assemble and required a little tidying and a mod as the fore sight wasn’t the best. very happy with it though nd is a nice finishing touch.


More pictures of the gun in the album if interested. Thanks

Simon Knight07/05/2018 08:15:05
127 forum posts
201 photos

So, the big day arrived yesterday, no excuse, get her up in the air or die trying. Ell it wasn’t long before she sounded ready. With the big prop she only turned at 8500rpm max and ticked over at 2500 so seemed ok but not much oomph.

Maiden flight was short (video to follow), just under 2 minutes after I thought the engine had cut but it didn’t then suddenly it did. Managed to get her down onto the hard standing with out damage so first landing successful but not where are wanted. I note that I obviously haven’t got enough of the tail skid into the fuse algae as it had twisted slightly on impact and my wood attached had also moved, but all fixable easily.

Time to try again. Thi sis when I realised i haven’t got the refill line ling enough and with the vowel on I can’t access it easily enough! Cowel off and refuel. For the next 10 minutes I can not get her started and decide to try a smaller 13x6 prop. Finallly starts with a very similar rev range.

Ok lets fly with cowel off and see how it goes this time. I get a further 3 flights of bout 4 minutes each a th tank isn’t huge. I do note however that whilst the revs are good and she flies very nicely and to scale I suppose, there is no power if yo want it.

On the 4th flight I try some loops which she can do with a bit of a dive first to build up speed. Interestingly, as she inverts, I hear the revs increase and then level they slow again. She is having to fly on max throttleprety much all the time so why is this? Could it be the tank needs to be higher? This will be a challenge of not impossible considering the small space to work in. Do I have to revert to a 12x6 prop which is the engines recommended largest size?

Aside form the engine issue, she flies really nicely has to be handled gently and will loop so that should be enough. The landings are very easy and she stops pretty sharpish. this was a pretty calm day and I think with a bit of a head wind we may have more challenges unless I can sort the revs. I have really enjoyed building this model, she went together nicely, the kit and manual were very good and I would recommend it to anyone, if you can find it!

Couple of final pics in the thread and video will follow this week if not later today. Thanks for any suggestions re the engine and revs and happy flying.




Edited By Simon Knight on 07/05/2018 08:16:20

brokenenglish07/05/2018 09:31:37
322 forum posts
23 photos

Simon, I really enjoyed this. Thanks! And it was/will be helpful.

Just a couple of engine suggestions.

Get the engine operation fully sorted on the bench, before installing it in a plane. You can simulate a flight sequence, as below, and make sure everything's OK (a bit late now!).

Then, when the engine is installed in the plane, run it through a simulated flight sequence, with starting, takeoff, medium cruising idle and slowest idle for landing, before even going to the field.

I'm lucky as I have a fairly big garden, and I taxy a new plane around the lawn for the above sequence, just blocking the plane by standing in front of the tailplane, for the medium/high power bits. But even without the garden, get the engine handling 100% before attempting flight, even if you have to do it at the field.

Respectfully, when you've built such a super plane (sincerely), you shouldn't be discovering that you have a fuel line routing problem when you're attempting the maiden!!!

Apart from that, Congratulations on the whole project. It's superb! But get the engine sorted 100% before risking such a lovely plane!!!

Edited By brokenenglish on 07/05/2018 09:33:06

Jon - Laser Engines07/05/2018 10:29:46
3920 forum posts
151 photos

I'm afraid I have to disagree with brokenenglish here as setting up the engine on the bench will do just that, set it up for the bench. you will then have to set it up again for the model as your tank installation is different to that of the test bench. It is also difficult to replicate on the ground the dynamic forces the model see in flight so I don't see that taxi tests or simulated flights on the ground have much value. Certainly most of my models would overheat and die if I did that to them on the ground as the cooling setup only works when the model is flying. I do agree with him 100% that the engine should have its main needle, slow needle and plumbing set up before there is air under the wheels. I do normally test run a model in the garden for this purpose before heading up the field.

If the engine revs increase as you roll the engine is going to leaner, likely due to a high tank position (high tanks give gravity assist to the fuel flow which turns to gravity resist when inverted causing a leaning of the mixture) so making the tank higher will make the problem worse. However, the fact that it didn't stop when inverted suggests that it is happy to run leaner and you are likely too rich in the first place so that could be the cause of your low power. If you lean it off further on the ground you may find that you need to keep some G loading on the model when inverted as it might go too lean in the air and stop if you unload it.

That said, 8500 is very healthy for the 15x5 and is in line with what I get from my similar engine on that prop. It should give you loads of thrust but not a great deal of speed. I flew a 72'' yt miss Elaine with this combo and it wafted about at around 1/2 throttle. be careful not to fly too fast. Most of us are used to sport models or WWII scale models and if you think that even an early spitfire flew at 3 times the speed of a sopwith pup it should give you an idea of how slow your model pup should be vs your yak for example. Very often WWI models are flown too fast so the next time you fly I suggest seeing how slowly you can fly it. You may find that it is only slow compared to your other models and your own expectation. Its likely it is in fact flying just right and once used to the low speed you will find it very rewarding.

Either way, great news on the successful flights and I look forward to the video

brokenenglish07/05/2018 11:27:11
322 forum posts
23 photos

Jon, I didn't mean (and didn't write) that bench running sorts the engine out for the plane but, obviously, there's not much point in putting any engine into a plane unless and until you're fully confident that the engine runs well and does everything the way it should.

Perhaps I didn't make it clear that the bench running isn't related to any particular plane. After running in, it's a preliminary setting up of the engine, making sure that you're getting all the performance characteristics you want, before putting into any plane. I did then mention the important bit of getting the engine sorted in the plane.

It must work because, looking back, I don't think I've ever had a "dead stick" or engine performance problems.

Jon - Laser Engines07/05/2018 13:08:38
3920 forum posts
151 photos

Sorry perhaps I misunderstood. i often see people suggest that if its set up in the bench and runs it will be fine in the plane as well. Clearly this is a load of toffee, but if you use the bench to verify that the engine is working correctly in the first place then that's fair enough. in all honesty though i just fit it to the model and set it up there. Its very rare to get a dud engine these days and i usually only bench test engines that have given me grief or are 2nd hand and i don't know the history.

As for running in, just get it in the air. I don't bother with long run in sessions any more. No more than 5 minutes on the ground before letting them loose. Lasers i run flat out from the get go, other brands i set to 90% of maximum performance for 2 or 3 tanks then i consider them done. Works well too, ASP 4 strokes run in this way have better compression after a year than those run in the 'normal' way.

Bob Cotsford07/05/2018 13:20:10
7327 forum posts
419 photos
Posted by Jon - Laser Engines on 07/05/2018 13:08:38: all honesty though i just fit it to the model and set it up there. Its very rare to get a dud engine these days and i usually only bench test engines that have given me grief or are 2nd hand and i don't know the history.


+1 - unless the neighbours have annoyed me, then I might opt for a long garden based set-up session!devil

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