DB 60" Sopwith Pup revisited

[Geoff S]

As some old forum members may vaguely recall, back in 2019 I was upset by someone here and decided to stop posting. This included my Sopwith Pup build. It's still there but the photos are not. Of course, I still have them all but it's impossible to add links into a very old thread.

 

Anyway, it got finished:

 

 

 

 

However, I got a message from another builder that his wings had folded in flight which worried me to such an extent that, instead of elastic rigging wire I fitted real wire, which is a bit of a fiddle to fit.  I don't really think it's a problem and I know I was careful when I joined the wings but, as they were not only covered but I'd spent a lot of time decorating them to match the prototype I'd chosen to model and it would have been a lot of work to access the join.

 

We had a new field in 2020 which is grass rather than the hard runway we have at Ashbourne (we have 2 sites for now) but the grass then was still a bit rough.  As I was taxiing to the take-off point for my maiden, it nosed over. It not only broke the prop but the motor mount as well and even though I shut the throttle quickly it damaged the dummy engine and dented the cowl.  I was so disappointed, I put it away without even examining the damage.  That's 2 years ago. 

 

Last week I needed a receiver for my Fokkler DVIII and decided to use the one still in the Pup.  I looked at the damage and decided enough time had passed to try a fix.  To my surprise it's not that bad.  The ply motor box is broken. It's only 3mm, so I've decided to beef it up and make a 6mm box, glued with epoxy with the additional support of some triangular balsa.  I'll remove some of the lead in the cowl (there's a lot!).  I've managed to squeeze out the worst of the dents and the dummy engine looks repairable, so I think it'll be ready for its maiden in a day or 3 though I'll leave it to the better weather next year.

 

Here's the cowl as it is now.  At least the paint has stayed on.

 

 

 

Here's the dummy engine. Repairable, I hope.

 

 

 

There's a fair bit of lead I can lose to compensate for the heavier motor box/mount

 

 

 

And here's the start of the repair.

 

 

 

I feel quite cheerful about it now 🙂

[EarlyBird]

10 hours ago, Geoff S said:

For some reason I can't delete the extra picture😬

Too late now, but to delete extra pictures.

 

 

 

Click on the black circle/white cross in the top right of the picture you wish to delete, in the uploaded images area of the editor.

 

BTW any pictures not used in the text are always added to the end.

 

 

 

 

 

 

Edited December 6, 2023 by EarlyBird
Extra pictures deleted

[Geoff S]

Thanks, EB.  I tried about 3 times by simply deleting the picture when I did the edit but it didn't work and it was too late to faff about trying to understand why.

[Geoff S]

I put it all back together this evening and found the prop driver is slightly bent (the motor is a 4Max 5055 559 rpm/v) so I've ordered a new one.  I've given up trying to effect a satisfactory repair to the dummy engine and ordered a Linsay (sp? But that's how he's described on the website)Todd 9 cylinder CNC cut 'radial engine' from Sarik Hobbies - it'll have to pretend it's a rotary.  I just hope I can retrofit it into the cowl.

 

I weighed it at just over 5kg including a 6S LiPo but I'd experimentally removed some lead but it will need to go back to get the CoG right.  The cowl, with all the lead ballast weighs 3lb (approx 1.5kg!) so 25% of the total weight.  It looks like I'll need a kw for 80 watts/lb.  The wing loading is 1.2lbs/squ ft.  I think it'll fly OK, but it won't be doing any 3D manoeuvres 🙂

 

Onwards and (hopefully) upwards.

[Glenn Philbrick]

Hi Geoff

It was my  DB pup that the wings folded up. I hope you have more luck when you come to get yours airborne.

I've since built a puppeteer from the plan and a set of ribs cut bought from a guy in scotland which I still fly.

[Geoff S]

1 hour ago, Glenn Philbrick said:

Hi Geoff

It was my  DB pup that the wings folded up. I hope you have more luck when you come to get yours airborne.

I've since built a puppeteer from the plan and a set of ribs cut bought from a guy in scotland which I still fly.

 

I think that would be Neil Gillies at igull.  I had some s/w from him to allow some mods on my Multiplex 3030 transmitter and he published a design I did for an optical rpm probe for the same transmitter.  He does a lot of CNC cut rib sets. 

 

I think adding the wire rigging, which, once the lengths are set, aren't too time-consuming to fit, should prevent any possible 'wing folding' incident 🤞   How heavy was yours?  Mine's quite light until the necessary ballast is added 🙂   One of the advantages of the Puppeteer is the longer nose (which is the main for its not being a scale Pup) thus being able to balance with little, or no, extra nose-weight.  I must get mine out again but it has an ASP 65 glow engine fitted and I'm not really equipped for glow engines these days.  The last time I flew it, it went dead-stick high up as I was trimming out.  I did a greaser landing right in the middle of the runway only to find it had no prop!  I think it must have kicked back and unscrewed.  I was upset as it was a brand-new prop - I even, foolishly, went to look for it.

[George P.]

Hi Geoff,

Well done! You have made a great job of repairing the Pup. 

Fingers crossed for some good weather next year so you can enjoy flying it.

[Geoff S]

31 minutes ago, George P. said:

Hi Geoff,

Well done! You have made a great job of repairing the Pup. 

Fingers crossed for some good weather next year so you can enjoy flying it.

 

It could even fly at the same time as your 1/4 scale version 🙂

[Geoff S]

Got the Pup finally ready to test fly today with a final motor check.  I didn't use my Wattmeter but relied on the telemetry from the installed 60 amp Frsky Neuron esc.  Not too bad and there's hope it will actually fly, though perhaps not quite as slowly as I'd prefer.

 

With a 13x6.5 ASP electric prop fitted the 4Max 5055 495 rpm/v motor turned at 10,500 rpm and drew 54 amps from the 6S LiPO (approx 1.2kw).  Should be more than enough to haul the 5.5kg model into the air but I'd prefer a lower wing loading.  The 1.5 kg of lead needed to get the CoG somewhere near the recommended place.

 

I beefed up the motor mount in view of the destruction caused by a simple nose over whilst taxiing.  I upped the cowl plywood insert from 3 to 6mm and replaced the dummy engine with one of Lindsay's CNC cut versions (which has a huge number of parts and no instructions apart from the illustration on Sarik's webpage 🙂 ) It represents a 9 cylinder radial rather than the rotary the Pup should have but looks reasonably OK if you don't look too closely.  I screw all the lead ballast to the 6mm ply disc that also supports the dummy engine.  The disc is held in place with 4 angle brackets mounted on the cowl itself - it's quite a tight fit anyway, so should hold OK 🤞

 

It's all now to be put away until Spring - out of sight and out of mind.

 

I took a few quick snaps outside after I'd done the motor tests (too much draft to do it in the workshop - there'd be bits of paper everywhere)  The garden's a bit scruffy just now.