Sopwith Pup - Scale 20", rubber-powered.

At last, back to some modelling after a remodelling of the hall ceiling...




I have now covered the Pup and the time is fast approaching to put the bits together, which brings me to my next big question: what are your thoughts on the angles of incidence of the wings and tailplane - there is no guidance given on the plan. I have searched long and hard and the answer seems to be: whatever works - which isn't much help for my first bipe. I'm thinking of just going 0/0/0 and trimming from there...

There's no easy way (that I can see) to make the angles adjustable once I've put the plane together, so it looks like a hard decision has to be made. All thoughts most welcome.

PS. I got out my little sportster, Storm Emma, last week and after some trimming issues managed to get her to spiral up, not down! My lifetime best flight was 26 seconds with the Me109 last year, Storm Emma smashed that record. She sailed up gloriously into the Big Blue, notching up a one minute twenty-four second flight, and that with only 500 turns. She looked absolutely glorious up there in the sky - fast disappearing... Since then, one minute flights have become the norm, but I know she'll crush two or three minutes with the right air and more motor winds. I am delighted, so thank you, everyone for all your past thoughts - they are making a difference! Let's hope the Pup can keep up with her.

Your Pup is looking really good. For incidence I would measure the incidence on your plan relative to the centre line and use that. I would hazard a guess at 3 deg positive for both wings with the tail at zero. I'm not sure 0/0/0 will work you will need some declage to get it fly

Squirrel net is correct Crashrr, you will need some decalage for stable flight. i.e. there must be a positive angle between the wing and the tailplane.

Outside of that, it's horses for courses. You'll get different advice from just about every modeller you ask, so pick the answer that you're happy with!

When I build biplanes, I normally match the incidence on the top wing with that on the bottom. Some modellers locate the top wing with a higher incidence than the bottom, and some visa versa. They all get their models to fly and all will give good reason as to why their method is the best...

On the other hand, most of us mount the tailplane with zero incidence, relying on positive incidence on the wings for the decalage required for stability.

I've attached a copy of the RFC Rigging Notes for the Pup. It has the wings at +1.5 degrees positive incidence and the tailplane at 0 degrees. For an out-and-out scale model, that is how you should rig yours. For a practical scale model, however, you would need more decalage - +3 degrees is the accepted figure. So I would mount the wings as Squirrelnet suggests at +3 degrees and the tailplane at 0 degrees.

I think I am right in suggesting that measuring the wing incidence using a flat plank on a RAF 15 section wing underside would result in the wing having a small degree of incidence (wing chord line) so setting 1.5 degrees to the tail plane would actually give an 'aerodynamic' incidence closer a bit closer to the suggested 3 degrees.
It will rather depend on the wing section the model actually uses.

Gotta say, I love it how an apparently simple 20" span rubber-powered model can throw up such hugely technical problems. It always makes me laugh when people think that aero-modelling is easy!

The wing section is exactly as per the original, or at least, that's what's on the plan, how it actually manifested (in a strict aero-dynamic sense) after the imperfections of model-making is obviously short of that ideal goal, but wouldn't be too far off.

In my earlier post I said that the flying surfaces will need to be unalterably fixed from the start, obviously, I wan't referring to the stab, which I will attach so it can be adjusted if necessary.

Many thanks for your help. I'll post some better photos as and when I've made a little more progress - can't wait to put the engine together!

Well, I dived in and began the rather tricky process of attaching the wings. It's difficult to know where to start, everything seems dependent on everything else! My start was not a good one, I incorrectly glued the wings a cm too aft... ouch! Today, I will begin the slow process of trying to loosen the glue and remove them with as little collateral damage as I can create...




The tail is now finished and sporting its bracing wires.



Unlike the two test wings I made, these new ones have not matched their strength, (the only difference being that I pre-alcohol shrank the tissue on these wings). In consequence, I don't think they'll last long in the field of combat... Three ribs have given up already, so it looks like I should have inserted vertical strengtheners between the split ribs. You build and learn... Anyway, I decided to put it all together and when these wings break, I'll rebuild them using a more robust construction and I won't bother with the concave under-camber which made them so thin and prone to warping.



I was reasonably pleased with my first attempt at making foam wheels, the suspension works almost as per the original.

The good news: I put everything aside and dived head-long into getting the Pup into flying condition while the mythical long grass grows in my field. She was fitted with her engine and working suspension.





I made a jig for the wings and they went on without any bother at all, I don't think I even needed the jig, I was amazed (all that care earlier on paid off!)









Then came the moment I could delay no more, chucking her into the azure infinity... Off the board, the CG came out close enough to warrant a test glide. I found the longest bit of grass, and gently released her. Holy Fokkers! She glided almost flat straight across the lawn into the bloody bird table. I never expected her to do that! I gave her a couple of hundred winds and the first powered flight was AMAZING! She just floated, somewhat erratically, but attractively nonetheless, and gently wafted up and down with the breeze, refusing to come down (well, it seemed like an age, but was probably only 15 seconds!) I dared to think that this was going to be easy... I was wrong.
The more I tried to rein her in and get her to describe a neat climbing circle, the more she misbehaved. However, in those rare moments when she flew, she looked magnificent.




At the end of day three, dozens of tweaks and about 30 kms of walking up and down my field (I have a step counter!) she finally relinquished her wayward peregrination and started behaving. I couldn't wait for tomorrow!
I gave her a new motor, and added a 1/32 shim to the rudder and WOW! She flew, beautifully. That was the first time I've ever got an exact scale plane to fly like the real thing. It was bloomin' marvellous. She repeated the flight and fortunately I videoed it.

The bad news: a while ago, I bought some rubber O-rings from SamsModels and when I re-motored her, I decided to use one. As advertised, it was indeed much easier to hook onto the winder. Unfortunately, on the third wind (of only 500 winds) it broke and, despite using a blast tube, the motor ripped out the side of the Pup... I was gutted, I had just got to the point where I could expect the best flight of my life...





Well, I set out to commemorate the great achievement of Sqn Cmdr Edwin Dunning and to honour his sacrifice to our nation, and in that I succeeded. I made the plane, and it flew. It's now back in the Aircraft Factory being repaired. With luck, the trim won't have been affected, too much. It's a funny hobby this, one minute elation, the next...

I will make a proper video of this project, but for now, here is that flight.

Oh yes, I forgot to mention. Regarding the setting of the wings, I got my self into a right tizz wondering how to set the angles correctly without ruining all the work I had put into my struts. Then I had the eureka moment: I put the wings in two foam jigs with their bases flat to the board, then simply raised the tail of the plane on a block. This gave me a very controllable method to set in a couple of degrees of positive incidence. The only adjustment I had to make was to sand a couple of millimetres from the two rear cabane struts. I kept the tailplane flat. (The top wing was designed with a tad more positive incidence relative to the lower wing.)

I should add that I have been amazed at how crash-resistent the wings have been. I thought they would be the first structure to fail, but no, they've taken a beating over the last three days of trimming - though, admittedly, into longish grass. One thing I will never do again is to put internal wire (cotton) cross-bracing - as per the real plane - into a model. It regularly got caught up in the rubber, creating a headache to release without damaging the plane. And I will never use a rubber O-ring again, too!

Bad luck!
I trust it is repairable.
Looking at the video it does look like it could do with a touch more down thrust.

Really cute - so maddening about the damage through no fault of man nor machine
MIke

So, next time you'll use a stronger blast tube, I'm sure!

As far as the 'O'rings go, I'd use a bespoke hook that i believe is also available through SAMS. You could also bend 'em up yourself. I'll post a picture when I get home as I'm on the road at the mo.

Good decision on the cotton bracing. I never saw the need myself as a slight give in the structure helps crash survival and in any event, more than required stiffness is imparted by the doped tissue.

The flight path in the video is a bit pitchy. Downthrust may not be the answer as the aircraft may be a bit pitchy on the glide without the power to hold the nose down. i would suggest a more forward c of g.

The blast tube was a disappointment, it's a piece of plumbing pipe so more than adequate. I can only surmise that the force of the rubber contracting pulled the tube sideways through the fuselage. I can't see how else it did so much damage. Though, some of it may have been collateral: when the band contracted to the rear peg, it certainly wrapped up some of the internal bracing, so that may explain the damage lower down. I can only hope it doesn't happen again.

I've always said I could have been a surgeon, so now's the time to prove it. The Pup has been booked in for repair.

As for flying, yes, the flight is a little up and downy, however, if you knew how long it took me to get to the point where it flew in a not too big, not too small circle, you'd take it! I must have altered that thrust angle ten times, the nose-weight, too, and then there was all the shenanigans with the decalage. When it's repaired I can fine tune the nose-weight and thrust angle (with a shim, I'm not touching the adjuster!). It's a lightish model (43g) and it was a tad breezy, so I'd like to see a few more flights, and see how she handles more power before I dive into more changes, this crate needs some height, so I can see how long that pattern holds. It may not be a perfect flight, but it was still as pretty as a picture against the vale. Pitchy or not, I could watch it flying all day! I will post an update when she's repaired.
I don't think I've reported that since my last post, I became a fully-paid up member of the Out of Sight Club... At my first appearance at my local flying club, Storm Emma flew off like a banshee, I chased her for two minutes, but the hedgerows got the better of me. I've been told that I'm guaranteed a respectful reception when I next return! In consequence to the loss, there's a new 18" sportster on the building board, Herb Kothe's GoDevil, and then it will be time to return to the Lockheed Vega...
Many thanks for all the support and suggestions.
Crashrr

Very bad luck, it's a great looking model, so chin up and tally ho, keep up the good work.

Superb build Crashr and great video. As you say it really does look a picture in flight. Glad to hear it's booked in for repairs as it clearly worth the effort, such a lovely little flyer. I would concur with Andy though, that a small forward shift in CG will make it even better, giving it a bit more stability and help stop it ballooning up into wind

Look forward to following progress on the Vega

Storm Emma an O/D? not heard of that model before.