DB Sport & Scale 82" Twin Tub with 2x OS.46 motors.

[Mike.K 60]

Looking for a user friendly twin engined airframe, the DB Twin Tub caught my eye. Although a large 82" model, with twin engine configuration, this vintage David Boddington design hit the spot for me. Essentially, its a Barnstormer with two engines mounted close inboard upon its high parasol wing configuration. Just a couple of images can be found on the DB order listing with the same ones appearing on Google. Other than that, I`ve not found any information on the model anywhere else than the DB sales listing. The images you see below appear to be the only ones around.

I`ve just ordered one of the typical "plan and timber packs" from Richard at DB. The kit is currently on special offer at £108 plus a tenners postage. This might suggest that Richard has a few on the shelf ready for dispatch. Previous order experience through DB suggests the kit may arrive with me in a couple of weeks if it has to be manufactured due to low stock levels. In the meantime I have a Seagull Steen Skybolt on order from Rob at Avicraft. I`m hoping to see that here sometime this week which should keep me occupied until the Twin Tub arrives.

Already to hand here are the wheels, coverings, two new fuel tanks with fuel tubing and filters, two OS.46 two strokes one of which has only been lightly run whilst its brother is new in box. Spinners and two new 13x6 props are to hand, various servo leads, Y-leads, control horns, wheel collets and most other commonly needed bits and pieces. I just need a few servos and some pushrod snakes.  The kit comes with a plan, pre-bent ali cabanes and landing gear, pre-cut major component parts and pre-cut wing ribs. In addition, an appropriate quantity of sheet balsa and strip is included together with pre-cut fuselage formers etc.

Watch this thread for further developments.

Mike

DBSS Twin Tub Instructions.pdf

[Trevor 25]

This looks like a nice stable twin.  Hope to see it fly sometime

[Mike.K 60]

Three weeks after the very basic kit arrived, the fuselage, tail feathers and hatches are complete and covered in the core white colour scheme. White? Why not...I bought a load at one of our club auctions last year. Whilst I`m the equivalent of three wing panels short of material, this is easily sorted by ordering a couple of extra rolls from Hobby King. The chord of the wing is around 300mm wide and the total wingspan some 2 metres plus. That makes for quite a large model that gobbles covering film like it`s going out of fashion!

The wings are about to be built but I`m waiting on Rob`s next supply delivery which hopefully will include a bundle of spruce for the wing spars.

As noted in the basic two pages of the "user manual", I found a comment about dropping off dihedral and re-inforcing the very light weight and rather flimsy tail plane. The model is from the 1960`s and David Boddingtons prototype only flew with throttle, rudder and elevator controls. One assumes the radio gear was very basic for the period and that the model probably wouldn`t have been flown as hard as we fly our models today. My model will include reduced dihedral, ailerons, larger elevators and rudder and the tailplane has been beefed up to stop the very evident torsional whip that was clearly present and rather undesirable.

In addition, I`ve discounted using the two OS .46 two stroke engines I had in mind for this model. Mr Boddingtons model used two small rectangular fuel tanks made from soldered tin or brass plate. Tankage was very small and rather awkward so I`ve had a change of plan as regards power plants. The model cries out for twin contra rotate electric motors with LiPo batteries to be housed in the fuselage. George at 4-Max specified the use of two PO3541 920Kv motors using two 40a ESC units with two 4S 3200 LiPo batteries. Two 10x5 timber props figure in the specification but one of them will be a "pusher" for contra rotation use. Don`t ask why a pusher is £2.50 more than a puller...... The motors, props and ESC units add around £102 plus post to the build bill, plus another 4S 3200 Lipo from Rob at around £43. The other I have in my usable LiPo stock.

So the cost of the build escalates at the usual exponential rate. ie think of a figure then triple the build cost! Yes, this model will cost twice the price of my original estimate. That is mainly down to power plant changing half way through the job.....

The kit plan is good. Its simple and straight forward and shouldn`t cause any reasonably competent builder any problems. The landing gear and cabane struts are made from dural strip which is pricey to buy. The wing rib pack is a useful addition to avoid the tedium of rib cutting. The fuselage formers included again save all the fiddly cutting and fettling needed if you cut them out by hand or using a band or jig saw. There are basic fuselage sides, wing tips and a few other parts included. All strip and sheet material has to be sourced by the builder. Whilst not outstanding value compared to some of the Far Eastern produced kits, one does have to remember that a UK producer has much higher overheads than his competition. You get what it says in the sales listing but nothing more. That does`nt decry the value of the kit because the dural work, the quality of the formers and ribs are great and what timber is in the kit is of excellent and appropriately graded material. I`d certainly be happy to buy another DB kit because they do build without issues.

Some images now with more once i`ve made a start on the wings.

Mike

Some images now.

Edited June 9, 2020 by Mike.K
Typo corrections.

[Gerard 10]

Lovely looking Model Mike.  Look forward to seeing it in full dress with everything fitted.

[Mike.K 60]

Thanks, Gerard. Good to hear from you again.

Yes, this TT certainly has raised some nice reactions within CAMFC and also with the Falcons. I`m a member of both clubs. I think this must be because the model immediately strikes one as a nice quirky odd ball but user friendly twin. Certainly it has loads of character. Its quite an unusual model but does not seem to have been that popular even in its heyday. I can`t quite think why this might of been other than that people might perhaps have wanted something rather more sporty. Only a few images appear of it on the internet and the kit is presently just £108. Perhaps the maker wants to shift a stock holding out of the door. Who knows.

Progress has again been rapid on the wing construction. The basis of it is simple enough. Rob sourced me some appropriately sized spruce for wing spars although I had to make scarf joints to eight of them because Rob could only get material which was about six inches too short. That was quite time consuming. Building and sheeting the wing only took three days, then the wok slowed again making servo mounts and locating wing mounting hard points in precisely the right positions. This was tricky to say the least with the front mounts being particularly difficult. To my astonishment, all four wing bolts passed through the cabane holes and aligned perfectly in the wing. I didn`t have to make any adjustments and I went to bed well happy. The fun started again next day making motor nacelles. Mother had a freaking fit due to my using my Fathers old Dremel fret saw which screams its heart out when running. Fortunately I have a new one due to arrive. The fret saw is a "must have" for bulkhead and other intricate ply cutting work. Fortunately I`m out of that hole now with all parts cut and the fret saw no longer needed on this build. Never buy a Dremel Moto-saw if you wish to keep friends. It's a noisy contraption and I`ll be pleased to press a rather more sophisticated and hopefully quieter Draper unit into action!

One and a half nacelles have been built today. There is a lot of wood butchery and glueing needed on this part of the model. Its been a bit like building two fuselage fronts with small parts and prerequisite accuracy needed at all stages. The work takes time and patience and would frustrate many people. You just have to keep going at it and keep the vision of the eventual prize in mind. Another day on the second nacelle should see things finished after which covering can start....that`s the easy part!

The model is quite a size. The wing is approximately a foot on the chord and seven feet in span. It gobbles materials, glue and coverings at a ferocious rate! Finished weight is looking to be about 9Lbs although I envisage having to add three or four ounces of lead ballast to the nose. No problem, the model has a quite massive wing area for its predicted final all up weight.

More on this build, shortly.

Mike

[Emma 47]

Looking good Mike x

[Mike.K 60]

The TT is almost finished. It's fully covered with just a pseudo basic white and RAF detailed colour scheme.  It resembles to a certain extent the colour scheme often seen on Coastal Command Sunderland flying boats. I think it suits the model reasonably well. My grand-daughter likes the model and I`ve told her it is likely to make an unusual trainer. Hopefully I can see if she might like to learn to fly in due course. She is only six and her attention span is still a little limited. Time will tell.

Presently an issue exists with the ESC units. Sourced from George at 4-Max there appears to be some kind of programming problem which causes both ESC units to bleep madly when the LiPo packs are disconnected. When I first came back to the hobby, George supplied a program card for my electric Ultra Stick for setting up its motor. Two years on, the design for the ESC units appears to have changed and another type of card is required for my TT set up. That is a bit of a groan as I`ve now got to add more cash to this build. I have to admit that this model has not been a cheap one even though I`ve drawn on used ESC, LiPo and motor combo from my existing electric power stock. If you were to build one of these models you will almost certainly need a full 10m roll of covering and brace yourself for double motor costs and at least 20 sheets of 2mm balsa at about £2.30 a sheet. Each LiPo cost £43 retail.

Here then are a few more images as this model nears completion. With motors correctly set up, the model will then be good to go.

Mike.

[Mike.K 60]

The TT is finished and ready to fly. Motors and ESC units are now harmonised to give identical starting and stopping. All done without buying another program card. Props are contra-rotate to avoid adverse torque reaction.

Flying weight is 10.8Lb/5Kg with LiPo packs onboard. Total wing area is almost exactly 7 square feet.

Just running the model across the drive revealed a landing gear tracking issue but that was quickly sorted by twisting the nose leg slightly until the model ran straight. Other than that, no further problems.

Together, the two motors certainly pack some punch. With luck the TT will just cruise around at half power or perhaps less. I really hope this model will allow it to be set up as a nice floaty, trainer type model. Test flights next week once the weather changes. Too hot for me presently. I was fried alive after just an hour last week. Being boiled up is not fun so test flights with the TT will have to wait until I`m happy with more moderate temperatures.

There we have it. Another build complete and a nice one at that. The main difficulties of a somewhat minor nature were getting the four wing bolts to align accurately (which they did) with the fixed point cabanes and the issues with the motors which are now sorted. All in all, this model was headache free.

More once I`ve flown the TT. It now resides in the garage with all its other brothers. Another air-frame to the collection.

Mike