Humbrol Tiger Moth

[Piecost]

This build is a continuation of a project started 40 years ago. My father and I constructed a 480mm (18.9") span Humbrol Tiger Moth.

The kit included nice light balsa for the sheet fuselage and tail, built-up wings and rather thick and heavy vacuum formed fuselage top decking and nose cowling.

We originally built it for rubber power, unpainted with a bright green propeller. I have a fond memory of it flying well for a short straight flight in my front garden. This strong positive memory ensired my motivation for free flight scale decades into the future.

Later; disaster struck when I was admiring (playing) with it on the floor when a large piece of chipboard was knocked over onto the model. On removing it; the plane resembled a swatted fly. The wings were intact, but the top wing was now touching the bottom with no gap. The fuselage was splintered and flat. Luckily; the vacformed parts were robust enough to survive. The undercarrage legs were splayed out wide, completing the swatted look.

This was a point of descision for me; was this  setback going to move me away from aeromodelling and onto something less risky, such as stamp collecting? I showed some strength of character and stayed with the hobby.

My brother, who I accused of knocking over the fateful board, a bureau lid, helped draw up replacement parts.

A new fuselage and tail were mated to the original wings, which were patched where the struts were forced through the tissue. The hardest part of the restoration was in digging out the ends of the broken struts from their recesses.

Unfortunately, this time I badly brush painted the model in unthinned Humbrol enamels. This increased the weight, which did not help the 2nd and last flight of the model.

A brand new Telco CO2 motor was installed with lots of downthrust and maybe some side thrust. A test flight was conducted over the short grass of a football pitch. A sharp left spiral dive into the frozen turf destroyed the inner rib bays of the upper and lower wings. This ended the career of the model. I kept the plan and the parts.

I was recently delighted to find the plan and print out of parts on Outerzone.
https://outerzone.co.uk/plan_details.asp?ID=13059
I was supprised to see the same funky green propeller and blue acetate for the windscreen.

Looking back, I am impressed with the kit. The design was simple, with the complex double curvature parts ready made, in plastic. The top deckings was rather thick and heavy; being.l made from the same plastic as the nose cowl, which the propeller nose bearing fitted to.

The balsa, in my particular kit, was nice and light. Important for the fuselage and empenage. The kit captured the important aspects of the full sized plane without the complexities of a strict scale model.

I decided to remake the kit and get it to fly! I will reproduce the attractive yellow scheme from the box photo and have procured some yellow Asuki tissue.

Annoyingly; I have the complete remains of the original model with the exception of the most complex and time consuming to reproduce part. The nose cowl.

Since I will have to make a form for this I decided to replace the three top decking parts as well.

I have rough cut the vac form moulds. These are the most onerous part of the build so I should concentrate on it. Once complete, it will be plane sailing for the rest.

I will power the model with a restored Telco CO2 motor. The original plan suppliment recomended no right thrust and  5 degrees downthrust.

Can anyone confirm this recondation or suggest more reasonable values to start with?

[TheLurker]

Good luck with the archaeology! 

[billdennis747]

That doesn't sound right unless there is some very unusual trim that I don't understand. If the wings are at about +3 degrees and the tail zero, the motor should be about 1 degree down and 1 degree (max) right. Top marks for perseverance!

[Piecost]

Thanks for the advice Bill. I attach the rather suspect instruction sheet from the kit.  I note that the tank is shown immediately behind the motor, where it will maximally effect the CG as the gas runs out. Whilst we unwisely replicated the downthrust; at least we installed the CO2 tank in the front cockpit, under the CG. We also installed a thick ply plate to screw the filler nozzle; as recommended by Telco. I will not be repeating this.

I have now carved an MDF form of the turtle deck and am about to make the first attempts at plunge forming. I am using disposable plastic plates. They used to be widely avaiable at party shops in a wide range of colours, but are now generally replaced with paper. So, I have to order them on line. Annoyingly, the last ones had a diamond pattern embossed on them. Luckily, this vanishes as the plastic reaches the correct forming temperature. Inhave ordered some yellow plates, which I hope will not stand out from the balsa under the tissue.

[Piecost]

I am also slightly baffled as to why the Humbrol CO2 motor is not shown mounted inverted, as we did with the Telco.

[billdennis747]

Yes there is no need to invert and it doesn't add much to the appearance!

[billdennis747]

It might be worth comparing with the excellent Stan Cole plan:
https://outerzone.co.uk/plan_details.asp?ID=3003

It shows 1 1/2 degrees down and 1 right, which sounds right to me.

[Pete Fardell]

This is a nice project. I wasn't aware of the Humbrol Tiggie. I checked out the other Humbrol plans on Outerzone too, and found the Wasp, which was a very simple stick fuselage rubber job, but with a built up wing. I made one about 50 something years ago after getting the kit as a birthday present. It came with an attractive black and yellow striped sticker saying 'WASP' to stick on the wing. So thanks for bringing back that memory!

[Piecost]

My first attempt at plunge forming the turtle deck. The photo shows my third piece of plastic moulding attempt using a rather roughly finished mould.  The mould is straight tapered in side profile, but curved in planform. I am confident that wetted 1/32" balsa could easily be made to fit. But, I want for the construction to be in keeping with the original.

Luckily, the mould just fits into the flat centre of a 9" disposable plastic party plate.  The plastic is sandwhiched between a 4mm MDF frame and thick card with an aperture with less than 1mm clearance to the male mould. Bulldog clips hold the assembly together whilst it is heated and inch or two from the nozzle of a heat gun set to 300 degrees C. I was annoyed when I bought the plates,  over mail order, that they had a diamond pattern and were not smooth. But, this pattern soon disapeared when the plastic was heated near the required temperature.

Several attempts at heating and plunging were needed. I wondered if oven heating might prove more straightforward.

I had earlier constructed a vacuum form box to fit the 9" plates. This seems unessarary so far, but may be needed when tacking the cowling with its concave contours.

The resulting part has a thickness of only 0.008", whilst one of the original parts was a rather substantial 0.034". It may prove too delicate to withstand being tissue covered. I might perform a trial of the tissue covering to find out, since I have not used Asuka before; in particular over curved sheet surfaces. I can always double or tripple the skin; if nessesary

[Anyun]

Interesting project, I didn't know that Humbrol made stick & tissue models (ok, stick, plastic & tissue..). I like the old silver and maroon paint scheme, even though the paint used didn't help with weight watching 

[Piecost]

I have started balsa bashing

I recall that the crash of the original model 4 decades ago caused the curved inboard trailing edges of the upper and lower wings to split along the grain. Whilst a cartwheel on frozen, short grass is always going to break the structure; I have ever since  disliked using a single piece of wood over on a curved part where the end grain is exposed.  I love the elegance and superior strength of laminated parts, even though the glue significantly increases the weight. So, I departed from the plan and am employing laminated parts.

I noted that the inside profile of this trailing edge piece "W6" approximated that of a real of tape. So, i cut around the tape onto 2mm depron to make a circular form. A mylar sheet was added tona foamboard base.

I found some nice fibreous 9 lb/ft^3 1/32" balsa and cut it into 2mm strips. They were soaked in boiling water for quater of an hour or so. Each strip was pulled in tension around an aerosol can lid to impart a curve. They were coated in aliphatic glue and pinned around the circular form.

However careful I am in ensuring each strip lies flat onto the base, I routinely get slightly uneven cross sectional profile due to gaps under some of the strips. So, I cut the strips over thickess and will sand the assembly down to 1/16" (1.5mm) thickness when dry.

I should be a able to get a full set of parts from this single lamination.

[Piecost]

Bill, thanks for going to the trouble of finding that nice plan showing more moderate thrust angles. I will apply them.

I have cut out the fuselage and empenage from nice, light 1/16" balsa. I plan to inset cross grained inserts into the fin and tailplane to prevent warping. As shown by the masking tape.

I will cover with yellow Asuka tissue. I am not aiming for a perfect finish or to completely fill the wood grain. I have bought some Deluxe Sand n Seal. Does anyone recommend that I apply before or after I apply the tissue?

I will apply a light coating of paint to acieve a uniform colour across the different construction materialz.

Anyun showed the Czech technique of colouring the balsa before covering, in his "Rieseler R III scale 1/25" thread. Much mass is typically added stopping the balsa from showing through the covering; more so than is required to give the general colour.

Does anyone think this sensible to pre-colour the whole fuselage and tail? It kind of defeats the object of weight saving if I paint such a large area.

I am considering a light dusting of Tamiya acrylic from an airbrush. Perhaps, this will help to unify the colour of the balsa/plastic/tissue areas.

[ZIP.58]

Good point. Tamiya paints are naturally thin and provide good coverage. Especially when they're stirred well—and all paints should be stirred, of course. I only use Tamiya paints on my models. Plus, they retain their coverage even when further thinned.
Have fun building your great model.

Peter