TECHNICAL SOLUTIONS for Large Scale Models. By Jan Hermkens. 

With the examples;

The B17 FLYING FORTRESS :  a.o. the EUROPEAN  CHAMPIONSMODEL  STAND-OFF SCALE '94+'95­+'96+’99 (Europa Star Cup)

The SHORT SUNDERLAND   :  a.o. WINNER EURO CUP SCALE-WATERFLYING  '94.

The P-61 BLACK WIDOW    :  a.o. the EUROPEAN  CHAMPIONSMODEL  STAND-OFF SCALE  2000+2001 (Europa Star Cup)

Built by Jan Hermkens from own Plans.  

My drawings (updated in 2010) are available; (see Downloads or Contact-Plans-Links)

But from the B-17 only the smaller version 1:10 of 1983 (spw 3,16m).

For the 1/8th version I have cut out the necessary parts from my own 1:10 plan and copied them 125%, and have adapted the constructions a

little bit for a fuselage splitting and extra wingsplittings.

P-61 Black Widow. Sp. 3,10m. Weight 18,5 kg.
2x 40cc Laser 240V-twin four-stroke

 FUSELAGE-TAILSECTION CONNECTION.

In relation to the transport and the manageable the tailsection had to be detachable, and therefore providings were attached for the Fuselage-Tailsection

joining and glued into some formers. At the joining so a dual former (Sandwich:2x 1mm ply with inbetween them 6mm balsa with plywood rings),

these are bolted together with 4 socket bolts and blind nuts M4 (2mm balsa strips between them, this for. The later on twosided  to fix on 1mm ply rings.

These as protection against damiging and for a perfect seamfitting of the fuselage parts).

The fuselage-joiner itself can be very light: flat springwire 6x1mm  in flat brass tubes 7x2mm. The flat brass tubes are provisional in one piece and on both sides, glued in 2 formers (front- and tailpiece must be sheeted apart) and later, after the bolt have been removed, sawn through between the the dual formers (perfect fitting).

Steering Rods:

Because all Fuselage-servos  are in the front of the nose (to avoid a lot of extra lead) and all linkages to the rudders are a closed-loop system (plastified control line wire), these linkages had to be disconnectable on the spot of the fuselage splitting (with exception of the P-61, there are the servo’s for rudder and elevator as far as possible forwards in the tailsection of both booms).

On a 3mm ply strip, in the front of the tailpiece, there are 3 cranks (3mm axle), which all are connected with kwiklinks and a closed-loop system to the inner control horns of rudder and elevator. On these 3 cranks there are also, all on the outside, threaded ball links (M2).

The connection forwards take place with alu. ball links and and moved on security clips, naturaly also with a closed-loop system to the servo’s.

The kwiklinks on the servo’s have to be disconnected every time! (not on the P-61)

STABILIZER- and WING JOINERS:

 
Stabilizer joining:

-On the Sunderland the stabilizer  has been glued, in one piece, into the Tailplane, the elevators are direct linked, internal via 2 apart built in cranked pianowires (3mm bended pianowire, bearinged in plastic tubes) with control horns. The elevators they have glued in tight fitted plastic tubes, and are slided over these cranked pianowires, not glued, so they are always removeable. So also the rudder.

Wing Joining:

-On the B-17 the wing consists of 2 halves , which are slided to the fuselage with wingjoiners. The wing joiner on the front is a loose thinwall

Dural tube Ø30mm and the rear a Ø18mm one. (for the 1/10th B-17 drawing I have updated it in 2010 with a loose thinwall dural tube Ø 25mm

and carbon tube Ø 11mm).

-On the P-61 the wing is also in 2 halves, the wing joining is the same as on the B-17, but now with dural tubes Ø35 and Ø20mm.

These tubes are thus loose and in a single piece and slided into fiberglass guide tubes (glued in to the fuselage and innerwing halves).

The wings, also provided with guide tubes, are slided over the stretched out tubes and secured with long “Parkers”, through abachi blocks

(glued on the guide tubes) into the tubes, which are provided internally with short and small  ash-tree or hickory blocks  (on her sides and so making

the tubes even stronger against nodding).

-Each winghalve on the B-17 and P-61 is also divisible in 2 parts  and also these are connected with wingjoiners, but now glued in.

The outer wingparts;

On the B-17: in front a Ø18mm dural tube and the rear one a Ø11mm carbon tube.

On the P-61: in front a Ø25mm dural tube and at the rear Ø11mm carbon tube.

The innerwing parts have on the outside glued in polyester guide tubes.

On the spot of the deviding there is of course a dual wingrib (for each part, one) and during the open construction, the joining has to been attached, this for an accurate fitting! The security is done, as with the fuselage-wingjoiners, with “parkers through abbachi blocks into the tubes, internally also provided with ash-tree or hickory blocks. The stabilizer joining with the fuselage consists of gluedin carbon tubes Ø11mm, forward and rear, which are slided into polyester guide tubes glued in the fuselage. Here also the security is done with “parkers”.

-At the Sunderland the wing only consists of 2 parts (stabilizer glued on), which are connected with each other by a wingjoiner of flat springsteel 1,5x15mm in gluedin brass flat tubes 2,5x16mm, forward with 2 of them above each other, a long one untill the First nacelle and a short one.

The rear is a short one 1,5x12mm in a brass tube 2,5x13mm. (in 2010 drawing updated, so now, loose thinwall dural  tube Ø 30mm and carbon tube Ø 12mm. So also for the 1/10th B-17, loose thinwall dural tube Ø 25mm and carbon tube Ø 11mm, and for the splitted Stabilizer Ø 9mm: Lighter).

The Winghalves for the Sunderland  are secured to each other with 2 alu. strips and parkers in abachi blocks, and than bolted on the fuselage with 4 long stainless steel bolts M6, in to the fuselage fixed metal inserts.

Over this than comes the long cockpithood, which stretch from nose to the rearend of the wing.

                       Cockpithood extending over the Wing  

FLAPS and SPOILERONS.

B-17 Split Flaps:

The real B-17 has splitflaps and on the model these were built directly against the wing underside, with clearfoil between it as a barrier.

The special flap hinges were attached, recessed into the flaps and wing under-surface. There is a gap between wing and under-surface when these are lowered, giving more lift and less drag!

The flaps are controlled with internaly M2,5 rods., and because of their huge surface linkaged to a 10 kg servo.

With the computer transmitter these servo’s were slow downed to 5 sec., so that the nose does not go up, because the model has so the time to adapt itself to the flap situation, every moment!

                                                     Splitflaps B-17

Short Sunderland Fowler Flaps:

This are Flaps moving simultaneous backwards and downwards, giving a lot of more lift in slow flying or allowing even a more slower landing.

At the Sunderland model that had to be max. 9 cm backwards and 40° downwards!

But how to make this complicated system practicable for a model?

The end result looks very simple and finally it is so! But before that it was a long way to go. A lot of experiments, hours! For certain, because the Flaps have a trapezium shape, so the travelway is on each outerside different, and adjusting of them did require a lot of time.

The Flap itself was constructed again, with clearfoil between it, against the hollow underside of the rear wingedge. Also here, each Flap is linkaged to a 10 kg servo, and for the same reason as at the B-17, slowed down to 5 sec.

From the servo there goes a rod (M3 with ballinks) to large cranks on both sides of each flap. From these cranks, there are leaving 2 rods, both connected on the same side of the crank. Eentje (de buitenste; M2 draadeind met kwiklinks), voor de aansturing van een 4mm dikke veerstalen schuifstang (de heen en weer beweging).One (the outer one; M2,5 rod with kwiklinks), goes to a rod of 3mm Pianowire (for the back- and forward movement). To this rod (beared in hardwood blocks provided with a piece of plastic tube) the Flap is connected, hinge jointed.

The second rod (the inner one; M3 rod with ballink and kwiklink) goes from the crank straight to the control horn of the Flap (the Up and Down movement).

How does it operates than?

Because the inner rod on the crank makes a shorter stroke than the outer one, the inner one really holds up the flap during the slide-movement,

so that the flap starts to turn over on his hinge-joint on the leading edge. The more larger sliding movement, the more turnover movement!

The extent of the turnover movement defines thus the angle of which the flap gets lowered and is thus dependent from the distance differance between the two side by side seated rods on the crank!

After a severe waterdamage, by a hole in the hull (an under water hidden boulder), the condition of the balsawood rapid declined, and at one point it was not justified to fly any longer with the model.

 P-61 Flaps and Spoillerons:

The P-61 has normal Flaps, max. 60º lowered, and are as well at the inner- as at the outerwing section, so total 4.

The special flaphinges are recessed into flap- and wing undersurface. Again there is a gap between wing undersurface and flaps, when these are lowered, giving more lift and less drag! They are linkaged with M2,5 rods and kwiklinks and controlled from 10 kg servo’s, and again slowed down to 5 sec.

The spoilerons are laminated, in a halfround and tapered moulding, of 3 sheets 0,4 ply, and between them carboncloth + epoxy.

They are hinged (almost at the rear, on the upperinside of the the outerwing), on a long 3mm pianowire in a plastic tube, so it can turn out of the wing (therefore in the ribs are sawed segment shaped slots), and is eccentrically controlled direct from a servo, turning up simultaneous with the small tip aileron on the same side. On the other wing the tip aileron is going down of course, but the spoileron remains, almost unmoved, inside the wing (on account of the eccentric control linkage).  

COWLINGS, MOTOR-DUMMIES, TURRETS, etc.

Cowlings Short Sunderland & B-17:

These have all over, the same cilindric dimensions. For the Short Sunderland & 1/10th B-17 ; Ø150mm (6") and for the 1/8th B-17 ; Ø180mm (7").

Therefore  these can be made from aluminium stove- or flue pipes (available in many diameters), the rounded nose cowlring can be made from GRP, with the so called balloon method (see further on!). A plywood ring has been glued  half into the pipe, on this the self formed GRP ring can be glued. For this ring you have to make a wooden mould (for example balsa). But first there can be glued a motor-dummy to the plywood ring!

Mouldings & Plugs for the B-17

Alum. Cowling with GRP nose-ring B-17 with radial Dummy

Balloon method.

Glue to the mould a Block or a attach a pin and jam this in a vice, and so, that the mould is free well! The mould has been covered with clearfoil (without fouldings), which is secured with sellotape.

Over it comes a 80 grams, or heavier, open wave mat. The whole is coated with polyester or epoxy fast-acting (10 min). Over this is loosely (no wrinkles) a clearfoil again. The start of hardening, (keep an eye on a residue in the pot very well), it begins after about 10 minutes. In the meantime, inflate a very large party balloon (For sale in a festive article shop, empty, up to 50cm diameter available. Advice Size: Balloon diameter 1.5 to 2x mould diameter, the larger ones to inflate with a bicycle pump or compressor).

This inflated balloon is kept ready just before the hardening process, together with a potential balsa inner ring (for forming a leading edge in certain types of cowlings) pushed against the front of the mould. Continue pressing, and let escape some air at the same time, until the balloon is at the back of the mould. Keep tension on the balloon and keep the trunk of the balloon tightly squeezed, and keep the balloon pressed over the mould with your arms. This is why not immediately the balloon is going to be pressed against the mould, because then you stand there, after at least 15 minutes, with an aching back!
After the start of hardening, the balloon and the outer clearfoil can be removed and then let it harden properly. Then the exterior can be sanded wet with waterproof sandpaper, cut off the folded back, slide the product of the mould and remove the inner clearfoil.

Naturally, this balloon method is also suitable for other types of polyester parts!

Cowlings P-61

These are not the same diameter over its entire length. Therefore a positive wooden mould have to be made first ​​(with plywood formers between balsa blocks, planing and sanding it in shape). Then the cowlings (largest diameter Ø210mm) were made ​​entirely of GRP with my balloon method above.

Radial Dummy Engines;
These can be made yourself ​​of plastic (hollow), or polyurethane foam (solid).
First make a positive mould with balsa parts, to glue on a plywood base, make a negative print of this in a tray form resin or plaster.
 

After hardening, there are three possibilities:
1) Treat the mould with a release stuff,  fill it with polyurethane foam and remove the product after hardening.

2) Alternatively; use the negative mould to form the dummies with GRP.
3) Using the positive mold and 1mm ABS or transparent PVC to vacuum form it.

The outer push rods can be made ​​from small pieces of 2mm plastic rod!                                                                                                                             

Turrets:

Sometimes you can buy them, also for some purchased plans, but certainly not for your own designs!
To make them our own, one must first produce a positive mould or plug (plywood formers and balsa filling, scraping, sanding, and for a vacuum method finishing it  with 25 grams mat and G4 polyurethane).
For the vacuum method one can contact hobby stores, some of them have the equipment to do this.
I myself apply the 20 years ago myself developed Kitchen oven method.

Kitchen oven methode:

Bond to the plug, a block as a spool handle. Then make an increased framework of 6 to 10mm plywood, make an opening, 1mm around larger than the basic shape of the plug, place over this a cockpits appropriate 0.5 to 1 mm thick plastic plate (clear PVC or Buyrate), tighted around, and place it in the kitchen oven (± 200° C).
Keep an eye on everything and good as the plastic begins to sag, take out the whole quickly from the oven and push the plug through it, until just below the edge of the baseplate. Immediately cool off with a damp cloth, so that the material shrinks tightly over the plug. One can take the product from the plug with sharp scissors and cut it to size.
 

Chin, Sperry Ball Turret, and Tail Turret of the B-17, the Top Turret and Nosedome of the P-61 were also formed with GRP on positive moulds, against which the large balloon was pushed again, as defined by the nose ring of the cowlings. For the round Sperry Ball Turret of the B-17, I have used the cup of one of my many trophies as a template! (just the right size).

UNDER-CARRIAGE

Short Sunderland:

The Sunderland was a flying boat and not an amphibian aircraft, so it really does not have an under-carriage for take-offs and landings on land!
The original could only be provided with a so-called beaching gear for maintenance on land. I copied this scale to be able to start on land, but spring Oleo's, also the tail wheelthing is scale, from this the original was towed out of the water.
The beaching gear can easily be expanded to a wider track, by pulling out both sides, otherwise it is too narrow for land take-offs. For waterflying it is removable, by pulling it out of the stainless steel tubes from both sides, which are going across through the hull.