TECHNICAL SOLUTIONS for Large Scale Models. By Jan Hermkens

Click on the Pictures
for larger Images.

 Click on the Pictures
for larger Images.

 

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)
The A-26B INVADER
              : Participated only in Scale & Warbird Meeting
s up to now.

 

Built by Jan Hermkens from own Plans.  

 

Specifications Models : (all Woodconstruction)

 

Boeing B-17 FLYING FORTRESS

SHORT SUNDERLAND

Northrop P-61 BLACK WIDOW

Douglas A-26B INVADER

Scale

1/8th (only the 1/10th plan is available !)

1/10th   

1/6,6th   

1/5,9th   

Wing Span

4,00m = 158

3,45m = 136

3,10m = 122

3,60m = 142

Fuselage Length

2,85m = 112

2,64m = 104

2,28m = 90

2,55m = 100

Wing Profile

NACA 4415 Root/ 2415 Tip

NACA 4415 Root / 2415 Tip

Ownmix NACA 2414-2314/ 0014 tip

Ownmix NACA 2414-2314/ 0014 tip

Rootrib Chord

75cm

67cm  

55cm

53,5cm

Stabilizer Span

164 cm 

110cm

78cm

117cm

Stabilizer Profile

NACA 0012

NACA 0012

NACA 0012

NACA 0012

Wingsurface

190 dm

180 dm

140 dm

  146 dm

Weight

19,3 kg

  18,5 kg

 18,5 kg

  21,5 kg

Engines

4x Laser 70 (11,5cm) four-stroke

4x Osmax 46SF (7,5cm) two-stroke

2x Laser 240-V twin (40cm) four-stroke

2x Laser 240-V twin (40cm) four-stroke

Prop

M.A. 13x6 (9000 RPM)

M.A. 12x6 (10000 RPM)

Engel Carbon 18x11 (8000 RPM)

Engel Carbon 18x11 (8000 RPM)

Retract

Own Construction; Electric

none (Flying Boat)

Own Construction; Electric  

Own Construction; Electric  

Reciever

2x GR-24 Hott +2x Engel PMS Plus Powerbox

2x PCM double Superhet

2x GR-24 Hott + 2x Engel PMS Plus Powerbox

2x GR-24 Hott + 2x Engel PMS Plus Powerbox

Servos

16 x

13x

27x

20x

Batteries

6x 

5x

6x

6x

 

My drawings  are available (P-61, B-17 & Short Sunderland plans updated in 2010). The A-26B Invader plan is available now;  28 March 2017;
(see Downloads or Contact-Plans-Links)                         

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

For my 1/8th version I have cut out the necessary parts from my own 1/10th plan and copied them 125%, and have adapted the constructions a little bit for a fuselage-splitting and extra wing-splittings.
 

    1/8th B-17 Flying Fortress. Sp. 4m. Weight 19,3 kg.
  4x 11,5cc Laser 70 four-stroke

       Short Sunderland. Sp. 3,45m. Weight 18,5 kg.
4x 7,5cc Osmax two-stroke

 

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


A-26B Invader. sp. 3,60m. Weight 21,5 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 four socket bolts and blind nuts M4 (2mm balsa strips between them, this for.
This later on two-sided  to fix on 1mm ply rings. These as protection against damaging 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 bolts have been removed, sawn through between the the dual formers (perfect fitting).

 


          Fuselage-Tail Splitting  Short Sunderland 
   
                   Fuselage-Tail Splitting  B-17                                                                 
Fuselage-Tail Splitting B-17 (detail)                                                     
 

                             Tail-Boom Splitting P-61 Black Widow
                                                                                                                                           

                     Fuselage-Tail Splitting A-26B Invader 

Steering Rods:

In the B-17 & Short Sunderland, all the 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.

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 servos.

The kwiklinks on the servos have to be disconnected every time!

In the P-61 & A-26,  the servos for rudder and elevators are as far as possible forwards in the tailsection (In the P-61 for both booms!).

 


                Linkage-Splitting Short Sunderland. 
    
            Linkage-Splitting B-17 just like the Sunderland.                                        Linkages-Splitting B-17 (servos all in the front of the nose!)

P-61 Elevator & Rudderservos (upsidedown) in front  of Tailplane.
   
   A-26B Elevator & Rudderservos in the front of the tailsection.                                 Linkages elevators & rudder of the A-26B Invader.             

STABILIZER- and WING JOINERS:


Stabilizer joining:

 

Short Sunderland;

-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.


Stabilizer Sunderland, in one piece (elevators and rudder are removeable

B-17 Flying Fortress, P-61 Black Widow & A-26B Invader;

 -On the B-17  & A-26B, the stabilizer is in 2 halves, removeable and joined to the fuselage with carbon tubes 11mm

(1/10th B-17 carbon tube 9mm; in updated drawing in 2010!).

-On the P-61 the Stabilizer is removeable between both booms and joined to the booms with carbon tubes 9mm.

 

The elevator linkage control is provided, by both, in the moment that the Stabilizers have been slided against the fuselage or  boom.

Solution for these 3 models:

Square brass tubes sliding in each other (5mm in 6mm).

The 5mm tubes in the elevators are provided with 1mm brass strips for more gluesurface against 2 ribs.

The brass tubes in the fuselage are splitted in a left and and right part (separated linkage for also here each an own servo),on the outer ends on the tubes

are soldered small pieces round brass tube and bearinged in paxolin strips. Each halve has so his own control horn for a separated linkage.

The P-61 however, has only one stabilizer with a single elevator, but is yet linkaged to 2 servos, in each boom 1 elevator-servo. (8kg servos, but

currentless to move with one finger!! In case one fails, it should not be a problem for the other servo, pulling this around too).

 


                            Left Stabilizer-part B-17   
    
                     Stabilizer P-61  with carbon join tubes                                        Stabilizer P-61 with the elevator control tubes (so also B-17) 

                 Elevator- and rudder linkage on the P-61.
  
                  A-26B Invader Stabilizer Joiners.                                                                                             A-26B Invader  Elevator linkages.

Wing Joining:

 

-On the 1/8th 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 30mm and the rear a 18mm one. (Each winghalve on the 1/8th B-17  is also divisible in 2 parts ).
(For the 1/10th B-17 drawing I have updated it in 2010 with a loose thinwall dural tube 25mm
and carbon tube 11mm).


-On the P-61 & A-26B,  the wing is also in 2 halves, the wing joining is the same as on the B-17, but now with dural tubes 35 and 20mm.

(Each winghalve on the  P-61 & A-26B is also divisible in 2 parts ).

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-wood or hickory blocks  (on her sides and so making

the tubes even stronger against nodding).

 


                    Winghalve B-17 (innner & outer part)


 
                     
 Winghalve P-61 (inner & outer part)                                         Winghalve A-26B (inner & outer part)

 

-Each winghalve on the 1/8th B-17 , P-61 & A-26B is also divisible in 2 parts  and also these are connected with wingjoiners, but now glued in, and not loose in one piece.

 

The outer wingparts;

On the B-17: in front a 18mm dural tube and the rear one a 11mm carbon tube.

On the P-61 & A-26B: in front a 25mm dural tube and at the rear 11mm 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-wood or hickory blocks. The stabilizer joining with the fuselage consists of glued in carbon tubes 11mm, forward and rear, which are slided into polyester guide tubes glued in the fuselage. Here also the security is done with parkers.

   


                            Splitted Winghalve B-17
    
 Dural and Carbon Wing & Stabizer Joiners                                                 Outer Winghalve P-61

              P-61 Inner Winghalve with Nacelle + Outer Winghalve.
  
       A-26B Inner left Winghalve with partly the Nacelle.                                   A-26B Inner right Winghalve with Nacelle.

                        

-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 30mm and carbon tube 12mm.  So also for the 1/10th B-17, loose thinwall dural tube 25mm and carbon tube 11mm, and for the splitted Stabilizer 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.

            


                      Wing-Joiner Short Sunderland
 

 


                       Cockpithood extending over the Wing  

 

FLAPS & 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 an 8kg servo.

With the computer transmitter these servos 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 (still to construct against the wing!)

                                                     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 an 8kg 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 both sides of each flap to large cranks. From these cranks there are leaving 2 rods, both connected on the same side of the crank. One (the outer one; M2 rod with kwiklinks) for the there and back movement. To this rod there (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).

 


Drawing; linkage Fowler Flaps Sunderland

 

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.

 


                  Fowler Flaps Short Sunderland  (upperside)

                  Fowler Flaps Short Sunderland (underside)

 

 P-61 Flaps and Spoillerons:

The P-61 had conventional slotted Flaps (Not the ZAP Flap as described in some articles  or books! These were only on the prototype XP-61 !).
They can be lowered max. 60, 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 by 8kg servos, 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).
  

 

    

 Flaps P-61 (on inner- and outerwing)+ spoileron & tiny tipailleron                                             Spoilleron-linkage P-61                                                           Spoilleron + tiny tipailleron P-61

 

  

     

 

A-26B Invader Flaps:
The A-26B  Flaps had Double-slotted Fowler Flaps, but for the model it was to complicated to make it scale! So I made normal Fowler Flaps (but the linkage is different as it is in the Short Sunderland model).
These Fowler Flaps are going backwards max. 50mm en max.
50 downwards.
An 8 kg servo (again slowed down to 5 sec.) controls a long 4mm pianowire via a controlhorn in the middle, on this axle, there are 2 more controlhorns en these are controlling 2 pushrods (through long guiding tubes), linked on the upperside of the Flap-leading edges. On the same controlhorns there are M3 rods, but a little bit closer to the axle and linked on the underside of the Flap-leading edges.
On one outerside of the flaps there is a third rod (also through along guiding tube), but not controlled, just for extra guiding!
Because these M3 rods are controlled closer to the axle, they make a shorter way than the upper pushrods, and so the Flaps are turned over, more and more, during pushing.
Very simple, but adjusting the whole, took a lot of time, because  the flaps are not rectangular but tapered!  So the push-movement is on both outersides different!

 
                       Fowler Flaps  A-26B Invader.

     
    Flap-linkage A-26B (inner Flap)                        Flap-linkages A-26B (upperside)                              Flap-linkages A-26B (underside)

 

 

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 ; 150mm (6") and for the 1/8th B-17 ; 180mm (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, like the other moulds(3m ply bottom + some 3mm ply cross-sections + filling with balsa, and than planing and sanding).
But first there can be glued a motor-dummy to the plywood ring!

 

      
       Short Sunderland Alum. Cowling with GRP nose cowl-ring.                                B-17 Alum. Cowling with GRP nose-ring.                                             

       
                Mouldings & Plugs for the Short Sunderland                                                    Mouldings & Plags for the 1/8th B-17

 
  


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 (less  fouldings as possible), 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 (less wrinkles as possible) 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, uninflated up to 50cm diameter available. Advice Size: Balloon diameter not inflated; 2.0 to 2,5x 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.

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

 

        
                                  Balloon method Polyester parts

     

 

Cowlings P-61 &  A-26B

These are not the same diameter over its entire length, so the methode for the Sunderland & B-17could not be used (aluminium stove- or flue pipe with a GRP nose cowl-ring).
Therefore a positive wooden mould have to be made first ​​(with 3mm plywood bottom former + some cross-sections and between them balsa blocks, than planing and sanding it in shape).
Then the
cowlings (largest diameter 210mm) were made ​​entirely of GRP with my balloon method above
.


 

 

 


P-61 Mouldings & Plugs for Cowlings,
Cockpit, etc.

                                
                     GRP Cowling P-61 with radial Dummy                            A-26 Mouldings & Plugs for Cowlings, Cockpit, etc.                         GRP Cowling A-26 with radial Dummy
 

 

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!
       

 

                                                    
          Selfmade Moulding for the Enginedummies                                            Vacuum formed Radial dummy engine.                                                                                                                                                                       

 

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 (3mm plywood bottom former + some ply cross-sections and between them balsa filling, than planing, sanding it in shape, 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.
 

  

                         Tail Turret Short Sunderland

                               Nose Turret Short Sunderland
 

Chin, Sperry Ball Turret, and Tail Turret of the B-17, the Top Turret and Nosedome of the P-61 & A-26B 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).


 


       Nosedome Plug B-17

                      Cheek Gunshields Plugs B-17

Nose Dome & Chin-Turret  B-17
      
                            Cheek Gunshield left side B-17                                                                 Removable Cockpit Hood B-17 with Top-Turret

 
                   Sperry-Ball Turret  B-17         

  



 
                  Turrets & Nosedome of the A-26B Invader                                                               Removable Cockpit Hood A-26B Invader

 

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 water-flying it is removable, by pulling it out of the stainless steel tubes from both sides, which are going across through the hull.


Removable & extensable Beaching Gear Short Sunderland

B-17, P-61 & A-26B:

They have a retractable undercarriage, an own construction and works via an electric motor, gears, micro switches and an M6 screwjack. This spindle is mounted in 2 alum. head walls and moves a bronze part back- and forwards, which is attached with two 3mm alum. Strips, hinged into flange bearings, to a forked and swivelable strutholder, which can tilt through it.
This strutholder can turn on a 6mm shaft (absorbs the landing shocks) in the sidewalls of aluminum, which are bolted to alum. Angles (to screw the retract on the hardwood bearers of the inner engine nacelles). At this strutholder, the strut is attached, which is made of stainless steel and dural, they are spring Oleo and have all kinds of details.

 

The micro switches are pressed down by adjustable rods, which in their turn are pressed by the spindle back- and forward moving part. Thus, the up- and downstroke can be set in any desired position. The whole is jointly controlled and reversed by one third and double microswitch in the fuselage (for example from Graupner, which fits on a servo).
In the B-17 are the struts (with 6wheels) retracted forwards with the wheels for 1/3 part strechted out, just like the original. Above them lies on a 1mm plywood bottom, the tanks for the inner engines. The scissors construction is working and therefore hard soldered. The strut in the middle is telescopic in the original plane and retracts the gear. At the model these struts are dummies of brass, but the middle one is also telescopic.


  Own constructed electric Retract  B-17,  with 6 wheel

             Own constructed electric Retract  B-17,  down.

 

At the P-61, the nose strut (with 4 wheel) is retracted backwards, which is also closing the welldoors. In the lowered position, the welldoors are kept open by self curved springs from 0.4mm piano wire.
The main legs (with 7 wheels) are also retracted backwards, and disappear entirely in the wheelwells, whose wheel welldoors exists of 3 parts; two main doors that also are closed when the landing gear is downwards (by the struts themselves via steel cables), and a small wheel welldoor next to the wheel strut, which remains open.

During retracting the gear, all doors, 5 seconds delayed, get closed by two 180 Servos.

 


          Own constructed electric Retract P-61                         

 The own constructed Retracts with plastic cogwheels as a gear
 

 

The plastic cogwheels as a gear, on the inside of the head wall (B-17), was exchanged later on the P-61 by a gearbox directly to 6V. speed 400 motor, because here was the pressure going towards the same head wall. (Struts on B-17 are retracted forwards, and on the P-61 backwards, and here was some pressure than on the plastic cogwheels, where they could not stand it!)

 


 At the P-61, the plastic gear has been exchanged now for a gearbox

        P-61; the 180 Servo for the mainwheel well doors

 


Main Strut P-61 with 7 wheel

                    Nose Strut P-61 with 4 wheel


 

At the A-26, the nose strut (with 5 wheel) is retracted backwards, which is also closing the welldoors. In the lowered position, the welldoors are kept open by self bended springs from 0.4mm piano wire.
The main legs (with 7 wheels) are also retracted backwards, and disappear entirely in the wheelwells, whose wheel welldoors exists of 2 parts,  which remains open.

During retracting the gear, all main-geardoors, 5 seconds delayed, get closed by 180 Servos.

 

             

                A-26B Electric Retracts. Own Construction                                        A-26B Retract of the right-innerwing with the wheelbay doors               Self bended springs for the wheelbay doors                     

 

    
     A-26B Invader. Rightside Mainwheel                                    A-26 Invader. Nose-guns & Nosewheel                                

 

 

ENGINE LINKAGES & ENGINE MIXERS.

 

The engines at my multi-engine models have no side thrust and little or zero down thrust (nacelles are being built on at 0 degrees).

-At the
Sunderland that were 4x two-stroke Osmax 46 SF (7.5 cc) with 12x6 props (10 000 RPM).

-At the B-17  (1/10th) that were 4x Osmax .40 FSR (6,5 cc) two-stroke, with MA 11x6 props. (11.000RPM)

-At the B-17 (1/8th) that are 4x four-stroke Lasers 70 (11.5 cc) with MA 13x6 props (9000 RPM), these have a very small overall height.

-At
the P-61 that are 2x four-stroke 240-V lasers (40cc) with 18x11 Engel props (8000 RPM), these also have a small overall height.
-At the A-26 that are 2x four-stroke 240-V lasers (40cc) with 18x11 Engel props (8000 RPM), these also have a small overall height.


The
laser engines run very smoothly and reliably, have no need for pre-glowing or nitro, starting immediately and have a very deep sound, like real!
In the Sunderland and B-17 the control of the throttle linkages in both wing halves is on a rotating rod of a 3 mm pianowire into a plastic tube with three horns linkaged to M2 rods

on the servo (in the center) and control cables (sullivan) to the 2 throttle horns.

For a better
taxi - take-off and / or planing on the water, the engines, left and right, have been mixed with the rudder, although synchronization of the RPM in flight is not critical, but yes the Sunderland on the water and especially during planing when the model is on his step!

And the B-17 is, due to its enormous tail fin in the start, with the wind is in an angle or cross, will rapidly break out to the wind direction.

Even
at the P-61 & A-26B this mixer is programmed, but has never been necessary, due to the existing nose wheel here.

Controlling the throttles happens here on both sides with control cables of sullivan, linkaged to a servo.

 

Mixing Rudder / Engines, B17 - Sunderland P-61 & A-26B:

 

For this we need 4 mixers, of which mixer  2-3-4 are on the same switch! (at my transmitter a switch on the throttle stick).

-Mixer 1: Left and right engine on a separate channel and 100% symetric mixed,  and whether or not on a switch (no switch for me).
-Mixer 2: Rudder with left engines a-symetric mixed;
                         Rudder Right: ofs 0-S = 40%  Left engine faster.
                         Rudder Left  : ofs 0+S = 20%  Left engines slower.
-Mixer 3: Rudder with right engines  a-symetric mixed;
                        Rudder Right: ofs 0-S = 20% Right engines slower.
                        Rudder Left  : ofs 0+S = 40% Right engines faster.
-Mixer 4: throttle reducing for lower RPM limit: 90%, to avoid cutting off in idle position at full rudder!

 

 

Never forget to switch off Mixer 2-3-4 after taking off! (otherwise the engines will react unintentional, when operating the rudder).