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Flying electric in the days before LiPo, NiMh, ESCs and foam!

quorneng

Active member
#1
Electric flying actually goes back a long way (Col Taplin converted a Radio queen to electric in 1954) but it was rather specialised and even more expensive than the then substantial cost of IC engines and RC equipment!
Like many young lads in that era I learned to build and fly (poorly) simple rubber powered models but living in the UK suitable days of weather condition for such lightweights were few and far between - and they still are!
At about that time the first of the cheap small lightweight Japanese (Mabuchi) motors appeared but without suitable batteries any form of electric free flight was no nearer. The only solution available to my budget was to fly electric was 'round the pole' and space limitation required short (6 foot!) lines as well which in turn meant the planes would have to be small and light.
Initial experiments did get things to fly but using 12 Volts on 3 Volt motors meant they did not last long. With the motors weighing more than the rest of the air frame it was not long before some form of elevator control was considered beneficial.
As a DC motor requires two wires why not make them act as 'control lines' as well.
With such short lines this required the control line mechanism to be operated from outside the flying circle.
The result of elevator and fully variable power allowed quite a range of lightweight 'balsa and tissue' planes to fly 'control line'.
A peanut scale Andreason A4b.
Peanut1.JPG
A slightly bigger Keil Kraft Fairy Gannet
SC-Gannet.jpg
A free lance transport 'twin'.
SC-Yellow_Brick-1.jpg
A sort of Liberator.
SC-Liberator.jpg
All the above direct drive with home made balsa props.
In fact control line RTP proved to be a very 'gentle' form of flying so even super light air frames could survive.
The rise of slot cars meant that small (1oz) powerful 12 V motors became available and suitably geared they could generate several ounces of thrust.
A true scale 20" Sopwith Pup.
rtpPUP.jpg
The wing section is scale so the cotton rigging is fully functional. The geared motor drives a scale carved balsa prop. It weighs just 2 oz and the motor accounts for 1 of that!
It flew well enough but that thin under cambered wing section meant that like the original any stall was to be avoided.
With lessons learned next was Fokker Triplane built to the same scale it has (I still have it 45 years on!) an 18" span.
SC-Triplane-1a.jpg
With its 'horse shoe' cowl the scale engine is rather more visible so it goes round with the prop!
To be continued!
 
Last edited:

quorneng

Active member
#2
The object with the Fokker Triplane was make full use of the delicate nature of RTP control line flying to make it as scale as possible both inside and out by copying virtually every piece of wood and rigging of the original.
This is the only picture I have of it under construction. Triplaneconstruction1.jpg
The fuselage is 1 mm round balsa to emulate the steel tubing of the full size. The sheet balsa is just 0.5 mm thick. The rigging is cotton thread.
The slot car motor and the Oberursel rotary that is geared down 2.3 : 1.
SC-Triplane-2.jpg
A neat touch is the scale pull/pull lines (cotton thread) from the elevator to the control column in the fully detailed cockpit. The control line bell crank is simply linked to the stick!
The cowling is spun from a sheet of aluminium over a hardwood mandrel. It does help if your Dad is also very competent model engineer!
Decorated in the colours of a Triplane flown by Werner Voss it weighs 2.25 oz and flies very nicely. The slot effect of the three wings with their relatively thick section allows it to 'hang on its prop' as high angles of attack just as did the original.
Now over 50 years old it is no longer flown but it does still run.

Having built scale models of 'wood and canvas' types I wondered if it would be possible to build an all sheet plane that would be small and light enough to be flown in the same sort of way.
What I needed was a plane that had a relatively small wing span along with a big propeller.
The elegant Martin-Baker MB5 seemed to fit the bill.
M.B.5proto.jpg
And with a motor driving each contra rotating prop it would in effect become a twin!
To be continued.
 

quorneng

Active member
#4
Being all sheet covered (except the rudder and elevator which were fabric) my main concern was to keep the weight within bounds. My super scale Triplane came in at 2.25 oz. The MB5 would have a bit more wing area but using two motors and a great deal more balsa I feared the wing loading would result in a flying speed (if indeed it had the power!) that would require a line length well beyond the indoor space I had access to.
So the target was to built entirely in 1/32 balsa as a stressed skin monocoque. I reasoned that for the forces involved provided the skin was sufficiently supported it would have more than enough strength and stiffness.
One saving grace was the MB5 had true flat sided fuselage over most of its length and i had a diagram showing the profile of the major fuselage formers. As a result the construction was almost 'conventional' although rather delicate.
These are the only construction pictures I have. Could only afford black and white film in 1969!
MB5fuse2.jpg
The 1/32 ring formers had inner flanges to give the necessary rigidity.
MB5fuse1.jpg
The 'curved' parts of the fuselage had to be planked. Each plank had in effect be to shaped to fit' along its length, glued and pinned in place, To prevent the stress of bending the planks creating a 'banana' fuselage the planks had to laid on alternate sides. A technique not dissimilar to carvel boat building but as a young man I had time and eye sight on my side!

By comparison the wings and tail were relatively simple with straight tapers. No spar anywhere just ribs and the 1/32 balsa skin.

My Dad very kindly cut me a pair of alloy gears that gave an 7:1 reduction to the high reving "slot car" motors.
By mounting the motors side by side each could drive its own gear fixed to concentric shafts (steel inner, alloy outer).
MB5motor.jpg
The motors are wired in parallel. The nose of the fuselage is quite rigid enough to carry the front bearing.
The spinners are solid soft balsa with individual carved balsa blades glued into them.
As there there are some nice period photos to work from a fully detailed cockpit was added.
MB5ckpitS.jpg
The complete MB5
MB5frontS.jpg
As I had no opportunity to test fly it I felt it was appropriate to complete all the decoration un flown, not something I normally do!
Does it fly?
Yes it does although I had to build a special raised flying 'circle', with safety netting, so it could have its maiden flight at a school open day!
With straight cut gears its hollow structure makes a wonderful sounding board so it has an impressive sound even if its more like a turbo prop than a Griffon!
'Retired' as it is now 45 years old so only a rather poor quality ground run video.