LINNEY

Greyhead - at last. Whilst flying, the upthrust on the wings (the factor which creates lift) attempts to break them off at the centre section. So wire (wires, plural,thanks) attached between the top wings at the tips and the lower fuselage hold them in place. And when bumping down on landing the wings will tend to carry on down to the ground so more wires, lower wing tips to upper fuselage (top of cabane struts of course) will reinforce. And the interplane struts will keep the wings paralell.
GOT IT! Many thank Greyhead. Incidentally, are you making adjustable incidence or is there no point since there will be no pilot to make adjustments? Unless you put a servo control inside so that with an extra Tx control you can alter that yourself as a "ground pilot"? Interesting!

Greyhead

Glad to be of assistance!

I have made the tail plane incidence adjustable but not “in flight”; once the incidence is correctly set it won’t need changing again so the extra weight of a servo plus the complications in design mean that it is not really a viable option, at least not at this scale. I have to admit that I’ve never heard of adjusting the wing incidence, except for banking using “wing warping”, by lifting the TE but with these early planes nothing surprises me!

I trim the model in flight using the elevator trim lever; if it’s not too far out I just leave it at that. If I consider it worthwhile to change the incidence I measure the elevator deflection at the TE, guesstimate the proportion of elevator to tail plane area, neutralise the elevator then adjust the tail plane incidence by the same proportion of the original elevator deflection.

In the case of the SE5a, say for instance if I needed 4mm down trim. Looking at the tail plane I’d say it is about 50 /50 fixed and elevator, so I’d neutralise the elevators and adjust the incidence to drop the TE by 2mm and try again.

Not very scientific I admit but it seems to work.

wonwinglo

Linney,do not take any modern day interpretations of wing incidence,dihedral etc too literally,aircraft of this period could be fairly easily rigged to suit who was flying them and that is what they often did ! riggers and fitters became versed in tweaking these biplanes for max performance and to suit the needs of the daring pilots who flew them.
Datum lines are normally taken from the main longeron,take a look at a Tiger Moth next time you see one and there are locating points along the fuselage which act as points to place the datum board,these in turn correspond with the longeron mentioned by the engineers at Shuttleworth,as regards wing incidence this too can be altered,dont forget that this also governs the all important 'decalarge' and wing stagger of any biplane.
Flying wires are the ones that take the 'flying load' of the aircraft whilst in flight,'landing wires' take the load of the aircraft whilst at rest,this applies whatever the aircraft type.
Keep your eyes open for period aviation manuals that are excellent guides for aircraft of this period,they do not come cheap but are a mine of knowledge,Shuttleworth may be able to do photo copies for a donation to the museum,you need to ask them for any specific requirements.

__________________
'And there I was oil on my goggles from a broken pipe,then I looked at the altimeter,all I could see was the makers name !'
www.wonwinglo.scale-models.net/

BobH

The SE5a that I built has 5 degrees of dihedral and 5 degrees of incidence on both wings. The same goes for the stab.. mine is fixed at 5 degrees as well. This gives the plane an effective 5 degrees of down thrust. Useful for countering all that lift.

BobH

LINNEY

Well many thanks chaps, a lot of useful stuff here. Wonwinglo as always with the background data which is so useful - and I have purchased several manuals, especially Windsock. It is also surprising if you "search" on the Net "SE5A images" and "SE5A video". Even the Museum of the RAF Halton Apprentices,of which my late father was a pioneer boy in 1922, has a starting-up procedure manual - but I cannot have a copy!
And of course Greybeard - he's been there, done that!
BobH yours looks very nice - appears to be a Viper-engined aircraft of 56-sqadron, yes? So the fundamental questions please, the span, the weight, the engine, the prop size and the engine speeds, both cruising and take-off? I'm thinking of electric and a "noise-maker" if I can discover what I need to emulate - but more of that later, life is domestically hectic at present!

LINNEY

I am back - and it is now nearly 4 weeks since I last got into my workshop! Family trials and tribulations, Grandparent duties etc etc, I am sure that there is someone out there old enough to know what I am talking about.
But to business, still on angle of incidence. I recall that when I went model flying with my Father and Uncle before the war (I was about 8-9 years old) my job was to set up wing position. My Father built with the upper fuselage sloping up in the approximate wing position area and when the wings were held on with rubber bands the forward position dictated incidence. I had to place the wings in what seemed to me a reasonable position (held with a thin pin) and throw the aircraft - without power - hard and horizontal. If it shot up into the air and fell back on its tail, too much incidence, pull the wings back. If it dived straight into the ground, put wings more forward and try again. A gentle gilde onto the grass and I passed the model to my Father. He would give a bit more lift and wind up the elastic - but this was the interesting bit. If he used really thick elastic then the power was enormous, with enough incidence the aircraft would shoot into the air perfectly, level out, then fall in on its tail when the elastic had unwound. Short duration flight, great height, super level fast flight for a very short while then impact! But if he used very thin elastic he had many more turns but there was very little power so less incidence was tolerable and the aircraft would fly straight and almost level at launch height for quite a while -success meant I had to run across two fields on aircraft recovery. But my Uncle came up with a compromise, thick rubber, high power enabling high lift - but a linkage gadget such that as the rubber unwound the wings fell back down the fuselage "slope" and the aircraft finished its flight as a glider. Took quite a bit of fiddling but that really started my life as an experimenter - later in the grown-up real world.

So what has this to do with an SE5a? Well, the whole technology is relevant to any aircraft - more power enables more lift, and that is where I am stuck at the moment, what power for my 6ft span model? I have said I am considering electric (with an engine noise generator) but that means questions have to be answered. An electric motor is much lighter than, say 120 i/c but what would probaly be 12 LiPo cells are much heavier than a tank of fuel. The total may not be too different but the positioning will be very different which will impact on fuselage inner construction.

I have actually built my fuselage - up to a point. Unlike Greyhead I built both sides full length up to the upper longeron, then built nominally the inner woodwork which is to hold the engine/motor, fuel tank/battery, servos and pilot.
And there lies the problem - what am I building? Well, I have compromised.
The only former which extends vertically and horizontally across the whole fuselage is F2 and this is a very solid piece of ply - proper hard thick ply. So I have screwed the fuselage sides to this and then glued the sides together to the rear of the cockpit complete with cross-members etc. The "nominal" inner section, built to the correct outer dimensions but of a doubtful inner layout, is actually held in place with Sellotape as is the nose and so when I have enough data to decide on a power system I can undo the screws, open up the front of the fuselage, make a new inner and re-assemble with glue (epoxy). Meanwhile I can experiment with cabane and wing centre-section construction because the fuselage is in effect complete. At the same time I have constructed the upper fuselage to the rear of the cockpit (a collection of stringers on separate formers) but made it detachable from the main fuselage for the time being. Held in place with pins it works as if it is finished but I can open up and "play" with servo links etc. One thing I have learned over time is if I fix stuff together too early then modifications can be difficult if not virtually impossible. Ever had a situation "Oh hell, why didn't I drill that hole in that former before I glued it in place?" I want to find those problems before its too late and by fixing in a temporary but robust manner you can make almost a whole aircraft and only finally glue in place when you think you have it right (and usually time and hindsight will show you to still have mistakes!) Unfortunately you cannot really adopt that technique with wings, but more of that later.

But what experiments? Well, read Greyhead and his storage problems - like me, no room for the whole finished assembly (who has) but a problem with removable wings. So can I make a removable cabane structure? O.K., the real thing may not be like that but if it looks right, who cares? The real thing had no servos, receiver, aerial etc but who can see these bits? Greyhead is solving his problem but I want to try for a different approach. If I fail I can at least copy Greyhead since my construction is "flexible" i.e. just unwrap the Sellotape and take out the pins!

Any way, more of that later. I have done some covering trials and wing-construction trials and I hope to have time to come back to that soon - oh, and paintwork investigation. PC10 is interesting.

Happy New Year

LINNEY

At last a few minutes available – and I have made a decision, I am going electric.
This raises questions requiring answers, some of which are guesses. For instance, what i/c engine will I be replacing? Well, generally it would seem that a 6ft biplane weighing about 15lbs (7Kg) needs a 120 4-stroke so I had in mind an RCV120SP which is fully in-cowl and radial-mounted. Because the RCV SP–series are geared and run at about 5,500 rpm maximum they can deliver high torque and hence can use quite large diameter, and necessarily large pitch, props hence a 4-blade 15.5x12 seemed very suitable. Many SE5A aircraft were fitted with 4-blade on Wolsley Viper 200h.p. engines and to emulate that set-up seems reasonable. So what electric motor matches this? Well, searching around an AXI5345/14 outrunner with a battery of 10 LiPo cells in series seems to match up so that is my thought but there is much to consider. Firstly the RCV120 weighs about 1.3Kg but the AXI only about 0.895Kg so I would make the nose very light – not a good idea. But 10 LiPo 4000mAh cells weigh about 0.65Kg as opposed to a 250ml tank of i/c fuel weighing about 0.350 Kg. However such a tank-load would probably give a flight time of 12-15 minutes whilst a 10S 4000mAh battery would give about 4 minutes. To equal the i/c duration I would need 30 LiPo cells connected 10S3P which would permit about 12 minutes duration – but such a pack would weigh about 2Kg giving motor plus battery all-up of 2.85Kg whilst the i/c set-up is only 1.65Kg. An extra 1.2Kg, not good. So O.K., compromise on flight duration and settle for 10S2P battery giving 37.5 volts (well nearer 40 volts actually) and 8000mAh of life and hence about 8 minutes flight time. Category 10C LiPo’s will permit an 80amp/3.2KW burst of power for take-off, should be enough.

So there is plan A, AXI plus 10S2P LiPo weighing 2.15Kg total, perhaps about 0.5Kg more than the RCV120 set-up. O.K., give it a go – but now it is “location, location, location”, I cannot have a light motor in front of the aircraft CofG and heavy battery behind so a bit of maths is essential. Remember maths lessons? A small boy, say 70lbs (5 stone) sits at one end of a see-saw say 10 feet from the central pivot, the fulcrum, thus he exerts a “MOMENT of LEVERAGE” of 70x10 =700 ft.lbs. If now a large oversize boy weighing 98lbs (7 stone) sits on the other end then in order to be in perfect balance he must sit 7.14 feet from the fulcrum – his Moment would be 98x7.14 = 700 ft.lbs so the 2 kids are balanced.

It is the same with my model, with the design Centre of Gravity (CofG) being the fulcrum and the Moments needing to be equal. So what are these Moments? I must assume that the plans were drawn up with i/c engine and fuel similar to those of my “guess” so lets look at figures. To have the 1.3Kg RCV at the correct position, permitting the prop to sit correctly, the weight centre of the RCV would be 29cms from the aircraft CofG and hence have a Moment of 1.3x29= 37.7Kg.cm. Now the centre of the fuel tank is best positioned directly under the CofG of the aircraft because as the fuel is used up and the weight drops it does so equally each side of the aircraft CofG and hence balance remains correct (if it was correct in the first place!) But my plans show the centre for the tank actually 1.5cms ahead of the aircraft CofG so there is 0.350x.1.5 = 0.52Kg.cm of moment which makes the total 38.22Kg.cm. I have to assume that the design takes this into account so if I go electric my motor plus battery must also have a total Moment of 38.22Kg.cm.

Well, the AXI in the right place has its centre 32cms ahead of the CofG and so it exerts a Moment of 0.895x32=28.65Kg.cm. Now as I need a total of 38.2Kg/cms my battery assembly needs to exert 9.57Kg.cm and since it weighs 1.3Kg its centre must lie 7.36cms ahead of the CofG (1.3x7.36=9.57) No problem, plenty of room, so now I have an electric flyer balanced just as its i/c counterpart, weighing about 0.5Kg more and with only two-thirds of the flight duration. Perhaps not too much of a bargain, but there are advantages. No messy fire-wall, no messy exhaust, no start-up problems, no dodgy plugs, etc. so here goes.

But then, think on. My models generally end up tail-heavy – a not uncommon occurrence with other chaps too so I gather – so I end up putting lead weights in the nose which always aggravates me. But now I have another option. The battery will be about 15cms long and at the balancing point, as calculated above, the front of it will sit about 7cms behind the motor. So if I make the battery holder a “trough” 25cms long placed 2cms behind the motor I can slide the battery forward or backward by 5 cms in order to compensate for other weight problems in my construction. Now this 5cms can give me an extra nose-down Moment of 1.3x5 = 6.5Kg.cm if I slide the battery forward. That would be the equivalent of putting, say, 500gms of lead on the nose some 13cms ahead of the CofG without actually adding anything! And of course if by chance I ended up nose heavy I could slide the battery backwards with the same effect. A certain winner. So that is Plan A. If it all turns out a disaster I can still go to Plan B – back to i/c!

And since up to now I have only joined up the front of my fuselage with pins, screws and tape I can pull it apart, take out most of the fuselage inner and replace with a battery trough – very open-structure to permit air-flow. In the same way, a new AXI radial-mounting bulkhead can easily be installed and since I am making the upper cowl removable then access to the battery and motor will be easy. Access to the servos will be by removing the upper fuselage cockpit area and now my thoughts on making a removable upper wing centre section and cabane can be abandoned – no need.
So, next, covering experiments. Interesting, well to me anyway.

Greyhead

I have no experience of constructing for electric so can be of little help except to state the obvious. It makes no difference where the motive power comes from be it ic, electric or a wind-up elastic band, so long as there is sufficient power it is the weight, lift and drag that will determine the success or otherwise of the model.

Being a scale model, there is nothing you can do about the lift and drag and as you have found out, to get the equivalent power from electric, with reasonable running times, involves a heavier power source so to keep the all-up weight within limits weight has to be saved elsewhere.

The only place to save weight is in the areas of the construction that are not visible on the finished model, but as the all-up weight will be the same , or very likely slightly more, strength has to be an issue.

I wish you luck!

wonwinglo

Linney,you are going to have to seriously think about a geared motor,or as a few modellers have successfully tried couple multi motors together to get the performance that you require,I witnessed a large D.H Gipsy Moth fly with coupled electric power,the builder was the then owner of DB Scale kits,he would be a useful contact for you regarding motor type and the method of coupling,not sure if they are still in business ?
It goes without saying that I doubt if there is a singular stock motor on the market suitable for your model,having only dealt with small electric flight models ( which have given me immense flying pleasure ) it is difficult to advise on your configuration,however the amount of batteries need to fire up the motor should not be under estimated.
Electric flight has great appeal especially for cleanliness and the ability to fly quietly,it has been my saviour as I can no longer use glo fuel, as it has affected my skin after many years of useage and literally many hundreds of hours flying models.
Can I suggest that you do a lot more research on electric powerplants of the large variety,consult the makers about performance and battery drain etc,these things are vital to your project.

__________________
'And there I was oil on my goggles from a broken pipe,then I looked at the altimeter,all I could see was the makers name !'
www.wonwinglo.scale-models.net/