Comparison of electric versus engine power.

Parts not needed for electric;- Engine Cooling ducts and inlets for the engine. Fuel tank, filters, pipes and fittings. Fuel bottle, pump and battery. Fuel! Silencer, and extreme heat from it. Glowplugs and batteries, or ignition system and battery Engine starter and battery. Chargers for above. Needles to adjust. Starting, Reliability. Oily, dirty model. Paint is attacked. Passing the noise test. Parts needed for electric. Motor, Batteries, controller. field chargers and power supply, or spare batteries charged at home. Only modest cooling needed. Advantages. No starting or running problems. Clean, no oil, no fuel proofing. Model remains pristine. No fuelling up, glow checking. Cheaper to buy, very cheap to run. No noise complaints Contest weight is without Batteries!! Disadvantages Less 'fun'. Limited number of flights in a day. Ok for contests. No lovely noise (just a little). (We are working on that one) (Actually, we find that with the right set-up we get a good noise from it)
Engine cooling. I often see quoted in magazines that the cooling outlet must be three times bigger than the inlet. What B...locks. Actually the same size outlet is OK. It will work because the air will simply exit at a higher speed than it entered. Look at the Spitfire cooling radiators. The inlet and outlet are about the same size, and the air is carefully ducted inside to reduce drag. The fact that the exit air travels faster means that it produces thrust, and I read that it added 5 mph to the aircraft's top speed! I have an inline twin engine in my model. People are always asking if the rear cylinder gets overheated. This assumes that the cooling air is entering the front of the cowling and exiting at the back, in a straight line. On my model the air enters in the scale air intake underneath, travels forwards, then sideways round both cylinders, then exits through the scale exhausts. When planning engine cooling inside a cowling, it should be borne in mind that the air may not travel the route you expect it to, so you may need to provide baffles or ducting to get the result you want. I have met several examples of mysterious engine cutting because of vapour lock. The engine stops dead, often when the throttle is closed, the fuel evaporates and the engine dies for lack of fuel. The cure is to move the fuel line to a cooler part of the cowl, or insulate it by wrapping or fitting air baffles. For a hot carb you will need cooling air ducted to the carb. Weight saving on 1/4 Spit (applicable to all models) Take a 1/4 Spit model with the CG 7" back from LE. The receiver switch is fitted in the scale hatch on the left fuselage roundel. A. Weight of hatch reinforcement. 20 gm (Guessed weight) B. switch and mounting. 20 gm. C. hinge and catch. 10 gm. D. extension lead. 10 gm. Total 60 gm. This is 60 gm, 26" back from CG, so torque is 60 x 26 "gm. To balance this at the firewall, say 15" ahead of CG, is 60 x 20, divided by 15. Result is 104 gm extra ballast to maintain correct CG. Total extra weight = 164 gm, 5.86 oz. Move the switch to the firewall. The 104 gm extra ballast is removed, and the 20 gm switch means another 20 gm ballast can be removed. Also saved items A,C,D, 50gm. Total weight saved. 174gm. 6.2 oz. Just from the Rx switch. We recently fitted a steel disc weighing 1 kg on Jim's engine shaft, ahead of the prop. To achieve the same effect with ballast on the firewall, it would need 1 1/2 kg. Do the same with all the equipment where possible, makes a difference!

Weights   oz sq ft Gm sq ft 1/64" Birch ply       1/64" Birch ply  +  filler 1.375 38.50 1/32" Birch ply   1.750 49.00 2mm Birch ply   5.200 145.60 3mm Birch ply   7.200 201.60 6mm Birch ply   14.000 392.00 2mm Lite ply       3mm Lite ply   4.500 126.00 6mm Lite ply   7.000 196.00 Grey Primer spray   0.20 6.00 1/8" Balsa ] 1.000 28.00 1/8" Balsa ] 1.500 42.00 1/8" Balsa+ Tissue/Talc 0.625 17.50 1/8" Balsa.+ epoxy/filler 0.750 21.00 1/8" Balsa/glass/ epoxy/fill   10 thou Styrene   0.750 21.00 15 thou Styrene   1.250 35.00 5 thou Litho   1.125 31.50

double side tape 0.075 2.10 1 1/2 thou Metalcoat   0.33 9.4 0.2 Proskin   1.250 35.00 0.3 "   2.500 70.00 0.4 "   3.125 87.50 light nylon       3.5 Solartex     0.580 8.5 Solarfilm     0.200 5.2 Solarspan   0.230 6.7 Litespan     0.100 2.80 Fibafilm     0.130 3.64 Glosstex     0.400 11.20 Airspan     0.080 2.24 Solarkote       7.0 Tissue/dope     2.5 Tissue/dope/Silk/ polycel/dope   8.5 Paint KlassKote epoxy Glosss 0.080 2.25 Useful weight chart for scale builders

Glass fibre 28 gm.cub inch ratio 1     carbon fibre 28 gm cub inch 1     Aluminium 43 1.5     Steel 126 4.5     brass 136 4.8

 

ENGINE TESTING without transmitter.
Have the throttle servo connector handily placed in the model, connect a servo tester to control the throttle.

Telescopic vision.

Let me relate some stories.

1. Over thirty years ago I was learning to fly RC with my Gangster 63. The flying field was quite big and had a large tree outside the field, perhaps three hundred yards away. I had seen models hit this tree a few times.
I was on landing approach, well inside the tree when I though 'No, I'll be safe and keep high a bit longer'. So I flew high until I was sure I was past the tree. Then I thought 'No, I will be absolutely sure'. So I continued flying high until the model was nearly at the strip, then I throttled back and dropped in to land. Straight in to the top of that distant tree! I could not believe it!

2. Two years ago I was landing the Hunter. I had got in the habit of long approaches with the jets to give more time to adjust the approach speed. I decide that a short approach would be easier and so tried that.
The model came on finals at low throttle and full flap, but was still off the end of the runway. It seemed to hover there without moving forward in the quite strong wind. I chickened out, expecting a tip stall [I was pleased to see that it did not] so I opened the throttle, lifted the gear, and wondered where the flap control was. I had to look down to find it and retracted the flaps. The model was quite happily coming towards us but had turned slightly off the runway and was just behind us.
As the model passed, we were able to hear that the engine was still running [could not hear it downwind]. So I turned into another landing circuit and throttled back.

This was meant to be a smaller circuit, but proved to exactly the same as the first one. Again I opened the throttle, lifted the gear, and this time the flaps straight away. The model was at about ten feet from the ground and a long distance away. The model again turned slightly off the runway and reached us a few yards behind where we were standing. I said to Jim 'Has the engine stopped' He agreed it had, so I thought No Problem, I'll land right here on the short grass. Two hundred yards away was the edge on the airfield with high security fence and massive prickly hedge. The model went behind the hedge. We both could not believe it! It looked like a full size Hunter in relation to the hedge. When we re-ran the video, again we got the same impression and had to run it several times until we could see that yes, it was a small model behind a large hedge.

3. This year I was flying my slow Bleriot on a calm day doing tight circuits and touch and goes. There was a small sapling 100 yards away and I was shocked to see the model pass behind it. Lucky not to have wrecked the model in the tree.

So it seems that when we fly RC models, our perception is distorted and we think the model is much closer than it is.

JET SPEED

I have flown all the jet models we produce and I estimated that the top speed was about 100 MPH.
Then two different customers told me they had carried GPS units in their Super Reapers to get a speed readout. The Super Reaper with 14 lbs thrust MW54 was doing 200 MPH in level flight, no retracts. I had to revise my thinking . I now think that all our jets will do similar speed on a normal 8kg thrust engine.
I had noticed that when flying jets, sometimes my 180 degree turn at the end would be very wide, with the model getting a long distance away. This was unpredictable and made positioning difficult.
I now think I understand. It is to do with the airspeed. At lower speeds, the model would turn much like a prop driven model, but at high speed the turns would be much bigger. A lot of elevator would be needed to get round and this was unexpected. I read somewhere that a full size Lightning would take twelve miles to turn at full speed. This makes sense and explains one of the difficulty with flying jets, you have to be more aware of the speed differential which is available, and how this affects handling.

JET THROTTLE

Another problem with flying jets is the lack of sound from the engine This is most apparent on the landing approach. I found that I would often approach with a much higher throttle setting than I thought I was using. I realised that when flying a prop driven model, I was judging the throttle opening not by the stick, but by the SOUND of the engine. This makes jet flying more difficult.

I Cut three notches in my Tx throttle quadrant to give a feel at 1/4, 1/2, and 3/4 throttle positions. This was not as effective as I had hoped.
I sometimes shut the throttle completely on the downwind pass to find the position of the stick, then open again to 1/4 for the approach.

 

Colour perception.

1. Colour perspective.
It is a common belief that scale models should not be painted in the exact same colours as the full-size, but that the colour intensity should be reduced. This is because of so called 'colour perspective'.
If you look at a scene of distant hills, it will often be seen that each row of hills appears in paler colour behind the hills in front. This is undoubtedly true. I think this is due to mist which has the effect of 'greying out' the image as it gets further away. But the same view in bright sunlight does not have the same effect. I have not as yet gathered any evidence for this.
However, when we are considering the colour of a scale model, we are not looking at the model from miles away, not even 100 feet away but just a few feet. In fact the most critical distance would be the five metres from the centre of the model, as in competition judging.
Consider this; The model is placed at 5 metres from the observer and the full size aeroplane is placed at a distance where it looks the same size as the model. So a 1/4 scale model would have the full size four times 5 meters = 20 meters away.
A 1/3 scale model would be 15 meters, and so on.
I have heared it stated that if you hold a colour sample up, with another sample some distance behind, the difference in colour strength can be seen. I did not agree with this so I did an experiment.

I took two green dustbins as my samples, on a bright sunny day and took digital photos of the two at various spacings relevant to model scales. The set-up is shown in the first photo.

The results are shown below.
I cut out small samples from each of the bins and overlaid the more distant sample in a small panel over the large panel which was the bin at 5 meters.

You wil notice that in samples 1 to 5 there is virtually no difference in the colours. Samples 6 and 7 were taken with the furthest bin rotated about 10 degrees out of square with the other bin to show how colour varies with angle of view. You can clearly see the changed of colour. The white streaks are scratches on the bins. The difference in colour between each of the separate photos [1 and 2 for example] are due to the fact that I used the camera in automatic mode, and each time the settings were slightly different. I should have set it in manual to avoid the changes, but still the results are valid as each pair of samples are on the same shot. I think this proves that for the purposes of scale model viewed at close quarters, colour perspective does not exist.

Further sections to be added

2. Paint.

3. Gloss.
Gloss and matt paint of the same colour look different. Gloss will reflect the colours of the surrounding scene like a mirror.
(Look at the side of a shiny car. You will see the scenery which is behind you, the skyline of trees and buildings, you own reflection, etc.)
Matt partly does this, but also scatters the light much more and this usually makes the matt colour look lighter.

4. Light.
The light from the sun varies with the time of day and weather conditions. This alters the colours perceived by the eyes.
However, the brain compensates for this, so we can tell colours without noticing the change, even when wearing sunglasses.

5. Shape.

6. Luminance.
We think of using bright colours to make a model easy to see in the sky.
But why are bright colours easy to see? The reason is that they are usually a contrast from the dull
background colours. But if you were in a sandy desert in bright sunshine, a bright orange-yellow would
be the worst colour to stand out.
The sky is not the same as the ground, it has high luminance compared to the ground in most conditions. Because of this the best colours to contrast with the sky are DARK colours. A white or yellow or orange model can become hard to see when its luminance becomes the same as the sky behind it. A black model is the easiest to see because it always contrasts with the sky.
Exceptions are when the model is below the horizon, when the reverse applies, and at night when any colour is black!

7. Reference

8.Weathering

9. Reproduction.

10. Perception.

Incidence, thrust lines, trims on scale models.

We get many enquiries about what incidence, side thrust etc should be used on our scale models.

The wing and tail incidences are to scale. They were chosen my the aircraft designer to suit the expected loads
and speeds of the aircraft. Our models are SCALE and so keep to these as they should be. To change them would
make the model non scale and would not look right.

Trims. The trims on a full-size aircraft are for the pilot to adjust so that the stick loads are reduced to suit
different speeds and loads. The trims would be changed often in flight.
On an R/C model we would set them for level flight at a cruise speed and normally not move them again.
Exceptions might be to set trims for lower speed on a flat calm day, or for full throttle flight in a gale.
I find that most of my models fly with quite a lot of down trim. This can be explained by the fact that the model is
much lighter by comparison with the full-size, and may be flying at higher than scale speed.
I also use right rudder trim. I notice many photos of the full-size Spit show it has a lot of down trim.

Free flight models use offset thrust lines to control the model as the power changes through the flight.
With R/C we have controls to do that job.
If you trim the model to cruise at mid throttle, then going to full power will make the model climb, but
that is probably what you wanted.

For competition aerobatics, offset thrust lines will make the model easier to fly
to accurate patterns. This would also be effective on a scale model, but would spoil the appearance.
Remember, the full-size version of your model would also react to power changes and the pilot would have to
adjust the controls accordingly, so you must do the same with your model.

So, build the model to the plans. Match the incidence as shown on the plans.
No need to ask how many degrees it should be. I don't know and I don't need to know.
Don't worry if your trims are not central - they don't need to be.

CG position. The plans show the CG position which was successful on my model. If a range is shown,
it means my model was test flown over that range. On the Javelin the range was five inches!
On tail draggers, a forward CG means nose-overs and heavy unresponsive controls, a rearward CG means
sensitive controls and difficult tracking on the ground,
So it is a compromise. If you have a model which noses over AND ground loops, you could say it has the perfect CG position!!

Flight attitude on a scale model.
I have heard it said by several well know modelers ‘that model is flying tail down, it must need more nose weight’ . This is quite wrong.
Aircraft attitude in level flight is determined by airspeed. The slower the airspeed, the higher the nose will be.
The wing has to support the weight of the machine, and it needs greater angle of attack to do this at lower speeds. The pilot has to pull the stick back to maintain level flight.
The effect can  easily be seen by flying at different speeds and observing the attitude, but it is not so obvious to the pilot inside the aircraft.
When an aircraft is landing, the attitude is nose up compared to high speed flight, but  the cg has not been moved!
CG position does affect the aircrafts attitude to a small degree, but in the opposite sense to that mentioned in the first sentence.
The most noticeable effect of CG position is on longitudinal stability. A rearward CG makes the elevator more sensitive, to the point of uncontrollability.
Many FF models use a rearward CG because it is more efficient. This makes the tail provide some of the lift but makes the model less stable. The wing now needs less lift and so the attitude is slightly less nose-up.
If the CG is moved very far forward, the tail has to balance this with a downwards force. The wing then needs extra lift to compensate, and so the attitude has to be slightly nose high.
So when you see an aircraft flying ‘tail down’, it is because it is flying slowly with stick held back.
To stop it, open the throttle and move the stick forward to keep in level flight.
I think the mistaken view was developed by free-flight modelers, because a FF model has no elevator or throttle controls.

Trim position.
I've heard this said.  "My model flies with down trim on the elevator, it should be level, so there must be something wrong."
Trim is provided on models and full size so that the aircraft can fly level "Hands off". The trim required depends on the airspeed, so slow flight needs UP trim
and high speed needs down trim. There will be a speed where the trim is central. All my models are set with some down trim because I fly fast for smooth flight and
to help in strong winds. On the rare occasions of still air, I can move the trim up and fly slowly.
It was pointed out to me that most photos of Spitfires in flight show them using down trim, just like my models!

 

Frequently asked questions.
What engine do you recommend? There are thousands of engines available. Most of them are good. I have never set eyes on most of them and certainly have no experience. The size range we suggest are valid, best to stick to them. The only piston engines we now use are Lasers.
What paint do you recommend? I have tried many types and have trouble with all of them! I am now returning to Epoxy paint with our own MrEpoxy.

I have now tried digital servos and found that , although the power quoted was no more than a normal servo, the HOLDING power was vastly better. Try moving a control surface against the servo holding power. You can easily back drive the servo. With a digital servo of the same torque, it is almost impossible to move the surface. Now that digital servos are cheaper, I will use more of them in future.

FLUTTER
My thoughts on control surface flutter are as follows.
Turbulence is usually present around control surfaces, and turbulence tends to be unstable. This means that the airflow oscillates from one side to the other. Models can often be seen to wobble slightly in flight and this is the result of this oscillation.
Experiment; Take a stick of balsa and push a screwdriver through the middle of the stick. Put a lump weight on one end of the stick. Hold the screwdriver so that the stick is free to revolve. With a gentle to and fro movement of the hand, the stick can be made to swing like a pendulum. It is quite easy to get the stick to spin round rapidly with very little hand movement. This is similar to the wobble in air turbulence making a control surface swing from side to side.
Now add another weight to the other end of the stick so that it balances exactly. Now you find that no matter how hard you swing your hand, you cannot make the stick swing at all. It needs the pendulum effect for it to work.
So if you add balance weights to your control surfaces, ahead of the hinge line it will no longer be possible for flutter to occur.
Of course you should still make a good job with your linkages and hinges, but this will not now be critical.

Flying safety.
The most common cause of crashes is, as we all know, pilot error. But some crashes are caused by mechanical failures and improvements to our installations can improve reliability.
       It is common practice to use a separate servo on each aileron, mainly because it is easier to do than using one servo and long linkages. A bi-product of this is better reliability. If one servo fails ,the remaining one will give enough control to safely land the model. On most of my models, I now do the same with the elevator control. Where the elevator is split, it is quite simple to work each half with its own servo. (Sopwiths, Javelin, Lightning. Spitfires etc.) I find that the cheapest servos are normally powerful enough, with two servos you have twice the power and much better reliability.
How much more reliable? Well, its not just twice as reliable, but much, much better.
Suppose your servos fail once every 1000 flights. The chance of both failing on the same flight are 1000 x 1000. Or once per million flights. Mathematically it is - [reliability factor, squared].

Batteries.
Some people try to improve reliability by using a separate battery for the receiver and the servos. They do not realise that this is in fact LESS reliable. As both batteries are needed to control the model, then failure of EITHER battery will result in loss of control. So, if the battery failure rate is once per 500 flights, then in this case it will become twice in 500 flights, HALF as reliable as one battery. The Multiplex 12 channel Rx. has a built in facility to use three separate batteries, which would reduce reliability to 1/3 that of a single battery!!!
There is a simple way to vastly improve this situation. Instead of buying say, one 2000 mAh battery, buy two 1000 mAh.
batteries, but connect them in parallel. This is done by using two standard switch harnesses, and plugging these into the receiver. Not into a Y lead, since this means you are relying on just one plug in the receiver. Fit one plug into the battery socket, and the other into any spare servo socket. If all servo sockets are in use, use a Y lead for one servo and the second battery. The reliability is now (for example) 500 x 500, = 250,000.
Yes this really works.
To illustrate this further, imagine if each battery was a chain holding the weight of your model. With the two separated batteries, it is like connecting one chain to the end of the other. If either chain breaks, the model falls. With my parallel system, it is like using each chain separately. If one breaks, the other still holds the model.
The system will always draw power from the best battery, or from both if they are both good. Any failure in one battery/switch/wiring or plug gives no problem, you carry on with the other battery.
It is good practice with this system to check each battery separately by moving the servo as you would normally do, but with just one switch ON. Then test with just the other switch ON. It is easy to detect if one battery is low. Of course you fly with both switches ON.
  It has always been said that Nicad batteries must never be connected in parallel. Paul Mitchel did some tests for JET magazine and found that this was NOT TRUE. In every test he tried there was no problem. He used different capacities, age of cell, and even different voltages! However, if you feel uncomfortable with this, it is a simple matter to fit 5 amp diodes into each battery lead to stop one battery discharging into the other one. One situation where this is vital is in the case where there is a dead short in the wiring on one harness ( it can happen). Fit the diode next to the receiver plug. The diode does reduce the voltage by 0.6 volts, so it is better to use 6volt packs, which will also give you improved servo performance.

FOAM WINGS
We are sometimes asked why we don't supply foam wings for all our models. Foam wings are great for a simple straight wing on a sports model like the Gangster range. Our Reaper and Assassin have foam wings. But on the Lightning, Javelin, Venom and Spitfire it was felt that the complexities of the internal structure would make it more difficult to build with a foam wing. The CNC cut rib set has the metal tube joining system and the retract mounting ready done for you. All the correct angles and strength are designed in. Just assemble the wing structure with retract mounting plates, slide in the metal tubes and you are ready to sheet the wing. The designs also include the flaps, airbrakes, tip tanks, U/C doors etc, as required.

TORQUEMASTER for Zenoah Titan 62
This unit bolts onto a Zenoah 62 engine and provides a belt driven reduction drive to a new prop shaft set in front of the cylinder. This enables a larger propeller to be driven, which is more efficient and gives greater thrust.
Why is a Reduction Drive needed and what advantage does it give? This is a difficult question to answer fully but a simple analogy will help. It's rather like the gear box on a car. Try pulling away in top gear and you will find that it is a great struggle and acceleration will be very slow until you reach a reasonable speed when the clutch can be fully engaged and the car will then accelerate to high speed. This situation can be compared to an engine fitted with a small diameter prop, or ducted fan or turbine. Acceleration from rest can be poor but performance is good once a high speed is reached.
The propeller or fan in this case is very inefficient at low speeds. Most of the energy is wasted in turbulence behind the model. Modern ducted fan models overcome the slow acceleration problem by using a very powerful engine, perhaps four times the power used in a similar sized propeller model.
The opposite case, pulling away with the car in bottom gear gives very good acceleration from rest but, of course, the car will not go very fast. If you are pulling a very heavy trailer uphill then bottom gear might be just right for the situation. The equivalent case for a model aircraft (or full size aircraft come to that) is a large, heavy, slow flying machine, where a high ratio reduction drive could turn a large prop to give the thrust needed to fly the model. But you don't get this extra thrust for nothing - the theoretical top speed available will be proportionately lower, although the model can actually reach a higher speed in practice because of the improved efficiency.
Most large scale models would lie somewhere between these two cases and most of these would benefit from using a reduction gear.
Propeller efficiency. This concept is rather difficult to explain. The propeller thrust must equal the drag of the model at a particular speed and the thrust is obtained by the propeller throwing back a column of air faster than the model is flying. The thrust is calculated from the mass of air x change in velocity.(MV) Therefore, a large prop, moving a large column (and mass) of air, can throw the air back at a low speed to achieve this thrust, whilst a small prop would need to provide a much higher speed column of air to get the same thrust. The difference between the rearward speed of the air from the prop and the forward speed of the aircraft is referred to as propeller slip and the greater the slip, the less efficiency.
Mathematical explanation:- Thrust is given by M x V , BUT the energy lost in the slipstream is given by 1/2MV2. Work it out and you find that the smaller prop with higher velocity change has much higher losses for the same thrust.
Deciding on whether a particular model would benefit , and deciding what prop size would be appropriate, is quite a problem. It is possible to calculate this provided all the facts are known but normally we do not have enough information available to make calculations worthwhile. You would need to know the speed and drag of the model; the torque curve of the engine; the thrust and torque absorption curves of various props etc. A more practical way to decide is to look at existing models which are successful with the standard engine and then look at slightly larger heavier models which can fly on the straight engine but where the performance is marginal during takeoff and climbing. This is where the torquemaster can be a real benefit. My 1/3 scale Camel is 112" span and weighs 3Olbs. The King 100 engine used in this model turned a 28 x 14" prop. at 42-4400 rpm. This gave good performance but fitting the Zenoah 62 and Torquemaster resulted in an extra 200 rpm on this prop and vertical performance with the much smaller engine.
A rule of thumb for deciding what propeller pitch to use is to aim for a 30% propeller slip. So if the model is flying at 40 mph it will require prop pitch equivalent to 57 mph ( 40 /0.7) At 5000 rpm this needs 12 inch pitch. ( MPH X 1056) RPM One would then adjust the prop diameter to reach the required rpm. The Manufacturers' power graphs for the Zenoah 62 suggest that maximum power is 4 BHP at 8500 rpm (silenced), and my engine appears to run quite happily at 9500 rpm. If you want maximum performance then you should select a prop which will allow the engine to reach these speeds, but a bigger prop might be preferred to reduce noise, engine wear and fuel consumption. My approach with the Camel was to prop for around 8000 engine rpm at full throttle, giving near maximum power but only using full throttle very rarely in flight. Level flight requires only 1/4 throttle and scale aerobatics can be done on about 1/2 throttle. It's nice to have the extra performance in hand for use when you want it.
I believe that use of the Torquemaster will give great improvements in models over 251bs and will give the impression that a larger engine is being used. Takeoff runs will be much shorter, climb outs can be steeper with good control authority, where using the standard engine would have meant a struggle to get airborne and a slow climb-out near the stall.

Builder of the model rule.

For many years I have felt that the competition rules were inadequate for dealing with this subject. The enforcing of the rule has been very lax. The statement from the modeller that he built the model has (as far as I know) always accepted without question. There have been many times when suspicions were that the rule was being broken, and I believe that often this applied to highly placed entries. I don't recall any time that the declaration of self-building was challenged. Of course it would be difficult to make a challenge without any direct evidence too back the challenge. I feel the rules should include ways of improving this situation in several ways.
First, instead of asking for a simple statement, with a list of exceptions (easy to forget to mention some of the items which might be marginal), There could be a series of boxes to fill in. This would mean the " cheater" would have to lie a number of times and would have a deterrent effect.
The first set would give the opportunity to disclose to true nature of the model and how it was built.
Example; Entrant must mark one of the following boxes.
Model was bought ready built. State who built it .
Model was bought ARTF. Manufacturer.
Model was bought as a prefabricated kit.
Most parts finished. Manufacturer.
Model was bought as a kit with some moulded parts or pre-formed parts. Manufacturer.
Model was built from a plan / with some formed parts bought. Designer.
Model was designed and built by entrant. Bought parts listed.
The second set would list most of the common parts of a model which might not have been made by the entrant. These would ALL have to be filled in with choice of answers. Example. Made it. Bought it. Bought & altered. Not on model. Deduct %
a. Fuselage.4%  b.Wings. 4% c. Tail, 3% d. Canopy 2%. U/C legs 2%. Decals/ scale markings 2%. g. moulded tip tanks etc1%. h. Guns/bombs 1% Cowling 2% Dummy engine2% Rigging wires/fittingsx 2% \par (More items to be listed. % figures adjusted to give suitable totals for types of aircraft. Maximum total will be 20%) A discussion of the various items would be in the judges guide, with guidance for adjustment to the % awarded. EG bought foam wings which had to be veneered, finished etc, would perhaps only get 1%. \par }plain NOTE. }{ When considering these parts, it must be remembered that only the aspect of the marks awarded for the part in static judging is important. {Thus items which are not judged are not considered in this context. Radio control equipment, model engine and equipment, common materials., screws, timber, metal, or retract mechanisms which are out of sight during static judging. It should be remembered that the Static marks awarded are for accuracy of the model. This is a result of the SKILL of the modeller, or the person who designed and produced the commercial part. This must be considered by the judges when deciding the % mark. The amount of work to produce a part is not relevant to the contest. A skilful worker can make a part quicker than the less able builder. Only the scale qualities matter.

My modelling history.

 When I was about seven, someone bought me a model kit. I think it was a KeilKraft Minimoa. Complex elliptical fuselage and gull wings. Various uncles had a go at it but I don’t think it ever got finished.
At school we had a modelling club. The favourites were the KeilKraft 1/8d series. ( or whatever the price was then). Rubber or jetex powered scale models. I found the Javelin or the Vulcan were the best – flown as chuck gliders. Cheaper than Jetex and better performance.
Then in teenage years I started with Frog 50, then Albon Dart deisals. Built semi scale freeflight models.
Then came the wonderful AM10 engine with lots of power. We started the Wanstead club with mostly control-line sport/Stunt/Combat models. Mine  were own designs- cheaper than kits.

I progressed through ED racers etc, then to Oliver Tigers. I ordered two tuned versions and waited nearly two years for delivery. When they came I quickly built a  new combat model and tried a new idea – curtain rings for line connectors. As the model was launched the lines went slack. As they snatched tight, the curtain rings opened and my new Oliver flew away and was lost on its first run!

I considered my main interest was stunt, with combat second, but I entered only a few local events. Like many others, I was still ‘practicing’.

At 18 I bought my first motorbike, a 1938 BSA 250 with hand gear change. I worked in a bank.

Then two years national service in the RAF. I bought a 500 Velocette for transport (60 MPH flat out), then a James 250 two stroke which was 10 MPH faster. The second year in the RAF I found out about the RAF championships which  were only two weeks away. They gave me a week off to go home and prepare my models, then a week at the championships playing with models, all with full pay plus expenses. Great. I won medals in combat and stunt.

After the RAF I lost interest in modelling. I got a job as a motorcycle mechanic, much more interesting than being a bank clerk.

I got interested in trials riding and spend two years messing about trying to build a cheap bike from unsuitable bits, and ‘practicing. One day one of my workmates suggested I enter the Traders Trial. ‘Whats that’ I asked. He said it was only a muck about event which the local mechanics etc entered for a bit of fun. I entered. I found I had been conned! The trial was a full national event with top works riders etc. I struggled round the circuit, getting exhausted. At one point I was on a narrow mud track , I was so tired I let the bike slide away and it trapped me under it. I was enjoying myself so much that I just laughed and laughed until I was too weak to move. Someone helped me up and I completed the course. I did not come last, but pretty near. I was filled with enthusiasm.

The next day I started sending in my entries to all the trials so that I would be riding every Sunday through the winter. I progressed well and started getting cups at the end of the season.

 I built a Norton featherbed bike with BSA 650 Super Rocket engine for road use, and a Greeves 250 for trials.

After 4 or five years I found I had ridden the whole season without any prizes. The annoying thing was that almost every time I was the highest placed rider that did not get an award! I found my thoughts returning to stunt flying.

After my experience in entering my first motorcycle trial, I decided the best thing to do was to enter the stunt event at the Nats. So I did, and then thought about building the model. I built a simple if ugly box shaped model. Flying was more important than looks. I did not come last at the Nats (quite) and I remember Peter Russell giving me encouragement by saying my loops were  the best he’d seen that day. (the rest was presumably rubbish).

I entered all the events I could, and started getting near  the top of the results after a year.

Moral : If you are interested in competition, the best way to learn is to ENTER. You learn more in one contest than in two years ‘practice’.

About two years after I had stopped trials riding, a friend called be to ask if I was riding in the local  club trial the next Sunday. Again I was conned. The trial was not just for the club but open to the whole country. I pulled my rusty bike from the shed got it started and rode round the garden a few times to get the rusty chains moving. That’s all the practice I had, yet I did the best I had ever done In trials. I won three cups that day!.

Moral: Practice is not always the best way to win.

Another occasion, again a friend called me at 10 pm on Saturday to ask for a lift to a stunt contest. I had not flown for some time. I got out an old retired model and stuck a bit of extra weight in the nose. At the contest next day, I was just about to start my engine when a reporter from the local paper came up and interviewed me. This was the first time ever and it left me in a daze. I did the flight but forgot to do the Triangular loops. I told the judges ‘sorry about the triangles’ The judge looked down. ‘You got 8 for them’ In spite of these handicaps I won my first stunt contest.

I carried on in stunt and becomed the countries top pilot in 1969, winning every event except the Nats. I never did win that.

At the stunt meetings, we had two or three flights and hung around the rest of the day. Sometimes there was a controline scale event next to us and I passed the time by watching this. The scale modellers were very bad at starting their engines, often spending 10 minutes or more and failing to start. In stunt, we had to start and take-off within one minute. Most of the scale models had no throttle. If they were lucky and got the thing started, they would run to the handle and their helper would release the model for a not very realistic full power take-off. None of the models was aerobatic so the flight schedule was very dull. Then they would fly round and round waiting for the engine to cut. Often they would throw rags into the prop to get it down so the next man could have his flight.

I thought ‘What a shambles, I’m sure I could do better’. So I built a scale Turbulent for amusement whilst I was waiting for my turn in stunt contests.

The model was reasonably accurate, but its main feature was a big engine (Merco 61) fitted with a throttle. I remember my first scale contest well.

I came forward for my flight and waited for the judges to say they were ready. The judges were chatting to each other and when I enquired they said ‘OK. Start when you like’.

So I started my engine in one flick. The judges had expected the usual 10 minutes starting time, and called for me to wait whilst they scrambled to get their score cards ready!

I signalled the helper to release the model and instead of taking off, it stood there at tick-over. I signalled and taxied forward, slowly building speed up to take-off.

I started with the usual dull manouevres, then into aerobatics. The judges had never seen this before. Loops, Inverted, Outside loops, figure eight, etc.

After this they expected the usual wait for the engine to stop. Of course I was able to signal, throttle back and land, then roll to a stop with the engine ticking over. All over? No.
I would signal again and taxi the model away. Walking with the handle to the edge of the circle and stop. Then another signal (WHATS he going to do NOW) I would cut the engine.

In spite of the fact that turbulents were not supposed to be aerobatic, the judges gave me the marks and the model went on to win most of the comps for the next two years, Except the Nats which I never won.

They introduced c/line carrier contest. For this you had to fly fast, then slowly, then land on a model aircraft carrier with an arrester hook.  I won the first Nationals with a very slow Mustang with Merco 35. It won because no one else could get a reliable flight and an arrested landing. The next year I built two Seamew models and won all the events.

It was announced that a new World Championship was to be started in 1970, for R/C and C/line scale. The first one was to be in England. I decided to enter and built my fully aerobatic Zlin.

The control line model was quite large for the time, and very light.

On its first flight I was alone and had to release the model with a string from the centre of the circle.

Something went wrong and the model flew knife edge across the circle at four feet with no control. I regained control on the other side and finished the flight. I was very lucky not to crash the model.

The team trials were very shortly after this. I had only flown the model a couple of times. I had charged my starting battery and spare battery well. In the trial I found both batteries were flat. I messed about for ten minutes and failed to start the engine. I heard a judge say ‘why don’t these people bother to prepare properly’. I managed to qualify for the British team, but only just.

At the World Champs there were some wonderful models. I did not think I would do very well. After the static judging was over, I found that I was in third place. The first place model was a wonderful FW 190 from USA. It even had working illuminated gun sights! This model had engine trouble and in the first round it could not complete ten laps to qualify. The Yanks were all busy on the model trying out different fuels etc.
In those days, the flight options had different scores according to the difficulty of the manouevre. So most models had to do low scoring options like Throttle Control (2). High flight (4) etc. I was able to include Figure Eight (8) etc. and so get a much higher flight score. I could not believe it when I was told I was leading after the first round. I was sure the FW would be sorted out and take the lead.
They did get the model working, but it could not beat the aerobatics of the Zlin and I became World Champion!  I was walking on clouds for the next few weeks.

For 1972 ChampsI thought I would enter both controlline and R/C. I started to learn to fly R/C. I built a Cassutt racer for my R/C entry. I had not been flying for very long when I entered the team trials. As I took off, something went very wrong. The model was very strange on aileron control. It would constantly roll too far in each turn and half my flight was in unintentional inverted. I completed the flight and looked at my Tx. The main stick seemed to have lost its return spring and the aileron would not return to centre. That was the trouble. I walked across to the judges and held out the Tx to demonstrate the fault at that moment the fault disappeared! It must have been a speck of grit caught in the stick base. The Judge did not believe me and made some comment about people not having bothered to practise.

Fuel systems for jets.
We have tried various arrangements and have now achieved reliability with full aerobatics and no flame-outs.
We always use a good fuel filter next to the engine. This filter stays on the engine when it is removed from the model.
We no longer use header tanks with central feed because these were not reliable.
The use of a felt klunks was found to give good protection from air bubbles and also filtered the fuel.
The Orbit klunk does the same job but even better. It will drain the tank down to the last 1/8" before letting any air through.
We would recomment the Orbit klunk on the last tank before the engine, and felt klunks on all other tanks.
Our KJ66 engines need 2 litres of fuel for an eight minute flight.
We have had success with three tank systems.
1. Reaper. [single tank]
A two litre Coke bottlle or a square white spirit bottle has one feed fitting in the cap, one vent fitting in the side of the bottle, and an Orbit klunk.
Another vent fitting is used in the bottom of the model for overflow.

2. Javelin. [2 tanks into 1]
Two 1 litre apple juice bottles, each with feed and vent fittings and felt klunks, are fed through a T fitting to the main tank.
This is a rigid 3/4 litre tank with vent connected to the T fitting. The feed to the pump uses an Orbit klunk.
This tank is a reserve and is normally still full at landing.

3. Lightning. [two tanks in line.]
A Dubro 1200cc tank with felt filter feeds to the vent of another similar tank, which feeds the engine.
The Orbit is too big to fit in the Dubro tank.

3b. The Lightning and Hunter now have a single 3 litre tank with orbit filter, as shown above.
Bigger size, lighter, cheaper, and easier to fit than the two dubro tanks!

TIP. Mount the pump as low as possible in the model.
It will prime more easily and will retain some fuel for a quick start next time.

 

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Duct design.
There is some disagreement about whether full ducting round the engine is desirable. Some say that full ducting will produce more
thrust and higher performance. I think that full ducting has very little or no influence on the static thrust, and its effect
in flight is difficult to assess. I have flown the same model with and without, and noticed no difference. I fly scale jets,
and my intention is always to try to fly at scale speed. This means throttling back after takeoff, to scale (slow) speed.
If full ducting does in fact help thrust at high speed, then it would only benefit if you want to fly very fast.
      To make a vertical climb in aerobatics requires more power than level flight. A model with very high static thrust
would be able to fly slowly and use extra power to climb to the top of a loop, reducing to idle power in the descent,
always keeping to a scale speed. A model with low thrust has to approach the loop at high speed to have enough
momentum to reach the top.
What is needed for a realistic scale model is high static thrust for take-off and climbing, but no need for high speed capability.
The disadvantages of full ducting are obvious.
Cost.
Extra work to install.
Taking up precious space in the model and making the rest of the installation, and later maintenance more difficult.
Extra weight.
Some people have used full ducting as a protection for the turbine from loose items inside the model. But how about FO (
foreign objects) entering the intakes and being directed straight to the turbine, causing FOD (foreign object damage)?
It seems to me that a simple metal gauze filter on the turbine intake is a better option. (and it works).
      Airflow around the turbine is not needed to 'keep the engine cool'. The high speed gas flow inside the engine determines
the case temperature.
The fuel is used to raise the temperature to produce thrust. A high temperature is desirable.
Its the inside of the model which you want to keep cool.
    Full ducting reduces the damage to the fuselage from flames during hot starts. True, but it also make hot starts invisible
and makes it much harder to deal with the fire. Without ducting, and with manuel start, a hot start can usually be
dealt with in 2/3 seconds and a normal start begun immediately. With full ducts and automatic start sequence,
a hot start can mean disaster (I've seen it happen).

One customer told me that his F15 gave very poor performance with full ducting. He now flies without the engine
access cover, and thrust has improved 50%.

Rear exhaust ducting.
I have done some bench testing of rear ducting. My tests suggest;
   1. All ducts reduce thrust. 1 to 2 Kg loss is typical.
   2. Duct sizes between 75mm and 95mm inlet diameter gave similar results, so this is not critical.
   3. Parallel or slight tapered ducts gave similar results.
   4. Air is drawn in to the duct with the jet stream. Enough space must be allowed for this.
A gap between the engine efflux and the duct inlet is needed, bigger gap for smaller pipe. About 20 mm gap is average.
   5. Longer ducts loose more thrust.
   6. Bifurcated ducts loose more thrust than single pipes.
   7. The higher the engine thrust, the greater the thrust loss.
   8. Any leak in the exhaust duct does not mean hot gas escaping , but more air being drawn in.
NEWS. Well, I was wrong. Work by John Wright has resulted in a lucky discovery.
The losses in the rear exhaust duct can be removed and a slight INCREASE in static thrust can be obtained.!
Johns results have been published, and I intend to make all my ducts to this concept in the future.

Of course you don't get this improvement for nothing. The disadvantage is that there will be a loss of thrust in flight at high speeds.
Important thing is- at what speed is the cross-over from thrust increase to thrust loss? My guess is that it will be over 300 MPH (480 kph)
so it wont bother most of us.
   

FAQ. "Will it fly off grass?". Yes, all our jets will fly off grass.
The relevant factors are - How long is the grass, is it wet grass,
is the ground smooth, how strong is the wind, are there obstructions in the fight path,
how much thrust do you have.
We have flown the Assassin and Venom off grass, the latter with only 10 lbs thrust.
Our flying field is tarmac so we dont get the chance to try grass very often.
Many of our Super Reaper customers fly off grass with MW54 engines.

See HOME page for FAQ on foam wings, servos, etc.

How does a model jet engine work?

The mechanics of typical model turbo jet are very simple.
A compressor fan at the front is driven by a turbine wheel at the back, both being mounted on a shaft with two bearings.
There are fixed vanes behind the front fan, and in front of the rear turbine. The space around the shaft in the middle
is occupied by the combustion chamber, which is like a tin can with many holes in it. Fuel is fed in from an electric pump
and on most designs, is evaporated inside hot metal tubes. There is usually an outlet nozzle bolted on the back, and a
glowplug for ignition.
The compressor is a standard item from a car turbo charger. The diffuser vanes behind this are machined into a light alloy plate
which is mounted in the outer case and supports the shaft bearings. The turbine is like propellor with about 23 blades, and is cast
in special Inconel material. It must stand very high forces at high temperatures. The guide vanes in front of the turbine must also
resist high temperatures, but as they are not spinning, the forces are low. There are pipes to supply oil to the bearings, and holes
feed air through the bearings to cool them. Most engines do not need an oil tank system. The fuel is mixed with about 3% oil,
and this feeds the bearings from the fuel supply.

How do you start a model jet?
A can of gas is connected to the engine, and the gas is ignited by a glowplug. The engine shaft is spun by and electric starter motor.
As soon as the gas is alight, the fuel is fed in.(there is no need to warm up the engine). The fuel ignites and the glow and
gas can be removed. The fuel feed is gradually increased as the engine RPM increases, until the idle speed is reached, about 35,000 RPM.
The engine is now ready for flight.
The control of fuel feed in usually done by an electronic control unit (ECU). This controls the fuel pump rate for starting and acceleration to
full power at about 120,000RPM, and also provides several safety cut-out systems.
So the start sequence is.
1 Turn on glow and gas.
2. Spin with the starter.
3. When ignition is heard, turn on the fuel.
4. Hold on the starter until idle speed is reached.
All the starting system can be carried on the model, and the ECU controls the system to give self-starting from the Tx.

PROSKIN

Fitting the top wing skin.
With the wing held on the building board, the ribs must be sanded using a straight sanding bar
so that they give a perfect level surface for the Pro-skin covering. The ply leading edge should
be given a champher to match the rib profile. Take care with this stage, the quality of the finished
wing will depend on it.
Cut a Proskin panel slightly over size, remove the protective film from each side and lay in place
on the wing. Mark register points at each end of the spar to align the skin at the glueing stage.


Now have a practice run at fitting the Pro-skin. Hold the skin down with straight bars and weights
similar to the picture. Tapeing the edges down is not good enough. There will be a rippling effect
between each piece of tape. A solid wood or metal bar can be clamped in place as shown.
Check carefully that the skin lies flat without ripples.
When you are satisfied, the skin can be glued in place.
Apply a thin bead of Pro-bond urathane adhesive to all parts of the wing, (or you can use slow
setting Cyano or epoxy)
Place the skin on to the alignment marks and fit the weights and clamps as before.
You must work quickly to fit the skin within 5 minutes.
Rub down the skin over all joints to squeeze out excess adhesive, and leave to dry for about 30 minutes.
If you make a mistake, it is possible to pull the skin off before the glue is fully hard.
The Pro-bond dries from moisture in the air and in average conditions, will be handleable in 20 minutes.
Full hardening will take 24 hours.
Trim off the skin edges.

Yamaha D-Deck with Tyros above.

The MIGHTY TYROS ORGAN! The Tyros is fitted on wall brackets over the Yamaha D-Deck organ. There is a 4 inch gap between which allows full access to the organ controls. The tyros is angled down at the front which makes it easier to see the controls from a seated positon. It works well without any connection between the two machines, but I have connected the two with Midi leads. The tyros speakers have been replaced with Sony home cinema six speaker system, bought from Empire Stores on line for £140. To set up;- Function, Midi, Midi pedal 2, Edit, Recieve. Using the Part button, Set the first line, channel 1 to keyboard. (upper on the organ) next line, Ch 2 to Left (lower on organ) Ch 3 to Style bass. (organ pedals) Next Page, you can set ch 2 & 3 to Root on or leave them off. This will give diferent results when you play chords. Next page, Chord Detect. Set Ch 2 & 3 on. save to user page.

I can now;- 1. Play the Tyros as normal. 2. Play the three right Tyros voices on the organ Upper manual. giving the full length manual to play on. Play the Tyros Left voice on the whole of the lower manual . Play the chords for the style anywhere on the lower manual. Play the tyros bass voice on the pedals, and this affects the root of the style. All the voices are selected by Tyros in regestrations, OTS, or with voice select buttons. 3. The organ can still be played as normal. Using the two swell pedals, the two instruments can be played seperately, or blended together - a fantastic sound. The Tyros bass voice is selected by the style and you cant change it. If Ch3 is assigned the left, the bass voice 4can now use all the voices and effects, but you then have have to assign one of the three upper voices to lower maual.