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Posts posted by Simon Chaddock
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Do not claim to be an expert but I wonder if they recommended RTV for a reason. A silicone sealant will have a measure of flexibility (vibration damping?) that epoxy does not. Just a thought.
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A 1/3 scale Merlin? That is BIG - like 3000cc! (183 cu in)
"Valves, rockers and camshafts". Looks great, but there is still quite a bit of difficult stuff to do!
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Lets try this explanation.
Aircraft wheels may have to take some side loads (unlike a two wheel bike) so the spokes need to be generously angled inwards from the centre towards the rim.
Most WW1 aircraft wheels are supported only on one side (unlike a bike fork) so to minmise the bending load on the stub axle the inner spokes are set perpendicular and the outer at an angle, hence the characterisitc shape.
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I would agree with JETSOME. Up elevator until the tail lifted is way too long. If the tail lifts with up elevator applied you must be at flying speed so as you are asking the plane to climb - it will try to.
Watch a full size tail dragger take off. Any up elevator is taken off pretty quickly so as flying speed is reached the elevator is more or less neutral and the plane just "flies off" the ground.
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From my own archive - the attic!
This was my first RC (1961?) - a single channel Macgregor Tone TX (valve) & TERRYTONE Mk2 (transistor) TX kits. Note the original boxes!
The transmitter case is a home build (neatly covered with leatherette) with most of space taken up by the HT and LT (3xU2!) batteries!
The receiver is definately NOT in the micro class but it all worked ok controlling a rubber driven escapement (one press for left, two presses for right).
When you took your finger off the button you hoped the model would sort itself out, fly straight and level and be ready for the next input. I even have the glider it flew in! Happy days.
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About the first model Merlin (1/5 scale) was built by Barry Hares between 1976 to 1981. There is a video of it running here.
Not content with that he went on to build a 1/5 scale model of the huge (46 litre) RR Eagle (24 cylinders, 2 cranks and sleeve valves!)
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Sealing the hinge to prevent flutter? I've not heard of that before.
I thought flutter was likely to be caused by slack or flexibility in the control circuit or the wing structure. Yes, reducing the leakage between the upper and lower wing surfaces improves aerodynamic efficiency.
Am I missing something?
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A great video and it certainly shows what it was like handling a WW1 type on the ground. Notice how the Camel rocks as the mag is blipped - 160hp on and off - ouch! Or the "missed beat" firing using the "reduced power" mag settings. I bet the Camel pilot kept a wary eye on that huge Merlin prop not far from his left side!
The amazing thing about the monosoupape (single valve) configuration is that it worked as well as it did - a sort of 2 stroke crankcase induction system but in a 4 stroke cycle. A good description and diagram here.
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The Meteor was indeed an unsupercharged Merlin but with more steel and less aluminium in it and was built by Rover. The story goes that Rover were having difficulty making the early gas turbines so RR did a straight swap - the tank engine for the gas turbine, a pretty shrewd move as it turned out.
The Meteor was used in nearly all late war and 1950s tanks (Cromwell, Comet, Centurion, Conqueror). There was also a cut down V8 version, the Meteorite, that was used in the Mighty Antar tank transporter that carried them about.
And navalised Packard Merlins were used in Motor Torpedo Boats as well.
The Merlin got everywhere!
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Do not be too dismissive of the performance of WW1 aircraft, full size or models.
Yes the drag tends to be high but the lower wing loading means plenty of lift. Their achilles heal was always engine reliability which should not be a problem for a model. For example the low engine speed and big efficient prop on the Fokker Triplane meant it could reach 20,000 ft on just 110hp, not many modern light aircraft can match that.
As Flanker says cross winds are a no no. WW1 airfields tended to be a just an area of grass with a wind sock in the middle, you ALWAYS took off and landed into the wind.
Some manoeuvres (loops and stall turns) a WW1 type biplane will do nicely, just don't expect it to knife edge between the pylons!
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Bill Gunston's book, RR Aero Engines, has 2 pictures and a description of the 2 stroke Crecy. It was Merlin size (26 litres) but with the banks at 90 rather than 60 degrees and sleeve valves that made the engine more compact. RR got it up to 2000 hp but with quite a few problems (only Bristol and Napier actually got a sleeve valve engine into production). The 3000 hp was an estimate with an exhaust turbine connected to the crankshaft i.e. a turbo compound, and only Wright ever got such an engine into production for the Lockheed Super Constellation.
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Hi Allan
Yes he was my dad!
He always intended this engine to be used, hence the development of the second performance carburettor and was a bit dismissive of engineering models for show.
I remember spending a evening with him experimenting with the fuel flow and ignition timing of John Lowden's 1/4 scale Gnome Monosuopape to get it to run properly on all of its 9 cylinders.
I understand when the first of the scale Merlins was demonstrated to him he was impressed but felt that it was not working nearly hard enough!
He never quite finished his V8 BRM (with its 4 cam shafts and 3 oil pumps) but calculated that it would produce peak power at well over 20,000 rpm and intended to find out if it did!
I trust that with a good airframe (e.g. a Ben Buckle Super 60) and modern radio gear the 5cc will not actually be at that much risk.
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Hi
I now have the 5cc petrol 4 stroke that my dad made, see previous post "4 stroke lubrication". It is complete and undamaged. Despite having been made nearly 40 years ago (it was one of the first small powerful 4 strokes) and not having been run for well over 25 years, it still has excellent compression.
My intention is to first get it running again, probably with a modern solid state ignition system (Just Engines?), and then to get it into the air.
It weighs 8.5 onzs (300 gms) dry, but including the 10x6 prop, which I believe it turns at about 12,000 rpm with the current performance carburettor. Unfortunately the engine cannot be inverted with this carburettor as the float chamber fouls the rear rocker cover when mounted the other way up although with the first carburettor design it could. Note the extra large finning on the head ot ensure adequate cooling when running at full power for long periods.
For the endurance attempt the engine would have to have been inverted so it could be gravity fed from the "wet" wing that was to carry the fuel.
Given the uniqueness of this engine I would appreciate any suggestions for a suitably docile design!
Simon
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I can confirm absolutely that Humbrol enamel will not stand glow fuel, particularly with any nitro content. Most of my tins are quite a bit older than 10 years!
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Wow! Now that is what I call scale building. That fuselage could be an "exhibition" model.
After all that work will you ever be able to pluck up the courage to fly it - no Depron crash resistance here!
I hope you do but I suspect you will find out why the Shuttleworth trust treat their full size planes pretty gently.
Will the controls surfaces be moved by scale cable control runs and with wing warping?
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Agree entirely - but its still a bang per cylinder every 2 revs (4 strokes) - not 4 revs. Ooooops!
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Eric
Burtonwood & M56? Yes the main runway was one of the longest in Europe but I did not know it stretched all the way across the Mersey!!!
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12 bangs per rev? come on Paul its a 4 stroke! As Sir Stanley Hooker commented 1 stroke for power, 3 to wear it out, so its only 6 bangs - not that you could ever call the Merlin exhaust a bang! Merlins sing, Griffons growl and the Bristol Centaurus sleeve valve woofles rather loudly.
Incidentaly RR did make a 2 stroke V12, the Crecy. It was as powerful as the Merlin but only a protoype. Just imagine what that must have sounded like!
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John
It seems to me that if you have indeed followed the plan, used the right material, put all the intended bits in the correct place and still need about 20% of the AUW as ballast to get the CofG correct, then the design is badly flawed!
What covering material does the plan suggest? It could be significant as most of the covering material is well behind the CofG.
As for adding all this weight to go round with the prop, not withstanding any gyroscopic effects, lead creeps under almost any load so perfect balance would not be maintained for long.
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Hi
The V8 was a quarter scale model of the 1.5 litre BRM grand prix racing engine - no prop!
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Hi Brian
I do wish I still had this engine. It was just about an equal bore/stoke and reasonably powerful. During testing it was also run as a glow on a methanol/nitro mix & produced about 25% more power but used nearly twice as much fuel.
Yes, there was a "banjo" disk at the back of the crank case that was rotated by the crank pin. Oil entered at the centre through a non return valve and was fed out to the hollow big end that had cross drilled oil holes. From there it sprayed about the crank case, the rotating crank web ensuring it did not pool anywhere until it was blown back to the tank through the outlet non return valve. Like all dry sump aero engines it was a good idea to hand crank it a few times to ensure any excess oil was cleared before it was started.
You will notice that it had a float carburettor as it was never intended for negative G aerobatics. As tested it could run at full power nearly 8 hours on 4 pints of petrol giving an estimated flight endurance of over 15. By the end of testing and development the engine had run for some 30 hours and was considered only just run in but unfortunately my dads next project (a 15cc V8!) rather took over.
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Hi
It did say it could be done.
My dad built a lightweight 5cc petrol 4 stroke and it just needed an oil tank and two neoprene connecting tubes. The actual additional components would only add marginal cost and weight.
Yes the crank and camshaft were on ball bearings so only needed splash lubrication but the big end was positively lubricated using the crankcase as a vacuum pump to suck oil directly from the tank into the bearing and then to blow the excess back into the oil tank. Effectively a dry sump engine it could run either way up, used 20/50 oil and 97 octane petrol. It could and did run continuously for long periods on the weakest possible mixture, a rather important attribute for a engine intended to break the model plane endurance record. It was featured in both the Model Engineer and Aero Modeller at the time but unfortunately I do know its current whereabouts although I do have some engineering drawings.
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Hi all
As a mechanical engineer it does seem a bit odd to me that aero modellers run their 4 strokes (unlike the rest of the world!) on a fuel/oil (2 stroke) mixture. Diluting lubricating oil in methanol (or pertrol) does not improve its properties. On a 2 stroke you have little option as the whole crankcase is part of the induction system but on 4 stroke everything below the piston (and above the cylinder head) is separate so why don't manufacturers arrange for a proper lubrication system?
I am sure the engines would last longer, possibly be more powerful (as all the fuel would be burnt), certainly use less fuel and I also suspect the spectre of wrecking an engine by lean running would diminish as well. No self respecting full size aero engine would consider anything less than positive lubrication to its bearings so why not ours? It can and has been done with surprisingly little extra complication.
Am I missing something?
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Gemma
To go back to your original post, if the pic is a model of the P51H then the main wheels WERE tiny, in fact small enough to eliminate the trade mark "kink" in the leading edge of all the preceding Mustang marks.
I know I am a bit of a scale freak but if scale u/c legs give the wrong stance to the model on the ground because the oleos do not compress then why not legs that do? It just requires a bit of engineering.
The 5cc found!
in IC Engines
Posted
The 5cc runs!
The follows pics show the engine mounted in its original (40 year old) test stand firmly srewed to the bench.
Note the full size 12V coil (I just wanted to make sure that sparks were not going to be a problem) and the oil tank.
It took a an evening of prop flicking to get it to run as I had no idea of any of the settings or even a starting routine but eventually it started "popping" and then burst into life. Only a couple of short low power runs so far - its 10pm and no silencer!
It will post a video of it running (with sound) when I get my new camera.